In computed tomography (single-slice spiral CT, conventional CT), in-plane (x-y plane) spatial resolution is consistently identified as depending on the detector density of the in-plane (x-y plane). However, we considered that the in-plane (x-y plane) spatial resolution of multi-slice CT (MSCT) was influenced by an error in the detector's sensitivity to the Z-axis and by the frequency of use of direct row data and comple-mentary row data when the image of spiral pitches(SP) was reconstructed. Our goal in this experiment was to analyze the relationship of the in-plane (x-y plane) spatial resolution of an asymmetric-type detector in MSCT to SP, tube current, and rotation time. By employing a tungsten wire phantom of 0.2 mm in diameter, we examined modulation transfer functions (MTF) by point-spread functions (PSF) of CT-images. Next, using the mean-square-root bandwidth theory, we analyzed the MTF of wire phantoms. The analysis of in-plane (x-y plane) spatial resolution revealed that various tube currents had no effect on the value of the mean-square-root bandwidth. However, rotation time and high spiral pitch did have an effect on mean-square-root bandwidth. Considering the results mentioned above, spiral pitch (z-axis reconstruction algorithm) had a slight effect on in-plane (x-y plane) spatial resolution of asymmetric-type detectors in MSCT. Accordingly, we proposed a new general view of VDDz(view/mm) in MSCT that considered view data density on the Z-axis according to spiral pitch (mm/rotation), rotation time (view/rotation), and slice collimation.
The X-ray systems study group used the Victoreen NERO mAx model 8000, a new non-invasive X-ray output analyzer, to measure the tube voltage, tube voltage waveform, tube current, and irradiation time for conditions corresponding to general radiography and mammography. The measurement results were then compared with those obtained using a conventional invasive measuring instrument. The peak values of the tube voltage measured by the NERO mAx and the invasive measuring instrument were compared. The NERO mAx had a good measurement error range of -1.2 to +0.9 kV. For tube current measurement by the NERO mAx, the maximum error for general radiography conditions was +11 mA and that for mammography conditions was +6 mA. For irradiation time measurement, the value for general radiography conditions was slightly greater and the value for mammography conditions was slightly less than the corresponding values obtained by the invasive measuring instrument. If radiation quality is changed during measurement of the characteristics, measurement values change. Since the NERO mAx incorporates two types of X-ray detectors, it shows good measurement reproducibility. The NERO mAx has been shown to have suitable characteristics for use as a measuring instrument for constancy tests. In the future, constancy tests should be used to quantitatively control the factors determining clinical image quality.
A convenient, accurate method to measure the modulation transfer function (MTF) of magnetic resonance(MR) images is discussed. To avoid any distortion of the edge spread function(ESF) which is inadvertently produced by the magnitude operator, the MTF was calculated from the ESF obtained from the salad-oil/water interface. Our MTF findings closely correlated with the MTF findings as calculated by an alternate method (Steckner et al.). Our method was only adapted to some specific sequences and some specific encoding directions, however, MTF was successfully obtained by the magnitude operator without any errors. In our method, the production and arrangement of phantoms were also easier to control. Our new method is therefore considered to be useful for evaluating the resolution property of MR images from various institutions.
Few reports have discussed the absorbed dose on CT units with increased scanning capacity even with the current widespread adoption of multi-slice CT units. To compare and investigate the dose indexes among CT units, we measured the absorbed dose on CT units operating in Nagano Prefecture Japan. The measurements showed proportionality between phantom absorbed dose and the exposured mAs values in conventional scanning operation. Further, the measurements showed that the absorbed dose in the center of the phantom differed by about 2.1-fold between the highest and lowest levels on individual CT units. Within a single company, multi-slice CT units of the same company gave absorbed doses of about 1.3 to 1.5 times those of conventional single-slice CT units under the same exposured conditions of conventional scanning. When the scanning pitch was reduced in helical scanning, the absorbed dose at the center of the phantom increased.
Auto mA is a function that automatically controls tube current so as to stabilize image quality. To determine the applicability of this function to routine inspection work, an evaluation was carried out by two doctors in the department of radiology and five technicians in the department of diagnostic radiology using home-made phantoms and phantoms for low contrast resolution determination. The phantom experiment provided an almost constant level of SD values in each Auto mA mode tested, independent of scanning type, slice thickness, and phantom shape. In addition, nearly stable low contrast resolution was attained independent of phantom shape, e.g., circle and ellipse. The results suggest that stable image quality is available in the clinical stage for individual patients and regions, independent of the size and shape of targets. As for the evaluation of clinical images, the image quality requested by clinical operations at our hospital was attained even in the low dose mode that provides the lowest dose level. In addition, for variations in tube current values for photographing in individual regions, both sustained image uniformity and exposure reduction were found to be satisfactory in comparison with constant tube current.
Total body irradiation (TBI) is being used as a method of preparation for bone marrow transplantation (BMT). In TBI, the dose calculation is based on dosimetry using a phantom. We measured the basic dose with a phantom using a 10 MV X-rays. We confirmed the accuracy of the dose calculation performed in our facilities and investigated a method of more accurate dosimetry. We measured the variation in dose according to the size of the phantom and the depth using a tough water phantom, and examined the difference in TMR according to SCD, field size, and size of the phantom. Consequently, the dose has been changed regardless of the size of the phantom at larger than 80 × 30 × 30 cm^3, and it is about 1% larger than 30 × 30 × 30 cm^3. Also TMR has changed according to various conditions, including the size of the phantom, field size, and SCD. Therefore, it was found that dosimetry using the 30 × 30 × 30 cm^3 phantom leads to under-estimation in dose calculation, and there is no difference in dose between the field size of 151.5 × 160 cm^2 and 151.5 × 80cm^2. It is also necessary to consider the effect of the vertical size of the phantom.
Purpose: To determine the relationship between patient factors and contrast medium factors, both of which influence contrast enhancement. Our goal was to achieve improved standardization and reproducibility of enhancement based on the findings of this study. Methods : Enhancement units(EU) and the contrast enhancement index (CE index) were calculated in the areas of the hepatic parenchyma and abdominal aorta in 370 subjects who underwent our hepatic dynamic study. We analyzed the obtained values in terms of differences in age, sex, body weight, iodine volume per body weight, and volume and concentration of contrast medium. Results : Changes in EU values were dependent on total iodine volume and body weight, showing a positive correlation with iodine volume per body weight. When assessed in terms of fixed total volume, the values were found to show a negative correlation with body weight. The obtained CE index values were closely distributed on a fixed iodine volume per weight, with slight variations that were related to sex, body weight, and age. Particularly, in the analysis of changes in enhancement levels according to age, a notable increase in contrast enhancement in inverse relationship with decline in glomerular filtration rate (GFR) with aging was observed.