CT-based AC of SPECT images consistently improved overall diagnostic performance of readers with different interpretive attitudes and experience. CT-based AC is well suited for routine use in clinical practice.

Respiratory and cardiac motions can degrade myocardial perfusion SPECT (MPS) image quality and reduce defect detection and quantitative accuracy. In this study, we developed a dual-respiratory and cardiac gating system for a high resolution fully stationary cardiac SPECT scanner in order to improve the image quality and defect detection. Respiratory motion was monitored using a compressive sensor pillow connected to a dual respiratory-cardiac gating box, which sends cardiac triggers only during end-expiration phases to the single cardiac trigger input on the SPECT scanners. The listmode data were rebinned retrospectively into end-expiration frames for respiratory motion reduction or 8 cardiac gates only during end-expiration phases to compensate for both respiratory and cardiac motions. The proposed method was first validated on a motion phantom in the presence and absence of multiple perfusion defects, and then applied on 11 patient studies with and without perfusion defects. In the normal phantom studies, the end-expiration gated SPECT (EXG-SPECT) reduced respiratory motion blur and increased myocardium to blood pool contrast by 51.2% as compared to the ungated images. The proposed method also yielded an average of 11.2% increase in myocardium to defect contrast as compared to the ungated images in the phantom studies with perfusion defects. In the patient studies, EXG-SPECT significantly improved the myocardium to blood pool contrast (p<0.005) by 24% on average as compared to the ungated images, and led to improved perfusion uniformity across segments on polar maps for normal patients. For a patient with defect, EXG-SPECT improved the defect contrast and definition. The dual respiratory-cardiac gating further reduced the blurring effect, increased the myocardium to blood pool contrast significantly by 36% (p<0.05) compared to EXG SPECT, and further improved defect characteristics and visualization of fine structures at the expense of increased noise on the patient with defect. The results showed that the proposed methods can effectively reduce motion blur in the images caused by both respiratory and cardiac motions, which may lead to more accurate defect detection and quantifications. This approach can be easily adapted in routine clinical practice on currently available commercial systems.

Conventional 2-dimensional planar imaging of 123 I-metaiodobenzylguanidine ( 123 I-mIBG) is not fully quantitative. To develop a more accurate quantitative imaging approach, we investigated dynamic SPECT imaging with kinetic modeling in healthy humans to obtain the myocardial volume of distribution (V T ) for 123 I-mIBG. Methods: Twelve healthy humans underwent 5 serial 15-min SPECT scans at 0, 15, 90, 120, and 180 min after bolus injection of 123 I-mIBG on a hybrid cadmium zinc telluride SPECT/CT system. Serial venous blood samples were obtained for radioactivity measurement and radiometabolite analysis. List-mode data of all the scans were binned into frames and reconstructed with attenuation and scatter corrections. Myocardial and blood-pool volumes of interest were drawn on the reconstructed images to derive the myocardial timeactivity curve and input function. A population-based blood-to-plasma ratio (BPR) curve was generated. Both the population-based metabolite correction (PBMC) and the individual metabolite correction (IMC) curves were generated for comparison. V T values were obtained from different compartment models, using different input functions with and without metabolite and BPR corrections. Results: The BPR curve reached the peak value of 2.1 at 13 min after injection. Parent fraction was approximately 58% ± 13% at 15 min and stabilized at approximately 40% ± 5% by 180 min after injection. Two radiometabolite species were observed. When the reversible 2-tissue-compartment fit was used, the mean V T value was 29.0 ± 12.4 mL/cm 3 with BPR correction and PBMC, a 188% ± 32% increase compared with that without corrections. There was significant difference in V T with BPR correction (P 5 2.3e-04) as well as with PBMC (P 5 1.6e-05). The mean difference in V T between PBMC and IMC was −3% ± 8%, which was insignificant (P 5 0.39). The intersubject coefficients of variation after PBMC (43%) and IMC (42%) were similar. Conclusion: The myocardial V T of 123 I-mIBG was established in healthy humans for the first time. Accurate kinetic modeling of 123 I-mIBG requires both BPR and metabolite corrections. Population-based BPR correction and metabolite correction curves were developed, allowing more convenient absolute quantification of dynamic 123 I-mIBG SPECT images. Met aiodobenzylguanidine labeled with 123 I ( 123 I-mIBG) is a norepinephrine analog that has a reuptake mechanism similar to that of norepinephrine without being catabolized in the myocardial sympathetic nerve endings and has been the most widely used sympathetic innervation imaging agent in research and clinical studies for risk stratification of patients with congestive heart failure (HF) (1-5). For conventional 123 I-mIBG imaging, early (15-30 min) and delayed (3-5 h) 2-dimensional (2D) planar images are typically acquired and used for calculating heart-to-mediastinum ratio (HMR) and washout rate (WOR). However, 2D planar imaging is not fully quantitative, because of the superposition of background structures with the 2D heart region of intere...

Their results demonstrate that using a large SM that incorporates a CT derived body contour in the reconstruction could improve quantitative accuracy within the FOV for clinical studies with high extracardiac activity.

The imaging of distributed sources with near-field coded aperture (CA) remains extremely challenging and is broadly considered unsuitable for single-photon emission computerized tomography (SPECT). This study proposes a novel CA SPECT reconstruction approach and evaluates the feasibilities of imaging and reconstructing distributed hot sources and cold lesions using near-field CA collimation and iterative image reconstruction. Computer simulations were designed to compare CA and pinhole collimations in two-dimensional radionuclide imaging. Digital phantoms were created and CA images of the phantoms were reconstructed using maximum likelihood expectation maximization (MLEM). Errors and the contrast-to-noise ratio (CNR) were calculated and image resolution was evaluated. An ex vivo rat heart with myocardial infarction was imaged using a micro-SPECT system equipped with a custom-made CA module and a commercial 5-pinhole collimator. Rat CA images were reconstructed via the three-dimensional (3-D) MLEM algorithm developed for CA SPECT with and without correction for a large projection angle, and 5-pinhole images were reconstructed using the commercial software provided by the SPECT system. Phantom images of CA were markedly improved in terms of image quality, quantitative root-mean-squared error, and CNR, as compared to pinhole images. CA and pinhole images yielded similar image resolution, while CA collimation resulted in fewer noise artifacts. CA and pinhole images of the rat heart were well reconstructed and the myocardial perfusion defects could be clearly discerned from 3-D CA and 5-pinhole SPECT images, whereas 5-pinhole SPECT images suffered from severe noise artifacts. Image contrast of CA SPECT was further improved after correction for the large projection angle used in the rat heart imaging. The computer simulations and small-animal imaging study presented herein indicate that the proposed 3-D CA SPECT imaging and reconstruction approaches worked reasonably well, demonstrating the feasibilities of achieving high sensitivity and high resolution SPECT using near-field CA collimation.