Cardiac Single Photon Emission Computed Tomography Research Articles

Limited-angle effect compensation for respiratory binned cardiac SPECT.

In cardiac single photon emission computed tomography (SPECT), respiratory-binned study is used to combat the motion blur associated with respiratory motion. However, owing to the variability in respiratory patterns during data acquisition, the acquired data counts can vary significantly both among respiratory bins and among projection angles within individual bins. If not properly accounted for, such variation could lead to artifacts similar to limited-angle effect in image reconstruction. In this work, the authors aim to investigate several reconstruction strategies for compensating the limited-angle effect in respiratory binned data for the purpose of reducing the image artifacts. The authors first consider a model based correction approach, in which the variation in acquisition time is directly incorporated into the imaging model, such that the data statistics are accurately described among both the projection angles and respiratory bins. Afterward, the authors consider an approximation approach, in which the acquired data are rescaled to accommodate the variation in acquisition time among different projection angles while the imaging model is kept unchanged. In addition, the authors also consider the use of a smoothing prior in reconstruction for suppressing the artifacts associated with limited-angle effect. In our evaluation study, the authors first used Monte Carlo simulated imaging with 4D NCAT phantom wherein the ground truth is known for quantitative comparison. The authors evaluated the accuracy of the reconstructed myocardium using a number of metrics, including regional and overall accuracy of the myocardium, uniformity and spatial resolution of the left ventricle (LV) wall, and detectability of perfusion defect using a channelized Hotelling observer. As a preliminary demonstration, the authors also tested the different approaches on five sets of clinical acquisitions. The quantitative evaluation results show that the three compensation methods could all, but to different extents, reduce the reconstruction artifacts over no compensation. In particular, the model based approach reduced the mean-squared-error of the reconstructed myocardium by as much as 40%. Compared to the approach of data rescaling, the model based approach further improved both the overall and regional accuracy of the myocardium; it also further improved the lesion detectability and the uniformity of the LV wall. When ML reconstruction was used, the model based approach was notably more effective for improving the LV wall; when MAP reconstruction was used, the smoothing prior could reduce the noise level and artifacts with little or no increase in bias, but at the cost of a slight resolution loss of the LV wall. The improvements in image quality by the different compensation methods were also observed in the clinical acquisitions. Compensating for the uneven distribution of acquisition time among both projection angles and respiratory bins can effectively reduce the limited-angle artifacts in respiratory-binned cardiac SPECT reconstruction. Direct incorporation of the time variation into the imaging model together with a smoothing prior in reconstruction can lead to the most improvement in the accuracy of the reconstructed myocardium.

Quantitatively accurate activity measurements with a dedicated cardiac SPECT camera: Physical phantom experiments.

