Ultrasound Imaging Participant Workbook PDF

B. Voc. in Medical Imaging Technology Advanced Diploma – Second Year SEMESTER 1 Ultrasound Imaging (MIT 9) LEARNER’S WORKBOOK Tiksna Livelihood Private Limited - Vertical Anchor for TISS ----------------------------------------------------------- TISS –...

B. Voc. in Medical Imaging Technology Advanced Diploma – Second Year SEMESTER 1 Ultrasound Imaging (MIT 9) LEARNER’S WORKBOOK Tiksna Livelihood Private Limited - Vertical Anchor for TISS ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- INDEX MIT 9 – Ultrasound Imaging Chapter No. Chapter Name Page No. 1. Basics of Ultrasound 4 2. Ultrasound Imaging Artifacts or Pitfalls 14 3. Transducer and Machines 22 4. Ultrasound Physics 29 5. Doppler 53 6. The Ultrasound Scanning Room 61 7. Abdomen 65 8. Abdominal Aorta 69 9. Inferior Vena Cava 74 10. Liver 76 11. Gall Bladder and Biliary Duct 81 12. Pancreas 91 13. Spleen 96 14. Peritoneal Cavity and Gastrointestinal Tract 100 15. Kidneys and Ureter 104 16. Urinary Bladder 110 17. Scrotum and Testis 113 18. Uterus and Fallopian tubes 117 19. Neonates 130 20. Neck 136 21. Ultrasound Guided Biopsies 139 ___________________________________________________________________________________ 3 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- 1. Basics of Ultrasound By the end of this chapter, you would be able to:  Explain the principle of ultrasonography  Discuss basics of acoustics  Describe the basic technique of ultrasound scan  Describe the different modes of ultrasound scan Introduction Ultrasonography basically is detection and display of high frequency sound (acoustic energy) reflected from interfaces within the body. Because ultrasound images are captured in real- time, they can show the structure and movement of the body's internal organs, as well as blood flowing through blood vessels. Ultrasound imaging is a non-invasive medical test that helps physicians to diagnose and treat medical conditions. Conventional ultrasound displays the images in thin flat sections of the body. Advancements in ultrasound technology include three-dimensional (3-D) ultrasound that formats the sound wave data into 3-D images. Four-dimensional (4-D) ultrasound is 3-D ultrasound in motion. Principles of Ultrasonography Ultrasonography basically is detection and display of high frequency sound (acoustic energy) reflected from interfaces within the body. Ultrasound is name given to high frequency sound waves, usually over 20,000 cycles per second (20 KHz). These sounds are transmitted in beams and reflection of these sounds from tissues within the body which is picked up by the transducer and with application of computer the image is generated. Ultrasound is usually in range of 2 to 10 MHz (megahertz) in present day scanners. These are inaudible to humans. Megahertz is 1,000,000 cycles per second. The duration of pulse is one microsecond and these pulses are repeated about 1000 times per second. As the beam of sound is passed, the different tissues alter the waves in- different ways depending upon the composition of the tissues; some reflect directly while other scatter the waves. The waves pass through tissues at different speeds. The reflected ultrasound pulses detected by the transducer are amplified within the scanners. The echoes from deeper layers of body are attenuated (decreased in intensity) that from superficial parts and are amplified. These echoes are 'reconstructed into two dimensional map and displayed on video (television) monitors. ___________________________________________________________________________________ 4 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Image Showing Propagation of Wave Basic Acoustics Wavelength and Frequency Sound travels in form of wave producing alternating compression and rarefaction. If these changes are plotted on a graph a sinusoidal wave form is produced. As you can see from graph that pressure changes are plotted against time and these define basic units of measurement of sound.  The distance between corresponding points on a time pressure curve is defined as wave length and is represented by A.  Sound is transmitted as series of alternating pressure waves producing compression and rarefaction of the conducting medium  The time for the pressure waves to pass a given point is the period. It is expressed in seconds.  A number of complete cycles in a unit of time is the frequency (f) of sound. ___________________________________________________________________________________ 5 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE ---------------------------------------------------------  Frequency and period are inversely related.  Unit of acoustic frequency is Hertz where 1 Hz is 1 cycle per second. Higher frequencies are expressed in Kilo hertz (1 KHz —10 Hz) or Mega hertz (1p00000 Hz) Acoustic Impedance Definition: Acoustic impedance is thus resistance offered by tissue to movement of particle caused by ultrasound waves. It is represented by Z. Presently ultrasound scanner relies on detection and display of reflected sound or echoes. To produce an echo, a reflecting interface is required. Sound passing through totally homogenous medium encounters no interface to reflect sound and this appears anechoic or cystic. When sound reaches the junction of tissues or materials of different physical properties it encounters acoustic interface and these are responsible for reflection of sound. The amount of reflection of sound is variable and is determined by difference in acoustic impedance of materials Acoustic impedance (Z) depends upon:  Density of medium propagating sound (p)  Propagation velocity of sound in that medium (c) Z = pc Acoustic Enhancement and Shadowing Clear liquid allow ultrasound to pass directly through without much alteration, so that echoes that come from tissues behind liquid are usually enhanced (brighter) this is known as "acoustic enhancement" drinking enough water to fill the stomach will displace gas -filled bowel, providing an acoustic window. This is particularly useful in visualizing the body and tail of the pancreas. Gas in the bowel or elsewhere can present a variety of sonographic patterns. The beam can be scattered, reflected absorbed, and refracted, making it very difficult to image underlying structures. For this reason ultrasound cannot be used to image the normal lungs or to demonstrate lung disease other than peripheral masses. A chest X-ray provides much better information. Dense materials such as bones or calculi (stones) cast shadows on structures behind then, because the ultrasound waves do not go through them. This is known as "acoustic shadowing" ___________________________________________________________________________________ 6 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Basics of Technique Orientation of the Image It is possible for the images on the monitor to be reversed so that, on transverse scans, the left side of the patient is seen on the right side of the screen. Although there may be an indicator on the transducer, it is essential before scanning to check visually which side of the transducer produces which side of the image. This is best done by putting a finger at one end of the transducer and seeing where it appears on the screen. If incorrect, rotate the transducer 1800 and check again. On longitudinal scans, the head of the patient should be on the left side and the feet on the right side of the screen. Contact with the Patients Skin The transducer must be moved across the patient; therefore, the patient's skin in the region to be examined must always.be sufficiently covered with a coupling agent to allow transmission of the ultrasound beam and easy movement of the transducer. Ultrasound gel: used to help the transfer of sound waves from the transducer to the patient as air is poor transmitter, of sound waves. It eliminates air pockets Transducer is moved slowly across the patient it must always be kept in close contact with the- skin through the coupling agent; movement must be continuous and gradual while the operator carefully watches the image on the screen. Background of the Image Normally we see background which white echoes if this is altered with white background with black echoes call the engineer and adjust the machine. Distribution of Ultrasound Body tissues reflect ultrasound in two different ways. Some tissues act like mirrors and reflect the waves directly back. While others scatter the waves in the way fog scatters a beam of light. The diaphragm is a “mirror” as a "specular reflector" liver on the other hand shows interferences pattern resulting from waves being scattered in different direction. Frequency and Resolution The higher the frequency of the ultrasound, the better is the resolution. This means that smaller details become visible when higher frequency is used. However the penetration of the ultrasound into body will be less. Scanning is therefore, a compromise and the highest frequency that is also sufficient to penetrate deeply enough should always be used. Focus of the Ultrasound Beam Because the organs or parts of the body that are of interest will be at different depths, the focus of the transducer should ideally be adjustable. If the focal distance is fixed, the most suitable transducer must be chosen for the particular examination. ___________________________________________________________________________________ 7 