Two algorithms for medical image processing are discussed: CAVITY DETECTOR, which solves the segm... more Two algorithms for medical image processing are discussed: CAVITY DETECTOR, which solves the segmentation problem of regions which are not completely surrounded by walls and EDGMENTATION, which is used for (i) preprocessing before segmentation, (ii) boundary refinement before edge detection, (iii) segmentation based on a modified split-and-merge approach, and (iiii) data reduction. In this paper, we describe the principles of the algorithms and illustrate their generic properties by discussing the results of applications in 2-D and 3-D cardiac MRI and 3-D and 4-D cardiac SPECT.
European Journal of Nuclear Medicine and Molecular Imaging, 2007
Purpose Low sensitivity can become a major problem when very small pinholes are used in SPECT ima... more Purpose Low sensitivity can become a major problem when very small pinholes are used in SPECT imaging. Although a larger pinhole aperture will improve the sensitivity, this will be at the cost of the spatial resolution. With a view to improving the resolution–sensitivity trade-off, this paper explores an iterative reconstruction algorithm that models the pinhole aperture based on multi-ray projections. Methods This new implementation was validated using simulated data and phantom experiments. Two approaches were investigated. Firstly, the pinhole aperture was modelled in both the forward and the back projector. Secondly, the dual matrix implementation was investigated by modelling the pinhole aperture only in the forward projector. The systematic error, the full-width at half-maximum (FWHM) and the statistical error were quantified using the simulated data. Experimental phantom data were acquired for visual comparison with the reconstructions obtained from the simulated data. Results For a predefined number of iterations, the systematic error, the FWHM and the statistical error could be decreased when the pinhole aperture was modelled during iterative reconstruction. For a fixed, predefined statistical error of ±10%, smaller systematic errors and smaller FWHM were obtained when modelling the pinhole opening. When the dual matrix implementation was used, equivalent results could be obtained as when modelling the pinhole opening in both the forward and the back projector. Conclusion The multi-ray method to accomplish resolution recovery during the reconstruction of pinhole SPECT projection images offers a better trade-off between spatial resolution and noise compared with a reconstruction which does not model the pinhole aperture.
European Journal of Nuclear Medicine and Molecular Imaging, 2003
Reducing the acquisition time of whole-body fluorine-18 fluorodeoxyglucose positron emission tomo... more Reducing the acquisition time of whole-body fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) (corrected for attenuation) is of major importance in clinical practice. With the introduction of lutetium oxyorthosilicate (LSO), the acquisition time can be dramatically reduced, provided that patients are injected with larger amounts of tracer and/or the system is operated in 3D mode. The aim of this study was to determine the optimal dose of 18F-FDG required in order to achieve good-to-excellent image quality when a "3-min emission, 2-min transmission/bed position" protocol is used for an LSO PET camera. A total of 218 consecutive whole-body 18F-FDG PET studies were evaluated retrospectively. After excluding patients with liver metastases, hyperglycaemia and paravenous injections, the final study population consisted of 186 subjects (112 men, 74 women, age 59±15 years). Patients were injected with an activity of 18F-FDG ranging from 2.23 to 15.21 MBq/kg. Whole-body images corrected for attenuation (3 min emission, 2 min transmission/bed position) were acquired with an LSO PET camera (Ecat Accel,Siemens) 60 min after tracer administration. Patients were positioned with their arms along the body. Image reconstruction was done iteratively and a post-reconstruction filter was applied. Image quality was scored visually by two independent observers using a five-point scoring scale (poor, reasonable, good, very good, excellent). In addition, the coefficient of variability (COV) was measured in a region of interest over the liver in order to quantify noise. Of the images obtained in 118 patients injected with ≥8 MBq/kg 18F-FDG, 92% and 90% were classified as good, very good or excellent by observer 1 and observer 2, respectively. The COV averaged 10.63%±3.19% for doses ≥8 MBq/kg and 16.46%±5.14% for doses 18F-FDG dose of ≥8 MBq/kg results in images of good to excellent quality in the vast majority of patients when using an LSO PET camera and applying a 3-min emission, 2-min transmission/bed position acquisition protocol. At lower doses, a rapid decline in image quality and increasing noise are observed. Alternative protocols should be adopted in order to compensate for the loss in image quality when doses
European Journal of Nuclear Medicine and Molecular Imaging, 2006
Purpose Cell therapy using bone marrow mesenchymal stem cells (BMSCs) shows promise in the treatm... more Purpose Cell therapy using bone marrow mesenchymal stem cells (BMSCs) shows promise in the treatment of myocardial infarction (MI) but accurate cell delivery within MI areas remains critical. In the present study, we tested the feasibility of in vivo pinhole SPECT imaging for monitoring the sites of intramyocardial implanted BMSCs in relation to targeted MI areas in rats. Methods BMSCs were labelled with 111In-oxine and injected within the fibrotic areas of 3-month-old MI in ten rats. Two days later, dual 111In/99mTc-sestamibi pinhole SPECT was recorded for localisation of 111In-BMSCs on a 15-segment left ventricular (LV) division. Additional 99mTc-sestamibi pinhole SPECT had been performed 1 month earlier and on the day before transplantation. In vitro counting on histological sections was used to validate the pinhole SPECT determination of 111In-BMSC activity within LV segments. Results The underperfused MI area (segments with 99mTc-sestamibi SPECT study recorded at 1 month (4.6±1.9 segments) and at 1 day (4.7±2.3 segments) before transplantation. 111In-BMSCs were detected by dual-energy SPECT in 56 segments: 33 (59%) were underperfused MI segments but 23 (41%) were not (14 adjacent and nine remote segments). Finally, 111In-labelled BMSCs were not detected in 14 out of the 47 (30%) underperfused MI segments. Conclusion When BMSCs are injected within MI areas in rats, sites of early cell retention do not always match the targeted MI areas. The dual-energy pinhole SPECT technique may be used for monitoring the sites of early retention of implanted BMSCs and the data obtained may have critical importance when analysing the effects of cardiac cell therapy.
