Reconstruction-based Compensation Research Articles

Optimization and evaluation of reconstruction-based compensation methods and reconstruction parameters for Tc-99m MIBI parathyroid SPECT

The value of Tc-99m MIBI parathyroid SPECT for localizing parathyroid hyperplasia in chronic renal failure patients remains inconclusive due to limited image quality. Advanced reconstruction methods to improve image quality have been developed but require optimization and evaluation. The goal of this study was to optimize and evaluate compensation methods and reconstruction parameters for Tc-99m MIBI parathyroid SPECT. A phantom population and projection data that modelled clinically realistic variations found in patients were simulated. The 3D OS-EM reconstruction with compensation for attenuation, detector response and scatter in various combinations were studied. For each compensation, the number of updates for OS-EM and the cutoff frequency of a 3D Butterworth filter were optimized and evaluated using anthropomorphic model observer. With optimal parameters, the method with compensation for attenuation and detector response, with or without the addition of scatter compensation, provided the highest lesion detectability for Tc-99m MIBI parathyroid SPECT.

Three-dimensional SPECT reconstruction with transmission-dependent scatter correction

The quality of single-photon emission computed tomography (SPECT) imaging is hampered by attenuation, collimator blurring, and scatter. Correction for all of these three factors is required for accurate reconstruction, but unfortunately, reconstruction-based compensation often leads to clinically unacceptable long reconstruction times. Especially, efficient scatter correction has proved to be difficult to achieve. The objective of this article was to extend the well-known transmission-dependent convolution subtraction (TDCS) scatter-correction approach into a rapid reconstruction-based scatter-compensation method and to include it into a fast 3D reconstruction algorithm with attenuation and collimator-blurring corrections. Ordered subsets expectation maximization algorithm with attenuation, collimator blurring, and accelerated transmission-dependent scatter compensation were implemented. The new reconstruction method was compared with TDCS-based scatter correction and with one other transmission-dependent scatter-correction method using Monte Carlo simulated projection data of (99m)Tc-ECD and (123)I-FP-CIT brain studies. The new reconstruction-based scatter compensation outperformed the other two scatter-correction methods in terms of quantitative accuracy and contrast measured with normalized mean-squared error, gray-to-white matter and striatum-to-background ratios, and also in visual quality. Highest accuracy was achieved when all the corrections (i.e., attenuation, collimator blurring, and scatter) were applied. The developed 3D reconstruction algorithm with transmission-dependent scatter compensation is a promising alternative to accurate and efficient SPECT reconstruction.

Partial volume effect compensation for quantitative brain SPECT imaging

Partial volume (PV) effects degrade the quantitative accuracy of SPECT brain images. In this paper, we extended a PV compensation (PVC) method originally developed for brain PET, the geometric transfer matrix (GTM) method, to brain SPECT using iterative reconstruction-based compensations. In the GTM method a linear transform between the true regional activities and the measured results was assumed. Elements of the GTM were calculated by projecting and reconstructing maps with uniform regions representing different structures. However, with iterative reconstruction methods, especially when reconstruction-based compensation for detector response was applied, we found that it was important to treat the region maps as a perturbation to the reconstructed image in the estimation of the GTM. This modified method, termed perturbation-based GTM (pGTM) was evaluated using Monte Carlo (MC) simulated and experimentally acquired data. Results showed great improvement of the quantitative accuracy in brain SPECT imaging. For MC simulated data, PVC using pGTM reduced the underestimation of striatal activities from 30% to less than 1.2%. For experimental data, PVC using pGTM reduced the underestimation of striatal activities from 36% to less than 7.8%. The underestimation of the striatum to background activity ratio was also improved from 31% to 2.7%.

Application of task-based measures of image quality to optimization and evaluation of three-dimensional reconstruction-based compensation methods in myocardial perfusion SPECT.

In this paper, we apply the channelized Hotelling observer (CHO) using a defect detection task to the optimization and evaluation of three-dimensional iterative reconstruction-based compensation methods for myocardial perfusion single-photon emission computed tomography (SPECT). We used a population of 24 mathematical cardiac-torso phantoms that realistically model the activity and attenuation distribution in three classes of patients: females, and males with flat diaphragms and raised diaphragms. Projection data were generated and subsequently reconstructed using methods based on the ordered subsets-expectation maximization (OSEM) algorithm. The methods evaluated included compensation for attenuation, detector response blurring, and scatter in various combinations. We applied the CHO to optimize the number of iterations for OSEM and the cutoff frequency and order of a three-dimensional postreconstruction Butterworth filter. Using the optimal parameters, we then compared the compensation methods. The index of comparison in these studies was the area under the receiver operating characteristics curve (AUC) for the CHO. We found that attenuation compensation with either detector response or scatter compensation gave statistically significant increases in the AUC compared to attenuation compensation alone. The greatest increase in the AUC occurred when all three compensations were applied. These results indicate that compensation for detector response and scatter, in addition to attenuation compensation, will improve defect detectability in myocardial SPECT images.