Cardiac Single Photon Emission Computed Tomography Research Articles

Impact of CT attenuation correction on viable myocardium detection in combined SPECT and PET/CT: A retrospective cohort study.

The influence of computed tomography attenuation correction (CTAC) on the accuracy of diagnosing viable myocardium using Tc-99m-MIBI dedicated cardiac cadmium-zinc-telluride (CZT) single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) combined with F-18-FDG Positron Emission Tomography/Computed Tomography (PET/CT) metabolic imaging, compared with conventional SPECT MPI, remains to be fully elucidated. To evaluate the impact of CTAC on the accuracy of diagnosing viable myocardium using Tc-99m-MIBI dedicated cardiac CZT SPECT MPI combined with F-18-FDG PET/CT, compared to conventional SPECT MPI. 193 patients underwent CZT SPECT and F-18-FDG PET/CT imaging, while 39 patients underwent conventional SPECT and F-18-FDG PET/CT imaging, with both groups utilizing CT for attenuation correction. The injured myocardium (hibernating and scarring) was quantified using the Q.PET software. After CTAC, both groups showed significant improvements in perfusion of the injured myocardial areas, particularly in the inferior wall (INF). The reduction in perfusion was more notable in the CZT SPECT group than that in the conventional group, particularly in the inferior and lateral walls. Among patients with large cardiac chambers, those undergoing MPI with CZT, with normal weights, or males, hibernating myocardium (HM) and scar post-CTAC reductions were particularly significant in the INF. If HM ≥ 10% is considered an indicator for recommended revascularization, among the 87 patients without prior cardiac bypass, 25 (28.7%) might not require revascularization treatment. Dedicated cardiac CZT SPECT and conventional SPECT MPI combined with F-18-FDG PET/CT significantly influenced the assessment of viable myocardium. The impact of CTAC was more profound in dedicated cardiac CZT SPECT, particularly in the INF region. CTAC significantly enhances the accuracy of viable myocardial assessment and may influence clinical decisions regarding revascularization therapy. Therefore, CTAC should be routinely used in dedicated cardiac CZT SPECT MPI combined with F-18-FDG PET/CT for myocardial viability diagnosis.

DuDoCFNet: Dual-Domain Coarse-to-Fine Progressive Network for Simultaneous Denoising, Limited-View Reconstruction, and Attenuation Correction of Cardiac SPECT.

Single-Photon Emission Computed Tomography (SPECT) is widely applied for the diagnosis of coronary artery diseases. Low-dose (LD) SPECT aims to minimize radiation exposure but leads to increased image noise. Limited-view (LV) SPECT, such as the latest GE MyoSPECT ES system, enables accelerated scanning and reduces hardware expenses but degrades reconstruction accuracy. Additionally, Computed Tomography (CT) is commonly used to derive attenuation maps ( μ -maps) for attenuation correction (AC) of cardiac SPECT, but it will introduce additional radiation exposure and SPECT-CT misalignments. Although various methods have been developed to solely focus on LD denoising, LV reconstruction, or CT-free AC in SPECT, the solution for simultaneously addressing these tasks remains challenging and under-explored. Furthermore, it is essential to explore the potential of fusing cross-domain and cross-modality information across these interrelated tasks to further enhance the accuracy of each task. Thus, we propose a Dual-Domain Coarse-to-Fine Progressive Network (DuDoCFNet), a multi-task learning method for simultaneous LD denoising, LV reconstruction, and CT-free μ -map generation of cardiac SPECT. Paired dual-domain networks in DuDoCFNet are cascaded using a multi-layer fusion mechanism for cross-domain and cross-modality feature fusion. Two-stage progressive learning strategies are applied in both projection and image domains to achieve coarse-to-fine estimations of SPECT projections and CT-derived μ -maps. Our experiments demonstrate DuDoCFNet's superior accuracy in estimating projections, generating μ -maps, and AC reconstructions compared to existing single- or multi-task learning methods, under various iterations and LD levels. The source code of this work is available at https://github.com/XiongchaoChen/DuDoCFNet-MultiTask.

Subtraction of single-photon emission computed tomography (SPECT) in radioembolization: a comparison of four methods

BackgroundSubtraction of single-photon emission computed tomography (SPECT) images has a number of clinical applications in e.g. foci localization in ictal/inter-ictal SPECT and defect detection in rest/stress cardiac SPECT. In this work, we investigated the technical performance of SPECT subtraction for the purpose of quantifying the effect of a vasoconstricting drug (angiotensin-II, or AT2) on the Tc-99m-MAA liver distribution in hepatic radioembolization using an innovative interventional hybrid C-arm scanner. Given that subtraction of SPECT images is challenging due to high noise levels and poor resolution, we compared four methods to obtain a difference image in terms of image quality and quantitative accuracy. These methods included (i) image subtraction: subtraction of independently reconstructed SPECT images, (ii) projection subtraction: reconstruction of a SPECT image from subtracted projections, (iii) projection addition: reconstruction by addition of projections as a background term during the iterative reconstruction, and (iv) image addition: simultaneous reconstruction of the difference image and the subtracted image.ResultsDigital simulations (XCAT) and phantom studies (NEMA-IQ and anthropomorphic torso) showed that all four methods were able to generate difference images but their performance on specific metrics varied substantially. Image subtraction had the best quantitative performance (activity recovery coefficient) but had the worst visual quality (contrast-to-noise ratio) due to high noise levels. Projection subtraction showed a slightly better visual quality than image subtraction, but also a slightly worse quantitative accuracy. Projection addition had a substantial bias in its quantitative accuracy which increased with less counts in the projections. Image addition resulted in the best visual image quality but had a quantitative bias when the two images to subtract contained opposing features.ConclusionAll four investigated methods of SPECT subtraction demonstrated the capacity to generate a feasible difference image from two SPECT images. Image subtraction is recommended when the user is only interested in quantitative values, whereas image addition is recommended when the user requires the best visual image quality. Since quantitative accuracy is most important for the dosimetric investigation of AT2 in radioembolization, we recommend using the image subtraction method for this purpose.

