확산강조영상(diffusion weighted image: DWI)은 병태생리학에 대한 특별한 정보를 제공하며, 특히 뇌 관련 질환뿐만 아니라 직장암, 유방암 등에서도 그 활용도가 높아지고 있다. 과거부터 사용했던 Conventional-DWI는 척추 주변의 자기장 불균질 물질, 척수의 작은 단면, 호흡, 뇌척수액으로 인해 척추 주변에 증가된 움직임 등을 수행하는데 사용되었으며, 기존의 자기공명영상검사(magnetic resonance image: MRI)에서 문제점으로 지적되어 왔던 위상부호화 방향에서의 긴 판독시간과 낮은 대역폭과 함께 기하학적 왜곡의 경향이 있어 이를 평행영상을 포함하여 조직을 다루기 위해 개발되었다. 하지만 이와 같은 영상판독 개발 및 발전에도 불구하고 여전히 영상왜곡은 존재하며, 이러한 영상왜곡을 감소하기 위한 여러 방법 중 FOCUS-DWI가 있다. 본 논문은 선택적인 위상 방향 및 슬라이스를 이용하는 FOCUS (FOV Optimized and Constrained Undistorted Single-shot-2D selective RF Excitation) DWI가 자기장 내 중심축에서 거리 변화에 따른 인공물, 균일도, 확산계수(b-factor)를 기존의 Conventional-DWI와 비교하여 그에 대한 유용성을 확인하고자 하였다.
영상획득을 위한 pulse sequence는 FOCUS-DWI와 Conventional-DWI를 사용하였고 중심축에서 우측으로 30 ㎜, 60 ㎜, 90 ㎜ 이동하여 각각 16개의 슬라이스로 검사하였다. 매개변수는 TR:4500 ms, TE:55 ms, matrix는 128×128, b-factor 400과 800 s/㎟로 나누었고 FOV는 240×120 ㎜, NEX는 6, slice thickness는 5 ㎜, gap는 0 ㎜로 검사하였다.
인공물 발생에 대한 결과는 Conventional-DWI 기법에서 불규칙적인 줄무늬 인공물이 발생하였는데 중심축에서 인공물의 발생이 심하게 나타났고 영상의 겹침 정도가 급격하게 증가하였다. 하지만 FOCUS-DWI 기법은 줄무늬 모양의 인공물 발생이 나타나지 않았고 영상의 겹침 정도도 적게 나타났다. 영역별 신호측정에 대한 균일도 결과는 b-factor 400을 기준으로 중심축 0 mm에서 FOCUS-DWI : 1062.19±197.26, Conventional-DWI : 1355.65±321.64이고, 30 mm에서 FOCUS-DWI : 1148.56±103.58이고 Conventional-DWI : 1396.48± 343.30이고, 60 mm에서 FOCUS-DWI :2853.56±199.16이고 Conventional- DWI : 1352.11±346.35이고, 90 mm에서 FOCUS-DWI :978.41±194.69이고 Conventional-DWI : 1264.87±329.68이었다. 영역별 신호측정에 대한 균일도 결과는 중심축에서 거리의 변화에 관계없이 FOCUS-DWI가 훨씬 우수한 기법 으로 나타났다. 확산계수(b-factor)의 변화에 따른 결과는 0 mm에서 FOCUS- DWI b-400 : 1062.19±197.26, FOCUS-DWI b-800 : 1069.88±211.72이고, 30 mm에서 FOCUS-DWI b-400 : 1148.56 ±103.58이고 FOCUS-DWI b-800 : 1057.03±197.93이고, 60 mm에서 FOCUS-DWI b-400 :2853.56±199.16이고 FOCUS-DWI b-800 : 1043.83±202.98이고, 90 mm에서 FOCUS-DWI b-400 :978.41±194.69이고 FOCUS-DWI b-800 : 938.63±198.39이었다. 확산계수에 따른 신호강도와 균일도는 별 다른 차이가 없는 것으로 나타났다.