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Different Modes of Ultrasound Various modes of returning echoes on amplitude mode: A mode: in this mode, echoes are shown as peaks and distance between various structures which can be measured. Nowadays not much is use except in field of ophthalmology Figure: A MODE B mode images are two dimensional: This type shows all the tissue traversed by ultrasound scan. Figure: B MODE Real time: It produces impression of motion of generating series of 2D (B mode) images at rates 15 — 60 frames per second. Thus it displays motion by showing images of part of body as visualised by transducer. This movement is shown on monitor. It is possible to freeze the displayed image in present day scanners. The real time images are mostly used nowadays and are useful for cardiac application or to slow foetal heart. Transducers used for real time scanning may be based their beam steering ability, can be mechanical steered transducers or electronically steered M Mode: This displays echo amplitude and shows position of the reflectors i.e. is another way of displaying motion. Most commonly used in cardiac imaging ultrasound and in foetal heart monitoring. ___________________________________________________________________________________ 8 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: M Mode Ultrasound Questions for Practice Q. 1. Fill in the blanks choosing the correct answer. 1. _____________ basically is detection and display of high frequency sound (acoustic energy) reflected from interfaces within the body. a) Ultrasonography b) EMG c) EEG d) None of the above 2. ____________is thus resistance offered by tissue to movement of particle caused by ultrasound waves. a) Acoustic enhancement b) Acoustic impedance c) Shadowing d) None of the above 3. The function of the ultrasound gel is to _________________. a) Transfer of sound waves from the transducer to the patient b) eliminate air pockets c) a and b d) None of the above 4. The diaphragm ________________ the sound waves while the liver ______________ them. a) absorbs b) reflects c) scatters d) none of the above 5. The _____________ mode of ultrasound shows all tissues transversed by ultrasound scan a) A mode b) B mode c) Real time d) M mode ___________________________________________________________________________________ 9 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 2. Match the columns. Column A: Modes of Ultrasound Answers Column B: Properties of Modes 1. A mode a. two dimensional 2. B Mode b. echoes are shown as peaks 3. Real time c. displays echo amplitude and shows position of the reflectors 4. M Mode d. displays motion by showing images of part of body Q. 3. State whether the following statements are true of false and correct the false statements. 1. Acoustic impedance depends on the source producing the sound wave. ___________________________________________________________________________ 2. The unit of Acoustic frequency is km/hr. ___________________________________________________________________________ 3. The M mode images are mostly used nowadays and are useful for cardiac application or to slow foetal heart. ___________________________________________________________________________ 4. Body tissues reflect ultrasound in two different ways. ___________________________________________________________________________ 5. Focus of the transducer in USG should ideally be adjustable ___________________________________________________________________________ ___________________________________________________________________________________ 10 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 4. Give Reasons. 1. A scan delay of 540 minutes for Head CECT is a must for evaluation of seizure disorder and meningitis. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ _______ Q. 5. Answer the following questions in one or two sentences. 1. Define Acoustic impedance. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ _______ 2. Define Acoustic enhancement. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ _____________________ 3. What is acoustic shadowing? ___________________________________________________________________________ ___________________________________________________________________________ ______________ 4. Which are the different modes of ultrasound? ___________________________________________________________________________ ___________________________________________________________________________ ______________ 5. Give the relation between frequency and resolution in acoustics? ___________________________________________________________________________ ___________________________________________________________________________ ______________ ___________________________________________________________________________________ 11 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 6. Write short notes. 1. Principle of Ultrasonography ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ 2. Basics techniques in USG ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________________ 12 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 7. Answer the following questions in 6 – 7 lines. 1. Explain the different mode of USG. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ********** ___________________________________________________________________________________ 13 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- 2. Ultrasound Imaging Artifacts or Pitfalls By the end of this chapter, you would be able to:  Explain on artifacts of ultrasound  Discuss different types of artifacts Introduction Artifacts are an additional, missing or distracted image not conforming to the real image of part under US beam. Some artifacts have beneficial effects in diagnosing of some diseases. Artifacts Artifacts are an additional, missing, or distracted image not conforming to the real image of part under US beam. Artifacts arise from the incorrect display of anatomy or noise during imaging. Some artifacts maybe avoidable and arise secondary to improper scanning technique. Other artifacts are generated by the physical limitations of the modality. The causes can be:-  Operator or machine related  Intrinsic to the characteristics and interactions of ultrasound with the tissues. Recognition of these artifacts is important because they may be clues to tissue composition and aid in diagnosis. The ability to recognize and remedy potentially US artifacts is important for image quality improvement and optimal patient care. Types of Artifacts Reverberation Artefact Arise when Ultrasound signal reflects repeatedly between highly reflective transducers. It reflects ultrasound energy back and forth during the acquisition of the signal and before the next pulse. They give false impression of solid structure in areas when fluid is present. They can be prevented by changing the scanning angle. They are mostly caused between reflective interfaces, such as metallic objects (e.g. bullet fragments). Also called ring down or comet-tail artifacts. ___________________________________________________________________________________ 14 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Sonogram demonstrating an in-plane view of a needle with reverberation Artefact. The needle tip is identified by the position of the yellow arrow. The equally spaced hyperechoic Artefact (blue arrows) is beneath the actual needle. Refraction Refraction is the change in the transmitted ultrasound pulse direction at a boundary with non-perpendicular incidence, when the two tissues have different speeds of sound. These reflections are then detected and displayed on the image. Thus structures that actually lie outside the volume appears on image. It causes misplaced anatomic position in the image. Anatomic displacement will vary with:  The position of the transducer  Angle of incidence with tissue boundaries  Types of Refraction include 1. Mis registration: Due to improper placement and results in distortion of size or shape. 2. Defocusing results in shadowing at the edge of large curved structures 3. Ghost image ___________________________________________________________________________________ 15 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Ultrasound of normal lung: note the mirror image Artefact: appearance of liver above and below the diaphragm (arrow) and the absence of a spine sign. Side Back artefacts These are important as they may create impression of structures or debris in fluid. The also cause error in measurement by reducing lateral resolution. Shadowing Shadowing is a hypointense signal area distal to an object or interface. It is caused by high attenuation or reflection of the incident beam. Highly attenuating objects e.g. bone or kidney stones reduce the intensity of the beam. It can induce low-intensity streaks in the image. Acoustic shadowing: anechoic or hypoechoic region seen deep to a highly attenuating medium. It prevents visualization of true anatomy and it is considered as a beneficial artefact. Figure: Shadowing Artefact Associated With Imaging A Fetal Cranium ___________________________________________________________________________________ 16 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Enhancement It occurs distal to objects having very low ultrasound attenuation. E.g. Fluid filled cavities (filled bladder or cyst). Hyperintense signals arise from increased transmission of sound by these structures. It is considered as a beneficial artifact. Figure: Enhancement - appears as a hypoechoic region that extends beneath structures with low attenuation  Artefacts due to poor penetration, poor scanning angle and poor resolution  If gain is too low: a solid mass may appear cystic without internal echoes. However there will be no back wall effect  If gain is too high fluid filled structure may resemble solid mass DICTUM: Adjust Near and Far Gain Carefully ********** ___________________________________________________________________________________ 17 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Questions for Practice Q. 1. Fill in the blanks choosing the correct answer. 