We evaluated the effect of changes in the direction of the coronary artery in terms of the accuracy and precision of vessel diameter measurement in a quantitative coronary angiography system(QCA system). Vessel phantoms sized 0.3, 0.5, 1.0, 1.5, 2.0, and 2.5 mm in diameter were evaluated. The phantoms were aligned on an acrylic plate, and the angle to the television (TV) camera was altered. The deployed angles were 0 (perpendicular), 45, 90, and 135 degrees in clockwise order. The phantoms were imaged with matrices of 1024×1024(1024^2), 512×512 (512^2), and 512×1024. Image size was 7 inches, and the frame rate was 15 frames per second. Minimal lumen diameters were measured on the ACA system. The results revealed that, in the 10242 matrix, overall accuracy for the 90-degree angle was significantly underestimated compared with the 0-degree angle(-0.14 vs. -0.014 mm; p=0.007). Accuracy for the 90-degree angle was better than that for the 0-degree angle when the vessel diameter was 1 mm or smaller(-0.02±0.16 vs. 0.10±0.22 mm). In addition, precision was better at the 90- degree angle than with the other angles in the 1024^2 matrix (overall precision=0.002 mm). In the 512^2 matrix, overall accuracy for the 90-degree angle was significantly underestimated compared with the 45-degree angle (-0.077 vs. 0.096 mm; p=0.02). In addition, accuracy for the 90-degree angle was better than that for the 45- degree angle below 1 mm (0.05 ±0.24 mm vs. 0.26±0.47 mm). In terms of overall accuracy, the 45-degree angle in the 512^2 matrix showed significant overestimation compared with that in the 1024^2 matrix (0.096 vs. -0.069 mm; p=0.015). There was no difference in accuracy in the 512×1024 matrix. Our results suggest that the direc- tion of the vessel against the TV image affects accuracy of measurement in the QCA system.
To achieve quantitative assessment of 3D dynamic motion of artificial knee implants under clinical con- ditions, we developed a 3D kinematic analysis system using X-ray fluoroscopic imaging. The 3D pose-estimation technique fpr.knee implants was built on a 2D/3D registration algorithm, which .determines the spatial pose for each .femoral and tibial component from the knee implant contours and cdmputer^assisted design ((DAD) models of the.'implant. In order, to validate the accuracy of the 3D pose, estimation and the system, computersimulationand in'vitro'tests were'performed using images of knee implants taken in 10 different poses with respect to X-ray focus. Computer simulation tests showed that the root mean square errors (RMSE) for all variables were less than I'.O'mm 1.0°. In vitro tests showed that the RMSE for trans- lation perpendicular to the X-ray image plane was about 1.5 mm, while the accuracy of the remaining two translational and three rotational variables wasifound to be sufficient for analyzing knee kinematics. Com- putation time in 3D pose estimation was then obtained in less than 30 seconds for each frame. In clinical application, dynamic movement in deep knee bending was quantitatively analyzed, and the feasibility and effectiveness of the system was demonstrated.
Aim: Super-paramagnetic iron oxide-enhanced magnetic resonance imaging (SPIO-MRl) is highly sensitive for liver tumors. This trial examined the optimal parameters of the fast recovery fast spin echo (FRFSE) method in SPIO-MRI. The FRFSE method is a pulse sequence with recovery of the compulsory longitudi- nal magnetization. The FRFSE method used in SPIO-MRI has better sensitivity for liver tumor, better tu- mor contrast, and can be used with respiratory gating. Materials and Methods: The phantoms used included a ferucarbotran phantom, water phantom, and gelatin phantom. Each phantom was scanned by the FRFSE method and fast spin echo (FSE) method, with changing of scanning parameters, and each CNR was mea- sured. Each CNR was given a point, and points were averaged according to each parameter. Parameters that obtained high average points were considered optimal parameters. Results: The optimal parameters were set to TE=50 ms in the FRFSE method. The scan parameters optimized from the phantom study were used in a clinical case, and good results were achieved, as in the phantom study. Conclusion: We optimized the scan parameters of the FRFSE method and were able to suggest the usefulness of the FRFSE method in SPIO-MRL
Spectra of scattered X-rays in the maze of a Linac (X-ray energies of 4, 6, and 10 MV)room were estimated by means of the Monte Carlo simulation, and air kerma transmission factors of the X-rays scat-tered through a lead shield were evaluated based on those spectra. Spectra of scattered X-rays showed a maximum in the energy area below 200 keV. The higher the accelerated electron energy, also, the smaller the scattering angle that tended to spread to the higher energy area of the distribution of spectra. The air kerma transmission factor of 120° scattered X-rays of 4 MV X-rays obtained in this study was larger than the transmission factors of 124° scattered photons of ^<60>Co gamma rays through a lead shield given in ICRP. The air kerma transmission factors of 120° scattered X-rays of 6 MV X-rays were smaller than the transmission factors of 90° scattered photons of ^<60>Co gamma rays. The air kerma transmission factors of 120° scattered X-rays of 10 MV X-rays was slightly larger than transmission factors of 90° scattered photons of ^<60>Co gamma rays. Therefore, in the case of a 4 MV X-ray Linac room, the calculation method given in the "Manual of Practical Shield Calculation of Radiation Facilities (2000)" causes underestimation of leakage doses.
