Ultrasound is used in medicine both for diagnostic imaging and for therapy. For
ID: 1391077 • Letter: U
Question
Ultrasound is used in medicine both for diagnostic imaging and for therapy. For diagnosis, short pulses of ultrasound are passed through the patient's body. An echo reflected from a structure of interest is recorded, and the distance to the structure can be determined from the time delay for the echo's return. To reveal detail, the wavelength of the reflected ultrasound must be small compared to the size of the object reflecting the wave. The speed of ultrasound in human tissue is about 1500 m/s (nearly the same as the speed of sound in water). B. Bencit/Photo Researchers. Inc. What is the wavelength of ultrasound with a frequency of 7.60 MHz? mm In the whole set of imaging techniques, frequencies in the range 1.00 MHz to 20.0 MHz are used. What is the range of wavelengths corresponding to this range of frequencies? longest wavelength mm shortest wavelength mumExplanation / Answer
a) Apply, v = lamda*f
==> lamda = v/f
= 1500/(7.6*10^6)
= 0.197 mm
b) when frequency is minimum wavelength is maximum
longest wavelength = v/fmin
= 1500/(1*10^6)
= 1.5 mm
c) when frequency is maximum wavelength is minimum
shortest wavelength = v/fmax
= 1500/(20*10^6)
= 75 micro m
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