Gastric carcinoma: Evaluation with diffusion-tensor MR imaging and tractography ex vivo

Purpose: To determine the feasibility of diffusion-tensor imaging (DTI) and tractography as means of evaluating the depth of mural invasion by gastric carcinomas. Materials and methods: This study was approved by our institutional review board, and written informed consent was obtained from each patient. Twenty gastric specimens containing a carcinoma were studied with a 7.0-T MR imaging system equipped with a four-channel phased-array surface coil. DTI was performed by using a field of view of 50-60 mm × 25-30 mm, matrix of 256 × 128, section thickness of 1 mm, b value of 1000 s/mm², and motion-probing gradients in seven noncollinear directions. The MR images were compared with the histopathologic findings as the reference standard. Results: In all 20 carcinomas (100%) the diffusion-weighted images, apparent diffusion coefficient (ADC) maps, fractional anisotropy (FA) maps, λ₁ maps, and direction-encoded color FA maps made it possible to identify the same depth of tumor invasion of the gastric wall as observed during histopathologic examination. The λ₁ maps provided the best contrast between the carcinomas and the layers of the gastric wall. The carcinomas also had lower ADC values and lower FA values than the normal gastric wall; thus, the carcinomas were clearly demarcated from the normal gastric wall. Tractography images were also useful for determining the depth of tumor invasion of the gastric wall. Conclusions: DTI and tractography are feasible means of evaluating gastric specimens and provide excellent diagnostic accuracy for evaluating mural invasion by gastric carcinomas.