Gil Kovalski

Correction of Heart Motion Due to Respiration in Clinical Myocardial Perfusion SPECT Scans Using Respiratory Gating

Several studies have described nonuniform blurring of myocardial perfusion imaging (MPI) due to respiration. This article describes a technique for correcting the respiration effect and assesses its effectiveness in clinical studies. Methods: Simulated phantoms, physical phantoms, and patient scans were used in this study. A heart phantom, which oscillated back and forth, was used to simulate respiration. The motion was measured on a γ-camera supporting list-mode functionality synchronized with an external respiratory strap or resistor sensor. Eight clinical scans were performed using a 1-d 99mTc-sestamibi protocol while recording the respiratory signal. The list-mode capability along with the strap or sensor signals was used to generate respiratory bin projection sets. A segmentation process was used to detect the shift between the respiratory bins. This shift was further projected to the acquired projection images for correction of the respiratory motion. The process was applied to the phantom and patient studies, and the rate of success of the correction was assessed using the conventional bulls eye maps. Results: The algorithm provided a good correction for the phantom studies. The shift after the correction, measured by a fitted ellipsoid, was <1 mm in the axial direction. The average motion due to respiration in the clinical studies was 9.1 mm in the axial direction. The average shift between the respiratory phases was reduced to 0.5 mm after correction. The maximal change in the bulls eye map for the clinical scans after the correction was 6%, with a mean of 3.75%. The postcorrection clinical summed perfusion images were more uniform, consistent, and, for some patients, clinically significant when compared with the images before correction for respiration. Conclusion: Myocardial motion generated by respiration during MPI SPECT affects perfusion image quality and accuracy. Motion introduced by respiration can be corrected using the proposed method. The degree of correction depends on the patient respiratory pattern and can be of clinical significance in certain cases.

Three-dimensional automatic quantitative analysis of intravascular ultrasound images

Intravascular ultrasound (IVUS) has established itself as a useful tool for coronary assessment. The vast amount of data obtained by a single IVUS study renders manual analysis impractical for clinical use. A computerized method is needed to accelerate the process and eliminate user-dependency. In this study, a new algorithm is used to identify the lumen border and the media-adventitia border (the external elastic membrane). Setting an initial surface on the IVUS catheter perimeter and using active contour principles, the surface inflates until virtual force equilibrium defined by the surface geometry and image features is reached. The method extracts these features in three dimensions (3-D). Eight IVUS procedures were performed using an automatic pullback device. Using the ECG signal for synchronization, sets of images covering the entire studied region and corresponding to the same cardiac phase were sampled. Lumen and media-adventitia border contours were traced manually and compared to the automatic results obtained by the suggested method. Linear regression results for vessel area enclosed by the lumen and media-adventitia border indicate high correlation between manual vs. automatic tracings (y = 1.07 x -0.38; r = 0.98; SD = 0.112 mm(2); n = 88). These results indicate that the suggested algorithm may potentially provide a clinical tool for accurate lumen and plaque assessment.

Correction for respiration artefacts in myocardial perfusion SPECT is more effective when reconstructions supporting collimator detector response compensation are applied

PurposeTo assess the impact of respiration on myocardial perfusion imaging (MPI) SPECT processed with advanced algorithmic reconstructions.MethodsSPECT studies obtained from a phantom simulation and 49 respiratory-gated, one-day 99mTc-sestamibi scans were corrected for respiratory-related cardiac movement. Three types of reconstruction algorithms: (a) filtered back projection (FBP), (b) ordered subset expectation maximization in which collimator detector response was incorporated (OSEM-CDR), and (c) OSEM-CDR with additional attenuation and scatter corrections (OSEM-CDR-ACSC) were applied to the corrected and uncorrected sets and analyzed quantitatively and qualitatively.ResultsA discrepancy between the corrected and uncorrected bull’s eye maps ≥10% was found in 2%, 10%, and 20% of the FBP, OSEM-CDR, and OSEM-CDR-ACSC scans, respectively. In studies with more than 10-mm respiratory motion, the effect of motion was greater in OSEM-CDR and OSEM-CDR-ACSC datasets as compared to FBP processing. Qualitative and quantitative differences between corrected and uncorrected sets were significantly larger in OSEM-CDR and OSEM-CDR-ACSC data than in those of FBP data.ConclusionsRespiratory-related cardiac motion significantly affects MPI-SPECT reconstructed with advanced high-resolution reconstruction algorithms such as OSEM-CDR and OSEM-CDR-ACSC and thus may justifies the application of respiratory gating.

