Abstract
To quantitatively improve brain SPECT (single photon emission computed tomography), we propose a noninvasive method for determining the speed of sound in skull bone and its thickness. We assume a spherical shell structure for the skull, and the speed of sound to be constant in the bone layer. Small ultrasonic transducers are arranged on the outer surface of the bone layer to form a transducer array. The array is excited to produce an ultrasonic pulse wave focused at a point on the inner surface by assigning an appropriate time delay to each of the transducers. The pulse is propagated to the focal point, and a reflected spherical pulse wave is produced at that point. The reflected pulse wave is detected by the same transducers, and the output from each transducer is added to give a summed signal. When the time delays are optimized, we obtain the maximum envelope amplitude for the signal. A simulation study is conducted to confirm the method, and the potential error is examined for ideal conditions. From the simulation results, we conclude that the proposed method is suitable for SPECT if the transducers are arrayed with a sufficiently large aperture.