Stress Perfusion Cardiac Magnetic Resonance vs SPECT Imaging for Detection of Coronary Artery Disease

BackgroundGadaCAD2 was 1 of 2 international, multicenter, prospective, Phase 3 clinical trials that led to U.S. Food and Drug Administration approval of gadobutrol to assess myocardial perfusion and late gadolinium enhancement (LGE) in adults with known or suspected coronary artery disease (CAD). ObjectivesA prespecified secondary objective was to determine if stress perfusion cardiovascular magnetic resonance (CMR) was noninferior to single-photon emission computed tomography (SPECT) for detecting significant CAD and for excluding significant CAD. MethodsParticipants with known or suspected CAD underwent a research rest and stress perfusion CMR that was compared with a gated SPECT performed using standard clinical protocols. For CMR, adenosine or regadenoson served as vasodilators. The total dose of gadobutrol was 0.1 mmol/kg body weight. The standard of reference was a 70% stenosis defined by quantitative coronary angiography (QCA). A negative coronary computed tomography angiography could exclude CAD. Analysis was per patient. CMR, SPECT, and QCA were evaluated by independent central core lab readers blinded to clinical information. ResultsParticipants were predominantly male (61.4% male; mean age 58.9 ± 10.2 years) and were recruited from the United States (75.0%), Australia (14.7%), Singapore (5.7%), and Canada (4.6%). The prevalence of significant CAD was 24.5% (n = 72 of 294). Stress perfusion CMR was statistically superior to gated SPECT for specificity (P = 0.002), area under the receiver operating characteristic curve (P < 0.001), accuracy (P = 0.003), positive predictive value (P < 0.001), and negative predictive value (P = 0.041). The sensitivity of CMR for a 70% QCA stenosis was noninferior and nonsuperior to gated SPECT. ConclusionsVasodilator stress perfusion CMR, as performed with gadobutrol 0.1 mmol/kg body weight, had superior diagnostic accuracy for diagnosis and exclusion of significant CAD vs gated SPECT.

DuSFE: Dual-Channel Squeeze-Fusion-Excitation co-attention for cross-modality registration of cardiac SPECT and CT.

Myocardial perfusion imaging (MPI) using single-photon emission computed tomography (SPECT) is widely applied for the diagnosis of cardiovascular diseases. Attenuation maps (μ-maps) derived from computed tomography (CT) are utilized for attenuation correction (AC) to improve the diagnostic accuracy of cardiac SPECT. However, in clinical practice, SPECT and CT scans are acquired sequentially, potentially inducing misregistration between the two images and further producing AC artifacts. Conventional intensity-based registration methods show poor performance in the cross-modality registration of SPECT and CT-derived μ-maps since the two imaging modalities might present totally different intensity patterns. Deep learning has shown great potential in medical imaging registration. However, existing deep learning strategies for medical image registration encoded the input images by simply concatenating the feature maps of different convolutional layers, which might not fully extract or fuse the input information. In addition, deep-learning-based cross-modality registration of cardiac SPECT and CT-derived μ-maps has not been investigated before. In this paper, we propose a novel Dual-Channel Squeeze-Fusion-Excitation (DuSFE) co-attention module for the cross-modality rigid registration of cardiac SPECT and CT-derived μ-maps. DuSFE is designed based on the co-attention mechanism of two cross-connected input data streams. The channel-wise or spatial features of SPECT and μ-maps are jointly encoded, fused, and recalibrated in the DuSFE module. DuSFE can be flexibly embedded at multiple convolutional layers to enable gradual feature fusion in different spatial dimensions. Our studies using clinical patient MPI studies demonstrated that the DuSFE-embedded neural network generated significantly lower registration errors and more accurate AC SPECT images than existing methods. We also showed that the DuSFE-embedded network did not over-correct or degrade the registration performance of motion-free cases. The source code of this work is available at https://github.com/XiongchaoChen/DuSFE_CrossRegistration.

High-sensitivity cardiac SPECT system design with collimator-less interspaced mosaic-patterned scintillators.

