The purpose of this study is to examine an antialiasing method in the breath-hold coronal imaging of the thorax or abdomen. This paper reports a new method of preventing the aliasing artifacts of arms using "Hertz^[R!○]II" as a electromagnetic-wave shield fabric(ESF), which is a very thin and flexible special synthetic fabric. In this study, the ESF method was compared with various conventional preventive measures. Temperature changed around the ESF was also measured by using a fiber optic temperature measurement system during the MR scanning procedure. In addition, the ESF method was tried to use for scanning with some volunteers and some patients in clinical examinations. The results of this study showed that the ESF method could efficiently prevent the aliasing of arms in the MR images. Furthermore, safety of the subjects was hardly affected by the ESF method during MR imaging. Therefore, we concluded that the ESF method was an effectual antialiasing method in the imaging of the thorax or abdomen by using the fast breath-hold scanning.
Recently, an increasing number of volumetric studies of the human brain have been reported, using three-dimensional magnetic resonance imaging(3D-MRI). To our knowledge, however, there are few investigations on the relation of the volume and shape of voxels which constitute an MR image to the accuracy in volume measurement of an imaged object. The purpose of this study was to evaluate the effect of a different shape of voxel, that is, isotropic or anisotropic, as well as the volume of a voxel on the volume measurement based on the original image data and multiplanar reconstruction(MPR) data, respectively. In the experiment, we repeatedly acquired contiguous sagittal images of a single globe phantom with a known volume under the condition in which the volume and shape of voxels varied, on a 1.5T MR scanner. We used a gradient echo sequence(3D FLASH). The volume of the globe phantom from both original images and MPR ones was measured on workstations employing a semi-automated local thresholding technique. As a result, the smaller volume of voxels tended to give us the more correct measurement, and an isotropic voxel reduced measurement errors as compared to an anisotropic one. Therefore, it is concluded that the setting of voxel with both an isotropic shape and small volume, e.g., a voxel of 1 mm × 1 mm × 1 mm at present, is recommended in order to get a precise volume measurement using 3D-MRI.
ECG synchronized technique on multi-slice CT provide the thinner(less 2 mm slice thickness) and faster(0.5sec/rotation) scan than that of the single detector CT and can acquire the coverage of the entire heart volume within one breath-hold. However, temporal resolution of multi-slice CT is insufficient on practical range of heart rate. The purpose of this study was to evaluate the accuracy of volumetry on cardiac function measurement in retrospective ECG-gated helical scan. We discussed the influence of the degradation of image quality and limitation of the heart rate in cardiac function measurement(volumetry) using motion phantom.
A scattered dose and a surface dose from phantom measurements during interventional procedures with computed tomography(IVR-CT) were evaluated. To reduce the personnel exposuer in IVR-CT, the new protective devices were developed and its effect evaluated. Two radiation protection devices were experimentally made using a lead vinyl sheet with lead equivalent 0.125mmPb. The first device is a lead curtain which shields the space of CT-gantry and phantom for the CT examination. The second device is a lead drape which shields on the phantom surface adjacent to the scanning plane for the CT-fluoroscopy. Scattered dose and phantom surface dose were measured with an abdominal phantom during Cine-CT(130 kV, 150 mA, 5 seconds, 10 mm section thickness). They were measured by using ionization chamber dosimeter. They were measured with and without a lead curtain and a leas drape. Scattered dose rate was measured at distance of 50-150 cm from the secanning plane. And, surface dose was measured at distance of 4-21 cm from the scanning plane on the phantom. On operator's standing position, scattered dose rates were from 8.4 to 11.6 μGy/sec at CT examination. The lead curtain and the lead drape reduced scattered dose rate at distance of 50 cm from the scanning plane by 66% and 58.3% respectively. Surface dose rate were 118μGy/sec at distance of 5 cm from the scanning plane at CT-fluoroscopy. The lead drape reduced the surface dose by 60.5%. High scattered exposure to personnel may occur during interventional procedures using CT. They were considerably reduced during CT-arteriography by attaching the lead curtain in CT equipment. And they were substantially reduced during CT-fluoroscopy by placing the lead drape adjacent to the scanning plane, in addition, operator's hand would be protected from unnecessary radiation scattered by phantom. It was suggested that the scattered exposure to personnel could be sufficiently reduced by using radiation protection devices in IVR-CT. The radiation protection devices and the CT equipment should be improved or developed based on the radiation protection.
We studied image quality(contrast) and patient dose reduction using heavy metal filters in lumbar spine and abdomen x-ray examination. Heavy metal filters used in this study are gadolinium, holmium and ytterbium and these combinations. These filters have k-absorption edge in the range from 50 to 70 keV. Image quality and patient dose in 70-90 kV tube voltage with heavy metal filters were compared with 80 kV tube voltage without filter. Image quality was improved in four percent and patient dose could be reduced by 30%. However, tube loading increased from 1.6 to 2.2 times. It was found that the best filter choices gave better image and reduced patient dose compared to without filter.
The Racetrack Microtron MM50 capable of taking out x-rays and electron beames having a high energy of up to 50 MeV was evaluated by a dosimetry of electron beams in comparison with Microtron MM22. The MM50 flattens the intensity of electron beams by using the beam scanning method while the MM22 utilizes the flattening-filter method. A percentage depth dose(PDD) curve was obtained through the dosimetry of electron beams using a water phantom. As compared with the MM22, the MM50 emits an electron beam that has an energy much closer to the nominal one, that is less contaminated by x-rays, and whose intensity decreases steeply down to near zero on the PDD curve. The MM50 has an electron beam dose distribution that is practically useful since the dose tends to be concentrated on the target volume.
We have especially the thing which experiences daily and which digital value dose saturate by the difference of patient, and the air content of internal organs, at the time of I.I.-DR gastrointestinal examination. In order to compensate digital value of those parts, the compensation filter by the remote operation formula was examined. The quality of the material of the created filter determined thickness and form from change of digital value when changing thickness, and a dose using aluminum. The image which carried our saturate as a result of analyzing this 500 images decreased to 15% to 3%. Moreover, the total skin dose decreased on the same photography conditions, and was almost equivalent in the time of phototimer use. The part not conventionally materialized as an image for saturation has been improved by using a compensation filter for gastrointestinal examination, and it was enabled to obtain a useful picture clinically.