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Updated: May 22, 2026
Noninvasive In Vivo Small Animal MRI and MRS: Basic Experimental Procedures
Published on: October 20, 2009
Whole-body kinetic image of a redox probe in mice using Overhauser-enhanced MRI
Nuttavut Kosem1, Tatsuya Naganuma, Kazuhiro Ichikawa
1Innovation Center for Medical Redox Navigation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Abstract:
Overhauser-enhanced MRI (OMRI) enables visualization of free radicals in animals based on dynamic nuclear polarization. Real-time data of tissue redox status gathered from kinetic images of redox-sensitive nitroxyl radical probes using OMRI provided both anatomic and physiological information. Phantom experiments demonstrated the linear correlation between the enhancement factor and the concentration of a membrane-impermeable probe, carboxy-PROXYL (3-carboxy-2,2,5,5-tetramethyl- pyrrolidine-1-oxyl). Whole-body OMRI images illustrated the in vivo kinetics of carboxy-PROXYL for 25 min. Initial distribution was observed in lung, heart, liver, and kidney, but not brain, corresponding to its minimal lipophilicity. Based on these images (pixel size, 1.33 × 1.33 mm; slice thickness, 50mm), a time-concentration curve with low coefficient of variance (<0.21) was created to assess pharmacokinetic behaviors. A biexponential curve showed a distribution phase from 1 to 10 min and an elimination phase from 15 to 25 min. The α rate constant was greater than the β rate constant in ROIs, confirming that its pharmacokinetics obeyed a two-compartment model. As a noninvasive technique, combining OMRI imaging with redox probes to monitor tissue redox status may be useful in acquiring valuable information regarding organ function for preclinical and clinical studies of oxidative diseases.
Insights
Overhauser-enhanced MRI (OMRI) visualizes free radicals in animals using dynamic nuclear polarization. This technique provides real-time tissue redox status, aiding organ function studies in oxidative diseases.
Area of Science:
- Biomedical Imaging
- Medical Physics
- Free Radical Chemistry
Background:
- Overhauser-enhanced MRI (OMRI) utilizes dynamic nuclear polarization for free radical visualization.
- Real-time kinetic imaging of redox-sensitive probes offers anatomical and physiological data.
- Understanding tissue redox status is crucial for studying oxidative diseases.
Purpose of the Study:
- To demonstrate the utility of OMRI for visualizing free radicals in vivo.
- To assess the pharmacokinetic behavior of a redox-sensitive probe (carboxy-PROXYL) using OMRI.
- To explore OMRI's potential for monitoring organ function in oxidative disease research.
Main Methods:
- Phantom experiments established a linear correlation between enhancement factor and carboxy-PROXYL concentration.
- Whole-body OMRI was performed on animals to track carboxy-PROXYL kinetics over 25 minutes.
- Pharmacokinetic analysis involved creating time-concentration curves from OMRI images to model distribution and elimination phases.
Main Results:
- OMRI successfully visualized the in vivo distribution of carboxy-PROXYL, with initial uptake in lung, heart, liver, and kidney.
- The probe's minimal lipophilicity correlated with its absence in the brain.
- Pharmacokinetic analysis revealed a two-compartment model with distinct distribution and elimination phases, confirmed by rate constants.
- A low coefficient of variance (<0.21) indicated reliable kinetic data acquisition.
Conclusions:
- OMRI, combined with redox probes like carboxy-PROXYL, serves as a noninvasive method for assessing tissue redox status.
- The technique provides valuable anatomical, physiological, and pharmacokinetic information.
- OMRI holds promise for preclinical and clinical studies of oxidative diseases and organ function assessment.
