Koch Kevin M, King Kevin F, Carl Michael, Hargreaves Brian A
GE Healthcare, Magnetic Resonance Division, Waukesha, Wisconsin, USA.
Magn Reson Med. 2014 Jun;71(6):2024-34. doi: 10.1002/mrm.24862. Epub 2013 Jul 10.
Magnetic resonance imaging capabilities in the direct vicinity of metallic devices have substantially improved with the recent development of three-dimensional multispectral imaging (3D-MSI) methods. When imaging near metallic hardware, the bulk image distortions in 3D-MSI techniques are reduced to the single-pixel level. However, commonly utilized MSI techniques are ultimately limited by frequency-encoding processes and reveal a class of residual intensity-based susceptibility artifacts that have yet to be formally analyzed.
Empirical measurements and simulation techniques are utilized to study the static local magnetic field gradients induced by metal implants and their general impact on frequency-encoding processes. The specific consequences of these gradients on 3D-MSI approaches are also analyzed using empirical and simulated approaches.
Close agreements between empirical and simulated measurements clearly demonstrate the effects of strong local gradients on frequency-encoded imaging capabilities near metallic implants.
3D-MSI techniques can enable substantially enhanced magnetic resonance imaging capabilities near metallic implants. However, strong local static field gradients generate residual artifacts whose direct mitigation are ultimately limited by frequency encoding processes. Applications of 3D encoding strategies or additional post processing may be required to further reduce residual artifacts in multispectral images near metal implants.
随着三维多光谱成像（3D-MSI）方法的最新发展，金属装置直接附近的磁共振成像能力有了显著提高。在对靠近金属硬件的区域进行成像时，3D-MSI技术中的整体图像失真被降低到单像素水平。然而，常用的MSI技术最终受到频率编码过程的限制，并显示出一类基于强度的残余磁化率伪影，尚未进行正式分析。
利用实证测量和模拟技术研究金属植入物引起的静态局部磁场梯度及其对频率编码过程的总体影响。还使用实证和模拟方法分析了这些梯度对3D-MSI方法的具体影响。
实证测量和模拟测量之间的密切一致性清楚地证明了强局部梯度对金属植入物附近频率编码成像能力的影响。
3D-MSI技术可以在金属植入物附近实现显著增强的磁共振成像能力。然而，强局部静态场梯度会产生残余伪影，其直接减轻最终受到频率编码过程的限制。可能需要应用3D编码策略或额外的后处理来进一步减少金属植入物附近多光谱图像中的残余伪影。