Purpose Overexpression of the epidermal growth factor receptor (EGFR) occurs with high incidence ... more Purpose Overexpression of the epidermal growth factor receptor (EGFR) occurs with high incidence in various carcinomas. The oncogenic expression of the receptor has been exploited for immunoglobulin-based diagnostics and therapeutics. We describe the use of a llama single-domain antibody fragment, termed Nanobody®, for the in vivo radioimmunodetection of EGFR overexpressing tumors using single photon emission computed tomography (SPECT) in mice. Methods Fluorescence-activated cell sorting (FACS) analysis was performed to evaluate the specificity and selectivity of 8B6 Nanobody to bind EGFR on EGFR overexpressing cells. The Nanobody was then labeled with 99mTc via its C-terminal histidine tail. Uptake in normal organs and tissues was assessed by ex vivo analysis. In vivo tumor targeting of 99mTc-8B6 Nanobody was evaluated via pinhole SPECT in mice bearing xenografts of tumor cells with either high (A431) or moderate (DU145) overexpression of EGFR. Results FACS analysis indicated that the 8B6 Nanobody only recognizes cells overexpressing EGFR. In vivo blood clearance of 99mTc-8B6 Nanobody is relatively fast (half-life, 1.5 h) and mainly via the kidneys. At 3 h postinjection, total kidney accumulation is high (46.6 ± 0.9%IA) compared to total liver uptake (18.9 ± 0.6%IA). Pinhole SPECT imaging of mice bearing A431 xenografts showed higher average tumor uptake (5.2 ± 0.5%IA/cm3) of 99mTc-8B6 Nanobody compared to DU145 xenografts (1.8 ± 0.3%IA/cm3, p Conclusion The EGFR-binding Nanobody investigated in this study shows high specificity and selectivity towards EGFR overexpressing cells. Pinhole SPECT analysis with 99mTc-8B6 Nanobody enabled in vivo discrimination between tumors with high and moderate EGFR overexpression. The favorable biodistribution further corroborates the suitability of Nanobodies for in vivo tumor imaging.
Background Tetrofosmin gated single photon emission computed tomography (SPECT) allows simultaneo... more Background Tetrofosmin gated single photon emission computed tomography (SPECT) allows simultaneous assessment of regional myocardial perfusion, global and regional left ventricular function, and function at rest and during pharmacologic intervention. SPECT with fatty acid analogues, such as β-methyl-iodophenyl-pentadecanoic acid (BMIPP), can be used to monitor metabolic changes induced by myocardial ischemia. In this work, the results of both studies obtained in patients with recent myocardial infarction are integrated. Methods Twenty patients underwent tetrofosmin and BMIPP scintigraphy with a 3-head camera. Two consecutive tetrofosmin gated SPECT acquisitions were performed 60 minutes after administration of technetium-99m tetrofosmin (925 MBq) at rest (3×20 stops of 9 s; matrix 64×64 over 360°. One acquisition was made at rest, and the second was made during dobutamine infusion (10 μg/kg/min). Regional functional abnormalities were quantified and expressed as wall thickening severity (WTsev) in arbitrary units. Left ventricular ejection fraction and volumes were assessed with the Cedars Sinai algorithm. BMIPP imaging started 20 minutes after iodine 123-BMIPP (150 MBq) administration at rest (3×32 stops of 60 s; matrix 64×64 over 360°; medium energy collimators). Tracer uptake was scored according to a 25-segment model. Results Sixteen of 18 patients had regional functional abnormalities at baseline (average WTsev 13.7 units). The WTsev score at baseline correlated well with the degree of residual perfusion. During dobutamine infusion, WTsev did not change (from 23.4 to 23.6 units) in 5 patients; it decreased (from 16.1 to 5.9 units) in 11 patients; and it increased (from 13.0 to 22.3 units) in 3 patients. An increase or decrease in WTsev during dobutamine infusion was associated with the presence of a considerable amount of BMIPP mismatched myocardium, whereas no change in WTsev was preferentially associated with a BMIPP matched pattern and perfusion defects with a higher severity score. Conclusion Immediately after infarction, the severity of regional dysfunction at rest correlated well with the perfusion defect severity. Improvement in regional function during dobutamine administration is associated with less severe perfusion defects and a considerable amount of BMIPP mismatched myocardium, both suggesting viability.
European Journal of Nuclear Medicine and Molecular Imaging, 1999
Electrocardiography gated single-photon emission tomography (gated SPET) allows the assessment of... more Electrocardiography gated single-photon emission tomography (gated SPET) allows the assessment of regional perfusion and function simultaneously and in full spatial congruency. In this study changes in global and regional left ventricular function in response to dobutamine infusion were assessed in ten healthy volunteers using sequential gated SPET myocardial perfusion acquisitions. Four consecutive gated SPET images were recorded 60 min after injection of 925 MBq technetium-99m tetrofosmin on a three-head camera equipped with focussing collimators. Two acquisitions were made at rest (baseline 1 and 2), and the third and fourth acquisitions were started 5 min after the beginning of the infusion of 5 and 10 µg kg–1 min–1 dobutamine, respectively. Systolic wall thickening (WT) was quantified using a method based on circumferential profile analysis. Left ventricular ejection fraction (LVEF) and volumes were calculated automatically using the Cedars-Sinai program. Nine of the ten subjects presented a definite increase in WT during dobutamine infusion. WT increased on average from 46%±14% at baseline to 71%±23% (range: 37%–106%; P–1 min–1 dobutamine infusion and to 85%±25% (range: 62%–123%; P–1 min–1) during 10 µg kg–1 min–1 dobutamine infusion. Apical segments showed the largest WT at baseline. The average WT response to dobutamine was similar for all parts of the myocardium. It is concluded that changes in WT induced by infusion of low-dose dobutamine can be assessed by sequential gated SPET myocardial perfusion studies. The ”stress gated SPET” protocol proposed in this study might be helpful to distinguish viable from scar tissue in patients with coronary artery disease, by demonstrating a preserved inotropic response in hypoperfused myocardium.
European Journal of Nuclear Medicine and Molecular Imaging, 2001
The distribution of 3-[123I]iodo-L-α-methyltyrosine (123I-3-IMT) in the tumour region of 21 patie... more The distribution of 3-[123I]iodo-L-α-methyltyrosine (123I-3-IMT) in the tumour region of 21 patients with clinically suspected recurrent squamous cell head and neck carcinoma was studied. Single-photon emission tomography (SPET) imaging of the head and neck region was performed 10 min after the injection of 130–170 MBq 123I-3-IMT using a dual-detector gamma camera. Images were interpreted visually and classified as positive or negative for recurrent disease. In addition, target to background ratios (T/B) were measured using semi-automated region of interest analysis. IMT-SPET results were compared with the data derived from clinicopathological follow-up. IMT-SPET detected recurrent disease in 14 of 15 patients (sensitivity 93%). T/B ratios ranged between 1.5 and 2.4 (mean 1.88). One patient with a small tumour (1.2 cm) had a false-negative result. This is attributed to the limited spatial resolution of the SPET system. Five of six patients were correctly diagnosed to be negative for tumour recurrence. T/B ratios ranged between 1.2 and 1.4 (mean 1.30). In one patient IMT-SPET was positive without evidence of recurrence based on clinicopathological follow up. This finding was probably due to uptake into inflammatory tissue. IMT-SPET appears to be a sensitive tool (93%) for the detection of recurrent head and neck squamous cell carcinoma. Further studies with 123I-3-IMT as a metabolic tracer for the detection of head and neck cancer recurrence using SPET are recommended.
