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

Design and development of the DE-SPECT system: a clinical SPECT system for broadband multi-isotope imaging of peripheral vascular disease

Objective. Peripheral Vascular Disease (PVD) affects more than 230 million people worldwide and is one of the leading causes of disability among people over age 60. Nowadays, PVD remains largely underdiagnosed and undertreated, and requires the development of tailored diagnostic approaches. We present the full design of the Dynamic Extremity SPECT (DE-SPECT) system, the first organ-dedicated SPECT system for lower extremity imaging, based on 1 cm thick Cadmium Zinc Telluride (CZT) spectrometers and a dynamic dual field-of-view (FOV) synthetic compound-eye (SCE) collimator.Approach. The proposed DE-SPECT detection system consists of 48 1 cm thick 3D-position-sensitive CZT spectrometers arranged in a partial ring of 59 cm in diameter in a checkerboard pattern. The detection system is coupled with a compact dynamic SCE collimator that allows the user to select between two different FOVs at any time during an imaging study: a wide-FOV (28 cm diameter) configuration for dual-leg or scout imaging or a high-resolution and high-sensitivity (HR-HS) FOV (16 cm diameter) for single-leg or focused imaging.Main results.The preliminary experimental data show that the CZT spectrometer achieves a 3D intrinsic spatial resolution of <0.75 mm FWHM and an excellent energy resolution over a broad energy range (2.6 keV FWHM at 218, 3.3 keV at 440 keV). From simulations, the wide-FOV configuration offers a 0.034% averaged sensitivity at 140 keV and <8 mm spatial resolution, whereas the HR-HS configuration presents a peak central sensitivity of 0.07% at 140 keV and a ∼5 mm spatial resolution. The dynamic SCE collimator enables the capability to perform joint reconstructions that would ensure an overall improvement in imaging performance.Significance. The DE-SPECT system is a stationary and high-performance SPECT system that offers an excellent spectroscopic performance with a unique computer-controlled dual-FOV imaging capability, and a relatively high sensitivity for multi-tracer and multi-functional SPECT imaging of the extremities.

Study of Attenuation Correction Using a Cardiac Dynamic Phantom: Synchronized Time-Phase-Gated Attenuation Correction Method

In cardiac nuclear medicine examinations, absorption in the body is the main factor in the degradation of the image quality. The Chang and external source methods were used to correct for absorption in the body. However, fundamental studies on attenuation correction for electrocardiogram (ECG)-synchronized CT imaging have not been performed. Therefore, we developed and improved an ECG-synchronized cardiac dynamic phantom and investigated the synchronized time-phase-gated attenuation correction (STPGAC) method using ECG-synchronized SPECT and CT images of the same time phase. Methods: As a basic study, SPECT was performed using synchronized time-phase-gated (STPG) SPECT and non-phase-gated (NPG) SPECT. The attenuation-corrected images were, first, CT images with the same time phase as the ECG waveform of the gated SPECT acquisition (with CT images with the ECG waveform of the CT acquisition as the reference); second, CT images with asynchronous ECG; third, CT images of the 75% region; and fourth, CT images of the 40% region. Results: In the analysis of cardiac function in the phantom experiment, left ventricle ejection fraction (heart rate, 11.5%-13.4%; myocardial wall, 49.8%-55.7%) in the CT images was compared with that in the STPGAC method (heart rate, 11.5%-13.3%; myocardial wall, 49.6%-55.5%), which was closer in value to that of the STPGAC method. In the phantom polar map segment analyses, none of the images showed variability (F (10,10) < 0.5, P = 0.05). All images were correlated (r = 0.824-1.00). Conclusion: In this study, we investigated the STPGAC method using a SPECT/CT system. The STPGAC method showed similar values of cardiac function analysis to the CT images, suggesting that the STPGAC method accurately reconstructed the distribution of blood flow in the myocardial region. However, the target area for attenuation correction of the heart region was smaller than that of the whole body, and changing the gated SPECT conditions and attenuation-corrected images did not affect myocardial blood flow analysis.

Myocardial blood flow quantification with SPECT

INTRODUCTION

The addition of absolute myocardial blood flow (MBF) data improves the diagnostic and prognostic accuracy of relative perfusion imaging with nuclear medicine. Cardiac-specific gamma cameras allow measurement of MBF with SPECT.

METHODS

This paper reviews the evidence supporting the use of SPECT to measure myocardial blood flow (MBF). Studies have evaluated SPECT MBF in large animal models and compared it in humans with invasive angiographic measurements and against the clinical standard of PET MBF. The repeatability of SPECT MBF has been determined in both single-site and multi-center trials.

RESULTS

SPECT MBF has excellent correlation with microspheres in an animal model, with the number of stenoses and fractional flow reserve, and with PET-derived MBF. The inter-user coefficient of variability is ∼20% while the COV of test-retest MBF is ∼30%. SPECT MBF improves the sensitivity and specificity of the detection of multi-vessel disease over relative perfusion imaging and provides incremental value in predicting adverse cardiac events.

CONCLUSION

SPECT MBF is a promising technique for providing clinically valuable information in the assessment of coronary artery disease.

Cardiovascular Imaging in Women

Multimodality cardiovascular imaging is a cornerstone diagnostic tool in the diagnosis, risk stratification, and management of cardiovascular diseases, whether those involving the coronary tree, myocardial, or pericardial diseases in general and particularly in women. This manuscript aims to shed some light and summarize the very features of cardiovascular disease in women, explore their unique characteristics and discuss the role of cardiovascular imaging in ischemic heart disease and cardiomyopathies. The role of four imaging modalities will be discussed including nuclear medicine, echocardiography, noninvasive coronary angiography, and cardiac magnetic resonance.

A Pictorial Review of I-123 MIBG Imaging of Neuroblastoma Utilizing a State-of-the-Art CZT SPECT/CT System

The field of nuclear medicine is entering a new era of gamma-camera technology. Solid-state SPECT/CT systems will gradually replace the thallium-activated sodium-iodide NaI(Tl) systems. This digital technology allows drastic improvements in image quality, radiotracer dose reduction, and procedure efficiency. This pictorial review presents our initial experience on an NM/CT 870 CZT system (GE Healthcare), equipped with dual-head cadmium zinc telluride (CZT) detectors, for I-123 metaiodobenzylguanidine (MIBG) imaging in pediatric neuroblastoma. On planar imaging, CZT shows greater image quality than at conventional gamma-camera using the Infinia Hawkeye (GE Healthcare). Physiologic structures such as salivary glands and myocardium show sharper borders with a more notable signal-to-noise ratio at CZT than conventional gamma camera. On SPECT imaging, the CZT scanner, combined with resolution recovery, demonstrates either comparable or greater image quality at 80% of the conventional gamma camera’s acquisition time. Due to the 2.46-mm detector pixel with fully registered collimator holes matching each pixel and direct conversion of photons into electrical signals, the CZT gamma camera system provides significant advantages in photon localization and energy resolution.

First clinical experience of a ring-configured cadmium zinc telluride camera: A comparative study versus conventional gamma camera systems

BACKGROUND

A novel semiconductor cadmium zinc telluride (CZT) gamma camera system using a block sequential regularized expectation maximization (BSREM) reconstruction algorithm is now clinically available. Here we investigate how a multi-purpose ring-configurated CZT system can be safely applied in clinics and describe the initial optimization process.

METHOD

Seventy-six patients (bone-, cardiac- and lung scan) were scanned on a conventional gamma camera (planar and/or single-photon emission computed tomography [SPECT]/SPECT-CT) used in clinical routine and on the ring-configurated CZT camera Starguide (GE Healthcare). These data were used to validate and optimize the Starguide system for routine clinical use.

