Biomedical subjects

Manoj V Narayanan

Publications and source records attributed to Manoj V Narayanan.

5 recordsLinked to original sources

PubMed2004

Assessment of scatter compensation strategies for (67)Ga SPECT using numerical observers and human LROC studies.

UNLABELLED: 67Ga citrate is an oncologic SPECT imaging agent often used to diagnose or stage patients with non-Hodgkin's lymphoma. As (67)Ga decay involves the emission of multiple-energy gamma-rays, significant photon downscatter will be present within each photopeak energy window. We have previously shown that the inclusion of these scattered photons significantly degrades lesion detectability. The goal of this study was to investigate the extent to which this decrease in detectability can be reversed by applying scatter compensation strategies. METHODS: We have compared 5 different scatter compensation methods to the case of no scatter compensation in iterative SPECT image reconstruction. The strategies consisted of (a). perfect scatter rejection, (b). ideal scatter compensation, (c). triple-energy window (TEW) scatter estimation, (d). effective scatter source estimation (ESSE), and (e). postreconstruction scatter subtraction. Reconstruction parameters used for each method were first optimized using a channelized Hotelling numerical observer. Strategies were then ranked in terms of lesion detectability using a human observer localization receiver operating characteristic (LROC) study. An additional comparison was made comparing the human LROC rankings with a recently developed channelized nonprewhitening (CNPW) LROC numerical observer. RESULTS: Using the area-under-the-LROC-curve (A(LROC)) as the assessment criterion, our results indicate that the TEW and ESSE scatter compensation methods are able to significantly improve lesion detectability over no compensation (A(LROC) = 0.75 and 0.73 vs. 0.67, respectively). However, these compensations failed to achieve the same detectability as perfect scatter rejection (A(LROC) = 0.84). Both ideal scatter compensation and postreconstruction scatter subtraction resulted in numerical increases in detection accuracy that were not statistically significant from no scatter compensation. Good agreement is seen between the CNPW observer and human LROC studies (Spearman rank order coefficient, r(s) = 0.74), thus indicating that the LROC observer may be a good predictor of human observer performance in (67)Ga SPECT. CONCLUSION: Scatter compensation in (67)Ga SPECT imaging using techniques such as TEW or ESSE is able to improve lesion detectability compared with no scatter compensation. A recently developed numerical observer model appears to be a good predictor of human observer performance and may be used to perform imaging optimizations, thereby reducing the need for human LROC studies.

Citrates↗

PubMed2003

Human-observer receiver-operating-characteristic evaluation of attenuation, scatter, and resolution compensation strategies for (99m)Tc myocardial perfusion imaging.

UNLABELLED: Nonuniform attenuation, scatter, and distance-dependent resolution are confounding factors inherent in SPECT imaging. Iterative reconstruction algorithms permit modeling and compensation of these degradations. We investigated through human-observer receiver-operating-characteristic (ROC) studies which (if any) combination of such compensation strategies best improves the accuracy of detection of coronary artery disease (CAD) when expert readers have only stress images for diagnosis. METHODS: A 3-headed SPECT system fitted with a (153)Gd line source was used to acquire simultaneously (99m)Tc-methoxyisobutylisonitrile (MIBI) images and transmission data. With these acquisitions, the accuracy of detecting CAD was evaluated for the following reconstruction strategies: filtered backprojection (FBP); ordered-subset expectation maximization (OSEM) with attenuation correction (AC); OSEM with AC and scatter correction (SC) (AC + SC); and OSEM with AC, SC, and resolution compensation (RC) (AC + SC + RC). Reconstruction parameters for OSEM were optimized by use of human-observer ROC studies with hybrid images, whereas standard clinical parameters were used for FBP. A total of 100 patients, including 55 patients referred for angiography and 45 patients with <5% likelihood for CAD, were included in the ROC studies. Images reconstructed with the 4 methods were rated independently with regard to the presence of CAD by 7 observers using a continuous scale for certainty. RESULTS: With area under the ROC curve (A(z)) as the criterion, the iterative reconstructions with compensation strategies (AC, AC + SC, and AC + SC + RC) demonstrated better detection accuracy than did FBP reconstructions for the overall detection of CAD as well as for the localization of perfusion defects in the 3 vascular territories. In general, the trend was for an increase in the A(z) for the progression from FBP to OSEM with AC, to OSEM with AC + SC, and to OSEM with AC + SC + RC. Statistically, the combination strategy with AC + SC + RC provided significantly higher A(z) values than did FBP images for the overall detection of CAD and the localization of perfusion defects in the left anterior descending coronary artery and left circumflex coronary artery territories, whereas AC + SC provided significantly better performance in the right coronary artery territory. CONCLUSION: The results indicate that OSEM with AC + SC + RC outperforms FBP reconstructions, indicating that the modeling of physical degradations can improve the accuracy of detection of CAD with cardiac perfusion SPECT reconstructions.

Coronary Circulation↗

PubMed2002

An iterative transmission algorithm incorporating cross-talk correction for SPECT.