European Journal of Nuclear Medicine and Molecular Imaging, 2005
Purpose The aim of this study was to investigate the intra-individual reproducibility of left ven... more Purpose The aim of this study was to investigate the intra-individual reproducibility of left ventricular volume and ejection fraction measurements in living rat using pinhole gated single-photon emission computed tomography (SPECT). Methods Eight normal male Wistar rats underwent four pinhole gated SPECT acquisitions over a 1-month period. Two pinhole gated myocardial perfusion SPECT studies were acquired at a 1-week interval after injecting the animals with 439±52 MBq of 99mTc-sestamibi. Subsequently, 1 week after the perfusion studies, two pinhole gated blood pool SPECT studies were acquired at a 1-week interval after in vivo labelling of the red blood cells using 520±49 MBq of 99mTc-pertechnetate. Pinhole gated SPECT acquisitions were done on a single-head gamma camera equipped with a pinhole collimator with a 3-mm opening and 165-mm focal length. Parameters of acquisition were as follows: 44 mm radius of rotation, 360° rotation using a circular orbit, 64 projections, 64×64 matrix, gating using 16 time frames and 22-min acquisition time. The projection data were reconstructed with a modified version of OSEM taking into account the pinhole geometry and incorporating a prior assumption about the temporal properties of gated SPECT studies to reduce noise. Left ventricular volumes and ejection fraction were measured using automatic quantification algorithms. Inter-study, inter-observer and intra-observer reproducibility was investigated. Results Pinhole gated myocardial perfusion and pinhole gated blood pool images were of high quality in all animals. No significant differences were observed between the repeated measurements. The pinhole gated myocardial perfusion SPECT studies indicated that differences between repeated measurements larger than 41 μl for end-diastolic volume, 17 μl for end-systolic volume and 3% for ejection fraction were significant. The pinhole gated blood pool SPECT studies indicated that differences between repeated measurements larger than 42 μl for end-diastolic volume, 38 μl for end-systolic volume and 5% for ejection fraction were significant. In addition to the reproducibility measures, the accuracy of volume measurements in pinhole gated blood pool SPECT was confirmed by a phantom study. Excellent correlations were observed between the measured volumes and the actual phantom volumes. Conclusion Pinhole gated SPECT is an accurate and reproducible technique for cardiac studies of small animals. Because this technique is non-invasive, the same animal can be imaged repetitively, allowing follow-up studies.
The paper investigates the geometric calibration of a rotating gamma camera for pinhole (PH) sing... more The paper investigates the geometric calibration of a rotating gamma camera for pinhole (PH) single photon emission computed tomography (SPECT) imaging. Most calibration methods previously applied in PH-SPECT assume that the motion of the camera around the object belongs to a well-defined class described by a small number of geometric parameters, for instance seven parameters for a circular acquisition with a single pinhole camera. The proposed new method refines an initial parametric calibration by applying to each position of the camera a rigid body transformation that is determined to improve the fit between the measured and calculated projections of the calibration sources. A stable estimate of this transformation can be obtained with only three calibration sources by linearizing the equations around the position estimated by the initial parametric calibration. The performance of the method is illustrated using simulated and measured micro-SPECT data.
European Journal of Nuclear Medicine and Molecular Imaging, 2008
Introduction In vivo bioluminescence imaging (BLI) is a promising technique for non-invasive tumo... more Introduction In vivo bioluminescence imaging (BLI) is a promising technique for non-invasive tumour imaging. d-luciferin can be administrated intraperitonealy or intravenously. This will influence its availability and, therefore, the bioluminescent signal. The aim of this study is to compare the repeatability of BLI measurement after IV versus IP administration of d-luciferin and assess the correlation between photon emission and histological cell count both in vitro and in vivo. Materials and methods Fluc-positive R1M cells were subcutaneously inoculated in nu/nu mice. Dynamic BLI was performed after IV or IP administration of d-luciferin. Maximal photon emission (PEmax) was calculated. For repeatability assessment, every acquisition was repeated after 4 h and analysed using Bland–Altman method. A second group of animals was serially imaged, alternating IV and IP administration up to 21 days. When mice were killed, PEmax after IV administration was correlated with histological cell number. Results The coefficients of repeatability were 80.2% (IV) versus 95.0% (IP). Time-to-peak is shorter, and its variance lower for IV (p max was 5.6 times higher for IV. A trend was observed towards lower photon emission per cell in larger tumours. Conclusion IV administration offers better repeatability and better sensitivity when compared to IP. In larger tumours, multiple factors may contribute to underestimation of tumour burden. It might, therefore, be beneficial to test novel therapeutics on small tumours to enable an accurate evaluation of tumour burden.
European Journal of Nuclear Medicine and Molecular Imaging, 2008
Purpose The aim of this study was to improve the uniformity of the axial spatial resolution and s... more Purpose The aim of this study was to improve the uniformity of the axial spatial resolution and sensitivity in pinhole single-photon emission computed tomography (SPECT) and to extend the axial field of view, by using a dedicated three-pinhole collimator. Methods A rectangular tungsten plate with three pinhole apertures of 1.5 mm diameter was designed to image a cylindrical field of view of 55 mm diameter and 160 mm axial length using a clinical gamma camera. To evaluate the non-uniformity of spatial resolution and noise, a multiple-disk phantom was built. The phantom was filled with Tc-99m, and data were acquired using a circular orbit and reconstructed with a dedicated iterative reconstruction algorithm. The axial spatial resolution together with the noise was measured in each disk. These measurements were compared to a single-pinhole system using an identical acquisition geometry and reconstruction. Results At the central slice, a spatial resolution of 2.7 mm was observed for both the three-pinhole and single-pinhole geometries. At 17.5 mm from the central slice, the axial spatial resolution deteriorated to 10.3 mm when using a single pinhole, while the spatial resolution remained 2.7 mm for the three-pinhole system. In the central slice, 19% noise was observed for both geometries. At 31.5 mm from this central slice, the noise remained 19% for the three-pinhole geometry, while it increased to 32% using a single pinhole. Conclusion The presented three-pinhole collimator improves the uniformity of the axial spatial resolution and sensitivity in pinhole SPECT and consequently extends the axial field of view, a requirement for whole-body small-animal imaging.
European Journal of Nuclear Medicine and Molecular Imaging, 1997
Cardiofocal collimators (CFCs) are more sensitive than parallel-hole collimators (PHCs) of the sa... more Cardiofocal collimators (CFCs) are more sensitive than parallel-hole collimators (PHCs) of the same resolution because the rays converge in the centre of the field of view. After reconstruction a useful field of view with a 10 cm radius in which both sensitivity and resolution are homogeneous is obtained. In this article the feasibility and accuracy of gated single-photon emission tomographic (gated SPET) myocardial perfusion imaging using a triple-head camera equipped with CFC, is evaluated. Twenty patients with a history of myocardial infarction were studied. SPET myocardial perfusion images, gated in eight time bins, were acquired in a random sequence with a PHC and a CFC for each patient. Imaging was started 60 min after the injection of 925 MBq of technetium-99m tetrofosmin at rest. Ninety-six projections over 360° were acquired, with 32 stops of 40 s for the PHC and 20 s for the CFC in order to obtain similar count densities. The extent (EXT) and severity (SEV) of perfusion defects were quantified on polar maps using the non-gated data. Left ventricular volumes [end-diastolic volume (EDV), end-systolic volume (ESV)] and ejection fraction (LVEF) were calculated from gated data using the Cedars-Sinai program. In 17 of 20 patients the complete left ventricle was positioned within the useful field of view of the CFC. The results in respect of perfusion, volumes and ejection fraction were almost identical to those obtained with the PHC. The mean difference±SD between the CFC and the PHC was −2.30±7.16 (% of LV area) for EXT, −0.48±2.90 for SEV (arbitrary units), −1,50±5.25 (ml) for EDV and 0.53±4.10 (%) for LVEF. The largest differences in EXT and LV volumes were observed in patients in whom a part of the LV was not positioned within the useful field of view. We conclude that, for the majority of patients, identical information with regard to both perfusion and function can be derived from gated SPET myocardial perfusion studies obtained with PHCs or with CFCs. Because of the greater sensitivity, however, a much shorter acquisition time is required with CFCs.
