The Alcyone CZT SPECT camera. Evaluation of performance using phantom measurement and Monte Carlo simulations

Background Coronary artery disease is one of the most common causes of death. A common cardiac examination is to give a visualization of the myocardial blood flow by injecting a radio pharmaceutical and detect the radiation with a camera. The camera has for decades been using thallium doped sodium iodide (NaI(Tl)) as the detector material. New detector materials have been developed because of the physical limits of the NaI(Tl). The new clinically available material is cadmium-zinc-telluride. One manufacturer has placed 19 detector panels with pinhole collimators sharing a common focal point. This camera is relatively new on the market and not thoroughly investigated. Purpose It has been investigated if the image quality could be improved with a narrower energy window, the sensitivity and spatial resolution within the field of view (FOV), whether the image was affected by different source locations was investigated. Finally the detection limit for heart defects in a physical phantom and in XCAT phantom was found. Material & method A list mode acquisition was performed with a Data Spectrum phantom with a cardiac insert containing a basal defect, which simulated a myocardial infarction. The energy window was changed from ±10% to ±5% and the acquisition time was changed acquire the same statistics. The resolution was determined by fitting a Gaussian curve to a line source measurement. The detector specific sensitivity and the sensitivity in the reconstructed images were measured by using a spot marker at different positions. The positioning effect were investigated by placing the Data Spectrum phantom with a cardiac insert without any defects at different positions, the measurements were also performed on a patient. The defect limit was investigated by simulating defects with different positions and wall thickness in a voxel based, CT-scanned, anthropomorphic phantom and a XCAT phantom using a verified Monte Carlo software. Results It was found that a reduction in energy window did not improve image quality and the acquisition time or activity had to be increased 25% in order to compensate of the loss of counts. The spatial resolution was unchanged over the investigated area. The detector specific sensitivity varied up to a factor 2 with the source position, but the sensitivity in the reconstructed images varied only 4%. A translation of 2 cm of the patient gives rise to positioning effect which are great enough to possibly change the diagnosis. The detection limit for defects in the anthropomorphic phantom was determined to be between 15% and 30% of the wall thickness. For the NaI(Tl) camera the detection limit have been found to be 50%. The detection limit for the XCAT phantom was not found

