b413h8af07answers_1

b413h8af07answers_1 - Due Tuesday Nov 20, 2007 BME-413...

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Due Tuesday Nov 20, 2007 BME-413 Biomedical Instrumentation Homework Answers #8a Fall 2007 1. Explain how an ultrasound image is made. What creates the image contrast? Ultrasound images are made through the emission of an ultrasound pulse and detection of echoes. Thousands of individual pulse echo measurements are made in a second and show in an image by a process of raster scanning over the body. The image contrast is determined by the acoustic impedances of the tissues. 2. Consult reference materials and determine the absorption of ultrasound energy (ie. the fraction remaining) after it passes through 1 cm of fat and 1 cm of muscle. Use the exponential decay formula A = A 0 exp – (ux) for each tissue type and multiply . Use values of attenuation coefficient μ as listed below. Afat= 0.99 Amuscle = 0.988 Atotal = 0.978 3. Determine how much ultrasound energy reflects (echoes) off an interface between fat and muscle using the acoustic impedance (Z) parameters given below. (ie. R=?) How much ultrasound then passes through the interface? (ie transmitted = 1-R) Reflects R=0.0039 Passes = 0.9961 4.
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b413h8af07answers_1 - Due Tuesday Nov 20, 2007 BME-413...

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