Background Two different algorithms, which are fast and automatic and which operate in 3-dimensio... more Background Two different algorithms, which are fast and automatic and which operate in 3-dimensional space, were compared in the same group of patients to compute left ventricular ejection fraction (LVEF) and volumes from gated blood pool tomography. One method, developed at Cedars-Sinai Medical Center (CS), was dependent on surface detection, whereas the other method, developed at the Free University of Brussels (UB), used image segmentation. Methods and Results Gated blood pool tomograms were acquired in 92 consecutive patients after injection of 740 MBq of technetium 99m-labeled human serum albumin. After reconstruction and reorientation according to the left ventricular long axis, LVEF and left ventricular volumes were measured with the CS and UB algorithms. Measurements of LVEF were validated against planar radionuclide angiocardiography (PRNA) results. The success rates of the algorithms were 87% for CS and 97% for UB. Agreement between LVEF measured with CS and UB (LVEFCS = 0.91 · LVEFUB - 0.85; r = 0.87) and between LVEF measured with CS and PRNA (LVEFCS = 1.04 · LVEFPRNA - 4.75; r = 0.80) and UB and PRNA (LVEFUB = 0.98 · LVEFPRNA + 4.42; r = 0.82) was good. For left ventricular volumes, linear regression analysis showed good correlation between both methods with regard to end-diastolic volumes (r = 0.81) and end-systolic volumes (r = 0.91). On average, end-diastolic volumes were similar and end-systolic volumes were slightly higher with CS than with UB. Consequently, significantly lower LVEFs were observed with CS than with UB. Conclusions Good correlation was observed between CS and UB for both left ventricular volumes and ejection fraction. In addition, measurements of LVEF obtained with both algorithms correlated fairly well with those obtained from conventional PRNA over a wide range of values.
European Journal of Nuclear Medicine and Molecular Imaging, 2000
Viability studies are often performed in patients receiving beta-blocking agents. However, the in... more Viability studies are often performed in patients receiving beta-blocking agents. However, the intake of beta-blocking agents could influence the identification of viable myocardium when low-dose dobutamine is used to demonstrate inotropic reserve. The aim of this study was to quantify the effect of beta-blockade on global and regional left ventricular function in healthy volunteers using low-dose dobutamine gated single-photon emission tomographic (SPET) myocardial perfusion scintigraphy. Ten subjects were studied once ”on” and once ”off” beta-blocker therapy (metoprolol succinate, 100 mg day–1). On each occasion four consecutive gated SPET acquisitions (of 7 min duration) were recorded after injection of 925 MBq technetium-99m tetrofosmin on a triple-headed camera equipped with focussing (Cardiofocal) collimators. Acquisitions were made at rest (baseline 1 and 2) and 5 min after the beginning of the infusion of 5 and 10 µg kg–1 min–1 dobutamine. Wall thickening (WT) was quantified using a method based on circumferential profile analysis. Left ventricular ejection fraction (LVEF) was obtained using the Cedars-Sinai algorithm. Blood pressure (BP) and heart rate (HR) were recorded at the end of each acquisition. At baseline LVEF, WT and systolic BP values under beta-blockade were not significantly different from those obtained in the non-beta-blocked state. The mean HR and diastolic BP at baseline were lower under beta-blockade. Dobutamine administration (at 5 and 10 µg kg–1 min–1) induced a significant increase in WT, LVEF and systolic BP in all subjects both on and off beta-blockade. The increases in WT, LVEF and systolic BP in the beta-blocked state were less pronounced but not significantly different. HR increased significantly at 10 µg kg–1 min–1 dobutamine without beta-blocker administration, while no increase in HR was observed in the beta-blocked state. Beta-blocker therapy in healthy subjects attenuates the inotropic and chronotropic myocardial response to low-dose dobutamine. At doses of 5 and 10 µg kg–1 min–1 dobutamine, however, significant increases in global and regional left ventricular function can still be measured using consecutive gated SPET myocardial perfusion scintigraphy acquisitions even under beta-blocker therapy.
European Journal of Nuclear Medicine and Molecular Imaging, 2000
Pinhole single-photon emission tomography (SPET) has been proposed to improve the trade-off betwe... more Pinhole single-photon emission tomography (SPET) has been proposed to improve the trade-off between sensitivity and resolution for small organs located in close proximity to the pinhole aperture. This technique is hampered by artefacts in the non-central slices. These artefacts are caused by truncation and by the fact that the pinhole SPET data collected in a circular orbit do not contain sufficient information for exact reconstruction. The ordered subsets expectation maximization (OS-EM) algorithm is a potential solution to these problems. In this study a three-dimensional OS-EM algorithm was implemented for data acquired on a single-head gamma camera equipped with a pinhole collimator (PH OS-EM). The aim of this study was to compare the PH OS-EM algorithm with the filtered back-projection algorithm of Feldkamp, Davis and Kress (FDK)and with the conventional parallel-hole geometry as a whole,using a line source phantom, Picker’s thyroid phantom and a phantom mimicking the human cervical column. Correction for the angular dependency of the sensitivity in the pinhole geometrywas based on a uniform flood acquisition. The projection data were shifted according to the measured centre of rotation. No correction was made for attenuation, scatter or distance-dependent camera resolution. The resolution measured with the line source phantom showed a significant improvement with PH OS-EM as compared with FDK, especially in the axial direction. Using Picker’s thyroid phantom, one iteration with eight subsets was sufficient to obtain images with similar noise levels in uniform regions of interest to those obtained with the FDK algorithm. With these parameters the reconstruction time was 2.5 times longer than for the FDK method. Furthermore, there was a reduction in the artefacts caused by the circular orbit SPET acquisition. The images obtained from the phantom mimicking the human cervical column indicated that the improvement in image quality with PH OS-EM is relevant for future clinical useand that the improvements obtained using the OS-EM algorithm are more significant for the pinhole geometry than for the conventional parallel-hole geometry. We conclude that PH OS-EM is a practical and promising alternative for pinhole SPET reconstruction.