Single-photon emission computed tomography (SPECT) is an important tool for myocardial perfusion imaging (MPI). Mechanical collimators cause the resolution-sensitivity trade-off in the existing cardiac SPECT systems, which hinders fast cardiac scan capability. In this work, we propose a novel collimator-less cardiac SPECT system with interspaced mosaic-patterned scintillators, aiming to significantly improve sensitivity and reduce scan time without trading-off image resolution. We propose to assemble a collimator-less cardiac SPECT with 7 mosaic-patterned detector modules forming a half-ring geometry. The detector module consists of 10 blocks, each of which is assembled with 768 sparsely distributed scintillators with a size of 1.68 mm × 1.68 mm × 20 mm, forming a mosaic pattern in the trans-axial direction. Each scintillator bar contains 5 GAGG(Ce) scintillators and 5 optical-guide elements, forming a mosaic pattern in the axial direction. In the Monte Carlo simulations, the in-plane resolution and axial resolution are evaluated using a hot-rod phantom and 5 disk phantoms, respectively. We simulate a cardiac phantom that is placed in a water-filled cylinder and evaluate the image performance with different data acquisition time. We perform image reconstruction with the expectation-maximization algorithm using system matrices derived from the simulation of a uniform cylindrical source filling the field-of-view (FOV). Besides, a 2-D prototype system is designed to demonstrate the feasibility of the collimator-less imaging concept. In the simulation system, the sensitivity is 16.31% ± 8.85% in a 180 mm (Φ) × 100 mm (L) FOV. The 6-mm rods in the hot rod phantom and the 5-mm disks in the disk phantom are clearly separable. Satisfactory MPI image quality is achieved in the cardiac phantom study with an acquisition time of 30 s. In prototype experiments, the point sources with an 8 mm center-to-center distance are clearly separable at different positions across the FOV. The study reveals a promising approach to high-sensitivity SPECT imaging without a heavy-metal collimator. In cardiac imaging, this approach opens the way to a very fast cardiac scan with good resolution. Further works are ongoing to build a practical 3-D imaging system based on the existing design.

Potential Role of Somatostatin Receptor Scintigraphy for In Vivo Imaging of Vulnerable Atherosclerotic Plaques and Its Association with Myocardial Perfusion Imaging Finding: A Preliminary Study.

This study was conducted to detect atherosclerotic plaques with somatostatin receptor scintigraphy (SRS) using Tc-99m-octreotide that binds to somatostatin receptor-2. Of the 783 patients referred for myocardial perfusion imaging (MPI), 52 underwent additional chest single-photon emission computed tomography (SPECT) with Tc-99m-octreotide and participated in this study. In addition, 43 patients who underwent Tc-99m-octreotide scan for neuroendocrine tumor (NET) also received cardiac SPECT. Angiography was performed within 1 month after SRS for 19 patients who showed intensive uptake in SRS and had cardiac risk factors. Of 52 patients who underwent MPI and SRS, 15 showed intensive cardiac uptake in SRS. Moreover, of 43 patients who were referred for NET, 4 patients had marked cardiac uptake in SRS in the heart. Nineteen patients including 12 women and 7 men aged 28 to 84 (58±8.04) years underwent coronary angiography. SRS and angiography in the left anterior descending territory were concordant in 15/19 (79%) patients, whereas only 7/15 (46%) cases had concordant MPI and angiography results. In the right coronary artery territory, SRS and angiography were concordant in 16/19 (84%) cases, while MPI and angiography were concordant in 11/15 (73%) cases. In the left circumflex artery territory, SRS and angiography were concordant in 15/19 (79%) cases, whereas MPI and angiography were concordant in 6/15 (40%) cases. In the remaining 76 patients who did not undergo coronary angiography based on cardiovascular profile and SRS, no cardiac events occurred in a follow-up of 2-11 months (7.52±2.71). Tc-99m-octreotide uptake was more concordant with coronary plaques relative to MPI findings, suggesting a potential role for Tc-99m-octreotide in the evaluation of atherosclerosis.

The impact of cardiac SPECT in risk stratification for women with suspected coronary artery disease in a very high cardiovascular risk country

Abstract Funding Acknowledgements Type of funding sources: None. Background Risk stratification has become increasingly important in the management of women with coronary artery disease (CAD). Population based cross-sectional study of cardiovascular risk (CVR) factors in Latvia revealed that women in age 25 -74 are in a very high CVR group: more than 60% of women have dyslipidemia, 30% have arterial hypertension (AH) and are overweight. Purpose To evaluate CVR factor profile in women with suspected CAD and performed cardiac single photon emission computed tomography (SPECT) and to prove the need of perfusion imaging for women in a very high cardiovascular risk population. Methods Cardiac SPECT for women with suspected CAD and positive or non-informative exercise test was performed in a single center from 2018 till 2022. The patients were analyzed by risk factors and perfusion test result, divided into 2 groups: normal myocardial perfusion or true myocardial perfusion defect. Results 466 patients without known CAD were analyzed. The mean age of cohort patients was 59.3±10.9 years. 28 (6.0%) patients had no CVR factors, 90 (19.3%) women had only 1, but the rest of them (348, 74.7%) had 2 or more CVR factors. Dyslipidemia was present in 358 (76.8%), AH in 282 (60.5%) and type 2 Diabetes mellitus (T2DM) in 27 (5.8%) patients. More than half of patients (n=303, 65.0%) were overweight (BMI&amp;gt;25.0 kg/m2). 65 (13.9%) women were current or ex-smokers. True myocardial perfusion defect was detected in 96 patients (20.6%). There was no statistically significant difference between CVR risk factor count and cardiac SPECT result (p=0.229), although there were patients with significant perfusion defect without any risk factor present. However, significant correlation between risk factors and detection of obstructive coronary artery disease (CAD) after positive cardiac SPECT was found (p&amp;lt;0.001). Totally in study was detected 71 patients with suspected ischemia with non-obstructive CAD (INOCA), but further investigation with intracoronary physiology measurements – coronary flow reserve (CFR), index of microvascular resistance (IMR) and acetylcholine provocation test is required to define INOCA endotype. Conclusions The cardiac SPECT is an appropriate diagnostic method for women patients with suspected CAD. Even in patients with no CVR factors, but with positive or non-informative exercise test, the CAD is present, therefore they should be referred to cardiac SPECT in a very high CVR country. In patients with significant perfusion defect and absence of obstructive CAD, the performance of intracoronary physiology measurements is required.

