Lewin J S, Duerk J L, Jain V R, Petersilge C A, Chao C P, Haaga J R
Department of Radiology, University Hospital of Cleveland, OH 44106 USA.
AJR Am J Roentgenol. 1996 Jun;166(6):1337-45. doi: 10.2214/ajr.166.6.8633445.
The purpose of this investigation was to evaluate the accuracy of MR Imaging for needle depiction at 0.2 and 1.5 T with multiple pulse sequences and needle orientations. The goal was to provide a framework for biopsy approach and imaging technique parameter selection that will ensure the safety and accuracy of MR-guided procedures.
Eight titanium and stainless steel alloy MR-compatible biopsy devices were immersed in fluid phantoms and placed into 1.5- and 0.2-T MR systems used for clinical imaging. Spin-echo, turbo spin-echo, and gradient-echo images were obtained with the needle shafts of the biopsy devices placed parallel to, perpendicular to, and at angles of 30 degrees and 60 degrees relative to the static magnetic field of the scanner. All images were obtained with the frequency-encoding direction parallel to and perpendicular to the needle shaft. Needle width and tip position were measured from images on a freestanding workstation, and the apparent tip position was compared with that obtained by direct measurement. The difference between these values was calculated for each needle type, imaging sequence, frequency-encoding direction, and needle orientation.
Artifactual widening was much more apparent at 1.5 T than at 0.2 T, as was error in determining needle tip position. Artifacts at both field strengths were most pronounced with gradient-echo sequences, less so with turbo spin-echo sequences, and least of all with spin-echo sequences. For spin-echo and turbo spin-echo sequences, when the frequency-encoding axis was perpendicular to the needle shaft, the apparent width of the needle was larger, but error in needle tip position was smaller. Artifacts were much less apparent, but error in tip position increased, as the orientation of the needle shaft became more parallel to the direction of the magnetic field.
Specific measurements differed with field strength, but needle tip localization within 1 mm was obtained at both 0.2 and 1.5 T with the appropriate frequency-encoding direction, pulse sequence, and imaging parameters. Orientation of the needle parallel to the magnetic field significantly reduced the apparent width of the needle at both field strengths but also decreased the accuracy of needle tip position localization.
本研究的目的是评估在0.2T和1.5T场强下，使用多种脉冲序列及不同针方向时，磁共振成像（MRI）对穿刺针显示的准确性。目标是提供一个活检方法及成像技术参数选择的框架，以确保磁共振引导操作的安全性和准确性。
将八个与磁共振兼容的钛合金和不锈钢合金活检装置浸入液体模体中，并放入用于临床成像的1.5T和0.2T磁共振系统中。在活检装置的针轴与扫描仪静磁场平行、垂直以及相对于静磁场呈30度和60度角的情况下，获取自旋回波、快速自旋回波和梯度回波图像。所有图像均在频率编码方向与针轴平行和垂直的情况下获取。在独立工作站上从图像测量针的宽度和针尖位置，并将表观针尖位置与直接测量获得的结果进行比较。针对每种针类型、成像序列、频率编码方向和针方向，计算这些值之间的差异。
在1.5T场强下，伪影加宽比在0.2T场强下更明显，确定针尖位置时的误差也是如此。在两个场强下，梯度回波序列的伪影最明显，快速自旋回波序列的伪影次之，自旋回波序列的伪影最不明显。对于自旋回波和快速自旋回波序列，当频率编码轴垂直于针轴时，针的表观宽度较大，但针尖位置的误差较小。随着针轴方向变得更平行于磁场方向，伪影明显减少，但针尖位置的误差增加。
特定测量因场强而异，但在0.2T和1.5T场强下，通过适当的频率编码方向、脉冲序列和成像参数，均可实现1mm内针尖定位。在两个场强下，针与磁场平行的方向显著减小了针的表观宽度，但也降低了针尖位置定位的准确性。
