[Clinical usefulness of "optimal threshold setting plan" for reconstruction of three-dimensional CT imaging: preliminary clinical study on hepatic tumors and hepatic parenchymal disease].

Clinical application of three-dimensional CT (3D-CT) angiography using the volumetric acquisition capabilities inherent in spiral CT has provided 3D-CT images of vascular structures as well as visceral organs. However, the standard method for deciding the threshold, which is an important process for defining regions of interest, has not yet been established. The setting of an inappropriate threshold may result in reconstruction of a 3D-CT image, leading to misdiagnosis. To simplify the determination of the optimal threshold in a way consistent with the purpose of reconstructing a 3D-CT image, we developed an Optimal Threshold Setting Plan (OPT Plan). With this method, an optimal 3D-CT image could be selected from among those multiple 3D-CT images that were reconstructed on the basis of the multiple thresholds input in advance by referring to attenuation values in both the hepatic lesion and its background on two-dimensional CT images. Clinical usefulness of the OPT Plan for the reconstruction of 3D-CT images was evaluated in 10 patients with hepatic tumors and hepatic parenchymal disease. We obtained 13 3D-CT images (on average) with threshold changes every 5 Hounsfield units, with a mean reconstruction time of 2 minutes 49 seconds, and easily selected an adequate 3D-CT image. Based upon this preliminary experience, the OPT Plan may resolve the difficulty encountered in the setting of thresholds for achieving 3D-CT images, and is considered to be useful for three-dimensional qualitative evaluation of hepatic lesions and hepatic parenchymal disease.