RESULTS

Comparable image quality for the Starguide system, to that of the conventional gamma camera, was achieved for bone scan (4 min/bed position [BP] using a relative difference prior [RDP] with gamma 2 and beta 0.4, along with 10 iterations and 10 subsets), cardiac scan (8 min [stress] and 3 min 20 s [rest] using median root prior [MRP] with beta 0.07 non attenuation corrected and 0.008 attenuation corrected and 50 interations and 10 subsets for both stress and rest) and lung scan (10 min [vent] and 5 min [perf] using RDP with gamma 0.5 and beta 0.03 [vent] and 0.02 [perf] and 20 interations and 10 subsets for both vent and perf).

CONCLUSIONS

It was possible to transition from a conventional gamma camera to the Starguide system as part of the clinical routine, with acceptable image quality. Images from the Starguide system were deemed to be at least as good as those from a conventional gamma camera.

Performance evaluation of resolution and sensitivity of C-SPECT's variable slat-stack collimator

BACKGROUND

Myocardial perfusion imaging is commonly performed using SPECT, where both general-purpose and dedicated scanners are available. A limitation with general-purpose systems has been the inability to image dynamically since different projections are obtained far apart in time due to scanner rotation. Dedicated systems can have this capability since they acquire completely sampled projections (i.e., those with enough angular views for reconstruction) with short time frames. C-SPECT, does not need any scanner or patient motion to obtain complete projections, allowing fast dynamics. When imaging fast dynamics, the optimal collimator settings are not necessarily the same as for static imaging, where longer acquisitions can be utilized. Thus, C-SPECT offers adaptive collimation in the transverse and axial directions.

PURPOSE

The performance of adaptation in the axial direction was characterized herein.

METHODS

The ratio of the resolution metric in high-sensitivity mode to that in the high-resolution mode, termed resolution boost factor, was determined. Analogously, the sensitivity boost factor was also determined. Comparisons were made with theory and simulations.

RESULTS

The boost factors for resolution and sensitivity, averaged over the 14 modules of the system, were determined to be 1.72 and 1.75, respectively.

CONCLUSIONS

The boost factors, which ideally would be two, were between 10% and 15% below optimal values and tracked each other, suggesting mechanical challenges in the apparatus, such as incomplete closure of adjacent slats, but show reasonably successful adaptation between modes.

Multicenter Evaluation of the Feasibility of Clinical Implementation of SPECT Myocardial Blood Flow Measurement: Intersite Variability and Imaging Time

BACKGROUND

Single-center studies have shown that single photon emission computed tomography myocardial blood flow (MBF) measurement is accurate compared with MBF measured with microspheres in a porcine model, positron emission tomography, and angiography. Clinical implementation requires consistency across multiple sites. The study goal is to determine the intersite processing repeatability of single photon emission computed tomography MBF and the additional camera time required.

METHODS

Five sites (Canada, Italy, Japan, Germany, and Singapore) each acquired 25 to 35 MBF studies at rest and with pharmacological stress using technetium-99m-tetrofosmin on a pinhole-collimated cadmium-zinc-telluride-based cardiac single photon emission computed tomography camera with standardized list-mode imaging and processing protocols. Patients had intermediate to high pretest probability of coronary artery disease. MBF was measured locally and at a core laboratory using commercially available software. The time a room was occupied for an MBF study was compared with that for a standard rest/stress myocardial perfusion study.

RESULTS

With motion correction, the overall correlation in MBF between core laboratory and local site was 0.93 (range, 0.87-0.97) at rest, 0.90 (range, 0.84-0.96) at stress, and 0.84 (range, 0.70-0.92) for myocardial flow reserve. The local-to-core difference in global MBF (bias-MBF) was 5.4% (-3.8% to 14.8%; median [interquartile range]) at rest and 5.4% (-6.2% to 19.4%) at stress. Between the 5 sites, bias-MBF ranged from -1.6% to 11.0% at rest and from -1.9% to 16.3% at stress; the interquartile range in bias-MBF was between 9.3% (4.8%-14.0%) and 22.3% (-10.3% to 12.0%) at rest and between 17.0% (-11.3% to 5.6%) and 33.3% (-10.4% to 22.9%) at stress and was not significantly different between most sites. Both bias and interquartile range were like previously reported interobserver variability and less than the SD of the test-retest difference of 30%. The overall difference in myocardial flow reserve was 1.52% (-10.6% to 11.3%). There were no significant differences between with and without motion correction. The average additional acquisition time varied between sites from 44 to 79 minutes.

CONCLUSIONS

The average bias-MBF and bias-MFR values were small with standard deviations substantially less than the test-retest variability. This demonstrates that MBF can be measured consistently across multiple sites and further supports that this technique can be reliably implemented.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT03427749.

Dose-consistent dynamic SPECT

BACKGROUND

Coronary flow reserve (CFR) values measured by dynamic SPECT systems are typically consistent with other modalities (e.g., PET). However, large discrepancies are often observed for individual patients. Positioning of the region-of-interest (ROI), representing the arterial input function (AIF) could explain some of these discrepancies. We explored the possibility of positioning the ROI in a manner that evaluates its consistency with patient-based injected radiotracer doses.

METHODS

Dose-consistent dynamic SPECT methodology was introduced, and its application was demonstrated in a twenty-patient clinical study. The effect of various ROI positions was investigated and comparison to myocardial perfusion imaging was performed.

RESULTS

Mean AIF ratios were consistent with the injected dose ratios for all examined ROI positions. Good agreement (> 80%) between total perfusion deficit and CFR was found in the detection of obstructive CAD patients for all ROIs considered. However, for individual patients, significant dependence on ROI position was observed (altering CFR by typically 30%). The proposed methodology's uncertainty was evaluated (~ 7%) and found to be smaller than the variability due to choice of ROI position.

CONCLUSION

Dose-consistent dynamic SPECT may contribute to evaluating uncertainty of CFR measurements and may potentially decrease uncertainty by allowing improved ROI positioning for individual patients.

Myocardial blood flow evaluation with dynamic cadmium-zinc-telluride single-photon emission computed tomography: Bright and dark sides

Myocardial blood flow (MBF) and myocardial perfusion reserve (MPR) assessment with non-invasive techniques represent an important tool to evaluate both coronary artery disease severity and extent. Currently, cardiac positron emission tomography-computed tomography (PET-CT) is the "gold standard" for the assessment of coronary function and provides accurate estimations of baseline and hyperemic MBF and MFR. Nevertheless, due to the high cost and complexity, PET-CT is not widely used in clinical practice. The introduction of cardiac-dedicated cadmium-zinc-telluride (CZT) cameras has renewed researchers' interest on MBF quantitation by single-photon emission computed tomography (SPECT). Indeed, many studies evaluated MPR and MBF measurements by dynamic CZT-SPECT in different cohorts of patients with suspected or overt coronary artery disease. As well, many others have compared the values obtained by CZT-SPECT to the ones by PET-CT, showing good correlations in detecting significant stenosis, although with different and non-standardized cut-off values. Nevertheless, the lack of standardized protocol for acquisition, reconstruction and elaboration makes more difficult to compare different studies and to further assess the real advantages of MBF quantitation by dynamic CZT-SPECT in clinical routine. Many are the issues involved in the bright and dark sides of dynamic CZT-SPECT. They include different type of CZT cameras, different execution protocols, different tracers with different myocardial extraction fraction and distribution, different software packages with different tools and algorithms, often requiring manual post-processing elaboration. This review article provides a clear summary of the state of the art on MBF and MPR evaluation by dynamic CZT-SPECT and outlines the major issues to solve to optimize this technique.

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

Purpose

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.

Methods

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.

Results

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.

Conclusion

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.