Two algorithms for medical image processing are discussed: CAVITY DETECTOR, which solves the segm... more Two algorithms for medical image processing are discussed: CAVITY DETECTOR, which solves the segmentation problem of regions which are not completely surrounded by walls and EDGMENTATION, which is used for (i) preprocessing before segmentation, (ii) boundary refinement before edge detection, (iii) segmentation based on a modified split-and-merge approach, and (iiii) data reduction. In this paper, we describe the principles of the algorithms and illustrate their generic properties by discussing the results of applications in 2-D and 3-D cardiac MRI and 3-D and 4-D cardiac SPECT.
European Journal of Nuclear Medicine and Molecular Imaging, 2007
Purpose Low sensitivity can become a major problem when very small pinholes are used in SPECT ima... more Purpose Low sensitivity can become a major problem when very small pinholes are used in SPECT imaging. Although a larger pinhole aperture will improve the sensitivity, this will be at the cost of the spatial resolution. With a view to improving the resolution–sensitivity trade-off, this paper explores an iterative reconstruction algorithm that models the pinhole aperture based on multi-ray projections. Methods This new implementation was validated using simulated data and phantom experiments. Two approaches were investigated. Firstly, the pinhole aperture was modelled in both the forward and the back projector. Secondly, the dual matrix implementation was investigated by modelling the pinhole aperture only in the forward projector. The systematic error, the full-width at half-maximum (FWHM) and the statistical error were quantified using the simulated data. Experimental phantom data were acquired for visual comparison with the reconstructions obtained from the simulated data. Results For a predefined number of iterations, the systematic error, the FWHM and the statistical error could be decreased when the pinhole aperture was modelled during iterative reconstruction. For a fixed, predefined statistical error of ±10%, smaller systematic errors and smaller FWHM were obtained when modelling the pinhole opening. When the dual matrix implementation was used, equivalent results could be obtained as when modelling the pinhole opening in both the forward and the back projector. Conclusion The multi-ray method to accomplish resolution recovery during the reconstruction of pinhole SPECT projection images offers a better trade-off between spatial resolution and noise compared with a reconstruction which does not model the pinhole aperture.
European Journal of Nuclear Medicine and Molecular Imaging, 2003
Reducing the acquisition time of whole-body fluorine-18 fluorodeoxyglucose positron emission tomo... more Reducing the acquisition time of whole-body fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) (corrected for attenuation) is of major importance in clinical practice. With the introduction of lutetium oxyorthosilicate (LSO), the acquisition time can be dramatically reduced, provided that patients are injected with larger amounts of tracer and/or the system is operated in 3D mode. The aim of this study was to determine the optimal dose of 18F-FDG required in order to achieve good-to-excellent image quality when a "3-min emission, 2-min transmission/bed position" protocol is used for an LSO PET camera. A total of 218 consecutive whole-body 18F-FDG PET studies were evaluated retrospectively. After excluding patients with liver metastases, hyperglycaemia and paravenous injections, the final study population consisted of 186 subjects (112 men, 74 women, age 59±15 years). Patients were injected with an activity of 18F-FDG ranging from 2.23 to 15.21 MBq/kg. Whole-body images corrected for attenuation (3 min emission, 2 min transmission/bed position) were acquired with an LSO PET camera (Ecat Accel,Siemens) 60 min after tracer administration. Patients were positioned with their arms along the body. Image reconstruction was done iteratively and a post-reconstruction filter was applied. Image quality was scored visually by two independent observers using a five-point scoring scale (poor, reasonable, good, very good, excellent). In addition, the coefficient of variability (COV) was measured in a region of interest over the liver in order to quantify noise. Of the images obtained in 118 patients injected with ≥8 MBq/kg 18F-FDG, 92% and 90% were classified as good, very good or excellent by observer 1 and observer 2, respectively. The COV averaged 10.63%±3.19% for doses ≥8 MBq/kg and 16.46%±5.14% for doses 18F-FDG dose of ≥8 MBq/kg results in images of good to excellent quality in the vast majority of patients when using an LSO PET camera and applying a 3-min emission, 2-min transmission/bed position acquisition protocol. At lower doses, a rapid decline in image quality and increasing noise are observed. Alternative protocols should be adopted in order to compensate for the loss in image quality when doses
European Journal of Nuclear Medicine and Molecular Imaging, 2006
Purpose Cell therapy using bone marrow mesenchymal stem cells (BMSCs) shows promise in the treatm... more Purpose Cell therapy using bone marrow mesenchymal stem cells (BMSCs) shows promise in the treatment of myocardial infarction (MI) but accurate cell delivery within MI areas remains critical. In the present study, we tested the feasibility of in vivo pinhole SPECT imaging for monitoring the sites of intramyocardial implanted BMSCs in relation to targeted MI areas in rats. Methods BMSCs were labelled with 111In-oxine and injected within the fibrotic areas of 3-month-old MI in ten rats. Two days later, dual 111In/99mTc-sestamibi pinhole SPECT was recorded for localisation of 111In-BMSCs on a 15-segment left ventricular (LV) division. Additional 99mTc-sestamibi pinhole SPECT had been performed 1 month earlier and on the day before transplantation. In vitro counting on histological sections was used to validate the pinhole SPECT determination of 111In-BMSC activity within LV segments. Results The underperfused MI area (segments with 99mTc-sestamibi SPECT study recorded at 1 month (4.6±1.9 segments) and at 1 day (4.7±2.3 segments) before transplantation. 111In-BMSCs were detected by dual-energy SPECT in 56 segments: 33 (59%) were underperfused MI segments but 23 (41%) were not (14 adjacent and nine remote segments). Finally, 111In-labelled BMSCs were not detected in 14 out of the 47 (30%) underperfused MI segments. Conclusion When BMSCs are injected within MI areas in rats, sites of early cell retention do not always match the targeted MI areas. The dual-energy pinhole SPECT technique may be used for monitoring the sites of early retention of implanted BMSCs and the data obtained may have critical importance when analysing the effects of cardiac cell therapy.
