[논문]손목관절 CT 검사 시 자세 변화와 채널 변경에 따른 MTF 평가 : Isocenter를 중심으로 X-축, Z-축 변화

서민재; 임종천; 정다빈; 한동균

doi:10.7742/jksr.2020.14.6.811

손목관절 CT 검사 시 자세 변화와 채널 변경에 따른 MTF 평가 : Isocenter를 중심으로 X-축, Z-축 변화
MTF Evaluation according to change in posture and channel during CT examination for wrist Joint : X-axis and Z-axis changes around Isocenter 원문보기

한국방사선학회 논문지 = Journal of the Korean Society of Radiology, v.14 no.6, 2020년, pp.811 - 817

서민재 (을지대학교 보건과학대학 방사선학과) , 임종천 (을지대학교 보건과학대학 방사선학과) , 정다빈 (을지대학교 대학원 방사선학과) , 한동균 (을지대학교 보건과학대학 방사선학과)

초록
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본 연구의 목적은 손목관절 CT 검사에서 환자 자세를 X-축, Y-축으로 변화시키고 CT 검사장치의 channel 변화에 따른 MTF 평가를 하는 것이다. CT 장치와 손목 팬텀을 이용하여 isocenter를 중심으로 X-축으로 0(일치), 5, 10, 15 cm 이동시켜 검사하고, Z-축은 반시계 방향으로 -20°, -40° 회전하여 검사하였다. 검사는 16, -40, 64 channel을 이용하여 channel 별 차이가 있는지도 확인하고자 하였다. 검사한 영상은 자뼈와 좌우측 노뼈의 MTF 값을 측정하여 비교하였다. isocenter를 중심으로 X-축으로 이동시킨 실험에서 이동 거리가 커질수록 MTF 값은 감소하였고, 이때 MTF 값은 channel과는 무관한 것으로 확인되었다. Z-축에서 반시계 방향으로 -20°, -40° 손목관절을 회전시킨 실험에서 회전정도와 MTF는 무관한 것으로 확인되었다. 또한 channel과도 무관하였다. 결론적으로 손목관절 CT 검사에서 손목은 X-축 방향으로 이동을 최대한 억제시키고, Z-축으로의 회전은 검사 대상자의 환경에 따라 변화하여도 영상의 MTF에는 큰 영향을 주지 않을 것이라 사료된다.

Abstract ▼ AI-Helper

This study aims to evaluate the Modulation Transfer Function (MTF) according to the change in the number of channels of the CT examination device by changing the posture of the patient to the X-axis and Y-axis in the wrist joint CT examination. Using a CT device and a wrist phantom, the test was performed by moving 0 (matched), 5, 10, and 15 cm in the X-axis around the isocenter, and the Z-axis was rotated by -20° and -40°. For the test, 16, -40 and 64 channels were used to check whether there was a difference for each number of channels. The examined images were compared by measuring the MTF values of the ulna and left and right sides of the radius. In the experiment where the isocenter was moved along the X-axis, the MTF value decreased with an increase in the moving distance, and the MTF value was found to be unaffected by the number of channels. In the experiment in which the wrist joint was rotated by -20° and -40° on the Z-axis, the degree of deviation and MTF were found to be irrelevant. It was not related to the number of channels either. In conclusion, the movement of the wrist along the X-axis should be restrained as much as possible for a wrist joint CT scan, whereas deviation around the Z-axis depending on the environment for the patient would not affect the MTF of the image.

주제어

표/그림 (5)

그림 Fig. 1. Experiment on the change in the distance of the subject along the X-axis in which the point where the X-axis meets the radio-ulna joint is moved to the left by 0 cm (A), 5 cm (B), 10 cm (C) and 15 cm (D)
표 Table 1. Scan Parameter
그림 Fig. 2. Experiment on the change in the angle of the subject around the Z-axis in which examination was performed while rotating the major axis of the wrist around the Z-axis by 0° (A), -20° (B) and -40° (C)
표 Table. 1. MTF value according to the distance along the X-axis for each number of channels
표 Table. 2. MTF value according to angle of deviation around the Z-axis for each number of channels

AI 본문요약
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문제 정의

Therefore, it is necessary to evaluate the image taken from a patient who is unable to keep the wrist in the isocenter while examining the wrist. Therefore, this study aims to evaluate the quality of wrist CT scan image by changing the central axis angle of the wrist and changing the number of channels of the device.

