Imaging Modalities PDF

Imaging Modalities Other Imaging Modalities 1. Ultrasound 2. Fluoroscopy 3. Computed and Digital Radiography 4. Computed Tomography 5. Magnetic Resonance Imaging 6. Nuclear Medicine 7. Bone Densitometry 8. PET Scan 9. SPECT Scan 10. Radiation Therapy Ultrasound Ultrasound imaging, also called s...

Imaging Modalities Other Imaging Modalities 1. Ultrasound 2. Fluoroscopy 3. Computed and Digital Radiography 4. Computed Tomography 5. Magnetic Resonance Imaging 6. Nuclear Medicine 7. Bone Densitometry 8. PET Scan 9. SPECT Scan 10. Radiation Therapy Ultrasound Ultrasound imaging, also called sonography It involves exposing part of the body to high-frequency sound waves to produce an image of a particular structure of the body. Ultrasound images are captured in real- time, it can show the structure and movement of the bodys internal organs, as well as blood flowing through blood vessels. Ultrasound scanners consist of a console containing a computer and electronics, a video display screen and a transducer that is used to do the scanning. Transducer The transducer is a small hand-held device that resembles a microphone, attached to the scanner by a cord. The transducer sends out inaudible high frequency sound waves into the body and then listens for the returning echoes from the tissues in the body. The ultrasound image is immediately visible on a video display screen that looks like a computer or television monitor.  The image is created based on the amplitude (strength), frequency and time it takes for the sound signal to return from the area of the patient being examined to the transducer and the type of body structure the sound travels through. The essential element of each ultrasound transducer is a piezoelectric crystal. It serves to generate as well as receive ultrasound waves. Types of Ultrasound Transducers 1. Linear Transducers  – the piezoelectric crystal arrangement is linear, the shape of the beam is rectangular, and the near-field resolution is good. – The footprint, frequency, and applications of the linear transducer depend on whether the product is for 2D or 3D imaging. – The linear transducer for 2D imaging has a wide footprint and its central frequency is 2.5Mhz – 12Mhz. can be use for various applications, such as: Vascular examination, Venipuncture, blood vessel visualization, Breast, Thyroid, Tendon. Types of Ultrasound Transducers – The linear transducer for 3D imaging has a wide footprint and a central frequency of 7.5Mhz – 11Mhz.  Can be use for various applications, such as: Breast, Thyroid Arteria carotis of vascular application. 2. Convex Transducers  – The convex ultrasound transducer type is also called the curved transducer because the piezoelectric crystal arrangement is curvilinear.  – The beam shape is convex and the transducer is good for in- depth examinations, even though the image resolution decreases when the depth increases.  – The footprint, frequency, and applications also depend on whether the product is for 2D or 3D imaging.  The convex transducer for 2D imaging has a wide footprint and its central frequency is 2.5MHz – 7.5MHz. Can be use for various applications, such as: Abdominal examinations, Diagnosis of organs Transvaginal and transrectal examinations The convex transducer for 3D imaging has a wide field of view and a central frequency of 3.5MHz – 6.5MHz. Can be use for abdominal examinations.  Phased Array Transducers  – This transducer is named after the piezoelectric crystal arrangement which is called phased-array and it is the most commonly used crystal Phased Array transducer. – Has a small footprint and low frequency (its central frequency is 2Mhz – 7.5Mhz) – The beam point is narrow but it expands depending on the applied frequency. – The beam shape is almost triangular and the near-field resolution is poor.  – Can be use for various applications, such as: Cardiac examinations, Abdominal examinations and Brain examinations Ultrasound machine has the following parts: 1. Transducer probe - probe that sends and receives the sound waves. 2. Central processing unit (CPU) - computer that does all of the calculations and contains the electrical power supplies for itself and the transducer probe 3. Transducer pulse controls - changes the amplitude, frequency and duration of the pulses emitted from the transducer probe 4. Display - displays the image from the ultrasound data processed by the CPU 5. Keyboard/cursor - inputs data and takes measurements from the display 6. Disk storage device (hard, floppy, CD) - stores the acquired images 7. Printer - prints the image from the displayed data Advantages Mobility Cost-effective patient-friendliness (no radiation) Applied in obstetrics, cardiology, inner medicine, urology Fluoroscopy The type of medical imaging that shows a continuous x-ray image on the monitor. Study of moving body structures. The primary function of the fluoroscope is to provide real-time dynamic viewing of anatomic structures.  