PubMed Health⌕ Search

Biomedical subjects

D Gibon

Publications and source records attributed to D Gibon.

17 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

[Comparison of conventional and conformational dosimetry in radiotherapy of cerebral neoplasms].

PURPOSE: We prospectively compared a conventional treatment planning (PT2D) and 3-dimensional conformal treatment planning (PT3D) for radiotherapy of cerebral tumours. PATIENTS AND METHODS: Patients treated between 1/10/98 and 1/4/99 by irradiation for cerebral tumours were analysed. For each case, we planned PT2D using conventional orthogonal x-ray films, and afterward, PT3D using CT scan. Gross tumor volume, planning target volume and normal tissue volumes were defined. Dose was prescribed according to report 50 of the International Commission on Radiation Units and Measurements (ICRU). We compared surfaces of sagittal view targets defined on PT2D and PT3D and called them S2D and S3D, respectively. Irradiated volumes by 90% isodoses (VE-90%) and normal tissue volumes irradiated by 20, 50, 90% isodoses were calculated and compared using Student's paired t-test. RESULTS: There was a concordance of 84% of target surfaces defined on PT2D and PT3D. Percentages of target surface under- or-over defined by PT2D were 16 and 13% respectively. VE-90% was decreased by 15% (p = 0.07) with PT3D. Normal brain volume irradiated by 90% isodose was decreased by 27% with PT3D (p = 0.04). CONCLUSION: For radiotherapy of cerebral tumors using only coplanar beams, PT3D leads to a reduction of normal brain tissue irradiated. We recommend PT3D for radiotherapy of cerebral tumors, particularly for low-grade or benign tumors (meningiomas, neuromas, etc.).

Brain Neoplasms↗
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

[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

De novo adhesions with extraperitoneal endosurgical para-aortic lymphadenectomy versus transperitoneal laparoscopic para-aortic lymphadenectomy: a randomized experimental study.

OBJECTIVE: The objective of this study was to compare the risk of adhesion formation and the site of postoperative adhesions after transperitoneal versus extraperitoneal laparoscopic para-aortic lymphadenectomy. STUDY DESIGN: A prospective study was conducted on 66 pigs, randomly allocated to 2 groups of 33 animals that underwent transperitoneal versus extraperitoneal laparoscopic para-aortic lymphadenectomy. RESULTS: No statistically significant difference was observed between the 2 techniques in terms of operating time, number of lymph nodes removed, and intraoperative and postoperative morbidity. More lymphoceles were observed in the extraperitoneal laparoscopy group (P =.0002). The overall adhesion rates were 76% in the transperitoneal group and 43.33% in the extraperitoneal group (P =.04). The adhesion score specific to the operative site was lower in the extraperitoneal group (P =.0005). A stereolocalization study showed that almost all adhesions after transperitoneal laparoscopy were situated in the para-aortic external irradiation field, whereas adhesions after extraperitoneal laparoscopy were predominantly situated outside this field. CONCLUSION: Extraperitoneal laparoscopy generates significantly fewer adhesions in the para-aortic irradiation field.

Animals↗
PubMed1999

Beam collimation and bolusing material optimizations for 10boron neutron capture enhancement of fast neutron (BNCEFN): definition of the optimum irradiation technique.

PURPOSE: In boron-10 neutron capture enhancement of fast neutron irradiation (BNCEFN), the dose enhancement is correlated to the 10B concentration and thermal neutron flux. A new irradiation technique is presented to optimize the thermal neutron flux. METHODS AND MATERIALS: The coupled FLUKA and MCNP-4A Monte Carlo codes were used to simulate the neutron production and transport for the Nice and Orleans facilities. RESULTS: The new irradiation technique consists of a 20-cm lead blocks additional collimator, placed close to the patient's head, which is embedded in a pure graphite cube. A 24-fold thermal neutron flux increase is calculated between a 5 x 5 cm2 primary collimated field, with the patient's head in the air, and the same field size irradiated with the optimum irradiation technique. This increase is more important for the p(60)+Be Nice beam than for the p(34)+Be Orleans one. The thermal neutron flux is 2.1 x 10(10) n(th)/Gy for each facility. Assuming a 100 microg/g 10B concentration, a physical dose enhancement of 22% is calculated. Moreover, the thermal neutron flux becomes independent of the field size and the phantom head size. CONCLUSION: This technique allows conformal irradiation of the tumor bed, while the thermal neutron flux is enhanced, and spreads far around the tumor.

Boron Neutron Capture Therapy↗
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↗
PubMed1997

Assessment of image intensifier and distortion for DSA localization studies.

