[A case of rectovaginal metastasis 6 years after initial resection of extra-gastrointestinal stromal tumor of vulvar origin].

A 53-year-old woman who had undergone excision of KIT-positive extra-gastrointestinal stromal tumor (EGIST) of the vulva 6 years ago presented to our hospital due to a positive fecal occult blood test. Colonoscopy revealed a submucosal tumor in the rectum ventral side. In addition, computed tomography and magnetic resonance imaging revealed a tumor in the rectovaginal septum. For diagnostic and therapeutic purposes, the tumor was resected via the perineal approach. The resected specimen analysis revealed a KIT-positive gastrointestinal stromal tumor (GIST). Following immunopathological and genetic mutation identifications, GIST of the rectovaginal septum from vulva EGIST metastasis was diagnosed. It is important to consider primary GIST and metastatic GIST as differential diagnoses in the case of a rectal submucosal tumor detected by endoscopy.

Spatial resolution compensation by adjusting the reconstruction kernels for iterative reconstruction images of computed tomography.

PURPOSE: Hybrid iterative reconstruction (IR) is useful to reduce noise in computed tomography (CT) images. However, it often decreases the spatial resolution. The ability of high spatial resolution kernels (harder kernels) to compensate for the decrease in the spatial resolution of hybrid IRs was investigated. METHODS: An elliptic cylindrical phantom simulating an adult abdomen was used. Two types of rod-shaped objects with ~330 and ~130 HU were inserted to simulate contrasts of arteries in CT angiography. Two multi-slice CT systems were used to scan the phantoms with 120 kVp and scan doses of 20 and 10 mGy. The task transfer functions (TTFs) were measured from the circular edges of the rod images. The noise power spectrum (NPS) was measured from the images of the water-only section. The CT images were reconstructed using a filtered back projection (FBP) with baseline kernels and two levels of hybrid IRs with harder kernels. The profiles of the clinical images across the aortic dissection flaps were measured to evaluate actual spatial resolutions. RESULTS: The TTF degradation of each hybrid IR was recovered by the harder kernels, whereas the noise reduction effect was retained, for both the 20 and 10 mGy. The profiles of the dissection flaps for the FBP were maintained by using the harder kernels. Even with the best combination of hybrid IR and harder kernel, the noise level at 10 mGy was not reduced to the level of FBP at 20 mGy, suggesting no capability of a 50% dose reduction while maintaining noise.