FIG. 4.

The whole-animal image acquired by a spiral orbit SPECT had high spatial resolution with great counting linearity. (A) Acquisition of a whole-animal image using five-pinhole collimators with a spiral orbit (right panel) offers increased spatial resolution as compared to a whole-animal image acquired using parallel-hole collimators (left panel). (B) Bivariate plot with regression lines demonstrated counting linearity, signal intensity, and scanning reproducibility of spiral-orbit SPECT imaging with five-pinhole collimators using Tc-99m pertechnetate phantoms. (C) Bivariate plots with regression lines indicated that reduction of total scan time from 60 to 30 minutes proportionally reduced the slope values of regression lines (signal intensity shown as counts/μCi), yet had little effect on counting linearity. Tc-99m pertechnetate phantoms were scanned using spiral orbit with five-pinhole collimators. In the figure label, 64–50 represents 64 projections per camera with 50 seconds per projection, and so forth. (D) Mice injected with ¹²³I NaI were scanned at 1, 6, and 24 hours postinjection using spiral orbit (64 projections per camera with 25 seconds per projection), and then immediately followed by another scan using circular orbit (32 projections per camera with 25 seconds per projection). Note that there was no significant difference in thyroidal %ID measured by spiral orbit versus circular orbit at three different time points in the same mouse. M1 and M2 represent two different male mice of 21 months old. SPECT, single-photon emission computed tomography; SGs, salivary glands, ST, stomach, B, bladder; %ID, percentage of injected dose.