Imaging of Oxygenation in Tumors
Ralph Peter Mason1

1Radiology, University of Texas Southwestern Medical Center, Dallas, TX, United States

Synopsis

Tumor hypoxia is associated with aggressive phenotypes and resistance to therapy. Several MRI approaches are being developed and evaluated to measure tumor oxygenation. Many use exogenous reporter molecules, whilst some exploit endogenous signal. This review will present strengths and weaknesses in terms of temporal and spatial resolution, precision and accuracy, ease of implementation and robustness of observations. Methods may provide qualitative or quantitative insights including dynamic response to interventions. Some are limited to pre-clinical studies, while others offer ready translation to human patients.

Highlights

1. Tumor hypoxia is associated with aggressive phenotypes, notably influencing angiogenesis, metastasis, and response to therapy. Therefore, the ability to identify hypoxia could allow stratification for optimized therapy.

2. MRI methods have been developed to quantify pO2, and hence tumor hypoxia, or provide pertinent surrogate biomarkers.

3. This presentation will consider opportunities and applications in the context of competing technologies.

4. Virtues and shortcomings of diverse techniques will be considered in terms of ease of implementation, nature of observations (spatial resolution, precision, dynamics, and need for exogenous reporter agents) and validity and robustness of measurements.

5. Examples will be drawn from pre-clinical studies of mice and rats, focusing on our own experience. I will indicate potential for translation to man.

Purpose

There is increasing evidence for the importance of tumor oxygenation in development, progression, and response to therapy. Consequently, many techniques have been developed to assess tumor oxygenation, as reviewed extensively (1-3). Methods may provide a qualitative impression of oxygenation status or rigorous quantitation. Techniques vary in spatial and temporal resolution and the ability to assess dynamic changes. Some exploit endogenous molecules or physical characteristics, while many apply reporter molecules to interrogate oxygen tension (pO2). This tutorial will focus on magnetic resonance approaches, but place them in the context of competing modalities.

Context

It has long been appreciated that hypoxic tumor cells are relatively resistant to radiotherapy (4). A threefold increase in radio resistance may occur when cells are irradiated under hypoxic conditions compared with pO2 > 15 Torr for a single radiation dose. However, modeling indicates that the proportion of cells in the range 0 - 20 Torr may be most significant in terms of surviving a course of fractionated radiotherapy (5). Recently, there is much evidence that hypoxia is associated with a more aggressive phenotype. Notably, low pO2 measurements in tumors using electrodes at many disease sites in patients have been associated with poor prognosis (6, 7). Electrode measurements are highly invasive, sample limited regions and are generally not suitable for evaluating dynamic response to interventions. Several nuclear medicine reporters have been used with PET (e.g., 18F-misonidazole), but these introduce the expense and technical challenges associated with radioactivity. Immunohistochemistry (IHC), based on biopsies has also been used to stratify patients for modified radiotherapy paradigms (ARCON), but it is invasive and precludes repeat measurements from individual areas (8). Thus, we actively search for non-invasive procedures allowing repeat measurements representing the whole tumor.

MRI Methodologies: Quantitative Oximetry: 19F MRI.