제안 방법

For each number of channels, the phantom was moved from the isocenter to the left and right along the X-axis and rotated -20° and -40° around the Z-axis, which was the major axis direction of the wrist, while performing examination.
In the experiment, the combination of MDCT detector array was changed to 16, -40 and 64 channels. For each number of channels, the phantom was moved from the isocenter to the left and right along the X-axis and rotated -20° and -40° around the Z-axis, which was the major axis direction of the wrist, while performing examination.
MTF is the normalized magnitude of the Fourier transform of the line-spread function (LSF). In this study, For LDF, the edge-spread function (ESF) was obtained through differentiation after setting the Region of Interest (ROI) in radius and ulna. At this time, the MTF evaluation method used the slanted-edge method^[5,6].
In the experiment on the change in the location of the subject along the X-axis, the phantom was moved from the isocenter of the CT device (o cm) to the left by 5, 10 and 15 cm for the examination as shown in Figure 1. It was examined 1-20 times in total: 10 times each for isocenter (0 cm), 5 cm, 10 cm and 15 cm for each of the 16, 40 and 64 channel scans.
It was examined 60 times in total: 10 times each for the -20° and -40° deviations from the isocenter (0°) for each of the 16, -40 and 64 channel scans.
Looking at the direction where the center line of the isocenter and the major axis of the wrist coincide with the Z-axis, if the patient's body cannot move outside the gantry of the CT device, the wrist usually rotates around the Z-axis. Therefore, an experiment was conducted to rotate the wrist phantom around the Z-axis. At this time, the clockwise deviation was not considered as it was almost improbable in terms of the actual anatomical structure.
However, there are not enough studies conducted on the wrist, and there is no evaluation of the image quality caused by the deviation of the major axis of the wrist in the Z-axis. Therefore, in this study, the image quality was evaluated using a wrist-only phantom assuming the cases in which the subject was moved from the CT isocenter to the left along the X-axis and the major axis of the wrist was rotated around the Z-axis. For each variable, the changes according to the number of channels of the CT device were observed as well.
This study conducted two types of experiments: the first experiment was conducted to examine the MTF changes according to the number of channels of the CT device and the X-axis distance, and the second experiment was on the MTF changes according to the deviation of the subject around the Z-axis.
When scanning a wrist, the wrist is placed in the isocenter of the CT device, and this time, considering the amount of radiation exposure and the quality of the image, the examination is performed with the patient’s hand raised above the head to avoid contact with other body organs.

대상 데이터

In this study, CT (Brilliance 64 slice, Philips, Holland) device and a wrist phantom (Hand/Wrist phantom RS-144T, Universal Medical, USA) were used. As shown in Table 1, conditions used for the test were kept constant in terms of the table height, window width/level, kV, mAs, SFOV, filter, etc.

데이터처리

At this time, the MTF evaluation method used the slanted-edge method^[5,6]. For statistics on the MTF value according to the distance along the X-axis for each number of channels, the average MTF value was analyzed through Kruskal Wallis test. The MTF calue according to angle of deviation around the Z-axis for each number of channels was subjected to an Mann-Whitney u-test.
For statistics on the MTF value according to the distance along the X-axis for each number of channels, the average MTF value was analyzed through Kruskal Wallis test. The MTF calue according to angle of deviation around the Z-axis for each number of channels was subjected to an Mann-Whitney u-test. At this time, when the p value was less than 0.

이론/모형

In this study, For LDF, the edge-spread function (ESF) was obtained through differentiation after setting the Region of Interest (ROI) in radius and ulna. At this time, the MTF evaluation method used the slanted-edge method^[5,6]. For statistics on the MTF value according to the distance along the X-axis for each number of channels, the average MTF value was analyzed through Kruskal Wallis test.

성능/효과

As a result of analyzing the MTF while moving the subject along the X-axis, in the 16-channel scan, the MTF was the highest at the point 0 cm away along the X-axis with 0.62±0.03, and the lowest at the point 15 cm away with 0.53±0.03(p<0.05).
For each variable, the changes according to the number of channels of the CT device were observed as well. As a result of the study, in the wrist examination with the subject moving along the X-axis, sharpness decreased as the distance from the isocenter increased, and there was no significant difference depending on the number of channels. Hara et.
In conclusion, the movement of the patient’s wrist from the isocenter along the X-axis should be restrained as much as possible for a wrist joint CT scan.
In particular, bone is a material with high X-ray absorption rate; therefore, CT imaging is used to diagnose fracture or dislocation and even to plan a surgery. ^[2]The wrist joint itself is small and complex as it consists of eight carpals surrounded by five metacarpals, radius and ulnar, and the carpal tunnel at the base of the wrist has a very complex structure with the presence of the median nerve and several tendons. ^[3]Therefore, when examining the wrist, increasing the image quality is helpful for diagnosis.

후속연구

Since this study did not evaluate SNR, additional SNR evaluation studies may be required. Therefore, this study is expected to provide basic data for the SNR evaluation studies in the future.

참고문헌 (12)

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저자의 다른 논문 :

표제어: PCR

동의어: Packet Collision Rate

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용어 설명: PCR은 세균 특이성이 있는 primer를 이용하여 적은 수의 세균이 있을지라도 쉽게 검출할 수 있는 유용한 방법이며, 이를 이용하여 구강 내 치면세균막이나 타액에서 직접 세균을 검출할 수 있게 되었다[8].

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