Simultaneous emission/transmission acquisitions in cardiac SPECT with a Tc99m/Gd153 source combination offer the capability for nonuniform attenuation correction. However, cross-talk of Tc99m photons downscattered into the Gd153 energy window contaminates the reconstructed transmission map used for attenuation correction. The estimated cross-talk contribution can be subtracted prior to transmission reconstruction or incorporated in the reconstruction algorithm itself. In this work, we propose an iterative transmission algorithm (MLTG-S) based on the maximum-likelihood gradient algorithm (MLTG) that explicitly accounts for this cross-talk estimate. Clinical images were acquired on a three-headed SPECT camera, acquiring Tc99m emission and Gd153 transmission images simultaneously. Subtracting the cross-talk estimate prior to transmission reconstruction can result in negative and zero values if the estimate is larger than or equal to the count in the transmission projection bin, especially with increased attenuator size or amount of cross-talk. This results in inaccurate attenuation coefficients for MLTG reconstructions with cross-talk subtraction. MLTG-S reconstructions on the other hand, yield better estimates of attenuation maps, by avoiding the subtraction of the cross-talk estimate. Comparison of emission slices corrected for nonuniform attenuation reveals that inaccuracies in the reconstructed attenuation map caused by cross-talk can artificially enhance the extra-cardiac activity, confounding the ability to visualize the left-ventricular walls.

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PubMedDate not supplied

Myocardial perfusion SPECT reconstruction: receiver operating characteristic comparison of CAD detection accuracy of filtered backprojection reconstruction with all of the clinical imaging information available to readers and solely stress slices iteratively reconstructed with combined compensation.

BACKGROUND: Past receiver operating characteristic (ROC) studies have demonstrated that single photon emission computed tomography (SPECT) perfusion imaging by use of iterative reconstruction with combined compensation for attenuation, scatter, and detector response leads to higher area under the ROC curve (A(z)) values for detection of coronary artery disease (CAD) in comparison to the use of filtered backprojection (FBP) with no compensations. A new ROC study was conducted to investigate whether this improvement still holds for iterative reconstruction when observers have available all of the imaging information normally presented to clinical interpreters when reading FBP SPECT perfusion slices. METHODS AND RESULTS: A total of 87 patient studies including 50 patients referred for angiography and 37 patients with a lower than 5% likelihood for CAD were included in the ROC study. The images from the two methods were read by 4 cardiology fellows and 3 attending nuclear cardiologists. Presented for the FBP readings were the short-axis, horizontal long-axis, and vertical long-axis slices for both the stress and rest images; cine images of both the stress and rest projection data; cine images of selected cardiac-gated slices; the CEQUAL-generated stress and rest polar maps; and an indication of patient gender. This was compared with reading solely the iterative reconstructed stress slices with combined compensation for attenuation, scatter, and resolution. With A(z) as the criterion, a 2-way analysis of variance showed a significant improvement in detection accuracy for CAD for the 7 observers (P = .018) for iterative reconstruction with combined compensation (A(z) of 0.895 +/- 0.016) over FBP even with the additional imaging information provided to the observers when scoring the FBP slices (A(z) of 0.869 +/- 0.030). When the groups of 3 attending physicians or 4 cardiology fellows were compared separately, the iterative technique was not statistically significantly better; however, the A(z) for each of the 7 observers individually was larger for iterative reconstruction than for FBP. Compared with results from our previous studies, the additional imaging information did increase the diagnostic accuracy of FBP for CAD but not enough to undo the statistically significantly higher diagnostic accuracy of iterative reconstruction with combined compensation. CONCLUSIONS: We have determined through an ROC investigation that included two classes of observers (experienced attending physicians and cardiology fellows in training) that iterative reconstruction with combined compensation provides statistically significantly better detection accuracy (larger A(z)) for CAD than FBP reconstructions even when the FBP studies were read with all of the extra clinical nuclear imaging information normally available.

Coronary Artery Disease↗

PubMedDate not supplied

Simultaneous assessment of cardiac perfusion and function using 5-dimensional imaging with Tc-99m teboroxime.

BACKGROUND: Dynamic single photon emission computed tomography (SPECT) acquisition and reconstruction of early poststress technetium 99m teboroxime washout images has been shown to be useful in the detection of coronary disease. Assessment of poststress regional wall motion may offer additional use in assessing coronary disease. Our goal was to investigate the feasibility of simultaneously imaging myocardial ischemia and transient poststress akinesis using gated-dynamic SPECT. METHODS AND RESULTS: A gated-dynamic mathematical cardiac torso (MCAT) phantom was developed to model both teboroxime kinetics and cardiac regional wall motion. A lesion was simulated as having delayed poststress teboroxime washout together with a transient poststress wall motion abnormality. Gated projection data were created to represent a 3-headed SPECT system undergoing a total rotation of 480 degrees . The dynamic expectation-maximization reconstruction algorithm with postsmoothing across gating intervals by Wiener filtering, and the ordered-subset expectation maximization reconstruction algorithm with 3-point smoothing across gating intervals were compared. Compared with the ordered-subset expectation maximization with 3-point smoothing, the dynamic expectation-maximization algorithm with Wiener filtering was able to produce visually higher-quality images and more accurate left ventricular ejection fraction estimates. CONCLUSION: From simulations, we conclude that changing cardiac function and tracer localization possibly can be assessed by using a gated-dynamic acquisition protocol combined with a 5-dimensional reconstruction strategy.

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