Determination of the lipid content of organic waste using time-domain nuclear magnetic resonance.

Time-Domain Nuclear Magnetic Resonance (TD-NMR) was used to quantify the lipid contents of 48 different organic waste substrates. Results obtained from TD-NMR were compared to those from Soxhlet extraction, currently the prevalent method for organic waste characterization, especially in the field of anaerobic digestion. Two calibration methods were tested. The first was a self-calibration process using pure oils (NMR1) which showed good repeatability compared to Soxhlet extraction with a better coefficient of variation (5%). Analyses of volatile fatty acids (VFA) and long-chain fatty acids (LCFA) by chromatography were carried out to understand why the NMR1 method produced underestimations for some samples. Statistical analysis showed that the presence of saturated fatty acids had a significant effect on differences between the Soxhlet and NMR1 methods. The second calibration method applied chemometrics to TD-NMR raw data (NMR2), taking Soxhlet extraction values as references. It provided a good prediction of lipid content and avoided the lengthy calibration procedure usually required for this type of study. Last, the NMR2 method was shown to be highly suited to the quantification of lipids in organic waste, demonstrating better repeatability than the classic Soxhlet method.

Quantitative study of signal decay due to magnetic susceptibility interfaces: MRI simulations and experiments.

Characterization of magnetic susceptibility artifacts is required in a wide range of MRI studies. Experiments with a 0.2T magnet and MRI simulations were used to assess the signal decay over echo time at different pixel sizes in the case of air-water interfaces. The specific experimental signal modulation which was reproduced in simulation was interpreted. Concordance between simulation and experiments should make possible further studies of magnetic susceptibility effects with more complex objects as in molecular imaging and in porous medium imaging.

Comparison of the lipid content and fatty acid composition of intermuscular and subcutaneous adipose tissues in pig carcasses.

Lipid contents and compositions were measured in 35 pigs from seven genotype-sex groups with large variations in body composition. The animals were slaughtered at 115kg live weight, and the left side was separated into four primal cuts: belly, ham, loin, and shoulder. Samples of adipose tissues were taken from flare fat and from subcutaneous and intermuscular adipose tissues in each of the four cuts. In the loin, the outer and inner layers of subcutaneous adipose tissue were sampled separately. Total lipid content was lower in intermuscular than in subcutaneous adipose tissue. It was the highest in flare fat. There was a gradient of decreasing unsaturation from the outer layer of subcutaneous adipose tissue, to the inner layer, to intermuscular adipose tissue, to flare fat. The monounsaturated fatty acid concentrations followed the same pattern. There was a statistically positive correlation between the linoleic acid concentration of the different adipose tissues and the half carcass muscle content.

Quantification of muscle, subcutaneous fat and intermuscular fat in pig carcasses and cuts by magnetic resonance imaging.

The aim of this study was to determine the suitability of magnetic resonance imaging (MRI) to predict tissue composition of pig carcasses and cuts. Twenty-four pig carcasses were cut into the four primary cuts that were analyzed with a low field MRI imager before a total dissection. Images were then processed to identify and quantify pixels representing muscle, subcutaneous fat and intermuscular fat fractions. MRI provided a good prediction of muscle content in cuts and carcasses, with R(2) ranging from 0.970 to 0.997. The prediction was slightly less accurate for total fat (0.951⩽R(2)⩽0.986) or subcutaneous fat (0.918⩽R(2)⩽0.994). Finally, the prediction of intermuscular fat content in considering intermuscular fat classified pixels was acceptable only for the belly (R(2)=0.837).

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.

Determination of the lean meat percentage of pig carcasses using magnetic resonance imaging.

The purpose of Workpackage 3 of the European Eupigclass project was to test indirect methods of measuring the lean meat percentage of a carcass that would be less costly, at least as accurate and more consistent than dissection. Magnetic resonance imaging was one of the three indirect methods tested to measure the lean meat weight and the lean meat percentage of pig carcasses, the other methods being X-ray CT and vision techniques. One hundred and twenty carcasses from three different genotypes and from both sexes were slaughtered. The left parts of the carcasses were fully dissected and the right parts were investigated with an indirect method using a 1.5T MRI system. The acquisition protocol was chosen to give an optimized contrast between fat and muscle tissues. Two different approaches, image segmentation and PLS regression, were used to extract information from the images. Automatic image segmentation was performed to quantify the volume of muscle in the images and gave a standard error of prediction using a linear regression with the dissection of the left half carcasses of 586g and 1.10% for lean meat weight and lean meat percentage, respectively. PLS regression using the signal intensities histograms gave an estimation error of 465g for lean meat weight. These results showed that MRI could be used in place of full dissection for authorizing and monitoring classification equipment of pig carcasses.

Correction of intensity nonuniformity in spin-echo T(1)-weighted images.

This paper presents a method to correct intensity nonuniformity in spin-echo T(1)-weighted images and particularly the inhomogeneities due to RF transmission imperfections which have tissue-dependent effects through the T(1) relaxation times. This method is based on the use of a uniform phantom, first for classic normalization by division by the phantom images, and second for T(1)-correction using the RF transmitted cartography. We present experimental results from a bi-phasic (oil/water) phantom and from a salmon with a 0.2 T imager. The results demonstrate the efficiency of the method in the two cases and its ability to cope with partial volume effect.

Estimation of poultry breastmeat yield: magnetic resonance imaging as a tool to improve the positioning of ultrasonic scanners.

Magnetic resonance imaging (MRI) was used to reconstruct three-dimensional breast muscle volume of 30 broilers and to locate the most suitable cross-sections to estimate breast muscle yield by ultrasonic scanner. The high accuracy of the determination of the breast muscle yield (R(2)=0.92) from the volume calculated by the sum of 6 mm-spaced MRI transverse images justified the choice of MRI as a reference method. Treatment of the images showed that it was possible to obtain acceptable breast meat yield prediction by MRI from a combination of two or three muscle transverse cross-section area measurements. It also showed that the need to find interfaces reflecting ultrasound is a considerable handicap for optimizing the ultrasonic technique. The oblique echotomographic plane crossing the coracoid bone lengthwise and the fore part of the breast bone appears to be the most appropriate to improve significantly the determination provided by the transverse image situated at the fore part of the breast bone.

Quality of pig adipose tissue: relationship between solid fat content and lipid composition.

The dependence of solid fat content at 20°C of adipose tissues on their fatty acid and triacylglycerol compositions was studied on lipids extracted from tissues from 166 pigs. The solid fat content (SFC20) was 20% on average but varied widely (9-35%). The SFC20 variability was closely related to the proportions of disaturated triacylglycerols and more specifically to palmitoyl-stearoyl-oleoyl-glycerol (R(2)=0.92). The SFC20 variability was also related to the proportions of the saturated fatty acids, palmitic and stearic acids (R(2)=0.94). The part of the variance of SFC20 explained by the proportion of polyunsaturated fatty acids was lower (R(2)=0.48). The iodine value showed a high correlation with SFC20 (R(2)=0.81) but carcass lean content was a poor indicator of the solid fat content of adipose tissues (R(2)=0.06).