Conventional Anger Camera Research Articles

Reduced acquisition time for thallium myocardial perfusion imaging with large field cadmium-zinc-telluride SPECT/CT cameras: An equivalence study

BackgroundCadmium-zinc-telluride (CZT) SPECT/CT cameras with large field of view offer a higher sensitivity than conventional Anger cameras. This prospective study aimed to determine the equivalence between a conventional protocol and a reduced acquisition time protocol for 201-Thallium myocardial perfusion imaging (MPI) using a whole-body CZT SPECT camera. Methods and ResultsStress MPI was obtained for 103 consecutive patients on a DISCOVERY-CZT camera. Images were anonymized and post-processed to simulate a 25% (D75 dataset) and 50% (D50 dataset) decrease in total recorded counts. Concerning the number of segments displaying a tracer uptake < 70% of maximum intensity per patient, equivalence was demonstrated for both count-reduced datasets with a good inter-observer agreement (between 0.90 and 0.88). When comparing the full-vs-D75 datasets and full-vs-D50 datasets, mean difference was 0.06 segment (CI95: [− 0.15;0.27], P < 0.001) and 0.518 segment (CI95: [0.28;0.76], P < 0.001) respectively. Inter-observer agreement was also moderate to good concerning the number of pathological segments (between 0.6 and 0.7) and excellent for functional parameters. ConclusionWhole-body CZT SPECT/CT cameras allow to reduce 201-Thallium MPI injected activity or acquisition time by 50% with an equivalence in the number of segments displaying a tracer uptake < 70% of maximum intensity and with a good inter-observer agreement.

Prospective Paired Comparison of 123I-FP-CIT SPECT Images Obtained With a 360°-CZT and a Conventional Camera.

This study aimed to compare 123I-FP-CIT SPECT imaging obtained from a 360° cadmium-zinc-telluride (CZT) camera with different focus configurations and from a conventional Anger camera. This prospective study (NCT03980418) included patients referred to 123I-FP-CIT SPECT imaging who consecutively underwent a 30-minute acquisition on a conventional camera immediately followed by two 15-minute acquisitions on the 360°-CZT camera with, respectively, striatum and brain focus and reconstruction parameters to give equivalent contrast ratios, albeit with higher spatial resolution for the CZT camera. Tomographic count sensitivities were calculated. The images were analyzed through visual, according to 5 independent physicians, and automatic semiquantitative analyses. Ninety-two patients were included in this study. The 360°-CZT camera tomographic count sensitivities showed increases of +25% and +18% for striatum and brain focus, respectively, as well as significantly higher quality scores (P ≤ 0.04) in comparison to the conventional camera. The κ scores of consensual visual analysis were 0.80 and 0.85, and correlation coefficients of semiquantitative analysis for striatum uptakes were 0.75 and 0.76 for the comparisons of images obtained with the 2 cameras, with striatum and brain focus, respectively, for the CZT camera. Advanced age was the single predictor of discordant cases (10/92 [11%]) showing systematically abnormal scans with the conventional camera, potentially as a result of partial volume effect. Irrespective of focus mode, this high-sensitivity 360°-CZT camera provides concordant 123I-FP-CIT SPECT results when compared with a conventional camera, but with shorter acquisition times, higher image quality, and few discordant cases possibly explained by its higher spatial resolution.

High-quality brain perfusion SPECT images may be achieved with a high-speed recording using 360\xb0 CZT camera

