End-expiration respiratory gating for a high-resolution stationary cardiac SPECT system

Abstract

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.

Noise suppressed partial volume correction for cardiac SPECT/CT

“…Both contrast CT and SPECT data were simulated at the enddiastolic and end-expiration phases as were acquired with dual cardiac and respiratory gating. 3 Collimator detector response of the GE Discovery NM 570c scanner and attenuation were modeled in the analytical simulator. Scatter was not simulated.…”

“…In our simulation studies, both SPECT and CT were generated at end-diastolic end-expiration phase to simulate a dual gated study. 3 In our animal study, the contrast CT was acquired during end-diastolic cardiac phase and endexpiration phase by temporarily disconnecting the ventilator. However, the SPECT images were not gated/motion corrected in order to assess the performance of different PVC methods at different noise levels.…”

“…The lack of cardiac motion correction could also lead to inaccurate modeling of the tissue-fraction effect in the templates. Since respiratory motion magnitude could be much larger in patients, dual respiratory and cardiac gating 3 and/or motion correction 46,47 are needed to generate motionfree emission data prior to the application of PVC using phase-matched contrast CT data. Furthermore, respiratory and cardiac motion could have a more severe impact on the MPI study than the RBC study due to differences in tracer concentrations in the thinner myocardium compared to the blood pool.…”

“…2 PVE can be further confounded by other factors that also lead to resolution degradation, such as stopping the iterative reconstruction earlier than convergence, smoothing introduced by penalized iterative reconstruction algorithms, postreconstruction smoothing (if applied), and cardiac/respiratory motions. 3 In cardiac imaging, PVE may lead to an apparent nonuniformity of uptake in the myocardium due to variations in wall thickness. 4,5 For example, it is challenging to accurately measure radiotracer uptake in fine structures, such as the left ventricle in the presence of myocardial infarction, which can result in thinning of the myocardial wall.…”

“…In addition to increased spatial variation, PVC has also been shown to increase ensemble variation, which can lead to reduced reproducibility. 7,24,25 With the increasing interest in dose reduction for both PET/CT and SPECT/CT applications, along with advanced applications such as respiratory and/or cardiac gating 3 and dynamic SPECT imaging with tracer kinetic modeling, 26,27 the reconstructed images are already plagued with high level of noise as only a fraction of the counts are used. However, little work has been done on performing postreconstruction PVC while penalizing noise for the low counts applications mentioned above.…”