pO2 may be measured directly using physical interactions between oxygen and reporter molecules. The most popular quantitative approach has exploited the oxygen-dependent 19F NMR spin lattice relaxation rate (R1=1/T1) of perfluorocarbons (PFCs) (9). A linear dependence R1= a + bpO2 is observed due to the ideal gas-liquid interaction of paramagnetic molecular oxygen (O2) dissolving in PFC. PFCs essentially act as molecular amplifiers, since the solubility of oxygen is greater than in water, but thermodynamics require that the pO2 in the PFC rapidly equilibrates with the surrounding medium. Importantly, ions do not enter the hydrophobic PFC phase, and thus, do not affect the bulk relaxation. Early studies focused on perfluorotributylamine (PFTB) and perfluorooctylbromide (PFOB) (10) and these were widely exploited for spectroscopy. However, multiple resonances can lead to chemical shift artifacts in images, requiring more sophisticated imaging approaches, which often sacrifice signal. Therefore, perfluoro-15-crown-5-ether (15C5) and hexafluorobenzene (HFB), are preferable since each exhibits a single 19F resonance, hence maximizing SNR (9). PFCs are extremely hydrophobic, but may be formulated as biocompatible emulsions for IV administration. Shortly after administration, PFC in the blood provides measurements of vascular pO2 (11), but clearance occurs within 1 to 2 days leading to extensive accumulation in the liver, spleen, and bone marrow, providing unique insight into these organs (12). Limited material does accumulate in other organs and oximetry has been reported with respect to myocardial ischemia (13). Accumulation in tumors occurs predominantly in regions of greater perfusion, often tumor periphery, potentially biasing measurements (14). Some PFCs show extended tissue retention allowing chronic studies during tumor development; progressive tumor hypoxiation has been observed over extended periods of many days (14, 15). It has been shown that stem cells may be loaded in vitro with PFC allowing subsequent cell tracking in vivo with the potential for local oximetry (16). Direct intratumoral (IT) injection of neat PFC allows any region of interest to be interrogated immediately and avoids reticuloendothelial uptake and bias towards well perfused tumor regions. A fine gauge needle ensures minimal tissue damage and provides measurements closely analogous to electrodes or fiber optic probes (17). We favor hexafluorobenzene (HFB) as a pO2 reporter because it exhibits a single 19F NMR resonance and a high sensitivity to changes in pO2, yet is minimally responsive to temperature (18). Typically 50 – 100 µl are introduced across the tumor to ensure that multiple regions are sampled. Recognizing that tumors are heterogeneous and that pO2 may fluctuate, we developed an imaging procedure [FREDOM (Fluorocarbon Relaxometry using Echo planar imaging for Dynamic Oxygen Mapping)], which allows repeated quantitative measurements of regional pO2 (typically, 50-150 voxels with 1.25 mm in plane resolution) simultaneously in 6.5 mins with a precision of 1-3 Torr, when pO2 is in the range 0-15 Torr (17). It should be noted that pO2 may be presented at Torr, which is equivalent to mmHg, or sometimes as %atmosphere, where 760 Torr = 1 atm. At 37 oC and 4.7 T: pO2 (Torr) = (R1(s-1) -0.0835)/0.001876, so that T1 reaches 12 s under anoxic conditions. To avoid excessive experimental acquisition time we favor pulse burst saturation recovery (PBSR) echo planar imaging (EPI) relaxometry. Traditional T1 measurement sequences acquire data with delays in monotonic order, whereas we alternate longer and shorter delays to minimize any systematic errors, which would be introduced, if the signal amplitude varies during the measurement (ARDVARC: Alternated Relaxation Delays with Variable Acquisitions to Reduce Clearance effects) (17). Gallez et al. have accelerated the acquisition to provide pO2 maps within 90 s based on a Look-Locker (SNAP-IR) approach (19) allowing spontaneous fluctuations in tumor oxygenation to be observed (20). The most powerful aspect of FREDOM is the ability to follow the fate of individual tissue regions of interest (voxels) with respect to interventions (e.g., Fig. 1). Most extensive investigations have focused on the response to respiratory challenge, often comparing the effects of oxygen (O2) versus carbogen (CB) gas breathing (2, 21-23). Most significantly, it has been shown that the ability to modulate pO2, as assessed using FREDOM correlated with tumor growth delay accompanying single high dose irradiation (24, 25). Other studies have examined response to vascular disrupting agents (VDAs) such as Combretastatin (CA4P) and OXi8007 revealing rapid hypoxiation of rat breast tumors (26, 27). Arsenic trioxide (ATO) has been described as a VDA (28), but Diepart et al. unexpectedly found increased pO2 within 30-90 minutes (depending on tumor type) of a relatively low dose (5 mg/kg) and demonstrated that this followed mitochondrial impairment (29). We believe that quantitative PFC oximetry provides a valuable pre-clinical tool and may serve as a benchmark to calibrate non-invasive observations such as BOLD and MOXI (a multi-parametric MR based technique) described below. We recognize that 19F remains quite esoteric on clinical scanners and thus proton MRI methods are preferable.

MRI Methodologies Quantitative Oximetry 1H MRI.