ObjectiveThe aim of this study was to compare brain perfusion SPECT obtained from a 360° CZT and a conventional Anger camera.MethodsThe 360° CZT camera utilizing a brain configuration, with 12 detectors surrounding the head, was compared to a 2-head Anger camera for count sensitivity and image quality on 30-min SPECT recordings from a brain phantom and from 99mTc-HMPAO brain perfusion in 2 groups of 21 patients investigated with the CZT and Anger cameras, respectively. Image reconstruction was adjusted according to image contrast for each camera.ResultsThe CZT camera provided more than 2-fold increase in count sensitivity, as compared with the Anger camera, as well as (1) lower sharpness indexes, giving evidence of higher spatial resolution, for both peripheral/central brain structures, with respective median values of 5.2%/3.7% versus 2.4%/1.9% for CZT and Anger camera respectively in patients (p < 0.01), and 8.0%/6.9% versus 6.2%/3.7% on phantom; and (2) higher gray/white matter contrast on peripheral/central structures, with respective ratio median values of 1.56/1.35 versus 1.11/1.20 for CZT and Anger camera respectively in patients (p < 0.05), and 2.57/2.17 versus 1.40/1.12 on phantom; and (3) no change in noise level. Image quality, scored visually by experienced physicians, was also significantly higher on CZT than on the Anger camera (+ 80%, p < 0.01), and all these results were unchanged on the CZT images obtained with only a 15 min recording time.ConclusionThe 360° CZT camera provides brain perfusion images of much higher quality than a conventional Anger camera, even with high-speed recordings, thus demonstrating the potential for repositioning brain perfusion SPECT to the forefront of brain imaging.

Long-term prognostic value of low-dose normal stress-only myocardial perfusion imaging by wide beam reconstruction: A competing risk analysis

BackgroundA normal stress myocardial perfusion single-photon emission computed tomography (MPS) is associated with a good clinical outcome. New iterative algorithms, such as wide beam reconstruction (WBR), which improve image interpretation with half-dose or half-time acquisition, have been proposed for cardiac MPS. The aim of this study was to assess the long-term predictive value of a low-dose normal stress-only MPS with WBR using conventional Anger camera in patients with known or suspected coronary artery disease (CAD). Methods and ResultsA total of 2106 patients with known or suspected CAD and normal perfusion at half-dose stress-only MPS protocol were followed for a mean of 6.6 ± 2.7 years. MPS data were reconstructed with WBR iterative algorithm. End-point events were cardiac death or nonfatal myocardial infarction. Noncardiac death was considered the competing event. During follow-up, 149 cardiac events occurred with an annualized event rate of 1.2%. Independent predictors of cardiac events at Cox analysis were age, male gender, diabetes mellitus, previous myocardial infarction and the need for pharmacologic stress testing. At Fine-Gray analysis the cumulative incidence of cardiac events progressively increases with age and in the presence of diabetes for any combination of gender and stress type. Survival tree analysis confirmed that long-term prognosis considerably varies according of risk factors profile. ConclusionsLow-dose normal stress-only WBR MPS has a reliable long-term prognostic value in patients with suspected or known CAD. This finding supports the introduction of such a method into clinical practice with a consistent dose optimization in the interest of patients and exposed staff.

Experimental Validation of a Gamma Detector With a Novel Light-Guide-PMT Geometry to Reduce Dead Edge Effects

Photomultiplier tube (PMT)-based scintillation cameras are predominant in molecular imaging but have the drawback that position estimation is severely degraded near the edges (dead edge effect). This leads to sensitivity losses and can cause severe problems in applications like molecular breast imaging and in certain SPECT devices. Using smaller light sensors or semiconductor detectors can solve this issue but leads to increased costs. Here we present a gamma detector based on standard PMTs with a novel light-guide-PMT geometry that strongly reduces dead edges. In our design, a monolithic NaI(Tl) scintillator is read out by square PMTs placed in a staggered arrangement. At the edge of the scintillator we inserted additional light-guides to emulate half-size PMTs. Detector performance was assessed for 99mTc imaging; an average spatial resolution of 3.6 mm was measured over the whole detector, degrading to 4.0 mm within 30 mm to the critical edge. The dead edge of the scintillator is <3 mm. Since a 12-mm seal was used, the overall dead edge is <15 mm, which is a significant improvement over conventional Anger cameras (~40-mm dead edge). Therefore, the presented geometry can be useful in creating economical gamma detectors with reduced dead edges.

