Influence of respiratory motion correction on quantification of myocardial perfusion SPECT

A novel tool for motion-related dose inaccuracies reduction in 99mTc-MAA SPECT/CT images for SIRT planning

INTRODUCTION

In Selective Internal Radiation Therapy (SIRT), ⁹⁰Y is administered to primary/secondary hepatic lesions. An accurate pre-treatment planning using ^99mTc-MAA SPECT/CT allows the assessment of its feasibility and of the activity to be injected. Unfortunately, SPECT/CT suffers from patient-specific respiratory motion which causes artifacts and absorbed dose inaccuracies. In this study, a data-driven solution was developed to correct the respiratory motion.

METHODS

The tool realigns the barycenter of SPECT projection images and shifts them to obtain a fine registration with the attenuation map. The tool was validated using a modified dynamic phantom with several breathing patterns. We compared the absorbed dose distributions derived from uncorrected(D_m)/corrected(D_c) images with static ones(D_s) in terms of γ-passing rates, 210 Gy isodose volumes, dose-volume histograms and percentage differences of mean doses (i.e., ΔD¯_m and ΔD¯_c, respectively). The tool was applied to twelve SIRT patients and the Bland-Altman analysis was performed on mean doses.

RESULTS

In the phantom study, the agreement between D_c and D_s was higher (γ-passing rates generally > 90%) than D_m and D_s. The isodose volumes in D_c were closer than D_m to D_s, with differences up to 10% and 30% respectively. A reduction from a median ΔD¯_m = -19.3% to ΔD¯_c = -0.9%, from ΔD¯_m = -42.8% to ΔD¯_c = -7.0% and from ΔD¯_m = 1586% to ΔD¯_c = 47.2% was observed in liver-, tumor- and lungs-like structures. The Bland-Altman analysis on patients showed variations (±50 Gy) and (±4 Gy) between D¯_c and D¯_m of tumor and lungs, respectively.

CONCLUSION

The proposed tool allowed the correction of ^99mTc-MAA SPECT/CT images, improving the accuracy of the absorbed dose distribution.

Motion in nuclear cardiology imaging: types, artifacts, detection and correction techniques

In this paper, the authors review the field of motion detection and correction in nuclear cardiology with single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging systems. We start with a brief overview of nuclear cardiology applications and description of SPECT and PET imaging systems, then explaining the different types of motion and their related artefacts. Moreover, we classify and describe various techniques for motion detection and correction, discussing their potential advantages including reference to metrics and tasks, particularly towards improvements in image quality and diagnostic performance. In addition, we emphasize limitations encountered in different motion detection and correction methods that may challenge routine clinical applications and diagnostic performance.

Recent advances in cardiac SPECT instrumentation and imaging methods

Cardiac SPECT continues to play a critical role in detecting and managing cardiovascular disease, in particularly coronary artery disease (CAD) (Jaarsma et al 2012 J. Am. Coll. Cardiol. 59 1719-28), (Agostini et al 2016 Eur. J. Nucl. Med. Mol. Imaging 43 2423-32). While conventional dual-head SPECT scanners using parallel-hole collimators and scintillation crystals with photomultiplier tubes are still the workhorse of cardiac SPECT, they have the limitations of low photon sensitivity (~130 count s^-1 MBq^-1), poor image resolution (~15 mm) (Imbert et al 2012 J. Nucl. Med. 53 1897-903), relatively long acquisition time, inefficient use of the detector, high radiation dose, etc. Recently our field observed an exciting growth of new developments of dedicated cardiac scanners and collimators, as well as novel imaging algorithms for quantitative cardiac SPECT. These developments have opened doors to new applications with potential clinical impact, including ultra-low-dose imaging, absolute quantification of myocardial blood flow (MBF) and coronary flow reserve (CFR), multi-radionuclide imaging, and improved image quality as a result of attenuation, scatter, motion, and partial volume corrections (PVCs). In this article, we review the recent advances in cardiac SPECT instrumentation and imaging methods. This review mainly focuses on the most recent developments published since 2012 and points to the future of cardiac SPECT from an imaging physics perspective.

Impact of data-driven cardiac respiratory motion correction on the extent and severity of myocardial perfusion defects with free-breathing CZT SPECT

BACKGROUND

We previously reported the clinical feasibility and positive impact on image characteristics of a data-driven cardiac respiratory motion (RM) correction method (REGAT) applicable to CZT SPECT myocardial perfusion imaging (MPI). Here, we evaluate its impact on the extent and severity of myocardial perfusion defects (MPD).

METHODS

We included 25 patients having a 1-day 99mTc-Tetrofosmin stress/rest MPI acquired with multi-pinhole CZT SPECT. Acquisitions were processed with REGAT to generate mean RM gated SPECT. These were summed either after (R-SPECT) or without realignment (NR-SPECT). We noted the maximal cardiac RM shift in the 3 axes of the left ventricle (LV). Both visual and semi-quantitative analyses of myocardial tracer uptake were realized. Studies were classified as having an impact on the extent/severity of MPD with REGAT if ≥1 segment presented a severity score changing by ≥1 level between NR-SPECT and R-SPECT. An impact on the extent of MPD was considered present if at least 1 segment shifted from normal (score = 0) to abnormal (score different from 0) or inversely.

