Phantom and clinical evaluation of bone SPECT/CT image reconstruction using novel conjugate gradient method
Abstract Background Two novel methods of image reconstruction, xSPECT Quant (xQ) and xSPECT Bone (xB) that use an ordered subset conjugate gradient minimizer (OSCGM) for bone SPECT/CT have been proposed. The present study compares the performance characteristics of xQ, xB and conventional Flash3D (F3D) reconstruction using images derived from phantoms and patients. Methods A custom-designed body phantom for bone SPECT was scanned using a Symbia Intevo (Siemens Healthineers) and reconstructed xSPECT images were evaluated. A phantom with 28-mm spheres containing a 99m Tc background, and having tumor-to-bone ratios (TBR) of 1, 2, 4 and 10, was evaluated as the convergence of 1 - 96 iterations. The full width at half maximum (FWHM) of a simulated spinous process (10 mm), coefficients of variance (CV) and recovery coefficients (RC) of a simulated spine on SPECT images determined using F3D, xQ, xB were compared in a phantom containing four spheres with diameters of 13, 17, 22, 28 mm at TBR4 containing a 99m Tc-background. Images from 20 patients with suspected bone metastases (male, n = 13) were acquired using 99m Tc-(H)MDP SPECT/CT, then the CV and standardized uptake value (SUV) at the 4 th vertebral body (L4) were compared with xQ and xB in a clinical setup. Results Mean radioactive concentrations with various TBR converged in accordance with increasing numbers of iterations. Spatial resolution was improved in the order of xB, xQ and F3D regardless of the number of iterations during reconstruction. The CV and RC were better for xQ and xB than F3D. The RC significantly differed between xQ and xB at lower numbers of iterations, whereas those of xQ and xB became almost saturated at higher iteration numbers. The CV and SUV for clinical patients did not significantly differ between xQ and xB. Conclusions The reconstructed xQ and xB images were better than those conventionally reconstructed using F3D. Bone SPECT xB imaging offered essentially unchanged spatial resolution even when the numbers of iterations did not converge. The xB further enhanced SPECT image quality using CT data. Our findings provide important evidence for understanding the performance characteristics of the novel xQ and xBalgorithms.