Purpose Overexpression of the epidermal growth factor receptor (EGFR) occurs with high incidence ... more Purpose Overexpression of the epidermal growth factor receptor (EGFR) occurs with high incidence in various carcinomas. The oncogenic expression of the receptor has been exploited for immunoglobulin-based diagnostics and therapeutics. We describe the use of a llama single-domain antibody fragment, termed Nanobody®, for the in vivo radioimmunodetection of EGFR overexpressing tumors using single photon emission computed tomography (SPECT) in mice. Methods Fluorescence-activated cell sorting (FACS) analysis was performed to evaluate the specificity and selectivity of 8B6 Nanobody to bind EGFR on EGFR overexpressing cells. The Nanobody was then labeled with 99mTc via its C-terminal histidine tail. Uptake in normal organs and tissues was assessed by ex vivo analysis. In vivo tumor targeting of 99mTc-8B6 Nanobody was evaluated via pinhole SPECT in mice bearing xenografts of tumor cells with either high (A431) or moderate (DU145) overexpression of EGFR. Results FACS analysis indicated that the 8B6 Nanobody only recognizes cells overexpressing EGFR. In vivo blood clearance of 99mTc-8B6 Nanobody is relatively fast (half-life, 1.5 h) and mainly via the kidneys. At 3 h postinjection, total kidney accumulation is high (46.6 ± 0.9%IA) compared to total liver uptake (18.9 ± 0.6%IA). Pinhole SPECT imaging of mice bearing A431 xenografts showed higher average tumor uptake (5.2 ± 0.5%IA/cm3) of 99mTc-8B6 Nanobody compared to DU145 xenografts (1.8 ± 0.3%IA/cm3, p Conclusion The EGFR-binding Nanobody investigated in this study shows high specificity and selectivity towards EGFR overexpressing cells. Pinhole SPECT analysis with 99mTc-8B6 Nanobody enabled in vivo discrimination between tumors with high and moderate EGFR overexpression. The favorable biodistribution further corroborates the suitability of Nanobodies for in vivo tumor imaging.
Background Tetrofosmin gated single photon emission computed tomography (SPECT) allows simultaneo... more Background Tetrofosmin gated single photon emission computed tomography (SPECT) allows simultaneous assessment of regional myocardial perfusion, global and regional left ventricular function, and function at rest and during pharmacologic intervention. SPECT with fatty acid analogues, such as β-methyl-iodophenyl-pentadecanoic acid (BMIPP), can be used to monitor metabolic changes induced by myocardial ischemia. In this work, the results of both studies obtained in patients with recent myocardial infarction are integrated. Methods Twenty patients underwent tetrofosmin and BMIPP scintigraphy with a 3-head camera. Two consecutive tetrofosmin gated SPECT acquisitions were performed 60 minutes after administration of technetium-99m tetrofosmin (925 MBq) at rest (3×20 stops of 9 s; matrix 64×64 over 360°. One acquisition was made at rest, and the second was made during dobutamine infusion (10 μg/kg/min). Regional functional abnormalities were quantified and expressed as wall thickening severity (WTsev) in arbitrary units. Left ventricular ejection fraction and volumes were assessed with the Cedars Sinai algorithm. BMIPP imaging started 20 minutes after iodine 123-BMIPP (150 MBq) administration at rest (3×32 stops of 60 s; matrix 64×64 over 360°; medium energy collimators). Tracer uptake was scored according to a 25-segment model. Results Sixteen of 18 patients had regional functional abnormalities at baseline (average WTsev 13.7 units). The WTsev score at baseline correlated well with the degree of residual perfusion. During dobutamine infusion, WTsev did not change (from 23.4 to 23.6 units) in 5 patients; it decreased (from 16.1 to 5.9 units) in 11 patients; and it increased (from 13.0 to 22.3 units) in 3 patients. An increase or decrease in WTsev during dobutamine infusion was associated with the presence of a considerable amount of BMIPP mismatched myocardium, whereas no change in WTsev was preferentially associated with a BMIPP matched pattern and perfusion defects with a higher severity score. Conclusion Immediately after infarction, the severity of regional dysfunction at rest correlated well with the perfusion defect severity. Improvement in regional function during dobutamine administration is associated with less severe perfusion defects and a considerable amount of BMIPP mismatched myocardium, both suggesting viability.
European Journal of Nuclear Medicine and Molecular Imaging, 1999
Electrocardiography gated single-photon emission tomography (gated SPET) allows the assessment of... more Electrocardiography gated single-photon emission tomography (gated SPET) allows the assessment of regional perfusion and function simultaneously and in full spatial congruency. In this study changes in global and regional left ventricular function in response to dobutamine infusion were assessed in ten healthy volunteers using sequential gated SPET myocardial perfusion acquisitions. Four consecutive gated SPET images were recorded 60 min after injection of 925 MBq technetium-99m tetrofosmin on a three-head camera equipped with focussing collimators. Two acquisitions were made at rest (baseline 1 and 2), and the third and fourth acquisitions were started 5 min after the beginning of the infusion of 5 and 10 µg kg–1 min–1 dobutamine, respectively. Systolic wall thickening (WT) was quantified using a method based on circumferential profile analysis. Left ventricular ejection fraction (LVEF) and volumes were calculated automatically using the Cedars-Sinai program. Nine of the ten subjects presented a definite increase in WT during dobutamine infusion. WT increased on average from 46%±14% at baseline to 71%±23% (range: 37%–106%; P–1 min–1 dobutamine infusion and to 85%±25% (range: 62%–123%; P–1 min–1) during 10 µg kg–1 min–1 dobutamine infusion. Apical segments showed the largest WT at baseline. The average WT response to dobutamine was similar for all parts of the myocardium. It is concluded that changes in WT induced by infusion of low-dose dobutamine can be assessed by sequential gated SPET myocardial perfusion studies. The ”stress gated SPET” protocol proposed in this study might be helpful to distinguish viable from scar tissue in patients with coronary artery disease, by demonstrating a preserved inotropic response in hypoperfused myocardium.
European Journal of Nuclear Medicine and Molecular Imaging, 2001
The distribution of 3-[123I]iodo-L-α-methyltyrosine (123I-3-IMT) in the tumour region of 21 patie... more The distribution of 3-[123I]iodo-L-α-methyltyrosine (123I-3-IMT) in the tumour region of 21 patients with clinically suspected recurrent squamous cell head and neck carcinoma was studied. Single-photon emission tomography (SPET) imaging of the head and neck region was performed 10 min after the injection of 130–170 MBq 123I-3-IMT using a dual-detector gamma camera. Images were interpreted visually and classified as positive or negative for recurrent disease. In addition, target to background ratios (T/B) were measured using semi-automated region of interest analysis. IMT-SPET results were compared with the data derived from clinicopathological follow-up. IMT-SPET detected recurrent disease in 14 of 15 patients (sensitivity 93%). T/B ratios ranged between 1.5 and 2.4 (mean 1.88). One patient with a small tumour (1.2 cm) had a false-negative result. This is attributed to the limited spatial resolution of the SPET system. Five of six patients were correctly diagnosed to be negative for tumour recurrence. T/B ratios ranged between 1.2 and 1.4 (mean 1.30). In one patient IMT-SPET was positive without evidence of recurrence based on clinicopathological follow up. This finding was probably due to uptake into inflammatory tissue. IMT-SPET appears to be a sensitive tool (93%) for the detection of recurrent head and neck squamous cell carcinoma. Further studies with 123I-3-IMT as a metabolic tracer for the detection of head and neck cancer recurrence using SPET are recommended.
