Comparison of field-of-view optimized and constrained undistorted single-shot diffusion-weighted imaging and conventional diffusion-weighted imaging of optic nerve and chiasma at 3T.

PURPOSE: Single-shot echo-planar imaging is the conventional diffusion-weighted imaging (C-DWI) sequence for evaluating orbital disease. However, its utility is restricted in small organs like the chiasma and optic nerve. This study was conducted to investigate the utility of field-of-view optimized and constrained undistorted single-shot diffusion-weighted imaging (FOCUS-DWI) for evaluating the chiasma and optic nerve in acute optic neuritis, making comparisons with C-DWI.
METHODS: FOCUS-DWI and C-DWI were performed on 36 acute optic neuritis patients and 16 normal controls. Two readers assessed image quality using 5-point Likert scales. Differences in the visual assessments and apparent diffusion coefficient (ADC) values between C-DWI and FOCUS-DWI were evaluated. Inter-observer agreement in the qualitative data was assessed using Cohen's kappa coefficients. Inter- and intra-observer agreements in the ADC values were evaluated using intraclass correlation coefficients.
RESULTS: FOCUS-DWI was superior to C-DWI in all aspects of the image evaluations. The Cohen's kappa coefficients for FOCUS-DWI were almost perfect (0.81-1) or substantial (0.61-0.80) for all the image quality categories. In the FOCUS-DWI images, the structural conspicuity of the chiasma and canalicular and cisternal segments was significantly superior on coronal views than on axial views (P < 0.0001). ROC analysis showed that in optic neuritis patients, the diagnostic value of ADC measurements on FOCUS-DWI was higher than ADC values measured on C-DWI.
CONCLUSION: The FOCUS-DWI technique can provide substantial improvements over C-DWI for imaging different aspects of the optic nerve and chiasma. The coronal scan direction is more suitable than the axial scan direction for FOCUS-DWI.