51 Multicentric performance assessment of VERITONTM 360° CZT-camera compared to conventional Anger-cameras: a phantom study

51 Multicentric performance assessment of VERITONTM 360° CZT-camera compared to conventional Anger-cameras: a phantom study

In vivo simultaneous imaging with 99mTc and 18F using a Compton camera

We have been developing a medical imaging technique using a Compton camera. This study evaluates the feasibility of clear imaging with 99mTc and 18F simultaneously, and demonstrates in vivo imaging with 99mTc and/or 18F. We used a Compton camera with silicon and cadmium telluride (Si/CdTe) semiconductors. We estimated the imaging performance of the Compton camera for 141 keV and 511 keV gamma rays from 99mTc and 22Na, respectively. Next, we simultaneously imaged 99mTc and 18F point sources to evaluate the cross-talk artifacts produced by a higher energy gamma-ray background. Then, in the in vivo experiments, three rats were injected with 99mTc-dimercaptosuccinic acid and/or 18F-fluorodeoxyglucose and imaged. The Compton images were compared with PET images. The rats were euthanized, and the activities in their organs were measured using a well counter. The energy resolution and spatial resolution were measured for the sources. No apparent cross-talk artifacts were observed in the practical-activity ratio (99mTc:18F = 1:16). We succeeded in imaging the distributions of 99mTc and 18F simultaneously, and the results were consistent with the PET images and well counter measurements. Our Si/CdTe Compton camera can thus work as a multi-tracer imager, covering various SPECT and PET probes, with less cross-talk artifacts in comparison to the conventional Anger cameras using a collimator. Our findings suggest the possibility of human trials.

Analysis of stress-only imaging, comparing upright and supine CZT camera acquisition to conventional gamma camera images with and without attenuation correction, with coronary angiography as a reference

BackgroundDiagnostic performance of stress-only imaging using a Cadmium-Zinc-Telluride (CZT) camera has not been directly compared in the same patients to stress-only attenuation-corrected conventional Anger camera images. Methods112 subjects with correlative coronary angiographic data and 40 subjects with <5% pre-test likelihood of coronary disease completed attenuation-corrected stress-only images on a conventional Anger camera and uncorrected upright and supine stress images on a CZT camera. Two readers provided independent, blinded interpretations of stress-only images. ResultsUpright and supine stress-only CZT images and attenuation-corrected Anger camera images provided similar positive (reader 1/reader 2, 50.0%/44.1% vs 46.4%/51.9%) and negative (66.7%/64.0% vs 67.9%/67.7%) predictive values (all P = NS) for obstructive coronary artery disease; however, the sensitivity was higher (81.3% vs 58.3%, P = .05), specificity lower (29.7% vs 50.0%, P = .005), and normalcy rate lower (87.5% vs 100%, P = .025) with attenuation-corrected Anger camera images for the first reader with no significant differences between cameras for the second reader. ConclusionsStress-only upright and supine CZT imaging was non-inferior statistically to attenuation-corrected stress-only Anger camera imaging. Nevertheless, stress-only CZT imaging may be associated with reduced diagnostic sensitivity for some readers compared to attenuation-corrected Anger camera images, which may be less acceptable clinically compared to stress plus rest images.

Comparison of CTAC and prone imaging for the detection of coronary artery disease using CZT SPECT

BackgroundCadmium-zinc-telluride (CZT) cameras have improved the evaluation of patients with chest pain. However, inferior/inferolateral attenuation artifacts similar to those seen with conventional Anger cameras persist. We added prone acquisitions and CT attenuation correction (CTAC) to the standard supine image acquisition and analyzed the resulting examinations.Methods and resultsSeventy-two patients referred for invasive coronary angiography (CAG), and who also underwent rest/stress myocardial perfusion imaging (MPI) on a CZT camera in the supine and prone positions plus CTAC imaging, to examine known or suspected CAD between April 2013 and March 2014 were included. A sixteen-slice CT scan acquired on a SPECT/CT scanner between rest and stress imaging provided data for iterative reconstruction. Sensitivity, specificity, accuracy, and positive and negative likelihood ratios (LRs) were calculated to compare MPI with CAG on a per-patient basis. Per-patient sensitivity, specificity, and accuracy of supine images to predict coronary abnormalities on CAG were 35% [95% confidence interval (CI) 19–52], 86% (95% CI 80–92), and 74% (95% CI 66–82); those of prone imaging were 65% (95% CI 45–81), 82% (95% CI 76–87), and 78% (95% CI 68–85); and those of CTAC were 59% (95% CI 41–71), 93% (95% CI 87–97), and 85% (95% CI 76–91), respectively.ConclusionsProne acquisition and CTAC images improve the ability to assess the inferior/inferolateral area.

