Introduction

This study evaluated the potential to reduce the scan duration in dopamine transporter (DAT) SPECT when using a second-generation multiple-pinhole (MPH) collimator designed for brain SPECT with improved count sensitivity and improved spatial resolution compared with parallel-hole and fanbeam collimators.

Methods

The retrospective study included 640 consecutive clinical DAT SPECT studies that had been acquired in list mode with a Mediso AnyScan®TRIO SPECT/CT system with MPH collimators and a 30-min net scan duration after injection of 181 ± 10 MBq of [123I]FP-CIT. Raw data corresponding to scan durations of 20, 15, 12, 8, 6, and 4 min were obtained by restricting the events to a proportionally reduced time interval of the list-mode data for each projection angle. SPECT images were reconstructed iteratively with the same parameter settings irrespective of scan duration.

Representative examples in which scan duration had no relevant impact down to 4 min (transversal 12-mm images; top: female, 44 y, 200 MBq, 186-min uptake period; bottom: female, 72 y, 200 MBq, 220-min uptake period).

The resulting 5, 120 SPECT images were assessed for a neurodegeneration-typical reduction in striatal signal by visual assessment, conventional specific binding ratio analysis, and a deep convolutional neural network trained on 30-min scans.

Results

Regarding visual interpretation, image quality was considered diagnostic for all 640 patients down to a 12-min scan duration. The proportion of discrepant visual interpretations between 30 and 12 min (1.2%) was not larger than the proportion of discrepant visual interpretations between 2 reading sessions of the same reader at a 30-min scan duration (1.5%). Agreement with the putamen specific binding ratio from the 30-min images was better than expected for 5% test–retest variability down to a 10-min scan duration. A relevant change in convolutional neural network–based automatic classification was observed at a 6-min scan duration or less. 

Scatterplots of unilateral putamen SBR (n = 1,280) with reduced vs. 30-min scan duration, and plot of R2. Dashed lines indicate R2 expected for putamen SBR from 2 short-term repeat DAT SPECT scans of same patient with 5% test–retest variability.

Conclusion

The Mediso AnyScan®TRIO SPECT/CT  with MPH collimators allows reliable DAT SPECT after administration of about 180 MBq of [123I]FP-CIT with a 12-min scan duration.

SPECT of striatal dopamine transporter (DAT) availability with N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-123I-iodophenyl)nortropane ([123I]FP-CIT) is widely used to support the diagnostic work-up in patients with a clinically uncertain parkinsonian syndrome or suspicion of dementia with Lewy bodies.

Multiple-pinhole (MPH) collimator technology has the potential to concurrently improve spatial resolution and count sensitivity compared with imaging with conventional parallel-hole and fanbeam collimators in clinical SPECT of small organs (7), including DAT SPECT with [123I]FP-CIT.

A recent prospective study showed that MPH collimators improve intra- and interreader agreement and the certainty of the visual interpretation of DAT SPECT compared with low-energy, high-resolution, high-sensitivity collimators (16). A technical performance evaluation of the triple-head camera with MPH collimators used in this previous (and in the current) study found a peak system sensitivity of 675 cps/MBq, which is about 3 times higher than the typical system sensitivity of double-head cameras with conventional parallel-hole or fanbeam collimators (7,15). This finding suggests that the triple-head camera equipped with MPH collimators allows a considerable reduction in scan duration in DAT SPECT. This reduction is desirable for better patient comfort, reduced risk of motion artifacts, and reduced costs (in terms of camera occupancy).

Against this background, the current study evaluated the impact of scan duration on MPH DAT SPECT with respect to visual interpretation, conventional semiquantitative analysis, and automatic classification with a deep convolutional neural network. The study retrospectively included 640 MPH DAT SPECT studies from clinical routine that had been acquired in list mode and therefore allowed realistic simulation of reduced scan duration.

Full article on Journal of Nuclear Medicine.