Single loop multi-gap resonator for whole body EPR imaging of mice at 1.2GHz

Abstract

For whole body EPR imaging of small animals, typically low frequencies of 250-750 MHz have been used due to the microwave losses at higher frequencies and the challenges in designing suitable resonators to accommodate these large lossy samples. However, low microwave frequency limits the obtainable sensitivity. L-band frequencies can provide higher sensitivity, and have been commonly used for localized in vivo EPR spectroscopy. Therefore, it would be highly desirable to develop an L-band microwave resonator suitable for in vivo whole body EPR imaging of small animals such as living mice. A 1.2 GHz 16 gap resonator with inner diameter of 43 mm and 48 mm length was designed and constructed for whole body EPR imaging of small animals. The resonator has good field homogeneity and stability to animal induced motional noise. Resonator stability was achieved with electrical and mechanical design utilizing a fixed position double coupling loop of novel geometry, thus minimizing the number of moving parts. Using this resonator, high quality EPR images of lossy phantoms and living mice were obtained. This design provides good sensitivity, ease of sample access, excellent stability and uniform B 1 field homogeneity for in vivo whole body EPR imaging of mice at 1.2 GHz.

Accelerated dynamic EPR imaging using fast acquisition and compressive recovery

“…A 8-gap loop-gap L-band resonator (1.24 GHz, ID = 43 mm, length = 48 mm) was similar to the one described in [34] and positioned orthogonally to the magnet bore. The 8-gap design with gaps oriented radially from the center enabled a larger-diameter resonator to be built for this frequency than would be possible with a lower number of similar gaps, provided good homogeneity of the B 1 magnetic field and good modulation field penetration.…”

Organ specific mapping of in vivo redox state in control and cigarette smoke-exposed mice using EPR/NMR co-imaging

“…The system utilizes a common magnet and gradient coils. This configuration was coupled with the previously reported dual-purpose resonator assembly [30]. This design eliminates the need to move the sample relative to the magnetic field gradient coordinate system.…”

“…This instrument intrinsically provides high quality free radical and anatomic image co-registration, enabling timely correlation of the information obtained from EPRI and PMRI. The uniqueness of this hybrid EPRI/PMRI instrument also lies in its specially designed dual EPR/NMR resonator assembly [30]. …”

In vivo multisite oximetry using EPR–NMR coimaging

“…2a. The EPR resonator was based on a single-loop multi-gap design [37] with ID of 39 mm and length of 32 mm. The resonator efficiency, measured by using a perturbing metal sphere [38], was $17\mu \mathrm{T}∕\sqrt{\mathrm{normalW}}$.…”