An APD-based iterative reconstruction method for simultaneous technetium-99m/iodine-123 SPECT imaging

Model-based correction for scatter and tailing effects in simultaneous 99mTc and 123I imaging for a CdZnTe cardiac SPECT camera

An advantage of semiconductor-based dedicated cardiac single photon emission computed tomography (SPECT) cameras when compared to conventional Anger cameras is superior energy resolution. This provides the potential for improved separation of the photopeaks in dual radionuclide imaging, such as combined use of (99m)Tc and (123)I . There is, however, the added complexity of tailing effects in the detectors that must be accounted for. In this paper we present a model-based correction algorithm which extracts the useful primary counts of (99m)Tc and (123)I from projection data. Equations describing the in-patient scatter and tailing effects in the detectors are iteratively solved for both radionuclides simultaneously using a maximum a posteriori probability algorithm with one-step-late evaluation. Energy window-dependent parameters for the equations describing in-patient scatter are estimated using Monte Carlo simulations. Parameters for the equations describing tailing effects are estimated using virtually scatter-free experimental measurements on a dedicated cardiac SPECT camera with CdZnTe-detectors. When applied to a phantom study with both (99m)Tc and (123)I, results show that the estimated spatial distribution of events from (99m)Tc in the (99m)Tc photopeak energy window is very similar to that measured in a single (99m)Tc phantom study. The extracted images of primary events display increased cold lesion contrasts for both (99m)Tc and (123)I.

Quantitative image reconstruction for dual-isotope parathyroid SPECT/CT: phantom experiments and sample patient studies

We investigated the quantitative accuracy of the model-based dual-isotope single-photon emission computed tomography (DI-SPECT) reconstructions that use Klein-Nishina expressions to estimate the scattered photon contributions to the projection data. Our objective was to examine the ability of the method to recover the absolute activities pertaining to both radiotracers: Tc-99m and I-123. We validated our method through a series of phantom experiments performed using a clinical hybrid SPECT/CT camera (Infinia Hawkeye, GE Healthcare). Different activity ratios and different attenuating media were used in these experiments to create cross-talk effects of varying severity, which can occur in clinical studies. Accurate model-based corrections for scatter and cross-talk with CT attenuation maps allowed for the recovery of the absolute activities from DI-SPECT/CT scans with errors that ranged 0-10% for both radiotracers. The unfavorable activity ratios increased the computational burden but practically did not affect the resulting accuracy. The visual analysis of parathyroid patient data demonstrated that our model-based processing improved adenoma/background contrast and enhanced localization of small or faint adenomas.

Dual-isotope acquisition for CT-SPECT registration of infection studies

The registration of CT and NM images can enhance patient diagnosis since it allows for the fusion of anatomical and functional information as well as attenuation correction of NM images. However, irrespective of the methods used, registration accuracy depends heavily on the characteristics of the input images and the degree of similarity between them. This poses a challenge for registering CT and NM images as they may have very different characteristics. To address the particular problem of CT and In-111 SPECT registration, we propose to perform a dual-isotope study which involves an additional injection of Tc-99m MDP to generate two inherently registered images: In-111 SPECT and Tc-99m SPECT. As skeletal structures are visible in both CT and Tc-99m SPECT, performing registration of these images may be much more effective. The very same spatial transformation derived can be immediately applied to complete the registration of CT and the corresponding In-111 SPECT. Accordingly, we hypothesize that the registration of CT and Tc-99m SPECT can be more accurately performed than the registration of CT and In-111 SPECT and seek to compare the accuracies between the aforementioned registrations. In this paper, we have collected three clinical datasets, with the ground-truth transformations known, and tested the proposed approach by using a mutual information-based algorithm to solve for the rigid/non-rigid misalignments introduced to them. Based on the results of our experiments, we conclude that registration using Tc-99m SPECT can achieve 100% success rate, and is thus much more superior to the registration using In-111 SPECT, which at best, achieves only 38% success rate. Clearly, the introduction of a dual-isotope acquisition can substantially improve the registration of SPECT and CT images.