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Biomedical subjects

J Rousseau

Publications and source records attributed to J Rousseau.

At least 19 recordsLinked to original sources
PubMed2001

3D reconstruction of the encapsulating contour of arteriovenous malformations for radiosurgery using digital subtraction angiography.

PURPOSE: Treatment planning for radiosurgery depends on the precise definition of radiation target volumes. For vascular pathologies such as arteriovenous malformations (AVM), the most usual technique remains standard X-ray projection imaging, most often carried out under stereotactic conditions. To further benefit from the advantages of two-dimensional digital subtraction angiography (DSA), the authors have developed a method for determining the three-dimensional shape of arteriovenous malformations from two views. METHODS AND MATERIALS: After correction of image intensifier distortion and calibration of both views, the 3D shape of the AVM was determined from two DSA projections using epipolarity geometry. The AVM-encapsulating contour was modeled by triangulation of a stack of almost parallel ellipses. The method was technically validated using artificial targets in a skull phantom. Clinical validation was carried out on 10 patients who were examined using both conventional angiography under stereotactic conditions (SX-ray) and DSA. RESULTS: There was excellent agreement between the artificial target volumes measured with SX-ray and with DSA. The correspondence between AVM volumes found for patients was not as good as with the phantom. CONCLUSIONS: The different image characteristics of the two modalities lead to some differences in AVM estimations. However, the results were sufficiently satisfactory to justify routine use of this AVM modeling technique for radiosurgery planning.

Angiography, Digital Subtraction↗
PubMed2001

Volume delineation by fusion of fuzzy sets obtained from multiplanar tomographic images.

Techniques of three-dimensional (3-D) volume delineation from tomographic medical imaging are usually based on 2-D contour definition. For a given structure, several different contours can be obtained depending on the segmentation method used or the user's choice. The goal of this work is to develop a new method that reduces the inaccuracies generally observed. A minimum volume that is certain to be included in the volume concerned (membership degree mu = 1), and a maximum volume outside which no part of the volume is expected to be found (membership degree mu = 0), are defined semi-automatically. The intermediate fuzziness region (0 < mu < 1) is processed using the theory of possibility. The resulting fuzzy volume is obtained after data fusion from multiplanar slices. The influence of the contrast-to-noise ratio was tested on simulated images. The influence of slice thickness as well as the accuracy of the method were studied on phantoms. The absolute volume error was less than 2% for phantom volumes of 2-8 cm3, whereas the values obtained with conventional methods were much larger than the actual volumes. Clinical experiments were conducted, and the fuzzy logic method gave a volume lower than that obtained with the conventional method. Our fuzzy logic method allows volumes to be determined with better accuracy and reproducibility.

Artificial Intelligence↗
PubMed2001

Involvement of occupational therapy departments in research: a provincial survey.

It is increasingly recognized that research is necessary to advance the practice of occupational therapy. The objective of this study was to determine whether occupational therapy departments in Quebec were commonly involved in research, and whether participation varied with the size of department and type of work setting. Secondly, enablers and barriers to participation in research were identified. A random sample of occupational therapy departments, stratified by size, were surveyed by mail. Participation rate was 74.8% (107/143). Participation in research was noted in half of the departments surveyed (51/107), most frequently as collaborator. Involvement in research was associated (p < .001) with a greater number of therapists in the department. Furthermore, occupational therapy departments in rehabilitation centres and in university hospitals were more likely to participate in research (79% and 90% respectively), whereas participation was lower for long-term care facilities (29%) and community health clinics (38%). When asked to rank factors that may facilitate participation in research, the highest rankings were given to: time allotted to research, research as a priority for administration, adequate financial support, and presence of an occupational therapy researcher and a research centre on site. This survey demonstrates that a number of factors can promote or prevent the realization of research activities within the clinical setting. Strategies are proposed to enhance the integration of research into clinical practice.

Humans↗
PubMed2001

[Dosimetry with radiosensitive gels in radiotherapy. Methods].

The goal of conformal radiotherapy is to concentrate the dose in a well-defined volume by avoiding the neighbouring healthy structures. This technique requires powerful treatment planning software and a rigorous control of estimated dosimetry. The usual dosimetric tools are not adapted to visualize and validate complex 3D treatment. Dosimetry by radiosensitive gel permits visualization and measurement of the three-dimensional dose distribution. The objective of this work is to report on current work in this field and, based on our results and our experience, to draw prospects for an optimal use of this technique. Further developments will relate to the realization of new radiosensitive gels satisfying, as well as possible, cost requirements, easy realization and use, magnetic resonance imagery (MRI) sensitivity, tissue equivalence, and stability. Other developments focus on scanning methods, especially in MRI to measure T1 and T2.