Deep learning-based denoising in projection-domain and reconstruction-domain for low-dose myocardial perfusion SPECT

BACKGROUND

Low-dose (LD) myocardial perfusion (MP) SPECT suffers from high noise level, leading to compromised diagnostic accuracy. Here we investigated the denoising performance for MP-SPECT using a conditional generative adversarial network (cGAN) in projection-domain (cGAN-prj) and reconstruction-domain (cGAN-recon).

METHODS

Sixty-four noisy SPECT projections were simulated for a population of 100 XCAT phantoms with different anatomical variations and 99mTc-sestamibi distributions. Series of LD projections were obtained by scaling the full dose (FD) count rate to be 1/20 to 1/2 of the original. Twenty patients with 99mTc-sestamibi stress SPECT/CT scans were retrospectively analyzed. For each patient, LD SPECT images (7/10 to 1/10 of FD) were generated from the FD list mode data. All projections were reconstructed by the quantitative OS-EM method. A 3D cGAN was implemented to predict FD images from their corresponding LD images in the projection- and reconstruction-domain. The denoised projections were reconstructed for analysis in various quantitative indices along with cGAN-recon, Gaussian, and Butterworth-filtered images.

RESULTS

cGAN denoising improves image quality as compared to LD and conventional post-reconstruction filtering. cGAN-prj can further reduce the dose level as compared to cGAN-recon without compromising the image quality.

CONCLUSIONS

Denoising based on cGAN-prj is superior to cGAN-recon for MP-SPECT.

Segmentation-Free PVC for Cardiac SPECT Using a Densely-Connected Multi-Dimensional Dynamic Network

In nuclear imaging, limited resolution causes partial volume effects (PVEs) that affect image sharpness and quantitative accuracy. Partial volume correction (PVC) methods incorporating high-resolution anatomical information from CT or MRI have been demonstrated to be effective. However, such anatomical-guided methods typically require tedious image registration and segmentation steps. Accurately segmented organ templates are also hard to obtain, particularly in cardiac SPECT imaging, due to the lack of hybrid SPECT/CT scanners with high-end CT and associated motion artifacts. Slight mis-registration/mis-segmentation would result in severe degradation in image quality after PVC. In this work, we develop a deep-learning-based method for fast cardiac SPECT PVC without anatomical information and associated organ segmentation. The proposed network involves a densely-connected multi-dimensional dynamic mechanism, allowing the convolutional kernels to be adapted based on the input images, even after the network is fully trained. Intramyocardial blood volume (IMBV) is introduced as an additional clinical-relevant loss function for network optimization. The proposed network demonstrated promising performance on 28 canine studies acquired on a GE Discovery NM/CT 570c dedicated cardiac SPECT scanner with a 64-slice CT using Technetium-99m-labeled red blood cells. This work showed that the proposed network with densely-connected dynamic mechanism produced superior results compared with the same network without such mechanism. Results also showed that the proposed network without anatomical information could produce images with statistically comparable IMBV measurements to the images generated by anatomical-guided PVC methods, which could be helpful in clinical translation.

Anthropomorphic cardiac phantom for dynamic SPECT

BACKGROUND

As myocardial blood flow measurement (MBF) in SPECT systems became recently available, significant effort has been devoted to its validation. For that purpose, we have developed a cardiac phantom that is able to mimic physiological radiotracer variation in the left ventricle cavity and in the myocardium, while performing beating-like motion. The new phantom is integrated inside a standard anthropomorphic torso allowing a realistic tissue attenuation and gamma-ray scattering METHODS AND RESULTS: A mechanical cardiac phantom was integrated in a commercially available anthropomorphic torso. Using a GE Discovery 530c SPECT, measurements were performed. It was found that gamma-ray attenuation effects are significant and limit the MBF measurements to global/three-vessel resolution. Dynamic SPECT experiments were performed to validate MBF accuracy and showed mean relative error of 14%. Finally, the effect of varying radiotracer dose on the accuracy of dynamic SPECT was studied CONCLUSIONS: A dynamic cardiac phantom has been developed and successfully integrated in a standard SPECT torso. A good agreement was found between SPECT-reported MBF values and the expected results. Despite increased noise-to-signal ratio when radiotracer doses were reduced, MBF uncertainty did not increase significantly down to very low doses, thanks to the temporal integration of the activity during the measurement.

Performance evaluation of a novel multi-pinhole collimator on triple-NaI-detector SPECT/CT for dedicated myocardial imaging

BACKGROUND

In this study we evaluated the imaging capabilities of a novel Multi-pinhole collimator (MPH-Cardiac) specially designed for nuclear cardiology imaging on a Triple-NaI-detector based SPECT/CT system.

METHODS

^99mTc point source measurements covering the field of view (FOV) were used to determine tomographic sensitivity (TS_pointsource) and spatial resolution. Organ-size tomographic sensitivity (TS_organ) was measured with a left ventricle (LV) phantom filled with typical myocardial activity of a patient scan. Reconstructed image uniformity was measured with a 140 mm diameter uniform cylinder phantom. Using the LV phantom once filled with ^99mTc and after with ¹²³I, Contrast-to-noise ratio (CNR) was measured on the reconstructed images by ROI analysis on the myocardium activity and on the LV cavity. Furthermore, a polar map analysis was performed determining Spill-Over-Ratio in water (SOR_water) and image noise. The results were compared with that of a dual-head parallel-hole low energy high resolution (LEHR) collimator system. A patient with suspected coronary artery disease (CAD) was scanned on the LEHR system using local protocol of 16 min total acquisition time, followed by a 4-min MPH-Cardiac scan.

RESULTS

Peak TS_pointsource was found to be 1013 cps/MBq in the axial center of the FOV while it was decreasing toward the radial edges. TS_organ in the CFOV was found to be 134 cps/MBq and 700 cps/MBq for the LEHR and MPH-Cardiac, respectively. Average spatial resolution throughout the FOV was 4.38 mm FWHM for the MPH-Cardiac collimator. Reconstructed image uniformity values were found to be 0.292% versus 0.214% for the LEHR and MPH-Cardiac measurements, respectively. CNR was found to be higher in case of MPH-Cardiac than for LEHR in case of ^99mTc (15.5 vs. 11.7) as well as for ¹²³I (13.5 vs. 8.3). SOR_water values were found to be 28.83% and 21.1% for the ^99mTc measurements, and 31.44% and 24.33% for the ¹²³I measurements for LEHR and MPH-Cardiac, respectively. Pixel noise of the ^99mTc polar maps resulted in values of 0.38% and 0.24% and of the ¹²³I polar maps 0.62% and 0.21% for LEHR and MPH-Cardiac, respectively. Visually interpreting the patient scan images, MPH-Cardiac resulted in better image contrast compared to the LEHR technique with four times shorter scan duration.

CONCLUSIONS

The significant image quality improvement achieved with dedicated MPH-Cardiac collimator on triple head SPECT/CT system paves the way for short acquisition and low-dose cardiovascular SPECT applications.

Quantitative Iodine-123 single-photon emission computed tomography/computed tomography for Iodine-131 therapy of an autonomously functioning thyroid nodule

PURPOSE

Autonomously functioning thyroid nodules (AFTNs) are treated with iodine-131 (I-131) therapy, which increases the risk of permanent hypothyroidism; however, the risk can be reduced by separately estimating the accumulated activity for the AFTN and extranodular thyroid tissue (ETT).

METHODS

A quantitative I-123 single-photon emission computed tomography (SPECT)/CT (5 mCi) was performed in one patient with unilateral AFTN and T3 thyrotoxicosis. The I-123 concentrations measured at 24 h were 12.26 µCi/mL and 0.11 µCi/mL in the AFTN and contralateral ETT, respectively. Thus, the I-131 concentrations and radioactive iodine uptake expected at 24 h by 5 mCi of I-131 were 38.59 µCi/mL and 0.31 for the AFTN and 0.34 µCi/mL and 0.007 for the contralateral ETT. The weight was calculated as CT-measured volume multiplied by 1.03.

