Temporoparietal hypoperfusion on SPECT is common to both AD and DLB. Occipital hypoperfusion is more frequently seen in DLB. Although not diagnostically specific in individual cases, occipital hypoperfusion on SPECT should raise suspicion that DLB may be the cause of dementia, prompting careful search for other features of the disorder.

Background: Dementia with Lewy bodies (DLB) is a common form of late-life dementia that can be difficult to differentiate from other disorders, especially Alzheimer disease (AD), during life. At autopsy the striatal dopaminergic transporter is reduced. Objectives: To examine the extent and pattern of dopamine transporter loss using iodine I 123-radiolabeled 2 ␤ -c a r b o m e t h o x y -3 ␤ -( 4 -i o d o p h e n y l ) -N -( 3fluoropropyl) nortropane (FP-CIT) with single-photon emission computed tomography (SPECT) in DLBs compared with other dementias and to assess its potential to enhance a differential diagnosis. Design: Cohort study comparing FP-CIT with criterion standard of consensus clinical diagnosis. Setting: General hospital. Participants: One hundred sixty-four older subjects (33 healthy older control subjects, 34 with NINCDS/ADRDA [National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association]-confirmed AD, 23 with consensus guideline-confirmed DLB, 38 with United Kingdom's Parkinson Disease Society Brain Bank-confirmed Parkinson disease [PD], and 36 with PD and dementia).Interventions: Injection of 123 I-2␤-carbomethoxy-3␤-(4-iodophenyl)-N-(3-fluoropropyl) nortropane with SPECT scan performed at 4 hours. Main Outcome Measures: Visual ratings of scans and region of interest analysis.Results: Significant reductions (PϽ.001) in FP-CIT binding occurred in the caudate and anterior and posterior putamens in subjects with DLB compared with subjects with AD and controls. Transporter loss in DLBs was of similar magnitude to that seen in PD, but with a flatter rostrocaudal (caudate-putamen) gradient (P=.001), while the greatest loss in all 3 areas was seen in those who had PD and dementia. Both region of interest analysis and visual ratings provided good separation between DLBs and AD (region of interest: sensitivity, 78%; specificity, 94%; positive predictive value, 90%) but not among subjects with DLB, PD, and PD with dementia.Conclusions: Dopamine transporter loss can be detected in vivo using FP-CIT SPECT in DLB. Further studies, especially of subjects with DLB without PD, are required to fully establish use in clinical practice.

The impact of density and atomic composition on the dosimetric response of various detectors in small photon radiation fields is characterized using a 'density-correction' factor, F(detector), defined as the ratio of Monte Carlo calculated doses delivered to water and detector voxels located on-axis, 5 cm deep in a water phantom with a SSD of 100 cm. The variation of F(detector) with field size has been computed for detector voxels of various materials and densities. For ion chambers and solid-state detectors, the well-known variation of F(detector) at small field sizes is shown to be due to differences between the densities of detector active volumes and water, rather than differences in atomic number. However, associated changes in the measured shapes of small-field profiles offset these variations in F(detector), so that integral doses measured using the different detectors are quite similar, at least for slit fields. Since changes in F(detector) with field size arise primarily from differences between the densities of the detector materials and water, ideal small-field relative dosimeters should have small active volumes and water-like density.