Recently, there has been increased interest in dedicated cardiac single photon emission computed tomography (SPECT) scanners with pinhole collimation and improved detector technology due to their improved count sensitivity and resolution over traditional parallel-hole cameras. With traditional cameras, energy-based approaches are often used in the clinic for scatter compensation because they are fast and easily implemented. Some of the cardiac cameras use cadmium-zinc-telluride (CZT) detectors which can complicate the use of energy-based scatter correction (SC) due to the low-energy tail-an increased number of unscattered photons detected with reduced energy. Modified energy-based scatter correction methods can be implemented, but their level of accuracy is unclear. In this study, the authors validated by physical phantom experiments the quantitative accuracy and reproducibility of easily implemented correction techniques applied to (99m)Tc myocardial imaging with a CZT-detector-based gamma camera with multiple heads, each with a single-pinhole collimator. Activity in the cardiac compartment of an Anthropomorphic Torso phantom (Data Spectrum Corporation) was measured through 15 (99m)Tc-SPECT acquisitions. The ratio of activity concentrations in organ compartments resembled a clinical (99m)Tc-sestamibi scan and was kept consistent across all experiments (1.2:1 heart to liver and 1.5:1 heart to lung). Two background activity levels were considered: no activity (cold) and an activity concentration 1/10th of the heart (hot). A plastic "lesion" was placed inside of the septal wall of the myocardial insert to simulate the presence of a region without tracer uptake and contrast in this lesion was calculated for all images. The true net activity in each compartment was measured with a dose calibrator (CRC-25R, Capintec, Inc.). A 10 min SPECT image was acquired using a dedicated cardiac camera with CZT detectors (Discovery NM530c, GE Healthcare), followed by a CT scan for attenuation correction (AC). For each experiment, separate images were created including reconstruction with no corrections (NC), with AC, with attenuation and dual-energy window (DEW) scatter correction (ACSC), with attenuation and partial volume correction (PVC) applied (ACPVC), and with attenuation, scatter, and PVC applied (ACSCPVC). The DEW SC method used was modified to account for the presence of the low-energy tail. T-tests showed that the mean error in absolute activity measurement was reduced significantly for AC and ACSC compared to NC for both (hot and cold) datasets (p < 0.001) and that ACSC, ACPVC, and ACSCPVC show significant reductions in mean differences compared to AC (p ≤ 0.001) without increasing the uncertainty (p > 0.4). The effect of SC and PVC was significant in reducing errors over AC in both datasets (p < 0.001 and p < 0.01, respectively), resulting in a mean error of 5% ± 4%. Quantitative measurements of cardiac (99m)Tc activity are achievable using attenuation and scatter corrections, with the authors' dedicated cardiac SPECT camera. Partial volume corrections offer improvements in measurement accuracy in AC images and ACSC images with elevated background activity; however, these improvements are not significant in ACSC images with low background activity.

Evaluation of varying physical acquisition parameters in gamma camera gated cardiac SPECT.

There are various physical factors that limit the quality of the Single Photon Emission Computed Tomography (SPECT) images such as number of frames per projection, number of projections per scan and time per projection in gated myocardial SPECT scan. The aim of the present work was to evaluate physical acquisition parameters affecting the cardiac imaging to optimize the patient's examination time and image quality that are acquired with the gamma camera and workers radiation protection (through reducing time of radiation exposure) in cardiac SPECT facility. Cardiac functional parameters like ejection fraction (EF), end diastole volume (EDV), end systole volume (ESV) and total perfusion defect (TPD) were evaluated. Thirty patients were divided into three groups as follows: 1- Group (1): contains two sub-groups, one scanned with 8 frames per projection, the other with 16 frames per projection. 2- Group (2): contains two sub-groups, one scanned with 32 projections per scan, the other with 16 projections per scan. 3- Group (3): contains two sub-groups, one scanned at a time per projection of 20 s and the other scanned at 10 s per projection. Parameters such as the Ejection Fraction (EF), End Diastole Volume (EDV), End Systole Volume (ESV) and Total Perfusion Defect (TPD) in SPECT were compared for each group. There was insignificant difference in the EF, EDV, ESV and TPD between the different groups concerning the number of frames per projection, number of projections per scan and time per projection. The reduction of scan time to half or the number of projections per scan to half or increasing the number of frames per scan from 8 to 16 at the same duration has insignificant effect in the cardiac functional parameters used with gated SPECT scan.

Geometric Calibration and Image Reconstruction for a Segmented Slant-Hole Stationary Cardiac SPECT System.

A dedicated stationary cardiac single-photon emission computed tomography (SPECT) system with a novel segmented slant-hole collimator has been developed. The goal of this paper is to calibrate this new imaging geometry with a point source. Unlike the commercially available dedicated cardiac SPECT systems, which are specialized and can be used only to image the heart, our proposed cardiac system is based on a conventional SPECT system but with a segmented slant-hole collimator replacing the collimator. For a dual-head SPECT system, 2 segmented collimators, each with 7 sections, are arranged in an L-shaped configuration such that they can produce a complete cardiac SPECT image with only one gantry position. A calibration method was developed to estimate the geometric parameters of each collimator section as well as the detector rotation radius, under the assumption that the point source location is calculated using the central-section data. With a point source located off the rotation axis, geometric parameters for each collimator section can be estimated independently. The parameters estimated individually are further improved by a joint objective function that uses all collimator sections simultaneously and incorporates the collimator symmetry information. Estimation results and images reconstructed from estimated parameters are presented for both simulated and real data acquired from a prototype collimator. The calibration accuracy was validated by computer simulations with an error of about 0.1° for the slant angles and about 1 mm for the rotation radius. Reconstructions of a heart-insert phantom did not show any image artifacts of inaccurate geometric parameters. Compared with the detector's intrinsic resolution, the estimation error is small and can be ignored. Therefore, the accuracy of the calibration is sufficient for cardiac SPECT imaging.

