新开发的金属组织标记(标记,3毫米长度;12、99.9%黄金材料,CareFusion,弗农山,IL)(图
1)被选为评估MRI在3特斯拉的问题。这个标记的特点包括它是相同的大小随着活检获得和配置(即。,an irregular surface allowing for growth of tissue around it) that is specially designed to prevent migration once it is deployed in tissue. The marker is supplied in a delivery device that approximates the same size of the biopsy device (Achieve Biopsy Device, CareFusion, Vernon Hills, IL), thus, permitting precise placement.
使用传输/接收进行了MRI在3特斯拉线圈射频(RF)的身体。核磁共振成像参数选择生成一个系统报道,全身平均的特定吸收率(SAR) 2.9 - w /公斤。相关的量热法值2.7 - w /公斤。(即土地标记位置。,the center position or anatomic region for the MRI) and section locations were selected to encompass the entire tissue marker.
与金属相关的构件组织标记进行评估在3特斯拉。标记是附加到一个塑料框架,放在一个塑料幻影充满掺入钆,盐水,这提供了一个高信号背景(
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10]。核磁共振进行了使用传输/接收射频头线圈(即。,for increased signal-to-noise) and the following pulse sequences: T1-weighted, spin echo, repetition time, 500-msec; echo time, 20-msec; matrix size, 256 × 256; section thickness, 10-mm; field of view, 24-cm; number of excitations, 2; bandwidth, 16 kHz, and gradient echo pulse sequence (GRE), repetition time, 100-msec; echo time, 15-msec; flip angle 30°; matrix size, 256 × 256; section thickness, 10-mm; field of view, 24-cm; number of excitations, 2; bandwidth, 16 kHz [
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10]。成像平面定位到包含组织的长轴和短轴标记。图像显示参数(即。,window and level settings, magnification, etc.) were selected and applied in a consistent manner to obtain accurate measurements of the sizes of the artifacts. Planimetry software provided with the MR system was used to measure (accuracy and resolution ±10%) the cross-sectional areas of the largest artifact size for each pulse sequence and imaging plane associated with the tissue marker [
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10]。值得注意的是,这种标准化的技术评估工件的工件特征被用于许多之前的研究,金属植入物,因此,提供了一个可接受的方法的比较
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10]。
3所示。结果
评估组织标记的磁场相互作用产生一个意味着偏转角度
2
±
0度。(即没有力矩。,rotational alignment) exhibited by the marker during the qualitative evaluation (i.e., mean torque value, 0, no torque). The MRI-related heating evaluation revealed that the highest change in temperature rise was 1.7°C with the tissue marker present in the phantom. By comparison, the highest temperature rise recorded during the background temperature evaluation was 1.6°C. Therefore, the temperature rise associated with the presence of the metallic tissue marker in the phantom was 0.1°C.
暴露的金属物体MRI在一定条件下有可能会使地球升温(
4,
5,
15]。因此,作为适当的核磁共振测试确保病人安全,标准化
在体外评估执行描述金属植入物的温度上升(
4,
5,
15]。组织标记的记录温度变化表明,最高温度变化仅为0.1°C以上背景温度最高时进行了核磁共振在全身平均SAR水平相对较高(2.9 - w /公斤)。显然,这个最小的温度上升不会对这种植入的病人构成风险。尽管高全身平均SAR水平(即可以使用。,the current upper limit is an SAR, 4-W/kg), this was not believed to be necessary because the experimental setup involved a nonperfused gelled-saline medium and, thus, created an extreme case for implant heating.
4.3。工件
金属植入物的存在在病人接受核磁共振成像通常会导致低强度信号丢失,在严重的情况下,图像的失真(
4,
5,
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10,
20.,
21]。这一主要因素影响的大小metal-related工件材料的磁化率(
24]。的工件观察组织标记由黄金(99.99%)出现局部信号损失相对较小的大小与它的大小和形状(请参考数据
2(一个)和
2 (b))。梯度回波脉冲序列(即。,representing an extreme condition for MRI-related artifacts), which is often used for evaluation of the breast or other tissues, produced larger artifacts than the T1-weighted, spin echo pulse sequence.