Calibration↗
PubMed2000

Gel electrophoretic mobility of single-stranded DNA: the two reptation field-dependent factors.

The reptation model is the dominant theory in understanding the electrophoretic separation of single-stranded DNA molecules in gels or entangled polymer solutions. Recently, we showed that the Ogston and reptation regimes are separated by an entropic trapping regime at low field intensities. Here, we report the first comparison of the field-dependent part of the DNA mobility for both small and long reptating molecules. We show that both mobilities increase linearly with field intensity, with the mobility of the longer (comigrating) fragments increasing faster than that of the smaller ones. We compare our results to the predictions of the biased reptation model.

DNA, Single-Stranded↗
PubMed2000

MR-guided balloon angioplasty of stenosed aorta: in vivo evaluation using near-standard instruments and a passive tracking technique.

The purpose of this study was to assess the feasibility of magnetic resonance (MR)-guided balloon angioplasty of a stenosed aorta on an open low-field magnet using a passive tracking technique. Visualization of vessels and position of instruments were realized by using a fast low-angle shot (FLASH) sequence. Catheters and guidewire were prepared for susceptibility-based MR visualization. Standard balloon catheters were inflated with diluted gadolinium, and nitinol guidewires were modified by incorporation of iron oxide markers into their walls. After validation on a flow phantom, balloon angioplasty was performed on an in vivo model of arterial stenosis. Creation of abdominal aorta stenosis was realized in five piglets. MR-guided balloon angioplasty of the aorta was performed with success in all but one. In one of them, stent implantation was achieved in the descending aorta. Balloon angioplasty using a passive tracking technique is a simple concept that can be realized with near-standard instruments and any MR imaging system. This represents an advance toward MR-guided vascular interventions in the future.

Angioplasty, Balloon↗
PubMed2000

Accurate localization of needle entry point in interventional MRI.

In interventional magnetic resonance imaging (MRI), the systems designed to help the surgeon during biopsy must provide accurate knowledge of the positions of the target and also the entry point of the needle on the skin of the patient. In some cases, this needle entry point can be outside the B(0) homogeneity area, where the distortions may be larger than a few millimeters. In that case, major correction for geometric deformation must be performed. Moreover, the use of markers to highlight the needle entry point is inaccurate. The aim of this study was to establish a three-dimensional coordinate correction according to the position of the entry point of the needle. We also describe a 2-degree of freedom electromechanical device that is used to determine the needle entry point on the patient's skin with a laser spot.

Biopsy, Needle↗
PubMed2000

(17alpha,20E/Z)-iodovinyl- and 16alpha-iodP618-homoestradiol derivatives: synthesis and evaluation for estrogen receptor imaging.

Three new 125I-radioiodinated estrogens featuring a 13beta-ethyl instead of the natural 13beta-methyl group, i.e. 18-homoestradiols, were synthesized and evaluated as potential estrogen receptor imaging agents. The 16alpha-iodo-18-methylestradiol and the 125I-labeled analog were synthesized from the corresponding 16beta-bromo analog by the halogen-exchange method. The cis-bromohydrin precursor was obtained by bromination of an estrone enolacetate, followed by epimerization and reduction. The isomeric (17alpha,20E/Z)-iodovinyl-18-methylestradiols were prepared via the vinyltin intermediates. Treatment of 18-methyl-17alpha-ethynylestradiol with tri-n-butyltin hydride, in the presence of azobisisobutyronitrile as catalyst and heating at 90-100 degrees C afforded the (17alpha,20E)-tri-n-butylstannyl isomer as the major product. Changing the catalyst for triethyl borane, at room temperature, mainly gave the 20Z-isomer. The nca 125I-labeled analogs were obtained from their corresponding tin intermediates upon treatment with [125I]NaI in the presence of H2O2. The 16alpha-[125I]iodo- and isomeric (17alpha,20E/Z)-[125I]iodovinyl-18-methylestradiols were evaluated for estrogen receptor-mediated uterine uptake in immature female rats. Homologation of the C13-methyl group did improve the uterine uptake of the iodovinyl derivatives, but also increased blood retention, resulting in lower target uptake ratios. In the case of the 16alpha-iodo analog uterine retention decreased upon C13-homologation.

Animals↗
PubMed1999

Brain metabolic alterations in Cushing's syndrome as monitored by proton magnetic resonance spectroscopy.

