Diffusion tensor imaging in evaluation of thigh muscles in patients with polymyositis and dermatomyositis.

OBJECTIVE: To explore the diffusion tensor imaging (DTI) characteristics of thigh muscles in patients with polymyositis (PM) and dermatomyositis (DM). METHODS: 12 patients with known PM/DM and 10 healthy volunteers were enrolled in this study. Both DTI and conventional MR sequences were performed on both thighs of all subjects. Apparent diffusion coefficient (ADC), fractional anisotropy (FA) and three eigenvalues were compared between the PM/DM group and the healthy group. One-way analysis of variance and Student's t-test were used for statistical analyses with a significance of p < 0.05. RESULTS: In the healthy group, the vastus intermedius muscle showed the highest ADC value and the gracilis (GA) muscle showed the lowest ADC value. These results were statistically significant when compared with other muscles (p < 0.05). The GA, semi-tendinosus and semi-membranosus muscles showed higher FA values than the other three thigh muscles (p < 0.05). The mean ADC value and three eigenvalues of oedematous muscles in the PM/DM group were higher on average and showed a statistically significant difference when compared with unaffected (non-oedematous muscles in patients) and normal muscles (p < 0.05). There was no statistical difference in the mean FA value between oedematous and normal muscles. The mean ADC, FA and three eigenvalues in unaffected muscles (in patients) showed no statistical differences from those in normal muscles (p > 0.05). CONCLUSION: DTI can be used to quantitatively evaluate the anisotropic diffusion characteristics of muscles in patients with PM/DM. ADVANCES IN KNOWLEDGE: A new application of DTI is proposed for inflammatory myopathies. The results show that ADC and the three eigenvalues were significantly different between diseased and normal muscles, a finding of potential value in both diagnosis and treatment monitoring of myopathies.

SU-E-I-68: The Effect of Partially Parallel Imaging on SNR Across Scanning Platforms.

PURPOSE: Different manufacturers implement partially parallel imaging (PPI) with different proprietary reconstruction methods and algorithms. Additionally, signal to noise ratio (SNR) associated with PPI is highly dependent on coil design and conformation, as quantified by the g-factor. This potentially leads to differences in SNR across coils and scanners. This study seeks to characterize the impact of PPI on SNR across four MRI platforms. METHODS: Turbo spin echo (TSE) scans of a spherical phantom filled with an aqueous solution were acquired in a head coil on a 3T Siemens Tim Trio, 3T Philips Achieva, 1.5T Toshiba Vantage and 3T GE Signa Excite HD. Scans at each available integer R-value and reconstruction method were taken on each scanner. SNR was measured in each image using the difference method. SNR was normalized to a maximum value of 1.0 for each reconstruction method. Linear regressions and percent change in SNR relative to R-value were determined for each reconstruction method. Coefficient of variation (CV) was used to determine the relationship between PPI implementations. RESULTS: Slopes of the linear regressions ranged from ×0.24 to ×0.27. Percent SNR on average was 67.3%±3.7%, 43.3%±2.9% and 27.4%±6.9% of the associated non-PPI scan at R=2, 3 and 4 respectively. The range of percent SNR relative to non-PPI scans was 62.1%-71.7%, 39.8%-46.8% and 20.7%-34.5% at R=2, 3 and 4 respectively. The CV was 7.75% at R=2, 16.05% at R=3 and 21.79% at R=4. CONCLUSIONS: Slopes of the linear regressions ranged from -0.24 to -0.27. Percent SNR on average was 67.3%±3.7%, 43.3%±2.9% and 27.4%±6.9% of the associated non-PPI scan at R=2, 3 and 4 respectively. The range of percent SNR relative to non-PPI scans was 62.1%-71.7%, 39.8%-46.8% and 20.7%-34.5% at R=2, 3 and 4 respectively. The CV was 7.75% at R=2, 16.05% at R=3 and 21.79% at R=4.