By analogy to 19F MRI oximetry the proton analog of HFB, hexamethyldisiloxane (HMDSO), has been used for 1H MRI oximetry. Like HFB, HMDSO is highly hydrophobic giving high gas solubility, and hence strong R1 response to changes in pO2. Symmetry provides a single proton resonance (δ = 0 ppm), which is well removed from water and fat allowing dynamic maps of tumor oxygenation to be achieved with respect to hyperoxic gas breathing challenge using PISTOL (Proton Imaging of Siloxanes to map Tissue Oxygenation Levels) (30).

Hypoxia

Techniques such as FREDOM and PISTOL provide quantitative pO2 measurements and histogram analysis can indicate hypoxic fraction (e.g., percentage measurements < 5 Torr). Hypoxia may also be assessed directly by analysis with PET and IHC approaches based on nitroimidazole trapping. Several 19F NMR hypoxia agents have been tested, e.g., hexafluoromisonidazole (CCI-103F), EF5, NLTQ-1, SR-4554, and Ro 07-0741). Variants have also been generated as 1H MR reporters both for spectroscopy (31) and imaging (32). Indeed the retention of GdDO3NI matched the pattern of oxygenation expected in Dunning prostate R3327-AT1 tumors based on extensive previous 19F oximetry imaging (32). Assessment of hypoxia is predicated on uptake and trapping of the reporter, assessed as the relative signal at various times (retention index) or based on the relative signals from tumor and surrounding control tissues. Weak 19F signals generally restrict measurements to a global value across the whole tumor. Trapping may also depend on expression of nitroreductases and be influenced by glutathione (33). Likewise, tumor perfusion may influence access of the agents to tumor tissue, particularly poorly perfused regions, which are expected to be hypoxic. Indeed, uptake of hypoxia reporters following administration of vascular disrupting agents, did not match hypoxia, presumably because access was hindered to the very regions which became hypoxic (34)

Non-invasive Oxygen Enhanced MRI:

Imaging per se is non-invasive and it would be particularly attractive to develop oximetry methods based on properties of endogenous molecules, rather than requiring administration of reporter agents. Lactate concentration has been associated with hypoxia as consistent with impaired oxidative phosphorylation and accelerated glycolysis, though many factors may influence this phenotype (35).

BOLD (Blood Oxygen level Dependent) contrast 1H MRI is directly sensitive to deoxyhemoglobin concentration and forms the basis of so-called functional MRI (fMRI), as used to reveal neuronal activation. Extensive studies have demonstrated BOLD effects in tumors most commonly in response to a hyperoxic gas breathing challenge (e.g., Fig. 2A). Several studies have demonstrated correlations between BOLD response and changes in pO2 in various tumor types (36-38). The dependence is often non-linear, but distinct trends have been observed. Early reports examined changes in T2*-weighted signal intensity (ΔSI), but it was rapidly appreciated that ΔSI is also subject to flow effects and the concept FLOOD (Flow and Oxygen Dependent) contrast was suggested (39). Quantitative measurement of R2* should mitigate flow effects. Rodrigues et al. demonstrated that tumors with fast R2* and large ΔR2* showed enhanced response to radiation when mice breathed CB, whereas RIF1 tumors showed much smaller effects and no benefit from CB breathing (40). BOLD depends on vascular deoxyhemoglobin and is therefore influenced by vascular extent, volume, flow and hematocrit. Indeed, an attempt to calibrate BOLD in terms of absolute pO2 based on a hypoxic endpoint (breathing nitrogen) in rat tumors generated a seemingly inconsistent result with R2* decreasing upon death, likely due to blood (viz. deoxyhemoglobin) leaving the tumor as a consequence of reduced systemic blood pressure (39). The recent availability of commercial photoacoustic tomography (PAT) should provide insights into BOLD effects (41). Specifically, changes in oxy- and deoxy-hemoglobin may be assessed at a resolution of 150 μm, visualizing blood vessels at the arteriolar level.

