Semi-automatic quantification of regional cerebral perfusion in primary degenerative dementia using 99m technetium-hexamethylpropylene amine oxime and single photon emission tomography

Choice of reference region in the quantification of single-photon emission tomography in primary degenerative dementia

This study evaluated the effect of using two different reference regions in the quantification of single-photon emission tomography (SPET). SPET scans of 30 patients with Alzheimer's disease (AD) and 30 patients with frontotemporal dementia were compared with the scans of ten age-matched controls. Regions of interest (ROIs) were defined on transaxial slices by a semi-automatic method. Regional cerebral blood flow indices (rCBFi) in each ROI were determined by normalizing the count densities to both cerebellar and occipital cortex reference regions. Mean rCBFi for each ROI were calculated for the patient and control groups and significant group differences determined. The number and topographical distribution of ROIs with significant group differences varied depending upon the choice of reference region. The magnitude of these differences was greatest when the cerebellum was used as the reference region. The disparity between results obtained with the two reference regions was most apparent in the AD group. The reasons for these differences are discussed and we conclude that the cerebellum is the more appropriate choice of reference region in the quantification of SPET in primary degenerative dementia.

MRI-guided region of interest placement on emission computed tomograms

The reliability of the placement of regions of interest (ROIs) on emission computed tomograms (ECT) with a semi-automated magnetic resonance image (MRI)-guided method was compared with the reliability of manual ROI placement. MRI-defined regions were transferred to the registered, co-planar ECT image after accounting for inter-image differences in rotation, translation, and scaling. Six single photon emission computed tomographic (SPECT) scans of normal control subjects were rated for caudate perfusion using the radiotracer N-isopropyl[I-123]-iodoamphetamine (IMP). The MRI-guided method had higher interrater reliability, lower variance of region location, and lower variance of region activity than the manual method. The manual method recorded higher mean regional activity than the MRI-guided method, possibly due to sample bias inherent in the manual method.

Quantitative analysis in single photon emission tomography (SPET)

Quantitative analysis can improve the sensitivity and specificity of single photon emission tomography (SPET) procedures, as well as reduce inter- and intraobserver variabilities. Quantification of the radioactivity distribution is the ultimate goal of SPET. In this review we consider the basic requirements for an optimum three-dimensional reconstruction of the radionuclide distribution to enable quantification. Attenuation and scatter correction as well as varying resolution are the major problems. In the older SPET systems quantification was hampered by the lack of system sensitivity and sufficient computer power. Therefore, the imaging system was often assumed to be shift invariant and linear and the attenuation throughout the object uniform. More sophisticated solutions have been proposed and with more or less success implemented, but not for application in daily practice. Knowledge (measurement) of the attenuation is often required. New generation SPET systems employing multi-detectors and super minicomputers will ease the implementation of these solutions.

Cortical circumferential profile of SPECT cerebral perfusion in Alzheimer's disease

We developed a semiautomatic method termed "cortical circumferential profiling" for objective analysis of cerebral cortex function in emission tomographic neuroimaging studies. This method treats cortex as a continuous ring near the outer brain edge. A computer algorithm samples the cortex at 60 contiguous, equiangular locations, using 1-cm2 samples. These values are plotted as a function of cortical angle to produce the cortical circumferential profile. This method was used in a study of regional cerebral perfusion in 15 patients with Alzheimer's disease and 8 elderly control subjects using N-isopropyl[I-123]-iodoamphetamine. Cortical circumferential profiling decreases variability, examines the entire cortex within slices at preselected levels above the orbital-meatal line, and facilitates intrasubject and intersubject comparisons.