Attenuation Correction for Dedicated Cardiac SPECT Imaging Without Using Transmission Data.

Attenuation correction (AC) using transmission scanning-like computed tomography (CT) is the standard method to increase the accuracy of cardiac single-photon emission computed tomography (SPECT) images. Recently developed dedicated cardiac SPECT do not support CT, and thus, scans on these systems are vulnerable to attenuation artifacts. This study presented a new method for generating an attenuation map directly from emission data by segmentation of precisely non-rigid registration extended cardiac-torso (XCAT)-digital phantom with cardiac SPECT images. In-house developed non-rigid registration algorithm automatically aligns the XCAT- phantom with cardiac SPECT image to precisely segment the contour of organs. Pre-defined attenuation coefficients for given photon energies were assigned to generate attenuation maps. The CT-based attenuation maps were used for validation with which cardiac SPECT/CT data of 38 patients were included. Segmental myocardial counts of a 17-segment model from these databases were compared based on the basis of the paired t-test. The mean, and standard deviation of the mean square error and structural similarity index measure of the female stress phase between the proposed attenuation maps and the CT attenuation maps were 6.99±1.23% and 92±2.0%, of the male stress were 6.87±3.8% and 96±1.0%. Proposed attenuation correction and computed tomography based attenuation correction average myocardial perfusion count was significantly higher than that in non-AC in the mid-inferior, mid-lateral, basal-inferior, and lateral regions (p<0.001). The proposed attenuation maps showed good agreement with the CT-based attenuation map. Therefore, it is feasible to enable AC for a dedicated cardiac SPECT or SPECT standalone scanners.

Correlation between coronary artery disease and coronary microvascular dysfunction symptoms and cardiac SPECT results in Latvian women patients

Abstract Introduction The clinical evaluation of symptomatic women is challenging due to their varying clinical presentation. Women patients with intermediate or high pre-test probability for coronary artery disease – even asymptomatic or with non-informative exercise test should be referred for further focused diagnostics. Myocardial perfusion imaging with single photon emission computed tomography (SPECT) is one of the most performed non-invasive cardiac imaging tests to diagnose CAD or coronary microvascular dysfunction (CMVD). Purpose To evaluate the correlation between various CAD symptoms and cardiac SPECT results in women patients undergoing examination due to diagnosis of CAD or CMVD. Methods During the period from 2018 till 2021 we performed cardiac SPECT for women patients with intermediate or high pre-test probability or non-informative exercise test. Patients were divided into 2 groups: normal myocardial perfusion or true myocardial perfusion defect, defined as area of ischemia ≥10% of the left ventricle myocardium mass. According to the clinical symptoms patients were categorized in “asymptomatic”, “atypical symptom” and “patients with chest pain” group. The presence of CMVD and CAD in each group was determined by invasive coronary angiography or computed tomography angiography. Results In 4 years, SPECT was performed in 726 women patients. The most common presented symptoms were: chest pain (n=487, 67.1%), dyspnea (n=323, 44.5%), tachycardia and palpitations (n=117, 16.1%), fatigue (n=129, 17.8%), headache (n=28, 3.86%) and excessive sweating (n=15, 2.1%). 104 (14.3%) patients were asymptomatic, 487 (67.1%) with chest pain and 135 (18.6%) with atypical symptoms. True myocardial perfusion defect was detected in 125 patients (17.2%). The obstructive CAD was found in 32 cases (25.6%; 4.4% of all SPECTs). The CMVD was diagnosed in 68 women (54.4%; 9.4% of all SPECTs). In asymptomatic patient group obstructive CAD was diagnosed in 5 (4.8%) cases, in chest pain group – 11 (2.3%) cases and in atypical symptom group – 16 (11.9%) patients (p&amp;lt;0.001). None of asymptomatic women had CMVD. The CMVD was detected in 53 (42.4%; 7.3% of all) cases in chest pain group and in 14 (11.3%; 1.9% of all) patients in atypical symptom group (p=0.006). Conclusion Women patients with typical chest pain were more likely to have CMVD, but with atypical symptoms – CAD. Since women are in a very high cardiovascular risk group in Latvia, the cardiac SPECT is highly recommended for detection of CAD and CMVD, especially in patients with atypical symptoms. Funding Acknowledgement Type of funding sources: None.

DuDoSS: Deep-learning-based dual-domain sinogram synthesis from sparsely sampled projections of cardiac SPECT.

