Evaluation of Image Degradation Factors and Correction Methods in DAT SPECT Using a Digital Population of Phantoms

Dopamine transporter (DAT) SPECT is a competent diagnostic tool for Parkinson’s disease (PD). However, image degradation factors like attenuation, scatter and penetration affect its image quality and quantitative accuracy. We aim to evaluate these factors and their correction methods for 2 common DAT SPECT tracers, i.e.,
^99m
Tc-TRODAT (
^99m
Tc) and
¹²³
I-ioflupane (
¹²³
I), using the SIMIND MC tool and a population of digital brain phantoms. We generated 40 phantoms based on clinical brain MRI data to model anatomical variations of striatum, brain background and head size. Striatal binding ratios (SBR) were varied according to different PD stages for 2 tracers (up to 6 for
^99m
Tc and up to 12 for
¹²³
I). We generated 120 noisy projections with 1.5 M counts for
¹²³
I and 3 M counts for
^99m
Tc based on a dual-head clinical SPECT scanner with low-energy high-resolution parallel-hole collimators. Projection count for all interactions (T), attenuation (A), scatter (S), penetration (P), and ideal situation with no scatter and attenuation modeled (AIR) were compared for both tracers. Projections were reconstructed with OS-EM algorithm (4 subsets and 8 iterations) with (i) CT-based attenuation correction (AC) and Dual Energy Window (DEW) scatter correction (AC+SC), (ii) with AC only, (iii) with SC only, and (iv) without AC and SC (NC). Mean square error (MSE), structural similarity index (SSIM), SBR and image profiles were evaluated. Projection count ratios of AIR:T:A:S:P were 231:100:77:17:5 for
^99m
Tc and 225:100:75:16:7 for
¹²³
I respectively. MSE, SSIM, SBR and profiles all showed that AC+SC substantially improved quantitative accuracy, followed by AC only, NC and SC only for both tracers. Attenuation impacted DAT SPECT the most, followed by scatter and penetration. CT-based AC and DEW are effective corrections for DAT SPECT.