Myocardial Perfusion Imaging With Rb-82 PET

Myocardial perfusion imaging (MPI) is an effective technique used to study the left ventricular ejection function (LVEF), myocardial perfusion, wall motion, and wall thickening. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are two modalities that can be used to quantify the left global and regional perfusion at rest and stress. While PET and SPECT rely on similar principles to produce images, important differences in instrumentation and experimental applications are dictated by inherent differences in their respective physics of radioactive decay. With a sensitivity \u3e 90% in combination with a high specificity, PET is today the best available nuclear imaging technique for the diagnosis of coronary artery disease (CAD). The short half-life of the perfusion tracers in combination with highly sophisticated hard- and software enables rapid PET studies with high patient throughput. Rubidium-82 (82Rb) is a PET perfusion imaging agent that has a shot half-life of 76 seconds which enables multiple sequential data acquisitions in a short duration of time. It also reduces the number of false-positive SPECT scans and artifacts from soft tissue attenuation due to the routine application of attenuation correction. However 82Rb PET imaging is under-utilized clinically due to difficulty optimizing the imaging parameters. The major challenge of 82Rb imaging is determining when to begin the image acquisition post infusion, as imaging too early results in images with high background (low contrast), and imaging too late results in noisy images due to low count statistics. 82Rb rest/stress dynamic and gated data from 16 patients were available for analysis. The FWHM of the 82Rb infusion, LV cavity and LV myocardial uptake in time activity curves were generated and compared to isolate the dominant parameter in determining image quality. The measured and actual infusion-time correlated only at rest (r = 0.93, P = 0.006). Splitting-time at rest and stress correlated (r = 0.74, P = 0.09). But the study was not able to identify a single dominant parameter that would determine the image quality due to the unpredictable nature of hemodynamics during the vasodilatory induced cardiovascular stress. First pass radionuclide angiography (FPRNA) is the gold standard for quantification of ejection fraction. We examined the quantification of the ejection function (LVEF) to determine whether the gated 82Rb PET data, using quantitative gated SPECT (QGS), would accurately predict changes in the chamber volume and correlated the results with those obtained from FPRNA technique. There was a good correlation between the resting FPRNA data and resting gated 82Rb QGS data (r= 0.81, P=0.0005) showing that this method can be applied to 82Rb PET.99mTc SPECT was considered the gold standard for this study, as it is the most widely used technique for myocardial perfusion imaging. The under-perfused area of the myocardium is defined as defect. 99mTc agents, 18F-FDG, and 82Rb can all be used for cardiac imaging 1-7. However, count rates, energy and camera differences can yield image differences that are independent of the actual biological distribution. We examined whether PET with an 82Rb-labeled tracer would provide information on defect size similar to that provided by 99mTc SPECT, using a cardiac phantom in which the true defect size is known. Since 82Rb has such a short half-life (76 seconds), filling and imaging a phantom was going be a great challenge. Hence 124I which is a high-energy radioisotope like 82Rb, was used in this phantom study as a surrogate for 82Rb. Static cardiac phantom studies with 99mTc, 18F and 124I (surrogate for 82Rb) were conducted. The percent defect sizes were measured and compared with the true defect size. Our results demonstrated that at 45% threshold, the measured defect size was representative of true defect size for 99mTc SPECT data. Using this threshold as the standard, we smoothed the 18F and 124I PET data until the measured defect size for PET was representative of the true defect size. An optimal filter cutoff frequency (Butterworth filter, cutoff = 0.80 cycles/pixel, order=5 at 45% threshold for 124I or 82Rb) was found for the PET data within the range of values studied, and this frequency was higher than the clinical norm for SPECT data. Our results also illustrated that the measured SPECT defect size varied greatly depending on the thresholds used to define a defect, whereas measure PET defect size was relatively constant over the range of cutoffs tested7. The optimal cutoff may depend on defect size, patient variability, and noise level. When assessing myocardial defect size, physical properties need to be taken into consideration, particularly when comparing images obtained using different nuclides (i.e. 82Rb or 99mTc agent perfusion and 18F FDG viability)