The authors present methods of correcting pincushion and S distortions of an image intensifier, and of measuring the geometrical parameters of the imaging device used for localization from digital subtraction angiography brain studies. Pincushion and S distortions of the image intensifier are corrected by a calibration grid. A test pattern is used to study effectiveness of the corrections. Intrinsic geometrical parameters (source-to-image distance, centre of X-ray projection) of the apparatus are measured by the use of a calibration phantom. Short-range and long-range time drift of the distortion, as well as influence of the parameters of image acquisition on the accuracy of the localization results, are considered. The results obtained successfully demonstrate the accuracy of the correction, provided that the apparatus is warm.

Angiography, Digital Subtraction↗
PubMed1997

[Determination of target volume for dosimetric planning in stereotactic radiosurgery].

Stereotactic radiosurgery needs an accurate determination of the target volumes to be irradiated and of sensitive volumes to be spared: position, external boundaries, internal volume. These parameters can be obtained by using either projection imaging (radiographs, digital angiography), or tomographic imaging (magnetic resonance imaging, computerized tomography). The authors describe the methods used in these different imaging modalities and the problems encountered in target determination. Methods of validations are described. Results obtained on phantoms and on actual target volume are given and discussed.

Humans↗
PubMed1995

Treatment planning optimization by conjugate gradients and simulated annealing methods in stereotactic radiosurgery.

PURPOSE: This paper presents a new optimization method of treatment planning in linac stereotactic radiosurgery. METHODS AND MATERIALS: On a workstation integrating x-rays, computed tomography (CT), magnetic resonance imaging (MRI), and digital subtracted angiography (DSA) images, we first determine the outlines of the target volume and surrounding healthy tissues to spare. To achieve complete optimization of the treatment plans, this method decomposes the optimization process in two steps. The position of the isocenters and the diameter of the collimators are first deduced by a conjugate gradients method, from the position and size of ellipsoids or spheres modeling the target volume. The other irradiation parameters, such as the isocenter dose, the aperture, and the weight of each irradiation plane and of their irradiation sectors are finally deduced by a simulated annealing optimization algorithm. RESULTS: The system can perform multitarget/multisector treatment plans that are automatically obtained in a satisfactory time (as a rule, 20 min for a two-target irradiation), much faster than the time needed for a manual treatment planning. We present the results in two cases: the simulation of a single-target treatment and a two-target real treatment with constraints. In these two cases, we can control the dose received by target and sensitive volumes. CONCLUSION: This method achieves an excellent conformation of the estimated isodose curves with the outlines of the target volume, which allows us to avoid the surrounding healthy tissues, thanks to the different weighting factors given on each volume concerned according to the importance we grant to each of them.

Angiography, Digital Subtraction↗
PubMed1995

A frameless stereotaxic localisation system using MRI, CT and DSA.

The authors present a method of stereotaxic localisation using magnetic resonance imaging (MRI) computerized tomography (CT) and digital subtracted angiography (DSA) which does not require localisation frams fixed to the patient's skull, but uses only four cranial landmarks corresponding to the holders of the neurosurgical stereotaxic frame. The method presents no major constraints in routine examinations. The geometrical distortions of the imaging devices are corrected. Three-dimensional localisation is performed using sagittal and axial slices in MRI, axial slices in CT and only two associated frontaly and lateral views in DSA. The images data are transferred to a PC-based system. By locating the landmarks on the images, the transformation matrixes can be computed to obtain the 3D coordinates of a target in the stereotaxic space and in any imaging modality. The results obtained show the precision of the corrections and the millimetre accuracy of pin-point target localisation.

Angiography, Digital Subtraction↗
PubMed1994

Technical note: magnetic resonance imaging of agarose gel phantom for assessment of three-dimensional dose distribution in linac radiosurgery.

An agarose gel phantom is used to evaluate the spatial distribution of the dose delivered by a linac radiosurgery device. Dependence of the absorbed dose on the T1 relaxation time is checked. T1 magnetic resonance images show the close correspondence between the actual absorbed dose distribution and the dose distribution expected by the treatment planning.

Gels↗
PubMed1993

Frameless method of stereotaxic localization with DSA.

PURPOSE: To improve a method of stereotaxic localization with digital subtraction angiography that does not require use of a localization frame fixed to the patient's skull during examination. MATERIALS AND METHODS: An independent, low-cost, stereotaxic computing system was devised. Software programs used magnetic resonance images, computed tomographic scans, and digitized radiographs of plastic bone implants with head landmarks to establish reference trihedrons in each imaging system, transpose target coordinates from one system to another, adjust surgical instruments, help plan radiation surgery, and compute and display isodose curves. RESULTS: The geometric distortions of the image intensifier were corrected. Distortion problems of the conic projection were solved, and three-dimensional localization was achieved with only two associated front and lateral views. Accuracy to within 1 mm was achieved for the three coordinates. CONCLUSION: This frameless stereotaxic localization technique is highly accurate and reliable. The system allows maximum automation of examination procedures.

Angiography, Digital Subtraction↗
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↗
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↗