Ravier S, Gangi A, Choquet P, Brunot B, Mertz L, Constantinesco A
Laboratoire de Biomécanique, CHU de Strasbourg-Hautepierre, Strasbourg.
J Radiol. 1996 Feb;77(2):105-10.
The excellent tissue differenciation provided by MRI in the three directions and the lack of ionizing radiations make it ideal for interventional procedures. Many problems must still be solved: the access to the patient, the size of the artefact produced by interventional instruments and the acquisition time. In this study, we evaluated the influence of field strength for standard imaging sequences on the MRI artefact of a non ferro-magnetic biopsy needle. Then, we developed very fast sequences on a opened 0.1 T dedicated magnet to test in vitro and ex vivo the potential ability of this system in the guidance of the needle.
The biopsy needle was a new stainless steel needle made of 49% Nickel. The needle artefact's size measurements were made at 0.1 T, 0.5 T and 1 T on a bicompartmental phantom (one compartment with a long T1 and another with a long T2), with standard gradient echo (400/12/90 degrees) and spin echo (500/25) sequences. At 0.1 T, we optimized very fast steady state 3D FAST (T1 weighted) and 3D CE-FAST (T2 weighted) sequences to reduce the acquisition time, preserving good image contrasts for a field of view reaching 38 mm and 48 x 64 or 24 x 32 matrix.
The larger needle artefact observed on gradient echo images varied from 3.6 mm at 0.1 T to 8.6 mm at 1 T. The shortest acquisition time for 4 contiguous slices of 2mm with a 1.2 mm/pixel resolution and a 24 x 32 matrix was 1.5 s for the 3D FAST (16/9/65 degrees) sequence and 3 s for the 3D CE-FAST (29/22/65 degrees) sequence. We realized a complete MRI guided abdominal puncture on a cat cadaver with 4 series of 15 s 3D FAST images (16/9/65 degrees, 4 slices, 5 excitations, 1.2 mm/pixel, FOV = 77 mm). Besides the cat positioning and the image reconstruction time, the whole puncture lasted 1 min (4 x 15 s).
Low field MRI (0.1 T) combined with very fast 3D steady state sequences is adapted for the real time guidance of biopsy needles.
磁共振成像（MRI）在三个方向上具有出色的组织分辨能力且无电离辐射，使其成为介入操作的理想选择。但仍有许多问题有待解决：患者的进针路径、介入器械产生的伪影大小以及采集时间。在本研究中，我们评估了标准成像序列的场强对非铁磁性活检针MRI伪影的影响。然后，我们在开放式0.1 T专用磁体上开发了超快速序列，以在体外和离体状态下测试该系统在引导活检针方面的潜在能力。
活检针是一种新型不锈钢针，含49%的镍。在一个双腔模型（一个腔室具有长T1，另一个具有长T2）上，使用标准梯度回波（400/12/90度）和自旋回波（500/25）序列，分别在0.1 T、0.5 T和1 T场强下测量针伪影的大小。在0.1 T场强下，我们优化了超快速稳态三维快速成像（T1加权）和三维对比增强快速成像（T2加权）序列，以减少采集时间，在视野达38 mm以及矩阵为48×64或24×32时保持良好的图像对比度。
在梯度回波图像上观察到的较大针伪影，在0.1 T时为3.6 mm，在1 T时为8.6 mm。对于分辨率为1.2 mm/像素、矩阵为24×32的4个相邻2 mm厚切片，三维快速成像（16/9/65度）序列的最短采集时间为1.5 s，三维对比增强快速成像（29/22/65度）序列为3 s。我们在一只猫的尸体上利用4组15 s的三维快速成像（16/9/65度，4层，5次激励，1.2 mm/像素，视野 = 77 mm）图像实现了完整的MRI引导下腹部穿刺。除了猫的定位和图像重建时间外，整个穿刺过程持续1分钟（4×15 s）。
低场强MRI（0.1 T）结合超快速三维稳态序列适用于活检针的实时引导。
