Spatial variation of ultrasonic attenuation and speed of sound in brain tissue visualized by parametric imaging

The ultrasonic properties of brain have been explored to a limited extent, however the spatial variation of these properties is not well characterized. The goal of this study was to measure the speed of sound and the frequency slope of attenuation in brain tissue at multiple locations to generate parametric images that characterize their spatial distribution. Tissue specimens were 1-cm thick slices of preserved sheep brain prepared from the coronal, sagittal and transverse anatomic planes. Ultrasonic measurements were performed using broadband transducers with center frequencies of 3.5, 5.0, 7.5, and 10 MHz. The transducers were mechanically scanned to acquire signals from all locations on each slice. Structures visible in the parametric images were consistent with the known morphologic features of the brain. White matter and gray matter appeared to be distinguishable in most images. Measured values for the spatial mean and standard deviation of the frequency slope of attenuation ranged between 0.723–1.06 and 0.194–0.501 dBcm⁻¹MHz⁻¹, respectively, depending on the tissue slice and transducer frequency. Measured values for the spatial mean and standard deviation of the speed of sound ranged between 1520–560 and 6–15 ms⁻¹, respectively. Spatial variation of these properties were clearly visualized in the parametric images.