Biomedical subjects

F Mariette

Publications and source records attributed to F Mariette.

5 recordsLinked to original sources

PubMed2005

Muscle and fat quantification in MRI gradient echo images using a partial volume detection method. Application to the characterization of pig belly tissue.

Complete dissection is the current reference method to quantify muscle and fat tissue on pig carcasses. Magnetic resonance imaging (MRI) is an appropriate nondestructive alternative method that can provide reliable and quantitative information on pig carcass composition without losing the spatial information. We have developed a method to quantify the amount of fat tissue and muscle in gradient echo MR images. This method is based on the method proposed by Shattuck et al. [12]. It provides segmentation of pure tissue and partial volume voxels, which allows separation of muscle and fat tissue including the fine insertions of intermuscular fat. Partial volume voxel signal is expected to be proportional to the signals of pure tissue constituting them or at least to vary monotonously with the proportion of each tissue. However, it is not always the case with gradient echo sequence due to the chemical shift effect. We studied this effect on a fat tissue/muscle interface model with variable proportion of water in the fat tissue and variable TE. We found that at TE=8 ms, for a 0.2-T MRI system, the requirement of Shattuck's method were filled thanks to the presence of water in fat tissue. Moreover, we extended the segmentation method with a simple correction scheme to compute more accurately the proportions of each tissue in partial volume voxels. We used this method to evaluate the fat tissue and muscle on 24 pig bellies using a gradient echo sequence (TR 700 ms, TE 8 ms, slice thickness 8 mm, number of averages 8, flip angle 90 degrees , FOV 512 mm, matrix 512*512, Rect. FOV 4/8, 19 slices, space between slices 2 mm). The image analysis results were compared with dissection results giving a prediction error of the muscle content (mean=2.7 kg) of 88.9 g and of the fat content (mean=2.7 kg) of 115.8 g without correction of the chemical shift effect in the computation of partial volume fat content. The correction scheme improved these results to, respectively, 81.5 and 107.1 g.

Abdomen↗

PubMed2004

Quantitative measurement of temperature by proton resonance frequency shift at low field: a general method to correct non-linear spatial and temporal phase deformations.

MRI thermometry methods are usually based on the temperature dependence of the proton resonance frequency. Unfortunately, these methods are very sensitive to the phase drift induced by the instability of the scanner which prevents any temperature mapping over long periods of time. A general method based on 3D spatial modelling of the phase drift as a function of time is presented. The MRI temperature measurements were validated on gel samples with uniform and constant temperature and with a linear temperature gradient. In the case of uniform temperature conditions, correction of the phase drift proved to be essential when long periods of acquisition were required, as bias could reach values of up to 200 degrees C in its absence. The temperature uncertainty measured by MRI was 1.2 degrees C in average over 290 min. This accuracy is coherent with the requirements for food applications especially when thermocouples are useless.

Journal Article↗

PubMed2004

Influence of MRI acquisition protocols and image intensity normalization methods on texture classification.

Texture analysis methods quantify the spatial variations in gray level values within an image and thus can provide useful information on the structures observed. However, they are sensitive to acquisition conditions due to the use of different protocols and to intra- and interscanner variations in the case of MRI. The influence was studied of two protocols and four different conditions of normalization of gray levels on the discrimination power of texture analysis methods applied to soft cheeses. Thirty-two samples of soft cheese were chosen at two different ripening periods (16 young and 16 old samples) in order to obtain two different microscopic structures of the protein gel. Proton density and T(2)-weighted MR images were acquired using a spin echo sequence on a 0.2 T scanner. Gray levels were normalized according to four methods: original gray levels, same maximum for all images, same mean for all images, and dynamics limited to micro +/- 3sigma. Regions of interest were automatically defined, and texture descriptors were then computed for the co-occurrence matrix, run length matrix, gradient matrix, autoregressive model, and wavelet transform. The features with the lowest probability of error and average correlation coefficient were selected and used for classification with 1-nearest neighbor (1-NN) classifier. The best results were obtained when using the limitation of dynamics to micro +/- 3sigma, which enhanced the differences between the two classes. The results demonstrated the influence of the normalization method and of the acquisition protocol on the effectiveness of the classification and also on the parameters selected for classification. These results indicate the need to evaluate sensitivity to MR acquisition protocols and to gray level normalization methods when texture analysis is required.

Cheese↗

PubMed2003

Effect of tamoxifen at low doses on ultrasensitive C-reactive protein in healthy women.

The use of tamoxifen as a breast cancer preventive agent may be contraindicated by an increased risk of endometrial cancer and venous thromboembolic events, particularly in postmenopausal women. Since these estrogenic effects may be dose-related, a dose reduction may reduce toxicity. We have recently shown a comparable activity of lower doses of tamoxifen on putative surrogate biomarkers of cardiovascular disease and breast cancer. To provide further insight into the effect of tamoxifen at low doses on the cardiovascular system, we compared the effect of three different doses on circulating levels of C-reactive protein (CRP), an independent risk marker for cardiovascular disease (CVD), which was lowered by tamoxifen at the standard dose of 20 mg day-1 in previous studies. We compared the changes in CRP after 2 months of either placebo (n = 24), or tamoxifen 10 mg alternate daily (n = 26), or 10 mg day-1 (n = 22), or 20 mg day-1 (n = 19) in healthy women aged 35-70 years. The median percent change was -2.2% (95% CI, -23.3 to 42.8) with placebo, -39.1 (95% CI, -59.9 to -28.7) with 10 mg alternate daily, -56.9% (95% CI, -68.6 to -38.4) with 10 mg day-1 and -42.9% (95% CI, -62.6 to 1.6) with 20 mg day-1 (P = 0.291 for the linear dose-response trend). Similar results were obtained when the data were classified according to blood tamoxifen concentrations, with a median reduction of 47% (95% CI, 65.5-36.3) for women with low tamoxifen concentrations (< 30 ng mL-1). We conclude that tamoxifen at low doses is able to lower ultrasensitive CRP and that this might be associated with a beneficial effect on CVD.

Adult↗

PubMed2000

1H nuclear magnetic resonance relaxometric characterization of fat and water states in soft and hard cheese.

The aim of this work was to study the spin spin (T2) relaxation components of one hard cheese and three soft cheeses to characterize fat and water states. NMR signals were measured at 6 degrees C with a 0.47 T NMR device. The transverse relaxation decay was fitted using the Marquardt method. The T2 relaxometric behaviour of the cheeses under consideration was characterized by four relaxation components. To understand the chemical composition of each NMR component, we studied anhydrous milk fat extracted from each cheese analysed. At 6 degrees C, the fat was 60% crystalline. In cheese, the solid fat was found mainly in the shorter relaxation component with a T2 of 17 micros. The intensity of the NMR relaxation with a T2 > 1 ms was explained by the amount of water, liquid fat and proteins, and the associated relaxation time varied as a function of the process used. The composition of each relaxation component was confirmed by the temperature effect and the influence of the fat content on the NMR cheese signal. NMR relaxometry was able to provide information on water behaviour (i.e. the quantity and level of interactions with proteins) and on the solid:liquid ratio of anhydrous milk fat in the cheese.

Cheese↗