Body‐loop related MRI radiofrequency‐induced heating hazards: Observations, characterizations, and recommendations

Abstract

To assess RF-induced heating hazards in 1.5T MR systems caused by body-loop postures. Methods: Twelve advanced high-resolution anatomically correct human body models with different body-loop postures are created based on poseable human adult male models. Numerical simulations are performed to assess the radiofrequency (RF)-induced heating of these 12 models at 11 landmarks. A customized phantom is developed to validate the numerical simulations and quantitatively analyze factors affecting the RF-induced heating, eg, the contact area, the loop size, and the loading position. The RF-induced heating inside three differently posed phantoms is measured. Results:The RF-induced heating from the body-loop postures can be up to 11 times higher than that from the original posture. The RF-induced heating increases with increasing body-loop size and decreasing contact area. The magnetic flux increases when the body-loop center and the RF coil isocenter are close to each other, leading to increased RF-induced heating. An air gap created in the body loop or generating a polarized magnetic field parallel to the body loop can reduce the heating by a factor of three at least. Experimental measurements are provided, validating the correctness of the numerical results. Conclusion: Safe patient posture during MR examinations is recommended with the use of insulation materials to prevent loop formation and consequently avoiding high RF-induced heating. If body loops cannot be avoided, the body loop should be placed outside the RF transmitting coil. In addition, linear polarization with magnetic fields parallel to the body loop can be used to circumvent high RF-induced heating.

Investigation of alternative RF power limit control methods for 0.5T, 1.5T, and 3T parallel transmission cardiac imaging: A simulation study

“…Eleven human voxel models (10 from the virtual population 71 plus the original XCAT model 72 ) were positioned for a cardiac exam (heart center at scanner coordinate $$$ z=0 $$$, backs resting on the $$$ y=-170\kern0.3em \mathrm{mm} $$$ plane), see Figure 1C. The arms of the posable model Jeduk were spread by 3° to avoid a pathologic body loop 73‐75 . Such loop in model Glenn at 0.5T was masked, see Figures S19 and S20.…”

“…The arms of the posable model Jeduk were spread by 3 • to avoid a pathologic body loop. [73][74][75] Such loop in model Glenn at 0.5T was masked, see Figures S19 and S20. While models XCAT and Eddie are based on the same male model of the visible human project, 76 the XCAT model is adjusted to conform to the 50% percentile of US adults.…”

Progress in Understanding Radiofrequency Heating and Burn Injuries for Safer MR Imaging

“…118 An experimental and simulation phantom study mimicking a human arm contacting the body trunk indicated that reducing the contact areas increases the temperature rise and the peak SAR of 1-g tissue. 144 The same tendency was simulated using a human model with two different postures of arm-arm contacts forming closed loops. This dependence of the contact area on the SAR is understood as a concentration of the magnetically induced currents.…”

“…2). 118 Although a further simulation study on the finger–thigh contact model indicated a significant reduction in the maximum local SAR with a 2-mm spacing, 144 the MRI guidelines provided by the MHRA recommended the use of 1–2-cm-thick foam pads to insulate the patient from cables, from the bore, and between limbs. 155 Therefore, the foam pads prevent RF burn injuries; however, the appropriate thicknesses and materials of the pads need to be determined.…”

“…155 Therefore, the foam pads prevent RF burn injuries; however, the appropriate thicknesses and materials of the pads need to be determined. Since wetting the pad reduces the effectiveness, 144 the hydroscopic properties of the pad materials should be considered as well.…”