European Journal of Nuclear Medicine and Molecular Imaging, 2005
Purpose The aim of this study was to investigate the intra-individual reproducibility of left ven... more Purpose The aim of this study was to investigate the intra-individual reproducibility of left ventricular volume and ejection fraction measurements in living rat using pinhole gated single-photon emission computed tomography (SPECT). Methods Eight normal male Wistar rats underwent four pinhole gated SPECT acquisitions over a 1-month period. Two pinhole gated myocardial perfusion SPECT studies were acquired at a 1-week interval after injecting the animals with 439±52 MBq of 99mTc-sestamibi. Subsequently, 1 week after the perfusion studies, two pinhole gated blood pool SPECT studies were acquired at a 1-week interval after in vivo labelling of the red blood cells using 520±49 MBq of 99mTc-pertechnetate. Pinhole gated SPECT acquisitions were done on a single-head gamma camera equipped with a pinhole collimator with a 3-mm opening and 165-mm focal length. Parameters of acquisition were as follows: 44 mm radius of rotation, 360° rotation using a circular orbit, 64 projections, 64×64 matrix, gating using 16 time frames and 22-min acquisition time. The projection data were reconstructed with a modified version of OSEM taking into account the pinhole geometry and incorporating a prior assumption about the temporal properties of gated SPECT studies to reduce noise. Left ventricular volumes and ejection fraction were measured using automatic quantification algorithms. Inter-study, inter-observer and intra-observer reproducibility was investigated. Results Pinhole gated myocardial perfusion and pinhole gated blood pool images were of high quality in all animals. No significant differences were observed between the repeated measurements. The pinhole gated myocardial perfusion SPECT studies indicated that differences between repeated measurements larger than 41 μl for end-diastolic volume, 17 μl for end-systolic volume and 3% for ejection fraction were significant. The pinhole gated blood pool SPECT studies indicated that differences between repeated measurements larger than 42 μl for end-diastolic volume, 38 μl for end-systolic volume and 5% for ejection fraction were significant. In addition to the reproducibility measures, the accuracy of volume measurements in pinhole gated blood pool SPECT was confirmed by a phantom study. Excellent correlations were observed between the measured volumes and the actual phantom volumes. Conclusion Pinhole gated SPECT is an accurate and reproducible technique for cardiac studies of small animals. Because this technique is non-invasive, the same animal can be imaged repetitively, allowing follow-up studies.
The paper investigates the geometric calibration of a rotating gamma camera for pinhole (PH) sing... more The paper investigates the geometric calibration of a rotating gamma camera for pinhole (PH) single photon emission computed tomography (SPECT) imaging. Most calibration methods previously applied in PH-SPECT assume that the motion of the camera around the object belongs to a well-defined class described by a small number of geometric parameters, for instance seven parameters for a circular acquisition with a single pinhole camera. The proposed new method refines an initial parametric calibration by applying to each position of the camera a rigid body transformation that is determined to improve the fit between the measured and calculated projections of the calibration sources. A stable estimate of this transformation can be obtained with only three calibration sources by linearizing the equations around the position estimated by the initial parametric calibration. The performance of the method is illustrated using simulated and measured micro-SPECT data.
European Journal of Nuclear Medicine and Molecular Imaging, 2008
Introduction In vivo bioluminescence imaging (BLI) is a promising technique for non-invasive tumo... more Introduction In vivo bioluminescence imaging (BLI) is a promising technique for non-invasive tumour imaging. d-luciferin can be administrated intraperitonealy or intravenously. This will influence its availability and, therefore, the bioluminescent signal. The aim of this study is to compare the repeatability of BLI measurement after IV versus IP administration of d-luciferin and assess the correlation between photon emission and histological cell count both in vitro and in vivo. Materials and methods Fluc-positive R1M cells were subcutaneously inoculated in nu/nu mice. Dynamic BLI was performed after IV or IP administration of d-luciferin. Maximal photon emission (PEmax) was calculated. For repeatability assessment, every acquisition was repeated after 4 h and analysed using Bland–Altman method. A second group of animals was serially imaged, alternating IV and IP administration up to 21 days. When mice were killed, PEmax after IV administration was correlated with histological cell number. Results The coefficients of repeatability were 80.2% (IV) versus 95.0% (IP). Time-to-peak is shorter, and its variance lower for IV (p max was 5.6 times higher for IV. A trend was observed towards lower photon emission per cell in larger tumours. Conclusion IV administration offers better repeatability and better sensitivity when compared to IP. In larger tumours, multiple factors may contribute to underestimation of tumour burden. It might, therefore, be beneficial to test novel therapeutics on small tumours to enable an accurate evaluation of tumour burden.
European Journal of Nuclear Medicine and Molecular Imaging, 2008
Purpose The aim of this study was to improve the uniformity of the axial spatial resolution and s... more Purpose The aim of this study was to improve the uniformity of the axial spatial resolution and sensitivity in pinhole single-photon emission computed tomography (SPECT) and to extend the axial field of view, by using a dedicated three-pinhole collimator. Methods A rectangular tungsten plate with three pinhole apertures of 1.5 mm diameter was designed to image a cylindrical field of view of 55 mm diameter and 160 mm axial length using a clinical gamma camera. To evaluate the non-uniformity of spatial resolution and noise, a multiple-disk phantom was built. The phantom was filled with Tc-99m, and data were acquired using a circular orbit and reconstructed with a dedicated iterative reconstruction algorithm. The axial spatial resolution together with the noise was measured in each disk. These measurements were compared to a single-pinhole system using an identical acquisition geometry and reconstruction. Results At the central slice, a spatial resolution of 2.7 mm was observed for both the three-pinhole and single-pinhole geometries. At 17.5 mm from the central slice, the axial spatial resolution deteriorated to 10.3 mm when using a single pinhole, while the spatial resolution remained 2.7 mm for the three-pinhole system. In the central slice, 19% noise was observed for both geometries. At 31.5 mm from this central slice, the noise remained 19% for the three-pinhole geometry, while it increased to 32% using a single pinhole. Conclusion The presented three-pinhole collimator improves the uniformity of the axial spatial resolution and sensitivity in pinhole SPECT and consequently extends the axial field of view, a requirement for whole-body small-animal imaging.
European Journal of Nuclear Medicine and Molecular Imaging, 1997
Cardiofocal collimators (CFCs) are more sensitive than parallel-hole collimators (PHCs) of the sa... more Cardiofocal collimators (CFCs) are more sensitive than parallel-hole collimators (PHCs) of the same resolution because the rays converge in the centre of the field of view. After reconstruction a useful field of view with a 10 cm radius in which both sensitivity and resolution are homogeneous is obtained. In this article the feasibility and accuracy of gated single-photon emission tomographic (gated SPET) myocardial perfusion imaging using a triple-head camera equipped with CFC, is evaluated. Twenty patients with a history of myocardial infarction were studied. SPET myocardial perfusion images, gated in eight time bins, were acquired in a random sequence with a PHC and a CFC for each patient. Imaging was started 60 min after the injection of 925 MBq of technetium-99m tetrofosmin at rest. Ninety-six projections over 360° were acquired, with 32 stops of 40 s for the PHC and 20 s for the CFC in order to obtain similar count densities. The extent (EXT) and severity (SEV) of perfusion defects were quantified on polar maps using the non-gated data. Left ventricular volumes [end-diastolic volume (EDV), end-systolic volume (ESV)] and ejection fraction (LVEF) were calculated from gated data using the Cedars-Sinai program. In 17 of 20 patients the complete left ventricle was positioned within the useful field of view of the CFC. The results in respect of perfusion, volumes and ejection fraction were almost identical to those obtained with the PHC. The mean difference±SD between the CFC and the PHC was −2.30±7.16 (% of LV area) for EXT, −0.48±2.90 for SEV (arbitrary units), −1,50±5.25 (ml) for EDV and 0.53±4.10 (%) for LVEF. The largest differences in EXT and LV volumes were observed in patients in whom a part of the LV was not positioned within the useful field of view. We conclude that, for the majority of patients, identical information with regard to both perfusion and function can be derived from gated SPET myocardial perfusion studies obtained with PHCs or with CFCs. Because of the greater sensitivity, however, a much shorter acquisition time is required with CFCs.
