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(Monday, 7/30/2018) 7:30 AM - 9:30 AM
Room: Karl Dean Ballroom A1
Purpose: To optimize the iThera Medical MSOT inVision 256-TF photoacoustic (PA) imaging system to quantitatively assess oxygen saturation (SO₂) in murine femoral bone marrow for the purpose of monitoring leukemia progression and treatment response.
Methods: C57 albino mice were imaged on the MSOT system; matched x-ray CT data were then co-registered with 800-nm PA data to confirm co-localization of the PA signature with the femoral bone marrow cavity. To select optimal parameters for linear unmixing of hemoglobin and calculation of SO₂, mice were imaged with different combinations of wavelengths (715, 730, 745, 760, 800, 850, 865, 880 nm) and frame averaging (5, 10, 20 averages per frame). An oxygen challenge (100% vs. 21% O₂) was performed to measure the frame rate needed to monitor SO₂ changes during changing inhalation conditions. Additionally, in a pilot study, three control (wild-type) and four leukemic mice were imaged; PA-based SO₂ estimates over the length of the femur were compared across five time-points.
Results: Between two- and five-wavelength unmixing, the mean SO₂ estimate differed by 4%; increasing the number of frame averages decreased variation in SO₂ estimates, but it did not statistically significantly (α=0.05) change the mean SO₂ estimate. In the oxygen challenge, the transient was observed to last longer than one minute; therefore, we determined that the five-wavelength/five-averages combination is acceptable (frame rate=2.5 seconds). In the pilot study, changes in mean SO₂ over the length of the femur increased from 5% (between baseline time-points) to 20% (between the terminal time-point and baseline) in leukemic mice.
Conclusion: We have designed an imaging protocol to obtain repeatable PA-based SO₂ estimates in murine femoral bone marrow. Results indicate that we can achieve repeated measure variability below 5% SO₂ in wild-type mice, which is far below pathologic-based variation (20%) observed in a pilot cohort of leukemic mice.
Keywords
Photoacoustics, Functional Imaging, Hypoxia
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