1. _____________ are an additional, missing, or distracted image not conforming to the real image of part under US beam. a) Acoustic impedance b) Refraction c) Artifacts d) None of the above 2. ____________is thus resistance offered by tissue to movement of particle caused by ultrasound waves. a) Acoustic enhancement b) Acoustic impedance c) Shadowing d) None of the above 3. The function of the ultrasound gel is to _________________. a) Transfer of sound waves from the transducer to the patient b) eliminate air pockets c) a and b d) None of the above 4. The diaphragm ________________ the sound waves while the liver ______________ them. a) absorbs b) reflects c) scatters d) none of the above 5. The _____________ mode of ultrasound shows all tissues transversed by ultrasound scan a) A mode b) B mode c) Real time d) M mode ___________________________________________________________________________________ 18 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 2. Match the columns. Column A: Types of Column B: Properties of Artifacts Answers types of artifacts 1. Reverberation a. Occurs distal to objects Artefact having very low ultrasound attenuation 2. Side Back artefacts b. A hypointense signal area distal to an object or interface 3. Shadowing c. Create impression of structures or debris in fluid 4. Enhancement d. US signal reflects repeatedly between highly reflective transducers Q. 3. State whether the following statements are true of false and correct the false statements. 1. Artifacts arise from the incorrect display of anatomy or noise during imaging. ___________________________________________________________________________ 2. Refraction in USG is due to improper placement and results in distortion of size or shape. ___________________________________________________________________________ 3. Some artifacts maybe avoidable and arise secondary to improper scanning technique. ___________________________________________________________________________ 4. Reverberation Artefact is also called ring down or comet-tail artifacts. ___________________________________________________________________________ 5. Acoustic shadowing is considered as a beneficial artefact. ____________________________________________________________________________ _______ ___________________________________________________________________________________ 19 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 4. Give Reasons. 1. Recognition of artifacts in USG is important. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ Q. 5. Answer the following questions in one or two sentences. 1. Define Artifacts in USG. ___________________________________________________________________________ ______ ___________________________________________________________________________ 2. What are Reverberation artifacts? ____________________________________________________________________________ ____________________________________________________________________________ ______________ 3. What is refraction in US? ____________________________________________________________________________ ____________________________________________________________________________ ______________ 4. What are the factors which causes anatomic displacement? ____________________________________________________________________________ ____________________________________________________________________________ ______________ 5. What is enhancement in US? ____________________________________________________________________________ ____________________________________________________________________________ ______________ ___________________________________________________________________________________ 20 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 6. Write short notes. 1. Artifacts ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ Q. 7. Answer the following questions in 6 – 7 lines. 1. Describe the types of artifacts. ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ________________________________________________________ ********** ___________________________________________________________________________________ 21 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- 3. Transducer and Machines By the end of this chapter, you would be able to:  Explain piezoelectric effect  Describe a Transducer  Describe the basics rules to choose scanner Introduction Ultrasonic transducers are used to convert an electric into ultrasonic energy that can be transmitted into tissues and to convert ultrasonic energy reflected back from the tissues into an electric signal. Piezoelectric Effects Piezoelectric effect was cut described by Pierre and Jacques Curie in 1880. Certain materials are such that the application of an electric field causes a change in their physical dimension or vice versa. This is called the "Piezoelectric effects". Piezoelectric materials are made up of innumerable dipoles arranged in a geometric manner. The positive and negative ends are arranged so that an electric filed will cause them to realign, thus changing the dimension of the crystal. The plating electrodes behave as capacitor, and it is the voltage between them that produces electric field and this in form causes crystal to change shape. Sudden burst of voltage. Causes crystal vibrates as crystal and generates sound wave When echoes passes from transducer into body, echoes reflect back towards transducer from tissue interface. These echoes carry energy which is transmitted to transducer causing physical compression of crystal and induces voltage between electrodes. This is amplified and serves signal for display. Naturally occurring materials like quartz possess piezoelectric properties. Manmade piezoelectric materials (ferroelectrics) are Barium titanate and lead zirconate titanate (PZT). Transducers A transducer is a device that can convert one form of energy into another. Ultrasonic transducers are used to convert an electric into ultrasonic energy that can be transmitted into tissues and to convert ultrasonic energy reflected back from the tissues into an electric signal. Transducers are based on piezoelectric properties. ___________________________________________________________________________________ 22 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- The most important component is a thin (approximately 0.5mm) piezoelectric crystal element located near the face of the transducer. The front and back faces of the crystal are coated with a thin conducting film to ensure good contact with the two electrodes that will be supply the electronic field used to strain the crystal. The surface of the crystal is plated with gold or silver electrodes. The outside electrodes are grounded to protect the patient from electrical shock, and its outside surface is coated with a water tight electrical insulator. The inside electrode abuts against a thick backing block that absorbs sound waves transmitted back into the transducer. The housing is usually a strong plastic. An acoustic insulation of the rubber or cork prevents the sound from passing into the housing. A large variety of sizes and shapes of transducer are available to perform specific functions, but they all have this general design. Basic Rules to Choose Scanner Choose a scanner that will perform the examinations needed at your hospital. A part from the technical specification there are some basic rules to be observed when choosing a scanner. The monitor The monitor (viewing screen) should be at least 13cmx 10 cm (or about 16 cm diagonally) The Scanner  The scanner must be suitable for use in the local climate that is protected from dust or capable of being used in high or low temperature as appropriate.  The scanner must be tough enough to withstand adverse transport and storage conditions. It should not be damaged by movement in an aircraft or a vehicle on rough roads.  The scanner must operate satisfactorily from the power supply in the hospital or clinical where it is going to be used. The unit should be compatible with local voltage and frequency, and it should be able to stabilize fluctuations in supply. ___________________________________________________________________________________ 23 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Servicing the Scanner Before purchasing it is necessary to see whether servicing is available in your area. Non- functioning machine adds to losses. See servicing is available within a reasonable distance. What controls are needed on the scanner? The scanner must be equipped with a video monitor (TV screen) and to control the images there must be;  An overall sensitivity control to alter the amount of information on the video screen.  