Noninvasive in vivo oximetric imaging by radiofrequency FT EPR

• Published in: Magnetic resonance in medicine Vol. 47; no. 5; pp. 1001 - 1008
• Main Authors: Subramanian, Sankaran, Yamada, Ken-Ichi, Irie, Akira, Murugesan, Ramachandran, Cook, John A., Devasahayam, Nallathamby, Van Dam, Gootzian M., Mitchell, James B., Krishna, Murali C.
• Format: Journal Article
• Language: English
• Published: New York Wiley Subscription Services, Inc., A Wiley Company 01.05.2002; Williams & Wilkins
• Subjects: Animals; Biological and medical sciences; Contrast Media; Electron Spin Resonance Spectroscopy - methods; EPR imaging; Female; in vivo imaging; Investigative techniques, diagnostic techniques (general aspects); Kidney - chemistry; Liver - chemistry; Medical sciences; Mice; Mice, Inbred C3H; Miscellaneous. Technology; Neoplasms, Experimental - chemistry; oximetry; Oximetry - methods; Phantoms, Imaging; Radiodiagnosis. Nmr imagery. Nmr spectrometry; RF FT-EPR; Blood gas; In vivo; Oxymetry; Time frequency domain method; Animal; Diagnosis; Electron paramagnetic resonance; Technique; Radiofrequency
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.10133

A novel method, called relaxo‐oximetry, for rapid spatially resolved in vivo measurements of oxygen concentration using time‐domain radiofrequency (RF) electron paramagnetic resonance (EPR) is described. Time‐domain data from triaryl methyl (TAM)‐based single‐electron contrast agents were processed by systematic deletion of the initial time points to arrive at T 2*‐weighted discrimination of signal amplitudes. In experiments involving phantoms, the line widths [∼ (T 2*)−1] increased as a function of oxygen, and the slope (line width/pO2) was the same for both absorption‐ and magnitude‐mode line shapes. Line widths derived from T 2* weighting and the computed pO2 values agreed favorably with the measured ones from phantoms of known oxygen tension. In vivo relaxo‐oximetry was performed on C3H mice, and it was found that the liver was more hypoxic than the kidneys. For tumors, 2D oxygen maps were generated while the animal breathed room air or Carbogen® (95% O2/5% CO2). Carbogen® enhanced oxygen concentration within the tumor, and the pO2 histograms showed considerable heterogeneity. Clark electrode oxygen measurements on organs and tumors were in good agreement with tissue oxygen measurements done by relaxo‐oximetry. Thus, from a single spatial image data set, pO2 measurements can be done noninvasively by relaxo‐oximetry, and 3D imaging can be performed in less than 3 min. Magn Reson Med 47:1001–1008, 2002. © 2002 Wiley‐Liss, Inc.