Technical Note: Building a combined cyclotron and MRI facility: Implications for interference

Purpose: With the introduction of hybrid PET/MRI systems, it has become more likely that the cyclotron and MRI systems will be located close to each other. This study considered the interference between a cyclotron and a superconducting MRI system. Methods: Interactions between cyclotrons and MRIs a...

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Bibliographic Details
Published in:	Medical physics (Lancaster) Vol. 40; no. 1; pp. 012303 - n/a
Main Authors:	Hofman, Mark B. M., Kuijer, Joost P. A., de Ridder, Jan Willem, Perk, Lars R., Verdaasdonk, Rudolf M.
Format:	Journal Article
Language:	English
Published:	United States American Association of Physicists in Medicine 01-01-2013
Subjects:	Arrangements or instruments for measuring magnetic variables Basic electromagnetic quantities biomedical MRI CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS cyclotron CYCLOTRONS INTERACTIONS INTERFERENCE Involving electronic [emr] or nuclear [nmr] magnetic resonance, e.g. magnetic resonance imaging magnetic dipole MAGNETIC DIPOLES magnetic field measurement Magnetic field measurements MAGNETIC FIELDS Magnetic resonance accelerators; Cyclotrons Magnetic resonance imaging Magnetic Resonance Imaging - instrumentation MAGNETIC SHIELDING magnetic switching Magnetoresistance Magnets Medical imaging Medical magnetic resonance imaging MEV RANGE 10-100 Models, Theoretical MRI NMR IMAGING Permanent magnets perturbation theory PLANNING RADIOLOGY AND NUCLEAR MEDICINE Reproducibility of Results Superconductivity Superconductivity models cyclotron interference magnetic dipole MRI
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Summary:	Purpose: With the introduction of hybrid PET/MRI systems, it has become more likely that the cyclotron and MRI systems will be located close to each other. This study considered the interference between a cyclotron and a superconducting MRI system. Methods: Interactions between cyclotrons and MRIs are theoretically considered. The main interference is expected to be the perturbation of the magnetic field in the MRI due to switching on or off the magnetic field of the cyclotron. MR imaging is distorted by a dynamic spatial gradient of an external inplane magnetic field larger than 0.5–0.04μT/m, depending on the specific MR application. From the design of a cyclotron, it is expected that the magnetic fringe field at large distances behaves as a magnetic dipolar field. This allows estimation of the full dipolar field and its spatial gradients from a single measurement. Around an 18 MeV cyclotron (Cyclone, IBA), magnetic field measurements were performed on 5 locations and compared with calculations based upon a dipolar field model. Results: At the measurement locations the estimated and measured values of the magnetic field component and its spatial gradients of the inplane component were compared, and found to agree within a factor 1.1 for the magnetic field and within a factor of 1.5 for the spatial gradients of the field. In the specific case of the 18 MeV cyclotron with a vertical magnetic field and a 3T superconducting whole body MR system, a minimum distance of 20 m has to be considered to prevent interference. Conclusions: This study showed that a dipole model is sufficiently accurate to predict the interference of a cyclotron on a MRI scanner, for site planning purposes. The cyclotron and a whole body MRI system considered in this study need to be placed more than 20 m apart, or magnetic shielding should be utilized.
Bibliography:	mbm.hofman@vumc.nl Author to whom correspondence should be addressed. Electronic mail ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0094-2405 2473-4209
DOI:	10.1118/1.4772188