Prognostic value of the cadmium-zinc-telluride camera: A comparison with a conventional (Anger) camera

BackgroundNew multipinhole cadmium-zinc-telluride (CZT) cameras allow for faster imaging and lower radiation doses for single photon emission computed tomography (SPECT) studies, but assessment of prognostic ability is necessary. Methods and ResultsWe collected data from all myocardial SPECT perfusion studies performed over 15 months at our institution, using either a CZT or conventional Anger camera. A Cox proportional hazards model was used to assess the relationship between camera type, imaging results, and either death or myocardial infarction (MI). Clinical variables including age, sex, body mass index (BMI), and historical risk factors were used for population description and model adjustments. We had 2,088 patients with a total of 69 deaths and 65 MIs (122 events altogether). A 3% increase in DDB (difference defect burden) represented a 12% increase in the risk of death or MI, whereas a 3% increase in rest defect burden or stress defect burden represented an 8% increase; these risks were the same for both cameras (P > .24, interaction tests). ConclusionsThe CZT camera has similar prognostic values for death and MI to conventional Anger cameras. This suggests that it may successfully be used to decrease patient dose.

17. Comparison of the sensitivity to cardiac motions of different cameras used for myocardial perfusion imaging

Introduction New solid-state CZT cameras provide high quality images, with a better spatial resolution than conventional Anger cameras [1] , but their robustness and sensitivity to cardiac motions remains to be assessed. The aim of this study was to compare the motion-related artefactual variations in the wall uptake of a cardiac phantom between the CZT cameras Discovery NM-530c (GE) and DSPECT (Spectrum Dynamics) and the Anger camera Symbia T2 (Siemens), which was equipped with an astigmatic (IQSPECT) or parallel-hole (conventional SPECT) collimator. Materials and methods Translations of a cardiac insert, which walls were filled-in with a solution containing 99mTc, were applied in 6 different directions (−X/+X, −Y/+Y et −Z/+Z) and with various amplitudes at half of each SPECT recording. Images were reconstructed with routine parameters [2] . The motion-related artefactual variations in myocardial uptake were assessed according to the difference in segmental uptake between each SPECT recorded with an insert translation and the corresponding normal SPECT-recording and by using a 17 segments division of the left ventricle [3] . Differences >10% were considered as significant. Results and conclusion For translations of only 5 mm, the variations in segmental uptake were not or only poorly significant whatever the camera type. For higher translation amplitudes, the CZT D530c camera exhibited the higher sensitivity to motion and the DSPECT, the lower one, whereas Anger cameras were at an intermediate level irrespective of the collimator type (parallel-hole or astigmatic).

Comparison of the prognostic value of myocardial perfusion imaging using a CZT-SPECT camera with a conventional anger camera

BackgroundRecent studies have shown that myocardial perfusion imaging (MPI) in cadmium-zinc-telluride (CZT) cameras allow faster exams with less radiation dose but there are little data comparing its prognosis information with that of dedicated cardiac Na-I SPECT cameras ObjectiveThe objective of this study is to compare the prognostic value of MPI using an ultrafast protocol with low radiation dose in a CZT-SPECT and a traditional one. MethodsGroup 1 was submitted to a two-day MIBI protocol in a conventional camera, and group 2 was submitted to a 1-day MIBI protocol in CZT camera. MPI were classified as normal or abnormal, and perfusion scores were calculated. Propensity score matching methods were performed Results3554 patients were followed during 33±8 months. Groups 1 and 2 had similar distribution of age, gender, body mass index, risk factors, previous revascularization, and use of pharmacological stress. Group 1 had more abnormal scans, higher scores than group 2. Annualized hard events rate was higher in group 1 with normal scans but frequency of revascularization was similar to normal group 2. Patients with abnormal scans had similar event rates in both groups ConclusionNew protocol of MPI in CZT-SPECT showed similar prognostic results to those obtained in dedicated cardiac Na-I SPECT camera, with lower prevalence of hard events in patients with normal scan.