Dynamic studies are examinations that show the motion of circulation or the motion of internal structures. Allows the physicians to view a continuous image of the internal structure while the x-ray tube is energized. The image intensifier is a complex electronic device that receives the remnant X-Ray beam, converts it into light, and increases the light intensity. Computed Radiography Digital radiography was introduced in 1981 by Fuji with the first commercial computed radiography (CR). Computed radiography is a form of digital radiography. A digital image acquisition process using a Conventional X-ray machines that produces images that have much better contrast than a Conventional X-ray film-screen system. A process of capturing radiographic data from a conventional X- ray machine and processing the data digitally to produce high quality radiographic images. For exposure, an Imaging Plate (IP) is placed in a cassette instead of a piece of film. The IP captures and "stores" the X-rays. Components of a CR System CR Workflow Screen-film Radiography Workflow CR Image Receptor Screen film imaging and CR imaging are similar, both modalities uses image receptor. – an x-ray–sensitive plate that is encased in a protective cassette. Both produce a latent image, in a different form, that must be made visible via processing. – However: In screen-film radiography the radiographic intensifying screen is a scintillator that emits light in response to an x-ray interaction. In CR the response to x-ray interaction is seen as trapped electrons in a higher energy metastable state. Imaging Plate (IP) The Imaging Plate looks like the intensifying screens found in Conventional film-screen cassettes Coated with photostimulable phosphor, also called storage phosphor. – The phosphor material is generally a kind of Barium fluorohalide.  The Imaging Plate also contains a protective coat, a conductive layer, support and laminate layers. Instead of emitting light immediately when exposed to X-rays, the photostimulable phosphor has the special property of storing the X-ray energy in a latent form and releasing the same when stimulated by a laser energy in the CR Reader /Digitizer. Digital Radiography A digital image acquisition process using a digital X-ray machines with flat panel detectors. Uses two types of detectors: – Direct – Indirect Computed Tomography First introduced in 1966 by Godfrey Hounsfield. Tomography is imaging of Layer/Slice. Computed tomography (CT), is the process of creating a cross-sectional tomographic plane of any part of the body. The patient is scanned by an x-ray tube rotating around the body part being examined. A detector assembly measures the radiation exiting the patient and feeds back the information, referred to as primary data, to the host computer.  Once the computer has compiled and calculated the data according to a pre-selected algorithm, it as embles the data in a matrix to form an axial image. Each image, or slice, is then displayed on a cathode ray tube (CRT) in a cross-sectional format.  In the CT examination, a tightly collimated x-ray beam is directed through the patient from different angles, resulting in an image that represents a cross section of the area scanned. This technique essentially the superimposition of body structures. The CT technologist controls the method of acquisition, the slice thickness, the reconstruction algorithm, and other factors related to image quality. CT-scan Equipment Large box-like machine with hole in the middle. Patient lies on narrow table that slides in and out of this hole. X-ray tube and electronic x-ray detectors rotate around you (gantry). Computer processes the information and is operated by a technologist who works scanners and monitors the exam.  CT Scan: Used For Diagnose cancers, CV disease, infectious disease, appendicitis, trauma. and muscular- skeletal disorders. Generatons of CT Imaging System 1. First-generation imaging system: translate and rotate, pencil beam, single detector, 5-minute imaging time. 2. Second-generation imaging system: translate and rotate, fan beam, detector array, 30-second imaging time. 3. Third-generation imaging system: rotate and rotate, fan beam, detector array, subsecond imaging time. 4. Fourth-generation CT imaging system: rotate and stationary, fan beam, detector array, subsecond imaging time. Magnetic Resonance Imaging Magnetic resonance imaging (MRI) is a technique that uses a magnetic field and radio waves to create detailed images of the organs and tissues within the body. History Nikola Tesla discovered the Rotating Magnetic Field in 1882 in Hungary.  In 1956, the "Tesla Unit" was proclaimed. All MRI machines are calibrated in "Tesla Units".  The strength of a magnetic field is measured in Tesla or Gauss Units. 1 Tesla = 10,000 Gauss  – Low-Field MRI= Under 0.2 Tesla (2,000 Gauss)  – Mid-Field MRI= 0.2 - 0.6 Tesla (2,000 - 6,000 Gauss) – High-Field MRI= 1.0 - 1.5 Tesla (10,000 - 15,000 Gauss)  In 1937, Professor Isidor I. Rabi, observed the quantum phenomenon dubbed nuclear magnetic resonance (NMR). – He recognized that the atomic nuclei show their presence by absorbing or emitting radiowaves when exposed to a sufficiently strong magnetic field. Raymond Damadian, a physician, discovered that hydrogen signal in cancerous tissue is different from that of healthy tissue because tumors contain more water. – More water means more hydrogen atoms. When the MRI machine was switched off, the bath of radio waves from  In 1973, Paul Lauterbur, a chemist, produced the first NMR image.  