Myocardial perfusion imaging (MPI) using single-photon emission-computed tomography (SPECT) is widely applied for the diagnosis of cardiovascular diseases. In clinical practice, the long scanning procedures and acquisition time might induce patient anxiety and discomfort, motion artifacts, and misalignments between SPECT and computed tomography (CT). Reducing the number of projection angles provides a solution that results in a shorter scanning time. However, fewer projection angles might cause lower reconstruction accuracy, higher noise level, and reconstruction artifacts due to reduced angular sampling. We developed a deep-learning-based approach for high-quality SPECT image reconstruction using sparsely sampled projections. We proposed a novel deep-learning-based dual-domain sinogram synthesis (DuDoSS) method to recover full-view projections from sparsely sampled projections of cardiac SPECT. DuDoSS utilized the SPECT images predicted in the image domain as guidance to generate synthetic full-view projections in the sinogram domain. The synthetic projections were then reconstructed into non-attenuation-corrected and attenuation-corrected (AC) SPECT images for voxel-wise and segment-wise quantitative evaluations in terms of normalized mean square error (NMSE) and absolute percent error (APE). Previous deep-learning-based approaches, including direct sinogram generation (Direct Sino2Sino) and direct image prediction (Direct Img2Img), were tested in this study for comparison. The dataset used in this study included a total of 500 anonymized clinical stress-state MPI studies acquired on a GE NM/CT 850 scanner with 60 projection angles following the injection of 99m Tc-tetrofosmin. Our proposed DuDoSS generated more consistent synthetic projections and SPECT images with the ground truth than other approaches. The average voxel-wise NMSE between the synthetic projections by DuDoSS and the ground-truth full-view projections was 2.08%±0.81%, as compared to 2.21%±0.86% (p<0.001) by Direct Sino2Sino. The averaged voxel-wise NMSE between the AC SPECT images by DuDoSS and the ground-truth AC SPECT images was 1.63%±0.72%, as compared to 1.84%±0.79% (p<0.001) by Direct Sino2Sino and 1.90%±0.66% (p<0.001) by Direct Img2Img. The averaged segment-wise APE between the AC SPECT images by DuDoSS and the ground-truth AC SPECT images was 3.87%±3.23%, as compared to 3.95%±3.21% (p=0.023) by Direct Img2Img and 4.46%±3.58% (p<0.001) by Direct Sino2Sino. Our proposed DuDoSS is feasible to generate accurate synthetic full-view projections from sparsely sampled projections for cardiac SPECT. The synthetic projections and reconstructed SPECT images generated from DuDoSS are more consistent with the ground-truth full-view projections and SPECT images than other approaches. DuDoSS can potentially enable fast data acquisition of cardiac SPECT.

Myocardial perfusion imaging using single-photon emission computed tomography with cadmium-zinc-telluride technology.

Myocardial perfusion imaging (MPI) with single-photon emission computed tomography (SPECT) is a well-established diagnostic approach for patients with suspected or confirmed coronary artery disease (CAD). In the present century, nuclear cardiology has benefited immensely from advances in imaging instrumentation and technology. Dedicated cardiac SPECT cameras incorporating novel, highly efficient cadmium-zinc-telluride (CZT) detectors, collimators, and system designs have evolved as a result of the expansion of nuclear cardiology. A vast amount of evidence is emerging, demonstrating the new technology's advantages over the traditional gamma cameras. Myocardial perfusion imaging (MPI) using gamma-cameras with CZT detectors may be performed with the limited injected activity of radiotracer and recorded times. The use of CZT's dynamic acquisition of myocardial perfusion imaging in clinical practice may help cardiologists in detecting hemodynamically significant CAD. In this article, we present the current state of knowledge on cardiac CZT-SPECT scanners, a summary of the literature published on validation studies, radiation dose reduction, and dynamic acquisition, as well as a comparison of conventional myocardial perfusion imaging with invasive coronary angiography.

Monte Carlo Simulation and Reconstruction: Assessment of Myocardial Perfusion Imaging of Tracer Dynamics With Cardiac Motion Due to Deformation and Respiration Using Gamma Camera With Continuous Acquisition.

PurposeMyocardial perfusion imaging (MPI) with single photon emission computed tomography (SPECT) is routinely used for stress testing in nuclear medicine. Recently, our group extended its potential going from 3D visual qualitative image analysis to 4D spatiotemporal reconstruction of dynamically acquired data to capture the time variation of the radiotracer concentration and the estimated myocardial blood flow (MBF) and coronary flow reserve (CFR). However, the quality of reconstructed image is compromised due to cardiac deformation and respiration. The work presented here develops an algorithm that reconstructs the dynamic sequence of separate respiratory and cardiac phases and evaluates the algorithm with data simulated with a Monte Carlo simulation for the continuous image acquisition and processing with a slowly rotating SPECT camera.MethodsA clinically realistic Monte Carlo (MC) simulation is developed using the 4D Extended Cardiac Torso (XCAT) digital phantom with respiratory and cardiac motion to model continuous data acquisition of dynamic cardiac SPECT with slowly rotating gamma cameras by incorporating deformation and displacement of the myocardium due to cardiac and respiratory motion. We extended our previously developed 4D maximum-likelihood expectation-maximization (MLEM) reconstruction algorithm for a data set binned from a continuous list mode (LM) simulation with cardiac and respiratory information. Our spatiotemporal image reconstruction uses splines to explicitly model the temporal change of the tracer for each cardiac and respiratory gate that delineates the myocardial spatial position as the tracer washes in and out. Unlike in a fully list-mode data acquisition and reconstruction the accumulated photons are binned over a specific but very short time interval corresponding to each cardiac and respiratory gate. Reconstruction results are presented showing the dynamics of the tracer in the myocardium as it continuously deforms. These results are then compared with the conventional 4D spatiotemporal reconstruction method that models only the temporal changes of the tracer activity. Mean Stabilized Activity (MSA), signal to noise ratio (SNR) and Bias for the myocardium activities for three different target-to-background ratios (TBRs) are evaluated. Dynamic quantitative indices such as wash-in (K1) and wash-out (k2) rates at each gate were also estimated.ResultsThe MSA and SNR are higher with higher TBRs while biases were improved with higher TBRs to less than 10%. The correlation between exhalation-inhalation sequence with the ground truth during respiratory cycle was excellent. Our reconstruction method showed better resolved myocardial walls during diastole to systole as compared to the ungated 4D image. Estimated values of K1 and k2 were also consistent with the ground truth.ConclusionThe continuous image acquisition for dynamic scan using conventional two-head gamma cameras can provide valuable information for MPI. Our study demonstrated the viability of using a continuous image acquisition method on a widely used clinical two-head SPECT system. Our reconstruction method showed better resolved myocardial walls during diastole to systole as compared to the ungated 4D image. Precise implementation of reconstruction algorithms, better segmentation techniques by generating images of different tissue types and background activity would improve the feasibility of the method in real clinical environment.