Separate controls to alter the surface (near) echoes and the deep (distant) echoes. These are known as near gain and far gain controls.  A control (frame freeze) to hold the image on the screen so that it can be viewed for as long as necessary.  Calliper control to measure the distance between two points shown on the image. Recording the image It should be possible to add patient identification and other details for patient medical record. This can be done by different methods:  The best and the most expensive method is to record image on X ray. This is done with a image processing unit and a special camera. It may be necessary to have a darkroom. Single emulsion X-ray filmare used. The system is expensive but not always of the same quality.  The next best method is a self — processing camera and film specifically designed to be attached to the ultrasound unit. It is also expensive  There are image — recording units that will print the image on special paper (this is much less expensive than using film). The images are quite satisfactory for routine records, but the paper must be protected from excessive heat and light. This is widely used ___________________________________________________________________________________ 24 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Choosing the Appropriate Transducer The best transducer for general work is a convex transducer of 3.5 MHz focused at 7-9 cm. If this type of transducer is not available then both liner and sector transducer of 3.5 MHz will be necessary. If children or thin adults are be scanned, an additional 5.0MHz transducer focused at 5-7 cm is help:  Obstetric ultrasound: If most of the ultrasound examinations will be for general obstetrics, the transducer should be linear or convex, either 3.5 or 5.0 MHz focused- at 7-9 cm. If only one transducer can be purchased, choose 3.5MHz. The 5MHz transducer is best during early pregnancy the 3.5 MHz is better in later pregnancy.  General purpose ultrasound: If the examinations will include the upper abdomen of adults and the pelvis, as well as obstetrics, a sector or convex transducer of 3.5 MHz focused at 7-9 cm is most suitable.  Paediatric ultrasound: For children a 5.0 MHz transducer with a focus of about 5-7 cm is needed. If neonatal brain scans are to be carried out, a sector transducer of 7.5 MHz focused at 4-5 cm will be required (and can be helpful for adult testis and neck). ********** ___________________________________________________________________________________ 25 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Questions for Practice Q. 1. Fill in the blanks choosing the correct answer. 1. A _____________ is a device that can convert one form of energy into another a) coupling agent b) transducer c) Artifacts d) None of the above 2 Certain materials are such that the application of an electric field causes a change in their physical dimension or vice versa. This is called the ________________. a) Piezoelectric effects. b) Acoustic impedance c) Shadowing d) None of the above 3 The monitor (viewing screen) should be at least ___________ diagonally. a) 10 cm b) 16 cm c) 20 cm d) 12 cm Q. 2. Match the columns. Column B: Transducer Column A: Category Answers frequency 1. Early pregnancy a. 3.5 MHz focused-at 7-9 cm. 2. Late pregnancy b. 5MHz focused-at 7-9 cm. 3. Children c. 7.5 MHz focused at 4-5 cm 4. Neonatal d. 5.0 MHz focused on 5-7 cm Q. 3. State whether the following statements are true of false and correct the false statements. 1. Gain controls are used to measure the distance between two points shown on the image. ___________________________________________________________________________ 2. Patient identification and other details for patient medical record can be added by recording image on X ray or with a self — processing camera and film. ___________________________________________________________________________ ___________________________________________________________________________________ 26 | Ultrasound Imaging | PW  ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 4. Answer the following questions in one or two sentences. 1. Define Ultrasound transducer. ____________________________________________________________________________ ____________________________________________________________________________ ______________ 2. What are near gain and far gain controls of a scanner? ____________________________________________________________________________ ____________________________________________________________________________ ______________ 3. Explain the general working of a transducer? ____________________________________________________________________________ ____________________________________________________________________________ ______________ Q. 5. Write short notes. 1. Piezoelectric Effects ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ __ ___________________________________________________________________________________ 27 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 6. Answer the following questions in 6 – 7 lines. 1. Explain the working of Transducer. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ____________________________________________ ********** ___________________________________________________________________________________ 28 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- 4. Ultrasound Physics By the end of this chapter, you would be able to: Describe the Principle of Ultrasound. Differentiate Ultrasound from X-rays. Explain the Characteristics of Sound. Explain the Principles of Piezoelectric Crystals and their use in Transducers. Understand the Different types of Transducers and Ultrasound Machines. Introduction Ultrasound is the term that describes sound waves of frequencies exceeding the range of human hearing and their propagation in a medium. Medical ultrasound is a modality that uses ultrasound energy and the acoustic properties of the body to produce image from stationary and moving tissues. Ultrasound imaging uses a pulse echo technique to synthesize a gray scale image of tissue based on the mechanical interaction of short pulse of high frequency sound waves and their returning echoes. Ultrasound provides a means by which abdominal organs, chest, small parts like scrotum and neck can be examined using ultrasonic waves. Unlike X rays these waves doesn't cause radiation so it can be safely used in pregnant women. History The first major attempt at a practical application was made in the unsuccessful search for the sunken Titanic in the north Atlantic in 1912. Techniques were not sufficiently developed, especially imaging techniques until the massive military research effort that accompanied World War II. Sonar (Sound Navigation and Ranging) was the first important successful application. The first step towards the use of sound waves in anatomical imaging was taken by the Austrian brothers Dussik in 1937. They scanned a human head immersed in water using a transmitter receiver pair of quartz crystal transducer and published the result in the 1942 Steven Garbar. The essential technological aspects of modern investigative ultrasound came to being in 1945 with digital processing coming to being soon afterwards. "Rayleigh" wrote a book called “theory of sound" in 1873 which has since remained a great classic text in physics. The physical phenomenon of Piezo-electric effect became a reality three years later by Steven Garber. The observations with piezo-electric crystals came in 1950s. Anil C R gave the first systematic review on safety of use of ultrasound. ___________________________________________________________________________________ 29 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Principles of Ultrasound  The ultrasound machine transmits high-frequency (1 to 12 megahertz) sound pulses into the body using a probe.  The sound waves travel into the body and hit a boundary between tissues e.g. (between fluid and soft tissue, soft tissue and bone).  Some of the sound waves reflect back to the probe, while some travel on further until they reach another boundary and then reflect back to the probe.  The reflected waves are detected by the probe and relayed to the machine.  The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (1540 m/s) and the time of the each echo's return (usually on the order of millionths of a second).  The machine (transducer) then converts this signal into electrical signal and then amplifies it.  And displays the distances and intensities of the echoes on the screen, forming a two dimensional image or three dimensional image. Figure: Work flow of ultrasound machine Ultrasound by definition has a frequency of greater than 20,000 cycles per second. The sonic beams used in diagnostic imaging have frequencies from 1,000,000 to 20,000,000 cycles per second. (One cycle per second is called a Hertz). It is an application of the pulse echo principle. Ultrasound probe generates Pulses of high frequency sound waves. These are transmitted into the patient & the echoes returning from various tissue boundaries (interfaces) are detected by the probe. The information from the probe is processed by the computer & is visualized as an image on the screen of the US equipment. ___________________________________________________________________________________ 30 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Main Differences Between Ultrasound & X-rays Diagnostic Ultrasound X-rays (Radiology) Wave Type Longitudinal Mechanical Electromagnetic Waves Waves Transmission Requirements Elastic Medium No Medium Generation Stressing the Medium Accelerating Electric Charges. Velocity Depends on the Medium It is relatively constant 299, through which it propagates. 