Biomedical Instrumentation II.


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The ultrasound recurrence is unaffected by changes in sound rate as ... Ultrasound wavelength decides the spatial determination achievable along the ...
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´╗┐Biomedical Instrumentation II Dr. Hugh Blanton ENTC 4370

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More ULTRASONOGRAPHY Dr. Blanton - ENTC 4370 - ULTRASONICS 2

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CHARACTERISTICS OF SOUND

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Propagation of Sound is mechanical vitality that spreads through a persistent, flexible medium by the pressure and rarefaction of "particles" that create it. Dr. Blanton - ENTC 4370 - ULTRASONICS 4

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Propagation of Sound Compression is brought on by a mechanical twisting incited by an outer power, with a resultant increment in the weight of the medium. Rarefaction happens taking after the pressure occasion. The packed particles exchange their vitality to adjoining particles, with a resulting decrease in the nearby weight sufficiency. While the medium itself is important for mechanical vitality exchange (i.e., sound proliferation), the constituent "particles" of the medium demonstration just to exchange mechanical vitality; these particles encounter just little forward and backward removals. Vitality engendering happens as a wave front toward vitality travel, known as an Iongitudinal wave. Dr. Blanton - ENTC 4370 - ULTRASONICS 5

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Wavelength, Frequency, and Speed The wavelength ( l ) of the ultrasound is the separation (normally communicated in millimeters or micrometers) between compressions or rarefactions, or between any two focuses that rehash on the sinusoidal rush of weight adequacy. The recurrence (f) is the quantity of times the wave wavers through a cycle every second (sec). Dr. Blanton - ENTC 4370 - ULTRASONICS 6

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Sound waves with frequencies under 15 cycles/sec (Hz) are called infrasound, and the extent between 15 Hz and 20 kHz contains the capable of being heard acoustic range. Ultrasound speaks to the recurrence range above 20 kHz. Medicinal ultrasound utilizes frequencies as a part of the scope of 2 MHz to 10 MHz, with particular ultrasound applications up to 50 MHz. Dr. Blanton - ENTC 4370 - ULTRASONICS 7

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The period is the time span of one wave cycle, and is equivalent to 1/f where f is communicated in cycles/sec. The rate of sound is the separation went by the wave per unit time and is equivalent to the wavelength partitioned by the period. Dr. Blanton - ENTC 4370 - ULTRASONICS 8

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Since period and recurrence are contrarily related, the relationship between pace, wavelength, and recurrence for sound waves is the place c (m/sec) is the rate of sound of ultrasound in the medium, l (m) is the wavelength, and f (cycleslsec) is the recurrence. The pace of sound is subject to the proliferation medium and fluctuates generally in various materials. Dr. Blanton - ENTC 4370 - ULTRASONICS 9

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The wave velocity is dictated by the proportion of the mass modulus ( b ) a measure of the firmness of a medium and its imperviousness to being packed, and the thickness ( r ) of the medium: SI units are kg/(m-sec 2 ) for b , kg/m 3 for r , and m/sec for c . Dr. Blanton - ENTC 4370 - ULTRASONICS 10

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An exceptionally compressible medium, for example, air, has a low speed of sound, while a less compressible medium, for example, bone, has a higher velocity of sound. A less thick medium has a higher rate of sound than a denser medium (e.g.. dry air versus muggy air). Dr. Blanton - ENTC 4370 - ULTRASONICS 11

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The paces of sound in materials experienced in medicinal ultrasound are recorded beneath. Dr. Blanton - ENTC 4370 - ULTRASONICS 12

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Of real significance are the velocity of sound in air (330 m/sec), the normal rate for delicate tissue (1,540 m/sec), and greasy tissue (1,450 m/sec). Dr. Blanton - ENTC 4370 - ULTRASONICS 13

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The distinction in the velocity of sound at tissue limits is a central reason for complexity in a ultrasound picture. Dr. Blanton - ENTC 4370 - ULTRASONICS 14

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Medical ultrasound machines accept a velocity of sound of 1,540 in/sec. The pace of sound in delicate tissue can be communicated in different units, for example, 154,000 cm/sec and 1.54 mm/m sec. Dr. Blanton - ENTC 4370 - ULTRASONICS 15

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The ultrasound recurrence is unaffected by changes in sound pace as the acoustic pillar spreads through different media. Along these lines, the ultrasound wavelength is reliant on the medium. Dr. Blanton - ENTC 4370 - ULTRASONICS 16

