Radiation induced current in the RF coils of integrated linac‐MR systems: The effect of buildup and magnetic field

Abstract

The RIC in RF coils results from the lack of electronic equilibrium in the coil conductor as the RIC in planar conductor was completely removed by identical buildup of adequate thickness to create electronic equilibrium. The buildup method of RIC removal is effective in cylindrical coil geometry when the coil conductor is in direct contact with the patient. The presence of air makes this method of RIC removal less effective although placing buildup still reduces the RIC by up to 60%. The RIC Monte Carlo simulation is a useful tool for practical coil design where radiation effects must be considered. The SNR is improved in the images obtained concurrently withradiation if buildup is applied to the coil.

Effect of radiation induced current on the quality of MR images in an integrated linac‐MR system

“…The buildup method used in our previous work showed that 55% of the lost SNR was recovered through the application of a simple buildup to the RF coil with a linac dose rate of 250 MU/min. 10 Our postprocessing algorithm compared very well to this as the data in Tables I-IV show recovery of 50%, 82%, 69%, and 38%, respectively, for the case of 250 MU/min dose rate. Both a median filter and an adaptive median filter were shown to be unsuitable for use in removing RIC from MR kspace data as they introduced signal intensity variations in the images.…”

“…In a separate investigation, we have shown that the RIC results from the lack of electronic equilibrium in the conductor of the RF coil. 10 In theory, the RIC can be reduced by establishing electronic equilibrium with appropriate buildup material and thickness. However, the placement of buildup may have negative consequences on the patient`s skin dose, thus we have attempted a postprocessing method of RIC removal in this investigation.…”

“…Our more recent results have shown that the RIC signal in RF coils can be reduced with the application of appropriate buildup material to the coils. 10 This buildup method was effective with planar or cylindrical coil geometries and was unhindered by the presence of magnetic fields. This work explores another method for RIC removal that does not involve altering the RF coils, but instead uses image processing techniques.…”

Proton beam deflection in MRI fields: Implications for MRI‐guided proton therapy

“…[12][13][14][15] Radiofrequency interference between the MRI and Linac has also been studied. 16,17 The various dosimetry changes caused by the magnetic fields are also described, including both transverse [18][19][20][21][22][23][24][25][26][27] and longitudinal magnetic fields. 22,[28][29][30] The performance of common radiation detectors in magnetic fields has also been investigated.…”

Impact of the MLC on the MRI field distortion of a prototype MRI‐linac

“…15 In the latter case, various studies exist which looked at the ability to take MRI images of phantoms while during linac irradiation 7,16 and investigated the effect of the radiation and RF noise from the linac on the gradient RF coils. 17,18 Recently, a proof-ofconcept study for tracking of a 1D pencil-beam navigator 19 and a study on tracking of phantom motion on 2D MRI images 20 have demonstrated that image acquisition is possible with MRI-linac prototypes incorporating a MLC.…”