792.456.2 m/s Similar Waves Seismic, Acoustic Radio, Light Characteristics of Sound Sound wave is mechanical energy that propagates through a continuous, elastic medium by compression and rarefaction of particle that composes it. Sound beam is similar to an X-ray beam in that both are waves transmitting energy. A more important difference is that X-rays pass readily through a vacuum whereas sound requires a medium for its transmission. Ultrasound pulses are transmuted through liquids as longitudinal waves. The term longitudinal waves means that the motion of the particles in the medium is parallel to the direction of wave propagation.The molecules of the conducting liquids move back & forth, producing bands of compression and rarefaction. The length of the wave is the distance between two bands of compression, or rarefaction. ___________________________________________________________________________________ 31 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Sound Transmission Characteristics of Ultrasound waves  Non ionizing longitudinal waves.  Need medium for propagation.  The signal is recorded in reflection rather than transmission mode.  Transmitted by mechanical vibrations forming bands of compression and rarefaction.  In liquid transmitted as longitudinal waves.  Wavelength: distance between two consequent bands of equal compression and rarefaction. Ultrasound Propagation Properties  Velocity of sound in soft tissue is nearly constant = 1500 m/sec.  Velocity of sound in bone and air differ greatly from soft tissue.  Velocity = Frequency x Wavelength.  Ultrasound implies freq > 1 MHz  Wavelength = velocity/ frequency. Figure: Relationship between Velocity & Wavelength ___________________________________________________________________________________ 32 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Ultrasound transmission properties  Frequency of ultrasound remains constant during propagation.  Wavelength changes in proportion to changes in the velocity of sound.  Sound bends at interfaces between tissues with different velocities of sound.  Bending increases as deviation from normal incidence increases.  Intensity of ultrasound decreases during propagation, measured in dB/cm. Transducers Definition and Principle A transducer is a device that converts one form of energy to another. Ultrasound transducers convert electrical energy to ultrasound energy and the reflected ultrasound waves from tissues are converted back to electrical clergy, which in turn gives rise to the ultrasound image. Ultrasound transducers work on the principle of piezoelectricity. This is the unique phenomenon by which certain materials respond to an applied electric field by changing shape. Changing the polarity of the applied voltage causes compression and expansion of the material which gives rise to Ultrasound waves. Components of the Transducer Transducers are the most important and expensive part of any ultrasound unit.  The piezoelectric crystal: About 0.5 mm in thickness and located near the face of the transducer is the critical component. Most modern transducers contain lead zirconium titanate (PZT) crystal. It produces ultrasound waves due to its unique property of piezoelectric effect. The piezoelectric phenomenon corresponds to an electrical potential on the surface of some crystals (quartz, turmalin, etc.) when they are mechanically deformed. The reverse effect, i.e. when the crystal is placed into an oscillating electrical field, the piezoelectric crystal starts to mechanically vibrate with the same frequency.  On either sides: crystal is coated with conducting film to ensure contact with the electrodes that will supply electric field used to strain the crystal.  Insulated cover: Outer side of the electrode is grounded and insulated to protect the patient from shock.  Backing block: Absorbs sound wave transmitted back into the transducer.  Housing: Whole unit is housed in a strong plastic case with rubber or cork as the acoustic insulator. ___________________________________________________________________________________ 33 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Ultrasound Transducer Characteristics of Piezoelectric Crystals Certain materials are such that the application of an electric field causes a change in their physical dimensions and vice versa. This is called piezoelectric effect, first described by Pierre and Jacques Curie in 1880. Piezoelectric elements are made of innumerable diploes in a geometric pattern. An Electric Dipole is a distorted molecule that appears to have a positive charge on one end and a negative charge on the other. The positive and negative ends are arranged so that an electric field will cause them to realign, thus changing the dimension of the crystal. The change is only a few microns. If the voltage is applied in sudden burst, or pulse, the crystal vibrates like a cymbal that has been struck a sharp blow and generates sound waves. The backing block quickly dampens the vibrations to prime the transducer for its second function, which is to detect returning echoes. As the sound pulse passes through the body, echoes reflect back toward the transducer from each tissue interface. These echoes carry energy and they transmit their energy to the transducer, from each tissue interface. These echoes carry energy and they transmit their energy to the Transducer, causing a Physical compression of the crystal element. This compression forces the tiny dipoles to change their orientation, which induces a voltage between the electrodes. The voltage is amplified and serves as the Ultrasound signal for display on an oscilloscope or TV monitor. Incidentally, the compression force and associated voltage are responsible for the name piezoelectricity, which means ‘Pressure Electricity’. Some naturally occurring materials possess piezoelectric properties (e.g. ,quartz). Most crystals used in medical US are man-made. This group of artificial piezoelectric materials is known as ferroelectrics. Barium titanate was the first of ceramic ferroelectrics ___________________________________________________________________________________ 34 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- to be discovered. This has been largely replaced by lead zirconate titanate, commonly known as PZT. A great advantage of piezoelectric ceramic is that they can be formed into different shapes, depending on the application for which they are intended. They can be made to vibrate in thickness or radial mode. Medical Crystals are designed to vibrate in the thickness mode. They still vibrate to lesser extent in the radial mode. How piezoelectric property is obtained? To possess piezoelectric characteristics, the dipoles must be arranged in a specific geometric configuration. To produce this polarization, the ceramic is heated to a high temperature in a strong electric field. At a high temperature the dipoles are free to move, and the electric field brings them into the desired alignment. The crystal is gradually cooled while subjected to a constant high voltage. As room temperature is reached, the diploes become fixed, and the crystal then possesses piezoelectric properties. Figure: Piezoelectric Crystals How piezoelectric property is lost? Piezoelectric crystals can be damaged by heat. Above a critical temperature, called the Curie temperature, crystal loses its polarization and loses its piezoelectric properties and becomes a worthless piece of ceramic. So obviously transducers should never be heated. The critical temperatures are as follows: Quartz 573 C Barium titanate 100 C PZT-4 328 C PZT-5A 365 C ___________________________________________________________________________________ 35 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- What is Resonant Frequency of Crystal? An ultrasound transducer is designed to be maximally sensitive to a certain natural frequency. The thickness of a piezoelectric crystals determine its natural frequency, called its RESONANT FREQUENCY. The surfaces of piezoelectric crystals behave like two identical cymbals, facing each other but separated in an open space. When one cymbal is struck, its vibrations set up sound waves that cause the other cymbal to vibrate. Vibrations are maximum in the second cymbal when the space separating the two is equal to one half of the wavelength of the sound. At this distance the sound waves from and the vibrations of the two cymbals are exactly synchronized. When a crystal is struck with a single sharp voltage spike, it vibrates at its natural frequency, which is determined by its thickness. The crystal is designed so that its thickness is equal to exactly half the wavelength of the ultrasound to be produced by the transducer. The crystal is said to resonate (i.e. oscillate most efficiently) at the frequency determined by its thickness. The frequency that corresponds to half of the wavelength thickness is called the FUNDAMENTAL RESONANCE FREQUENCY. Thus, a 2 MHz piezoelectric crystal made of PZT-4 will have a thickness of 0.001 m (1 mm). Similarly, a 1- MHz crystal will be 0.002 m thick. Note how crystals designed to resonate at high megahertz frequencies will be extremely thin. What is Transducer Q