Real time 3D ultrasound imaging of the brain
We tested the feasibility of real time three dimensional ultrasound imaging in the brain with a 2.5MHz 2D array using a Volumetrics Model 1 scanner. In a human subject, the real time 3D scans produced simultaneous transcranial axial, coronal and saggital image planes and real time volume rendered images of the gross anatomy of the brain. In a transcranial sheep model we obtained real time 3D color flow Doppler scans of cerebral vessels as well as perfusion images using bolus injection of contrast agents into the internal carotid artery. Our long term goal includes phase aberration correction of the skull using the 2D array. Phase aberration measurements have been made from both polymer castings of the temporal bone region and of a fixed human parietal bone. For the casting, average measurements have yielded an rms phase variation of 95 nsec, i.e. approximately λ/4 at 2.5MHz, with a correlation length of only 1.5 mm. The parietal bone sample had an rms phase variation of 55 nsec and a correlation length of 1.6mm. Such severe aberration data from the skull bone indicate a significant potential improvement in image quality yet to be realized in real time transcranial sonography. Using the multi-lag least-squares cross-correlation method we have corrected an electronically aberrated 3D scan, leading to an increase in contrast-to speckle ratio (CSR) and contrast in a cyst phantom. © 2004 IEEE.