On July 3, 1977, the first human scan was made as the first MRI prototype. (The process took 5 hours). Mechanism of action Magnetic field temporarily realigns hydrogen atoms in the body. Radio waves cause these aligned atoms to produce signals. Signals used to create cross-sectional MRI images Components of MRI Magnet Gradient Coils Radio Frequency (RF) coils MRI Patient Table Antenna/Computer System Magnet Has a horizontal tube that runs through the magnet and is called a bore. Most MRI magnets use a magnetic field of 0.5 to 2.0 tesla. (Earth’s magnetic field is only 0.5 gauss.) The magnetic field is produced by passing current through multiple coils that are inside the magnet. Gradient Coils There are three different gradient coils located within the main magnet. Each one of these produce three different magnetic fields that are less strong than the main field. The gradient coils create a variable field (x, y, z) that can be increased or decreased to allow specific and different parts of the body to be scanned by altering and adjusting the main magnetic field. Frequency (RF) Coils Transmit radio frequency waves into the patient’s body. There are different coils located inside the MRI scanner to transmit waves into different body parts. If a certain area of the body is specified, then all the RF coils usually become focused on the body part being imaged to allow for a better scan. Patient Table This component simply slides the patient into the MRI machine. The position at which the patient lies down on the table is determined by the part of the body that is being scanned. Area under examination is placed in the exact centre of the magnetic field (isocentre). Antenna/Computer System The antenna detects the RF signals emitted by a patient’s body and feeds this information into the computer system. The computer system: function is to receive, record, and analyze the images of the patient. It interprets the data produce an understandable image. Advantages Scanning and detection of abnormalities in soft tissue. There is no involvement of any kind of radiations. MRI scan can provide information about the blood circulation  Painless Images may be acquired in multiple planes (Axial, Sagittal, Coronal, or Oblique) without repositioning the patient. MRI images demonstrate superior soft tissue contrast than CT scans and plain films making it the ideal examination of the brain, spine, joints and other soft tissue body parts  Disadvantages The powerful magnetic fields generated by the MRI scanner will attract metal objects. The magnetic field of the MRI scanner can also pull on any metal-containing object in the body, such as medicine pumps and aneurysm clips. Medical implants may heat up during the scan as a result of the technology.  MRI scans can cause heart pacemakers, defibrillation devices and cochlear implants to malfunction. Expensive Nuclear Medicine Nuclear medicine is a medical specialty that focuses on the use of radioactive materials called radiopharmaceuticals for diagnosis, therapy, and medical research. Determine the cause of a medical problem based on organ or tissue function (physiology). Radioactive Tracer The radioactive material, or tracer; is generally introduced into the body by injection, swallowing, or inhalation. Different tracers are used to study different parts of the body. Tracers are selected that localize in specific organs or tissues. The amount of radioactive tracer material is selected carefully to provide the lowest amount of radiation exposure to the patient and still ensure a satisfactory examination or therapeutic goal. Radioactive tracers produce gamma-ray emissions from within the organ being studied.  A special piece of equipment, known as a gamma or scintillation camera, is used to transform these emissions into image that provide information about the function and anatomy of the organ or system being studied. – An electronic device that detects gamma rays emitted by radio pharmaceautical that have been introduced into the body as tracers. The camera records this information on a computer or on film. Bone Densitometry Measure the density or thickness of bones. It measures the amount of mineral (calcium) in a specific area of the bone. The bone measurement values are used to assess bone strength, diagnoses diseases associated with low bone density (especially osteoporosis), monitor the effects of therapy for such diseases, and predict risk of future fractures. The more mineral in the bone measured, the greater is the bone density or bone mass. BMD test can: Measure the density of bones Detect osteoporosis before a fracture occurs Help to predict chances of fracturing in the future Monitor the effectiveness of treatments for osteoporosis