Quantitative Multiplexed Multi-pinhole Small-Animal SPECT

Small-animal microSPECT is an important research tool for the development of clinical diagnostic tests, evaluation of novel pharmaceuticals, and basic science research. Experimentally quantifying the accuracy of microSPECT — the reproducibility of measurements made using microSPECT, and how well the reconstructed microSPECT data correlates to the true tracer distribution — is therefore essential. Photon attenuation and scatter complicate the problem of acquiring quantitatively accurate information from SPECT.In this work, the reproducibility of cardiac measurements made in rats using the nanoSPECT/CT scanner (Bioscan, Washington, DC) is first evaluated without scatter or attenuation correction. For relative perfusion measurements of rat myocardia, normal databases for 99mTc-tetrofosmin and 201Tl imaging are created and it is shown that the relative myocardial perfusion measurements made using either tracer are reproducible over repeated scans and over multiple rats with standard deviations of 3% and 4% respectively.Attenuation and scatter compensation are implemented in the SPECT reconstruction algorithm to evaluate the accuracy of using nanoSPECT to recover absolute tracer concentrations in phantoms and in vivo. With attenuation and scatter compensation, absolute tracer concentration is measured using SPECT images with systematic and random uncertainties as low as 1% in phantoms, relative to dose calibrator measurements. The systematic and random uncertainties for measurements of total cardiac tracer uptake in vivo compared to well chamber measurements ex vivo were as small as –1% and 3% respectively.Reevaluation of the reproducibility of the cardiac measurements with attenuation and scatter correction demonstrates that neither correction strongly influences the relative perfusion measurements or their reproducibility. However, it is shown that attenuation correction does significantly modify the relationship between body weight and absolute tracer uptake.