The influence of measurement uncertainties on the evaluation of the distribution volume ratio and binding potential in rat studies on a microPET® R4: a phantom study

Abstract

In small animal positron emission tomography (PET) imaging, the injectable radiotracer dose is often limited by the tracer mass which, together with the tracer kinetics and scanner sensitivity, dictates the statistical quality of the time activity curves (TACs) used to extract biological parameters. We investigated the effect of measurement uncertainty on the determination of the distribution volume ratio (DVR) and binding potential (BP) as estimated using the tissue input Logan (DVRL, BPL) and the ratio (DVRr, BPr) methods for two tracers, with the Concorde microPET® R4 camera. Parameters' coefficients of variation (COV) were estimated from a combination of rat and phantom data. For 11C-dihydrotetrabenazine, the COV was 11% for the BPL and 13.4% for the BPr when using TACs obtained from individual regions of interest (ROIs) and segmented attenuation correction. The COVs were reduced to 7.5% (BPL) and 8.6% (BPr) when the striatal and cerebellar TACs were estimated as averages of 3 and 2 ROIs respectively. Results obtained for 11C-methylphenidate (MP) yielded approximately 30% higher COVs. With measured attenuation correction, the COVs were on average 100% higher. The presented method can be used to examine the contribution of a variety of imaging conditions to the uncertainty of biologically meaningful parameters.