Model-based correction for scatter and tailing effects in simultaneous 99mTc and 123I imaging for a CdZnTe cardiac SPECT camera

An advantage of semiconductor-based dedicated cardiac single photon emission computed tomography (SPECT) cameras when compared to conventional Anger cameras is superior energy resolution. This provides the potential for improved separation of the photopeaks in dual radionuclide imaging, such as combined use of 99mTc and 123I . There is, however, the added complexity of tailing effects in the detectors that must be accounted for. In this paper we present a model-based correction algorithm which extracts the useful primary counts of 99mTc and 123I from projection data. Equations describing the in-patient scatter and tailing effects in the detectors are iteratively solved for both radionuclides simultaneously using a maximum a posteriori probability algorithm with one-step-late evaluation. Energy window-dependent parameters for the equations describing in-patient scatter are estimated using Monte Carlo simulations. Parameters for the equations describing tailing effects are estimated using virtually scatter-free experimental measurements on a dedicated cardiac SPECT camera with CdZnTe-detectors. When applied to a phantom study with both 99mTc and 123I, results show that the estimated spatial distribution of events from 99mTc in the 99mTc photopeak energy window is very similar to that measured in a single 99mTc phantom study. The extracted images of primary events display increased cold lesion contrasts for both 99mTc and 123I.

Sci—Thur PM: Imaging — 01: Position‐sensitive noise characteristics in multi‐pinhole cardiac SPECT imaging

Myocardial perfusion imaging (MPI) with Single Photon Emission Computed Tomography (SPECT) is invaluable in the diagnosis and management of heart disease. It provides essential information on myocardial blood flow and ischemia. Multi‐pinhole dedicated cardiac‐SPECT cameras offer improved count sensitivity, and spatial and energy resolutions over parallel‐hole camera designs however variable sensitivity across the field‐of‐view (FOV) can lead to position‐dependent noise variations. Since MPI evaluates differences in the signal‐to‐noise ratio, noise variations in the camera could significantly impact the sensitivity of the test for ischemia. We evaluated the noise characteristics of GE Healthcare's Discovery NM530c camera with a goal of optimizing the accuracy of our patient assessment and thereby improving outcomes. Theoretical sensitivity maps of the camera FOV, including attenuation effects, were estimated analytically based on the distance and angle between the spatial position of a given voxel and each pinhole. The standard deviation in counts, σ was inferred for each voxel position from the square root of the sensitivity mapped at that position. Noise was measured experimentally from repeated (N=16) acquisitions of a uniform spherical Tc‐99m‐water phantom. The mean (μ) and standard deviation (σ) were calculated for each voxel position in the reconstructed FOV. Noise increased ∼2.1× across a 12 cm sphere. A correlation of 0.53 is seen when experimental noise is compared with theory suggesting that ∼53% of the noise is attributed to the combined effects of attenuation and the multi‐pinhole geometry. Further investigations are warranted to determine the clinical impact of the position‐dependent noise variation.

Quantification of myocardial blood flow using (201)Tl SPECT and population-based input function.

