Ultrasound in Medicine 2023 PDF

Medical Physics Ultrasound in Medicine PA RT 2 D R. E N T I D H A R A LTA E E  Topics of the Lecture Principle of Sonar US generation US Generation Production of US image  Image quality US imaging modes  Physiological effects of US Ultrasound waves Ultrasound is sound with a fr...

Medical Physics Ultrasound in Medicine PA RT 2 D R. E N T I D H A R A LTA E E  Topics of the Lecture Principle of Sonar US generation US Generation Production of US image  Image quality US imaging modes  Physiological effects of US Ultrasound waves Ultrasound is sound with a frequency 20kHz to 1GHZ (for medical applications). It is greater than the upper limit of human hearing.  SONAR (SOund NAvigation and Ranging)- SONAR - It is a device that uses an US waves to generate an image of a particular soft tissue structure in the body. Transducers Types Transducer - Converts electrical energy to mechanical (ultrasound) energy and vice versa. There are many types of transducers which are different in frequency and foot print: Basic Principle of SONAR  In medical diagnosis, ultrasound pulses are transmitted into the body by placing the US transducer in close contact with the skin, using water or a jelly paste to eliminate the air and create a good impedance matching between the transducer and skin. The backed echoes are detected as a weak signal amplified and displayed on an oscilloscope. US Generation Piezoelectric principle  The ultrasound signal is generated and detected by the sensor. The transducer based on piezoelectric principle. Many crystals can be used so that AC voltage (electrical energy) across the crystal will produce a vibration of the crystal (mechanical energy), thus generating an ultrasound wave and vice versa.  In clinical application the piston is represented by the transducer, when an electric potential difference is applied between the faces of a piezoelectric crystal, the crystal will respond by expanding or contracting. The push–pull action of the transducer causes regions of compression and rarefaction, pass out from the transducer face into the tissue.  US Image Production Three concepts that are affects US image production:  1. Focal zone  2. Acoustic impedance  3. Refraction Focal zone Acoustic impedance When an ultrasound wave encounters a boundary between two tissues with different values of Z, a certain fraction of the wave energy is backscattered (or reflected) towards the transducer, with the remainder being istransmitted common to through the boundary use a thick liquid deeper(jelly) between into the body the transducer and the patients skin. The thick liquid helps to keep away air bubbles and allows easy passage of the ultrasound waves (small Az). Refraction It is a change in direction of the sound wave as it passes from one tissue to a tissue of higher or lower sound velocity. To minimize refraction the artifacts (errors) in US US transducer should be image due to the change in perpendicular to the the US wave path. interface between the two media. Quality of ultrasound imaging The quality of ultrasound imaging is determined by the interaction of the acoustic wave with the body tissue, these interactions includes: spatial resolution, attenuation and reflection and transmission. spatial -1 resolution Quality of ultrasound imaging :Attenuation It is the reduction in intensity (I) of US.wave as it passes through the tissue (x) Image Quality The choice of the ultrasound is determined by a compromise between good resolution and deep penetration. Reflection Perpendicular reflection originates the echo signal, while non-perpendicular reflection causes an intensity loss in echo signal, as shown in the figure. Smooth surface → low scattering → good image Rough surface → high scattering → bad image US Image Modes A-Mode (1D) : It is used to obtain diagnostic information about the depth of structure (image with 1-dimention).  In this mode an US waves send into the body and measure the time required to receive the reflected sound (echoes) from the interface between the different tissues. The depth of the interface recorded is proportional to the time it takes for the echo to return. Depth= Velocity x time  Using a sound velocity of 1540 m/sec in average soft tissue, the echo takes 13 µsec at a depth of 1 cm  A-mode is used to detect the brain tumors and eye diseases.  :Applications of A- mode scan A. Echo encephalography: It is used in the detection of brain tumors.  Pulses of ultrasound are sent to a thin region of the skull above the ear and the echoes from different structures are displayed on the oscilloscope.  Compare the echoes from the left side of the head to the right side, and find the shift in the middle structure: - If the shift > 3 mm for an adult (abnormal) If the shift > 2 mm for a child (abnormal) :Opthalmology  It is used ultrasound frequencies of up to 20 MHz, this high frequency is used because: a) It gives good resolution. b) It isn’t hazard because there is no bone in the eye  In this case the A- mode is used for:  The diagnosis of the eye tumors, foreign bodies and detachment of retina.  It is used in biometry (measurements of the distances in the eye e.g. lens thickness, depth from the cornea to the eye lens US Image Modes B-Mode (2D) (Brightness) It is used to obtain 2D images of the body. The principle is the same as in A-mode except that transducer is moving. A storage oscilloscope is usually used to form the image. B-mode is providing information about the internal structure of the body, such as size, location and change with time of the eye, liver, breast, heart, and fetus. US Image Modes M- Mode (2D +motion) It is used to study motion such as that of heart and heart valves (image with 2D + motion). M-mode combines between features of A- and B- mode. The transducer is held stationary as in A-mode and the echoes appear as dots as in B-mode. It is used in diagnostic information about the heart (mitral valve) and detection of pericardial US Image Modes D- Mode (3D + motion; or 4D): D- Mode takes 3-dimentionanl US images and adds the element of time to the process (image with 3D with motion).  Physiological effects of ultrasound in therapy Various physiological and chemical effects occur when ultrasonic waves pass through the body, and they can cause physiological effects. The magnitude of physiological effects depends on the frequency and amplitude of the sound.  Low intensity US (~ 0.01 W/cm²) → no harmful effects are observed → used for diagnostic work (as in the sonar). Continues US (~1 W/cm²) → deep heating effect (diathermy) → temperature raise due to the absorption of acoustic energy in the tissue. Continues US (1-10 W/cm²) → sound moves through→ region of compression and rarefactions → pressure differences in adjacent regions of tissues (micromassage). Continues US (~ 35 W/cm²) →tissue destroying effect → rupture DNA molecules. Continues and focused US (~ 10³ W/cm²) → selective destroying of deep tissue using a focused ultrasound beam. Q/Sound travels at 1400m/s in water. If a ship sends a sonar signal to map the bottom of the ocean and it returns after 2 seconds, how deep is the ocean?Hq Q/What are two ways that an ultrasound is used? A. transverse waves and longitudinal waves B. hertz and meters C. sonar and ultrasound imaging D. music instruments and amplify the sound.Q/Ultrasound occurs at frequencies above 20,000 Hz True False ?Q/What is an echo A. The vibrations of sound. B. The reflected sound waves. C. The changes of sound frequency. D. The sound waves which are absorbed.ter. If a ship sends a sonar signal to map the bottom of the ocean and it returns after 2 seconds, how deep is the ocean?