Biomedical subjects

Y D'Asseler

Publications and source records attributed to Y D'Asseler.

13 recordsLinked to original sources

PubMed2001

Transfer of normal 99mTc-ECD brain SPET databases between different gamma cameras.

A stereotactic, normal perfusion database is imperative for optimal clinical brain single-photon emission tomography (SPET). However, interdepartmental use of normal data necessitates accurate transferability of these data sets. The aim of this study was to investigate transfer of three normal perfusion databases obtained in the same large population of healthy volunteers who underwent sequential scanning using multihead gamma cameras with different resolution. Eighty-nine healthy adults (46 females, 43 males; aged 20-81 years) were thoroughly screened by history, biochemistry, physical and full neurological examination, neuropsychological testing and magnetic resonance imaging. After injection of 925 MBq technetium-99m labelled ethyl cysteinate dimer (ECD) under standard conditions, 101 scans were acquired from all subjects (12 repeat studies) on a triple-head Toshiba GCA-9300A (measured average FWHM 8.1 mm). Ninety-one sequential scans were performed on a dual-head Elscint Helix camera (FWHM 9.6 mm) and 22 subjects also underwent imaging on a triple-head Prism 3000 (FWHM 9.6 mm). Images were transferred to the same processing platform and reconstructed by filtered back-projection with the same Butterworth filter (order 8, cut-off 0.9 cycles/cm) and uniform Sorensen attenuation correction (mu = 0.09). After automated rigid intrasubject registration, all subjects were automatically reoriented to a stereotactic template by a nine-parameter affine transformation. The databases were analysed using 35 predefined volumes of interest (VOIs) with normalisation on total VOI counts. For comparison, the high-resolution data were smoothed with a 3D Gaussian kernel to achieve more similar spatial resolution. Hoffman phantom measurements were conducted on all cameras. Partial volume effects after smoothing varied between -6.5% and 10%, depending on VOI size. Between-camera reproducibility was 2.5% and 2.7% for the Toshiba camera versus the Helix and the Prism database, respectively. The highest reduction in between-camera variability was achieved by resolution adjustment in combination with linear washout correction and a Hoffman phantom-based correction. In conclusion, transfer of normal perfusion data between multihead gamma cameras can be accurately achieved, thereby enabling widespread interdepartmental use, which is likely to have a positive impact on the diagnostic capabilities of clinical brain perfusion SPET.

Adult↗

PubMed2001

99Tc(m) labelled HL91 versus computed tomography and biopsy for the visualization of tumour recurrence of squamous head and neck carcinoma.

This phase I pilot study reports on (1) the safety and feasibility of 99Tc(m)-HL91, an amine oxime core radioligand that has shown oxygen dependent binding, and imaging; and (2) its usefulness for the visualization of local tumour recurrence of a biopsy proven squamous cell carcinoma of the head and neck (SCCHN) as compared to spiral computed tomogaphy (CT) and biopsy. Nine men (mean age 33 years, range 34-74 years) were prospectively included. For safety measurements, vital signs were recorded and serum chemical analysis carried out, with a complete blood cell count and urine analysis, and an ECG was performed prior to injection of 99Tc(m)-HL91 and repeated during the investigation. Single photon emission computed tomography (SPECT) scans of the head and neck, and of a standard, were performed at 2 h and 4 h post-injection of 740 MBq 99Tc(m)-HL91. Tumour-to-normal tissue background (T/N) ratios and percentage uptake were measured for all 99Tc(m)-HL91 scans. Spiral CT scans were obtained using a Somaton 4+ Siemens scanner within 1 week from the 99Tc(m)-HL91 scans. Based on CT and the 99Tc(m)-HL91 scan findings guided biopsies were performed. No adverse or subjective side effects were noticed. Vital signs, ECG findings, clinical laboratory, blood and urine assays remained stable in all patients. Spiral CT suggested local recurrence in 5/9 patients accompanied by nodal involvement in three, all of which proved positive on biopsy. 99Tc(m)-HL91 scintigraphy was false positive in one patient and true positive (TP) in 3/5 local recurrences and two out of three sites of lymph node involvement depicted by spiral CT. The mean T/N ratios at 2 h and 4 h in TPs were 1.28 (range 1.1-1.66) and 1.40 (range 1.0-1.6), respectively. The corresponding absolute percentages of 99Tc(m)-HL91 lesional uptake at 2 h and 4 h were mu = 0.05% (SD = 0.03%) and mu = 0.048% (SD = 0.035%). The findings suggest 99Tc(m)-HL91 is a safe radioligand and that metabolic binding in a large fraction but not all of local SCCHN recurrences may be expected. The inference that tumour 99Tc(m)-HL91 avidity could be a non-invasive measure of tumour hypoxia deserves however independent confirmation with needle oximetry.

