Attenuation and velocity in normal brain

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Abstract
Attenuation and propagation velocity at 1, 3, and 5 MHz were measured in vitro at six anatomic sites in seven normal human brains obtained at autopsy. Piezoelectric transducer method gave attenuation values about 50% higher than radiation force method. Age at death for adults (20–72 yrs) was not a significant variable. A three-day-old infant brain, however, showed attenuation about one third that for adult. Formalin fixing increases attenuation by about 30% and reduces velocity by less than 1%. Five-day aging of unfixed tissue reduces attenuation by about 20%. White matter has higher attenuation (which is also a stronger function of frequency) than gray or mixed matter. Attenuation is a negative function of temperature. The magnitude of temperature coefficient or attenuation is greater for lower temperatures or higher frequencies. Velocity vs temperature curves exhibit a minimum at about 15°C. These observations indicate that for attenuation and velocity measurements in normal brain in the 1 to 5 MHz range, temperature must be closely controlled, and aging and fixing of tissue must be taken into account when analysing attenuation data. [Work supported by NINCDS.]

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