RESULTS

In the AFTN patient with thyrotoxicosis, we administered 30 mCi of I-131, which would maximize the 24-h I-131 concentration in the AFTN (226.86 µCi/g) and maintain a tolerable concentration in the ETT (1.97 µCi/g). The percentage of I-131 uptake at 48 h post I-131 administration was 62.6%. The patient achieved a euthyroid state at 14 weeks and maintained the state until 2 years post I-131 administration with an AFTN volume reduction of 61.38%.

CONCLUSION

The pre-therapeutic planning of quantitative I-123 SPECT/CT may enable a therapeutic window for I-131 therapy, which directs optimal I-131 activity to effectively treat AFTN while preserving the normal thyroid tissue.

Fast myocardial perfusion SPECT denoising using an attention-guided generative adversarial network

Purpose

Deep learning-based denoising is promising for myocardial perfusion (MP) SPECT. However, conventional convolutional neural network (CNN)-based methods use fixed-sized convolutional kernels to convolute one region within the receptive field at a time, which would be ineffective for learning the feature dependencies across large regions. The attention mechanism (Att) is able to learn the relationships between the local receptive field and other voxels in the image. In this study, we propose a 3D attention-guided generative adversarial network (AttGAN) for denoising fast MP-SPECT images.

Methods

Fifty patients who underwent 1184 MBq ^99mTc-sestamibi stress SPECT/CT scan were retrospectively recruited. Sixty projections were acquired over 180° and the acquisition time was 10 s/view for the full time (FT) mode. Fast MP-SPECT projection images (1 s to 7 s) were generated from the FT list mode data. We further incorporated binary patient defect information (0 = without defect, 1 = with defect) into AttGAN (AttGAN-def). AttGAN, AttGAN-def, cGAN, and Unet were implemented using Tensorflow with the Adam optimizer running up to 400 epochs. FT and fast MP-SPECT projection pairs of 35 patients were used for training the networks for each acquisition time, while 5 and 10 patients were applied for validation and testing. Five-fold cross-validation was performed and data for all 50 patients were tested. Voxel-based error indices, joint histogram, linear regression, and perfusion defect size (PDS) were analyzed.

Results

All quantitative indices of AttGAN-based networks are superior to cGAN and Unet on all acquisition time images. AttGAN-def further improves AttGAN performance. The mean absolute error of PDS by AttcGAN-def was 1.60 on acquisition time of 1 s/prj, as compared to 2.36, 2.76, and 3.02 by AttGAN, cGAN, and Unet.

Conclusion

Denoising based on AttGAN is superior to conventional CNN-based networks for MP-SPECT.

Increasing angular sampling through deep learning for stationary cardiac SPECT image reconstruction

BACKGROUND

The GE Discovery NM (DNM) 530c/570c are dedicated cardiac SPECT scanners with 19 detector modules designed for stationary imaging. This study aims to incorporate additional projection angular sampling to improve reconstruction quality. A deep learning method is also proposed to generate synthetic dense-view image volumes from few-view counterparts.

METHODS

By moving the detector array, a total of four projection angle sets were acquired and combined for image reconstructions. A deep neural network is proposed to generate synthetic four-angle images with 76 ([Formula: see text]) projections from corresponding one-angle images with 19 projections. Simulated data, pig, physical phantom, and human studies were used for network training and evaluation. Reconstruction results were quantitatively evaluated using representative image metrics. The myocardial perfusion defect size of different subjects was quantified using an FDA-cleared clinical software.

RESULTS

Multi-angle reconstructions and network results have higher image resolution, improved uniformity on normal myocardium, more accurate defect quantification, and superior quantitative values on all the testing data. As validated against cardiac catheterization and diagnostic results, deep learning results showed improved image quality with better defect contrast on human studies.

CONCLUSION

Increasing angular sampling can substantially improve image quality on DNM, and deep learning can be implemented to improve reconstruction quality in case of stationary imaging.

Quantification of intramyocardial blood volume using 99mTc-RBC SPECT/CT: a pilot human study

BACKGROUND

Quantification of intramyocardial blood volume (IMBV), the fraction of myocardium that is occupied by blood, is a promising Index to measure microcirculatory functions. In previous large animal SPECT/CT studies injected with 99mTc-labeled Red Blood Cell (RBC) and validated by ex vivo microCT, we have demonstrated that accurate IMBV can be measured. In this study, we report the data processing methods and results of the first-in-human pilot study.

METHODS

Data from three subjects have been included to date. Each subject underwent rest and adenosine-induced stress 99mTc-RBC SPECT/CT on a dedicated cardiac system with both non-contrast and contrast-enhanced CT acquired. Corrections of attenuation (AC) and scatter (SC), respiratory and cardiac gating, and partial volume correction (PVC) were applied. We also performed automatic segmentation and registration approach based on the blood pool topology in both SPECT and CT images.

RESULTS

The quantified IMBV across all subjects under resting conditions were 35.0% ± 3.3% for the end-diastolic phase and 24.1% ± 2.7% for the end-systolic phase. The cycle-dependent change in IMBV (ΔIMBV) between diastolic and systolic phases was 31.5% ± 3.0%. Under stress, IMBV were 40.6% ± 4.2% for the end-diastolic phase and 26.5% ± 2.8% for the end-systolic phase, and ΔIMBV was 34.7% ± 7.4%.

CONCLUSIONS

It is feasible to quantify IMBV in resting and stress conditions in human studies using SPECT/CT with 99mTc-RBC.

Deep-Learning-Based Few-Angle Cardiac SPECT Reconstruction Using Transformer

Convolutional neural networks (CNNs) have been extremely successful in various medical imaging tasks. However, because the size of the convolutional kernel used in a CNN is much smaller than the image size, CNN has a strong spatial inductive bias and lacks a global understanding of the input images. Vision Transformer, a recently emerged network structure in computer vision, can potentially overcome the limitations of CNNs for image-reconstruction tasks. In this work, we proposed a slice-by-slice Transformer network (SSTrans-3D) to reconstruct cardiac SPECT images from 3D few-angle data. To be specific, the network reconstructs the whole 3D volume using a slice-by-slice scheme. By doing so, SSTrans-3D alleviates the memory burden required by 3D reconstructions using Transformer. The network can still obtain a global understanding of the image volume with the Transformer attention blocks. Lastly, already reconstructed slices are used as the input to the network so that SSTrans-3D can potentially obtain more informative features from these slices. Validated on porcine, phantom, and human studies acquired using a GE dedicated cardiac SPECT scanner, the proposed method produced images with clearer heart cavity, higher cardiac defect contrast, and more accurate quantitative measurements on the testing data as compared with a deep U-net.

Myocardial Perfusion and Coronary Physiology Assessment of Microvascular Dysfunction in Patients Undergoing Transcatheter Aortic Valve Implantation-Rationale and Design

The prevalence of coronary artery disease (CAD) in patients with severe aortic stenosis (AS) is 30-68%. Nevertheless, there is still not enough evidence to use invasive assessment of lesion severity, because the hemodynamic milieu of AS may impact the fractional flow reserve (FFR) and non-hyperemic indices. Therefore, the aim of the study is two-fold. First, to measure acute and long-term changes of FFR, index of microvascular resistance (IMR), and coronary flow reserve (CFR) in patients undergoing TAVI procedure. Second, to compare the diagnostic accuracy of intracoronary indices with myocardial perfusion measured by cadmium-zinc-telluride single-photon emission tomography (CZT-SPECT) and find cut-off values defining significant stenosis. We plan to enroll 40 patients eligible for TAVI with intermediate stenosis (30-70%) in the left anterior descending (LAD) coronary artery. In each patient FFR, CFR, and IMR will be measured in addition to myocardial blood flow calculated by CZT-SPECT before and either immediately after TAVI (acute cohort) or in 6 months (late cohort) after the procedure. FFR, CFR, and IMR will be matched with the results of myocardial perfusion measured by CZT-SPECT in the area of LAD. As a result, cut-off values of FFR, CFR, and IMR defining the decreased blood flow will be found.

