Use of magnetic resonance imaging for noninvasive characterization and follow-up of an experimental injury to normal mouse muscles.

A magnetic resonance imaging protocol was tested in a cardiotoxin-induced myonecrosis of hindlimb muscles of three normal mice to assess the usefulness of data provided by longitudinal follow-up of a few individuals. Magnetic resonance imaging examinations were performed sequentially at 4 T between days 1 and 11 post-injury. Axial T1-weighted images after injection of a paramagnetic contrast agent were used to determine the volume of lesions from regions of increased signal intensity. T2 measurements were performed from a single-slice ten-echo acquisition centered upon the largest section of lesion. Early after injury, a very large T2 increase was observed. As recovery proceeded, T2 values progressively decreased toward normal values. Similarly, the volumes of lesions decreased to virtually zero by days 10-11. The evolution of these indices followed the same time scheme observed in histological studies. The use of a volume probe allowed accurate measurement of T2 values, and the acquisition of volumetric data. Such magnetic resonance imaging follow-up should help gather valuable information using few animals.

Muscular transverse relaxation time measurement by magnetic resonance imaging at 4 Tesla in normal and dystrophic dy/dy and dy(2j)/dy(2j) mice.

Muscular transverse relaxation times values were measured in vivo in normal mice (strain C57BL6/J, n=14) and in murine models of human congenital muscular dystrophy (dy/dy, n=9; dy(2j)/dy(2j), n=8). A single-slice multi-echo sequence was used. Gastrocnemius/soleus complex, thigh and buttock muscles were studied. Muscular transverse relaxation times values were compared between different muscle groups in each type of animal and between animal groups. Differences were observed between normal and dy(2j)/dy(2j) mice from 3 to 12 weeks of age, and between normal and dy/dy mice at 6 weeks. In specific age ranges, the values of muscular transverse relaxation times in two dystrophic models are different from those in normal mice, and could thus be used as an index of modifications in dystrophic muscle to evaluate therapies.

[Role of MRI in the diagnosis of breast diseases]. / Place de l'IRM dans le diagnostic des affections mammaires.

UNLABELLED: ADVANTAGES AND LIMITATIONS: Magnetic resonance imaging of the breast is probably the most sensitive method for detecting or ruling out breast disease. It is however not as specific as expected. TECHNIQUE: All examinations are performed with and without gadolinium intravenous administration, excepted in the case of silicone implant reconstruction mammoplasty. Dynamic contrast-enhanced MRI sequences are necessary with a permanent balance between temporal resolution, spatial resolution, and signal. MRI of the breast is not indicated as a routine examination in a screening program, neither to improve the specificity of infra-clinic lesions, nor in simply dense breasts without any known risk factor or in circumscribed masses. INDICATIONS: MRI is best used to improved the sensitivity of mammography and sonography in selected patients. The selected indications are: evaluation of the volume and extension of breast lesions evaluation of the therapeutic response after chemotherapy, and detection or exclusion of the local recurrence in patients with breast conservation therapy. PERSPECTIVES: The future indications and perspectives of MRI include interventional breast radiology (MRI-guided core biopsy), and thermocoagulation therapy. It may be interesting for the evaluation of patients with contrast enhanced MRI lesions with normal mammography and sonography, and also in woman with a genetically defined high breast cancer risk.