Thallium-201 ((201)Tl) single photon emission computed tomography (SPECT) is an important tool in the diagnosis of ischemic heart disease. Absolute quantification of myocardial blood flow (MBF) has the potential to provide more useful information on myocardial perfusion than semi-quantitative assessments. This study aimed to validate the quantification of MBF using (201)Tl cardiac SPECT based on a population-averaged input function (STD-IF) and one-point blood sample technique. (201)Tl emission and computed tomography (CT)-based attenuation scans were performed on 11 healthy volunteers at rest using a SPECT/CT scanner. Individual input functions (IND-IFs) during the emission scans were based on arterial blood samples. The STD-IF technique was validated as follows: (1) optimal time to calibrate a STD-IF was determined to minimize differences between the calibrated STD-IF and the IND-IFs. (2) Tissue time-activity curves (TTACs) were generated based on a single-tissue compartment model for MBFtrue=0.5, 1.0, 1.5, and 2.0mL/min/g, a constant distribution volume of 45mL/mL, and IND-IFs. The pseudo STD-IF for each subject was generated using the leave-one-out technique. Using the optimal calibration time and the pseudo STD-IFs, MBF values were estimated on the TTACs with an autoradiography method. Optimal mid-scan time (MST) with a fixed duration of 20min was determined to minimize intersubject variation in estimated MBF errors, and (3) Global and regional MBF values estimated with pseudo STD-IFs were compared to those with IND-IFs using the optimal calibration time and MST. The optimal calibration time and MST were both 20min after (201)Tl injection. Global MBF determined using both IND-IFs and pseudo STD-IF showed significant correlations with rate-pressure products, R (2)=0.645; p<0.01 and R (2)=0.303; p<0.05, respectively. The mean percent error in regional MBF using pseudo STD-IFs was 0.69±7.80% (-12.80 to 14.25%). No significant difference was observed between regional MBF values using IND-IFs and pseudo STD-IFs. This study demonstrated that the proposed technique based on a STD-IF and one-point blood sample provided hemodynamically reasonable global MBF values and the regional MBF values comparable to those with IND-IFs.

Achieving very-low-dose radiation exposure in cardiac computed tomography, single-photon emission computed tomography, and positron emission tomography.

During the past several years, the need to reduce radiation has become a central issue in cardiac imaging. During this time, radiation dose to the patient in cardiac computed tomography (CT), single-photon emission computed tomography (SPECT), and positron emission tomography (PET) has seen significant reductions without compromising image quality, primarily because of new developments in scanner hardware and reconstruction software. Sub-mSv radiation doses have been reported for cardiac CT.1–5 Stress and rest SPECT myocardial perfusion imaging (MPI) traditionally required ≈15 minutes to register the required number of photon events. New SPECT camera instrumentation and software have now enabled acquisition times as short as 2 minutes, to increase counting efficiency by up to a factor of 7.6 These new systems can also be used to reduce radiation exposure to patients during the MPI scan, allowing a corresponding marked reduction in the administered dose of radioactivity when used with the standard imaging time.7 It is important to keep radiation exposure as low as reasonably achievable. In this review, therefore, we briefly summarize recent technical advances in scanner hardware and reconstruction software, as well as the steps recommended to achieve very low radiation dose in cardiac imaging. We also review the current status of radiation in cardiac CT, SPECT, and PET as reported in multicenter studies and registries, as well as current clinical reports of radiation dose reduction, which illustrate the potential of the newest technology. Direct imaging of the coronary arteries is challenging because of their small sizes and rapid motion. Cardiac CT requires high temporal resolution to freeze such motion and therefore has benefited from steadily increasing CT gantry rotation speed. Imaging of the coronary arteries also requires high spatial resolution and reconstruction of submillimeter slices. Multiple transaxial slices need to be acquired simultaneously for complete …

Cardiac ⁹⁹mTc sestamibi SPECT and ¹⁸F FDG PET as viability markers in Takotsubo cardiomyopathy.

