Journal Article EPR based Oximetric Imaging: A Combination of Single Point based Spatial Encoding & T1 Weighted pO2 Assessment

Ken-ichiro, Matsumoto  ,  Kishimoto, Shun  ,  Devasahayam, Nallathamby  ,  V. R. Chandramouli, Gadisetti  ,  Ogawa, Yukihiro  ,  Matsumoto, Shingo  ,  C. Krishna, Murali  ,  Subramanian, Sankaran

2018-02 , Wiley-Blackwell
Purpose: A spin-lattice relaxation time (T1) weighted time-domain EPR oximetry is reported for in vivo applications using a paramagnetic probe, a trityl based Oxo71.Methods: The T1 dependence of the trityl probe Oxo71 on pO2 was assessed using single point imaging (SPI) mode of spatial encoding combined with rapid repetition, similar to T1-weighted MRI, where T1 was determined from 22 repetition times (TRs) ranging from 2.1–40.0 μs.Results: The pO2 maps of a phantom with three tubes containing 2 mM Oxo71 solutions equilibrated at 0%, 2% and 5% of oxygen were determined by T1 and apparent spin-spin relaxation time (T2*) simultaneously. Both the pO2 maps derived from T1 and T2* agreed well with the pO2 levels of the solutions in the phantom. However, the histograms of pO2 maps revealed that T1 offers better pO2 resolution than T2* in low pO2 regions. The standard deviations of pixels at 2% pO2 were about 5 times lower in T1 based estimation than T2* based estimation. The in vivo pO2 map obtained from T1 based assessment displayed heterogenous profile in low pO2 regions in tumor xenograft consistent with previous reports on T2* based oximetric imaging. The scan time to obtain T1 map can be significantly reduced using three TRs ranging from 4.0‒12.0 μs.Conclusion: Using the SPI modality, T1-based oximetry imaging with useful spatial and oxygen resolutions for small animal imaging was demonstrated.

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