Magnetic resonance T2* mapping sequence for imaging of talar cartilage injury under traction with the small field of view coil.

Background: The accurate diagnosis of talus cartilage injury is difficult to achieve on conventional sequences. This study aimed to assess the application values of axial traction during high resolution 3.0-T magnetic resonance imaging (MRI) of the ankle on T2* mapping quantitative assessment of talar cartilage imaging with a small field of view (FOV) coil. Methods: A prospective study of 18 volunteers and 31 patients undergoing high-resolution MRI of the ankle with an FOV coil with and without axial traction (5 kg) was performed. Quantitative cartilage assessment included three T2* mapping sequences: (I) dedicated ankle-foot coil without traction, (II) small FOV coil without traction, and (III) small FOV coil with axial traction. Noise and motion artifacts, surface contour, and layer-by-layer display of the talar cartilage on three kinds of T2* mapping images were evaluated on a four-point scale. Subsequently, the T2* values of the different layers of cartilage in the medial, middle, and lateral zones of the talus in the volunteer group and different types of cartilage injuries and noninjured regions in the patient group were compared. Coronal proton density (PD)-weighted turbo spin echo (TSE) BLADE sequences were acquired for morphological evaluation under ankle axial traction, and it was determined whether there was a difference between the BLADE sequence and the T2* mapping sequence in detecting the number of talar cartilage injuries. Statistical analysis included analysis of variance tests with Bonferroni correction. Results: The T2* mapping sequence with axial traction in noise and motion artifacts, surface contour, and layer-by-layer display of the talar cartilage were rated superior (P<0.05) as compared to the BLADE sequence, while noise and artifacts before and after the small FOV coil traction were not significantly different (P=1).Significant differences in T2* values were present between cartilage layers across the medial, middle, and lateral talar dome zones in the volunteer group (P<0.001) but not between the superficial and radial layers in the middle zone (P=0.145). In the patient group, T2* mapping with traction detected 11 more injuries than did the BLADE sequence. The mean T2* values of different types of cartilage injuries differed significantly from those of noninjured regions (P<0.001). Pairwise comparisons revealed significant differences between noninjured cartilage and each type of cartilage injury (P<0.05). Significant differences were also observed in all comparisons between different cartilage injury subgroups (P<0.05), except between cartilage fractures and signal alterations (P=1.0). Conclusions: Quantitative T2* mapping sequence for the imaging of talar cartilage injury under axial traction with the small FOV coil increased the joint space width, allowed for better visualization of the surface contour and layers of talar cartilage, reduced noise and motion artifacts, and improved the display discrimination ability of T2* mapping sequence for different injuries to the talar cartilage.