title: Advantageous application of a surface coil to EPR irradiation in overhauser-enhanced MRI.
abstract: The present study describes the advantageous application of a surface coil to electron paramagnetic resonance (EPR) irradiation in Overhauser-enhanced MRI (OMRI). OMRI is a double-resonance method for imaging free radicals based on the Overhauser effect. Proton NMR images are recorded without and with EPR irradiation of the free radical resonance, which results in a difference proton image that shows signal enhancement in spatial regions that contain the free radical. To obtain good signal enhancement in OMRI, very high RF power and a long EPR irradiation time are required. To improve sensitivity and shorten the image acquisition time, especially for localized (and topical) applications, we developed and tested a surface-coil-type EPR irradiation coil. Theoretical calculations and experimental data showed that EPR irradiation through the surface coil could ameliorate the localized Overhauser enhancement, which was related to the ratio of B(1) surface coil/B(1) volume coil in the region of interest (ROI), as expected. The increased sensitivity could also be converted into a shortened EPR irradiation time, resulting in fast data acquisition. For biomedical applications, the use of a surface coil (as opposed to a conventional volume coil) could decrease the total RF power deposition in the sample required to obtain the same Overhauser enhancement in the ROI.
authors: Department of Biofunctional Science, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
authors: Shingo
authors: S
authors: Matsumoto
authors: Kenichi
authors: K
authors: Yamada
authors: Hiroshi
authors: H
authors: Hirata
authors: Keiji
authors: K
authors: Yasukawa
authors: Fuminori
authors: F
authors: Hyodo
authors: Kazuhiro
authors: K
authors: Ichikawa
authors: Hideo
authors: H
authors: Utsumi
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000008:administration & dosage; D003497:Cyclic N-Oxides / Q000008:administration & dosage; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation*; D004867:Equipment Design; D005609:Free Radicals; D007668:Kidney / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008297:Male; D019047:Phantoms, Imaging; D011759:Pyrrolidines / Q000008:administration & dosage; D051381:Rats; D017208:Rats, Wistar
chemical_list: D003287:Contrast Media; D003497:Cyclic N-Oxides; D005609:Free Radicals; D011759:Pyrrolidines; C077426:3-carbamoyl-2,2,5,5-tetramethyl-1-pyrrolidinyl-N-oxyl