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Investigation of electron trajectories of an x‐ray tube in magnetic fields of MR scanners
Author(s) -
Wen Zhifei,
Fahrig Rebecca,
Conolly Steven,
Pelc Norbert J.
Publication year - 2007
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 - 10.1118/1.2733798
Subject(s) - magnet , magnetic field , deflection (physics) , electron , physics , electromagnet , cathode ray , optics , perpendicular , x ray tube , nuclear magnetic resonance , nuclear physics , anode , geometry , mathematics , quantum mechanics , electrode
A hybrid x‐ray/MR system combining an x‐ray fluoroscopic system and an open‐bore magnetic resonance (MR) system offers advantages from both powerful imaging modalities and thus can benefit numerous image‐guided interventional procedures. In our hybrid system configurations, the x‐ray tube and detector are placed in the MR magnet and therefore experience a strong magnetic field. The electron beam inside the x‐ray tube can be deflected by a misaligned magnetic field, which may damage the tube. Understanding the deflection process is crucial to predicting the electron beam deflection and avoiding potential damage to the x‐ray tube. For this purpose, the motion of an electron in combined electric ( E ) and magnetic ( B ) fields was analyzed theoretically to provide general solutions that can be applied to different geometries. For two specific cases, a slightly misaligned strong field and a perpendicular weak field, computer simulations were performed with a finite‐element method program. In addition, experiments were conducted using an open MRI magnet and an inserted electromagnet to quantitatively verify the relationship between the deflections and the field misalignment. In a strong ( B ≫ E ∕ c ; c : speed of light) and slightly misaligned magnetic field, the deflection in the plane of E and B caused by electrons following the magnetic field lines is the dominant component compared to the deflection in the E × B direction due to the drift of electrons. In a weak magnetic field ( B ≤ E ∕ c ) , the main deflection is in the E × B direction and is caused by the perpendicular component of the magnetic field.