In patients with heart failure (HF) due to coronary disease, a combined evaluation of perfusion and glucose metabolism by cardiac single photon emission computed tomography (SPECT)/positron emission tomography (PET) can be used to distinguish viable from non-viable myocardium, and current guidelines recommend cardiac SPECT and fluorodeoxyglucose (FDG) PET for viability assessment. Takotsubo cardiomyopathy (TTC) is a disease characterized by acute but reversible HF leaving no scarring. To explore how robust the semi-quantitative viability criteria used in cardiac SPECT and FDG PET stands their ground in a population with TTC. From 1 September 2009 to 1 October 2012, 24 patients suspected of TTC were enrolled in a multimodality cardiac imaging research project. Echocardiography, (99m)Tc SPECT, and (18)F FDG PET were performed during the acute admission and at follow-up 4 months later. Nineteen patients had a final diagnosis of TTC consistent with Mayo Clinic Diagnostic Criteria. Three of these patients were excluded from further analysis, since wall motion abnormalities were not persistent at the time of nuclear imaging. The remaining sixteen patients exhibited a distinct pattern with HF, "apical ballooning" and a perfusion-metabolism defect in the midventricular/apical region. When viability criteria were applied, they identified significant scarring/limited hibernation in the akinetic part of the left ventricle. However, full recovery was found in all TTC patients on follow-up. Using the current guideline-endorsed viability criteria for semiquantitative cardiac SPECT and FDG PET, these modalities failed to demonstrate the presence of viability in the acute state of TTC.

Influence of typical angina versus inducible myocardial ischemia in the contemporary management of stable coronary artery disease.

To investigate, in patients with known or suspected coronary artery disease (CAD) undergoing myocardial perfusion single-photon emission computed tomography (MPS),the interaction between patient symptoms and single-photon emission computed tomography (SPECT) results, and their effects on patient outcomes. Previous data have shown that medical treatment may be as beneficial as invasive treatment for most patients with stable CAD. Nonetheless, patient presentation with typical angina (TA) seems to still lead to more aggressive management, regardless of the amount of myocardial ischemia detected by noninvasive methods. Over 33 ± 20 months, 2958 patients undergoing stress/rest cardiac SPECT were followed. Summed stress, rest and difference scores (SSS, SRS and SDS, respectively) were analyzed. Abnormal SPECT was defined as a SSS>3, and ischemic SPECT as a SDS>1. During follow up, cardiac catheterization (CATH), myocardial revascularization (either percutaneous or surgical), myocardial infarction (MI) and all-cause death were evaluated. TA was found in 228 patients (7.7%). Comparing patients with TA with those without it, the former more often had had abnormal (43.0% versus 34.3%, p < 0.001) and ischemic SPECT (25.9% versus 13.6%, p < 0.001). Also, higher rates of MI (2.0% versus 0.6%, p < 0.001), CATH (10.1% versus 4.7%, p < 0.001) and revascularization (7.8% versus 3.0%, p < 0.001) were observed, while death was not significantly different (1.5% versus 1.0%, p = 0.2). Even in the absence of ischemia in SPECT, patients with TA had higher CATH and revascularization rates; death, again, was not significantly increased. Although patients with TA more often had ischemic SPECT, all-cause death was not significantly increased. Nonetheless, TA was associated with more frequent referrals for CATH and revascularization, even with nonischemic SPECT. This may suggest that despite current evidence, the management of stable patients with known or suspected CAD is influenced by symptom type.

A Sex-Based Comparison of Cardiac MRI and SPECT for Diagnosing Coronary Artery Disease

In the single-center CE-MARC trial, cardiac magnetic resonance imaging (cMRI) outperformed single-photon emission computed tomography (SPECT) for

An evaluation of data-driven motion estimation in comparison to the usage of external-surrogates in cardiac SPECT imaging