0005 : Prognostic value of myocardial perfusion SPECT without significant perfusion defect using a dual isotope protocol and a novel CZT camera: interim results of the PROMHETE study

New dedicated cardiac gamma cameras using CZT detectors have shown significant improvement over the Anger camera regarding physical parameters, and their diagnostic performances have been validated in clinical studies. To date, few studies have evaluated the prognostic value of a low to intermediate risk single-photon emission tomography (SPECT) myocardial perfusion imaging (MPI) with these cameras, and only one with a HSDI stress thallium-201/rest Technetium-99m protocol on a CZT camera. The study included patients who had no or minimal perfusion defects (<10% of the LV myocardium) on a HS-DI MPI following a symptom-limited treadmill test or a pharmacological stress testing. These 578 patients were followed for 3.3±0.4 years (95% complete). The main endpoint was the occurrence a hard cardiac event (cardiac death or nonfatal myocardial infarction). 212 patients (37%) underwent exercise stress and 366 (63%) had pharmacological stress (of which 89% had dipyridamole and 11% had dobutamine). Mean summed stress score was 0.95±1.2 [0-5]. During the follow-up period 25 hard cardiac events occurred. Annualized event rate was 1.3%/y. In the subgroup of patients undergoing exercise stress test, annualized event rate was 0.43%/y. Multivariate Cox analysis identified age (HR 1.14 [1.08; 1.20], p<0.0001) and rest LVEF (HR 0.95 [0.92; 0.98], p=0.008) as independent predictors of cardiac death or myocardial infarction. Survival analysis showed that the occurrence of cardiac events was significantly higher in patients who had an altered LVEF compared to patients with a normal LVEF (16% vs. 3.8%, p=0.003). The use of a HS-DI protocol on a CZT camera provides prognostic information, comparable to single-isotope protocols on conventional Anger camera, while reducing imaging time and without increasing the injected activity. The author hereby declares no conflict of interest

Clinical Performance of the Discovery NM530c in Japanese Patients

The Discovery NM530 is a new generation of SPECT cameras equipped with semiconductor cadmium-zinctelluride (CZT) detector technology. It provides a shorter scan time and reduces the patient’s radiation exposure wthout loss of image quality compared with the conventional Anger camera. Combined supine and prone imaging with the Discovery NM530c is usefulfor reducing the false-positive rate in the infero-posterior or inferolateral segment associated with supine imaging. As studied by multicenter registry, 74% sensitivity, 85% specificity, and 81% accuracy for left anterior descending coronary artery stenosis, 76% sensitivity, 89% specificity, and 85% accuracy for left circumflex coronary artery stenosis, and 72% sensitivity, 86% specificity, and 82% accuracy for right coronary artery stenosis were observed in detecting an angiographic diameter narrowing of ≥75% on visualestimation. Using a l technetium- 99 m( 185/370 MBq) 1-day protocolwith an effective dose of ≤5 mSv, CZT SPECT demonstrated an acceptable diagnostic yield in detecting a significant coronary stenosis as assessed by fractional flow reserve (FFR). As for limiting to 92 coronary lesions in which FFR was measured, stress SPECT showed 77% sensitivity, 91% specificity, and 84% accuracy, whereas the diagnostic value decreased to 52% sensitivity, 68% specificity, and 58% accuracy based only on visual estimation of ≥ 75% diameter narrowing. In addition, the quantification of myocardialperfusion reserve derived by dynamic SPECT imaging using the Discovery NM530c may help identify balanced ischemia in patients with left main or 3-vesseldisease.

Dose optimization for myocardial perfusion CZT-SPECT imaging: Why and how?