CLINICAL CHARACTERISTICS OF WOMEN REFERRED TO CARDIAC SPECT: WHEN AND WHO? DATA FROM LATVIAN CARDIAC SPECT REGISTRY

Objective: Population based cross-sectional study of cardiovascular risk (CVR) factors in Latvia from year 2009 till 2019 revealed that women in age 25 -74 are in a very high CVR group: 61% of women have dyslipidemia, more than 33% have arterial hypertension (AH) and 28% are overweight. The data indicates the necessity for focused diagnostics and early detection of cardiovascular disease. The aim of study was to define the clinical profile and risk factors for women with suspected coronary artery disease (CAD) reffered to cardiac single photon emission computed tomography (SPECT) in Latvia and to find out the correlation between nuclear test result and patient clinical presentation. Design and method: Cardiac SPECT was performed in a single centre from 2018 till 2021. The women patients were analyzed by risk factors and previous diagnosis of CAD. Exercise test was performed in all cases. Patients were divided into 2 groups: normal myocardial perfusion or true myocardial perfusion defect, defined as area of ischemia more than 10% of the left ventricle myocardium mass. Results: 726 SPECT data were analyzed. The mean age of women patients was 62.6 ± 10.6 years. More than half of the patients (n = 486,66.9%) were overweight (BMI&gt; 25.0 kg/m2) and 33.3%(n = 242) were obese (BMI&gt; 30.0 kg/m2). 87 (11.9%) women were current or ex-smokers. Dyslipidemia was present in in 614 (84.6%), AH in 535 (73.7%) and type 2 Diabetes mellitus (T2DM) in 60 (8.3%) patients. 104 (14.3%) patients were asymptomatic, but with intermediate to high pre-test probability for CAD. Known CAD was present in 298 (41.0%) patients. Exercise test was found positive in 306 (42.1%) patients and the test result was not always associated with ischaemia in SPECT (p = 0.063). True myocardial perfusion defect was detected in 125 patients (17.2%). Correlation was found between significant perfusion defect in SPECT and risk factors - AH (p = 0.013) and dyslipidemia (p = 0.029). Conclusions: The registry proves the high value of imaging with cardiac SPECT for diagnostics of CAD. Women patients with intermediate or high pre-test probability – even asymptomatic or with non informative exercise test should be reffered for cardiac SPECT.

Low-dose CT from myocardial perfusion SPECT/CT allows the detection of anemia in preoperative patients

BackgroundTo assess whether low-dose CT for attenuation correction of myocardial perfusion single-photon emission computed tomography (SPECT) allows for identification of anemic patients and grading anemia severity. Methods and ResultsPatients who underwent a preoperative blood-test and low-dose CT scan, as a part of a cardiac SPECT exam, between 01 January 2015 and 31 December 2017 were enrolled in this retrospective study. Hemoglobin (Hb) levels and hematocrit were derived from clinical records. CT images were visually assessed (qualitative analysis) for the detection of inter-ventricular septum sign (IVSS) and aortic rim sign (ARS) and quantitative analysis were performed. The diagnostic accuracy for detecting anemia was compared using Hb values as the standard of reference. A total of 229 patients were included (110 with anemia; 57 mild; 46 moderate; 7 severe). The AUC of IVSS and ARS were 0.830 and 0.669, respectively (p<0.0001). The quantitative analysis outperformed ARS and IVSS; (AUC of 0.893, p=0.29). The optimal anemia cut-off using Youden index was 4.5 HU. ConclusionQuantitative analysis derived from low-dose CT images, as a part of cardiac SPECT exams, have a diagnostic accuracy similar to that of hematocrit for the detection of anemia and may allow discriminating different anemia severities. Graphical abstract▪

Accuracy of global longitudinal and territorial longitudinal strain in determining myocardial viability in out of window period Anterior wall myocardial infarction patients

