A versatile 250 MHz pulse electron paramagnetic resonance (EPR) instrument for imaging of small animals is presented. Flexible design of the imager hardware and software makes it possible to use virtually any pulse EPR imaging modality. A fast pulse generation and data acquisition system based on general purpose PCI boards performs measurements with minimal additional delays. Careful design of receiver protection circuitry allowed us to achieve very high sensitivity of the instrument. In this article we demonstrate the ability of the instrument to obtain three dimensional images using the electron spin echo (ESE) and single point imaging (SPI) methods. In a phantom that contains a 1 mM solution of narrow line (16 μT, peak-to-peak) paramagnetic spin probe we achieved an acquisition time of 32 seconds per image with a fast 3D ESE imaging protocol. Using an 18 minute 3D phase relaxation (T2e) ESE imaging protocol in a homogeneous sample a spatial resolution of 1.4 mm and a standard deviation of T2e of 8.5% were achieved. When applied to in vivo imaging this precision of T2e determination would be equivalent to 2 torr resolution of oxygen partial pressure in animal tissues.
The use of spin echoes to obtain spectroscopic EPR images (spectral-spatial images) at 250 MHz is described. The advantages of spin echoes-larger signals than the free induction decay, better phase characteristics for Fourier transformation, and decay shapes undistorted by instrumental dead time-are clearly shown. An advantage is gained from using a crossed loop resonator that isolates the 250-W pump power by greater than 50 dB from the observer arm preamplifiers. The echo decay rates can be used to determine the oxygen content in solutions containing 1 mM trityl concentrations. Two-and three-dimensional images of oxygen concentration are presented. Magn Reson Med 55:904 -912, 2006.
This article presents the first experimental demonstration that electron paramagnetic resonance oxygen image guided radiation therapy increases tumor control with hypoxic boost doses relative to well-oxygenated tumor boosts of roughly the same volume in mouse fibrosarcoma models. This is the first demonstration of the effectiveness of targeting specific hypoxic tumor in mammalian systems.Purpose: It has been known for over 100 years that tumor hypoxia, a near-universal characteristic of solid tumors, decreases the curative effectiveness of radiation therapy. However, to date, there are no reports that demonstrate an improvement in radiation effectiveness in a mammalian tumor on the basis of tumor hypoxia localization and local hypoxia treatment. Methods and Materials:For radiation targeting of hypoxic subregions in mouse fibrosarcoma, we used oxygen images obtained using pulse electron paramagnetic resonance pO 2 imaging combined with 3D-printed radiation blocks. This achieved conformal radiation delivery to all hypoxic areas in FSa fibrosarcomas in mice. Results:We demonstrate that treatment delivering a radiation boost to hypoxic volumes has a significant (P = .04) doubling of tumor control relative to boosts to well-oxygenated volumes. Additional dose to well-oxygenated tumor regions minimally increases tumor control beyond the 15% control dose to the entire tumor. If we can identify portions of the tumor that are more resistant to radiation, it might be possible to reduce the dose to more sensitive tumor volumes without significant compromise in tumor control.
Purpose:The authors compare two electron paramagnetic resonance imaging modalities at 250 MHz to determine advantages and disadvantages of those modalities for in vivo oxygen imaging. Methods: Electron spin echo ͑ESE͒ and continuous wave ͑CW͒ methodologies were used to obtain three-dimensional images of a narrow linewidth, water soluble, nontoxic oxygen-sensitive trityl molecule OX063 in vitro and in vivo. The authors also examined sequential images obtained from the same animal injected intravenously with trityl spin probe to determine temporal stability of methodologies. Results: A study of phantoms with different oxygen concentrations revealed a threefold advantage of the ESE methodology in terms of reduced imaging time and more precise oxygen resolution for samples with less than 70 torr oxygen partial pressure. Above ϳ100 torr, CW performed better. The images produced by both methodologies showed pO 2 distributions with similar mean values. However, ESE images demonstrated superior performance in low pO 2 regions while missing voxels in high pO 2 regions. Conclusions: ESE and CW have different areas of applicability. ESE is superior for hypoxia studies in tumors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.