Scatter correction based on an artificial neural network for 99mTc and 123I dual-isotope SPECT in myocardial and brain imaging
The aim of this study was to elucidate the clinical usefulness of scatter correction with an artificial neural network (ANN) in 99mTc and 123I dual-isotope SPECT. Two algorithms for ANN scatter correction were tested: ANN-10 and ANN-3 employing 10 and 3 energy windows for data acquisition, respectively. Three patients underwent myocardial or brain SPECT with one of the following combinations of radiopharmaceuticals administered: 99mTc-tetrofosmin and 123I-metaiodobenzylguanidine (MIBG), 99mTc-methoxyisobutylisonitrile (MIBI) and 123I-beta-methyl-paraiodophenyl-pentadecanoic acid (BMIPP), or 99mTc-ethyl-cistainate dimmer (ECD) and 123I-iomazenil. The patients were also referred for single-isotope imaging incorporating conventional triple-energy window (TEW) scatter correction. Crosstalk- and scatter-corrected 99mTc- and 123I-SPECT images in dual-isotope acquisition with ANN were compared with those in single-isotope acquisition. The ANN method well separated 123I and 99mTc primary photons. Although ANN-10 yielded images of poor quality, ANN-3 offered comparable image quality with the single-isotope scan without significant increase of acquisition time. The proposed method is clinically useful because it provides various combinations of information without anatomical misregistration with one acquisition.
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[Show abstract] [Hide abstract] ABSTRACT: Although the heart-to-mediastinum (H/M) ratio in a planar image has been used for practical quantification in (123)I-metaiodobenzylguanidine (MIBG) imaging, standardization of the parameter is not yet established. We hypothesized that the value of the H/M ratio could be standardized to the various camera-collimator combinations. Standard phantoms consisting of the heart and mediastinum were made. A low-energy high-resolution (LEHR) collimator and a medium-energy (ME) collimator were used. We examined multi-window correction methods with (123)I- dual-window (IDW) acquisition, and planar images were obtained with IDW correction and the LEHR collimator. The images were obtained using the following gamma camera systems: GCA 9300A (Toshiba, Tokyo), E.CAM Signature (Toshiba/Siemens, Tokyo) and Varicam (GE, Tokyo). Cardiac phantom studies demonstrated that contamination of the H/M count ratio was greater with the LEHR collimator and least with the ME collimator. The corrected H/M ratio with the LEHR collimator was similar to that with ME collimators. The uncorrected H/M ratio with the ME collimator was linearly related to the H/M ratio with IDW correction with the LEHR collimator. The relationship between the uncorrected H/M ratios determined with the LEHR (E.CAM) and the ME collimators was y = 0.56x + 0.49, where y = H/M ratio with the E.CAM and x = H/M ratio with the ME collimator. The average normal values for the low-energy collimator (n=18) were 2.2+/-0.2 (initial H/M ratio) and 2.42+/-0.2 (delayed H/M ratio), and for the low/medium-energy (LME) collimator (n=14) were 2.63+/-0.25 (initial H/M ratio) and 2.87+/-0.19 (delayed H/M ratio). H/M ratios in previous clinical studies using LEHR collimators are comparable to those with ME collimators. The IDW-corrected H/M ratios determined with the LEHR collimator were similar to those determined with the ME collimator. This finding could make it possible to standardize the H/M ratio in planar imaging among various collimators in the clinical setting.
- "In published 123I-MIBG studies, we could divide into two groups of values of H/M, although the precise collimator information was not available from all studies. In one group, the delayed H/M ratio ranged from 2.1 to 2.4, using LEHR or LEGP collimators [7,14,24,25]. Another group showed a comparatively higher delayed H/M ratio, from 2.8 to 3.0. "
- [Show abstract] [Hide abstract] ABSTRACT: Radionuclide imaging has the potential to be used in quantitative analysis of the regional function of organs. However, quantification of SPECT images is degraded by many factors such as Compton photon scattering. This could have a destructive effect on clinical reports so it is important to do scatter correction to get better quality SPECT images. We intended to determine how scatter correction with the TEW method can help physicians who look at heart SPECT images, get better reports. This study used the TEW method for scatter correction, which was proposed by Ogawa et al.,(9) using the two narrow windows on either side of the photopeak (20% down and 20% up of the photopeak respectively). Injection of radiopharmaceutical 99mTc was used for medical imaging. In the Shariati Hospital, Tehran, we studied a total of 80 patients with heart disease indications (43 men and 37 women) over the ages of 30-80 years. Contrast and sharpness were considerably improved after scatter correction so physicians could look at defects better. In a few cases scatter correction changed heart defect reports to normal. Using TEW, sensitivity and specificity increased from 86% to 94% and from 61% to 84% respectively. This method was simple to use in clinics.
- [Show abstract] [Hide abstract] ABSTRACT: Simultaneous multi-isotope SPECT imaging has a number of applications, for example, cardiac, brain and cancer imaging. The major concern in simultaneous multi-isotope is the significant crosstalk contamination between the different isotopes used. The current study focuses on a method of crosstalk compensation between two isotopes in simultaneous dual isotope SPECT acquisition applied to cancer imaging using 99mTc/111In. Monte Carlo (MC), which is thought to offer the most realistic crosstalk and scatter compensation modeling, in typical implementations, has inherent long calculation times (often several hours or days) associated with it. This makes MC unsuitable for clinical applications. We have previously incorporated convolution based forced detection into SIMIND Monte Carlo program which have made MC feasible to use in clinical time frames. In order to evaluate the accuracy of our accelerated MC program a number of point source simulation results were compared to experimentally acquired data in terms of spatial resolution and detector sensitivity. We have developed an iterative MC-based image reconstruction technique that simulates the photon downscatter from one isotope into the acquisition window of a second isotope. The MC based estimation of scatter contamination contained in projection views is then used to compensate for the photon contamination during iterative reconstruction. We use a modified ordered subset-expectation maximization (OS-EM), named as simultaneous ordered subset-expectation maximization (Sim-OSEM), to perform this step. We have undertaken a number of simulation tests and phantom studies to verify this approach. The proposed reconstruction technique also evaluated by reconstruction of experimentally acquired projection phantom data. Reconstruction using Sim-OSEM showed very promising results in terms of crosstalk and scatter compensation and uniformity of background compared to analytical attenuation based reconstruc- ion after triple energy window (TEW) based scatter correction of projection data. In our case images obtained using Sim-OSEM showed better scatter compensation and more uniform background when compared to the images reconstructed for separately acquired projection data using analytical attenuation based reconstruction.