Exploratory study of geometric distortion correction of prostate diffusion-weighted imaging using B0 map acquisition

Abstract

Background: Evaluation of prostate MRI relies on diffusion-weighted imaging (DWI), commonly distorted by susceptibility artifacts, thereby creating a need for approaches to correct such distortion.

Purpose: To compare geometric distortion on prostate MRI between standard DWI and a geometric distortion correction method for DWI described as static distortion correction DWI (SDC DWI).

Study type: Retrospective case study.

Population: Thirty patients (ages 31-81 years) undergoing prostate MRI.

Sequence: Geometric distortions from echo planar imaging were corrected with the SDC DWI protocol, which first acquires a B₀ -field map to estimate geometric distortions.

Assessment: Contours of the prostate were placed on axial T₂ -weighted imaging (T₂ WI) as an anatomic standard. Pixel shifts and apparent diffusion coefficient (ADC) values were compared between prostate contours applied to the SDC DWI and standard DWI sequences. Detailed characterization of the impact of SDC DWI was performed in three representative patients.

Statistical tests: One-way analysis of variance (ANOVA) test, Spearman correlation test, and Bland-Altman plots were calculated.

Results: There was significantly greater overlap of the SDC DWI prostate region of interest (ROI) with T₂ WI than standard DWI with T₂ WI (10.56 cm² ± 3.14, P < 0.05). R² of ADC values from standard DWI vs. SDC DWI in the 30 patients ranged from 0.02-0.94 (mean 0.60). A patient without susceptibility artifact demonstrated minimal pixel shift ranging from 0.6-1.3 mm and high correlation of ADC values (R² = 0.89) between SDC DWI and standard DWI. A patient with rectal gas showed greater pixel shift (range: -2.5 to -0.5 mm) and less ADC value correlation (R² = 0.69). A patient with a pelvic phlebolith adjacent to the prostate showed an even greater pixel shift (range: 10-16 mm) and decreased ADC correlation (R² = 0.21).

Data conclusion: SDC DWI appears to correct for susceptibility-related pixel shifts in the prostate compared with standard DWI, which may have value for assessing prostate lesions obscured by geometric warping. Level of Evidence 4 Technical Efficacy Stage 1 J. Magn. Reson. Imaging 2019;50:1614-1619.

Keywords: DWI; geometric distortion correction; prostate MRI.