preliminary clinical evaluation of the ASTRA4D algorithm

Objectives. To propose and evaluate a four-dimensional (4D) algorithm for joint motion elimination and spatiotemporal noise reduction in low-dose dynamic myocardial computed tomography perfusion (CTP). Methods. Thirty patients with suspected or confirmed coronary artery disease were prospectively included und underwent dynamic contrast-enhanced 320-row CTP. The presented deformable image registration method ASTRA4D identifies a low-dimensional linear model of contrast propagation (by principal component analysis, PCA) of the ex-ante temporally smoothed time-intensity curves (by local polynomial regression). Quantitative (standard deviation, signal-to-noise ratio (SNR), temporal variation, volumetric deformation) and qualitative (motion, contrast, contour sharpness; 1, poor; 5, excellent) measures of CTP quality were assessed for the original and motion-compensated volumes (without and with temporal filtering, PCA/ASTRA4D). Following visual myocardial perfusion deficit detection by two readers, diagnostic accuracy was evaluated using 1.5T magnetic resonance (MR) myocardial perfusion imaging as the reference standard in 15 patients. Results. Registration using ASTRA4D was successful in all 30 patients and resulted in comparison with the benchmark PCA in significantly (p<0.001) reduced noise over time (-83%, 178.5 vs 29.9) and spatially (-34%, 21.4 vs 14.1) as well as improved SNR (+47%, 3.6 vs 5.3) and subjective image quality (motion, contrast, contour sharpness: +1.0, +1.0, +0.5). ASTRA4D resulted in significantly improved per-segment sensitivity of 91% (58/64) and similar specificity of 96% (429/446) compared with PCA (52%, 33/64; 98%, 435/446; p=0.011) and the original sequence (45%, 29/64; 98%, 438/446; p=0.003) in the visual detection of perfusion deficits. Conclusions. The proposed functional approach to temporal denoising and morphologic alignment was shown to improve quality metrics and sensitivity of 4D CTP in the detection of myocardial ischemia.Zielsetzung. Die Entwicklung und Bewertung einer Methode zur simultanen Rauschreduktion und Bewegungskorrektur für niedrig dosierte dynamische CT Myokardperfusion. Methoden. Dreißig prospektiv eingeschlossene Patienten mit vermuteter oder bestätigter koronarer Herzkrankheit wurden einer dynamischen CT Myokardperfusionsuntersuchung unterzogen. Die präsentierte Registrierungsmethode ASTRA4D ermittelt ein niedrigdimensionales Modell des Kontrastmittelflusses (mittels einer Hauptkomponentenanalyse, PCA) der vorab zeitlich geglätteten Intensitätskurven (mittels lokaler polynomialer Regression). Quantitative (Standardabweichung, Signal-Rausch-Verhältnis (SNR), zeitliche Schwankung, räumliche Verformung) und qualitative (Bewegung, Kontrast, Kantenschärfe; 1, schlecht; 5, ausgezeichnet) Kennzahlen der unbearbeiteten und bewegungskorrigierten Perfusionsdatensätze (ohne und mit zeitlicher Glättung PCA/ASTRA4D) wurden ermittelt. Nach visueller Beurteilung von myokardialen Perfusionsdefiziten durch zwei Radiologen wurde die diagnostische Genauigkeit im Verhältnis zu 1.5T Magnetresonanztomographie in 15 Patienten ermittelt. Resultate. Bewegungskorrektur mit ASTRA4D war in allen 30 Patienten erfolgreich und resultierte im Vergleich mit der PCA Methode in signifikant (p<0.001) verringerter zeitlicher Schwankung (-83%, 178.5 gegenüber 29.9) und räumlichem Rauschen (-34%, 21.4 gegenüber 14.1) sowie verbesserter SNR (+47%, 3.6 gegenüber 5.3) und subjektiven Qualitätskriterien (Bewegung, Kontrast, Kantenschärfe: +1.0, +1.0, +0.5). ASTRA4D resultierte in signifikant verbesserter segmentweiser Sensitivität 91% (58/64) und ähnlicher Spezifizität 96% (429/446) verglichen mit der PCA Methode (52%, 33/64; 98%, 435/446; p=0.011) und dem unbearbeiteten Perfusionsdatensatz (45%, 29/64; 98%, 438/446; p=0.003) in der visuellen Beurteilung von myokardialen Perfusionsdefiziten. Schlussfolgerungen. Der vorgeschlagene funktionale Ansatz zur simultanen Rauschreduktion und Bewegungskorrektur verbesserte Qualitätskriterien und Sensitivität von dynamischer CT Perfusion in der visuellen Erkennung von Myokardischämie

Procedural recommendations of cardiac PET/CT imaging: standardization in inflammatory-, infective-, infiltrative-, and innervation (4Is)-related cardiovascular diseases: a joint collaboration of the EACVI and the EANM

With this document, we provide a standard for PET/(diagnostic) CT imaging procedures in cardiovascular diseases that are inflammatory, infective, infiltrative, or associated with dysfunctional innervation (4Is). This standard should be applied in clinical practice and integrated in clinical (multicenter) trials for optimal procedural standardization. A major focus is put on procedures using [18F]FDG, but 4Is PET radiopharmaceuticals beyond [18F]FDG are also described in this document. Whilst these novel tracers are currently mainly applied in early clinical trials, some multicenter trials are underway and we foresee in the near future their use in clinical care and inclusion in the clinical guidelines. Finally, PET/MR applications in 4Is cardiovascular diseases are also briefly described. Diagnosis and management of 4Is-related cardiovascular diseases are generally complex and often require a multidisciplinary approach by a team of experts. The new standards described herein should be applied when using PET/CT and PET/MR, within a multimodality imaging framework both in clinical practice and in clinical trials for 4Is cardiovascular indications