and osteopenia. PET Scan Positron emission tomography (PET)" is a non-invasive nuclear imaging technique that involves the administration of a radioactive molecule and subsequent imaging of the distribution and kinetics of the radioactive material as it moves into and out of tissues. The tracers are introduced into the body, by either injection or inhalation of a gas. PET scanner is used to produce an image showing the distribution of the tracer in the body. Clinical Applications of PET Oncology – Role in lesion detection, lesion characterization, staging of malignant lesions and assessment of the therapeutic response. Brain – PET Study the brain's blood flow and metabolic activity. It aid in discovery of nervous system problems, such as Alzheimer's disease, Parkinson's disease etc.  Heart – PET can help find damaged heart tissue especially after a heart attack and can help choose the best treatment such as coronary bypass heart surgery for a person with heart disease. Detector Comprised of an 8 x 8 scintillation, inorganic crystals which emits light photons after the interaction of photons and a 4 photomultiplier tubes (PMTs) arranged in a circular pattern around the patient. Septa Lead or tungsten circular shield mounted between the detector rings  Limits scattered radiation from the object reaching the detector (scattered out the transverse plane). Coincidence Circuit Specific electronic circuits "coincidence" circuits pick up gamma pairs due to the two gamma rays emitted during the positron annihilation almost simultaneously.  The coincidence is a very strong signature that distinguishes them from other photons.  On the image it is requested that the signals coming from the scintillators A and B coincide within 12 billionths of a second (nanosecond). Cyclotron A machine used to produce the radioisotopes (radioactive chemical elements) which are used to synthesize the radiopharmaceuticals.  The most frequently used radioisotopes in PET are: Carbon-11 Nitrogen-13 Oxygen-15 Fluorine-18 18FDG (Fluorodeoxyglucose) is the most widely used PET tracer.  Bed – capable of moving in and out of the scanner to measure the distribution of PET radiopharmaceuticals throughout the body, and it adjusts to a very low position for easy patient access Computer  – A computer analyzes the gamma rays and uses the information to create an image map of the organ or tissue being studied. Principle of PET Positron Emission Positron Emission occurs when the isotope decays and a proton decays to a Neutron, a Positron and a Neutrino. After traveling a short distance (3-5mm), the positron emitted encounters an electron from the surrounding environment.   The two particles combine and "annihilate" each other, resulting in the emission of two gamma rays in opposite directions of 0.511 MeV each. As positron annihilation occurs, the detector detects the isotope's location and concentration.   The resultant light photons are converted to electrical signals that are registered by the system electronics almost instantly. The reconstruction software then takes the coincidence events measured at all angular and linear positions to reconstruct an image. SPECT Scan SPECT Single Photon Emission Computed Tomography is a: Nuclear Medicine imaging modality, which involves the use of radionuclides injected intravenously into the body, to produce a 3D distribution of the gamma rays emitted by the radionuclide, giving physiological information about the organ of interest. SPECT is the 3D version of the 2D (planar imaging) gamma camera technology.  It uses 1 or more gamma camera heads rotated round the patient.   SPECT combines conventional scintigraphic and computed tomographic methods.  So it gives 3D functional information about the patient in more detail and higher contrast than found in planar imaging. SPECT avoids the superposition of active and non-active layers, which restricts the accurate measurement of organ functions found in the planar gamma camera. How SPECT works? A radiopharmaceutical is injected into the patient’s body. It travels into the blood stream, and concentrates in the Region of Interest. There, it decays, emitting gamma rays. The gamma rays travel out of the patient’s body, and are detected by the gamma camera head of the SPECT machine. The gamma ray is collimated by the collimators to minimize scatter, and improve image quality.  The collimated gamma rays hit the crystal detector, usually Sodium Iodide crystals doped with Thallium [NaI (Tl)], which converts the energy of the gamma rays to visible light. As visible light travel through the Photo Multiplier Tubes (PMT), they absorb the light and emit electrons. The electrons emitted are used for image formation. They are detected by a Positioning and Summing Circuit, which decode the body position of the original photon.  