Tumor hypoxia causes resistance to radiotherapy. A non-invasive imaging method is needed to quantitatively measure tumor hypoxia to predict radiotherapy response before starting treatment. Furthermore, radiotherapy can damage blood vessels, which can reduce vascular perfusion and oxygen delivery. We have developed Oxygen Enhanced – Dynamic Contrast Enhanced Multispectral Optoacoustic Tomography (OE-DCE MSOT) that can evaluate hypoxia and vascular perfusion in a single scan session. OE MSOT measures oxygen saturation with medical grade air (%sO2air using 21% O2) breathing gas and 100% breathing gas (%sO2O2), and the “available oxygen capacity” (ΔsO2) that is the difference between %sO2air and %sO2air . DCE MSOT uses the normalized pharmacokinetics profile of an exogenous contrast agent in a tumor to calculate NKtrans and kep, which indicate the wash-in and wash-out vascular perfusion rates, respectively. We have shown that our DCE MSOT methodology avoids the problem of variable fluence within in vivo tissues. We applied OE-DCE MSOT to study the effect of radiotherapy on three tumor models that have different levels of vascular perfusion and hypoxia. Our results showed that %sO2 air , %sO2O2 , ΔsO2 identified normoxic, mildly hypoxic, and hypoxic models, which was related to the high-to-low status of vascular perfusing as measured with NKtrans . A change in ΔsO2 and NKtrans indicated early response to radiotherapy. These results demonstrate the advantages of OE-DCE MSOT for simultaneously evaluating tumor hypoxia and vascular perfusion before and soon after treatment.
KEYWORDS: Computed tomography, Image registration, Magnetic resonance imaging, 3D image processing, Image segmentation, Tissues, In vivo imaging, Optical coherence tomography, Positron emission tomography, Medical imaging
Histopathology is the accepted gold standard for identifying cancerous tissues. Validation of in vivo imaging signals with precisely correlated histopathology can potentially improve the delineation of tumors in medical images for focal therapy planning, guidance, and assessment. Registration of histopathology with other imaging modalities is challenging due to soft tissue deformations that occur between imaging and histological processing of tissue. In this paper, a framework for precise registration of medical images and pathology using white-light images (photographs) is presented. A euthanized normal mouse was imaged using four imaging modalities: CBCT, PET-CT, MRI and micro CT. The mouse was then fixed in an embedding medium, optical cutting temperature (OCT) compound, with co-registration markers and sliced at 50 m intervals in a cryostatmicrotome. The device automatically photographed each slice with a mounted camera and reconstructed the 3D white-light image of the mouse through co-registering of consecutive slices. The white-light image was registered to the four imaging modalities based on the external contours of the mouse. Six organs (brain, liver, stomach, pancreas, kidneys and bladder) were contoured on the MR image while the skeletal structure and lungs were segmented on the CBCT image. The contours of these structures were propagated to the additional imaging modalities based on the registrations to the white-light image and were analyzed qualitatively by developing an anatomical atlas of normal mouse defined using three imaging modalities. This work will serve as the foundation to include histopathology through the transfer of the imaged slice onto tape for histological processing.
Acute lymphoblastic leukemia (ALL) interacts with bone marrow cells, creating hypoxic niches that stabilize HIF-1α and promote chemotherapeutic resistance. Spectrosocopic photoacoustic (PA) imaging is a label-free, noninvasive technique that probes the in vivo oxygenation status of hemoglobin, resulting in a measurement of oxygen saturation (SO2) and providing a surrogate measure of tissue hypoxia. This work investigates multispectral PA imaging to assess the SO2 in the femoral bone marrow in mice. Preliminary work was performed to assess the capability of imaging through bone, followed by an oxygen challenge to determine the magnitude of systemic SO2 changes measurable in wild type mice. Furthermore, a pilot study to compare SO2 measured in a murine model of ALL versus in healthy controls was performed to investigate a correlation between SO2 changes in the femoral bone marrow and disease progression. Study results show that femoral SO2 can be measured with a variation less than 10% in wild type mice over multiple time-points. In the oxygen challenge, a 10% difference in systemic SO2 was observed between 100% and 21% O2 inhalation conditions. Additionally, leukemic mice demonstrate significantly more variation in femoral SO2 over the length of the femur than control mice at day 14 post-inoculation, indicating that femoral SO2 is affected by leukemic disease progression. This work demonstrates the feasibility of observing changes in leukemic disease progression through the measurement of SO2 with spectroscopic PA imaging, which could help develop a more complete understanding of the interplay of the local microenvironment with leukemogenesis.
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