Procedural recommendations of cardiac PET/CT imaging:standardization in inflammatory-, infective-, infiltrative-, and innervation (4Is)-related cardiovascular diseases: a joint collaboration of the EACVI and the EANM

With this document, we provide a standard for PET/(diagnostic) CT imaging procedures in cardiovascular diseases that are inflammatory, infective, infiltrative, or associated with dysfunctional innervation (4Is). This standard should be applied in clinical practice and integrated in clinical (multicenter) trials for optimal procedural standardization. A major focus is put on procedures using [18F]FDG, but 4Is PET radiopharmaceuticals beyond [18F]FDG are also described in this document. Whilst these novel tracers are currently mainly applied in early clinical trials, some multicenter trials are underway and we foresee in the near future their use in clinical care and inclusion in the clinical guidelines. Finally, PET/MR applications in 4Is cardiovascular diseases are also briefly described. Diagnosis and management of 4Is-related cardiovascular diseases are generally complex and often require a multidisciplinary approach by a team of experts. The new standards described herein should be applied when using PET/CT and PET/MR, within a multimodality imaging framework both in clinical practice and in clinical trials for 4Is cardiovascular indications.</p

DEMIST: A deep-learning-based task-specific denoising approach for myocardial perfusion SPECT

There is an important need for methods to process myocardial perfusion imaging (MPI) SPECT images acquired at lower radiation dose and/or acquisition time such that the processed images improve observer performance on the clinical task of detecting perfusion defects. To address this need, we build upon concepts from model-observer theory and our understanding of the human visual system to propose a Detection task-specific deep-learning-based approach for denoising MPI SPECT images (DEMIST). The approach, while performing denoising, is designed to preserve features that influence observer performance on detection tasks. We objectively evaluated DEMIST on the task of detecting perfusion defects using a retrospective study with anonymized clinical data in patients who underwent MPI studies across two scanners (N = 338). The evaluation was performed at low-dose levels of 6.25%, 12.5% and 25% and using an anthropomorphic channelized Hotelling observer. Performance was quantified using area under the receiver operating characteristics curve (AUC). Images denoised with DEMIST yielded significantly higher AUC compared to corresponding low-dose images and images denoised with a commonly used task-agnostic DL-based denoising method. Similar results were observed with stratified analysis based on patient sex and defect type. Additionally, DEMIST improved visual fidelity of the low-dose images as quantified using root mean squared error and structural similarity index metric. A mathematical analysis revealed that DEMIST preserved features that assist in detection tasks while improving the noise properties, resulting in improved observer performance. The results provide strong evidence for further clinical evaluation of DEMIST to denoise low-count images in MPI SPECT

Image processing techniques in nuclear medicine

The application of image processing techniques to radionuclide images acquired on a gamma camera - computer system has been investigated. Hepatic perfusion imaging studies with 99Tcm-tin colloid were performed in patients with primary colorectal carcimma. The hepatic perfusion index performed poorly in the detection of those patients with occult or overt hepatic metastastes, as did mean transit times of liver colloid flow derived from deconvolution analysis. A discriminant function was developed which separated those patients with occult metastases from those without liver disease. A fully automatic algorithm to derive a left ventricular edge from each frame of an ECG gated cardiac blood pool study was developed and validated in patient studies. Left ventricular ejection fractions calculated from count rates within the edge were reproducible and correlated well with ejection fractions derived from the same images by a manual technique, and with ejection fractions derived from left ventricular cineangiography. Studies were performed in patients to evaluate the effectiveness of tomographic imaging of the myocardial perfusion imaging agent 99Tcm-tBIN for detection of ischaemic heart disease. Tomographic reconstructions in the planes of the axes of the left ventricle gave better results than transaxial reconstructions or planar imaging. Choice of the optimum reconstruction filter for use in tomography using 99Tcm-tBIN was examined by means of patient am phantom studies. These showed that more accurate diagnoses and better reconstructions were obtained with smoothing filters than by the use of sharp reconstruction filters. This work shows that optimum image processing techniques must be established to attain the best possible results with new radiopharmaceuticals for nuclear medicine investigations

Cardiac PET/CT with Rb-82: optimization of image acquisition and reconstruction parameters.

