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Sci—Fri AM(2): Brachy—07: Investigation of the Sources of RF Noise from the Modulator of a Linac
Author(s) -
Lamey M,
Rathee S,
Fallone BG
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3244199
Subject(s) - linear particle accelerator , noise (video) , radio frequency , physics , electromagnetic coil , electromagnetic interference , electromagnetic shielding , acoustics , electrical engineering , nuclear magnetic resonance , optics , computer science , engineering , beam (structure) , quantum mechanics , artificial intelligence , image (mathematics)
Introduction: One of the possible complications associated with the integration of an MR with a linac is the RF noise interference. Significant work at our lab is underway to identify and separate various noise sources associated with a linac from the MR data acquisition chain. This work reports upon the study of possible sources of RF noise in the modulator of a linac. Materials/Methods: A commercially available near field probe set was used to measure the RF noise generated from a modulator, loaded with either a magnetron or a high power rated 400 Ω resistive load. In a separate investigation MultiSIM was used to reproduce the currents and voltages in a modulator, the simulated PFN coil currents were then used as inputs into COMSOL Multiphysics to determine the electromagnetic fields produced around the coil during PFN discharge. For experimental comparison, a Hall probe was used to measure the low frequency response of the fields from a modulator of a linac and near field electromagnetic probes were used to measure the higher frequency response. Results/Discussion: Our measurements show a significant reduction in RF noise when the magnetron was replaced with a purely resistive load. These results suggest that it is particularly important for linac‐MR systems to shield the magnetron. Our simulations also suggest that the fields from the PFN coil during PFN discharge are only significant at lower frequencies. The significance of a large spike just before PFN discharge, due to the thyratron, is being investigated.