Adult↗

PubMed2001

57Co SPECT, 99mTc-ECD SPECT, MRI and neuropsychological testing in senile dementia of the Alzheimer type.

Inflammatory mechanisms contribute to the pathophysiology of senile dementia of the Alzheimer type (sDAT). Previous studies have shown that 57Co single photon emission computed tomography (SPECT) is able to visualize inflammatory lesions, probably by means of the final common pathway of Ca2+ homeostasis disturbance in both neuronal degeneration and inflammation. The aims of this study were: (1) to detect 57Co SPECT changes in sDAT patients; (2) to correlate these findings with those of conventional neuroimaging techniques and neuropsychological testing (NPT); and (3) to compare 57Co SPECT findings in sDAT patients with those in other types of dementia. Six patients suffering from probable sDAT were included and compared with four patients suffering from other types of dementia. All patients had a magnetic resonance imaging (MRI) scan, NPT, 57Co and 99mTc-ethyl cysteinate dimer (ECD) SPECT scan. Perfusion SPECT images were semiquantitatively evaluated by comparison with an age-matched normal database, while 57Co SPECT scans were assessed qualitatively. MRI and 99mTc-ECD SPECT scans yielded conclusive results with regard to the exclusion of other pathologies and the confirmation of the diagnosis. Using visual analysis, 57Co SPECT scans were unable to show any regional raised uptake, irrespective of the disorder, depth or extent of the perfusion defects, presence of atrophy on MRI or the results of NPT.

Aged↗

PubMed2001

Automated stereotactic standardization of brain SPECT receptor data using single-photon transmission images.

UNLABELLED: Intra- or intersubject registration of anatomically poorly defined SPECT data, such as in neuroreceptor imaging, is important for longitudinal or group analysis. However, accurate registration is difficult with only emission CT (ECT) data. We investigated fully automated registration using transmission CT (TCT) data as an intermediary image set. METHODS: The accuracy of TCT registration was compared to that of ECT registration for four types of data: gray-matter distribution (with [99mTc]ethylcysteinate dimer (ECD)), neocortical distribution (with [123I]R91150, a highly specific 5-HT2a receptor ligand), and striatal distribution of the D2-receptor ligand (with [123I]iodobenzamide (IBZM)) and the dopamine transporter ligand (with [123I]2beta-carbomethoxy-3beta-(4-fluorophenyl)tropane (CIT)). In total, 10 datasets of the various study types were used, all collected on a Toshiba GCA9300 gamma camera with super-high-resolution fanbeam collimators and 3 x 370 MBq of 153Gd transmission sources (4-min sequential TCT scanning for receptor studies and 20-min simultaneous scanning for [99mTc]ECD studies). Per dataset, 15 random misalignments of 9 rigid-body parameters (translation, rotation, and anisotropic scaling) were conducted. All coregistrations were done twice, both to the subject's original scan and to a study-specific template. This was done manually by two independent experienced observers and with three automated voxel similarity algorithms: mutual information (M.I.), count difference (C.D.), and uniformity index (U.I.). As an outcome measure, the impact of misregistration on semiquantification for the various study types was established. RESULTS: TCT matching allowed registration within 3.3 mm, 2.4 degrees, and 1.2% scaling (mean squared values for all directions) with an overall accuracy decrease in the following order: C.D. > M.I. > manual > U.I. For [99mTc]ECD and [123I]IBZM, TCT registration was as accurate as ECT registration, while it was far superior for the other receptor data types, especially for abnormal studies. The automated TCT registration accuracy corresponded to average quantification errors of 2.9% ([99mTc]ECD), 4.2% ([123I]BZM), 5.7% ([123I]R91150), and 6.1% ([123I]beta-CIT). CONCLUSION: Fully automated registration through intermediary TCT images is clinically feasible, fast, and accurate. In addition to nonuniform attenuation correction, TCT scanning therefore allows coregistration for group comparisons of SPECT receptor data on a standardized or pixel-by-pixel basis.