Motion estimation methods in single photon emission computed tomography (SPECT) can be classified into methods which depend on just the emission data (data-driven), or those that use some other source of information such as an external surrogate. The surrogate-based methods estimate the motion exhibited externally which may not correlate exactly with the movement of organs inside the body. The accuracy of data-driven strategies on the other hand is affected by the type and timing of motion occurrence during acquisition, the source distribution, and various degrading factors such as attenuation, scatter, and system spatial resolution. The goal of this paper is to investigate the performance of two data-driven motion estimation schemes based on the rigid-body registration of projections of motion-transformed source distributions to the acquired projection data for cardiac SPECT studies. Comparison is also made of six intensity based registration metrics to an external surrogate-based method. In the data-driven schemes, a partially reconstructed heart is used as the initial source distribution. The partially-reconstructed heart has inaccuracies due to limited angle artifacts resulting from using only a part of the SPECT projections acquired while the patient maintained the same pose. The performance of different cost functions in quantifying consistency with the SPECT projection data in the data-driven schemes was compared for clinically realistic patient motion occurring as discrete pose changes, one or two times during acquisition. The six intensity-based metrics studied were mean-squared difference, mutual information, normalized mutual information (NMI), pattern intensity (PI), normalized cross-correlation and entropy of the difference. Quantitative and qualitative analysis of the performance is reported using Monte-Carlo simulations of a realistic heart phantom including degradation factors such as attenuation, scatter and system spatial resolution. Further the visual appearance of motion-corrected images using data-driven motion estimates was compared to that obtained using the external motion-tracking system in patient studies. Pattern intensity and normalized mutual information cost functions were observed to have the best performance in terms of lowest average position error and stability with degradation of image quality of the partial reconstruction in simulations. In all patients, the visual quality of PI-based estimation was either significantly better or comparable to NMI-based estimation. Best visual quality was obtained with PI-based estimation in one of the five patient studies, and with external-surrogate based correction in three out of five patients. In the remaining patient study there was little motion and all methods yielded similar visual image quality.

Taking the perfect nuclear image: Quality control, acquisition, and processing techniques for cardiac SPECT, PET, and hybrid imaging

Nuclear Cardiology for the past 40 years has distinguished itself in its ability to non-invasively assess regional myocardial blood flow and identify obstructive coronary disease. This has led to advances in managing the diagnosis, risk stratification, and prognostic assessment of cardiac patients. These advances have all been predicated on the collection of high quality nuclear image data. National and international professional societies have established guidelines for nuclear laboratories to maintain high quality nuclear cardiology services. In addition, laboratory accreditation has further advanced the goal of the establishing high quality standards for the provision of nuclear cardiology services. This article summarizes the principles of nuclear cardiology single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging and techniques for maintaining quality: from the calibration of imaging equipment to post processing techniques. It also will explore the quality considerations of newer technologies such as cadmium zinc telleride (CZT)-based SPECT systems and absolute blood flow measurement techniques using PET.

Perfusión y función ventricular en SPECT cardiaco y coronariografía del mismo día según localización en enfermedad de un vaso

Single-photon emission computed tomography (SPECT) can be used as a non-invasive tool for the assessment of coronary perfusion. To assess ventricular perfusion and function by SPECT in patients with single vessel coronary artery disease. Among patients with indications for a coronary artery angiography, those with significant lesions in one vessel, were selected for the study. Within 24 hours, cardiac SPECT examinations on basal conditions and after high doses of dipyridamole, were performed. SPECT data from 38 patients with a low probability of coronary artery disease was used for comparisons. Ten patients aged 61 ± 8 years (seven men) were studied. Visual analysis of SPECT revealed signs suggestive of ischemia in eight patients. The remaining two patients did not have perfusion disturbances. SPECT detected eight of ten abnormal vessels reported in the coronary artery angiography. There were two false negative results Summed stress, summed rest and summed difference scores were 9.78 ± 6.51, 3.22 ± 5.07 and 6.33 ± 4.97, respectively. The ejection fractions under stress and at rest were 53 ± 11.7% and 61 ± 15.7% respectively (p < 0.01). The figures for the control group were 69.1 ± 13.5% and 75.2 ± 12.04% respectively (significantly different from patients). Two patients had a summed motion score above 14.9. Likewise, two patients had a summed thickening score above 10.9. SPECT detected 80% of coronary lesions found during coronary artery angiography. Visual analysis of perfusion is highly reliable for diagnosis. Quantitative parameters must be considered only as reference parameters.

Ischemic heart disease detection using selected machine learning methods

This article presents a method based on support vector machines (SVMs) and the Osuna–Platt algorithm used to diagnose the ischemic heart disease. It also includes the necessary concepts from the optimization theory which make it possible to formulate the problem for support vectors and the Osuna–Platt algorithm applied. Next, a principal component analysis (PCA) algorithm used is also presented. Heart images acquired using Single Photon Emission Computed Tomography (SPECT) have been used in the experimental part. Results of classifying cardiac SPECT images using SVM, PCA and neural networks are compared here with those obtained using another method of machine learning – CLIP3 – a combination of the decision tree algorithm and the rule induction algorithm. Tests against an SPECT image database have shown that SVMs are generally more accurate and specific, while the PCA algorithm is the most sensitive for all data sets analysed in this research project.