Factor? The Q factor refers to -- purity of their sound and the length of time that the sound persists. - The Q factor is a measure of the purity of tone (narrowness of frequency range). A high -- Q transducer produces a nearly pure sound made up of a narrow range of frequencies, whereas a low - Q transducer produces a whole spectrum of sound covering a much wider range of frequencies. When an unsupported high Q crystal is struck by a short voltage pulse, it vibrates for a long time and produces a long continuous sound. The interval between initiation of the wave and complete cessation of vibrations is called the ring down—time. ___________________________________________________________________________________ 36 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Transducer Q factor The ring down—time is the time that it takes a transducer to stop vibrating. The transducer system, which produces a narrow range of sound frequencies and has a long ring down time and is useful for Doppler Ultrasound Transducers. The transducer system with broad frequency range and short ring down time, is needed for organ imaging (pulse echo operation) because it can furnish short ultrasound pulses and will respond to a broad range of returning frequencies. The Q factor of piezoelectric materials can be controlled by altering the characteristics of the backing block of the transducer. A backing block is incorporated to quench the vibrations and to shorten the sonic pulse. The ideal backing material should accept all sound waves that reach it (i.e., not reflect any back into the crystal) and should then completely absorb the energy from these waves. Backing Blocks are generally made of a combination of tungsten & rubber powder in an epoxy resin. As a general rule, high—Q crystals are more efficient transmitters and low Q crystals are more efficient receivers. Types of Transducers Ultrasound transducers are basically divided into Mechanical transducers and Electronic array transducer. A. Mechanical Transducers A conventional singe element transducer or a group of single element transducer is mechanically moved to form images in real time. The images are in sector format encompassing an arc between 45 and 90 degrees. Decreasing this sector angle increases the resolution of the image. ___________________________________________________________________________________ 37 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- There are 3 types of mechanical transducers:- 1) Oscillating transducer-unenclosed crystal: In this a single transducer crystal is made to oscillate through an angle (15 - 60degrees) at a frame rate of 15-30/second, which depends on the rate of oscillation. Figure: Oscillating Transducers 2) Oscillating Transducer – enclosed crystal: In this the transducer is enclosed in oil or water filled container and is driven by a motor of electromagnet. The type of image produced depends on the distance between the transducer and the front surface of the casing. If near a sector image is produced; if the distance is more a trapezoid image is produced. Figure: Oscillating Transducer 3) Rotating Wheel Transducer: 3-4 transducers are mounted 90 or 120 degrees apart on a wheel and this is rotated at a constant rate in one direction. Only the transducer behind the acoustic window at a particular time can transmit or receive the ultrasound waves. Depending upon the design sector or trapezoid images are produced. ___________________________________________________________________________________ 38 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure:Rotating Wheel Transducer B. Electronic Array Transducers These consist of an array of small rectangular transducers arranged adjacent to one another. They do not move but are activated electronically so that the ultrasound beam sweeps across the patient. There are 3 types of electronic array transducers: 1. Linear array transducers: In these rectangular transducer elements are arranged in a line with their narrow dimensions ion contact. There are 64-200 transducers forming an array 4- 10cm long at a frequency of 2-3Mhz. The transducer elements are usually pulsed in groups of 4 at slightly different times to achieve a focused image. The scans from a linear array transducer are rectangular in format. Linear array transducers are especially useful in obstetric scans and in scanning of the breast and thyroid. Figure: Linear array transducers 2. Phased or Steered array transducers: These are used for real time scanning. By electronically controlled steering and focusing the ultrasound beam is made to sweep back and forth across the patient. A typical transducer contains 32 elements and operates at a frequency of 2-3MHz. ln this all the elements are pulsed to form each line of the image as against linear array transducer in which only a few elements (typically 4) form each line of the image. The scans obtained are fan shaped or sector scans. This is of advantage when scanning is to be done through very small acoustic window as in upper abdomen, gynecological and cardiologic examinations. ___________________________________________________________________________________ 39 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Phased Array Transducers 3. Convex transducers: The scans produced from convex transducers are midway between those from linear and sector scanners. Convex transducers of 3.5MHz and focus of 7-9 cm are best for general-purpose ultrasound examinations. In case of thin adults or children 5MHz transducer with a focus of 5-7cm is ideal. These cannot be used for echocardiography. Figure: Types of Transducers ___________________________________________________________________________________ 40 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Shows different shapes of Images Characteristics of Ultrasound Beam The ultrasound beam originating from the transducer consists of multiple sound waves originating from each of the piezoelectric crystals in the transducer. The wave front is not uniform when they arise from the transducer surface. But at variable distance from the transducer face the waves become synchronous, depending on the wavelength and hence the frequency of the sound waves. The shorter the wavelength, the closer the front forms to the surface of the transducer. Figure: Superimposition of waves to form a wave front The intensity of ultrasound beam varies longitudinally along the length of the beam. As the wave front travels through the medium the intensity of the ultrasound decreases. The high ___________________________________________________________________________________ 41 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- intensity parallel beam is called the Fresnel Zone and the low intensity diverging beam away from the transducer is called Fraunhofer zone. Fresnel zone is the longest with large transducers and high frequency. The divergence of the ultrasound beam depends on the size of the transducer and the frequency of the wave. The Fresnel zone (the frequency parallel beam) elongates with increasing frequencies. Also, when transducer size increases there is a proportional increase in the Fresnel zone. Figure: Zones of Ultrasound beams The high frequency waves are advantageous than the low frequency waves as the depth resolution is superior and the Fresnel zone is longer. But the disadvantage for the high frequency wave is their low tissue penetration. Figure: Elongation of near zone with increasing frequencies Figure: Elongation of near zone with increasing transducer size ___________________________________________________________________________________ 42 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Interaction between Ultrasound and Matter Ultrasound interactions are determined by the acoustic properties of matter. There are mainly 4 types of interaction. 1. Reflection: The ultrasound image formation depends on the reflected sound waves. The reflections at tissue interfaces depend on acoustic impedance difference between the tissues and the angle of incidence of the sound wave. The acoustic impedance is a characteristic of tissues. The impedance of the material is the product of density and velocity of sound in the material. Z = Density x Velocity Unit is Rayls The amount of reflection is determined by the angle of incidence of between the sound beam and the reflecting surface. The higher the angle of incidence (i.e the closer it to a right angle), the less the amount of reflected sound. At a tissue interface a definite percentage of the ultrasound is reflected and the rest is transmitted. This transmitted sound will undergo refraction, which we will discuss shortly. This transmitted sound is also important, as it is this fraction of the sound waves, which produce echoes from the deep tissues. The sound wave behaves in the same manner as light when it undergoes reflection and refraction. As you will remember, the angle of incidence and angle of reflection are same (diagram.). As the incident beam becomes closer to the perpendicular to the tissue interface, lesser will be the reflection (transmitted or refracted beam will be more). Figure: Refraction and Reflection of sound Waves 2.Refraction: When the ultrasound beams pass from one tissue into another there is a change in velocity of the sound beam depending on the acoustic impedance of the tissue. ___________________________________________________________________________________ 43 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- You will remember the equation: Velocity = Frequency X Wavelength The frequency of the sound beam does not change as it passes from one medium to another. So to accommodate the change in velocity, there should be a change in the wavelength and direction of the beam. This is called refraction. The fraction of the refracted beam increases, as the beam gets closer to perpendicular to the interface. Refraction is important cause of artifacts, Spatial distortion &Loss of Resolution. Figure: Refraction of Sound Waves 3. Absorption: When the ultrasound passes through tissues, there is a decrease in the intensity of the sound beam due to absorption in the tissues. This absorbed part of ultrasound wave is converted into thermal energy or heat. The absorption of the sound beam is higher in higher viscosity mediums and when we use high frequency sound beam. 4. Scatter: When sound encounters structures smaller than wavelength e.g. RBC Ultrasound Display Ultrasonic image is the electronic representation of the data generated from returning echoes displayed on a TV monitor. 