Proton magnetic resonance spectroscopy ((1)H MRS) was used to evaluate changes in cerebral metabolites in 13 patients with Cushing's syndrome (including seven with pituitary corticotroph adenomas and six with primary adrenal disease) as compared to 40 normal subjects. Data were recorded in the frontal, thalamic and temporal areas; quantification of the MRS signals demonstrated a statistically significant decrease of the Cho/Cr ratio in the frontal and thalamic areas but not in the temporal area for patients with Cushing's syndrome. The largest decrease in Cho/Cr was measured in the thalamic area of patients with a Cushing's syndrome secondary to an adrenal disease. No statistically significant changes in the NAA/Cr ratio were measured in any of the areas studied. These results suggest that the quantification of choline levels could be helpful for monitoring the cerebral metabolite alterations in patients with hypercortisolism.

Adult↗
PubMed1999

3D reconstruction of the cerebral arterial network from stereotactic DSA.

The authors present an automatic algorithm for 3D reconstruction of cerebral blood vessels by digital subtracted angiography. The patient is localized by a stereotactic method. The reconstruction algorithm includes two steps: first vessel extraction then 2D matching and reconstruction. Accurate vessel skeletons are generated by a combination of mathematical morphological algorithms and adaptive filters. The 3D reconstruction algorithm is based on the reconstruction of vessels center lines. For that purpose, three different projections of the vascular network are used. Reconstruction is computed segment by segment (a curved line between two nodes). For each segment point, the algorithm defines all epipolar solutions on the other views. These epipolar solutions are sorted and pooled by 2D continuity and 3D proximity criteria resulting in a 3D graph. Optimal 3D segment is defined by a recursive algorithm that looks up the better path in the 3D graph. The algorithms have been implemented on a Compatible-PC computer in C language. More than 95% of static copper phantom was reconstructed in 5 min and with 1 mm 3D accuracy. 70% of arteries (from carotid to the seventh node) of a true patient arterial network were reconstructed is less than 30 min.

Algorithms↗
PubMed1999

Automatic quality assessment protocol for MRI equipment.

The authors have developed a protocol and software for the quality assessment of MRI equipment with a commercial test object. Automatic image analysis consists of detecting surfaces and objects, defining regions of interest, acquiring reference point coordinates and establishing gray level profiles. Signal-to-noise ratio, image uniformity, geometrical distortion, slice thickness, slice profile, and spatial resolution are checked. The results are periodically analyzed to evaluate possible drifts with time. The measurements are performed weekly on three MRI scanners made by the Siemens Company (VISION 1.5T, EXPERT 1.0T, and OPEN 0.2T). The results obtained for the three scanners over approximately 3.5 years are presented, analyzed, and compared.

Image Processing, Computer-Assisted↗
PubMed1999

[Interventional MRI. Analysis of data and prospects].

In spite of its many advantages: 3D imaging, improved tissue characterization, and lack of ionizing radiation, interventional MRI remains seldom used. Several factors are involved. The purpose of this paper is to analyze the factors preventing or slowing the development of this technique based on a review of data from the literature, work presented at the second symposium on interventional MRI (Düsseldorf, 1997), and our own experimental data. The following elements will be discussed: difficulties related to image quality and open magnets, control of targeted image acquisitions, MR environment and problems related to asepsis, as well as advances of other techniques. Finally, short-term and mid-term perspectives will be presented. These are related to the goals of the technique: open or short bore closed magnets? MR unit installed in a radiology department? MR unit dedicated to interventional procedures only or mixed diagnostic-interventional unit? interventional MR unit placed in a neurosurgery operating room? interventional MR unit installed in a general surgery operating room?

Analgesia↗
PubMed1998

Design of a privileging program for diagnostic imaging: costs and implications for a large insurer in Massachusetts.

PURPOSE: To evaluate the results of a privileging program aimed to ensure that health care providers and facilities adhere to standards of care. MATERIALS AND METHODS: Technical and professional privileging applications were mailed to more than 1,800 diagnostic imaging facilities and more than 6,000 professional providers of services to members of a health care plan. Site inspections were used to determine whether facilities met standards of care. Specialty providers were assigned a range of current procedural terminology codes for which they had privileges to bill the payer. RESULTS: Of 1,004 imaging sites inspected, 197 (20%) failed with the ability to remedy the violation, 106 (10%) failed with fundamental and serious deficiencies, and 701 (70%) passed. Site inspection pass rates varied substantially by specialty. Chiropractors and podiatrists were more likely to fail than medical and surgical specialists. A strong correlation was found between refusal to participate in the inspection and failure rate. Results suggest that reduction of the number of professional claims billed led to a 2% decline in total imaging expenditures, or a more than 10:1 return on the cost of implementing technical and professional privileging programs. CONCLUSION: Health care plans can positively influence costs and quality by developing, monitoring, and enforcing their own quality standards for diagnostic imaging.