Abstract Funding Acknowledgements Type of funding sources: None. Background Primary percutaneous intervention remains the principal treatment modality for anterior wall myocardial infarction (AWMI). However, a large fraction of patients especially in the developing countries present outside the window period (OWP) with no chest pain and akinetic left anterior descending (LAD) territory on echocardiography. Revascularization in these patients is primarily guided by viability status. Purpose This study was conducted to determine the accuracy of strain echocardiographic parameters compared to single-photon emission computed tomography (SPECT) in predicting myocardial viability in patients of AWMI presenting OWP. Methods All patients presenting with AWMI-OWP without ongoing chest pain and akinetic LAD territory on echocardiography from December 2020 to June 2021 were recruited. All patients underwent determination of both Global longitudinal strain (GLS) and territorial longitudinal strain (TLS) within 24-72 hours on AWMI. In addition, all underwent SPECT to determine the percentage of non-viable myocardium. On SPECT, a defect &amp;gt;5% myocardial territory showing severe reperfusion defect was considered as a marker of non-viability. Results A total of 27 patients were recruited. The mean age of the population was 61.66 + 12.6 years. Acute left ventricular failure (LVF) and cardiogenic shock (CS) was present in 6 (22.2%) and 5 (18.5%) patients respectively. Out of 22 patients who underwent angiography, majority of the patients 19 (86%) had single vessel disease involving the LAD. The mean left ventricular ejection fraction (LVEF) of the study group was 29.6 + 6.5%. The mean GLS and LAD territory TLS of the study group was -11.13 + 3.14% and -7.2 + 2.75% respectively. On SPECT, 8 (29.6%) patients had non-viable underlying myocardium. Parameters that very significantly associated with non-viability on SPECT included past history of CAD (p = 0.004), smoking (p = 0.05) and presentation with LVF (p = 0.0008) and CS (p = 0.001). The mean LVEF was significantly lower in the group with non-viability on SPECT (32.3 + 5.1% vs 23.1 + 4.5%; p &amp;lt; 0.001). Both GLS (-12.8 + 1.4% vs -7.1+ 2.3%; p &amp;lt; 0.001) and TLS (-8.7 + 1.4% vs -3.8 + 1.8%; p &amp;lt; 0.001) were significantly lower in group showing non-viability on SPECT. On receiver operating curves, a GLS of &amp;gt; -10.45% and TLS of &amp;gt; -6.65%, both had a sensitivity of 87.5% and specificity of 89.5% in predicting non-viability on SPECT. Both showed good accuracy in predicting non-viability on overall quality model. (Figures 1 and 2) Conclusion Modalities like cardiac magnetic resonance, SPECT or positron emission tomography are resource dependent and take time to be performed. Hence, performing these investigations is challenging in unstable patients. Strain echocardiography provides GLS of the myocardium which has good sensitivity and specificity in predicting viability and can be performed safely and quickly in this high-risk group. Abstract Figure. Abstract Figure. Overall quality model

Data-driven respiratory signal estimation from temporally finely sampled projection data in conventional cardiac perfusion SPECT imaging.

The aim of this work was to revisit the data-driven approach of axial center-of-mass (COM) measurements to recover a surrogate respiratory signal from finely sampled (100ms) single photon emission computed tomography (SPECT) projection data derived from list-mode acquisitions. For our initial evaluation, we acquired list-mode projection data from an anthropomorphic cardiac phantom mounted on a Quasar respiratory motion platform simulating 15mm amplitude respiratory motion. We also selected 302 consecutive patients (138 males, 164 females) with list-mode acquisitions, external respiratory motion tracking, and written consent to evaluate the clinical efficacy of our data-driven approach. Linear regression, Pearson's correlation coefficient (r), and standard error of the estimates (SEE) between the respiratory signals obtained with a visual tracking system (VTS) and COM measurements were calculated for individual projection data sets and for the patient group as a whole. Both the VTS- and COM-derived respiratory signals were used to estimate and correct respiratory motion. The reconstruction for six-degree of freedom rigid-body motion estimation was done in two ways: (1) using three iterations of ordered-subsets expectation-maximization (OSEM) with four subsets (16 projection angles per subset), or 12 iterations of maximum-likelihood expectation-maximization (MLEM). Respiratory motion compensation was done employing either OSEM with 16 subsets (four projection angles per subset) and five iterations or MLEM and 80 iterations, using the two respiratory estimates, respectively. Polar map quantification was also performed, calculating the percentage count difference (%Diff) between polar maps without and with respiratory motion included. Average % Diff was calculated in 17 segments (defined according to ASNC Guidelines). Paired t-tests were used to determine significance (p-values). The r-value calculated when comparing the VTS and COM respiratory signals varied widely between -0.01 and 0.96 with an average of 0.70, while the SEE varied between 0.80 and 6.48mm with an average of 2.05mm for our patient set, while the same values for the one anthropomorphic phantom acquisition are 0.91 and 1.11mm, respectively. A comparison between the respiratory motion estimates for VTS and COM in the S-I direction yielded an r=0.90 (0.94), and an SEE of 1.56mm (1.20mm) for OSEM (MLEM), respectively. Bland-Altman plots and calculated intraclass correlation coefficients also showed excellent agreement between the VTS and COM respiratory motion estimates. Average S-I respiratory estimates for the VTS (COM) were 9.04 (9.2mm) and 9.01mm (9.14mm) for the OSEM and MLEM, respectively. The paired t-test approached significance when comparing VTS and COM estimated respiratory signals with p-values of 0.069 and 0.051 for OSEM and MLEM. The respiratory estimates from the anthropomorphic cardiac phantom experiment using the VTS (COM) were 12.62 (14.10mm) and 12.55mm (14.29mm) for OSEM and MLEM, respectively. Polar map quantification yielded average % Diff consistently better when employing VTS-derived respiratory estimates to correct for respiration compared to the COM-derived estimates. The results indicate that our COM method has the potential to provide an automated data-driven correction of cardiac respiratory motion without the drawbacks of our VTS methodology. However, it is not generally equivalent to the VTS method in extent of correction.

Frequent cyclic variation of heart rate is associated with left ventricular diastolic dysfunction in patients without ischemia.