The current status of CZT SPECT myocardial blood flow and reserve assessment: Tips and tricks

Cardiac PET-derived measurements of myocardial blood flow (MBF) and myocardial flow reserve (MFR) are proven robust indexes of the severity of coronary artery disease (CAD). They facilitate the diagnosis of diffuse epicardial and microvascular disease and are also of prognostic significance. However, low availability and high cost have limited their wide clinical implementation. Over the last 15 years, cadmium zinc telluride (CZT)-based detectors have been implemented into SPECT imaging devices. Myocardial perfusion scintigraphy can be performed faster and with less radiation exposure as compared with standard gamma cameras. Rapid dynamic SPECT studies with higher count rates can be performed. This technological breakthrough has renewed the interest in SPECT MBF assessment in patients with CAD. Currently, two cardiac-centered CZT gamma cameras are available commercially-Discovery NM530c and D-SPECT. They differ in parameters such as collimator design, number of detectors, sensitivity, spatial resolution and image reconstruction. A number of publications have focused on the feasibility of dynamic CZT SPECT and on the correlation with cardiac PET and invasive coronary angiography measurements of fractional flow reserve. Current study reviews the present status of MBF and MFR assessment with CZT SPECT. It also aims to provide an overview of specific issues related to acquisition, processing and interpretation of quantitative studies in patients with CAD.

Myocardial flow reserve estimation with contemporary CZT-SPECT and 99mTc-tracers lacks precision for routine clinical application

BACKGROUND

PET myocardial flow reserve (MFR) has established diagnostic and prognostic value. Technological advances have now enabled SPECT MFR quantification. We investigated whether SPECT MFR precision is sufficient for clinical categorization of patients.

METHODS

Validation studies vs invasive flow measurements and PET MFR were reviewed to determine global SPECT MFR thresholds. Studies vs PET and a SPECT MFR repeatability study were used to establish imprecision in SPECT MFR measurements as the standard deviation of the difference between SPECT and PET MFR, or test-retest SPECT MFR. Simulations were used to evaluate the impact of SPECT MFR imprecision on confidence of clinically relevant categorization.

RESULTS

Based on validation studies, the typical PET MFR categories were used for SPECT MFR classification (< 1.5, 1.5-2.0, > 2.0). Imprecision vs PET MFR ranged from 0.556 to 0.829, and test-retest imprecision was 0.781-0.878. Simulations showed correct classification of up to only 34% of patients when 1.5 ≤ true MFR ≤ 2.0. Categorization with high confidence (> 80%) was only achieved for extreme MFR values (< 1.0 or > 2.5), with correct classification in only 15% of patients in a typical lab with MFR of 1.8 ± 0.5.

CONCLUSIONS

Current SPECT-derived estimates of MFR lack precision and require further optimization for clinical risk stratification.

A study protocol for an observational cohort investigating cardiac transthyretin amyloidosis flow reserve before and after Tafamidis treatment: The AMYTRE study

Introduction

Anginal symptoms and signs of ischemia have been reported in some patients with cardiac transthyretin amyloidosis (ATTR) without obstructive epicardial coronary artery disease (CAD). Few studies found that coronary microvascular dysfunction was highly prevalent in subjects with cardiac amyloidosis, even in the absence of epicardial CAD. The purpose of this study is to confirm the coronary microvascular dysfunction, and to go further with evaluation of the effect of Tafamidis on microvascular dysfunction after 24 months of treatment.

Methods and analysis

This study is a multicentric, prospective, observational cohort study. Adult patients with confirmed ATTR cardiomyopathy seen in the nuclear medicine departments of three large referral centers and treated with Tafamidis will be included. At baseline, patients will have a clinical and echocardiography evaluation. They will undergo a dynamic rest/stress cardiac scintigraphy with flow and reserve measurements before and 24 months after Tafamidis introduction. The primary outcome of this study will be the variation of stress and rest myocardial blood flow and flow reserve between baseline and 24 months after treatment. The effect of Tafamidis will be assessed by an intention to treat analysis.

Ethics and dissemination

The study has received the following approvals: Orleans Hospital Research Committee (CHRO-2021-05) and Sud-Mediterranée IV Regional Ethics Committee (21 06 02). Results will be made available to physicians, the funders, and other researchers.

Clinical trial registration

[https://clinicaltrials.gov/ct2/show/NCT05103943], identifier [NCT05103943].

Diagnostic accuracy of dynamic CZT-SPECT in coronary artery disease. A systematic review and meta-analysis

BACKGROUND

With the appearance of cadmium-zinc-telluride (CZT) cameras, dynamic myocardial perfusion imaging (MPI) has been introduced, but comparable data to other MPI modalities, such as quantitative coronary angiography (CAG) with fractional flow reserve (FFR) and positron emission tomography (PET), are lacking. This study aimed to evaluate the diagnostic accuracy of dynamic CZT single-photon emission tomography (SPECT) in coronary artery disease compared to quantitative CAG, FFR, and PET as reference.

MATERIALS AND METHODS

Different databases were screened for eligible citations performing dynamic CZT-SPECT against CAG, FFR, or PET. PubMed, OvidSP (Medline), Web of Science, the Cochrane Library, and EMBASE were searched on the 5th of July 2020. Studies had to meet the following pre-established inclusion criteria: randomized controlled trials, retrospective trails or observational studies relevant for the diagnosis of coronary artery disease, and performing CZT-SPECT and within half a year the methodological references. Studies which considered coronary stenosis between 50% and 70% as significant based only on CAG were excluded. Data extracted were sensitivity, specificity, likelihood ratios, and diagnostic odds ratios. Quality was assessed with QUADAS-2 and statistical analysis was performed using a bivariate model.

RESULTS

Based on our criteria, a total of 9 studies containing 421 patients were included. For the assessment of CZT-SPECT, the diagnostic value pooled analysis with a bivariate model was calculated and yielded a sensitivity of 0.79 (% CI 0.73 to 0.85) and a specificity of 0.85 (95% CI 0.74 to 0.92). Diagnostic odds ratio (DOR) was 17.82 (95% CI 8.80 to 36.08, P < 0.001). Positive likelihood ratio (PLR) and negative likelihood ratio (NLR) were 3.86 (95% CI 2.76 to 5.38, P < 0.001) and 0.21 (95% CI 0.13 to 0.33, P < 0.001), respectively.

CONCLUSION

Based on the results of the current systematic review and meta-analysis, dynamic CZT-SPECT MPI demonstrated a good sensitivity and specificity to diagnose CAD as compared to the gold standards. However, due to the heterogeneity of the methodologies between the CZT-SPECT MPI studies and the relatively small number of included studies, it warrants further well-defined study protocols.