A Pulse Height Analyzer (PHA) decodes the energy of the emitted photon. The information is passed on to a digital circuit on a computer, where algorithms are used to reconstruct the image. The resultant image gives a physiological state of the organ. Hot spots (areas of increased uptake) and cold/dark spots or photopenia (areas of decreased intake) may indicate pathology, such as arthritis, infections, fractures, tumours. Radiation Therapy Radiation has been an effective tool for treating cancer for more than 100 years. Radiation oncologists are doctors trained to use radiation to eradicate cancer. About two-thirds of all cancer patients will receive radiation therapy as part of their treatment. Radiation Therapy Radiation therapy works by damaging the DNA within cancer cells and destroying their ability to reproduce. When the damaged cancer cells are destroyed by radiation, the body naturally eliminates them. Normal cells can be affected by radiation, but they are able to repair themselves. Sometimes radiation therapy is the only treatment a patient needs. Other times, it is combined with other treatments, like surgery and chemotherapy. History of Radiation Therapy The first patient was treated with radiation in 1896, two months after the discovery of the X-ray. Back then, both doctors and non-physicians treated cancer patients with radiation. Rapid technology advances began in the early 1950s with cobalt units followed by linear accelerators a few years later. Recent technology advances have made radiation more effective and precise. How Is Radiation Therapy Used? Radiation therapy is used in two different ways. – To cure cancer: Destroy tumors that have not spread to other body parts. Reduce the risk that cancer will return after surgery or chemotherapy. – To reduce symptoms: – Shrink tumors affecting quality of life, like a lung tumor that is causing shortness of breath. – Alleviate pain by reducing the size of a tumor. Radiation Oncology Team Radiation Oncologist – The doctor who oversees the radiation therapy treatments. Medical Radiation Physicist – Ensures that complex treatment plans are properly tailored for each patient. Dosimetrist – Works with the radiation oncologist and medical physicist to calculate the proper dose of radiation given to the tumor. Radiation Therapist – Administers the daily radiation under the doctor’s prescription and supervision. Radiation Oncology Nurse – Cares for the patient and family by providing education, emotional support and tips for managing side effects. Types of Radiation Therapy Radiation therapy can be delivered two ways: – Externally External beam radiation therapy delivers radiation using a linear accelerator. – Internally Internal radiation therapy, called brachytherapy or seed implants, involves placing radioactive sources inside the patient. The type of treatment used will depend on the location, size and type of cancer. Planning Radiation Therapy - Simulation Each treatment is mapped out in detail using treatment planning software. Radiation therapy must be aimed at the same target every time. Doctors use several devices to do this: – Skin markings or tattoos – Immobilization devices casts molds headrests External Radiation Therapy Specialized types of external beam radiation therapy – Three-dimensional conformal radiation therapy (3D-CRT) – Uses CT or MRI scans to create a 3-D picture of the tumor. Beams are precisely directed to avoid radiating normal tissue. Intensity modulated radiation therapy (IMRT) – A specialized form of 3D-CRT. – Radiation is broken into many “beamlets” and the intensity of each can be adjusted individually.  Proton Beam Therapy – Uses protons rather than X-rays to treat certain types of cancer. – Allows doctors to better focus the dose on the tumor with the potential to reduce the dose to nearby healthy tissue. Neutron Beam Therapy – A specialized form of radiation therapy that can be used to treat certain tumors that are very difficult to kill using conventional radiation therapy.  Stereotactic Radiotherapy – Sometimes called stereotactic radiosurgery – This technique allows the radiation oncologist to precisely focus beams of radiation to destroy certain tumors, sometimes in only one treatment. Internal Radiation Therapy Places radioactive material into tumor or surrounding tissue. Also called brachytherapy – brachy Greek for “short distance.” Radiation sources placed close to the tumor so large doses can hit the cancer cells. Allows minimal radiation exposure to normal tissue. Radioactive sources used are thin wires, ribbons, capsules or seeds. These can be either permanently or temporarily placed in the body. Side Effects of Radiation Therapy Side effects, like skin tenderness, are generally limited to the area receiving radiation. Unlike chemotherapy, radiation usually doesn’t cause hair loss or nausea. Most side effects begin during the second or third week of treatment. Side effects may last for several weeks after the final treatment Is Radiation Therapy Safe? Many advances have been made in the field to ensure it remains safe and effective. Multiple healthcare professionals develop and review the treatment plan to ensure that the target area is receiving the dose of radiation needed. The treatment plan and equipment are constantly checked to ensure proper treatment is being given.