Hexamethyldisiloxane-based nanoprobes for 1H MRI oximetry

Praveen K. Gulaka, Ujjawal Rastogi, Madalyn A. McKay, Xianghui Wang, Ralph P. Mason, Vikram D. Kodibagkar

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Quantitative in vivo oximetry has been reported using 19F MRI in conjunction with reporter molecules, such as perfluorocarbons, for tissue oxygenation (pO 2). Recently, hexamethyldisiloxane (HMDSO) has been proposed as a promising alternative reporter molecule for 1H MRI-based measurement of pO 2. To aid biocompatibility for potential systemic administration, we prepared various nanoemulsion formulations using a wide range of HMDSO volume fractions and HMDSO to surfactant ratios. Calibration curves (R 1 versus pO 2) for all emulsion formulations were found to be linear and similar to neat HMDSO for low surfactant concentrations (<10% v/v). A small temperature dependence in the calibration curves was observed, similar to previous reports on neat HMDSO, and was characterized to be approximately 1Torr/°C under hypoxic conditions. To demonstrate application in vivo, 100μL of this nanoemulsion was administered to healthy rat thigh muscle (Fisher 344, n=6). Dynamic changes in mean thigh tissue pO 2 were measured using the PISTOL (proton imaging of siloxanes to map tissue oxygenation levels) technique in response to oxygen challenge. Changing the inhaled gas to oxygen for 30min increased the mean pO 2 significantly (p<0.001) from 39±7 to 275±27Torr. When the breathing gas was switched back to air, the tissue pO 2 decreased to a mean value of 45±6Torr, not significantly different from baseline (p>0.05), in 25min. A first-order exponential fit to this part of the pO 2 data (i.e. after oxygen challenge) yielded an oxygen consumption-related kinetic parameter k=0.21±0.04min -1. These results demonstrate the feasibility of using HMDSO nanoemulsions as nanoprobes of pO 2 and their utility to assess oxygen dynamics in vivo, further developing quantitative 1H MRI oximetry.

Original languageEnglish (US)
Pages (from-to)1226-1234
Number of pages9
JournalNMR in Biomedicine
Issue number10
StatePublished - Dec 2011
Externally publishedYes


  • Hexamethyldisiloxane
  • MR oximetry
  • Nanoemulsions
  • Oxygen consumption
  • Oxygen tension

ASJC Scopus subject areas

  • Molecular Medicine
  • Radiology Nuclear Medicine and imaging
  • Spectroscopy


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