결론적으로 FOCUS-DWI 기법은 인공물, 영상의 겹침 정도, 균일도 측정에서 Conventional-DWI 기법보다 우수한 결과를 보였고, 거리의 변화에 따른 두 기법에서는 차이가 없게 나타났다. 따라서 FOCUS-DWI 기법은 영상의 왜곡 정도가 적고 화질이 우수하여 임상에서 활용도가 높을 것이라 사료된다.

Diffusion Weighted Image (DWI) provides special information to pathology. In particular, using DWI in rectal cancer and breast cancer as well as diseases related to brain has increased. The Conventional-DWI which has been used for years was employed to detect magnetic field inhomogeneities around spine, the small cross section of the spinal cord, and increased movements around spine because of breathing and cerebrospinal fluid (CSF). The problem that the existing the magnetic resonance image (MRI) was prone to have not only long readout duration and low bandwidth in the phase-encode direction, but also geometric distortion was pointed out. Thus, the Conventional-DWI was developed to detect the tissue, including parallel imaging.
However, despite the development of imaging readout, there still takes place imaging distortion. There are a lot of efforts to decrease imaging distortion. Of them, there is the FOCUS (Fov Optimized and Constrained Undistorted Single-shot-2D selective RF Excitation)-DWI technique. The purpose of this study is to identify the usefulness of FOCUS-DWI through comparing FOCUS-DWI with the Conventional-DWI on a degree of uniformity, b-factor, and artifacts caused by the distance change in the central axis within the magnetic field.
Pulse sequence to gain imaging used FOCUS-DWI and the Conventional-DWI. 30 mm, 60 mm, and 90 mm in the right direction from the central axis were moved and respectively 16 slices from 30 mm, 60 mm, and 90 mm were examined. This study was conducted under following conditions. Parameters were TR: 4500 ms and TE: 55 ms. The matrix was 128×128, and b-factor 400, which was divided by 800 s/mm². FOV was 240×120 mm. NEX was 6. Slice thickness was 5 mm. Gap was 0 mm.
In terms of artifacts, there happened irregular striped artifacts in the Conventional-DWI technique, which in particular, more often arose in the central axis. Also, the overlap of imaging drastically increased. By contrast, there were no irregular striped artifacts in the FOCUS-DWI technique. Furthermore, there took place rarely the overlap of imaging. Results from a degree of uniformity for measuring signals depending on regions were as follows. When the standard of b-factor was 400 in 0 mm of the central axis, FOCUS-DWI was 1062.19±197.26 and the Conventional-DWI was 1355.65±321.64. In 30 mm, FOCUS-DWI was 1148.56±103.58 and the Conventional-DWI was 1396.48±343.30. In 60 mm, FOCUS-DWI was 2853.56±199.16 and the Conventional-DWI was 1352.11±346.35. In 90 mm, FOCUS-DWI was 978.41±194.69 and the Conventional-DWI was 1264.87±329.68. In sum, it was verified that the FOCUS-DWI technique was much superior to the Conventional-DWI technique in terms of a degree of uniformity for measuring signals depending on regions, regardless of the change in distance from the central axis. As for b-factor, in 0 mm, FOCUS-DWI b-400 was 1062.19±197.26 and FOCUS-DWI b-800 was 1069.88±211.72. In 30 mm, FOCUS-DWI b-400 was 1148.56±103.58 and FOCUS-DWI b-800 was 1057.03±197.93. In 60 mm, FOCUS-DWI b-400 was 2853.56±199.16 and FOCUS-DWI b-800 was 1043.83±202.98. In 90 mm, FOCUS-DWI b-400 was 978.41±194.69 and FOCUS-DWI b-800 was 938.63±198.39. It presented that there was no difference in signal intensity and a degree of uniformity depending on b-factor.
In conclusion, it was found that the FOCUS-DWI technique was superior to the Conventional-DWI technique in terms of artifacts, the overlap of imaging, and a degree of uniformity. In addition, there was no difference of the change in distance from the central axis between the FOCUS-DWI technique and the Conventional-DWI technique. Thus, it is considered the FOCUS-DWI technique having less imaging distortion and high image quality will be highly clinically used.