G. El Fakhri et al., Absolute activity quantitation from projections using an analytical approach: Comparison with iterative methods in Tc-99m and I-123 brain SPECT, IEEE NUCL S, 48(3), 2001, pp. 768-773
Estimates of SPECT activity within certain deep brain structures could be u
seful for clinical tasks such as early prediction of Alzheimer's disease wi
th Tc-99m or Parkinson's disease with I-123; however, such estimates are bi
ased by poor spatial resolution and inaccurate scatter and attenuation corr
ections. We compared an analytical approach (AA) of more accurate quantitat
ion to a slower iterative approach (TA). Monte Carlo simulated projections
of 12 normal and 12 pathologic Tc-99m perfusion studies, as well as 12 norm
al and 12 pathologic I-123 neurotransmission studies, were generated using
a digital brain phantom and corrected for scatter by a multispectral fittin
g procedure. The AA included attenuation correction by a modified Metz-Pan
algorithm and activity estimation by a technique that incorporated Metz fil
tering to compensate for variable collimator response (VCR), IA-modeled att
enuation, and VCR in the projector/backprojector of an ordered subsets-expe
ctation maximization (OSEM) algorithm. Bias and standard deviation over the
12 normal and 12 pathologic patients were calculated with respect to the r
eference values in the corpus callosum, caudate nucleus, and putamen. The I
A and AA yielded similar quantitation results in both Tc-99m and I-123 stud
ies in all brain structures considered in both normal and pathologic patien
ts. The bias with respect to the reference activity distributions was less
than 7% for Tc-99m studies, but greater than 30% for I-123 studies, due to
partial volume effect in the striata. Our results were validated using I-12
3 physical acquisitions of an anthropomorphic brain phantom. The AA yielded
quantitation accuracy comparable to that obtained with IA, while requiring
much less processing time. However. in most conditions, IA yielded lower n
oise for the same bias than did AA.