Application of ultrasound

This slide contain application of ultrasound and biological effects of ultrasound , ppt contains many GIF files and notes , which may not be accessible here ,,

1. Application of Ultrasound and Biological effect Presenter :- Yashawant Kumar Yadav BSc. MIT 3 rd yr NAMS , Bir Hospital 1

2. OUTLINE Introduction of Ultrasound Modes of Ultrasound with application Doppler US and types with application Different kinds of probes with medical application Biological effect References 2

3. Intro….. Any sound with a frequency above 20,000 Hz (or 20 kHz)that is, above the highest audible frequency—is defined to be ultrasound.  1Hz = 1 cycle / vibration 1kHz = 1000 cycle per second 1MHz = 1 million vibrations per second. 3

4. Contd …. A sound wave can be described as a mechanical, longitudinal wave composed of cyclic compressions and rarefactions of molecules in a medium. 4

5. Interaction Reflection Refraction Absorption Scattering Acoustic impedance   Z  =  ρv , The units for  Z  are therefore kg/(m 2  · s). Matching layer ??? Z of PZC is 15 times higher than skin 5

6. Parameters Amplitude : Power :- (joules /s) (A 2 ) Intensity :- The energy per unit cross-sectional area in a sound beam, Intensity is expressed in joules/second/square centimeter. Joule/second = watt (w/cm 2 ) 6

7. Contd … Relative scale intensity is defined in units of the decibel (dB) In common practice, the lowest-intensity audible sound (10 -12 W /M 2 ) is assigned the value of 0 dB. 10dB = 10 2 Times of 0dB So 120 dB = 10 12 times i.e 1 trillion times of 0 dB 7

8. Production of US in Medicine Piezoelectric US generation. Natural -- - (quartz, and lead titanate) Piezoelectric crystals Barium titanate,(BaTiO 3 ) (1 st discovered ) Rochelle salts, ( KNaC 4 H 4 O 6 ·4H 2 O) Potassium niobate (KNbO 3) Ammonium dihydrogen phosphate (ADP) lead zirconate titanate . (Pb[ ZRxTi ]O 3 ) Sodium tungstate (N2WO 3 ) Sodium potassium niobate (NKN) lead free 8

9. Pulse acoustic phenomenon Continuous waves are not useful for structural imaging. One pulse typically consists of three to five cycles. Pulse US parameters Pulse duration (0.5 to 3 µs). Pulse repetition period: ( 0.1 to 1 ms. ) Spatial pulse length: (0.1 to 1 mm). Duty factor (0.1 % to 1 %. ) Pulse repetition frequency (PRF): (1 OOO to 10,000 Hz ) PRF is inversely proportional to imaging depth. 9

10. Tissues attenuation Bone is represented as a very bright structure and appears ‘hyperechoic ’. Muscle presents as hypoechoic , with some internal signals as a result of collagen fibers.   Tendon show tightly packed hyperechoic lines representing the fibrils of the tendon. 10

11. Contd …. Nerves as ‘honeycomb’ like structures composed of hypoechoic spots embedded in a hyperechoic background.  Fluid presents has an anechoic appearance on ultrasound. Air bubbles reflect much of the US that engages them and appear very echo dense (bright). Ligament 11

12. Medical application Ultrasound is used in medicine for therapy and diagnosis. In diagnosis : Ultrasound have 4 basic mode :- A – amplitude mode B – brightness mode M- motion mode Doppler 12

13. A-amplitude mode (10–20 MHz) Mode A is a one-dimensional process, and simplest type of US . Basically used to determine depth of abnormality . (function of depth ) Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy. As an example on how Mode A can be applied, US encephalography, and US ophthalmology 13

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15. Contd … In a case where the middle brain structures have been displaced (for example by the presence of an odd mass in a lobe that pushes them into the other lobe) 15