1. A mode (Amplitude mode) In the A mode the echoes returning from the interfaces are displayed as spikes projecting from a base line. The spike height is proportional to the intensity of the sound beam and the distance in the horizontal axis to the spike measures the depth of the interface. In the diagram the interface 'a' lies closer to the surface than the interfaces 'b' and 'c'. It is used in ophthalmology, echocardiography and with B Mode for depth. ___________________________________________________________________________________ 44 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: A Mode 2. TM mode (Time — Motion mode) The TM mode the echoes are displayed as dots. It is used in the imaging of moving structures. The dots move back and forth indicating the movement of the tissue interface. A permanent record can also be made. The diagram below depicts a permanent record made from imaging the chest. The signals are coming from chest wall (straight line as there is no motion), from the initial valve leaflet (shows maximum movement) and from posterior wall of the heart. This mode is most useful in Echocardiography. Figure: TM Mode 3. B mode (Brightness mode) In the B mode echoes are displayed as dots. The B mode produces an image of a slice of tissue. In B mode the transducer is moved back and forth without moving from one point or moved across the body while rotating to take multiple images from the region of interest and the images are stored and assembled by the use of a computer. Gray scale imaging: In the gray scale imaging the echoes are displayed as dots in various shades of gray. In this mode a scan conversion memory tube is used. An electron beam in the scan conversion memory tube writes, reads and erases the information on the target There are two types of scan conversion memory tubes analog and digital. ___________________________________________________________________________________ 45 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Simple sector B Scan (A) and compound contact B Scan (B) Knobs and Controls in the Ultrasound Machine There are various knobs in the ultrasound machine, which should be understood for the proper imaging techniques.  Power: a knob that varies the amount of energy that the transducer transmits to the patient.  Annotation Keys: allow labeling of image. Letters and numbers can be used.  Backspace: misspelled image labeling can be erased using this key.  Caps lock: allows the use of either the upper case or lower case characters to be typed.  Cineloop: the system memory stores the most recent sequence of images in a cineloop before the freeze button is pressed.  Dual image: the screen can be split in order to display two views of an image or to compare the anatomy of the abnormal side with that of the normal side.  Field of view: gives 4 or 5 choices to the sonographer to make maximal use of the screen's resolution and yet display all the relevant area.  Freeze: all display data stop and start with this control.  Zoom: the zoom places a box on the screen. The material within the box can be expanded to fill the screen.  Video invert: allows one to select a positive or negative image i.e„ a white or black background.  Reversals: changes the image from left to right or right to left.  Track ball: controls the movements of the annotation markers, the distance markers and cineloop.  Transducer choice: Most units allow the use of more than one transducer to be plugged in at the same time. This control permits a choice between the transducers that are plugged to the system. ___________________________________________________________________________________ 46 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Shows ultrasound machine keyboard There are various controls in the ultrasound machine, which are used for the optimal visualization of the image.  Time gain compensator: the echoes from the deep tissues will be very small and attenuated. Time gain compensator amplifies these signals and the echoes from different tissue interfaces are made up into echoes with similar amplitude. Figure: Time gain compensation  Delay control: This control regulates the depth at which the TGC starts to augment the weaker signals.  Intensity control: increases the potential difference across the transducer and thereby produces more energetic ultrasound beard and thus stronger echoes at all levels  Coarse gain: Increases all the echoes proportionately. The initial echoes can be enhanced to twice or thrice their amplitude by increasing coarse gain.  Reject control: this control discriminates against the echoes those below minimum amplitude. It helps to clean up the image by removing small useless signals. It controls the noise of image.  Enhancement: Enhances a localized portion of the TG C curve Or in simpe words it acts like a lens. ___________________________________________________________________________________ 47 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Gain controls Figure: Reject controls Ultrasound Scanners All scanners consist of similar basic components,  Transmitter/Pulser to energise transducer.  Transducer.  Receiver and processor: to detect and amplify the back scattered energy and manipulate the reflected signals for display.  Display: presents ultrasound image or data in a form suitable for analysis and interpretation.  A method to record/store ultrasound image. Portable Ultrasound It consists of 3.6 MHz curvilinear probe. It is lightweight so it can be transported easily wherever it is needed It can be used to do scan at bedside, terminally ill patients and in cases of trauma where patient should be immobilized. So it can be used for general abdominal and pelvic ultrasound, guided procedures like pleural and peritoneal aspiration, biopsy. ___________________________________________________________________________________ 48 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Doppler Instrumentation Basically display flow information by using pulsed wave Doppler. There are different manufacturing companies like — Siemens, Toshiba etc. Probes — usually wideband probes. 1) 5-10 1v11-1z linear probe. 2) 5-9 MHz sector probe 3) 3-8 MHz curvilinear probe. 4) Endocorporal probe - Transvaginal and Transrectal ultrasound. So we can do 1. Abdominal and Pelvic ultrasound, Obstetric ultrasound and Doppler 2. Ultrasound of small parts like thyroid, scrotum. 3. Doppler of various vessels like carotid arteries, abdominal aorta, Renal vessels, arteries and veins of upper and lower limbs. ********** ___________________________________________________________________________________ 49 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Questions for Practice Q. 1. Fill in the blanks choosing the correct answer. 1. The ultrasound machine transmits high-frequency of _________sound pulses into the body using a probe. a) 12 to 24 megahertz b) 14 to 20 megahertz c) 1 to 12 megahertz d) None of the above 2. Ultrasound waves are similar to ____________ waves a) Seismic b) Acoustic c) Radio and Light d) a and b 3. _______ pass readily through a vacuum whereas _______requires a medium for its transmission. a) X-rays b) gamma rays c) sound d) None of the above Q. 2. Write the Difference between. Diagnostic Ultrasound X-rays (Radiology) ___________________________________________________________________________________ 50 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 3. State whether the following statements are true of false and correct the false statements. 1. Bending of ultrasound waves increases as deviation from normal incidence increases. ___________________________________________________________________________ 2. Velocity of sound in bone and air are same as soft tissue. ___________________________________________________________________________ Q. 4. Answer the following questions in one or two sentences. 1. List the different types of interactions between Ultrasound and Matter. ____________________________________________________________________________ ____________________________________________________________________________ ______________ 2. List the types of transducers. ____________________________________________________________________________ ____________________________________________________________________________ ______________ 3. What is Transducer Q Factor? ____________________________________________________________________________ ____________________________________________________________________________ ______________ Q. 5. Write short notes. 