Noninvasive measurement of anatomic structure and intraluminal oxygenation in the gastrointestinal tract of living mice with spatial and spectral EPR imaging

Abstract

EPR imaging has emerged as an important tool for noninvasive three-dimensional (3D) spatial mapping of free radicals in biological tissues. Spectral-spatial EPR imaging enables mapping of the spectral information at each spatial position, and, from the observed line width, the localized tissue oxygenation can be mapped. We report the development of EPR imaging instrumentation enabling 3D spatial and spectral-spatial EPR imaging of small animals. This instrumentation, along with the use of a biocompatible charcoal oximetry-probe suspension, enabled 3D spatial imaging of the gastrointestinal (GI) tract, along with mapping of oxygenation in living mice. By using these techniques, the oxygen tension was mapped at different levels of the GI tract from the stomach to the rectum. The results clearly show the presence of a marked oxygen gradient from the proximal to the distal GI tract, which decreases after respiratory arrest. This technique for in vivo mapping of oxygenation is a promising method, enabling the noninvasive imaging of oxygen within the normal GI tract. This method should be useful in determining the alterations in oxygenation associated with disease.

EPR/NMR co‐imaging for anatomic registration of free‐radical images

“…The EPR spectroscopy and imaging experiments were performed on a custom-built 750 MHz spectrometer with spectroscopy and imaging capability (18). The system has powerful 3D gradients capable of achieving gradient magnitudes of up to 1000 mT/m with a linearity of better than 1% over a 6-cm sphere.…”

“…The system has powerful 3D gradients capable of achieving gradient magnitudes of up to 1000 mT/m with a linearity of better than 1% over a 6-cm sphere. The microwave bridge, the transversely-oriented electric field reentrant resonator (TERR) with ATC and ACC provisions, the three sets of watercooled gradient coils, and the imaging acquisition/reconstruction software were as reported previously (16,18). The parameters for EPRI were as follows: frequency ϭ 750 MHz; microwave power ϭ 50 mW; modulation amplitude ϭ 0.1 mT; scan width ϭ 3.2 mT; scan time ϭ 15 s; time constant ϭ 80 ms; field gradient ϭ 80 mT/m along the y and z directions and 40 mT/m along the x direction; and spatial window size ϭ 40 ϫ 80 ϫ 40 mm.…”

Cardiac applications of EPR imaging

“…Hence low-frequency spectrometers operating in the range 200 MHz to 3 GHz were developed to enable EPR measurements on large aqueous samples. 7,14,15,[27][28][29][30][31] The main feature of these low-frequency spectrometers is the resonators capable of accommodating large aqueous samples with minimal dielectric dissipation. However, there is a disadvantage in the use of lower frequencies as the sensitivity of the measurement is directly related to the square of the operating frequency.…”

“…Over the last decade a variety of low-frequency instrumentation suitable for lossy biological samples have been developed, which enabled spectroscopic measurements on biological samples of sizes up to a whole rat. 7,14,15,[27][28][29][30][31] …”

“…3,6 During the last few years significant progress has been made to enable the performance of EPR imaging of biological samples with improved image modality, resolution and quality to obtain useful information. [9][10][11][12][13][14][15][16][17][18] Over the last decade we have focused on developing instrumentation optimized for measurements of free radicals in isolated beating hearts, and in recent several years we have extended our efforts to develop hardware and software to enable spatial and spectral-spatial imaging of free radicals in the heart. 9,[19][20][21][22][23][24][25] This review provides a summary of the development and application of the imaging techniques with examples including imaging of stable free radical labels, oxygen concentrations and nitric oxide generation in the normal or ischemic heart.…”