Application of a variable filter for presampled modulation transfer function analysis with the edge method

13301甲第4298号博士（保健学）金沢大学博士論文本文Full 以下に掲載：Radiological Physics and Technology 8(2) pp.320-330 2015. Springer International Publishing. 共著者：Ryo Higashide, Katsuhiro Ichikawa, Hiroshi Kunitomo, Kazuya Ohash

Application of a variable filter for presampled modulation transfer function analysis with the edge method

We devised a new noise filtering method to reduce the noise in the line spread function (LSF) for presampled modulation transfer function (MTF) analysis with the edge method. A filter was designed to reduce noise effectively using a position-dependent filter controlled by the boundary frequency b for low-pass filtering, which is calculated by 1/2d (d: distance from the LSF center). In this filtering process, strong filters with very low b can be applied to regions distant from the LSF center, and the region near the LSF center can be maintained simultaneously by a correspondingly high b. Presampled MTF accuracies derived by use of the proposed method and an edge spread function (ESF)-fitting method were compared by use of simulated ESFs with and without noise, resembling a computed radiography (CR) and an indirect-type flat panel detector (FPD), respectively. In addition, the edge images of clinical CR, indirect-type FPD, and direct-type FPD systems were examined. For a simulated ESF without noise, the calculated MTFs of the variable filtering method agreed precisely with the true MTFs. The excellent noise-reduction ability of the variable filter was demonstrated for all simulated noisy ESFs and those of three clinical systems. Although the ESF-fitting method provided excellent noise reduction only for the CR-like simulated ESF with noise, its noise elimination performance could not be demonstrated due to the lesser robustness of the fitting. © 2015, Japanese Society of Radiological Technology and Japan Society of Medical Physics.発行後1年より全文公

Ovarian torsion due to ovarian hyperstimulation syndrome diagnosed by sonographic whirlpool sign in the first trimester of pregnancy: A case report

Ovarian torsion during pregnancy is a rare condition that needs prompt diagnosis and detorsion in order to preserve ovarian function. Diagnosing ovarian torsion is a difficult procedure especially in pregnant cases since radiation exposure should be avoided. Detecting the whirlpool sign by ultrasonography is a highly useful technique as it is noninvasive, less time-consuming, and radiation-free. Here is a case of ovarian torsion due to ovarian hyperstimulation syndrome diagnosed solely by sonographic features and in which laparoscopic detorsion was promptly performed.A 26-year-old woman in her sixth week of pregnancy visited a tertiary hospital with sudden onset lower abdomen pain. Transvaginal ultrasound detected an 8 cm left ovary and a whirlpool sign between the uterus and left ovary. Ovarian torsion was suspected and laparoscopic surgery was performed. Intraoperatively, an enlarged left ovary was twisted at 540° involving the left fallopian tube. After detorsion, bilateral ovaries were preserved and the postoperative course was uneventful. Ovarian torsion was suspected solely by ultrasonographic features which led to surgical detorsion quickly, resulting in the preservation of bilateral ovaries. Detecting the whirlpool sign when ovarian torsion is suspected is useful, especially in pregnant women