Blue Cross Blue Shield Insurance Plans↗
PubMed1997

Synthesis and tissue distribution of substituted [125I]iodophenylamine derivatives: possible brain imaging agents.

The synthesis and brain uptake in mice of the radioiodinated derivatives of N,N-dimethyl-N'-(iododimethoxyphenyl)-1,3-propanediamine, as well as the N-substituted derivatives of (iodoalkylphenyl)isopropyl, iodoalkylphenylethylamine and 3,4-(methylenedioxy)phenyl-amphetamine (MDA) are described. These compounds contain structural features of both IMP and HIPDM, the cerebral perfusion agents currently in clinical use. The radiolabeled analogs were obtained via the [125I]I exchange method, or by [125I]NaI treatment of the iodo-free precursor in the presence of an oxidant. Following intravenous injection in mice, all compounds showed important radioactivity concentrations in the lungs and kidneys. The N-substituted (iodoalkylphenyl)isopropyl and iodoalkylphenyl-ethylamine derivatives displayed a high initial brain uptake (> 10% IDg-1) followed by a rapid clearance phase, resulting in lower brain-to-blood ratios as those reported for IMP and HIPDM. In contrast, N,N-dimethyl-N'-(iododimethyphenyl)-1,3-propanediamine derivatives featuring the iodo substituent on the benzene carbon adjacent to the methyl amine group and the methoxy substituents on the 2,5- or 2,4-positions, showed low but more persistant brain uptake. Combined with fast blood clearance, this resulted in high brain-to-blood ratios at later time points. Among all compounds tested, the highest brain-to-blood ratio was observed with compound N,N-dimethyl-N'-(6-iodo-3,4-dimethyoxyphenyl)-1,3-propanediamine (27e), reaching a maximum of > 20 at 12 h post-injection.

Aniline Compounds↗
PubMed1997

Mutations that prevent associative learning in C. elegans.

The nematode Caenorhabditis elegans offers a promising system for the reductionist study of learning and memory. In this article, classical conditioning in C. elegans is demonstrated with a variety of associative learning assays. These assays allowed for the isolation and behavioral characterization of 2 mutant C. elegans lines impaired in associative learning. Both lines show no short-term or long-term associative conditioning; however, they appear relatively normal in tests of nonassociative learning and sensorimotor function. In combination with the well-described genetics and neuroanatomy of C. elegans, the isolation of mutants selectively, yet completely, blocked in associative learning provides the basis for an effective characterization of the cellular and molecular aspects of associative learning.

Animals↗
PubMed1997

Visuvalve software: an aid to the diagnosis of shunt failure.

Software designed to help the neurosurgeon in the diagnosis of shunt malfunction is presented. This software allows the possibility to record on a 3.5 diskette a patient's clinical information and four views of a CT scan performed when the patient was doing perfectly well with his shunt. This diskette, operated by MS-DOS on any IBM-compatible personal computer, can be read at any time, anywhere. The evaluation of the system demonstrated it was safe, with an excellent adhesion of the patients and of their families.

Cerebral Ventriculography↗
PubMed1997

Postoperative interstitial radiotherapy of keloids by iridium 192: a retrospective study of 46 treated scars.

BACKGROUND: Keloids are clinically vexacious scars characterized by a high recurrence rate after excision alone (50-100%). Many adjuvant techniques have been used with more or less convincing results. OBJECTIVE: The aim of this study is to show the efficiency of keloidectomy and postoperative interstitial radiotherapy by an iridium 192 wire. METHODS: During a 14-year period, 39 patients with keloids (46 keloids) were treated by this regimen. Seven patients had been previously treated by intralesional corticosteroids, surgery alone or postoperative interstitial radiotherapy, without improvement. A dose of 12 Gy (7 keloids) to 15 Gy (22 keloids) was delivered at a point 2.5 mm from the axis of the wire. For 17 keloids the dose schedule was 15 Gy at a point 5 mm to the wire. The median follow-up was 7 months. RESULTS: The overall success rate is close to 63%. A recurrence occurred in 14 cases without relation to the method used, the age or the localization of the lesions. There were no side effects observed. CONCLUSIONS: Postoperative interstitial radiotherapy represents an effective, unconstraining and safe treatment for keloids if the contraindications are respected.

Adolescent↗