MRI OF HUMAN KNEE AT 7 T WITH DEDICATED RADIOFREQUENCY COILS

Magnetic Resonance (MR) Imaging is a valuable tool in the diagnosis and monitoring of various musculoskeletal pathologies. New Ultra-High Field (UHF) 7 T MRI systems, with their enhanced Signal-to-Noise Ratio, may offer increased image quality in terms of spatial resolution and/or shorter scanning time compared to lower field systems. However, these benefits can be difficult to obtain because of increased radio-frequency (RF) inhomogeneity, increased Specific Absorption Rate (SAR) and the relative lack of specialized and commercially available RF coils compared to lower field systems. The IMAGO7 Foundation in Pisa (Italy) owns the first and only 7 Tesla whole-body MR scanner (950-MR scanner, GE Medical Systems) in Italy. In this framework, a research collaboration between the IMAGO7 Foundation and the Italian National Institute for Nuclear Physics (INFN) aims to develop RF coils for specific MR applications, and to exploit the UHF potential in several research areas, including MSK imaging. This study reports the feasibility of imaging in trabecular bones and cartilages at UHF by means of dedicated radio-frequency coils for proton imaging which have been designed, developed, optimized and validated in vivo, and are now ready for clinical research studies. UHF MRI of the knee can allow an accurate characterization of morphology and biochemical quality of the cartilages for clinical assessment of early pathological conditions of cartilage in osteoarthritis. Six healthy (age 24-61y) and one pathological (alteration of the patellar cartilage, 62y) volunteers were considered for preliminary acquisitions. Morphological images have been acquired by means of 3D FIESTA (0.156 mm in-plane resolution, FA = 20, TR = 6.3 ms, TE = 2.5 ms, thickness = 0.8 mm sequences). The patellar cartilages was then segmented and the volumes of the segmented cartilages have been quantified. In order to evaluate also the biochemical behaviour of the cartilage in the pathological subject, T2 (with multi echo SE with 4 echo times sequence) and T2* (by 3D MERGE with 6 echo times sequence) maps have been also computed. The obtained results demonstrate that the research in trabecular bone and cartilages characterization, comprising quantitative assessment of cartilage volume and evaluation of biochemical behaviour, can take advantage from UHF MRI with dedicated coils.