Scatter and crosstalk corrections for (99m)Tc/(123)I dual-radionuclide imaging using a CZT SPECT system with pinhole collimators

• Published in: Medical physics (Lancaster) 2015-12, Vol.42 (12), p.6895-6911
• Main Authors: Fan, Peng, Hutton, Brian F, Holstensson, Maria, Ljungberg, Michael, Pretorius, P Hendrik, Prasad, Rameshwar, Ma, Tianyu, Liu, Yaqiang, Wang, Shi, Thorn, Stephanie L, Stacy, Mitchel R, Sinusas, Albert J, Liu, Chi
• Format: Article
• Language: English
• Subjects: 60 APPLIED LIFE SCIENCES; BIOMEDICAL RADIOGRAPHY; BLOOD; Cadmium; Clinical Medicine; COLLIMATORS; Computer Simulation; COMPUTERIZED SIMULATION; CORRECTIONS; Heart - diagnostic imaging; Humans; IMAGE PROCESSING; IODINE 123; Iodine Radioisotopes; ITERATIVE METHODS; Klinisk medicin; Likelihood Functions; Medical and Health Sciences; Medicin och hälsovetenskap; Models, Biological; MONTE CARLO METHOD; MYOCARDIUM; PHANTOMS; Phantoms, Imaging; Photons; POINT SOURCES; RADIOISOTOPE SCANNING; Radiologi och bildbehandling; RADIOLOGY AND NUCLEAR MEDICINE; Radiology, Nuclear Medicine and Medical Imaging; Radiopharmaceuticals; Scattering, Radiation; SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY; Technetium; TECHNETIUM 99; TELLURIDES; Tellurium; Tomography, Emission-Computed, Single-Photon - instrumentation; Tomography, Emission-Computed, Single-Photon - methods; Tomography, X-Ray Computed; Zinc
• ISSN: 0094-2405; 2473-4209; 2473-4209
• DOI: 10.1118/1.4934830

The energy spectrum for a cadmium zinc telluride (CZT) detector has a low energy tail due to incomplete charge collection and intercrystal scattering. Due to these solid-state detector effects, scatter would be overestimated if the conventional triple-energy window (TEW) method is used for scatter and crosstalk corrections in CZT-based imaging systems. The objective of this work is to develop a scatter and crosstalk correction method for (99m)Tc/(123)I dual-radionuclide imaging for a CZT-based dedicated cardiac SPECT system with pinhole collimators (GE Discovery NM 530c/570c). A tailing model was developed to account for the low energy tail effects of the CZT detector. The parameters of the model were obtained using (99m)Tc and (123)I point source measurements. A scatter model was defined to characterize the relationship between down-scatter and self-scatter projections. The parameters for this model were obtained from Monte Carlo simulation using SIMIND. The tailing and scatter models were further incorporated into a projection count model, and the primary and self-scatter projections of each radionuclide were determined with a maximum likelihood expectation maximization (MLEM) iterative estimation approach. The extracted scatter and crosstalk projections were then incorporated into MLEM image reconstruction as an additive term in forward projection to obtain scatter- and crosstalk-corrected images. The proposed method was validated using Monte Carlo simulation, line source experiment, anthropomorphic torso phantom studies, and patient studies. The performance of the proposed method was also compared to that obtained with the conventional TEW method. Monte Carlo simulations and line source experiment demonstrated that the TEW method overestimated scatter while their proposed method provided more accurate scatter estimation by considering the low energy tail effect. In the phantom study, improved defect contrasts were observed with both correction methods compared to no correction, especially for the images of (99m)Tc in dual-radionuclide imaging where there is heavy contamination from (123)I. In this case, the nontransmural defect contrast was improved from 0.39 to 0.47 with the TEW method and to 0.51 with their proposed method and the transmural defect contrast was improved from 0.62 to 0.74 with the TEW method and to 0.73 with their proposed method. In the patient study, the proposed method provided higher myocardium-to-blood pool contrast than that of