Abstract
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Objectives To investigate the feasibility of measuring kinetic parameters of neurotransmitters using a high-sensitivity cardiac SPECT instrument.
Methods High-count projections of three compartments (left and right striata and background) of a brain phantom were acquired on the Spectrum Dynamics D-SPECT, a dedicated cardiac SPECT system. These data were used to synthesize projection datasets for calculation of Cramer-Rao bounds (CRB) on precision of striatal and background activity concentration estimates for points on the expected I-123-altropane striatal and occipital time-activity curves (TAC) for normal subjects. 500 noisy TAC were generated, with variances at each time point determined by the appropriate CRB, for three temporal sampling rates (3-, 6-, and 12-min acquisitions). More finely sampled TAC were similarly generated using CRB based on estimation from individual projections. Estimates of binding potential (BP) were derived for each noise realization by nonlinear least squares fitting to a published model.
Results For data acquired on this high-sensitivity instrument, precise (~3% standard deviation) estimates of BP from image datasets were obtained for all but the coarsest temporal sampling rate. Although the fitting procedure did not converge in this case for estimation from complete image datasets, it was still possible to estimate BP directly from individual projection data.
Conclusions High-sensitivity cardiac SPECT systems can be used for quantitative brain imaging and, furthermore, for direct estimation, from individual projections, of kinetic parameters of fast tracers that concentrate in a small number of brain structures.
Research Support This research was supported by the NIH under grants R01 EB 000802 and R01 EB 001989.
- © 2009 by Society of Nuclear Medicine