X-Ray CT High Density Artifact Suppression in Cryosurgery

X-ray CT provides imaging guidance for cryosurgery that allows 3D visualization of frozen and unfrozen tissue. Temperature in the tissue water-ice interface (0 to −10 °C) may be calibrated to Hounsfield units. However x-ray CT images and their thermal calibration can be compromised by the cryoprobes generating high-density streak artifacts. A new subtraction technique for suppression of these artifacts is proposed and tested in prostate cryosurgery simulations. By subtracting the profile without cryoprobes from the profile with cryoprobes and iceballs, we can get the combined profile of the cryoprobes and a low value background. A polynomial interpolation is performed to obtain the background profile, which is then added back to the original profile without probes. The resulting profile is then fed to a conventional filtered back-projection routine to reconstruct the probe-free image. Finally the cryoprobe pixels in the originally constructed image with probes are added back to the probe-free image to get the final artifact-suppressed image. The major advantage of this subtraction technique is that it can successfully suppress the high-density artifacts in bone abundant body regions. X-ray CT images of cryoprobe arrays in a homogeneous gelatin phantom and the pelvic region of an anthropomorphic Rando phantom containing a human skeleton were generated. After suppression, cryoprobe metal artifact streaks are reduced and visualization of the positions and dimensions of the cryoprobes are well preserved. In-vivo canine studies are planned to test this new suppression technique for cryosurgery use.