Applicability of a high-resolution small semiconductor gamma camera to small animal imaging

Recently, small semiconductor gamma cameras (SSGCs) with high resolution and sensitivity, which are much more convenient to use as compared with SPECT and PET, have been developed for mapping the sentinel lymph node. The high resolution and sensitivity of the SSGCs may make them useful for small animal imaging. Therefore, we assessed the applicability of the SSGC to small animal imaging using a rat model of focal cerebral ischaemia.

The right middle cerebral artery (MCA) of anaesthetized rats was occluded intraluminally with a nylon monofilament. Twenty-four hours after the occlusion, 99mTc-HMPAO (3.7 MBq) was injected and a static acquisition (5 min) was performed using the SSGC. Regions of interest (ROIs) were set on each hemisphere of the horizontal brain images. After the acquisition, the brains were removed and the radioactivity in each hemisphere was measured using an NaI scintillation counter.

Reduced CBF in the right MCA territory was clearly visualized with the SSGC in vivo. The radioactivity in the ROIs determined by the SSGC was significantly correlated with that determined by the ex vivo counting method (P<0.001, R2=0.74). Furthermore, in both of the in-vivo imaging and ex-vivo counting methods, the right to left count ratio (R/L ratio) was significantly lower in the MCA-occluded rats than that in normal rats (MCA-occluded rats: 0.77+/-0.08, normal rats: 1.01+/-0.07, P<0.005).

The SSGC clearly visualized and quantitatively detected the reduced CBF in MCA-occluded rats. Furthermore, these high resolution and sensitivity of SSGC can avoid the disadvantage of small animal imaging with PET and SPECT, such as a large mass injected tracer and the exposure of investigators to radiation. Thus, the high resolution and sensitivity of the SSGC make it useful for small animal imaging.