Adolescent↗

PubMed2000

Automatic quantification of defect size using normal templates: a comparative clinical study of three commercially available algorithms.

Infarct size assessed by myocardial single-photon emission tomography (SPET) imaging is an important prognostic parameter after myocardial infarction (MI). We compared three commercially available automatic quantification algorithms that make use of normal templates for the evaluation of infarct extent and severity in a large population of patients with remote MI. We studied 100 consecutive patients (80 men, mean age 63 +/- 11 years, mean LVEF 47% +/- 15%) with a remote MI who underwent resting technetium-99m tetrofosmin gated SPET study for infarct extent and severity quantification. The quantification algorithms used for comparison were a short-axis algorithm (Cedars-Emory quantitative analysis software, CEqual), a vertical long-axis algorithm (VLAX) and a three-dimensional fitting algorithm (Perfit). Semiquantitative visual infarct extent and severity assessment using a 20-segment model with a 5-point score and the relation of infarct extent and severity with rest LVEF determined by quantitative gated SPET (QGS) were used as standards to compare the different algorithms. Mean infarct extent was similar for visual analysis (30% +/- 21%) and the VLAX algorithm (25% +/- 17%), but CEqual (15% +/- 11%) and Perfit (5% +/- 6%) mean infarct extents were significantly lower compared with visual analysis and the VLAX algorithm. Moreover, infarct extent determined by Perfit was significantly lower than infarct extent determined by CEqual. Correlations between automatic and visual infarct extent and severity evaluations were moderate (r = 0.47, P < 0.0001 to r = 0.62, P < 0.0001) but comparable for all three algorithms. Correlations between LVEF and visual evaluation of infarct extent (r = -0.80, P < 0.0001) and severity (r = -0.82, P < 0.0001) were good but correlations were significantly lower for all three algorithms (r = -0.48, P < 0.0001 to r = -0.65, P < 0.0001). Systematically lower correlations were found in non-anterior infarctions (n = 69) and obese patients (BMI > or = 30 kg/m2, n = 32) compared with anterior infarctions and non-obese patients for all three algorithms. In this large series of post-MI patients, results of infarct extent and severity determination by automatic quantification algorithms that make use of normal templates were not interchangeable and correlated only moderately with semiquantitative visual analysis and LVEF.

Adult↗

PubMed2000

Cardiac fluorine-18 fluorodeoxyglucose imaging using a dual-head gamma camera with coincidence detection: a clinical pilot study.

Dual-headed gamma cameras with coincidence detection (MCD) are increasingly used for imaging of positron-emitting tracers, such as fluorine-18 fluorodeoxyglucose (FDG). In this study, we examined differences between FDG MCD and FDG positron emission tomography (PET) as the gold standard to determine whether FDG MCD could be used for assessment of myocardial viability in daily practice. Nineteen patients with a previous myocardial infarction (17 men; mean left ventricular ejection fraction 44%+/-13%) underwent FDG MCD, FDG PET, resting echocardiography and technetium-99m tetrofosmin gated single-photon emission tomography (SPET). At the 50% threshold value for FDG PET, the area under the receiver operating characteristic curve for FDG MCD was 0.77+/-0.03. In 107 dyssynergic segments on echocardiography and 151 segments with hypoperfusion on 99mTc-tetrofosmin SPET, the specificity of FDG MCD for the detection of myocardial viability was 72% and 76% respectively, with a sensitivity of 69% and 72% respectively. Regional analysis showed a significantly lower agreement of FDG MCD and FDG PET in the inferior and septal regions (58% for dyssynergic segments and 65% for segments with hypoperfusion), as compared with the other regions (85% for dyssynergic regions, P<0.05, and 86% for segments with hypoperfusion, P<0.05). Five patients (26%), who all had a body mass index > or =25% kg/m2, showed more than 25% disagreement between FDG MCD and FDG PET. Because of the moderate overall agreement with FDG PET, the low sensitivity in akinetic or dyskinetic regions and the low agreement in the inferior and septal regions, further studies and implementations of technical developments are needed before FDG MCD can be introduced into clinical practice for the assessment of myocardial viability.

