Biomedical subjects

Takanori Hara

Publications and source records attributed to Takanori Hara.

5 recordsLinked to original sources

PubMed2006

[Evaluation of change in the optimal image reconstruction phase in retrospective ECG-gated reconstruction].

The purpose of this study was to optimize the reconstruction phase in order to improve depiction of the coronary artery in the relative delay method of the retrospective electrocardiogram (ECG)-gated reconstruction technique using a multi-slice computed tomography (MSCT) scanner with four channels. The following items were evaluated; 1) image quality of the coronary arteriogram, 2) degree of difference between the standard phase corresponding to the diastasis period and the selected phase, which was determined in each case to obtain the best image, and 3) the factors causing the phase difference. The image quality in the selected phase was better than that in the standard phase. A positive correlation was observed between the degree of phase difference and the median value and standard deviation of the heart rate. The degradation of image quality was remarkable in cases showing a large degree of phase difference. A negative correlation was observed between image quality in the selected phase and the degree of phase difference. Individualizing the reconstruction phase is required to improve the image quality of coronary arteriograms with MSCT. It should be noted that the condition of a low and stable heart rate results in reduction in the degree of phase difference, which is useful for the acquisition of better images.

Adolescent↗

PubMed2005

[Characteristic of evaluation of new image filter devised for improvement of workflow in CT examination].

In this study, we processed reconstructed images with a new image filter (Siemens Medical Systems, Adaptive Image Filter: AIF). As one of its characteristics, the filter uses low-pass filtering. When an image that emphasizes a high-frequency element is changed to one with a reduced high-frequency element, an image suitable for clinical use can be obtained. For the resolving characteristic and the noise characteristic, we evaluated the degree of transition, using the modulation transfer factor (MTF) and Wiener spectrum (WS). Moreover, we used the signal-to-noise ratio (SNR) to examine the total loss of signal detection capability after use of the AIF. The results showed that, when we changed to images using the AIF and made it the same level as B30 and U40, we had to hold down the kernel level to at least B60 and U80. The use of an image filter did not recognize less of an SNR in comparison with the reconstruction image. In this study, changes in detailed characteristics of the image and SNR could be evaluated objectively using the AIF. As for the effective method by AIF that raw data isn't used for is available for the control of an image (times) using reconstruction and the change of an image on database. Therefore, we consider the AIF useful to improve workflow in CT examinations.

Phantoms, Imaging↗

PubMed2003

[Measurement of modulation transfer function in Z-axis for multi-slice spiral CT using the micro-disk method: comparison with the bead method and examination of geometric influence].

Many methods of measuring the section-sensitive profile (SSP) of computed tomography (CT) by the input of a delta function have been reported. In Japan, the bead method is used as a common measurement because of the high flexibility of the multi-purpose method. However, the intensity of the response of the bead method tends to decline, creating a relatively large error in the base of section-sensitive profiles. A problem is considered to be the accuracy of measurement in evaluating spatial resolution along the z-axis in multi-slice spiral/helical CT (MSCT). We therefore evaluated the modulation transfer function (MTF) by conducting research with the micro-disk method (100 micro m thickness and 1.0 mmphi diameter) and the bead method (1.0 mmphi diameter) for the same input width. Moreover, in the micro-disk method, we also examined alignment, circular region of interest (ROI), and the energy characteristic. Our comparison of MTFs obtained by the micro-disk method and the bead method showed that the former resulted in a higher value and lower standard deviation. The difference was significant at p<0.01. Measurement using the micro-disk method did not show significant differences in terms of alignment and ROIs. Moreover, the energy characteristic was not indicated. This research demonstrated that the accuracy of MTF measurement with the micro-disk method was greater than that with the bead method, and it was found that there was no influence on the actual measurement level of the geometric structure with the micro-disk method.

Phantoms, Imaging↗

PubMed2003

[Complexity evaluation of data transfer in the Z-axis direction in 4-row multislice spiral CT using fractal dimension analysis].

Image reconstruction in multislice spiral/helical computed tomography (MSCT) consists of a package of data on the arbitrary direction of the Z-axis that can be collected by active detector arrays. Thus the recombined data vary with each spiral pitch. In certain cases of spiral pitch, data compression can occur, and the spiral artifacts that are characteristic of MSCT would change. In our study, we evaluated image complications by fractal dimensions, because the geometrical patterns from a conic phantom are closely related to data transfer in the direction of the Z-axis in spiral pitches. We hoped to establish useful spiral pitches and slice collimation for clinical use in a 4-row MSCT scanner. By employing a conic phantom of 120 mm in diameter and a cone angle of 100 degrees, we measured the fractal dimension of the conic phantom image by making a binary to outline from 2.0 to 8.0 of various slice collimations. Moreover, in order to evaluate the correlation between fractal dimensions and image artifacts, we confirmed the influence of spiral pitch and reconstruction slice thickness for clinical use. We found that, when the reconstruction slice thickness was the same, the cross section of the conic phantom that was from thin-slice collimations was more similar to an actual circle than that of wide-slice collimations. The former deserved a low value and showed slight changes, and, therefore, its fractal dimensions were fixed. As a phenomenon worthy of attention, when we employed wide-slice collimations (4x5.0 mm) during peculiar low spiral pitches of 2.5 to 3.0 fractal dimensions remained low and similar to an actual circle. By these analyses of the influence of data transfer in the direction of the Z-axis, we found that spiral pitch influenced the rate of slice collimation used for data acquisition closely to the reconstruction slice thickness. Based on these findings, when slice collimations and reconstruction slice thickness should be made equal, we estimated that spiral pitches of low image artifacts in 4row MSCT ranged from 2.5 to 3.0 using fractal dimensions. We consider that a new adaptation of fractal dimension analysis is possible when it is used as an index in determining protocols.

Artifacts↗

PubMed2002

[Basic examination of in-plane spatial resolution in multi-slice CT].

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 complementary 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.

Tomography, Spiral Computed↗