TOLD (Tissue Oxygen level Dependent) It has been suggested that tissue water R1 should more closely match changes in pO2 based on paramagnetic properties of dissolved O2. While the dependence of R1 on pO2 in tissues has long been recognized (42, 43) it has been recently been applied as the so-called TOLD (Tissue Oxygen Level Dependent) concept (44). Several studies have now reported T1 response to interventions such as oxygen breathing challenge (Fig. 2B) (45-48). Logically, one might expect BOLD changes to be followed by TOLD response based on progressive vascular oxygenation followed by diffusion of oxygen into tissues generating elevated pO2 (45). TOLD response to changes in pO2 is generally smaller than BOLD (Figs. 2,3). Garbow et al. demonstrated correlations between ΔR1 and pO2 assessed with a fluorescent probe in rat brain tumors (49). They also demonstrated the ability to differentiate radiation necrosis from tumors based on TOLD response to oxygen breathing challenge. O’Connor et al. compared OE-MRI and pimonidazole based hypoxia and found better correlation in some tumor types when DCE MRI was also included to identify and exclude non-perfused regions (50). Several studies have now shown close correlation between BOLD and TOLD responses, but some tumor types show distinct mismatch. It must be remembered that deoxyhemoglobin also has a small effect on T1, while [O2] can affect T2* and therefore under specific conditions one or other effect may dominate based on vascular extent and perfusion. We recently showed that a large TOLD response to oxygen breathing challenge prior to irradiation indicated which tumors would benefit from rats breathing oxygen during irradiation (45).

MOBILE Recognizing the greater solubility of oxygen in lipids as compared with water, Gallez et al. recently proposed MOBILE (Mapping of Oxygen By Imaging Lipids relaxation Enhancement) (51). They specifically showed that changes in lipid relaxation were greater than water: about 2 and 11 fold greater for the resonances at 1.2 and 4 ppm, respectively. Observations were reported in mice, with respect to ischemia, liver steatosis, and tumors (52). Pilot studies have also been reported in human volunteers (53).

MOXI Recently, Zhang et al. (54) demonstrated that a multi parametric analysis of tumor water signal could directly provide estimates of pO2. Specifically, biexponential analysis of IVIM (Intra Voxel Incoherent Motion) allowed estimation of tumor vascular volume; then in combination with R1 and biexponential analysis of CPMG-based R2, yielding the extravascular component, an accurate measurement of pO2 was achieved, as validated using 19F MRI of PFC. The current measurements are limited to air breathing due to model assumptions, but can provide an effective quantitative baseline maps from which to evaluate BOLD and TOLD responses to interventions (Fig. 4).

Conclusion

Beyond pre-clinical investigations, it is noteworthy that BOLD, TOLD, and MOBILE MRI have been successfully applied in studies of normal human volunteers and patients enrolled in trials with respect to cancer in various disease sites including breast, cervix, prostate and brain (46, 53, 55-62). It remains to be seen which parameter is most useful in identifying patients to characterize tumors for optimal therapy. Quantitative 19F oximetry is a valuable pre-clinical tool and continues to serve as a validation for less invasive approaches, but is likely impractical in man due to the sparse availability of clinical 19F MRI and need for approval of contrast agents. BOLD and TOLD are being evaluated in patients. The enhanced oxygen sensitivity of MOBILE and quantitative estimates provided by MOXI are very promising though their general applicability remains to be evaluated. Today, there are many therapeutic options, but prognostic imaging with respect to hypoxia remains a work-in progress. The radiation oncology community recognizes the need to routinely measure tumor oxygenation, as part of precision medicine; ultimately, MR oximetry methods should provide evidence based choice of therapy including radiation dose painting, heavy ion beam or application of hypoxic cell selective cytotoxins.

Acknowledgements

Research presented in this tutorial was supported by CPRIT RP140285 and previously DOD and NIH. I am grateful to colleagues Drs. Jesus Pacheco Torres, Rami Hallac, and Heling Zhou for inspiring suggestions in preparing this tutorial.

References

1. Mason, R. P., Zhao, D., Pacheco-Torres, J., Cui, W., Kodibagkar, V. D., Gulaka, P. K., Hao, G., Thorpe, P., Hahn, E. W., and Peschke, P. Multimodality imaging of hypoxia in preclinical settings. QJ Nucl. Med. Mol. Imaging 2010; 54, 259-280.

