Single CT for attenuation correction of rest/stress cardiac SPECT perfusion imaging

Development and evolution of nuclear cardiology and cardiac PET in Canada

Gated radionuclide angiography and myocardial perfusion imaging were developed in the United States and Europe in the 1970's and soon adopted in Canadian centers. Much of the early development of nuclear cardiology in Canada was in Toronto, Ontario and was quickly followed by new programs across the country. Clinical research in Canada contributed to the further development of nuclear cardiology and cardiac PET. The Canadian Nuclear Cardiology Society (CNCS) was formed in 1995 and became the Canadian Society of Cardiovascular Nuclear and CT Imaging (CNCT) in 2014. The CNCS had a major role in education and advocacy for cardiovascular nuclear medicine testing. The CNCS established the Dr Robert Burns Lecture and CNCT named the Canadian Society of Cardiovascular Nuclear and CT Imaging Annual Achievement Award for Dr Michael Freeman in memoriam of these two outstanding Canadian leaders in nuclear cardiology. The future of nuclear cardiology in Canada is exciting with the expanding use of SPECT imaging to include Tc-99m-pyrophosphate for diagnosis of transthyretin cardiac amyloidosis and the ongoing introduction of cardiac PET imaging.

Can retrospectively fusing SPECT to CT images reduce radiation doses in myocardial perfusion imaging?

INTRODUCTION

To establish if the CT dataset acquired during the stress element of myocardial perfusion imaging can be fused to the subsequent rest scan to reduce radiation doses from these procedures.

METHODS

86 rest scans were processed and evaluated using a self-designed project specific tool. Recording processing time, the time between the two data sets selected for fusion and assessing radiographic reports to ensure produced images were of diagnostic quality.

RESULTS

70% of fused scans were acquired 6-7 days apart; the mean (SD) processing time was calculated as 2.03 (0.36) minutes. The Pearson's correlation between these two variables was determined to be 0.22, showing a slight positive correlation although not statistically significant. 100% of the images produced were of diagnostic quality.

CONCLUSION

Rest scans can be fused to a previously acquired CT, careful consideration should be given when positioning the patient and to the time interval between acquiring the two data sets, departmental guidelines can assist with this. Staff training may also be beneficial to ensure staff can assess if data sets are fusible prior to completing a scan.

IMPLICATIONS FOR PRACTICE

This data provides evidence that retrospective fusion can reduce patient radiation doses in myocardial perfusion imaging without compromising diagnostic outcomes. Dose optimisation is an essential part of the ionising radiation (medical exposure) regulations therefore retrospective fusion should be considered in practice to ensure departmental compliance, although it is noteworthy this study is solely based in a single centred one camera department.

The Comparison of Quantitative Evaluation Results of the MPS SPECT/CT and Coronary Angiography: Determining the Most Valuable Quantitative Evaluation Score

Objectives:

This study aimed to determine the most important perfusion score in patient selection for coronary angiography (CA) by quantitatively evaluating myocardial perfusion scintigraphy (MPS).

Methods:

Patients who underwent MPS single-photon emission computerized tomography/computed tomograph imaging in our clinic between December 2017 and January 2019, without coronary artery disease (CAD) history, followed by CA were included in the study. CA was considered positive when there is a stenosis of 70% or more in at least one coronary vessel. The summed stress score, rest score, and differential score; total perfusion deficit (TPD); and the defect’s extent obtained from non-attenuation-corrected (NC) and attenuation-corrected (AC) images of 80 patients were evaluated using the Mann-Whitney U test. A p value of <0.05 was considered significant. Receiver operating characteristic (ROC) analysis was performed.

Results:

The scores obtained from NC and AC images showed a significant difference between the two groups for all scores except for the extent and TPD scores at rest from AC images. The applied ROC curves’ highest diagnostic value was determined as the TPD score at stress (TPDS) obtained from NC images (area under the curve: 0.880, 95% confidence interval, 0.807-0.952, p<0.001). The cut-off value obtained for the TPDS from the ROC curve was found to be 5.5.

Conclusion:

The scores obtained from NC images have more power to detect CAD than those obtained from AC images. Patients with no prior CAD history with TPDS score higher than 5 in MPS should be referred for CA with priority.

Evaluating the effectiveness of a single CT method for attenuation correction in stress-rest myocardial perfusion imaging with thallium-201 chloride SPECT

This study aimed to evaluate the effectiveness of a single computed tomography (CT) based attenuation correction method using thallium-201 chloride (²⁰¹TlCl) in stress-rest myocardial perfusion imaging (MPI). The data of 106 patients who underwent MPI with single photon emission computed tomography (SPECT) using ²⁰¹TlCl were retrospectively reviewed. MPI SPECT images were reconstructed using stress SPECT and stress CT (SI_O), rest SPECT and rest CT (RI_O), and rest SPECT and stress CT (RI_A). The accuracy of alignment between the SPECT and CT images was evaluated with normalized cross-correlation (NCC) and visual examination. The summed rest score (SRS) was used to evaluate hypoperfusion at rest; washout rate (WO) was used to assess ischemia; and left ventricular ejection fraction (LVEF) was used to evaluate the left ventricle (LV) function. There was no significant difference in NCC and visual evaluation in all three dimensions. The SRS of both RI_O and RI_A (7.5 ± 7.7 and 7.7 ± 7.6, respectively) did not differ significantly. However, SRSs of RI_O and RI_A showed a strong correlation (r = 0.98). The WO was 39.0 ± 0.98% for both RI_O and RI_A, with a strong correlation between the two values (r = 1.00). LVEF was 61.1 ± 17.4% for RI_O and 61.3 ± 17.4% for RI_A, and a strong correlation was observed between the two values (r = 1.00). In conclusion, the single CT-based attenuation correction method with ²⁰¹TlCl SPECT has an accuracy equivalent to that of the conventional two CT-based attenuation correction method.

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.

Comparison of attenuation, dual-energy-window, and model-based scatter correction of low-count SPECT to 82Rb PET/CT quantified myocardial perfusion scores

BACKGROUND

New reconstruction algorithms allow reduction in acquisition times or the amount of injected radioactivity. We examined the impact of different corrections on low-count clinical SPECT myocardial perfusion images (MPI) and compared to (82)Rb PET/CT. We compared no corrections (NC) to attenuation correction (AC) with and without scatter correction by either a dual-energy-window (AC-DEW) or model-based (AC-ESSE) approach. All reconstructions included resolution recovery.

METHODS

56 patients were imaged using a standard rest/stress Tc-99m-tetrofosmin MPI SPECT/CT protocol with an additional half-time acquisition. A (82)Rb-rest/stress PET/CT MPI was acquired within 4 weeks. Reconstruction methods were compared using summed rest/stress/difference scores from an objective algorithm (SRS/SSS/SDS).

RESULTS

The SRS and SSS for NC were significantly (P < .01) higher than for AC, but well correlated (r ≥ 0.87). The correlation in SRS/SSS among AC, AC-DEW, and AC-ESSE was excellent (r ≥ 0.98). AC-ESSE and AC-DEW had higher SRS (P ≤ .05) than AC, but the SDS values were not significantly different. Concordance with PET normal/abnormal classification was 76% for NC and ≥85% for the AC methods.

CONCLUSION

AC significantly improves the accuracy of low-count myocardial perfusion SPECT half-time imaging for the detection of disease compared to NC. Compared to PET, there was no significant difference among AC, AC-DEW, and AC-ESSE.