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17. B – Brightness mode The B-mode is a two-dimensional (2D) image of the area that is simultaneously scanned by a linear array of 100–300 piezoelectric elements rather than a single one as in A-mode  B-Mode composed of bright dots representing the ultrasound echoes. The brightness of each dot is determined by the amplitude of the returned echo signal.  17

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19. M- Motion Mode A continuous B-mode display. Displays one scan line versus time. Allows for a high frame rate, accuracy of linear measurements, and tracking of motion of reflectors (x-axis: time; y-axis: reflector depth). . M-mode is used extensively in cardiac and fetal cardiac imaging. Its an application of B - mode imaging 19

20. Doppler mode The Doppler effect is defined as the change in the frequency of sound emitted or reflected by a moving object. The amount of change is termed the Doppler shift. 20

21. Th is angle is known as the angle of insonation . 21

22. Contd … The highest Doppler frequency shift from any specific vessel occurs when the vessel and the beam are aligned; that is, when the angle of insonation is zero and the cosine function has the value of 1.0. The least desirable situation occurs when the angle approaches 90° as then the Doppler frequency shift will be minimum. In clinical practice it is often not possible to align the beam and the vessel. As a rule, provided the angle is less than about 60°, good-quality spectral waveforms can be obtained. 22

23. Application of doppler 1. Peripheral vascular system - Arteries and veins of the extremities 2. Central arteries / veins - Abdominal aorta, IVC, mesenteric vessels 3. Cerebrovascular system - 4. Cardiology 5. Obstetrics and Gynecology - IUGR, Uterine arteries, Ovarian torsion 6. Renovascular hypertension 7. Male infertility / erectile dysfunction, testicular torsion 8. Tumors, AV malformations. 23

24. Contd … There are five methods of imaging by employing Doppler principle. a ) Continuous wave doppler b) Pulsed wave Doppler c) Color Doppler d) Power Doppler e) Spectral Doppler or Duplex scanning 24

25. CONTINIOUS WAVE DOPPLER This employs two piezoelectric crystals, both contained in a single head. One crystal transmits a continuous sonic signal at a known frequency (3-8 MHz). The other crystal receives the returning echoes and records their frequency. It is employed in detection of blood flow but does not give information of depth, direction and velocity of flow. From a practical standpoint, continuous wave Doppler should be used when measuring velocities > 1.2 m/s. (e.g., regurgitant jets, stenotic valves). No depth resolution 25

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27. Contd … Pulsed wave Doppler (PW):- Provide depth information , variable depth can be acquired by changing beam frequency (low for high penetration and high for low penetration) Three factors affects PWD To evaluate mobile structure High pulse repetition frequency Optimum transducer frequency Insonation angle (less than 60 ) It is customarily combined with a B mode / 2-Dimensional mode imaging, which is then called duplex scanning . measuring relatively low-flow velocities ( < ~ 1.2 m/s) in specific areas of interest (e.g., pulmonary vein flow, mitral valve inflow). 27

28. Contd.. Because sampling is intermittent, the pulse repetition frequency limits the maximum Doppler shift (and thus maximum velocity) that can be measured accurately. Velocities higher than this maximum velocity will appear to wrap around on the display, a phenomenon known as aliasing. The Doppler frequency shift at which aliasing occurs, equal to PRF divided by 2, is termed the Nyquist limit. 28

29. Contd.. Doppler shift (expressed in Hz) = (2 · v · Fi cosine ϴ )/c (if ϴ = 0/180 =1/-1) Doppler shift= (v· Fi)/770 v = 770· (Doppler shift/Fi) if a 5-MHz transducer can only send out about 15,000 pulses per second, the Nyquist limit is 7500 Hz (15,000/2). Using the velocity equation shown earlier, the maximum velocity that can be measured without aliasing is about 1.15m/s (770 X (7500/5,000,000)). 29

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31. Color doppler ( Also called color flow imaging (CFI) or color velocity imaging (CVI) ) Ten or more pulse packets are used to produce an estimate of mean velocity of all reflectors. This data is assigned color by the machine and is superimposed on B mode data from stationary structures. 31