The Effect of an Energy Window with an Ellipsoid Phantom on the Differential Defect Contrast on Myocardial SPECT Images

Good quality single-photon emission computed tomography (SPECT) images are required to achieve a perfect diagnosis and determine the severity of defects within the myocardial wall. There are many techniques that can support the diagnosis of defect formations in acquired images and contribute to avoiding errors before image construction. The main aim of this study was to determine the effect of energy width (15%, 20%, and 25%) on defect contrast in myocardial SPECT images correlated with the decentralization of positioning of a phantom. A phantom of polyethylene plastic was used to mimic the myocardial wall of the left ventricle. The phantom consists of two chambers, inner and outer. Two rectangular pieces of plastic were placed in anterior and inferior locations in the mid-region of the myocardial phantom to simulate myocardial infarction (defects). The average defect contrast for all phantom positions using 15% to 20% energy was (1.2, 1.6) for the anterior region and (1.1, 2) for the inferior region, respectively. Additionally, the energy window width was >25% with a large displacement of the positioning off center, leading to loss of the defect contrast in myocardial SPECT images, particularly in the inferior region. The study showed decreasing defect contrast in both locations, anterior and inferior, with increasing energy window width correlated with eccentricity positioning of the phantom on an imaging table.

Monte Carlo modelling of a compact CZT-based gamma camera with application to 177Lu imaging

Background

Semiconductor gamma-camera systems based on cadmium zinc telluride (CZT) detectors present new challenges due to an energy-response that includes effects of low-energy tailing. In particular, such energy tails produce effects that need to be considered when imaging radionuclides with multiple emissions such as $$^{177}{\mathrm {Lu}}$$ 177 Lu . Monte Carlo simulation can be used to investigate the behaviour of such systems and optimise their use, provided that the detector model closely reflects the real physical detector. The aim of this work is to develop a CZT model applicable for simulation of CZT-based gamma cameras.

Methods

The equations describing the charge transport and signal induction are considered in three dimensions and are solved numerically, and the CZT model is then realised by coupling the detector-response to the photon-transport handled by the SIMIND Monte Carlo program. The CZT model is tuned to reproduce experimentally measured energy spectra of a hand-held gamma camera system for multiple radionuclides ($$^{99\mathrm {m}}{\mathrm {Tc}}$$ 99 m Tc , $$^{123}{\mathrm {I}}$$ 123 I and $$^{177}{\mathrm {Lu}}$$ 177 Lu ) and parallel-hole collimators (MEGP, LEHR) as well as an uncollimated system.

Results

Overall, the model results agree well with measurements across the range of experimental conditions. The applicability of the model is demonstrated by separating energy spectra into components to investigate the interference of high-energy photons on lower energy-windows, where pronounced effects of low-energy tailing for $$^{177}{\mathrm {Lu}}$$ 177 Lu are observed.

Conclusions

The developed model provides understanding of the specifics of the camera response and is expected to be helpful for future optimisation of gamma camera applications.

Three-dimensional semiquantitative analysis of gastric emptying SPECT

OBJECTIVE

We used dynamic single-photon emission computed tomography (D-SPECT) to overcome the interference of the planar dynamic imaging due to the overlap of internal organs, thus more accurate physiological function can be obtained.

METHODS

3D printed gastric phantom was used to simulate gastric emptying (GE). First, the planar dynamic liquid GE procedure was used and served as the reference value; second, D-SPECT followed by repeated liquid GE procedures with three gamma cameras were used. The emptying flow rate of the gastric phantom simulated three flow rates of liquid, semisolid and solid. Third, we simulated the intestinal activity that interfered with the residual value obtained by 2D dynamic imaging, which was compared with D-SPECT. Then, we brought the 3D VOI data into the postprocessing program to obtain the residual activity curve and residual percentage.

RESULTS

The residual amount obtained in the phantom at 60th minutes in the first stage is 14.57%; the residual amount of liquid emptying are Siemens: 3.33%, GE: 15.06%, PHILIPS: 1.12%; residual amount for semisolid are Siemens: 47.36%, GE: 54.25%, PHILIPS: 51.57%; residual amount for solids are Siemens: 63.98%, GE: 66.88%, PHILIPS: 63.76%. All values are within the normal range. Then, we simulated the intestinal activity that interfered with the residual value obtained by 2D dynamic imaging: 75-90 min: 10.42, 19.48, 19.51 and 11.02%; however, the residual values obtained with 3D SPECT VOI data: 75-90 min: 1.42, 1.41, 1.35 and 1.02%. These results show that the emptying data errors caused by intestinal overlap can be effectively corrected (P = 0.017).

CONCLUSION

D-SPECT imaging can overcome the interference in the semiquantitative data of residual GE caused in 2D mode.

Impact of attenuation correction for CZT-SPECT measurement of myocardial blood flow

OBJECTIVES

Most of cardiac dedicated CZT-SPECT systems are not equipped with CT, whereas PET systems are. We evaluated the impact of AC correction on CZT-SPECT myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements.

METHODS

104 patients were included. SPECT data were acquired on cadmium zinc telluride (CZT)-based pinhole cardiac camera in listmode using a stress (250 ± 17 MBq)/rest (511 ± 23 MBq) 1-day Tc-99m-tetrofosmin protocol. Low-dose CT was acquired on another SPECT/CT camera in the same position. All analysis was performed using Corridor4DM.

RESULTS

Stress and rest MBF were significantly lower when AC was applied (P < 0.001). For regional and global MFR, there was no significant difference between AC and NAC measurements (P > 0.25 at least). Mean global LV MFR was 2.43 ± 0.87 and 2.33 ± 0.89, respectively, for NAC and AC measurements. Using a threshold of 2, 86 patients (83%) remained classified as normal and abnormal regarding global LV MFR whether AC was applied or not. Mean difference between NAC and AC values for the 18 other patients was 0.3.

CONCLUSION

AC correction does not significantly affect MFR measurement both in regional and global LV analyses.

CZT camera systems may provide better risk stratification for low-risk patients

BACKGROUND

The photon sensitivity and spatial resolution of single-photon emission-computed tomography (SPECT) has been significantly improved by solid-state camera systems using cadmium zinc telluride (CZT) detectors. While the diagnostic accuracy of these systems is well established, there is little evidence directly comparing the prognostic utility to conventional NaI cameras.

METHODS AND RESULTS

Retrospective analysis of patients undergoing SPECT between 2008 and 2012. Visual SPECT assessment was performed utilizing the 17-segment model to determine summed stress scores (SSS). We identified 12,830 consecutive patients, mean age 63.2 ± 13.7 and 56.1% male, 5072 of whom underwent CZT and 7758 NaI imaging. During a median follow-up duration of 7.0 years (IQR 5.5-8.2), a total of 2788 (21.7%) patients died. Compared to SSS 0, minimal perfusion abnormality (SSS 1-3) was associated with increased all-cause mortality with CZT camera (adjusted HR 1.32, P = .017) and NaI camera (adjusted HR 1.29, P = .001, interaction P = .803). Increasing stress abnormality was associated with a similar increase in risk with CZT or NaI imaging (interaction P > .500). In a propensity matched analysis, patients with normal perfusion stress perfusion assessed with a CZT was associated with decreased mortality compared to normal perfusion assessed by a NaI camera system (hazard ratio .88, 95% CI .78-.99, P = .040).

CONCLUSIONS

Increasing stress perfusion abnormality was associated with similar increase in all-cause mortality with CZT or NaI cameras. CZT and NaI camera systems provide similar risk stratification, however, normal myocardial perfusion may be associated with a more benign prognosis when assessed with a CZT camera system.

Reduced acquisition times for measurement of myocardial blood flow with 99mTc-tetrofosmin and solid-state detector SPECT

BACKGROUND

Measurement of myocardial blood flow (MBF) is feasible using SPECT imaging but the acquisition requires more time than usual. Our study assessed the impact of reducing acquisition times on the accuracy and repeatability of the uptake rate constant (K1).

