Measurements of the Ripple Effect and Geometric Distribution of Switched Gradient Fields Inside a Magnetic Resonance Scanner
2015 (English)In: Bioelectromagnetics, ISSN 0197-8462, E-ISSN 1521-186X, Vol. 36, no 2, 162-168 p.Article in journal (Refereed) Published
Knowledge of patient exposure during magnetic resonance imaging (MRI) procedures is limited, and the need for such knowledge has been demonstrated in recent in vitro and in vivo studies of the genotoxic effects of MRI. This study focuses on the dB/dt of the switched gradient field (SGF) and its geometric distribution. These values were characterized by measuring the peak dB/dt generated by a programmed gradient current of alternating triangles inside a 1.5T MR scanner. The maximum dB/dt exposure to the gradient field was 6-14T/s, and this occurred at the edges of the field of view (FOV) 20-25cm from the isocenter in the longitudinal direction. The dB/dt exposure dropped off to roughly half the maximum (3-7T/s) at the edge of the bore. It was found that the dB/dt of the SGF was distorted by a 200kHz ripple arising from the amplifier. The ripple is small in terms of B-field, but the high frequency content contributes to a peak dB/dt up to 18 times larger than that predicted by the slew rate (4T/sm) and the distance from the isocenter. Measurements on a 3T MRI scanner, however, revealed a much smaller filtered ripple of 100kHz in dB/dt. These findings suggest that the gradient current to each coil together with information on the geometrical distribution of the gradient field and ripple effects could be used to assess the SGF exposure within an MRI bore.
Place, publisher, year, edition, pages
2015. Vol. 36, no 2, 162-168 p.
MRI patient exposure, gradient ripple, 1, 5T MR, peak dB, dt
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:umu:diva-100959DOI: 10.1002/bem.21884ISI: 000349650400007PubMedID: 25399749OAI: oai:DiVA.org:umu-100959DiVA: diva2:796229