Olivieri Laura J, Cross Russell R, O'Brien Kendall E, Ratnayaka Kanishka, Hansen Michael S
Division of Cardiology, Children's National Health System, W3-200, 111 Michigan Ave. NW, Washington, DC, 20010, USA,
Pediatr Radiol. 2015 Sep;45(10):1455-64. doi: 10.1007/s00247-015-3366-0. Epub 2015 Jun 4.
Cardiac magnetic resonance (MR) imaging is a valuable tool in congenital heart disease; however patients frequently have metal devices in the chest from the treatment of their disease that complicate imaging. Methods are needed to improve imaging around metal implants near the heart. Basic sequence parameter manipulations have the potential to minimize artifact while limiting effects on image resolution and quality.
Our objective was to design cine and static cardiac imaging sequences to minimize metal artifact while maintaining image quality.
Using systematic variation of standard imaging parameters on a fluid-filled phantom containing commonly used metal cardiac devices, we developed optimized sequences for steady-state free precession (SSFP), gradient recalled echo (GRE) cine imaging, and turbo spin-echo (TSE) black-blood imaging. We imaged 17 consecutive patients undergoing routine cardiac MR with 25 metal implants of various origins using both standard and optimized imaging protocols for a given slice position. We rated images for quality and metal artifact size by measuring metal artifact in two orthogonal planes within the image.
All metal artifacts were reduced with optimized imaging. The average metal artifact reduction for the optimized SSFP cine was 1.5+/-1.8 mm, and for the optimized GRE cine the reduction was 4.6+/-4.5 mm (P < 0.05). Quality ratings favored the optimized GRE cine. Similarly, the average metal artifact reduction for the optimized TSE images was 1.6+/-1.7 mm (P < 0.05), and quality ratings favored the optimized TSE imaging.
Imaging sequences tailored to minimize metal artifact are easily created by modifying basic sequence parameters, and images are superior to standard imaging sequences in both quality and artifact size. Specifically, for optimized cine imaging a GRE sequence should be used with settings that favor short echo time, i.e. flow compensation off, weak asymmetrical echo and a relatively high receiver bandwidth. For static black-blood imaging, a TSE sequence should be used with fat saturation turned off and high receiver bandwidth.
心脏磁共振成像（MR）是先天性心脏病诊断中的一项重要工具；然而，患者因疾病治疗胸部常带有金属装置，这给成像带来了困难。需要改进心脏附近金属植入物周围的成像方法。基本序列参数调整有可能在限制对图像分辨率和质量影响的同时，将伪影降至最低。
我们的目的是设计电影和静态心脏成像序列，在保持图像质量的同时尽量减少金属伪影。
通过在含有常用心脏金属装置的充液模型上系统地改变标准成像参数，我们开发了用于稳态自由进动（SSFP）、梯度回波（GRE）电影成像和快速自旋回波（TSE）黑血成像的优化序列。我们使用标准和优化成像方案，对给定切片位置的17例接受常规心脏MR检查且带有25个不同来源金属植入物的连续患者进行成像。通过在图像内两个正交平面测量金属伪影，对图像的质量和金属伪影大小进行评分。
优化成像后所有金属伪影均减少。优化后的SSFP电影成像平均金属伪影减少1.5±1.8毫米，优化后的GRE电影成像减少4.6±4.5毫米（P<0.05）。质量评分更倾向于优化后的GRE电影成像。同样，优化后的TSE图像平均金属伪影减少1.6±1.7毫米（P<0.05），质量评分更倾向于优化后的TSE成像。
通过修改基本序列参数可轻松创建针对最小化金属伪影的成像序列，且这些图像在质量和伪影大小方面均优于标准成像序列。具体而言，对于优化的电影成像应使用GRE序列，设置为有利于短回波时间，即关闭血流补偿、采用弱非对称回波和相对较高的接收带宽。对于静态黑血成像，应使用TSE序列，关闭脂肪饱和并采用高接收带宽。
