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P Choquet

Publications and source records attributed to P Choquet.

12 recordsLinked to original sources
PubMed2005

Potential applications of laser polarised xenon for CBF measurements by NMR.

Laser polarised (hyperpolarised) 129Xe offers a new potential way for assessment of cerebral blood flow (CBF) by nuclear magnetic resonance (NMR). We present the basic physical principles underlying noble gases'laser polarisation. Distinguishing characteristics of 129Xe NMR properties as well as theoretical basis for CBF measurement using laser polarised 129Xe are emphasized. Recent results are briefly presented and potential applications as well as current limitations of 129Xe in CBF studies are discussed.

Brain Diseases↗
PubMed2001

Xenon-129 MR imaging and spectroscopy of rat brain using arterial delivery of hyperpolarized xenon in a lipid emulsion.

Hyperpolarized (129)Xe dissolved in a lipid emulsion constitutes an NMR tracer that can be injected into the blood stream, enabling blood-flow measurement and perfusion imaging. A small volume (0.15 ml) of this tracer was injected in 1.5 s in rat carotid and (129)Xe MR spectra and images were acquired at 2.35 T to evaluate the potential of this approach for cerebral studies. Xenon spectra consistently showed two resonances, at 194.5 ppm and 199.0 ppm relative to the gas peak. The signal-to-noise ratio (SNR) obtained for the two peaks was sufficient (ranging from 12 to 90) to follow their time courses. 2D transverse-projection xenon images were obtained with an in-plane resolution of 900 microm per pixel (SNR range 8-15). Histological analysis revealed no brain damage except in two rats that had received three injections.

Animals↗
PubMed2000

In vivo 129Xe NMR in rat brain during intra-arterial injection of hyperpolarized 129Xe dissolved in a lipid emulsion.

Hyperpolarized 129Xe was dissolved in a lipid emulsion and administered to anaesthetized rats by manual injections into the carotid (approximately 1-1.5 mL in a maximum time of 30 s). During injection, 129Xe NMR brain spectra at 2.35 T were recorded over 51 s, with a repetition time of 253 ms. Two peaks assigned to dissolved 129Xe were observed (the larger at 194 +/- 1 ppm assigned to intravascular xenon and the smaller at 199 +/- 1 ppm to xenon dissolved in the brain tissue). Their kinetics revealed a rapid intensity increase, followed by a plateau (approximately 15 s duration) and then a decrease over 5 s. This behaviour was attributed to combined influences of the T1 relaxation of the tracer, of radiofrequency sampling, and of the tracer perfusion rate in rat brain. Similar kinetics were observed in experiments carried out on a simple micro-vessel phantom. An identical experimental set-up was used to acquire a series of 2D projection 129Xe images on the phantom and the rat brain.

Animals↗
PubMed1999

Ex vivo high resolution MR imaging of the human lip with a dedicated low field system.

Histological correlations of the human lip with corresponding magnetic resonance (MR) images obtained ex vivo are presented. MR images were acquired with a dedicated low-field (0.1 T) MR system, with a resolution of 100 x 100 micron2 and a slice thickness of 1 mm using 3D-FLASH sequences. The outermost tissues visible on images are of high signal intensity, while the innermost connective tissues are of low signal intensity, both for skin and oral mucosa. It is possible to use a low-field system to obtain high resolution images of small biological samples.

Biopsy, Needle↗
PubMed1998

Low-field dedicated magnetic resonance imaging: a potential tool for assisting perinatal autopsy.

Although the practice of perinatal autopsy has increased in recent years, examination of the fetus and especially of the fetal brain during the first trimester or the beginning of the second trimester remains difficult. Postmortem high-resolution images of the brain of a normal and an abnormal fetus of the same gestational age (22 weeks) were obtained with a low-field (0.1 T) dedicated magnetic resonance imaging (MRI) system. We demonstrated that a small MRI machine supplemented data from classical necropsy and may help in the interpretation of in utero ultrasound and magnetic resonance images for the antenatal diagnosis of fetal malformations.

Adult↗
PubMed1996

[Interventional MRI. Value of low field strength and very fast 3D steady state imaging sequences for the guidance of a "non" ferromagnetic needle].

PURPOSE: The excellent tissue differenciation provided by MRI in the three directions and the lack of ionizing radiations make it ideal for interventional procedures. Many problems must still be solved: the access to the patient, the size of the artefact produced by interventional instruments and the acquisition time. In this study, we evaluated the influence of field strength for standard imaging sequences on the MRI artefact of a non ferro-magnetic biopsy needle. Then, we developed very fast sequences on a opened 0.1 T dedicated magnet to test in vitro and ex vivo the potential ability of this system in the guidance of the needle. MATERIAL AND METHODS: The biopsy needle was a new stainless steel needle made of 49% Nickel. The needle artefact's size measurements were made at 0.1 T, 0.5 T and 1 T on a bicompartmental phantom (one compartment with a long T1 and another with a long T2), with standard gradient echo (400/12/90 degrees) and spin echo (500/25) sequences. At 0.1 T, we optimized very fast steady state 3D FAST (T1 weighted) and 3D CE-FAST (T2 weighted) sequences to reduce the acquisition time, preserving good image contrasts for a field of view reaching 38 mm and 48 x 64 or 24 x 32 matrix. RESULTS: The larger needle artefact observed on gradient echo images varied from 3.6 mm at 0.1 T to 8.6 mm at 1 T. The shortest acquisition time for 4 contiguous slices of 2mm with a 1.2 mm/pixel resolution and a 24 x 32 matrix was 1.5 s for the 3D FAST (16/9/65 degrees) sequence and 3 s for the 3D CE-FAST (29/22/65 degrees) sequence. We realized a complete MRI guided abdominal puncture on a cat cadaver with 4 series of 15 s 3D FAST images (16/9/65 degrees, 4 slices, 5 excitations, 1.2 mm/pixel, FOV = 77 mm). Besides the cat positioning and the image reconstruction time, the whole puncture lasted 1 min (4 x 15 s). CONCLUSION: Low field MRI (0.1 T) combined with very fast 3D steady state sequences is adapted for the real time guidance of biopsy needles.

Biopsy, Needle↗
PubMed1995

An in vitro study at low field for MR guidance of a biopsy needle.

The aim of this study is to demonstrate in vitro that low field strength can be used for MR interventional procedures. At 0.1 T, we developed 3D, T1-, and T2-weighted fast steady state sequences and measured the artifact created by an MR biopsy needle (22 gauge, 0.7 mm diameter) on a bicompartmental phantom. The artifact generated by the needle placed perpendicular to B0 did not exceed 3.6 mm for 3D steady state sequences and acquisition times reaching 1.5 s. Corresponding artifacts at higher field strength were 7.6 mm for 0.5 T and 8.6 mm for 1 T. Low field MRI proved to be potentially adaptable for the guidance of MR biopsy needles.

Artifacts↗
PubMed1994

Detection of glomus tumor of the finger by dedicated MRI at 0.1 T.

Three glomus tumors of the fingers were detected using a dedicated hand and wrist low field (0.1 T) MR imager equipped with solenoidal coils allowing a FOV of 2 cm. Three-dimensional T1-, T*2-, or T2-weighted images were used (8 contiguous slices of 2 mm thickness). Glomus tumors had low or intermediate signal intensity (2 cases) or no signal (1 case) on T1-weighted images. On T*2- or T2-weighted images they had high signal intensity. MRI findings correlate well with surgery and biopsy.

Adult↗