Dzwonczyk Roger, Fujii Jeffrey T, Simonetti Orlando, Nieves-Ramos Ricardo, Bergese Sergio D
Departments of Anesthesiology, The Ohio State University, Columbus, Ohio 43214, USA.
Anesth Analg. 2009 Jan;108(1):181-6. doi: 10.1213/ane.0b013e31818f8777.
Intraoperative magnetic resonance imaging (iMRI) is a tool now commonly used in neurosurgery. Safe and reliable patient care in this (or any other) operating room setting depends on an environment, where electrical noise (EN) does not interfere with the operation of the electronic monitoring or imaging equipment. In this investigation, we evaluated the EN generated by the iMRI system and the anesthesia patient monitor used at this institution that impacts the performance of these two devices.
We measured the EN generated by our iMRI-compatible anesthesia patient monitor as detected by the EN analysis algorithm in our iMRI system. We measured the EN generated by our iMRI system during scanning as detected in the electrocardiogram (ECG) waveform of our patient monitor. We analyzed the effects on EN reduction and signal quality of the ECG noise filters provided in our iMRI-compatible anesthesia patient monitor.
Our patient monitor generated EN that was detectable by the iMRI EN analysis algorithm; however, this interference was within the iMRI manufacturer's acceptable limits for an iMRI scan (<10% more than background system-level noise). In the clinical case analyzed, the iMRI generated a narrow-band low-frequency (20 Hz) relatively high-energy EN that interfered with the ECG signal of our patient monitor during an iMRI scan. This EN was correlated with the acoustic noise from the iMRI system during the scan and was associated with the radio frequency (RF) and magnetic gradient pulsations of the iMRI system. The integrity of the ECG waveform was nearly entirely lost during a scan. The filters of the ECG monitor diminished but did not entirely eliminate this 20 Hz interference. We found that the filters alter the morphology of the ECG signal, which may make it difficult to identify clinically relevant ECG changes.
The EN generated by our anesthesia patient monitor is within acceptable limits for the iMRI system. The iMRI generates EN which renders the ECG unreadable in the most commonly used filter mode. The monitor's filters diminish this noise but also alter the morphology of the ECG waveform. The anesthesiologist must be cognizant of these technical compromises and recognize that adjusting the ECG filters on the monitor is required to obtain a useful ECG signal for patient monitoring during the iMRI scan but that the diagnostic value of the ECG will be reduced.
术中磁共振成像（iMRI）是目前神经外科常用的一种工具。在这种（或任何其他）手术室环境中，安全可靠的患者护理依赖于一个电气噪声（EN）不会干扰电子监测或成像设备运行的环境。在本研究中，我们评估了iMRI系统和本机构使用的麻醉患者监护仪产生的电气噪声对这两种设备性能的影响。
我们测量了iMRI系统中的电气噪声分析算法检测到的与iMRI兼容的麻醉患者监护仪产生的电气噪声。我们测量了在扫描过程中iMRI系统产生的电气噪声，该噪声在患者监护仪的心电图（ECG）波形中被检测到。我们分析了与iMRI兼容的麻醉患者监护仪中提供的ECG噪声滤波器对降低电气噪声和信号质量的影响。
我们的患者监护仪产生的电气噪声可被iMRI电气噪声分析算法检测到；然而，这种干扰在iMRI制造商对iMRI扫描可接受的限度内（比背景系统级噪声高不到10%）。在分析的临床病例中，iMRI在扫描过程中产生了一种窄带低频（20 Hz）相对高能的电气噪声，干扰了我们患者监护仪的ECG信号。这种电气噪声与扫描过程中iMRI系统的声学噪声相关，并且与iMRI系统的射频（RF）和磁梯度脉动有关。在扫描过程中，ECG波形的完整性几乎完全丧失。ECG监护仪的滤波器减少了但并未完全消除这种20 Hz的干扰。我们发现这些滤波器改变了ECG信号的形态，这可能使得难以识别临床上相关的ECG变化。
我们的麻醉患者监护仪产生的电气噪声在iMRI系统可接受的限度内。iMRI产生的电气噪声使得在最常用的滤波模式下ECG无法读取。监护仪的滤波器减少了这种噪声，但也改变了ECG波形的形态。麻醉医生必须认识到这些技术上的折衷，并认识到在iMRI扫描期间需要调整监护仪上的ECG滤波器以获得用于患者监测的有用ECG信号，但ECG的诊断价值将会降低。
