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Biomedical subjects

J Rousseau

Publications and source records attributed to J Rousseau.

At least 181 records · Page 10Linked to original sources
PubMedDate not supplied

[Progress in dosage optimization for stereotactic radiosurgery].

Stereotactic radiosurgery is a technique for treatment of intracranial lesions requiring high precision in all steps--from image acquisition to final irradiation. One of most difficult steps is the treatment planning phase, consisting of determination of irradiation parameters sufficient to cover the target volume by avoiding sensitive volumes. A manual and empirical definition can be very long and difficult, especially in the case of complex target volumes situated in sensitive zones. As in conventional radiotherapy, stereotactic radiosurgery has taken advantages from dosimetric optimization. The question is: "What is the configuration of irradiation parameters used in order to obtain the treatment plan by satisfying defined constraints?". The purpose of this article is to summarize optimization methods used in radiosurgery and to describe the technical alternatives proposed for this treatment as well as the possibilities of plan evaluation between different techniques. This purpose will be illustrated by the optimization methodology used in the Center Oscar Lambret of Lille, France for the radiosurgical treatment with linear accelerator.

Algorithms↗
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[Dosimetric quality control in stereotactic radiotherapy with the aid of radiosensitivity].

Typical dosimeters used in stereotactic radiation therapy, such as ionization chambers, films, and thermoluminescent diodes, allow basic physical measurements. They are, however, neither well suited to discern small target volumes with high dose gradient, nor suitable for three-dimensional (3D) dose measurements. Gel dosimetry is becoming more and more interesting, owing to magnetic resonance imaging (MRI). It permits isocenter position planning verification of accuracy and the precision of the 3D dose mapping in the brain (when irradiated in realistic conditions), especially when several different targets are concerned. Many authors have assessed stereotactic radiation therapy quality control using different gels, and different irradiation procedures. This paper consists of the review of these different methods to assess quality control. Gel dosimetry cannot provide absolute dose measurements. However, gels can be used to check the 3D dose mapping with a high degree of detail. In our experiment, the difference between the stereotactic frame center and the isocenter is about 1 mm. The difference between the theoretical isodoses obtained by the treatment planning system and the experimental isodoses obtained by the MRI gray level calibration is also about 1 mm, the order of magnitude of the MRI pixel size.

Gels↗
PubMedDate not supplied

[Stereotactic localization in medical imaging. Technical and methodologic aspects].

Stereotactic neurosurgery and stereotactic radiation therapy require the three-dimensional localization of lesions for biopsy or for treatment planning. The aim of this paper is the description of methods used in the different imaging modalities: x-ray teleradiography, digital subtracted angiography, computed tomography, and nuclear magnetic resonance imaging. The simple pin-target locating techniques are distinguished from those serving to the definition of volumes target necessary to treatment planning. Performances and difficulties of these techniques are emphasized. The specific methodology developed in Lille is described as an example. Organizational aspects and necessary quality controls for a good progress of the entire procedure, from imaging to treatment, are also discussed.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Validation of a new method for stereotactic localization using MR imaging.

Magnetic resonance is recognized as potentially the best imaging procedure for localization in stereotactic neurosurgery. However, special difficulties necessitate specific adaptation to localize targets in the stereotactic frame. We developed a new method for stereotactic localization. The MR studies were performed using a 0.5 T imager. Four small boxes filled with CuSO4 solution were inserted into the intracranial holders of a Talairach frame. Using fast sequences, thirty 7-mm thick contiguous sagittal slices and twenty 5-mm thick axial slices enabled us to image the entire brain. The image data were transferred for analysis to an image processing station, including special software to handle stereotactic calculations. The accuracy of the origin of the trihedron and systematic geometrical errors were carefully evaluated using a cubic phantom, and corrective algorithms were applied when needed. Moreover, checks have been designed to detect geometrical distortion due to ferromagnetic artifacts, alterations in gradient calibration, or movements made by the patient. This localization method does not necessitate the use of stereotactic frames and appears to be precise enough for clinical use. Duration of MR examination is not a restricting factor, mainly because the patient can be positioned easily.

Calibration↗
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Fat suppression in MR imaging: techniques and pitfalls.

Fat suppression is commonly used in magnetic resonance (MR) imaging to suppress the signal from adipose tissue or detect adipose tissue. Fat suppression can be achieved with three methods: fat saturation, inversion-recovery imaging, and opposed-phase imaging. Selection of a fat suppression technique should depend on the purpose of the fat suppression (contrast enhancement vs tissue characterization) and the amount of fat in the tissue being studied. Fat saturation is recommended for suppression of signal from large amounts of fat and reliable acquisition of contrast material-enhanced images. The main drawbacks of this technique are sensitivity to magnetic field nonuniformity, misregistration artifacts, and unreliability when used with low-field-strength magnets. Inversion-recovery imaging allows homogeneous and global fat suppression and can be used with low-field-strength magnets. However, this technique is not specific for fat, and the signal intensity of tissue with a long T1 and tissue with a short T1 may be ambiguous. Opposed-phase imaging is a fast and readily available technique. This method is recommended for demonstration of lesions that contain small amounts of fat. The main drawback of opposed-phase imaging is unreliability in the detection of small tumors embedded in fatty tissue.

Adipose Tissue↗
PubMedDate not supplied

Methicillin-resistant Staphylococcus aureus in horses at a veterinary teaching hospital: frequency, characterization, and association with clinical disease.

Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging equine pathogen. To attempt to control nosocomial and zoonotic transmission, an MRSA screening program was established for all horses admitted to the Ontario Veterinary College Veterinary Teaching Hospital, whereby nasal screening swabs were collected at admission, weekly during hospitalization, and at discharge. MRSA was isolated from 120 (5.3%) of 2,283 horses: 61 (50.8%) at the time of admission, 53 (44.2%) during hospitalization, and 6 from which the origin was unclear because an admission swab had not been collected. Clinical infections attributable to MRSA were present or developed in 14 (11.7%) of 120 horses. The overall rate of community-associated colonization was 27 per 1,000 admissions. Horses colonized at admission were more likely to develop clinical MRSA infection than those not colonized at admission (OR 38.9, 95% CI 9.49 160, P < 0.0001). The overall nosocomial MRSA colonization incidence rate was 23 per 1,000 admissions. The incidence rate of nosocomial MRSA infection was at the rate of 1.8 per 1,000 admissions, with an incidence density of 0.88 per 1,000 patient days. Administration of ceftiofur or aminoglycosides during hospitalization was the only risk factor associated with nosocomial MRSA colonization. MRSA screening of horses admitted to a veterinary hospital was useful for identification of community-associated and nosocomial colonization and infection, and for monitoring of infection control practices.

Animals↗
PubMedDate not supplied

[Constrictive pericarditis and post-radiotherapy myocarditis with mitral incompetence (author's transl)].

The cardiac complications of radiotherapy of the thorax (e.g. for Hodgkin's disease and carcinoma of the breast) are various: 1) Pleural effusions, occurring a few months to two years after radiotherapy, spontaneously curable but may give signs of tamponnade or lead to constriction. 2) Constrictive pericarditis often several years after irradiation, with a poor prognosis in spite of attempts at pericardectomy which is indicated at the stage of hemodynamic constriction. 3) Myocardial involvement with advanced fibrosis and with various clinical presentations. The failure of pericardectomy and mitral incompetence were evidence of myocarditis in the case reported here.

Adolescent↗