Dynamic 3D Analysis of Myocardial Sympathetic Innervation: An Experimental Study Using 123I-MIBG and a CZT Camera

Data on the in vivo myocardial kinetics of 123I-metaiodobenzylguanidine (123I-MIBG) are scarce and have always been obtained using planar acquisitions. To clarify the normal kinetics of 123I-MIBG in vivo over time, we designed an experimental protocol using a 3-dimensional (3D) dynamic approach with a cadmium zinc telluride (CZT) camera. Methods: We studied 6 anesthetized pigs (mean body weight, 37 ± 4 kg). Left ventricular myocardial perfusion and sympathetic innervation were assessed using 99mTc-tetrofosmin (26 ± 6 MBq), 123I-MIBG (54 ± 14 MBq), and a CZT camera. A normal perfusion/function match on gated SPECT was the inclusion criterion. A dynamic acquisition in list mode started simultaneously with the bolus injection of 123I-MIBG, and data were collected every 5 min for the first 20 min and then at acquisition steps of 30, 60, 90, and 120 min. Each step was reconstructed using dedicate software and reframed (60 s/frame). On the reconstructed transaxial slice that best showed the left ventricular cavity, regions of interest were drawn to obtain myocardial and blood pool activities. Myocardial time–activity curves were generated by interpolating data between contiguous acquisition steps, corrected for radiotracer decay and injected dose, and fitted to a bicompartmental model. Time to myocardial maximum signal intensity (MSI), MSI value, radiotracer retention index (RI, myocardial activity/blood pool integral), and washout rate were calculated. The mediastinal signal was measured and fitted to a linear model. Results: The myocardial MSI of 123I-MIBG was reached within 5.57 ± 4.23 min (range, 2–12 min). The mean MSI was 0.426% ± 0.092%. Myocardial RI decreased over time and reached point zero at 176 ± 31 min (range, 140–229 min). The ratio between myocardial and mediastinal signal at 15 and 125 min and extrapolated at 176 and 4 h was 5.45% ± 0.61%, 4.33% ± 1.23% (not statistically significant vs. 15 min), 3.95% ± 1.46% (P < 0.03 vs. 125 min), and 3.63% ± 1.64% (P < 0.03 vs. 176 min), respectively. Mean global washout rate at 125 min was 15% ± 14% (range, 0%–34%), and extrapolated data at 176 min and 4 h were 18% ± 18% (range, 0.49%–45%) and 25% ± 23% (range, 1.7%–56.2%; not statistically significant vs. 176 min), respectively. Conclusion: 3D dynamic analysis of 123I-MIBG suggests that myocardial peak uptake is reached more quickly than previously described. Myocardial RI decreases over time and, on average, is null about 3 h after injection. The combination of an early peak and variations in delayed myocardial uptake could result in a wide physiologic range of washout rates. Mediastinal activity appears to be constant over time and significantly lower than previously described in planar studies, resulting in a higher heart-to-mediastinum ratio.

Combined assessment of myocardial perfusion and left ventricular function by nuclear cardiology: The value of high-efficiency SPECT

The introduction of ECG gating to myocardial perfusion SPECT imaging (MPI) more than 20 years ago provided the opportunity for the combined assessment of myocardial perfusion and left ventricular (LV) function with a single radiotracer injection. Software for automatic quantification of left ventricular volume and ejection fraction (EF) was developed, and ECGgated SPECT became a widespread, routine part of MPI acquisition and interpretation. Although simultaneously acquired, myocardial perfusion images represent coronary flow distribution at peak stress, whereas gated images demonstrate LV function at the time of acquisition. It has soon been realized that stress-induced ischemia was frequently associated with lower poststress EF than resting EF. This post-stress stunning phenomenon of global LV function was further supported by the identification of post-stress regional wall motion abnormality, indicating severe obstructive coronary artery disease (CAD). Post-stress stunning is transient in nature, and recovers often over 60 minutes after stress cessation. Its early detection using a conventional Anger-camera is limited by several technologically inherent pitfalls: First, the need to wait for at least 15 minutes, and sometimes up to 60 minutes following a radiotracer injection before initiating image acquisition because of hepatic uptake; second, acquisition time itself is very long, frequently more than ten minutes, allowing partial recovery of the LV function during the acquisition itself. Thus, acquiring images at peak stress or very early post-stress using a conventional camera is unfeasible. Nevertheless, previous studies demonstrated the added diagnostic value of conventional post-stress gated SPECT in the detection of severe coronary artery disease, and the incremental prognostic value of post-stress EF and end-systolic volume over the extent, and severity of perfusion defects in predicting future cardiac events. In this issue of the journal, Brodov et al from Cedars-Sinai Medical Center and Oregon Heart and Vascular Institute demonstrated for the first time the feasibility to obtain early gated stress acquisitions of acceptable quality using a high-efficiency SPECT camera, and to detect early stunning and its recovery over time. They evaluated 50 patients who underwent regadenoson same-day rest/stress MPI, using the D-SPECT CZT camera (Spectrum Dynamics, Caesarea, Israel). Following regadenoson and Tc-99m injection, sequential 2-minute acquisitions were performed starting at 1, 5, 9, 13, and 17 minutes, and a last 4-minute acquisition starting 21 minutes following injection. The first acquisition, starting one minute after injection was of unacceptable quality, and discarded from the analysis. EF reserve was calculated as the absolute difference between stress and rest EF for each of the sequential post-stress acquisitions. Significant ischemia was defined as ischemic total perfusion deficit C5%, and a 50-patient group was divided into two subgroups based on this cutoff value. The results demonstrated that patients with ischemia had negative EF reserve with the most negative mean value of -4.2% depicted at the Reprint requests: Tali Sharir, MD, Department of Nuclear Cardiology, Assuta Medical Centers, 96 Igal Alon, C Building, 67891, Tel Aviv, Israel; tsharir@gmail.com J Nucl Cardiol 2016;23:1262–5. 1071-3581/

Advances in imaging instrumentation for nuclear cardiology

34.00 Copyright 2016 American Society of Nuclear Cardiology.

Absolute myocardial blood flow vs relative myocardial perfusion: Which one is better?