32. Contd … Flow that travels away from the transducer (negative Doppler shift) is depicted in blue, Flow that is traveling toward the transducer (positive Doppler shift) is depicted in red, with lighter shades of each color denoting higher velocities. A third color, usually green or yellow, is often used to denote areas of high flow turbulence.  Clinical use :- overall blood flow to a region of interest. Depiction of the general velocity and direction of blood flow within the heart and blood vessels.   It also allows the. generation of unique phenomena such as the  fluid color sign 32

33. Contd … The  fluid color sign  is a diagnostic sign to differentiate a  pleural effusion  from  pleural thickening  by means of  color Doppler  ultrasound. In the case of pleural effusion a color signal is seen in the pleural fluid during respiratory and cardiac movement, whereas this color signal is not seen in the case of pleural thickening. 33

34. Power Doppler or Energy mode imaging An alternative processing method. which ignores the velocity and simply estimates the strength/amplitude of the Doppler signal detected from each location. And encoded as a color . The Energy mode image is continuous and hence not sensitive to relative flow direction. It does not give the absolute values of velocity but only gives the strength of the Doppler signal. 34

35. Contd …. The higher sensitivity to slow flow. Power Doppler is particularly useful when examining superficial structures, like thyroid, testis, renal grafts and subcutaneous lesions. It may be used to look for tumor vessels, to evaluate tiny low-flow vessels and detect subtle ischemic areas. 35

36. Contd … Advantages of Power Doppler over Color flow imaging More sensitive to flow states (3-5% more sensitive than CFD) Angle effects are ignored unless the angle is close to 90° Aliasing is not applicable. There are disadvantages also Values of velocity and the direction of blood flow cannot be assessed. Because of more averaging of information at slower frame rates. slow moving soft tissue signals appear as flash artifacts 36

37. Spectral doppler Spectral Doppler displays the blood flow measurements graphically, displaying flow velocities recorded over time. For spectral Doppler , the machine represents the movement of blood via an audible flow sound, and a graph depicting flow velocities in relation to time. This mode is ideal for measuring lower velocities at chosen anatomic locations, 37

38. ULTRASOUND PROBES Linear array Curvilinear array Phased array linear array, “L” electronic linear scanning, “E” in the xz plane Curve scan “C” “E< xz ” electronically focus 38

39. Acoustic window’s An  acoustic window  is the location from which an  ultrasound  probe makes it's scan. 39

40. Linear (5-15MHz) Designed to make contact with flat surfaces, with the footprint decreasing in size with increasing frequency. Here rectangular and trapezoidal formats provide appropriate viewing areas. With abdominal imaging, to increase the viewing area with minimal increases of the contact area Use for high-resolution imaging of superficial structures, 40

41. Contd.. This probe is ideal for ultrasound-guided needle entry (particularly vascular access), evaluation of deep venous thrombosis, chest imaging for pleural lines (pneumothorax), skin and soft tissue imaging for abscesses. Nerve blocks Ophthalmologic Joint /tendon Thyroid/breast Evaluation of superficial structure 41

42. Curve linear array (1-8MHz) convex arrays designed to make surface contact in deformable soft areas of the body. The curvilinear (convex) array probe is used for scanning deeper structures, The crystal alignment along a curved surface generates a beam that fans outward. The result is a field of view wider than the probe’s footprint, These probes are most often used in abdominal and pelvic diagnostic applications. 42

43. Contd …. These probes are most often used in abdominal and pelvic diagnostic applications. Hepatobiliary Renal Appendix (pediatric ) Aorta Focus assessment in case of trauma Fetal heart tones and obstetric complication (pregnancy ) Emergency lung examination Paracentesis and thoracentesis 43

