[Evaluation of an adaptive filter for CT under low-CNR condition: comparison with linear filter].

The use of an adaptive filter for CT images is becoming a common procedure and is said to reduce image noise while preserving sharpness and helping to reduce the required X-ray dose. Although many reports support this view, the validity of such evaluations is arguable. When the linearity of a system is in question, physical performance indexes should be measured under conditions similar to those of clinical use. Evaluations of diagnosis using clinical images may be fallible because the non-filtered image used as the reference might not have been optimally reconstructed. We have chosen simple, but commonly used, adaptive filters for our evaluation. As a reference for comparing performance, we designed linear filters that best approximate the noise characteristics of the adaptive filters. MTF is measured through observation of the edge-spread function. Clinical abdominal images are used to compare the performance of adaptive filters and linear filters. We conclude that the performance of the type of adaptive filter we have chosen is virtually the same as that of the linear filter, as long as the image quality of soft tissues is our interest. Both the noise SD and MTF are virtually the same if the contrast of the object is not substantially higher than 150 HU. Images of soft tissues obtained with the use of adaptive filters are also virtually the same as those obtained by linear filters. The edge-preservation characteristic of this adaptive filter is not observable for soft tissues.

[Slice profile measurement using a crossed thin-ramps method in three-dimensional magnetic resonance imaging].

Recent progress in variable-flip-angle fast spin-echo technology has further extended the utility of three-dimensional (3D) magnetic resonance imaging (MRI) for clinical application. The slice profile in 3D MRI is the point spread function that has a sync form in principle, whereas a slice profile in 2D imaging provides information on characteristics of selective radio frequency excitation. We investigated the optimal condition to measure 3D slice profiles using a crossed thin-ramps phantom. We found that the profile data should cover a large area in order to evaluate both the main lobe and side lobes in the slice profile, and that the appropriate slice thickness was 2 mm. We also found that artifacts in the direction perpendicular to the slice create an offset error in the measured slice profile when 3D imaging. In this paper, we describe the optimal condition and some remarks on the slice profile evaluation for 3D MRI.

Uterine relaxation by sacral surface electrical stimulation on the day of embryo transfer.

The peak power of uterine peristalses after sacral surface electrical stimulation (ssES) treatment decreased markedly in comparison with that measured before ssES on the day of embryo transfer (ET). This suppression effect of uterine peristalses was stronger on day 5 of ET than on day 3. Because the uterus at the time of ET is sensitive to ssES, this electrical neuromodulation may be an effective method to induce uterine relaxation for ET.

Magnetic resonance imaging of morphological and functional changes of the uterus induced by sacral surface electrical stimulation.

The purpose of this study is to examine the morphological and kinematical changes of the uterus induced by electrical stimulation applied to the skin just above the second and fourth posterior sacral foramens (sacral surface electrical stimulation [ssES]) in 26 healthy subjects. Out of them, eight subjects who had severe pain subjectively during every menstruation received ssES just in menstruation. Morphological and functional changes of the uterus were examined by using T2-weighted magnetic resonance (MR) imaging and T1-weighted MR cinematography, respectively. Cyclic electrical stimulation for 15 min with 5 sec ON and 5 sec OFF was applied just before MR scanning. A decrease in thickness of the muscular layer of the uterus was observed in every subject after ssES for 15 min and was significant as compared with the thickness before ssES. Periodic uterine movement during menstruation was observed in the subjects with severe menstrual pain in MR cine and the power spectrum analysis of the movement showed a marked decrease in peak power and frequency after ssES treatment. We conclude that ssES causes a reduction of static muscle tension of the uterus in all menstrual cycle periods and suppression of uterine peristalsis during menstruation in the subjects with severe menstrual pain. Possible neural mechanisms for these static and dynamic effects of ssES on the uterus at spinal level are discussed.