Parallel-transmit-accelerated spatially-selective excitation MRI for reduced-FOV diffusion-weighted-imaging of the pancreas

CONCLUSIONS: PTX-accelerated EPI with spatially-selective excitation and reduced FOV leads to substantial improvements in DWI of the pancreas with respect to different aspects of image quality without significantly influencing the ADC values.

OBJECTIVES: To find out whether the use of accelerated 2D-selective parallel-transmit excitation MRI for diffusion-weighted EPI (pTX-EPI) offers advantages over conventional single-shot EPI (c-EPI) with respect to different aspects of image quality in the MRI of the pancreas.

MATERIALS AND METHODS: The MRI examinations of 33 consecutive patients were evaluated in this prospective and IRB-approved study. PTX-EPI was performed with a reduced (zoomed) FOV of 230 × 118 mm(2). The 2D-RF pulse of pTX-EPI was accelerated, i.e. shortened by a factor of 1.7 (pTX-acceleration factor). C-EPI used a full-FOV of 380 × 285 mm(2). In a qualitative analysis, two experienced readers evaluated 3 different aspects of image quality on 3- to 5-point Likert scales. Additionally, apparent diffusion coefficients (ADCs) were determined in both c-EPI and pTX-EPI in normal-appearing pancreatic tissue using regions of interests (ROIs). Mean ADC values and standard deviations were compared between the two techniques.

RESULTS: The reduced-FOV pTX-EPI was superior to c-EPI with respect to overall image quality (p<0.0001) and identifiability of the pancreatic ducts (p<0.01). Artifacts were significantly less severe in pTX-EPI (p<0.01). The mean ADC values of c-EPI (1.29 ± 0.19 × 10(-3)mm(2)/s) and pTX-EPI (1.27 ± 0.17 × 10(-3)mm(2)/s) did not differ significantly between the two techniques (p=0.44). The variation within the ROIs as measured by the standard deviation was significantly lower in pTX-EPI (0.095 × 10(-3)mm(2)/s) than in c-EPI (0.135 × 10(-3)mm(2)/s), p<0.05.