BackgroundCyclic variation of heart rate (CVHR) associated with sleep‐disordered breathing reflects cardiac autonomic responses to apneic/hypoxic stress. However, the association of CVHR with cardiac function is unclear.MethodsWe investigated a total of 181 patients who underwent both 24‐hour Holter electrocardiography (ECG) and quantitative gated single‐photon emission computed tomography (SPECT) myocardial functional imaging, excluding patients with atrial fibrillation, myocardial infarction, structural heart disease, and implantable devices, from January 2017 to July 2018. The number of CVHR per hour (CVHR index) in sleeping‐time Holter ECG was compared with the parameters of left ventricular (LV) systolic and diastolic functions assessed by cardiac SPECT functional imaging, peak filling rate (PFR), first‐third mean filling rate (1/3 MFR), and time to peak filling rate (TTPF).ResultsIn all patients, the CVHR index was not associated with any parameters of cardiac functions. However, in a propensity score–matched subgroup of patients without ischemia (N = 39), the CVHR index was negatively correlated with PFR (r = −0.35, P < .05) and 1/3 MFR (r = −0.37, P < .05) but positively correlated with TTPF (r = 0.43, P < .01) and was not correlated with LV ejection fraction. Multivariate linear regression analysis revealed that high CVHR index was independently associated with LV diastolic dysfunction, even after adjusting for the relative wall thickness and LV mass index assessed by echocardiography.ConclusionThese results indicate that the high frequency of CVHR in sleeping time is associated with LV diastolic dysfunction in nonischemic patients, irrespective of LV geometry.

Prognostic Significance of Cardiac 123I-MIBG SPECT Imaging in Heart Failure Patients With Preserved Ejection Fraction

ObjectivesThe authors sought to elucidate the prognostic value of cardiac sympathetic nerve dysfunction as evaluated using iodine-123-labeled metaiodobenzylguanidine (123I-MIBG) single-photon emission computed tomography (SPECT) imaging in patients with heart failure (HF) with preserved left ventricular ejection fraction (HFpEF). BackgroundCardiac sympathetic nerve dysfunction assessed by 123I-MIBG imaging is associated with poor outcomes in chronic HF patients with reduced left ventricular ejection fraction (HFrEF). However, no information is available on the prognostic vale of cardiac 123I-MIBG SPECT imaging in patients with HFpEF. MethodsWe studied 148 patients admitted for acute decompensated HF (ADHF) with nonischemic HFpEF and who underwent cardiac 123I-MIBG imaging at discharge. The cardiac 123I-MIBG heart-to-mediastinum ratio (H/M) was measured on the delayed planar image (late H/M). SPECT analysis of the delayed image was conducted, and the tracer uptake in all 17 regions on the polar map was scored on a 5-point scale by comparison with a sex-matched normal control database. The total defect score (TDS) was calculated by summing the score of each of the 17 segments. The primary endpoint was the association between TDS and cardiac events (the composite of emergent HF hospitalization and cardiac death). ResultsDuring a mean follow-up period of 2.4 ± 1.6 years, 61 patients experienced cardiac events. TDS was significantly associated with cardiac events after multivariate Cox adjustment (P < 0.0001). Patients with high TDS levels had a significantly greater risk of cardiac events than those with middle or low TDS levels (63% vs 40% vs 20%, respectively; P < 0.0001; HR: 4.69; 95% CI: 2.29 to 9.61; and HR: 2.46; 95% CI: 1.14 to 5.29). C-statistic of TDS was 0.730 (95% CI: 0.651 to 0.799), which was significantly higher than that of late H/M (0.607; 95% CI: 0.524 to 0.686; P = 0.0228). ConclusionsCardiac 123I-MIBG SPECT imaging provided useful prognostic information in nonischemic ADHF patients with HFpEF. (Clinical Trial: Osaka Prefectural Acute Heart Failure Syndrome Registry [OPAR]: UMIN000015246)

Inhibition of the Hepatic Uptake of 99mTc-Tetrofosmin Using an Organic Cation Transporter Blocker.

The accumulation of high levels of 99mTc-tetrofosmin (99mTc-TF) in the hepatobiliary system can lead to imaging artifacts and interference with diagnosis. The present study investigated the transport mechanisms of 99mTc-TF and attempted to apply competitive inhibition using a specific inhibitor to reduce 99mTc-TF hepatic accumulation. In this in vitro study, 99mTc-TF was incubated in HEK293 cells expressing human organic anion transporting polypeptide 1B1 (OATP1B1), OATP1B3, OATP2B1, organic anion transporter 2 (OAT2), organic cation transporter 1 (OCT1), OCT2, and Na+-taurocholate cotransporting polypeptide with or without each specific inhibitor to evaluate the contribution of each transporter to 99mTc-TF transportation. In vivo studies, dynamic planar imaging, and single photon emission computed tomography (SPECT) experiments with rats were performed to observe alterations to 99mTc-TF pharmacokinetics using cimetidine (CMT) as an OCT1 inhibitor. Time–activity curves in the liver and heart were acquired from dynamic data, and the 99mTc-TF uptake ratio was calculated from SPECT. From the in vitro study, 99mTc-TF was found to be transported by OCT1 and OCT2. When CMT-preloaded rats and control rats were compared, the hepatic accumulation of the 99mTc-TF was reduced, and the time to peak heart count shifted to an earlier stage. The hepatic accumulation of 99mTc-TF was markedly suppressed, and the heart-to-liver ratio increased 1.6-fold. The pharmacokinetics of 99mTc-TF were greatly changed by OCT1 inhibitor. Even in humans, the administration of OCT1 inhibitor before cardiac SPECT examination may reduce 99mTc-TF hepatic accumulation and contribute to the suppression of artifacts and the improvement of SPECT image quality.