Magnetic resonance imaging assessment of skeletal muscle changes following chronic denervation in the dog

This study sought to evaluate the effect of presumed chronic denervation (due to brachial plexus mass lesions) on the magnetic resonance imaging (MRI) appearance of muscle in the dog. One of the features of denervation that has been described is fat infiltration; prior to defining the effect of the brachial plexus mass lesions, this study first attempted to define the normal patterns of fat deposition with increasing body condition scores. MRI assessment of subcutaneous and intramuscular fat deposition was compared against two previously described methods of body condition scoring in the dog. There was a significant relationship between the 9-point body score (BCS) assessment and body fat percentages calculated on the basis of girth and hock measurements. Both of these methods correlated well with MRI determination of subcutaneous fat (SCF) thickness in the dorsal lumbar area and with total (dorsal and ventral) SCF in the cervical area. What was evident from the MRI evaluation of fat deposition was that the pattern of fat deposition in these regions differed, being predominantly subcutaneous in the lumbar region, but with fat deposition in both the subcutaneous and intermuscular regions in the cervical region. In both regions the amount of fat deposition increased from cranial to caudal. Intramuscular fat deposition assessed in terms of T1W signal hyperintensity in the lumbar epaxial muscles correlated well with BCS, though for cervical muscles the correlation was weaker and increasing BCS appeared to have less effect on MRI signal change in normal neck muscle. Having decided to focus on brachial plexus mass lesions, the ability to identify the individual proximal thoracic limb muscles by MRI was assessed. Proximal thoracic limb muscles identification and MRI appearance were found to depend on the MRI plane position, relative to the spine of the scapula. Better results for the identification of individual muscles were achieved on images with the plane aligned parallel to the spine of the scapula or at 90 degree angle to it, and with the limbs positioned in extension along the body and symmetrically to each other. Transverse images permitted better muscle detection. MRI of the proximal thoracic limb of 19 dogs with brachial plexus mass lesions showed a mixed pattern of T1W and T2W hyperintensity and variable degrees of muscles atrophy. Mass lesions were found in three shapes – globoid, tubular and fusiform. Multiple lesions were detected in 9 cases, and in 6 out of 9 cases these included lesions within the thoracic cavity. In 9 cases vertebral canal involvement was evident. Mass lesions were best detectable on the short tau inversion recovery sequence (STIR) followed by T2W and T1FatSat with contrast

Quantitative CT imaging for adipose tissue analysis in mouse model of obesity

International audienceIn obese humans CT imaging is a validated method for follow up studies of adipose tissue distribution and quantification of visceral and subcutaneous fat. Equivalent methods in murine models of obesity are still lacking. Current small animal micro-CT involves long-term X-ray exposure precluding longitudinal studies. We have overcome this limitation by using a human medical CT which allows very fast 3D imaging (2 sec) and minimal radiation exposure. This work presents novel methods fitted to in vivo investigations of mice model of obesity, allowing (i) automated detection of adipose tissue in abdominal regions of interest, (ii) quantification of visceral and subcutaneous fat. For each mouse, 1000 slices (100μm thickness, 160 μm resolution) were acquired in 2 sec using a Toshiba medical CT (135 kV, 400mAs). A Gaussian mixture model of the Hounsfield curve of 2D slices was computed with the Expectation Maximization algorithm. Identification of each Gaussian part allowed the automatic classification of adipose tissue voxels. The abdominal region of interest (umbilical) was automatically detected as the slice showing the highest ratio of the Gaussian proportion between adipose and lean tissues. Segmentation of visceral and subcutaneous fat compartments was achieved with 2D ½ level set methods. Our results show that the application of human clinical CT to mice is a promising approach for the study of obesity, allowing valuable comparison between species using the same imaging materials and software analysi