Receiver Operator Characteristic Confirmation of Potential for Radiation Dose Reduction with Improved Reconstruction for Cardiac SPECT
P. Hendrik PretoriusAlbert Juan RamonMichael A. KingArda KönikSeth T. DahlbergMatthew W. ParkerKaren L. JohnsonYongyi YangMiles N. Wernick
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Dose fractionation is a popular proposed method to lower the radioactive exposure to patients undergoing myocardial perfusion imaging (MPI) SPECT/CT. Recently, we optimized reconstruction strategies employed during dose fractionation in MPI using polar maps in combination with the calculation of total perfusion deficit (TPD) scores employing hybrid defects of various sizes. Although observed to agree well with experienced observers, TPD scores have not been used to judge the impact of reduced dose SPECT imaging for standard two-headed SPECT systems. Thus, the aim of this study was to confirm that the optimized reconstruction strategies are indeed ranked accordingly by TPD in comparison to human observers reading hybrid cardiac defects studies with known truth. We setup our human observer study with 126 test cases and 44 training cases. Four observers participated by reading three different reconstruction strategies, ordered-subset expectation maximization with the original dose, (OSEM100), OSEM with only 25% of the dose (OSEM25), and filtered backprojection with the original dose (FBP100). Before commencing the reading of the actual test cases, training with feedback were done for each of the reconstruction strategies. The test cases were read in nine randomized sessions (42 test cases per session), three for each reconstruction strategy with 8 training images as a warm-up with feedback (50 image sets per reading session). The order of reading the different sets as well as the order of the test cases were different for each observer. ROCKIT (University of Chicago) software was used to analyze the observer data. Areas under the curve (AUC) values of 0.786, 0.754, and 0.643 were recorded for OSEM100, OSEM25, and FBP100 respectively. The ranking of the reconstruction strategies is the same as for the TPD scoring method, while the observers performed worse scoring FBP100.Keywords:
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Diagnostic tests and clinical prediction rules are frequently used to help estimate the probability of a disease or outcome. How well a test or rule distinguishes between disease or no disease (discrimination) can be measured by plotting a receiver operating characteristic (ROC) curve and calculating the area under it (AUROC). In this paper, we review the features of ROC curves and interpretation of ROC curves and AUROC values. We highlight 5 underappreciated features of ROC curves: (1) the slope of the ROC curve over a test result interval is the likelihood ratio for that interval; (2) the optimal cutoff for calling a test positive depends not only on the shape of the ROC curve, but also on the pretest probability of disease and relative harms of false-positive and false-negative results; (3) the AUROC measures discrimination only, not the accuracy of the predicted probabilities; (4) the AUROC is not a good measure of discrimination if the slope of the ROC curve is not consistently decreasing; and (5) the AUROC can be increased by including a large number of people correctly identified as being at very low risk for the outcome of interest. We illustrate this last concept using 3 published studies.
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To reduce scanning time in SPECT brain imaging, we investigate new brain imaging procedures, that include both scanning protocols and image processing methods, while at the same time, retain the comparable image quality for brain SPECT study. We apply our previously proposed fast convergent reconstruction along with some post-processing methods for the few view data. In the preliminary results from our simulations and physical phantom studies, the mean reconstructed ROI to background (R/B) ratio remains relatively stable with few variation. This result illustrates that a substantial saving of acquisition time can be achieved by reducing the number of projection views in the brain SPECT studies. The result is achieved without a significant loss in quantitative accuracy by using an improved reconstruction method in combination with additional data processing procedures.
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Single photon emission computer tomography (SPECT) myocardial perfusion imaging (MPI) employing technetium-99m (Tc-99m)-based imaging tracers is the mainstay of nuclear cardiology for the detection of myocardial ischemia. Current guidelines for same day rest/stress Tc-99m-sestamibi SPECT MPI recommend image acquisition 15-60 minutes after the stress testing. A novel sensitive SPECT imaging technique, D-SPECT, allows fast acquisition of images and captures rapid changes in radiotracer distribution. Here we report 2 cases of SPECT MPI in patients with angiographically confirmed coronary artery disease (CAD) where Tc-99m-sestamibi exhibited marked redistribution between early (6-8 min) and late (60-70 min) post-stress imaging leading to an underestimation of the extent and severity of ischemia on late images. These observations suggest that early imaging maybe more sensitive for CAD detection. Fast SPECT imaging techniques, such as D-SPECT, will facilitate similar studies in the future as they will allow fast image acquisition at several time points after the stress test.
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The quality of reconstructed image in Single-Photon Emission Computed Tomography (SPECT) is strongly degraded by the photon attenuation. In general, the attenuation correction on SPECT images requires the data to be known over 2π (full-scan). The reduction of data acquisition from 2π to π (half-scan) in SPECT is recommended because it reduces the scanning time; thereby, minimizing the patient’s motion and making the exam less uncomfortable for the patient. Algorithms
and numerical research has been developed on image reconstruction from data acquired over π in SPECT with non-uniform attenuation. However, it remains theoretically unknown whether data, acquired only over π in SPECT with nonuniform attenuation, contain complete information for accurate image reconstruction.
In this work, we present numerical results on image reconstruction in halfscan SPECT with non-uniform attenuation. The numerical simulations are based on a new iterative reconstruction algorithm that introduces exact and implicit attenuation
correction. Specifically, we show that the algorithm is able to reconstruct images, in half-scan SPECT, with quality very similar to those reconstructed in full-scan SPECT. Moreover, the numerical simulations show that the algorithm is stable and convergent.
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Single photon emission computed tomography (SPECT) is an important nuclear medicine imaging technique and has been using in clinical diagnoses. The SPECT image can reflect not only organizational structure but also functional activities of human body, therefore diseases can be found much earlier. In SPECT, the reconstruction is based on the measurement of gamma photons emitted by the radiotracer. The number of gamma photons detected is proportional to the dose of radiopharmaceutical, but the dose is limited because of patient safety. There is an upper limit in the number of gamma photons that can be detected per unit time, so it takes a long time to acquire SPECT projection data. Sometimes we just can obtain highly under-sampled projection data because of the limit of the scanning time or imaging hardware. How to reconstruct an image using highly under-sampled projection data is an interesting problem. One method is to minimize the total variation (TV) of the reconstructed image during the iterative reconstruction. In this work, we developed an OSEM-TV SPECT reconstruction algorithm, which could reconstruct the image from highly under-sampled projection data with non-uniform attenuation. Simulation results demonstrate that the OSEM-TV algorithm performs well in SPECT reconstruction with non-uniform attenuation.
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Cardiac imaging with gated single-photon emission computed tomography (SPECT) allows the evaluation of myocardial perfusion and analysis of global and regional left ventricular function. Gated SPECT is a validated and established diagnostic and prognostic method for evaluation of patients with suspected and known coronary artery disease. Significant improvements in software and gamma camera technology in SPECT cardiac imaging have been obtained. New detectors open a scenario for faster imaging with lower radiation dose to the patient. Appropriate use of the SPECT imaging is regulated by evidence-based guidelines and appropriateness criteria as well as by third-party payers in an effort to restrain the unsustainable growth of imaging testing recently observed. Future of cardiac SPECT imaging will be driven by societal demand for cost effective, accurate, and safe testing, which will improve meaningfully patients' management and outcomes.
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