1. Definition, principles and components of transducer. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________________ 51 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Q. 6. Answer the following questions in 6 – 7 lines. 1. Explain the principles of ultrasound. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ _______ ********** ___________________________________________________________________________________ 52 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- 5. Doppler By the end of this chapter, you would be able to: Explain the basics of Doppler Discuss the types of Doppler transducer Explain the other factors related to Doppler Introduction The Doppler Effect was first described by Christian Doppler in 1893. The Doppler Effect is a change in the perceived frequency of sound emitted by a moving source. Doppler ultrasound is used to primarily study the blood flow in the circulatory system. Doppler Ultrasound Doppler ultrasound is based on the shift of frequency in an ultrasound wave caused by a moving reflector. The moving reflectors in the body are blood cells. By comparing the incident ultrasound frequency with the reflected ultrasound frequency from the Blood Cells, it is possible to distinguish the velocity of Blood. It is used to create color blood flow map of the vasculature. The Doppler Effect is a change in the perceived frequency of sound emitted by a moving source. For example: the perceived frequency of sound of siren emitted by an ambulance moving towards a stationary observer is higher than the true frequency of the siren. Similarly the frequency would be lower if the ambulance was moving away from the stationary observer. Similar principle is made use of in Doppler ultrasound, primarily to study the Blood flow in the circulatory system. Types of Doppler Transducers There are two types of Doppler transducers  Continuous wave Doppler  Pulsed Doppler ___________________________________________________________________________________ 53 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Continuous wave Doppler This mode employs two piezoelectric elements both contained in a single head. One crystal transmits a continuous sonic signal at a known frequency, usually between 3 and 8 MHz. The other crystal receives the returning echoes and records their frequency. The frequency of the initial signal is algebraically subtracted from that of the returning echoes. The difference, the Doppler shift, usually falls within the frequency range detectable by the human ear, after amplification. This Doppler shift is the audio signal. Although able to detect the presence and direction of blood flow, continuous wave devices are unable to distinguish signals arising from vessels at different depths. It provides velocity information of blood. Figure: A typical Doppler ultrasound transducer with inclined transducer elements Pulsed Doppler It has provided the means of detecting the depth at which a returning signal has originated. It has the same crystal to transmit and receive the signals at precisely timed intervals. Thus pulsed-wave Doppler permits the sampling of flow data from selected depths by processing only the signals that return to the transducer after precisely timed intervals. A new pulse is not transmitted until the echoes from the previous pulse have been detected. The depth at which returning signal originated can be determined by knowing the time of transmission of the signal and the time of its return.(i.e. time of flight to an interface and subsequent return). The Doppler beam is thus used to detect the motion of blood within the blood vessels. lt provides both velocity and position information simultaneously. ___________________________________________________________________________________ 54 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: block diagram of continuous wave doppler Doppler Shift Equation The Doppler shift is difference between the incident frequency and reflected frequency. The frequency change of back-scattered echoes can be calculated by the Doppler shift equation: 2vs 𝛿V = ------------ cos θ v ∆v = Frequency change (doppler shift in Hz) vs --- velocity of blood (m/s) v = velocity of sound (1540 m/s) θ = angle between sound beam and direction of blood flow (Doppler angle) The vector of blood cell motion toward the transducer is represented by cos θ in the equation. At frequencies between 2 and 10 MHz, the Doppler shift falls in the audible range for most physiologic motions. An experienced listener can learn a great deal about the status of the circulatory system with a Doppler device. Doppler can be used to detect presence or absence of blood flow in both arteries and veins, to identify vascular constrictions with their associated eddy currents and venturi jets, and to detect fetal heart motion earlier than with any other method. ___________________________________________________________________________________ 55 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Figure: Image shows Doppler angle Other Factors Related to Doppler Scattering of Ultrasound by Blood Ultrasound encountering blood is not reflected, it is scattered in all directions. This scattering is referred to as Rayleigh-Tyndall scattering, and is caused by the red blood cells as their size is much smaller than the wavelength of ultrasound beam used. Therefore, a typical sonogram displays blood vessels as echo-free or dark structures. The Duplex Scanner The duplex scanner is obtained by coupling the Doppler system with real time Ultrasound imaging. Duplex systems can be used to estimate velocity of flow in the vessel. Real time Image is frozen and using pulsed Doppler mode: the cursor is positioned to exact area from where the Doppler signal is to be obtained. In this way one can accurately define the area of interest by direct visualization. Doppler Color Flow Imaging One limit of duplex ultrasonic imaging is that flow information is obtained only from the small area for which the Doppler signals are determined, and flow is not evaluated in rest of the image. Thus the examiner should sample the proper sites throughout the lumen of the vessel. Clinical applications include carotid, cardiac, and peripheral arterial and venous imaging, evaluation of deep vessels in abdomen, pelvis and fetus, and investigation of organ and tumor perfusion. Color Doppler presents flow information by superimposing a color image on the gray-scale real-time image. This presents a real-time image of both anatomy and blood flow. Detected motion is assigned a color, usually red or blue. Color choice is arbitrary arid usually under ___________________________________________________________________________________ 56 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- the control of the operator. Usually red is assigned to arteries and blue to veins. The hue and intensity of color change with changes on Doppler shift frequency. Usually a dim color is used to designate high velocity. Thus today Doppler color flow imaging has become a very important part of diagnostic imaging in renal, abdominal, fetal, carotid and peripheral vascular imaging. Power Mode Doppler Power mode Doppler uses a color map that displays the integrated power of the Doppler signal instead of its main frequency shift. Since frequency shift data are not displayed, there is no aliasing. The image does not provide any information related to flow direction or velocity and power mode Doppler is much less angle dependent than frequency based color flow Doppler display. Surrounding noise is assigned a homogenous black background color. All these increase the sensitivity for flow detection. ___________________________________________________________________________________ 57 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE --------------------------------------------------------- Knobs and Controls on the Machine Controls present on a Doppler machine in addition to the ultrasound controls are:- Doppler gain: similar to the time gain control but increases the intensity of color signal from the flowing blood.  Angle control: manipulates angle of the ultrasound beam to obis correct flow velocities.  Colour flow control: places the Doppler area on the ultrasound image to see for flow.  Range gate cursor: cursor, which may be presented as a box or lv parallel bars, shown in the screen which indicates the depth and area from which the Doppler signal is obtained. Doppler cursor: places the cursor in the Doppler field, which can then be moved to the desired position to record velocities. Power Doppler: switches to power Doppler mode. Sweep Speed: this control helps to adjust the rate at which the spectral information is displayed. Three speeds: slow, moderate and high can be selected. Wall filter: to filter out the noise and artifact caused by the patient respiration and vessel motion. The higher the filter setting, lesser the information displayed in the Doppler signal. ********** ___________________________________________________________________________________ 58 | Ultrasound Imaging | PW ----------------------------------------------------------- TISS – SVE ------------------------------