2. Krohn, K. A., Link, J. M., and Mason, R. P. Molecular Imaging of Hypoxia. J. Nucl. Med. 2008; 49, 129S-148S.

3. Tatum, J. L., Kelloff, G. J., Gillies, R. J., Arbeit, J. M., Brown, J. M., Chao, K. S. C., Chapman, J. D., Eckelman, W. C., Fyles, A. W., Giaccia, A. J., Hill, R. P., Koch, C. J., Krishna, M. C., Krohn, K. A., Lewis, J. S., Mason, R. P., Melillo, G., Padhani, A. R., Powis, G., Rajendran, J. G., Reba, R., Robinson, S. P., Semenza, G. L., Swartz, H. M., Vaupel, P., Yang, D., Croft, B., Hoffman, J., Liu, G. Y., Stone, H., and Sullivan, D. Hypoxia: Importance in tumor biology, noninvasive measurement by imaging, and value of its measurement in the management of cancer therapy. Int. J. Radiat. Biol. 2006; 82, 699-757.

4. Overgaard, J. Hypoxic radiosensitization: Adored and ignored. J. Clin. Oncol. 2007; 25, 4066-4074.

5. Wouters, B. G., and Brown, J. M. Cells at intermediate oxygen levels can be more important than the "hypoxic fraction" in determining tumor response to fractionated radiotherapy. Radiat. Res. 1997; 147, 541-550.

6. Le, Q. T., Chen, E., Salim, A., Cao, H. B., Kong, C. S., Whyte, R., Donington, J., Cannon, W., Wakelee, H., Tibshirani, R., Mitchell, J. D., Richardson, D., O'Byrne, K. J., Koong, A. C., and Giaccia, A. J. An evaluation of tumor oxygenation and gene expression in patients with early stage non-small cell lung cancers. Clin. Cancer Res. 2006; 12, 1507-1514.

7. Turaka, A., Buyyounouski, M. K., Hanlon, A. L., Horwitz, E. M., Greenberg, R. E., and Movsas, B. Hypoxic Prostate/Muscle PO2 Ratio Predicts for Outcome in Patients With Localized Prostate Cancer: Long-Term Results. Int. J. Radiat. Oncol. Biol. Phys. 2012; 82, E433-E439.

8. Kaanders, J. H. A. M., Bussink, J., and van der Kogel, A. J. Clinical studies of hypoxia modification in radiotherapy. Sem. Radiat. Oncol. 2004; 14, 233-240.

9. Yu, J.-X., Hallac, R. R., Chiguru, S., and Mason, R. P. New frontiers and developing applications in 19F NMR. Progr. Nucl. Magn. Reson. Spectrosc. 2013; 70, 25-49.

10. Mason, R. P. Non-invasive physiology: 19F NMR of perfluorocarbon. Art. Cells, Blood Sub. & Immob. Biotech. 1994; 22, 1141-1153.

11. Eidelberg, D., Johnson, G., Barnes, D., Tofts, P. S., Delpy, D., Plummer, D., and McDonald, W. I. 19F NMR imaging of blood oxygenation in the brain. Magn. Reson. Med. 1988; 6, 344-352.

12. Kucejova, B., Sunny, N. E., Nguyen, A. D., Hallac, R., Fu, X., Pena-Llopis, S., Mason, R. P., DeBerardinis, R. J., Xie, X. J., DeBose-Boyd, R., Kodibagkar, V. D., Burgess, S. C., and Brugarolas, J. Uncoupling hypoxia signaling from oxygen sensing in the liver results in hypoketotic hypoglycemic death. Oncogene 2011; 30, 2147-2160.

13. Mason, R. P., Jeffrey, F. M. H., Malloy, C. R., Babcock, E. E., and Antich, P. P. A noninvasive assessment of myocardial oxygen tension: 19F NMR spectroscopy of sequestered perfluorocarbon emulsion. Magn. Reson. Med. 1992; 27, 310-317.

14. Mason, R. P., Antich, P. P., Babcock, E. E., Constantinescu, A., Peschke, P., and Hahn, E. W. Non-invasive determination of tumor oxygen tension and local variation with growth. Int. J. Radiat. Oncol. Biol. Phys. 1994; 29, 95-103.

15. Baldwin, N. J., and Ng, T. C. Oxygenation and metabolic status of KHT tumors as measured simultaneously by F-19 magnetic resonance imaging and P-31 magnetic resonance spectroscopy. Magn. Reson. Imaging 1996; 14, 541-551.

16. Ruiz-Cabello, J., Barnett, B. P., Bottomley, P. A., and Bulte, J. W. M. Fluorine (19F) MRS and MRI in biomedicine. NMRBiomed. 2011; 24, 114-129.

