SPECT IMAGING OF I-123 IMP IN DEMENTIA

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Abstract
Tomographic images of the cerebral distribution of N-isopropyl p-iodoamphetamine (IMP) labeled with hi-purity I-123 (p,5n) was obtained in multiple slices parallel to the O-M line in normals (N) and ambulatory patients with Alzheimer's Disease (AD) or Multiple Infarct Dementia(MID). Imaging began 15–30 minutes after IV injection of 1 mg IMP labeled with 3–5 mC1 of I-123. Limited angle tomography (LAT) was performed in 14 subjects (N=5, AD=6, MID=3) with a mobile camera (Technicare S420) and a rotating, slant-hole collimator plus a microcomputer (VIP-550) using commercial software. Full angle tomography (FAT) was performed in 9 subjects (N=2, AD=4, MID=3) with a rotating camera (Siemen's: Rota Camera) equipped with a medium energy collimator and a minicomputer (DEC:PDP 11/34A) using software developed by the U of Utrecht, Holland. A symmetrical distribution of IMP with highest uptake in the gray matter was seen in N with both LAT and FAT. Multiple asymmetrical defects involving primarily gray matter were seen with both methods in MID. Patients with advanced AD had decreased uptake of IMP in the parieto-occipital cortex and were easily distinguished from N and MID by LAT. Patients with early AD could not definitely be separated from N by LAT. AD could not be reliabily diagnosed with FAT using a medium energy collimator. LAT with I-123 IMP is useful for the diagnosis of MID and advanced AD. Spatial resolution was better with LAT than with FAT. This appeared to be mainly due to the low count rate (max 1.3 mil. counts) and suboptimal collimation. Recent studies using a low energy I-123 collimator produced improved sensitivity (max 2.7 mil. counts). Multiple parameters must be optimized for adequate resolution and quantitative studies of I-123 IMP with FAT.

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