Parallel-transmit-accelerated spatially-selective excitation mri for reduced-fov diffusion-weighted-imaging of the pancreas

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 mm². 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 mm². 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 mm²/s) and pTX-EPI (1.27 ± 0.17 × 10⁻³ mm²/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 mm²/s) than in c-EPI (0.135 × 10⁻³ mm²/s), p < 0.05.

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.