Adult↗

PubMed2000

PACS and multimodality in medical imaging.

A PACS (Picture Archiving and Communication System) is a system that is able to store, exchange, display and manipulate images and associated diagnoses from any modality within a hospital in a timely and cost-effective way. Several developments, such as the DICOM standard, fast and convenient networking, and new storage solutions for large amounts of data, make the setup of such a PACS system possible. As the information acquired with various imaging modalities is then available and often complementary, it is desirable for the clinician to have a point-by-point spatial co-registration of images from different modalities in order to enable a synergistic use of the multimodality imaging of a patient for increased diagnostic accuracy. Various types of algorithms are available for the matching of medical images from the same or from different modalities. Co-registration algorithms based on voxel properties consist of a similarity or dissimilarity measure and an iterative or non-iterative method minimizing the dissimilarity or maximizing the similarity between the two images by a transformation of one image relative to the other.

Belgium↗

PubMed1999

MRI-SPET and SPET-SPET brain co-registration: evaluation of the performance of eight different algorithms.

The aim of this study was to assess the accuracy and computing time needed for MRI-SPET and SPET-SPET brain co-registration using eight different algorithms (Hermes software from Nuclear Diagnostics Ltd run on a SUN Ultra Sparc 2) to determine the clinically most suitable algorithm. MRI-SPET co-registration was evaluated using phantom studies. To approximate clinical dual-headed SPET studies, a Hoffman brain phantom was filled with 99Tcm. For MRI imaging (1.5 Tesla), the phantom was filled with water and doped with Gd-DTPA for contrast enhancement. For both modalities, phantom images were acquired and reconstructed using a routine clinical protocol. MRI and SPET images were matched by Downhill Simplex minimization of the sum of absolute Count Differences (CD), the sum of the Square Root of absolute count differences (SR), the Difference in Shape between the binary masks (SD), the number of Sign Changes in the subtracted image (SC), the Variance of intensities between corresponding pixels (VAR), the sum of absolute count differences between the 2D- and 3D-Gradient images (2DG-3DG) and, finally, the standard deviation of the Uniformity Index (UI), that is the intensity ratio between spatially corresponding voxels. Six degrees of freedom were allowed (three translation and three rotation parameters, three scaling parameters were constrained). The accuracy of the matching process with these different similarity measures was evaluated via the residual mismatch between external markers. We found that CD, SR, VAR nad UI give the most accurate registration compared with the other similarity measures. For the evaluation of SPET-SPET co-registration, five 99Tcm-ECD brain perfusion SPET scans were performed with a dual-headed gamma camera. These studies were then manually misaligned, and subsequently re-aligned using the methods outlined above. For this application, CD, SR and VAR were also found to give the most accurate registration. For all of these algorithms, the computing time required was clinically acceptable (i.e. less than 10 min).

Algorithms↗

PubMed1998

Optimizing background correction when calculating differential renal function in the presence of hydroureteronephrosis using 99Tc(m)-DTPA.