The prognostic value of cardiac SPECT performed at the primary care physician’s office

BackgroundThe prognostic value of single-photon emission computed-tomography (SPECT)-myocardial perfusion imaging (MPI) is well documented. However, the utility of SPECT-MPI when performed at a low-volume primary care physician’s (PCP's) office is unknown. MethodsWe conducted a prospective cohort study of consecutive patients referred by their PCP to undergo a stress-MPI at the PCP's office using a mobile laboratory. Major adverse cardiovascular events (MACE) of death, myocardial infarction (MI), and coronary revascularization were prospectively tabulated using mail and telephone interviews, chart review, and social security death index. ResultsOne thousand three hundred ninety subjects [mean age 58 ± 13 years; 44% women] were followed for 27 ± 9 months, with a 99% complete follow-up rate. Subjects with abnormal MPI [174 (12.5%)] had significantly higher rates of all-cause mortality [5.2% vs 1.0%, P < .001], death, or MI [5.7% vs 1.5%, P = .001], and the composite of death, MI, or late revascularization (>60 days post-MPI) [12.6 vs 2.7%, P < .001]. Overall MACE risk was associated with the total perfusion abnormality burden, while the revascularization rate was related to the reversible perfusion abnormality burden. ConclusionContemporary SPECT-MPI performed in the setting of a PCP's office carries a robust prognostic value, similar to that reported in tertiary or large-volume practice settings.

New Software Solutions for Cardiac SPECT Imaging

Recent advances in myocardial perfusion single photon emission computed tomography (SPECT) processing software, incorporating iterative reconstruction, resolution recovery, and noise compensation, now provide the ability to acquire high quality scans despite reduced administered activity, shortened acquisition time, or both. These methods have thereby provided imaging protocol flexibility and facilitated patient-centered imaging. Other software methods allow for improved image quality by prescribing an image acquisition time that will yield optimal SPECT image count density. On some new solid state cameras list mode acquisition is now available, whereby suboptimal acquisition stops such as those with patient motion can be eliminated prior to SPECT reconstruction. Still other methods, incorporating phase analysis of gated perfusion SPECT, provide a quantitative analysis of left ventricular dyssynchrony, aiding in the selection of patients for whom cardiac resynchronization therapy is most beneficial.

Performance of a high‐sensitivity dedicated cardiac SPECT scanner for striatal uptake quantification in the brain based on analysis of projection data

The authors have previously reported the advantages of high-sensitivity single-photon emission computed tomography (SPECT) systems for imaging structures located deep inside the brain. DaTscan (Isoflupane I-123) is a dopamine transporter (DaT) imaging agent that has shown potential for early detection of Parkinson disease (PD), as well as for monitoring progression of the disease. Realizing the full potential of DaTscan requires efficient estimation of striatal uptake from SPECT images. They have evaluated two SPECT systems, a conventional dual-head gamma camera with low-energy high-resolution collimators (conventional) and a dedicated high-sensitivity multidetector cardiac imaging system (dedicated) for imaging tasks related to PD. Cramer-Rao bounds (CRB) on precision of estimates of striatal and background activity concentrations were calculated from high-count, separate acquisitions of the compartments (right striata, left striata, background) of a striatal phantom. CRB on striatal and background activity concentration were calculated from essentially noise-free projection datasets, synthesized by scaling and summing the compartment projection datasets, for a range of total detected counts. They also calculated variances of estimates of specific-to-nonspecific binding ratios (BR) and asymmetry indices from these values using propagation of error analysis, as well as the precision of measuring changes in BR on the order of the average annual decline in early PD. Under typical clinical conditions, the conventional camera detected 2 M counts while the dedicated camera detected 12 M counts. Assuming a normal BR of 5, the standard deviation of BR estimates was 0.042 and 0.021 for the conventional and dedicated system, respectively. For an 8% decrease to BR = 4.6, the signal-to-noise ratio were 6.8 (conventional) and 13.3 (dedicated); for a 5% decrease, they were 4.2 (conventional) and 8.3 (dedicated). This implies that PD can be detected earlier with the dedicated system than with the conventional system; therefore, earlier identification of PD progression should be possible with the high-sensitivity dedicated SPECT camera.

