TECHNICAL ARTICLE: Fusion of high b‐value diffusion‐weighted and T2‐weighted MR images improves identification of lymph nodes in the pelvis

Abstract

Accurate identification of lymph nodes facilitates nodal assessment by size, morphological or MR lymphographic criteria. We compared the MR detection of lymph nodes in patients with pelvic cancers using T2-weighted imaging, and fusion of diffusion-weighted imaging (DWI) and T2-weighted imaging. Twenty patients with pelvic tumours underwent 5-mm axial T2-weighted and DWI (b-values 0-750 s/mm(2)) on a 1.5T system. Fusion images of b = 750 s/mm(2) diffusion-weighted MR and T2-weighted images were created. Two radiologists evaluated in consensus the T2-weighted images and fusion images independently. For each image set, the location and diameter of pelvic nodes were recorded, and nodal visibility was scored using a 4-point scale (0-3). Nodal visualisation was compared using Relative to an Identified Distribution (RIDIT) analysis. The mean RIDIT score describes the probability that a randomly selected node will be better visualised relative to the other image set. One hundred fourteen pelvic nodes (mean 5.9 mm; 2-10 mm) were identified on T2-weighted images and 161 nodes (mean 4.3 mm; 2-10 mm) on fusion images. Using fusion images, 47 additional nodes were detected compared with T2-weighted images alone (eight external iliac, 24 inguinal, 12 obturator, two peri-rectal, one presacral). Nodes detected only on fusion images were 2-9 mm (mean 3.7 mm). Nodal visualisation was better using fusion images compared with T2-weighted images (mean RIDIT score 0.689 vs 0.302). Fusion of diffusion-weighted MR with T2-weighted images improves identification of pelvic lymph nodes compared with T2-weighted images alone. The improved nodal identification may aid treatment planning and further nodal characterisation.

Diffusion-weighted MR imaging of the rectum: Clinical applications

“…As far as nodal staging is concerned, DW-MRI does improve lymph node detection [47][48][49] but, when used alone, is not reliable for differentiating between benign and malignant lymph nodes [33,50]. In our experience and accordingly to the ESGAR's guidelines for rectal tumor imaging [21], there is no evidence so far that DW-MRI improves rectal primary staging.…”

Urinary Bladder Cancer: Role of MR Imaging

“…According to recent published reports, diffusion-weighted imaging has shown promise in differentiating benign from malignant lymph nodes (Fig 12). Larger-scale studies will be required to determine the value of diffusionweighted imaging in assessing early lymph node disease (62,63). .…”

Fusion and subtraction post-processing in body MRI

“…Ideally intravenous access should be obtained prior to commencement to avoid misregistration between pre-and post-contrast imaging. Fusion of a diffusion sequence with a T2-weighted sequence has shown value in the detection of pelvic lymph nodes [6] and breast malignancy [7]. To the best of our knowledge, this is a unique description of its use in children.…”