Fig. 1.

The two methods used for measuring the striatal specific binding ratio (SBR), defined as the ratio of specific to non-specific striatal count concentrations, SBR = c _s /c _ns. Top: BRASS quantification method [4]. c _s and c _ns are measured from count concentrations using anatomical VOIs for the sub-striatal structures (caudate and putamen) and the occipital lobes, respectively. The striatal SBR used in this work was obtained by dividing the total counts from these two VOIs by their combined volume. The small volumes of these structures render these concentration measurements susceptible to partial volume losses. Bottom: Southampton quantification method [5]. c _s is derived from a measure of total counts in a geometrical VOI for the striatum. The generous dimensions of this VOI ensure that all counts related to striatal binding are captured, including those detected outside the anatomical boundary, thus averting under-estimations due to partial volume losses. c _ns is also measured from a large VOI, encompassing the whole cortex with the exception of the striata and excluding the outer rim beset by peripheral partial volume losses