17. Zhao, D., Jiang, L., and Mason, R. P. Measuring Changes in Tumor Oxygenation. Methods Enzymol 2004; 386, 378-418.

18. Mason, R. P., Rodbumrung, W., and Antich, P. P. Hexafluorobenzene: a sensitive 19F NMR indicator of tumor oxygenation. NMRBiomed. 1996; 9, 125-134.

19. Jordan, B. F., Cron, G. O., and Gallez, B. Rapid monitoring of oxygenation by 19F magnetic resonance imaging: Simultaneous comparison with fluorescence quenching. Magn. Reson. Med. 2009; 61, 634-638.

20. Magat, J., Jordan, B. F., Cron, G. O., and Gallez, B. Noninvasive mapping of spontaneous fluctuations in tumor oxygenation using F-19 MRI. Med. Phys. 2010; 37, 5434-5441.

21. Xia, M., Kodibagkar, V., Liu, H., and Mason, R. P. Tumour oxygen dynamics measured simultaneously by near infrared spectroscopy and 19F magnetic resonance imaging in rats. Phys. Med. Biol. 2006; 51, 45-60.

22. Song, Y., Constantinescu, A., and Mason, R. P. Dynamic breast tumor oximetry: the development of prognostic radiology. Technol. Cancer Res. Treat. 2002; 1, 471-478.

23. Zhao, D., Constantinescu, A., Hahn, E. W., and Mason, R. P. Tumor oxygen dynamics with respect to growth and respiratory challenge: investigation of the Dunning prostate R3327-HI tumor. Radiat. Res. 2001; 156, 510-520.

24. Zhao, D., Constantinescu, A., Chang, C.-H., Hahn, E. W., and Mason, R. P. Correlation of Tumor Oxygen Dynamics with Radiation Response of the Dunning Prostate R3327-HI Tumor. Radiat. Res. 2003; 159, 621-631.

25. Bourke, V. A., Zhao, D., Gilio, J., Chang, C.-H., Jiang, L., Hahn, E. W., and Mason, R. P. Correlation of Radiation Response with Tumor Oxygenation in the Dunning Prostate R3327-AT1 Tumor. Int. J. Radiat. Oncol. Biol. Phys. 2007; 67, 1179-1186.

26. Zhao, D., Jiang, L., Hahn, E. W., and Mason, R. P. Tumor physiological response to combretastatin A4 phosphate assessed by MRI. Int. J. Radiat. Oncol. Biol. Phys 2005; 62, 872-880.

27. Zhou, H., Hallac, R. R., Lopez, R. R., Denney, R., MacDonough, M. T., Li, L. L., L., Graves, E. E., Trawick, M. L., Pinney, K. G., and Mason, R. P. Evaluation of tumor ischemia in response to an indole-based vascular disrupting agent using BLI and 19F MRI. Am J Nucl Med Mol Imaging 2015; 5, 143-153.

28. Alhasan, M. K., Liu, L., Lewis, M. A., Magnusson, J., and Mason, R. P. Comparison of Optical and Power Doppler Ultrasound Imaging for Non-Invasive Evaluation of Arsenic Trioxide as a Vascular Disrupting Agent in Tumors. PLoS ONE 2012; 7, e46106.

29. Diepart, C., Karroum, O., Magat, J., Feron, O., Verrax, J., Calderon, P. B., Gregoire, V., Leveque, P., Stockis, J., Dauguet, N., Jordan, B. F., and Gallez, B. Arsenic Trioxide Treatment Decreases the Oxygen Consumption Rate of Tumor Cells and Radiosensitizes Solid Tumors. Cancer Res. 2012; 72, 482-490.

30. Kodibagkar, V. D., Wang, X., Pacheco-Torres, J., Gulaka, P., and Mason, R. P. Proton Imaging of Siloxanes to map Tissue Oxygenation Levels (PISTOL): a tool for quantitative tissue oximetry. NMRBiomed 2008; 21, 899-907.

31. Pacheco-Torres, J., López-Larrubia, P., Ballesteros, P., and Cerdán, S. Imaging tumor hypoxia by magnetic resonance methods. NMR Biomed. 2011; 24, 1-16.

