[Report on 18th Short-time Overseas Study in the University of Chicago].
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Chicago↗
Biomedical subjects
Yuji Ogata
Publications and source records attributed to Yuji Ogata.
[Visualization by dynamic CT: invention of 2D-CT chronogram].
Dynamic computed tomography is one of the methods used for the functional analysis of blood flow information. We devised a simple method of visualization for dynamic CT. Re-sliced images were stacked as multi-slice images for the different acquisition times to show a continuous spatial arrangement with dynamic data. Images processed into re-sliced images termed 2D-CT Chronograms were observed in many directions and were useful for comprehending the blood flow function of the target organ. Time-density curves with motion dependency and color displays similar to those of ultrasound images are easily acquired from the 2D-Chronogram. We introduce some clinical applications of the 2-D Chronogram.
Contrast Media↗
[Evaluation of the retrospective ECG-gated helical scan using half-second multi-slice CT: motion phantom study for volumetry].
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.
Electrocardiography↗
[Evaluation of compensation filter in I.I.-DR gastrointestinal examination using image pick-up tube].
We have especially the thing which experiences daily and which digital value does 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 out 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.
Digestive System↗
[Hologic's Flat-Panel Detector].
We measured and evaluated digital, pre-sampling and overall imaging properties (characteristic curve, Modulation Transfer Function (MTF), Wiener spectrum (WS), Noise Equivalent Quanta (NEQ) and Detective Quantum Efficiency (DQE)) for Hologic's direct type and Cannon's indirect type of Flat-Panel Detector (FPD). First, the digital and overall characteristic curves of both types of FPD were more wide dynamic range than that of the S/F system. Second, the pre-sampling and overall MTF of the direct-type FPD system were superior to those of the indirect-type FPD system. Third, for identical exposures, the digital and overall WS of the direct-type FPD system were similar or worse than those of the indirect-type FPD system, and for larger exposure, the digital WS of the both types of FPD system were smaller, but the overall WS of the both types of FPD systems were larger. Fourth, the digital and overall NEQ and DQE of the direct-type FPD system were worse than those of the indirect-type FPD system at lower spatial frequencies than 1.75 - 2.0 mm(-1), but were worse at higher spatial frequencies than 1.75 - 2.0 mm(-1). We show radiographs made with the direct type of FPD system. Radiographs of square wave chart show the difference in MTF and contrast of the both types of FPD systems. As the result of evaluation of radiographs of chest phantom in point of noise by radiologists and radiological technologists, the direct type of FPD system needed double or more exposure dose than own standard condition, this dose was same as the indirect-type FPD system. And radiologists evaluated radiographs of human body, spatial resolution was very good, but contrast was much more likely to high at standard parameter. Therefore we have to consider exposure condition and image processing for the direct type of FPD system.
Humans↗