METHODS

Twenty-nine patients underwent two rest/stress studies with Tc-99m-tetrofosmin 18 ± 13 days apart, using a one-day rest/stress dynamic SPECT imaging protocol with a solid-state cardiac camera. A 5-minute static image was acquired prior to tracer injection for subtraction of residual activity, followed immediately by 11-minute of list-mode data collection. Static image acquisition times of 0.5, 1, and 3 minutes and dynamic imaging times of 5, 7, and 9 minutes were simulated by truncating list-mode data. Images were reconstructed with/without attenuation correction and with/without motion correction. Kinetic parameters were calculated using a 1-tissue-compartment model.

RESULTS

K1 increased with reduced dynamic but not static imaging time (P < 0.001). The increase in K1 for a 9-minute scan was small (4.7 ± 5.3%) compared with full-length studies. The repeatability of K1 did not change significantly (13 ± 12%, P > 0.17).

CONCLUSIONS

A shortened imaging protocol of 3-minute (rest) or 30-second (stress) static image acquisition and 9 minutes of dynamic image acquisition altered K1 by less than 5% compared to a previously validated 11-minute acquisition.

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

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

Combining flow and reserve measurement during myocardial perfusion imaging: A new era for myocardial perfusion scintigraphy?

Myocardial flow reserve represents the ratio of myocardial blood flow between stress and rest, giving functional information about both macrocirculation and microcirculation; it has been reported extensively in positron emission tomography, with an increase in diagnostic performance, providing important prognostic information and being a powerful tool to guide therapy. Advances in single photon emission computed tomography, with the widespread availability of "cadmium zinc telluride" single photon emission computed tomography cameras, raise the question of myocardial flow reserve use in daily clinical practice. In this article, we review the pathophysiology of myocardial blood flow and myocardial flow reserve, and the initial data available from single photon emission computed tomography myocardial blood flow and myocardial flow reserve evaluation; we also discuss potential limitations to the wider implementation of flow evaluation in single photon emission computed tomography.

A new cardiac phantom for dynamic SPECT

BACKGROUND

In recent years, with the advance of myocardial blood flow (MBF) measurement capability in dynamic single photon emission computerized tomography (SPECT) systems, significant effort has been devoted to validation of the new capability. Unfortunately, the mechanical phantoms available for the validation process lack essential features-they either have a constant radiotracer concentration or they have rigid (static) walls unable to simulate cardiac beating.

METHODS AND RESULTS

We have developed a mechanical cardiac phantom that is able to mimic physiological radiotracer variation in the left ventricle (LV) cavity and in the myocardium (M), while performing beating-like motion. We have also developed a mathematical model of the phantom, allowing a description of the radiotracer concentrations in both regions (LV, M) as a function of time, which served as a tool for experiment planning and to accurately mimic physiological-like time-activity curves (TACs). A net retention model for the phantom was also developed, which served to compute the theoretical (i.e., expected) MBF of the phantom from measured quantities only, and thus validate the MBF reported by the SPECT system. In this paper, phantom experiments were performed on a GE Discovery NM 530c SPECT system.

CONCLUSIONS

A novel dynamic cardiac phantom for emission tomography has been developed. The new phantom is capable of producing a wide range of TACs that can mimic physiological (and potentially in the future, pathological) curves, similar to those observed in dynamic SPECT systems. SPECT-reported MBF values were validated against known (measured) activity of the injected radiotracer from phantom experiments, which allowed to determine the accuracy of the GE Discovery 530c SPECT system.

Self-Collimating SPECT With Multi-Layer Interspaced Mosaic Detectors

Conventional single photon emission computed tomography (SPECT) relies on mechanical collimation whose resolution and sensitivity are interdependent, the best performance a SPECT system can attain is only a compromise of these two equally desired properties. To simultaneously achieve high resolution and sensitivity, we propose to use sensitive detectors constructed in a multi-layer in ter spaced mosaicdetectors (MATRICES) architecture to accomplish part of the collimation needed. We name this new approach self-collimation. We evaluate three self-collimating SPECT systems and report their imaging performance: 1) A simulated human brain SPECT achieves 3.88% sensitivity, it clearly resolves 0.5-mm and 1.0-mm hot-rod patterns at noise-free and realistic count-levels, respectively; 2) a simulated mouse SPECT achieves 1.25% sensitivity, it clearly resolves 50- [Formula: see text] and 100- [Formula: see text] hot-rod patterns at noise-free and realistic count-levels, respectively; 3) a SPECT prototype achieves 0.14% sensitivity and clearly separates 0.3-mm-diameter point sources of which the center-to-center neighbor distance is also 0.3 mm. Simulated contrast phantom studies show excellent resolution and signal-to-noise performance. The unprecedented system performance demonstrated by these 3 SPECT scanners is a clear manifestation of the superiority of the self-collimating approach over conventional mechanical collimation. It represents a potential paradigm shift in SPECT technology development.

Feasibility of attenuation map alignment in pinhole cardiac SPECT using exponential data consistency conditions

PURPOSE

Dedicated cardiac SPECT systems do not typically include an integrated CT scanner and thus attenuation correction requires registration of separately acquired transmission scans. Data consistency conditions are equations that express the redundancy between projections while taking into account the attenuation effects. This study assessed the feasibility of applying exponential data consistency conditions to rebinned pinhole projections for attenuation-map registration in pinhole cardiac SPECT.

METHODS

Simulations of an anthropomorphic computer phantom with three different tracer activity distributions were performed with and without clinical levels of noise in the projection data. The first activity distribution contained activity only within the myocardium which satisfied the assumptions of the data consistency conditions. The other two distributions violated these assumptions by adding background activity and uptake in the liver. Simulations included acquisitions with 360, 31, and 9 pinhole projections and detector pixel sizes of 0.75 and 2.5 mm. A metric based on the average difference between pairs of exponential projections was used to evaluate registration accuracy.

RESULTS

When activity is restricted to the myocardium, the registration error was 3.0 mm for 31 noisy pinhole projections with a detector size of 2.5 mm. When activity is added to the background and the liver, a correction for the extra-cardiac activity is needed but when applied, a registration error of 6.0 mm was achieved.

CONCLUSION

These results suggest that it may be feasible to use exponential data consistency conditions to register pinhole cardiac SPECT and CT transmission data. Taxonomy: 8-6 (IM-SPECT/Registration).

Myocardial Flow Reserve Measurement During CZT-SPECT Perfusion Imaging for Coronary Artery Disease Screening: Correlation With Clinical Findings and Invasive Coronary Angiography-The CFR-OR Study

Purpose: The aim of this study was to assess the results of cadmium zinc telluride (CZT)- single-photon emission computed tomography (SPECT) myocardial flow reserve (MFR) in coronary artery disease (CAD) screening regarding clinical risk and its correlation to invasive coronary angiography (ICA). Methods: A total of 137 patients (61 male and 76 female) referred for CAD screening myocardial perfusion imaging (MPI) between November 2018 and April 2020 were included in the CFR-OR prospective trial. The 10-year risk of cardiovascular death according to the European Society of Cardiology (SCORE) was calculated. SPECT 1-day 99mTc-tetrofosmin protocol was acquired on CZT cardiac-dedicated pinhole cameras. Low-dose thoracic CT was used for coronary calcium score (CCS) evaluation. ICA, when performed within 3 months, was also analyzed. Results: Mean SCORE and mean global MFR were, respectively, 4 ± 3.1% and 2.50 ± 0.74; 34 patients had impaired CFR (using a threshold of 2). There was a significant inverse correlation between MFR and SCORE (p = 0.006), gender (p = 0.019), and number of cardiovascular risk factors (p = 0.01). MFR was significantly reduced in patients with CCS above 1 (p = 0.01). No significant correlation was found between MFR and individual cardiovascular risk factors (dyslipidemia, hypertension, diabetes, or family history of CAD). A total of 23 patients underwent ICA. Global MFR SPECT sensitivity and specificity were 83.3 and 100 %, respectively, with an area under the curve of 0.94. Conclusion: Adding MFR to SPECT MPI for CAD screening on CZT camera may contribute to high-risk patient identification and enhance diagnostic performances. MFR could help physician decision to perform ICA.