We performed a prospective study to establish the optimal background correction algorithm for the determination of differential renal function (DRF), using 99Tc(m)-diethylenetriamine pentaacetate (99Tc(m)-DTPA) in the presence of unilateral hydronephrosis, with 24 h 99Tc(m)-dimercaptosuccinic acid (99Tc(m)-DMSA) uptake as the 'gold standard'. From September 1996 to June 1997, 12 males and 4 females (mean age 10 years, range 1 month to 72 years), presenting with unilateral hydronephrosis, were studied. All patients underwent both DTPA renography and quantitative DMSA scintigraphy within 24 h. In all patients, using a surface method, the DRF of the obstructed kidney was determined using infrarenal, suprarenal and perirenal background correction, time intervals of 60-180 s (t1), 120-180 s (t2) and 80-140 s (t3), and the application or non-application of a Rutland-Patlak correction (RPC). In the absence of RPC, for all three types of background correction, no difference in DTPA DRF for any of the three time intervals was noted; higher DTPA DRF values were found (mean +/- S.D.: overestimates of 7.8+/-24.4%, 6.5+/-9.5% and 3.3+/-14.9% for suprarenal, infrarenal and perirenal background correction, respectively). Application of RPC resulted in an overall decrease in both the mean and standard deviation values, which was most pronounced with infrarenal background correction: -0.38+/-6.5% for t1, 0.31+/-6.3% for t2 and -1.3 +/-6.9% for t3 (t1 vs t2, P = 0.06; t3 vs t1 or t2, P = 0.04). Our results suggest that infrarenal background correction using t1 or t2 and RPC is the best algorithm for DRF estimation using 99Tc(m)-DTPA renography.

Adult↗

PubMedDate not supplied

PET imaging using gamma cameras.

This paper will review the recent advances and future developments in the field of coincidence imaging of positron emitters with a conventional Anger-type gamma camera. FDG imaging has shown high clinical importance in cardiology, neurology and especially oncology. Since access to full ring PET is mainly limited to university hospitals, there have been new developments allowing PET imaging on the standard Anger gamma camera. First the principles of coincidence imaging on a gamma camera will be reviewed. We will discuss the limitations of this technique, and the techniques used to partly overcome these limitations. The different configurations of the gamma camera operating in coincidence mode are pointed out. Different corrections for image degrading effects and reconstruction methods are evaluated in the final part.

Calibration↗

PubMedDate not supplied

Iterative reconstruction algorithms in nuclear medicine.

Iterative reconstruction algorithms produce accurate images without streak artifacts as in filtered backprojection. They allow improved incorporation of important corrections for image degrading effects, such as attenuation, scatter and depth-dependent resolution. Only some corrections, which are important for accurate reconstruction in positron emission tomography and single photon emission computed tomography, can be applied to the data before filtered backprojection. The main limitation for introducing iterative algorithms in nuclear medicine has been computation time, which is much longer for iterative techniques than for filtered backprojection. Modern algorithms make use of acceleration techniques to speed up the reconstruction. These acceleration techniques and the development in computer processors have introduced iterative reconstruction in daily nuclear medicine routine. We give an overview of the most important iterative techniques and discuss the different corrections that can be incorporated to improve the image quality.

Algorithms↗

PubMedDate not supplied

Image-correction techniques in SPECT.

This overview takes a look at different correction techniques for Single Photon Emission Computed Tomography (SPECT). We discuss the influence of the detection system followed by the scatter and attenuation caused by the object of investigation. When possible we describe how the correction methods for the different physical effects can be incorporated in the reconstruction method, being either filtered backprojection or iterative reconstruction.

Algorithms↗

PubMedDate not supplied

Coincidence camera FDG imaging for the diagnosis of chronic orthopedic infections: a feasibility study.

PURPOSE: Results of dedicated [(18)F]fluoro-2-deoxy-d-glucose (FDG) PET imaging in patients with suspected orthopedic infections are promising. This study evaluates the feasibility of dual-head gamma-camera coincidence (DHC) imaging in this population. METHOD: Twenty-four patients, referred for the confirmation or exclusion of orthopedic infection, were prospectively studied with consecutive FDG-dedicated PET and FDG DHC imaging. Images were read by two blinded readers experienced with FDG PET and compared with the final diagnosis, obtained by microbiologic proof in 11 patients and clinical follow-up of at least 9 months in 13 patients. RESULTS: Nine patients had osseous infection on final diagnosis. Sensitivity, specificity, and accuracy in this limited series were (Reader 1/Reader 2), respectively, 100/100, 86/86, and 92/92% for FDG-dedicated PET and 89/89, 100/93, and 96/92% for FDG DHC imaging. CONCLUSION: Despite lower image quality for FDG DHC imaging, results in this limited series were comparable with the results of FDG-dedicated PET. Further studies are needed to confirm the utility of FDG DHC imaging in suspected chronic orthopedic infections in larger patient groups.

Adult↗