Our aim was to characterize the influence of time-of-flight (TOF) and point spread function (PSF) recovery corrections, as well as ordered subset expectation maximization (OSEM) reconstruction parameters, in (82)Rb PET/CT quantification of myocardial blood flow (MBF) and myocardial flow reserve (MFR). Rest and stress list-mode dynamic (82)Rb PET acquisition data from 10 patients without myocardial flow defects and 10 patients with myocardial blood flow defects were reconstructed retrospectively. OSEM reconstructions were performed with Gaussian filters of 4, 6, and 8 mm, different iterations, and subset numbers (2 × 24; 2 × 16; 3 × 16; 4 × 16). Rest and stress global, regional, and segmental MBF and MFR were computed from time activity curves with FlowQuant(©) software. Left ventricular segmentation using the 17-segment American Heart Association model was obtained. Whole left ventricle (LV) MBF at rest and stress were 0.97 ± 0.30 and 2.30 ± 1.00 mL/min/g, respectively, and MFR was 2.40 ± 1.13. Concordance was excellent and all reconstruction parameters had no significant impact on MBF, except for the exclusion of TOF which led to significantly decreased concordance in rest and stress MBF in patients with or without perfusion defects on a coronary artery basis and in MFR in patients with perfusion defects. Changes in reconstruction parameters in perfusion (82)Rb PET/CT studies influence quantitative MBF analysis. The inclusion of TOF information in the tomographic reconstructions had significant impact in MBF quantification

The Performance of MLEM for Dynamic Imaging From Simulated Few-View, Multi-Pinhole SPECT

Stationary small-animal SPECT systems are being developed for rapid dynamic imaging from limited angular views. This work quantified, through simulations, the performance of Maximum Likelihood Expectation Maximization (MLEM) for reconstructing a time-activity curve (TAC) with uptake duration of a few seconds from a stationary, three-camera multi-pinhole SPECT system. The study also quantified the benefits of a heuristic method of initializing the reconstruction with a prior image reconstructed from a conventional number of views, for example from data acquired during the late-study portion of the dynamic TAC. We refer to MLEM reconstruction initialized by a prior-image initial guess (IG) as MLEMig. The effect of the prior-image initial guess on the depiction of contrast between two regions of a static phantom was quantified over a range of angular sampling schemes. A TAC was modeled from the experimentally measured uptake of 99mTc-hexamethylpropyleneamine oxime (HMPAO) in the rat lung. The resulting time series of simulated images was quantitatively analyzed with respect to the accuracy of the estimated exponential washin and washout parameters. In both static and dynamic phantom studies, the prior-image initial guess improved the spatial depiction of the phantom, for example improved definition of the cylinder boundaries and more accurate quantification of relative contrast between cylinders. For example in the dynamic study, there was ~ 50% error in relative contrast for MLEM reconstructions compared to ~ 25-30% error for MLEMig. In the static phantom study, the benefits of the initial guess decreased as the number of views increased. The prior-image initial guess introduced an additive offset in the reconstructed dynamic images, likely due to biases introduced by the prior image. MLEM initialized with a uniform initial guess yielded images that faithfully reproduced the time dependence of the simulated TAC; there were no s- atistically significant differences in the mean exponential washin/washout parameters estimated from MLEM reconstructions compared to the true values. Washout parameters estimated from MLEMig reconstructions did not differ significantly from the true values, however the estimated washin parameter differed significantly from the true value in some cases. Overall, MLEM reconstruction from few views and a uniform initial guess accurately quantified the time dependance of the TAC while introducing errors in the spatial depiction of the object. Initializing the reconstruction with a late-study initial guess improved spatial accuracy while decreasing temporal accuracy in some cases