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Example A 2-MHz bar has a wavelength in delicate tissue of A 10-MHz ultrasound pillar has a relating wavelength in delicate tissue of So, higher recurrence sound has shorter wavelength. Dr. Blanton - ENTC 4370 - ULTRASONICS 17

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Example: A 5-MHz bar goes from delicate tissue into fat. Compute the wavelength in every medium, and decide the percent wavelength change. In delicate tissue, In fat, A diminishing in wavelength of 5.8% happens in going from delicate tissue into fat, because of the distinctions in the rate of sound. Dr. Blanton - ENTC 4370 - ULTRASONICS 18

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The wavelength in mm in delicate tissue can be computed from the recurrence indicated in MHz utilizing the rough speed of sound in delicate tissue (c = 1540 m/sec = 1.54 mm/m sec): An adjustment in rate at an interface between two media causes a change in waveIength. Dr. Blanton - ENTC 4370 - ULTRASONICS 19

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The determination of the ultrasound picture and the constriction of the ultrasound pillar vitality rely on upon the wavelength and recurrence. Ultrasound wavelength decides the spatial determination achievable along the course of the shaft. A high-recurrence ultrasound shaft (little wavelength) gives prevalent determination and picture point of interest than a low-recurrence pillar. Be that as it may, the profundity of bar infiltration is diminished at higher recurrence. Lower recurrence ultrasound has longer wavelength and less determination, however a more noteworthy infiltration profundity. Dr. Blanton - ENTC 4370 - ULTRASONICS 20

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Ultrasound frequencies chose for imaging are dictated by the imaging application. For thick body parts (e.g., stomach imaging), a lower recurrence ultrasound wave is utilized (3.5 to 5 MHz) to picture structures at noteworthy profundities, though For little body parts or organs near the skin surface (e.g., thyroid, bosom), a higher recurrence is utilized (7.5 to 10 MHz). Most restorative imaging applications use frequencies in the scope of 2 to 10 MHz. Dr. Blanton - ENTC 4370 - ULTRASONICS 21

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Modern ultrasound gear comprises of different sound transmitters that make sound shafts free of each other. Association of two or more separate ultrasound bars in a medium results in helpful and/or ruinous wave obstruction. Valuable wave obstruction results in an expansion in the plentifulness of the bar, while damaging wave impedance results in lost adequacy. Dr. Blanton - ENTC 4370 - ULTRASONICS 22

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The measure of useful or dangerous impedance relies on upon a few elements, yet the most critical are the stage (position of the intermittent wave as for a reference point) and sufficiency of the cooperating pillars. At the point when the shafts are precisely in stage and at the same recurrence, the outcome is the helpful expansion of the amplitudes. For equivalent recurrence and a 180-degree stage distinction, the outcome will be the dangerous subtraction of the resultant shaft sufficiency. With stage and recurrence contrasts, the aftereffects of the bar cooperation can produce an intricate obstruction design. The valuable and ruinous impedance wonders are vital in forming and controlling the ultrasound bar. Dr. Blanton - ENTC 4370 - ULTRASONICS 23

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When the bars are precisely in stage and at the same recurrence, the outcome is the valuable expansion of the amplitudes. Dr. Blanton - ENTC 4370 - ULTRASONICS 24

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For equivalent recurrence and a 180-degree stage distinction, the outcome will be the damaging subtraction of the resultant shaft adequacy. Dr. Blanton - ENTC 4370 - ULTRASONICS 25

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With stage and recurrence contrasts, the consequences of the shaft connection can create an unpredictable impedance design. The useful and ruinous impedance marvels are essential in molding and directing the ultrasound bar. Dr. Blanton - ENTC 4370 - ULTRASONICS 26

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Pressure, Intensity, and the dB Scale

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Sound vitality causes molecule removals and varieties in nearby weight in the proliferation medium. The weight varieties are frequently portrayed as weight abundancy (P). Weight sufficiency is characterized as the crest greatest or top least esteem from the normal weight on the medium without a sound wave. Dr. Blanton - ENTC 4370 - ULTRASONICS 28

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For the situation of a symmetrical waveform, the positive and negative weight amplitudes are equivalent; be that as it may, in most symptomatic ultrasound applications, the compressional plentifulness altogether surpasses the rarefactional adequacy. Dr. Blanton - ENTC 4370 - ULTRASONICS 29

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The SI unit of weight is the pascal (Pa), characterized as one newton for every square meter (N/m 2 ). The normal barometrical weight on earth adrift level of 14.7 pounds for each square creep is roughly equivalent to 100,000 Pa. Indicative ultrasound bars typica

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