Quantification of myocardial flow reserve using a gamma camera with solid-state cadmium-zinc-telluride detectors: Relation to angiographic coronary artery disease

BACKGROUND

Previous studies have suggested using gamma cameras with cadmium-zinc-telluride (CZT) detectors to quantify myocardial blood flow (MBF) and flow reserve (MFR). In this study, we aimed to evaluate the feasibility and accuracy of MFR quantification using a CZT camera compared to coronary angiography.

METHODS

Forty-one participants referred for coronary angiography underwent a rest/stress one-day myocardial perfusion imaging protocol using a CZT gamma camera. Rest and stress dynamic phases were followed by acquisition of traditional perfusion images and time-activity curves were generated. Angiographic and perfusion results were compared to MFR.

RESULTS

Patients with abnormal perfusion presented reduced MFR (2.01 [1.48-2.77] vs. 2.94 [2.38-3.64], P = 0.002), and reduced stress MBF. Patients with high-risk CAD had lower global MFR compared to patients without obstructive disease (1.99 [1.22-2.84] vs. 2.89 [2.22-3.58], P = 0.026). Obstructed vessels showed lower regional MFR when compared to non-obstructed (1.81 [1.19-2.67] vs. 2.75 [2.13-3.42], P < 0.001). A regional MFR of 2.2 provided a sensitivity of 63.2% and specificity of 74.1% to identify an obstructive lesion in the corresponding artery.

CONCLUSION

In patients undergoing invasive coronary angiography for the evaluation of CAD, quantifying MBF and MFR in a CZT gamma camera is feasible and reflects underlying disease. In these patients, reduced regional MFR suggests the presence of obstructive lesion(s).

Application-specific nuclear medicalin vivoimaging devices

Nuclear medical imaging devices, such as those enabling photon emission imaging (gamma camera, single photon emission computed tomography, or positron emission imaging), that are typically used in today's clinics are optimized for assessing large portions of the human body, and are classified as whole-body imaging systems. These systems have known limitations for organ imaging, therefore application-specific devices have been designed, constructed and evaluated. These devices, given their compact nature and superior technical characteristics, such as their higher detection sensitivity and spatial resolution for organ imaging compared to whole-body imaging systems, have shown promise for niche applications. Several of these devices have further been integrated with complementary anatomical imaging devices. The objectives of this review article are to (1) provide an overview of such application-specific nuclear imaging devices that were developed over the past two decades (in the twenty-first century), with emphasis on brain, cardiac, breast, and prostate imaging; and (2) discuss the rationale, advantages and challenges associated with the translation of these devices for routine clinical imaging. Finally, a perspective on the future prospects for application-specific devices is provided, which is that sustained effort is required both to overcome design limitations which impact their utility (where these exist) and to collect the data required to define their clinical value.

Feasibility of simultaneous 99mTc-tetrofosmin and 123I-BMIPP dual-tracer imaging with cadmium-zinc-telluride detectors in patients undergoing primary coronary intervention for acute myocardial infarction

BACKGROUND

Simultaneous dual-tracer imaging using isotopes with close photo-peaks may benefit from improved properties of cadmium-zinc-telluride (CZT)-based scanners.

METHODS

Thirty patients having undergone primary percutaneous coronary intervention for acute myocardial infarction underwent single-(99mTc-tetrofosmin (TF) or 123I-BMIPP first) followed by simultaneous 99mTc-TF /123I-BMIPP dual-tracer imaging using a Discovery NM/CT 670 CZT. The values for the quantitative gated-SPECT (QGS) and the quantitative perfusion SPECT (QPS) were assessed.

RESULTS

The intra-class correlation (ICC) coefficients between the single- and dual-tracer imaging were high in all the QGS and QPS data (Summed motion score: 0.95, summed thickening score: 0.94, ejection fraction: 0.98, SRS for 99mTc-TF: 0.97/ for 123I-BMIPP: 0.95). Wall motion, wall thickening and rest scores per coronary-territory-based regions were also comparable between the single- and dual imaging (ICC coefficient > 0.91). The interrater concordance in the visual analysis for the infarction and perfusion-metabolism mismatch was significant for the global and regional left ventricle (P < 0.001).

CONCLUSION

The quantitative/semi-quantitative values for global and regional left-ventricular function, perfusion, and fatty acid metabolism were closely comparable between the dual-tracer imaging and the single-tracer mode. These data suggests the feasibility of the novel CZT-based scanner for the simultaneous 99mTc-TF /123I-BMIPP dual-tracer acquisitions in clinical settings.

Patient-specific SPECT imaging protocols to standardize image noise

BACKGROUND

In addition to acquired photon counts, image noise depends on the image reconstruction algorithm. This work develops patient-specific activity or acquisition time protocols to standardize the average noise in a reconstructed image for different patients, cameras, and reconstruction algorithms.

METHODS

Image noise was calculated for images from 43 patients acquired on both a conventional and a multiple-pinhole cardiac SPECT camera. Functions were found to relate image noise to radiotracer activity, scan time, and body mass and were validated by normalizing the image noise in a test set of 58 patients.

RESULTS

There was a 3.6-fold difference in photon sensitivity between the two cameras but a 16-fold difference in activity-scan time was necessary to match the noise levels. Image noise doubled from 45 to 128 kg for the conventional camera (12.8 minutes) and tripled for the multiple-pinhole camera (5 minutes) for 350 MBq (9.5 mCi) 99mTc-tetrofosmin. It was 16.3% and 6.1% respectively for an average sized patient.

CONCLUSIONS

A linear scaling of activity with respect to the patient weight normalizes image noise but the scaling factors depend on the choice of camera and image reconstruction parameters. Therefore, equivalent numbers of acquired photon counts are not sufficient to guarantee equivalent image noise.

Stress CMR in Known or Suspected CAD: Diagnostic and Prognostic Role

The recently published 2019 guidelines on chronic coronary syndromes (CCS) focus on the need for noninvasive imaging modalities to accurately establish the diagnosis of coronary artery disease (CAD) and assess the risk of clinical scenario occurrence. Appropriate patient management should rely on controlling symptoms, improving prognosis, and guiding each therapeutic strategy as well as monitoring disease progress. Among the noninvasive imaging modalities, cardiovascular magnetic resonance (CMR) has gained broad acceptance in past years due to its unique features in providing a complete assessment of CAD through data on cardiac anatomy and function and myocardial viability, with high spatial and temporal resolution and without ionizing radiation. In detail, evaluation of the presence and extent of myocardial ischemia through stress CMR (S-CMR) has shown a high rule-in power in detecting functionally significant coronary artery stenosis in patients suspected of CCS. Moreover, S-CMR technique may add significant prognostic value, as demonstrated by different studies which have progressively evidenced the valuable power of this multiparametric imaging modality in predicting adverse cardiac events. The latest scientific progress supports a greater expansion of S-CMR with improvement of quantitative myocardial perfusion analysis, myocardial strain, and native mapping within the same examination. Although further study is warranted, these techniques, which are currently mostly restricted to the research field, are likely to become increasingly prevalent in the clinical setting with the scope of increasing accuracy in the selection of patients to be sent to invasive revascularization. This review investigates the diagnostic and prognostic role of S-CMR in the context of CAD, by analysing a strong, long-standing, scientific evidence together with an appraisal of new advanced techniques which may potentially enrich CAD management in the next future.