The purpose of this study was to find an equation between signal-to-noise ratio(SNR.) and repetition time (TR) in order to adjust SNR by changing TR in magnetic resonance imaging(MRl)examinations. Using a phantom for SNR measurement, according to NEMA MS 1-1988, measurement of SNR was performed by spin-echo pulse sequences for various TR values. An equation of SNR and scanning parameters include- ing TR were obtained from these results. In order to determine the range of TR where the images showed contrast suitable for diagnosis, the contrast-to-noise ratio(CNR) was measured for various TR values. CNR measurement was performed by scanning a brain phantom, and CNR was defined as the contrast of white matter and gray matter divided by noise. Scanning of a resolution phantom was carried out with various scanning parameters, and the usefulness of the equation obtained was determined by whether or not pins in the phantom were visible. The reliability of the equation was confirmed from this verification. Results showed that TR can be used for the adjustment of SNR using the equation obtained in this study.
In three-dimensional CT angiography (3DCTA) studies, the CT values within blood vessels ideally should be uniform because the reproducibility and detectability of the morphological characteristics of blood ves-sels change depending on the threshold value selected. The time-density curve (TDC) therefore should be maintained at a certain level. However, conventional contrast medium injectors have a fixed injection speed, and the injection speed must therefore be changed in a stepwise manner. This means that it is not possible to maintain the TDC precisely. However, recent advances in the performance capabilities of contrast medium injectors allow the injection speed to be changed continuously with a user-selectable injection-speed ratio, permitting studies to be performed using the so-called "variable-speed injection method". We have conducted studies using this new method to determine the optimal injection speed ratio that permits the TDC to be maintained at the desired level. Our results showed that an injection-speed ratio of 0.5 permits the TDC to be maintained at the optimal level, improving the reproducibility and detectability of blood vessel morphology in 3DCTA studies. In addition, when contrast medium injection was terminated at a time point ≥50% of the preset contrast medium injection time, the mean CT value was not adversely affected (I.e., was not significantly reduced), making it possible to reduce the amount of contrast medium administered to the patient.
We evaluated the usefulness of two-dimensional time-of-flight(2D TOF) MR venography (MRV) of the lower extremity using the respiratory compensation (RC) technique. In addition, six variations in patient positioning of the leg and knee were investigated to determine the best method of visualizing the dee popliteal veins and lower leg. All data sets were reviewed and graded for visualization of the deep veins at the pelvis, thigh, and leg portion (4-point scale)by two radiologists and three radiological technologists. The same veins demonstrated with various positions of the patient were also evaluated in the same manner. In conclusion, 2D TOF MRV with RC resulted in increased uniformity of vein signal in the pelvic area. Furthermore, we should position the patient's leg so as not to compress the vein at the posterior portion of the leg, and not to over-extend the knee joint. This enabled the best results to be obtained in MRV of the lower extremity.
We have reported that, using the bolus-tracking method synchronized with an injector, the injection of contrast medium in a single phase up to 10 sec before the end of the study (referred to as "single-stage injection") or the combination of single-stage injection stopped 15 sec before the end of the study and a physiological saline solution flush (referred to as "saline solution flush") makes it possible to minimize the amount of contrast medium employed in 3D-CTA of the head and neck in a scanning time of approximately 30 sec. If the continuous variable method of contrast medium injection (referred to as "variable injection") can provide the same level of contrast enhancement as that obtained with a single-stage injector for constant-rate injection, it should be possible to eliminate cumbersome study procedures associated with the saline solution flush and to simplify the study protocol. We therefore performed a comparative study to assess the contrast enhancement effect in variable injection. The results showed that variable injection provided almost the same degree of contrast enhancement as single-stage injection + saline solution flush, while permitting the amount of contrast medium to be reduced. It was concluded that variable injection (with a variation parameter of 0.5) is an effective method of improving the contrast enhancement effect and minimizing the amount of contrast medium employed, as compared with the saline solution flush method. Furthermore, it permits the examination procedures to be simplified.