RESULTS

Cardiac RM was >10 mm in 55% of studies. With visual and semi-quantitative analyses, an impact on the extent/severity MPD was observed in 14% of all studies (7/49) and 60% of studies with cardiac RM >15 mm. An impact on the extent of MPD was observed in 5 of the 7 upper listed studies. All studies presenting an impact on MPD had RM in the anterior to inferior LV axis >10 mm.

CONCLUSIONS

A substantial number of MPI studies presented significant cardiac RM. Cardiac RM compensation showed a frequent impact on the extent/severity of MPD.

Usefulness of abdominal belt for restricting respiratory cardiac motion and improving image quality in myocardial perfusion PET

BACKGROUND

The current study evaluated the usefulness of a belt technique for restricting respiratory motion of the heart and for improving image quality of 13N-ammonia myocardial PET/CT, and it assessed the tolerability of the belt technique in the clinical setting.

METHODS

Myocardial 13N-ammonia PET/CT scanning was performed in 8 volunteers on Discovery PET/CT 690 with an optical respiratory motion tracking system. Emission scans were performed with and without an abdominal belt. The amplitude of left ventricular (LV) respiratory motion was measured on respiratory-gated PET images. The degree of erroneous decreases in regional myocardial uptake was visually assessed on ungated PET images using a 5-point scale (0 = normal, 1/2/3 = mild/moderate/severe decrease, 4 = defect). The tolerability of the belt technique was evaluated in 53 patients.

RESULTS

All subjects tolerated the belt procedure. The amplitude of the LV respiratory motion decreased significantly with the belt (8.1 ± 7.1 vs 12.1 ± 6.1 mm, P = .0078). The belt significantly improved the image quality scores in the anterior (0.29 ± 0.81 vs 0.71 ± 1.04, P = .015) and inferior (0.33 ± 0.92 vs 1.04 ± 1.04, P < .0001) wall. No adverse events related to the belt technique were observed.

CONCLUSIONS

The belt technique restricts LV respiratory motion and improves the image quality of myocardial PET/CT, and it is well tolerated by patients.

Application of the 4-D XCAT Phantoms in Biomedical Imaging and Beyond

The four-dimensional (4-D) eXtended CArdiac-Torso (XCAT) series of phantoms was developed to provide accurate computerized models of the human anatomy and physiology. The XCAT series encompasses a vast population of phantoms of varying ages from newborn to adult, each including parameterized models for the cardiac and respiratory motions. With great flexibility in the XCAT's design, any number of body sizes, different anatomies, cardiac or respiratory motions or patterns, patient positions and orientations, and spatial resolutions can be simulated. As such, the XCAT phantoms are gaining a wide use in biomedical imaging research. There they can provide a virtual patient base from which to quantitatively evaluate and improve imaging instrumentation, data acquisition, techniques, and image reconstruction and processing methods which can lead to improved image quality and more accurate clinical diagnoses. The phantoms have also found great use in radiation dosimetry, radiation therapy, medical device design, and even the security and defense industry. This review paper highlights some specific areas in which the XCAT phantoms have found use within biomedical imaging and other fields. From these examples, we illustrate the increasingly important role that computerized phantoms and computer simulation are playing in the research community.

Impact of respiratory motion and acquisition settings on SPECT liver dosimetry for radioembolization

PURPOSE

Respiratory motion may impose significant inaccuracies on emission activity estimation in quantitative SPECT. This effect may be a major issue in dosimetry as used in the management of liver radioembolization. The purpose of this study was to investigate the impact of respiratory motion on radioembolization liver dosimetry for different SPECT acquisition settings.

METHODS

In a series of SPECT/CT Monte Carlo simulations using several digital XCAT phantoms, the following parameters were varied: breathing/nonbreathing, liver tumor size (0.3-35 ml) and location, patient properties (body mass index ranging from underweight to obese; male and female), acquisition time (10-30 s/view), collimator setup (High Sensitivity, High Resolution, Ultra High Resolution) and tumor VOI. The effect of applying a respiratory gating scheme was examined as well.

RESULTS

Breathing decreased activity recovery and tumor/non-tumor (T/N) ratios on average from 90% to 66%. VOIs based on SPECT images instead of breath-hold CT improved T/N values significantly. The most accurate results were obtained using a gating scheme combined with SPECT-based VOIs. Scan duration, body mass index, sex, and location all had a minor effect. Lung shunt fraction estimations were relatively unaffected by any of the varied parameters.

CONCLUSIONS

Respiratory motion has a large effect on SPECT activity quantitation of liver tumors as used in radioembolization treatment planning and assessment. As compared with the other parameters that were varied in this study, respiration is the predominant degrading effect on image quantitation. Gating alleviates much of this detrimental effect.