Advances in imaging instrumentation and technology have greatly contributed to nuclear cardiology. Dedicated cardiac SPECT cameras incorporating novel, highly efficient detector, collimator, and system designs have emerged with the expansion of nuclear cardiology. Solid-state radiation detectors incorporating cadmium zinc telluride, which directly convert radiation to electrical signals and yield improved energy resolution and spatial resolution and enhanced count sensitivity geometries, are increasingly gaining favor as the detector of choice for application in dedicated cardiac SPECT systems. Additionally, hybrid imaging systems in which SPECT and PET are combined with X-ray CT are currently widely used, with PET/MRI hybrid systems having also been recently introduced. The improved quantitative SPECT/CT has the potential to measure the absolute quantification of myocardial blood flow and flow reserve. Rapid development of silicon photomultipliers leads to enhancement in PET image quality and count rates. In addition, the reduction of emission–transmission mismatch artifacts via application of accurate time-of-flight information, and cardiac motion de-blurring aided by anatomical images, are emerging techniques for further improvement of cardiac PET. This article reviews recent advances such as these in nuclear cardiology imaging instrumentation and technology, and the corresponding diagnostic benefits.

A fast cardiac gamma camera with dynamic SPECT capabilities: design, system validation and future potential.

Nuclear cardiology provides valuable information in the non-invasive assessment of coronary artery disease (CAD). Initially, single-photon emission computed tomography (SPECT) has been introduced, generating semi-quantitative relative myocardial perfusion imaging (MPI). This approach demonstrates myocardial regions with reduced tracer uptake relative to a normal region and allows assessment of the ischemic burden. Over the past 30 years, SPECT-MPI has become a well-established, widely used method for diagnosis and risk stratification of patients with CAD. In recent years, positron emission tomography (PET) has been increasingly used in the diagnosis and risk stratification of patients with CAD. Compared to SPECT, PET/CT is characterized by higher photon sensitivity, radiotracers with higher extraction fraction, and robust attenuation correction. Therefore, PET/CT provides high quality MPI, and allows dynamic firstpass imaging with quantification of absolute myocardial blood flow. The rate of tracer uptake from the arterial blood into the myocardial tissue (k1) is assessed using time–activity curves and a kinetic model, providing an estimation of absolute myocardial blood flow (MBF), expressed in mL/min/g. The ratio between stress and rest MBF is the myocardial flow reserve (MFR), sometimes referred to as coronary flow reserve (CFR). To date, most nuclear cardiac studies are performed using SPECT systems, exceeding the number of PET scanners by more than 10 to 1 ratio. It appears impractical to perform both MPI and quantitative flow to all patients referred for nuclear testing due to system availability and additional work required. The questions are as follows: Are quantitative MBF and MFR measurements superior to relative myocardial perfusion, or do they provide complimentary information for the diagnosis of obstructive CAD? Who are the patients most likely to benefit from the combined assessment of flow and perfusion? Is it possible to perform quantitative flow measurements using SPECT systems as well? In this issue of the journal, Giubbini et al compared between MPI and MBF among 47 patients who underwent stress–rest PET/CT using N-13 ammonia for clinical evaluation of known or suspected CAD. Using the summed difference score (SDS) for 17 myocardial segments, patients were divided into two groups: with ischemia (SDS[ 1) and without ischemia (SDS B 1). The investigators demonstrated that average global stress–rest difference of MBF (DMBF) and global CFR were not significantly different among the two patient sub-groups. However, DMBF and CFR per-vascular territory were significantly lower among patients with ischemia compared to those without ischemia. Defining CFR\ 2.5, DMBF\ 1.1 mL/min/g, and SDS[ 1 as abnormal, agreement between regional CFR and MBF versus regional SDS was 56% (79/141) and 69% (97/ 141), respectively. Noteworthy, among segments without ischemia (SDS B 1), 46% had reduced CFR, and 30% had reduced DMBF. Among segments with ischemia, *30% had normal CFR and DMBF. Thus, discordant results were observed in a considerable number of vascular territories. This study lacks a gold standard of coronary angiography or fractional flow reserve (FFR). Yet, it is important showing the correlation between relative perfusion and quantitative MBF. The study emphasizes the differences between perReprint requests: Tali Sharir MD, Department of Nuclear Cardiology, Assuta Medical Center, 96 Igal Alon, C Building, 67891 Tel Aviv, Israel; tsharir@gmail.com J Nucl Cardiol 2018;25:1629–32. 1071-3581/

Comparison of the diagnostic accuracies of very low stress-dose with standard-dose myocardial perfusion imaging: Automated quantification of one-day, stress-first SPECT using a CZT camera

34.00 Copyright 2017 American Society of Nuclear Cardiology.