Kännälä Sami, Toivo Tim, Alanko Tommi, Jokela Kari
STUK-Radiation and Nuclear Safety Authority, 00881 Helsinki, Finland.
Phys Med Biol. 2009 Apr 7;54(7):2243-57. doi: 10.1088/0031-9155/54/7/026. Epub 2009 Mar 17.
Recent advances in magnetic resonance imaging (MRI) have increased occupational exposure to magnetic fields. In this study, we examined the assessment of occupational exposure to gradient magnetic fields and time-varying magnetic fields generated by motion in non-homogeneous static magnetic fields of MRI scanners. These magnetic field components can be measured simultaneously with an induction coil setup that detects the time rate of change of magnetic flux density (dB/dt). The setup developed was used to measure the field components around two MRI units (1 T open and 3 T conventional). The measured values can be compared with dB/dt reference levels derived from magnetic flux density reference levels given by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The measured motion-induced dB/dt values were above the dB/dt reference levels for both MRI units. The measured values for the gradient fields (echo planar imaging (EPI) and fast field echo (FFE) sequences) also exceeded the dB/dt reference levels in positions where the medical staff may have access during interventional procedures. The highest motion-induced dB/dt values were 0.7 T s(-1) for the 1 T scanner and 3 T s(-1) for the 3 T scanner when only the static field was present. Even higher values (6.5 T s(-1)) were measured for simultaneous exposure to motion-induced and gradient fields in the vicinity of the 3 T scanner.
磁共振成像（MRI）的最新进展增加了职业性磁场暴露。在本研究中，我们考察了对MRI扫描仪非均匀静磁场中运动产生的梯度磁场和时变磁场的职业暴露评估。这些磁场分量可通过检测磁通密度变化率（dB/dt）的感应线圈装置同时进行测量。所开发的装置用于测量两台MRI设备（1T开放式和3T传统式）周围的场分量。测量值可与国际非电离辐射防护委员会（ICNIRP）给出的磁通密度参考水平推导得出的dB/dt参考水平进行比较。两台MRI设备的测量运动感应dB/dt值均高于dB/dt参考水平。梯度场（回波平面成像（EPI）和快速场回波（FFE）序列）的测量值在介入操作期间医护人员可能接触的位置也超过了dB/dt参考水平。仅存在静磁场时，1T扫描仪的最高运动感应dB/dt值为0.7T s⁻¹，3T扫描仪为3T s⁻¹。在3T扫描仪附近同时暴露于运动感应场和梯度场时，测量到的值甚至更高（6.5T s⁻¹）。
