Affiliations: Graduate School of Health Sciences, Okayama
University, Shikata-cho, Okayama, Japan | Department of Radiology, Kitagawa Hospital, Wake-cho,
Wake, Japan | Central Division of Radiology, Okayama University
Hospital, Shikata-cho, Okayama, Japan | Murakami Neurosurgery Internal Medicine, Oiminami,
Kasaoka, Japan | Department of Radiology, Shimane University Hospital,
Enya-cho, Izumo, Japan | Graduate School of Medicine, Dentistry and
Pharmaceutical Sciences, Okayama University, Shikata-cho, Okayama, Japan
Note: [] Corresponding author: Hirokazu Kato, Department of Radiological
Technology, Graduate School of Health Sciences, Okayama University, Okayama
City, Okayama 700-8558, Japan. Tel.: +81 86 235 6845; Fax: +81 86 235 6845;
E-mail: [email protected]
Abstract: In proton density-weighted (PDW) MR imaging, the patterns of signal
intensity vary depending on the imaged material, and change with the flip angle
(FA) applied to the imaged material. The correlation between the pre-determined
FA and the actual FA applied to imaged objects was investigated using 4 types
of phantoms having different dielectric properties. PDW images were acquired
using the spin-echo (SE) method and different pre-determined FA. Dependency of
the signal intensity distribution in the phantom on the pre-determined FA
differed among phantoms: patterns for water and 0.402 w/w% saline solution
phantoms changed with the pre-determined FA, whereas those for olive oil and
4.02 w/w% saline solution phantoms were barely affected by the
pre-determined FA. Causes of these phenomena were considered to be the
differences between the pre-determined FA and the actual FA among the phantoms;
differences were also influenced by the positioning of the phantom. Our study
showed that the actual FA in the phantom is greater than the pre-determined FA
in high permittivity media, whereas it is reduced by an increased conductivity of the media.
Keywords: MRI, flip angle, signal intensity distribution, permittivity, conductivity, RF magnetic field, finite element method
