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Y Picard

Publications and source records attributed to Y Picard.

7 recordsLinked to original sources
PubMed2001

A novel mutation in the anti-müllerian hormone gene as cause of persistent müllerian duct syndrome.

UNLABELLED: Persistent müllerian duct syndrome is a relatively rare inherited defect of sexual differentiation characterised by failure of regression of the müllerian ducts in males. In affected individuals, uterus and tubes are present because of defects of synthesis or action of anti-müllerian hormone (AMH), normally produced by the Sertoli cells of the testis. Patients are normally virilised, although mono- or bilateral cryptorchidism may be present. We observed two brothers (chromosomes 46 XY), aged 11 years and 2 months and 8 years and 3 months respectively, with bilateral cryptorchidism. The diagnosis of persistent müllerian duct syndrome was made on the basis of laparoscopic evidence of uterus and tubes, undetectable plasma levels of AMH and a 23 base pair duplicative insertion in exon 5 of the AMH gene, causing the introduction of a premature stop codon, homozygous in the two brothers. The surgical correction of the genital abnormalities was successfully carried out by laparoscopic orchidopexy according to Fowler-Stephens. CONCLUSION: Persistent müllerian duct syndrome should be taken into consideration in all cases of bilateral cryptorchidism. Laparoscopy is the elective procedure for diagnosis of this disease and laparoscopic surgery for orchidopexy of intra-abdominal testes. Mutation analysis of the anti-müllerian hormone gene in these patients helps to understand the structure-function relationship of the anti-müllerian hormone protein, although it is not clear at present whether anti-müllerian hormone is necessary to maintain normal testicular function.

Anti-Mullerian Hormone↗
PubMed1997

Motion correction of PET images using multiple acquisition frames.

Positron emission tomography (PET) is a relatively lengthy brain imaging method. Because it is difficult for the subject to stay still during the data acquisition, head motion during scans is a source of image degradation. A simple data acquisition technique to reduce the effect of this problem is described. The technique associates the incoming data with the real-space position of the head. During the PET scan, the head position is constantly monitored with two video cameras and compared to its initial position. Every time the displacement for a region within the field of view (FOV) is larger than a specified threshold displacement, the PET data acquisition system starts to save the PET data in a new frame. The total number of frames required for a complete study depends on the magnitude of the head motion during the study and on the threshold displacement. At the end of the study, all the acquired frames are reconstructed independently and each image is rotated and translated to coincide with the initial position. When these images are summed, they produce a final image with fewer motion artefacts.

Artifacts↗
PubMed1992

PETSIM: Monte Carlo simulation of all sensitivity and resolution parameters of cylindrical positron imaging systems.

Monte Carlo simulation techniques are applied to track the annihilation photons from positron decay, and store the photon histories. Reasonably realistic models of the isotope distribution in the brain and heart during typical PET studies, as well as the traditional phantoms used for measuring PET scanner performance can be built out of up to 10 hollow or solid cylinders. Separate programs model the source distribution and its attenuation characteristics, the collimators and the detectors. These modules are connected by compact gamma history files which are stored on disc or tape. Over 50 million gamma ray histories can be saved on a 1 Gbyte disc, representing the decay of several billion atoms. This allows for good precision even for single thin slices in scanners with wide axial acceptance. The simulation results include spectrum analysis, sensitivity to true coincident events, scattered coincident and single rays, and the effects on these parameters of detector dead time. The storage of intermediate results on tape reduces simulation time, since most common source geometries need be generated only once. The sensitivities in multi-slice systems are presented as matrices of coincident crystal planes. The matrix shows the true count sensitivity and the scatter fraction together for each valid combination of planes. This presentation is very useful for assessing the effects of various degrees of inter-plane collimation. The spatial resolution analysis includes the effects of positron range, non-collinearity of the gamma rays, multiple interaction within the detectors, and the effects of quantization into single crystals in multiple-crystal block detectors. Each of these effects can be turned on or off without repeating the simulation. Both in-plane and axial resolutions are calculated as a function of location of the positron-emitting nucleus and the angle of incidence of gamma rays on the crystals. Single crystals, blocks and crystals with depth of interaction encoding can be specified, as can the method of backprojection (planar, or 3D), so that the detector geometry can be optimized.

Computer Simulation↗