Myocardial perfusion SPECT imaging (MPI) is able to provide a physiological assessment during physical exercise and is widely used for diagnosing coronary artery disease and assessing cardiac risk. Until recently, however, MPI needed to provide a lower radiation exposure, especially for the growing number of patients referred for repeated ionizing procedures throughout the course of their life. This goal has been partly attained with the advent of new imaging systems dedicated to nuclear cardiology and equipped with semiconductor cadmium zinc telluride (CZT) detectors, new collimation systems, and novel reconstruction software. Two CZT cameras are currently commercially available and when compared with conventional Anger cameras, they offer much higher energy resolutions and count sensitivities, allowing image quality to be improved as well as acquisition times and injected activities to be markedly reduced. Low-dose protocols have already been assessed with these CZT cameras, leading to a mean effective dose not exceeding 9 mSv per patient and thus, at a much lower level than that currently achieved with single-day protocols on conventional cameras (around 14 mSv). These doses can furthermore be reduced to less than 4 mSv, on average, owing to the use of a stress-first protocol, where the normality of stress images may lead to avoiding rest imaging. In the near future, effective doses will likely be further decreased to a lower level with technical improvements leading to minimizing the reconstructed noise and attenuation artifacts while at the same time optimizing and better tailoring the injection protocols to the individual patient.

L’évaluation de la fonction ventriculaire gauche, avec une caméra à semi-conducteurs et un protocole à faible dose

IntroductionNew gamma camera technology with Cadmium-Zinc-Telluride (CZT) semiconductor detectors provides better myocardial perfusion imaging (MPI) resolution and, given the detector's high-sensitivity (better spatial and energy resolution), it reduces imaging time and radiopharmaceutical doses (better detection sensitivity). The purpose of this study was to evaluate the left ventricular function parameters obtained by a fast low-dose clinical protocol on a CZT camera (D-SPECT), compared to the measurement on cardiac magnetic resonance imaging. MethodsWe retrospectively included patients who underwent MPI on D-SPECT camera with a low-dose of Sestamibi-99mTc (120MBq for stress and 360MBq at rest for a patient of 75kg weight), and a cardiac magnetic resonance imaging, with a time less than two months. The left ventricular function was obtained at rest, with 8-frame reformatted, and analysis was performed using Quantitative Gated SPECT (QGS®) software. ResultsSeventy-seven patients were included and their mean ejection fraction (EF) was 45±13% at MRI. For D-SPECT recording, mean activity within heart area was 527±104kcps, for mean recording time 3.5±2.2min and mean of the total activity was 420±185MBq (effective dose: 3.7±1.6mSv). Correlation between D-SPECT and MRI was very good for EF (r=0.88), end-diastolic volume (EDV, r=0.90) and end-systolic volume (ESV, r=0.96), but with an underestimation of all these parameters by the D-SPECT (on average, 5% absolute value for EF, and −16% and −24% in relative values for respectively ESV and EDV). ConclusionThe evaluation of left ventricular function using the D-SPECT camera and with a fast low-dose protocol correlates well with that obtained by cardiac MRI, in the same patient. EF and ventricular volumes are however underestimated, in agreement with that previously documented with conventional Anger cameras.

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

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

Sensitivity degradation of an anger camera operated in SPECT-like mode under the influence of a strong external magnetic field

The purpose of this work was to experimentally determine the degradation in sensitivity of an Anger camera rotated in SPECT-like orbits around the transverse and sagittal planes of the magnetic field produced by a conventional, dual coil, 1T electromagnet. A 74 photomultiplier Siemens Basicam Anger camera with a 29cm radius crystal and an Isotrak 35cm diameter, 46MBq (1.25mCi), Co-57 disk source attached to a low energy general purpose collimator, were used for all measurements. A custom made, air-cooled, dual coil, 1T electromagnet was used to produce the external magnetic field. A map of the magnetic field was obtained by taking intensity measurements around the sagittal and transverse planes of the magnet. Camera sensitivity – defined as the measured count rate for a given activity of a radionuclide in a defined geometry – was first measured around the transverse plane at angles of 0°, 90°, and 270°, with, and without, the magnetic field present. At each angle, three 30min measurements were made and the average count rate was calculated. A similar protocol was used for measurements upon rotation in the sagittal plane: counts per 30min interval were measured for 20 angles, with a 15° increment between measurements. Camera sensitivity as a function of field strength was also determined by collecting counts over 30min intervals at a fixed angle (90°) with magnet currents of 0.00A, 2.65A, and 5.30A. In the transverse plane, at 0° under a field intensity of 21mT, the loss in sensitivity was 18.14%, at 90° (B=37mT) the loss was 30.5%, and at 270° (B=38mT) the loss was 34.9%. Thus for rotation in the transverse plane, the sensitivity is monotonically reduced with an increase in field intensity. On rotation in the sagittal plane, sensitivity degradation ranged between 50.3% at a 22° angle, and 59.1% at 315°. Broad sensitivity peaks were observed at 105° and 195°, with minima at 60°, 135°, and 260°, consistent with our theoretical predictions, as well as previously reported measurements. In this work, the sensitivity variations of a conventional Anger camera rotated in SPECT-like orbits around a conventional dual solenoid electromagnet were measured. Sensitivity variations were studied upon rotations in the transverse and sagittal planes of the magnet. Measured sensitivity losses upon rotation in the transverse plane ranged between 18% and 35%; those in the sagittal plane ranged between 51% and 59%. Upon rotation in the transverse plane, the camera sensitivity is monotonically reduced with an increase in B field intensity. Upon rotation in the sagittal plane, cyclic variations with an angular period of approximately 90° were observed, consistent with theoretical considerations and previously published work.

