biostudies-literatureMatsumoto KIIntramural NIH HHS2275-2287https://www.ebi.ac.uk/biostudies/studies/S-EPMC8080971biostudies-literatureUnknown80(5)<h4>Purpose</h4>Spin-lattice relaxation rate (R₁ )-based time-domain EPR oximetry is reported for in vivo applications using a paramagnetic probe, a trityl-based Oxo71.<h4>Methods</h4>The R₁ dependence of the trityl probe Oxo71 on partial oxygen pressure (pO₂ ) was assessed using single-point imaging mode of spatial encoding combined with rapid repetition, similar to T₁ -weighted MRI, for which R₁ was determined from 22 repetition times ranging from 2.1 to 40.0 μs at 300 MHz. The pO₂ maps of a phantom with 3 tubes containing 2 mM Oxo71 solutions equilibrated at 0%, 2%, and 5% oxygen were determined by R₁ and apparent spin-spin relaxation rate ( R2*) simultaneously.<h4>Results</h4>The pO₂ maps derived from R₁ and R2* agreed with the known pO₂ levels in the tubes of Oxo71. However, the histograms of pO₂ revealed that R₁ offers better pO₂ resolution than R2* in low pO₂ regions. The SDs of pixels at 2% pO₂ (15.2 mmHg) were about 5 times lower in R₁ -based estimation than R2*-based estimation (mean ± SD: 13.9 ± 1.77 mmHg and 18.3 ± 8.70 mmHg, respectively). The in vivo pO₂ map obtained from R₁ -based assessment displayed a homogeneous profile in low pO₂ regions in tumor xenografts, consistent with previous reports on R2*-based oximetric imaging. The scan time to obtain the R₁ map can be significantly reduced using 3 repetition times ranging from 4.0 to 12.0 μs.<h4>Conclusion</h4>Using the single-point imaging modality, R₁ -based oximetry imaging with useful spatial and oxygen resolutions for small animals was demonstrated.Magnetic resonance in medicineEPR-based oximetric imaging: a combination of single point-based spatial encoding and T₁ weighting.PMC8080971Z01 BC010476Matsumoto SOgawa YMatsumoto KIKrishna MCChandramouli GVRDevasahayam NKishimoto SSubramanian SfalseEPR-based oximetric imaging: a combination of single point-based spatial encoding and T₁ weighting.<h4>Purpose</h4>Spin-lattice relaxation rate (R₁ )-based time-domain EPR oximetry is reported for in vivo applications using a paramagnetic probe, a trityl-based Oxo71.<h4>Methods</h4>The R₁ dependence of the trityl probe Oxo71 on partial oxygen pressure (pO₂ ) was assessed using single-point imaging mode of spatial encoding combined with rapid repetition, similar to T₁ -weighted MRI, for which R₁ was determined from 22 repetition times ranging from 2.1 to 40.0 μs at 300 MHz. The pO₂ maps of a phantom with 3 tubes containing 2 mM Oxo71 solutions equilibrated at 0%, 2%, and 5% oxygen were determined by R₁ and apparent spin-spin relaxation rate ( R2*) simultaneously.<h4>Results</h4>The pO₂ maps derived from R₁ and R2* agreed with the known pO₂ levels in the tubes of Oxo71. However, the histograms of pO₂ revealed that R₁ offers better pO₂ resolution than R2* in low pO₂ regions. The SDs of pixels at 2% pO₂ (15.2 mmHg) were about 5 times lower in R₁ -based estimation than R2*-based estimation (mean ± SD: 13.9 ± 1.77 mmHg and 18.3 ± 8.70 mmHg, respectively). The in vivo pO₂ map obtained from R₁ -based assessment displayed a homogeneous profile in low pO₂ regions in tumor xenografts, consistent with previous reports on R2*-based oximetric imaging. The scan time to obtain the R₁ map can be significantly reduced using 3 repetition times ranging from 4.0 to 12.0 μs.<h4>Conclusion</h4>Using the single-point imaging modality, R₁ -based oximetry imaging with useful spatial and oxygen resolutions for small animals was demonstrated.2018-01-01T00:00:00Z2018 Nov2025-04-26T09:22:12.735Z2022-02-09T17:49:04.787ZS-EPMC80809712958245810.1002/mrm.27182