Shortened acquisition time or reduced-activity dose for gated myocardial perfusion SPECT with new reconstruction algorithm

To confirm that shortened acquisition time or reduced-activity dose in single-photon emission computed tomography (SPECT) myocardial perfusion imaging reconstructed with Astonish software (AS) does not compromise image quality or diagnostic accuracy. One hundred patients referred for SPECT myocardial perfusion imaging were prospectively studied. The patients were randomly selected to receive the full-dose protocol (group A, n = 54) or the half-dose protocol (group B, n = 46). The patients of group A underwent a 2-day stress/rest protocol. After half-time acquisition, they underwent a full-time acquisition for stress and rest SPECT. Group B underwent a 1-day stress/rest protocol. During peak stress, all patients received an intravenous injection of (99m)Tc-methoxyisobutylisonitrile (MIBI; 5.2 ± 0.6 mCi). After the full-time stress acquisition, the patients underwent a double-time stress acquisition. If the stress image showed a defect, a patient received (99m)Tc-MIBI (19.5 ± 1.7 mCi) at rest on the same day. The rest SPECT acquisition protocol was the same in both groups. The low count (LC) and high count (HC) were acquired for each patient. AS and filtered back projection (FBP) reconstructed each set of raw data. Image quality of perfusion was assessed on a four-point scale. Perfusion parameters and function parameters were calculated by quantitative perfusion SPECT and quantitative gated SPECT. Mean image quality for LC-AS and HC-AS (3.5 ± 0.5 and 3.7 ± 0.5, respectively) was superior to HC-FBP (3.1 ± 0.4) in group A (for all, p < 0.001). LC-AS and HC-AS (3.5 ± 0.5 and 3.6 ± 0.5, respectively) in group B were superior to HC-FBP (3.1 ± 0.3) (for all, p < 0.001). LC-AS, HC-AS and LC-FBP showed high diagnostic concordance with HC-FBP (kappa value was 0.92, 0.92, and 0.94, respectively; all p < 0.001). Cardiac SPECT studies can be acquired with half of the scan time or reduced radioactivity dose and reconstructed by using the AS algorithm without compromising image quality.

A head-to-head comparison of the coronary calcium score by computed tomography with myocardial perfusion imaging in predicting coronary artery disease

ObjectivesThe coronary artery calcium (CAC) score has been shown to predict future cardiac events. However the extent to which the added value of a CAC score to the diagnostic performance of myocardial perfusion imaging (MPI) by single photon emission computed tomography (SPECT) is unclear. The purpose of this study is to investigate the correlation between CAC score and SPECT in patients with suspected coronary artery disease.MethodsA retrospective review of the CAC scores by use of the Agatston calcium scoring method and cardiac SPECT diagnostic reports was conducted in 48 patients, who underwent both coronary computed tomography (CT) and SPECT examinations due to suspected coronary artery disease. A Pearson correlation test was used to determine the relation between CAC scores and MPI-SPECT assessments with regard to the evaluation of the extent of disease.ResultsForty-seven percent of the patients had CAC scores more than 100, while 42% of these patients demonstrated abnormal, or probably abnormal, MPI-SPECT. Of the 23% of patients with a zero CAC score, only 7% had normal MPI-SPECT findings. No significant correlation was found between the CAC scores and MPI-SPECT assessments (r value ranged from 0.012 to 0.080), regardless of the degree of coronary calcification.ConclusionsThere is a lack of correlation between the CAC scores and the MPI-SPECT findings in the assessment of the extent of coronary artery disease. CAC scores and MPI-SPECT should be considered complementary approaches in the evaluation of patients with suspected coronary artery disease.