Optimal design of anger camera for bremsstrahlung imaging: monte carlo evaluation.

A conventional Anger camera is not adapted to bremsstrahlung imaging and, as a result, even using a reduced energy acquisition window, geometric x-rays represent <15% of the recorded events. This increases noise, limits the contrast, and reduces the quantification accuracy. Monte Carlo (MC) simulations of energy spectra showed that a camera based on a 30-mm-thick BGO crystal and equipped with a high energy pinhole collimator is well-adapted to bremsstrahlung imaging. The total scatter contamination is reduced by a factor 10 versus a conventional NaI camera equipped with a high energy parallel hole collimator enabling acquisition using an extended energy window ranging from 50 to 350 keV. By using the recorded event energy in the reconstruction method, shorter acquisition time and reduced orbit range will be usable allowing the design of a simplified mobile gantry. This is more convenient for use in a busy catheterization room. After injecting a safe activity, a fast single photon emission computed tomography could be performed without moving the catheter tip in order to assess the liver dosimetry and estimate the additional safe activity that could still be injected. Further long running time MC simulations of realistic acquisitions will allow assessing the quantification capability of such system. Simultaneously, a dedicated bremsstrahlung prototype camera reusing PMT–BGO blocks coming from a retired PET system is currently under design for further evaluation.

Factors affecting the myocardial activity acquired during exercise SPECT with a high-sensitivity cardiac CZT camera as compared with conventional Anger camera

Injected doses are difficult to optimize for exercise SPECT since they depend on the myocardial fraction of injected activity (MFI) that is detected by the camera. The aim of this study was to analyse the factors affecting MFI determined using a cardiac CZT camera as compared with those determined using conventional Anger cameras. Factors affecting MFI were determined and compared in patients who had consecutive exercise SPECT acquisitions with (201)Tl (84 patients) or (99m)Tc-sestamibi (87 patients) with an Anger or a CZT camera. A predictive model was validated in a group of patients routinely referred for (201)Tl (78 patients) or (99m)Tc-sestamibi (80 patients) exercise CZT SPECT. The predictive model involved: (1) camera type, adjusted mean MFI being ninefold higher for CZT than for Anger SPECT, (2) tracer type, adjusted mean MFI being twofold higher for (201)Tl than for (99m)Tc-sestamibi, and (3) logarithm of body weight. The CZT SPECT model led to a +1 ± 26% error in the prediction of the actual MFI from the validation group. The mean MFI values estimated for CZT SPECT were more than twofold higher in patients with a body weight of 60 kg than in patients with a body weight of 120 kg (15.9 and 6.8 ppm for (99m)Tc-sestamibi and 30.5 and 13.1ppm for (201)Tl, respectively), and for a 14-min acquisition of up to one million myocardial counts, the corresponding injected activities were only 80 and 186 MBq for (99m)Tc-sestamibi and 39 and 91 MBq for (201)Tl, respectively. Myocardial activities acquired during exercise CZT SPECT are strongly influenced by body weight and tracer type, and are dramatically higher than those obtained using an Anger camera, allowing very low-dose protocols to be planned, especially for (99m)Tc-sestamibi and in non-obese subjects.