Free-breathing diffusion-weighted single-shot echo-planar MR imaging using parallel imaging (GRAPPA 2) and high b value for the detection of primary rectal adenocarcinoma

Abstract

Our objective was to determine the diagnostic accuracy of a free-breathing diffusion-weighted single-shot echo-planar magnetic resonance imaging (FBDW-SSEPI) technique with parallel imaging and high diffusion factor value (b = 1000 s/mm2) in the detection of primary rectal adenocarcinomas. Thirty-one patients (14M and 17F; mean age 67 years) with histopathologically proven primary rectal adenocarcinomas and 31 patients without rectal malignancies (14M and 17F; mean age 63.6 years) were examined with FBDW-SSEPI (repetition time (TR/echo time (TE) 3900/91 ms, gradient strength 45 mT/m, acquisition time 2 min) at 1.5 T using generalized autocalibrating partially parallel acquisitions (GRAPPA, acceleration factor 2) and a b value of 1000 s/mm2. Apparent diffusion coefficients (ADCs) of rectal adenocarcinomas and normal rectal wall were measured. FBDW-SSEPI images were evaluated for tumour detection by 2 readers. Sensitivity, specificity, accuracy and Youden score for rectal adenocarcinoma detection were calculated with their 95% confidence intervals (CI) for ADC value measurement and visual image analysis. Rectal adenocarcinomas had significantly lower ADCs (mean 1.036 x 10(-3)+/- 0.107 x 10(-3) mm2/s; median 1.015 x 10(-3) mm2/s; range (0.827-1.239) x 10(-3) mm2/s) compared with the rectal wall of control subjects (mean 1.387 x 10(-3)+/- 0.106 x 10(-3) mm2/s; median 1.385 x 10(-3) mm2/s; range (1.176-1.612) x 10(-3) mm2/s) (p < 0.0001). Using a threshold value < or = 1.240 x 10(-3) mm2/s, all rectal adenocarcinomas were correctly categorized and 100% sensitivity (31/31; 95% CI 95-100%), 94% specificity (31/33; 95% CI 88-100%), 97% accuracy (60/62; 95% CI 92-100%) and Youden index 0.94 were obtained for the diagnosis of rectal adenocarcinoma. FBDW-SSEPI image analysis allowed depiction of all rectal adenocarcinomas but resulted in 2 false-positive findings, yielding 100% sensitivity (31/31; 95% CI 95-100%), 94% specificity (31/33; 95% CI 88-100%), 97% accuracy (60/62; 95% CI 92-100%) and Youden index 0.94 for the diagnosis of primary rectal adenocarcinoma. We can conclude that FBDW-SSEPI using parallel imaging and high b value may be helpful in the detection of primary rectal adenocarcinomas.

Figure 1

Box plots of ADC values, which differed significantly between rectal adenocarcinomas (cancer) and normal rectal wall (control). Boxes stretch across the interquartile range (IR), i.e. from lower quartile (Q1) to upper quartile (Q2); whiskers show smallest data point that is greater than (Q1−1.5 × IR) and largest data point that is smaller than (Q2 + 1.5 × IR). The vertical line through each box represents the median value. Blue dots indicate outliers. ADC values of rectal adenocarcinomas overlapped with those of normal rectal wall.

Figure 2

An 80-year-old woman with adenocarcinoma of the upper third of the rectum, at the rectosigmoid junction. (A) Axial ADC map obtained with b = 1000 s/mm shows tumour (arrows). ADC is 1.195 × 10⁻³ mm/s. (B) Axial FBDW-SSEPI image obtained with b = 1000 s/mm and displayed using black and white reversed contrast shows dark well-defined areas (arrows) that were correctly classified as rectal cancer by the 2 reviewers (true-positive case). (C) Optical colonoscopic view confirms the rectal tumour that was classified as a T2 well-differentiated adenocarcinoma at histopathologic analysis after surgical resection.

Figure 3

A 56-year-old woman without rectal adenocarcinoma who had pelvic MR imaging for the evaluation of uterine fibroids (control subject). (A) Axial ADC map obtained with b = 1000 s/mm shows normal rectal wall (arrows). ADC is 1.364 × 10⁻³ mm/s. (B) An axial FBDW-SSEPI image obtained with b = 1000 s/mm and displayed using black and white reversed contrast; no dark areas are visible within the rectal wall (arrows). This case was correctly classified as normal by the 2 reviewers (true-negative case).

Figure 4

A 49-year-old woman without rectal adenocarcinoma who had pelvic MR imaging for pelvic pain and suspected Crohn disease (control subject). (A) Axial ADC map obtained with b = 1000 s/mm shows asymmetric thickening of the rectal wall (arrow). ADC is 1.176 × 10⁻³ mm/s. (B) Axial FBDW-SSEPI image obtained with b = 1000 s/mm and black and white reversed contrast shows a dark well-defined area at the left lateral aspect of the rectal wall (arrows) which was erroneously classified as rectal cancer by the 2 reviewers (false-positive case). Optical colonoscopy excluded Crohn disease and rectal cancer.