Background Two different algorithms, which are fast and automatic and which operate in 3-dimensio... more Background Two different algorithms, which are fast and automatic and which operate in 3-dimensional space, were compared in the same group of patients to compute left ventricular ejection fraction (LVEF) and volumes from gated blood pool tomography. One method, developed at Cedars-Sinai Medical Center (CS), was dependent on surface detection, whereas the other method, developed at the Free University of Brussels (UB), used image segmentation. Methods and Results Gated blood pool tomograms were acquired in 92 consecutive patients after injection of 740 MBq of technetium 99m-labeled human serum albumin. After reconstruction and reorientation according to the left ventricular long axis, LVEF and left ventricular volumes were measured with the CS and UB algorithms. Measurements of LVEF were validated against planar radionuclide angiocardiography (PRNA) results. The success rates of the algorithms were 87% for CS and 97% for UB. Agreement between LVEF measured with CS and UB (LVEFCS = 0.91 · LVEFUB - 0.85; r = 0.87) and between LVEF measured with CS and PRNA (LVEFCS = 1.04 · LVEFPRNA - 4.75; r = 0.80) and UB and PRNA (LVEFUB = 0.98 · LVEFPRNA + 4.42; r = 0.82) was good. For left ventricular volumes, linear regression analysis showed good correlation between both methods with regard to end-diastolic volumes (r = 0.81) and end-systolic volumes (r = 0.91). On average, end-diastolic volumes were similar and end-systolic volumes were slightly higher with CS than with UB. Consequently, significantly lower LVEFs were observed with CS than with UB. Conclusions Good correlation was observed between CS and UB for both left ventricular volumes and ejection fraction. In addition, measurements of LVEF obtained with both algorithms correlated fairly well with those obtained from conventional PRNA over a wide range of values.
European Journal of Nuclear Medicine and Molecular Imaging, 2000
Viability studies are often performed in patients receiving beta-blocking agents. However, the in... more Viability studies are often performed in patients receiving beta-blocking agents. However, the intake of beta-blocking agents could influence the identification of viable myocardium when low-dose dobutamine is used to demonstrate inotropic reserve. The aim of this study was to quantify the effect of beta-blockade on global and regional left ventricular function in healthy volunteers using low-dose dobutamine gated single-photon emission tomographic (SPET) myocardial perfusion scintigraphy. Ten subjects were studied once ”on” and once ”off” beta-blocker therapy (metoprolol succinate, 100 mg day–1). On each occasion four consecutive gated SPET acquisitions (of 7 min duration) were recorded after injection of 925 MBq technetium-99m tetrofosmin on a triple-headed camera equipped with focussing (Cardiofocal) collimators. Acquisitions were made at rest (baseline 1 and 2) and 5 min after the beginning of the infusion of 5 and 10 µg kg–1 min–1 dobutamine. Wall thickening (WT) was quantified using a method based on circumferential profile analysis. Left ventricular ejection fraction (LVEF) was obtained using the Cedars-Sinai algorithm. Blood pressure (BP) and heart rate (HR) were recorded at the end of each acquisition. At baseline LVEF, WT and systolic BP values under beta-blockade were not significantly different from those obtained in the non-beta-blocked state. The mean HR and diastolic BP at baseline were lower under beta-blockade. Dobutamine administration (at 5 and 10 µg kg–1 min–1) induced a significant increase in WT, LVEF and systolic BP in all subjects both on and off beta-blockade. The increases in WT, LVEF and systolic BP in the beta-blocked state were less pronounced but not significantly different. HR increased significantly at 10 µg kg–1 min–1 dobutamine without beta-blocker administration, while no increase in HR was observed in the beta-blocked state. Beta-blocker therapy in healthy subjects attenuates the inotropic and chronotropic myocardial response to low-dose dobutamine. At doses of 5 and 10 µg kg–1 min–1 dobutamine, however, significant increases in global and regional left ventricular function can still be measured using consecutive gated SPET myocardial perfusion scintigraphy acquisitions even under beta-blocker therapy.
European Journal of Nuclear Medicine and Molecular Imaging, 2000
Pinhole single-photon emission tomography (SPET) has been proposed to improve the trade-off betwe... more Pinhole single-photon emission tomography (SPET) has been proposed to improve the trade-off between sensitivity and resolution for small organs located in close proximity to the pinhole aperture. This technique is hampered by artefacts in the non-central slices. These artefacts are caused by truncation and by the fact that the pinhole SPET data collected in a circular orbit do not contain sufficient information for exact reconstruction. The ordered subsets expectation maximization (OS-EM) algorithm is a potential solution to these problems. In this study a three-dimensional OS-EM algorithm was implemented for data acquired on a single-head gamma camera equipped with a pinhole collimator (PH OS-EM). The aim of this study was to compare the PH OS-EM algorithm with the filtered back-projection algorithm of Feldkamp, Davis and Kress (FDK)and with the conventional parallel-hole geometry as a whole,using a line source phantom, Picker’s thyroid phantom and a phantom mimicking the human cervical column. Correction for the angular dependency of the sensitivity in the pinhole geometrywas based on a uniform flood acquisition. The projection data were shifted according to the measured centre of rotation. No correction was made for attenuation, scatter or distance-dependent camera resolution. The resolution measured with the line source phantom showed a significant improvement with PH OS-EM as compared with FDK, especially in the axial direction. Using Picker’s thyroid phantom, one iteration with eight subsets was sufficient to obtain images with similar noise levels in uniform regions of interest to those obtained with the FDK algorithm. With these parameters the reconstruction time was 2.5 times longer than for the FDK method. Furthermore, there was a reduction in the artefacts caused by the circular orbit SPET acquisition. The images obtained from the phantom mimicking the human cervical column indicated that the improvement in image quality with PH OS-EM is relevant for future clinical useand that the improvements obtained using the OS-EM algorithm are more significant for the pinhole geometry than for the conventional parallel-hole geometry. We conclude that PH OS-EM is a practical and promising alternative for pinhole SPET reconstruction.
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Papers by Christian Vanhove