Performance of the AdaptiSPECT-C system for tumor quantification, detection, and localization in123I-CLINDE brain SPECT imaging (2021)

1400 Objectives: Due to its higher tumor affinity, the 123I-CLINDE agent has recently come to the forefront as an improved alternative to available agents for cerebral tumor imaging [1]. The AdaptiSPECT-C, a brain dedicated multi-pinhole system with adaptable pinhole configuration, is being designed and constructed by our team [2-4]. In this simulation work, we evaluated through numerical observer and quantification studies the detection/localization capabilities and quantitative accuracies of AdaptiSPECT-C with various pinhole configuration for 123I-CLINDE imaging in comparison to a dual-head parallel-hole system commonly employed for brain imaging.
 Methods: The AdaptiSPECT-C design simulated consists of 24 square detector modules, each irradiated by up to 5 pinhole apertures. Each of the apertures is adaptable in size (i.e., 1.2, 2.6, and 4 mm) and can be opened or closed independently [3,4]. Through task-based performance studies, we determined detection and localization capabilities using the non-pre whitening matched-filter scanning observer for the 3 pinhole sizes and 3 pinhole combinations: 1 central, 4 oblique, and central+oblique pinholes. Results were compared with that of a dual-head system employing parallel-hole LEHR collimators [5]. The dataset consisted of 198 digital phantoms, 99 without lesion and 99 with spherical tumors, 1 cm in diameter, spatially distributed within one transverse slice of the brain of an XCAT phantom [6]. The tumor size and the tumor-to-background contrast of 1.8 were selected on the basis they correspond to the lowest range of measurable tumor sizes and contrasts seen clinically [7]. Simulations were performed in GATE [8], and projection were reconstructed with a pixel based OSEM reconstruction with 16 subsets [9]. The 9-pinhole combinations were compared for an equal imaging time based on the simulated sensitivity compared to clinical imaging performed with the dual-head parallel system. The reconstructed images with lesion were compared to the ground truth images in terms of lesion activity and contrast recoveries, the NRMSE, and the PSNR for a region of interest of 8 mm in radius placed around each lesion location. The task-based performance studies on tumor detection and localization were performed in 2D over a single slice of the reconstruction. For the low-sensitivity high-resolution pinhole configurations (i.e., 1.2 mm), we investigated post-reconstruction Gaussian filtering to improve control of the statistical noise.
 Results: The oblique and central+oblique configurations of AdaptiSPECT-C for all the pinhole sizes showed considerable improvements in terms of quantification in the lesion regions and tumor detection/localization compared to that of a dual-head parallel system. The central combination with a 2.6 mm diameter led to the best tumor detection capability at low iteration. For the same size, the oblique and central+oblique combinations showed similar detection at higher iteration and improved quantification. However, the solely central configuration was the worst combination for accurate tumor localization. The 2.6 mm size in an oblique or central+oblique combination showed improved localization capability at low and medium iteration, while the 4 mm size due to higher sensitivity required more iteration to achieve similar performance. The 1.2 mm size strongly impacted by statistical noise led to poor localization and quantification. Post-reconstruction Gaussian filtering slightly improved the localization accuracy at high iteration while degrading the detection capability.
 Conclusions: In this work, we demonstrated that a 2.6 mm diameter pinhole in oblique or central+oblique combinations for AdpatiSPECT-C is suited for improved quantification, detection, and localization of cerebral tumors for 123I-CLINDE imaging.
Research Support: NIBIB/NIH Grant (R01EB022521).