The Impact of Dual and Triple Energy Window Scatter Correction on I-123 Postsurgical Thyroid SPECT/CT Imaging Using a Phantom with Small Sizes of Thyroid Remnants.

I-123 is preferential over I-131 for diagnostic SPECT imaging after a thyroidectomy to determine the presence and size of residual thyroid tissue for radioiodine ablation. Scattering degrades the quality of I-123 SPECT images, primarily due to the penetration of high-energy photons into the main photopeak. The objective of this study was to quantitatively and qualitatively investigate the impact of two widely used window-based scatter correction techniques, the dual energy window (DEW) and triple energy window (TEW) techniques, in I-123 postsurgical SPECT/CT thyroid imaging using an anthropomorphic phantom with small sizes of remnants and anatomically correct surrounding structures. For this purpose, non-scatter-corrected, DEW and TEW scatter-corrected SPECT/CT acquisitions were performed for 0.5-10 mL remnants within a phantom, with 0.5-12.6 MBq administered activities within the remnants, and without and with background-to-remnant activity ratios of 5% and 10%. The decrease in photons, the noise and non-uniformity in the background region due to scatter correction were measured, as well as the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) from small remnants. The images were also visually evaluated by two experienced nuclear medicine physicians. Scatter correction decreased photons to a higher extent in larger regions than smaller regions. Larger remnants yielded higher SNR and CNR values, particularly at lower background activities. It was found from the quantitative analysis and the qualitative evaluation that TEW scatter correction performed better than DEW scatter correction, particularly at higher background activities, while no significant differences were reported at lower background activities. Scatter correction should be applied in I-123 postsurgical SPECT/CT imaging to improve the image contrast and detectability of small remnants within the background.

A Neck-Thyroid Phantom with Small Sizes of Thyroid Remnants for Postsurgical I-123 and I-131 SPECT/CT Imaging.

Post-surgical I-123 and I-131 SPECT/CT imaging can provide information on the presence and sizes of thyroid remnants and/or metastasis for an accurate re-staging of disease to apply an individualized radioiodine therapy. The purpose of this study was to develop and validate a neck-thyroid phantom with small sizes of thyroid remnants to be utilized for the optimization of post-surgical SPECT/CT imaging. 3D printing and molding techniques were used to develop the hollow human-shaped and -sized phantom which enclosed the trachea, esophagus, cervical spine, clavicle, and multiple detachable sections with different sizes of thyroid remnant in clinically relevant positions. CT images were acquired to evaluate the morphology of the phantom and the sizes of remnants. Triple-energy window scattered and attenuation corrected SPECT images were acquired for this phantom and for a modified RS-542 commercial solid neck-thyroid phantom. The response and sensitivity of the SPECT modality for different administered I-123 and I-131 activities within the equal-size remnants of both phantoms were calculated. When we compared the phantoms, using the same radiopharmaceutical and similar activities, we found that the measured sensitivities were comparable. In all cases, the I-123 counting rate was higher than the I-131 one. This phantom with capabilities to insert different small sizes of remnants and simulate different background-to-remnants activity ratios can be utilized to evaluate postsurgical thyroid SPECT/CT imaging procedures.

Characterization of attenuation and respiratory motion artifacts and their influence on SPECT MP image evaluation using a dynamic phantom assembly with variable cardiac defects.

BACKGROUND: A phantom assembly that simulates the respiratory motion of the heart was used to investigate artifacts and their impact on defect detection. METHODS: SPECT/CT images were acquired for phantoms with and without small and large cardiac defects during normal and deep breathing, and also at four static respiratory phases. Acquisitions were reconstructed with and without AC, and with misalignment of transmission and emission scans. A quantitative analysis was performed to assess artifacts. Two physicians reported on defect presence or absence and their results were evaluated. RESULTS: All large defects were correctly reported. Attenuation reduced uptake in the basal LV walls, increasing FN physicians' reports for small defects. Respiratory motion reduced uptake mainly in the anterior and inferior walls increasing FP and FN reports on images without and with small defects, respectively. Artifacts due to misalignment between CT and SPECT scans in normal breathing phantoms did not influence the physicians' reports. CONCLUSIONS: Attenuation and respiratory motion correction should be applied to reduce artifacts before reporting on small defects in deep breathing conditions. Artifacts due to misalignment between CT and SPECT scans do not affect defect detection in normal breathing when the LV is co-registered in SPECT and CT images prior to AC.

Impact of respiratory motion correction on SPECT myocardial perfusion imaging using a mechanically moving phantom assembly with variable cardiac defects.

BACKGROUND: The aim of this study was to determine the impact of respiratory motion correction on SPECT MPI and on defect detection using a phantom assembly. METHODS: SPECT/CT data were acquired using an anthropomorphic phantom with inflatable lungs and with an ECG beating and moving cardiac compartment. The heart motion followed the respiratory pattern in the cranio-caudal direction to simulate normal or deep breathing. Small or large transmural defects were inserted into the myocardial wall of the left ventricle. SPECT/CT images were acquired for each of the four respiratory phases, from exhale to inhale. A respiratory motion correction was applied using an image-based method with transformation parameters derived from the SPECT data by a non-rigid registration algorithm. A report on defect detection from two physicians and a quantitative analysis on MPI data were performed before and after applying motion correction. RESULTS: Respiratory motion correction eliminated artifacts present in the images, resulting in a uniform uptake and reduction of motion blurring, especially in the inferior and anterior regions of the LV myocardial walls. The physicians' report after motion correction showed that images were corrected for motion. CONCLUSIONS: A combination of motion correction with attenuation correction reduces artifacts in SPECT MPI. AC-SPECT images with and without motion correction should be simultaneously inspected to report on small defects.

Diagnostic sensitivity of SPECT myocardial perfusion imaging using a pumping cardiac phantom with inserted variable defects.

BACKGROUND: The diagnostic sensitivity of various SPECT MPI procedures was assessed using a pumping cardiac phantom with variable defects inserted in the myocardial wall of the left ventricle. METHODS AND RESULTS: A diagnostic evaluation of 142 myocardial defects was performed. A diagnosis blinded to prior-known conditions was compared to the known defects severity (transmural, subendocardial) and defects position within the myocardial wall of the left ventricle (apical, anterior, inferior) for three body types (average male, large male, large female). Non-attenuation corrected, attenuation corrected and gated SPECT MPI were performed. The diagnostic sensitivity was improved when applying attenuation correction or gating techniques to identify subendocardial defects in the inferior, anterior and apical segments of the myocardial wall of the left ventricle for all three body types. Transmural defects could be identified without any attenuation correction or gating. CONCLUSIONS: The diagnostic sensitivity was improved when applying AC or GSPECT techniques.