44. Phase array (2-7.5MHz) Consisting of 64-128 elements. It is a smaller assembly . The phased array probe is a lower frequency probe. Beam can be steer electronically , variable field shape can be acquired . The smaller footprint allows for image acquisition between the ribs, and the slightly convex surface produces a fanning beam with a sector-shaped image. 44

45. Contd ….. This probe is used for echocardiography and thoracic imaging but can be applied to abdominal and pelvic imaging as well. Procedure guide Alternative to curvilinear for abdominal structure evaluation Pericardiocentesis Thoracentesis 45

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47. Biological effect Energy deposition in biological tissue. With CW ultrasound, the tissues are irradiated throughout the duration of the exposure, and the total energy deposited in tissue will be much more in comparison to PW irradiation over the same total exposure duration, Consequences of high intensity, prolonged exposures Elevation of tissue temperature (thermal effect ) Cavitation in liquids (non thermal effect ) Interlinked 47

48. Elevation of temperature The mechanical energy of ultrasound can be transformed into heat through absorption in tissue, resulting in the elevation of tissue temperature. Temperatures exceeding 4°C above normal body temperature, maintained for long periods of time, may be harmful to the embryo and fetus, leading to a variety of biological changes which can result in abortion, fetal death, or developmental abnormalities,(teratogenic effect ) These effects have been seen following whole body heating of both the mother and the offspring, (approx. 0.5°C min −1 ) 48

49. Contd.. The World Federation for Ultrasound in Medicine and Biology (WFUMB) recommends that diagnostic exposures that produce a maximum temperature rise of 1.5 c above the normal physiological level of 37°C Ultrasound heating is very rapid . In addition, ultrasound exposures in pregnancy only subject a small fraction of the maternal volume to a potential temperature rise, and thus any heating of the embryo is likely to be rapidly dissipated.  49

50. Cavitation in liquids( non thermal effect ) Cavitation is a phenomenon which takes place in liquid cavities exposed to very high intensities of ultrasound The presence of gas within the volume of the liquid may lead to the formation of micro bubbles during the low pressure phase (rarefaction) of the ultrasound wave cycle. With changes in pressure, the bubbles may grow in size. During the high pressure phase (compression), The micro bubbles may collapse a with the release of large quantities of mechanical energy which can cause biological damage. 50

51. Contd.. cavitation can also be the cause of free radical formation. Free radicals are highly reactive chemical species which can attack bio molecules through a chain of chemical reactions, producing toxic bio products. This leads to damage of biological matter not only locally, but also remotely through diffusion of toxic products. cavitation is unlikely to occur with PW ultrasound 51

52. Drug delivery ( Sonoporation ) Refers to a technique capable of controlling drug delivery efficiency by maximizing the drug permeability of surrounding tissues or cells using a reaction mechanism between microbubbles and ultrasonic waves. Injecting microbubbles intravenously can minimize drug side effects that may cause nonspecific delivery of drugs into healthy organs because the microbubbles only collapse in specific diseased areas due to focused ultrasound irradiation. 52

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54. Contd … ultrasound-mediated microbubble destruction (UMMD)  ultrasound-targeted microbubble destruction (UTMD). 54

55. THANK YOU 55

56. References https://theultrasoundsite.co.uk/ultrasound-case-studies/starting-article-2-different-tissues-ultrasound-look-like/ https://www.nysora.com/foundations-of-regional-anesthesia/equipment/physics-of-ultrasound/ https://radiologykey.com/doppler-imaging-2/ https://radiopaedia.org/articles/phased-array https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6208473/ Martinoli , C., Pretolesi , F., Crespi , G., Bianchi, S., Gandolfo, N., Valle, M., & Derchi , L. E. (1998). Power Doppler sonography: clinical applications.  European journal of radiology ,  27 Suppl 2 , S133–S140. https://doi.org/10.1016/s0720-048x(98)00054-0 https://echocardiographer.org/Echo%20Physics/spectral%20doppler.html 56

57. 1. Cavitation effect in microbubble contrast agent ?? 57