Two-dimensional mapping of the reflection coefficient and acoustic impedance of brain

Brain is inhomogeneous due to its composition of different tissue types (gray and white matter), anatomical structures (e.g. thalamus and cerebellum), and cavities in the brain (ventricles). These inhomogeneities lead to spatial variations in the ultrasonic properties of the organ. 1-cm-thick slices of tissue from the coronal, sagittal and transverse cardinal planes were prepared from 12 brains. Pulse-echo measurements were performed using broadband transducers with center frequencies of 3.5, 5.0, 7.5 and 10 MHz. By mechanically scanning the transducers over the specimens, detailed, two-dimensional maps of acoustic impedance and reflection coefficient were produced, providing a clear visualization of the spatial variation of these ultrasonic properties of normal mammalian brain.