First imaging results obtained with a multimodal apparatus combining low-field (35.7 mT) MRI and pulsed EPRI

Abstract

Nuclear magnetic resonance imaging (MRI) provides excellent images of organs and is an essential diagnostic tool in the medical field. Electron paramagnetic resonance imaging (EPRI) is being increasingly used in the biomedical field because of recent hardware advances. We present the first images obtained with a low-field (35.7 mT) multimodal apparatus that combines MRI and pulsed EPRI. For this purpose, the sample is composed of two sections, one sensitive to MRI and the other sensitive to EPRI. The MRI section of the sample is composed of three tubes containing 7 ml of a 10 mM CuSO4 water solution. The EPR section of the sample is composed of two tubes containing 350 mg of lithium phthalocyanine. The EPR image represents the two-dimensional projection of the whole sample and is reconstructed from 32 one-dimensional projections by using the Fourier reconstruction method. The MRI image is obtained by selecting a sample slice, 10 mm in thickness, by using a spin-echo sequence and the two-dimensional fast Fourier transform. The experimental results obtained with this apparatus show that the spatial resolution is better than 1 mm for the MRI section and better than 7 mm for the EPRI section. The measured SNR of the MRI and EPRI images were about 60 and 160, respectively. A detailed description of the hardware, pulse sequences and image reconstruction techniques is reported.

Use of multi-coil parallel-gap resonators for co-registration EPR/NMR imaging

“…The resonator system is simple and easy to implement. The MCPGRs used here are more efficient at generating an RF magnetic field than the composite resonator system previously reported [8,9,26]. The MCPGR for EPR was 2-fold more efficient than the bridged LGR used in a composite resonator; the MCPGR for NMR was 10-fold more efficient than the solenoidal coil used in a composite resonator [26].…”

“…The unification of proton-MRI and EPRI, called coregistration electron paramagnetic resonance/nuclear magnetic resonance (EPR/NMR) imaging, requires technological advances in magnets, RF coils, and software [8,9]. Sato et al [1] reported their EPR/NMR imaging instrument.…”

Systematic approach to cutoff frequency selection in continuous-wave electron paramagnetic resonance imaging

“…Since an electron spin system has an extremely short relaxation time compared to that of a nuclear spin system, most EPR imaging uses a continuous-wave (CW) detection protocol. While time-domain EPR spectroscopy and imaging at frequencies below 1 GHz are available for animal experiments at some laboratories [12][13][14], EPR imaging still requires CW-EPR instruments for paramagnetic materials with broader EPR absorption spectra.…”

Radio frequency continuous‐wave and time‐domain EPR imaging and Overhauser‐enhanced magnetic resonance imaging of small animals: instrumental developments and comparison of relative merits for functional imaging

“…One way to get around this is to perform a CT or MR image of the same subject under identical posture, so that one can co-register spin distribution and the related anatomical features. Attempts have been made to co-register EPRI with MRI, 122,123 OMRI with BOLD-MRI etc. Such co-registration strategies will be very useful in the unambiguous interpretation of physiology.…”