32. Gulaka, K., Rojas-Quijano, F., Kovacs, Z., Mason, R. P., Sherry, A. D., and D, K. V. GdDO3NI, a nitroimidazole-based T1 MRI contrast agent for imaging tumor hypoxia in vivo. J. Bio. Inorg. Chem 2014; 33. Robinson, S. P., and Griffiths, J. R. Current Issues in the Utility of 19F Nuclear Magnetic Resonance Methodologies for the Assessment of Tumour Hypoxia. Phil. Trans Biol. Sci. 2004; 359, 987-996.

34. Oehler, C., O'Donoghue, J. A., Russell, J., Zanzonico, P., Lorenzen, S., Ling, C. C., and Carlin, S. F-18-Fluromisonidazole PET Imaging as a Biomarker for the Response to 5,6-Dimethylxanthenone-4-Acetic Acid in Colorectal Xenograft Tumors. J. Nucl. Med. 2011; 52, 437-444.

35. Gatenby, R. A., and Gillies, R. J. Why do cancers have high aerobic glycolysis? Nature Rev. Cancer 2004; 4, 891-899.

36. Baudelet, C., and Gallez, B. How does blood oxygen level-dependent (BOLD) contrast correlate with oxygen partial pressure (pO2) inside tumors? Magn. Reson. Med. 2002; 48, 980-986.

37. Zhao, D., Jiang, L., Hahn, E. W., and Mason, R. P. Comparison of 1H blood oxygen level-dependent (BOLD) and 19F MRI to investigate tumor oxygenation. Magn. Reson. Med. 2009; 62, 357-364.

38. Al-Hallaq, H. A., River, J. N., Zamora, M., Oikawa, H., and Karczmar, G. S. Correlation of magnetic resonance and oxygen microelectrode measurements of carbogen-induced changes in tumor oxygenation. Int. J. Radiat. Oncol. Biol. Phys. 1998; 41, 151-159.

39. Howe, F. A., Robinson, S. P., McIntyre, D. J. O., Stubbs, M., and Griffiths, J. R. Issues in flow and oxygenation dependent contrast (FLOOD) imaging of tumours. NMR Biomed. 2001; 14, 497-506.

40. Rodrigues, L. M., Howe, F. A., Griffiths, J. R., and Robinson, S. P. Tumor R-2 * is a prognostic indicator of acute radiotherapeutic response in rodent tumors. J. Magn. Reson. Imaging 2004; 19, 482-488.

41. Mason, R. P. Commentary on Photoacoustic Tomography. Journal of Nuclear Medicine 2015; 56, 1815-1816.

42. Edelman, R. R., Hatabu, H., Tadamura, E., Li, W., and Prasad, P. V. Noninvasive assessment of regional ventilation in the human lung using oxygen-enhanced magnetic resonance imaging. Nature Medicine 1996; 2, 1236-1239.

43. Berkowitz, B. A., McDonald, C., Ito, Y., Tofts, P. S., Latif, Z., and Gross, J. Measuring the human retinal oxygenation response to a hyperoxic challenge using MRI: Eliminating blinking artifacts and demonstrating proof of concept. Magn. Reson. Med. 2001; 46, 412-416.

44. Matsumoto, K., Bernardo, M., Subramanian, S., Choyke, P., Mitchell, J. B., Krishna, M. C., and Lizak, M. J. MR assessment of changes of tumor in response to hyperbaric oxygen treatment. Magn. Reson. Med. 2006; 56, 240-246.

45. Hallac, R. R., Zhou, H., Pidikiti, R., Song, K., Stojadinovic, S., Zhao, D., Solberg, T., Peschke, P., and Mason, R. P. Correlations of noninvasive BOLD and TOLD MRI with pO2 and relevance to tumor radiation response. Magn. Reson. Med. 2014; 71, 1863-1873.

46. O'Connor, J. P. B., Naish, J. H., Parker, G. J. M., Waterton, J. C., Watson, Y., Jayson, G. C., Buonaccorsi, G. A., Cheung, S., Buckley, D. L., McGrath, D. M., West, C. M. L., Davidson, S. E., Roberts, C., Mills, S. J., Mitchell, C. L., Hope, L., Ton, C., and Jackson, A. Preliminary Study of Oxygen-Enhanced Longitudinal Relaxation in MRI: a Potential Novel Biomarker of Oxygenation Changes in Solid Tumors. Int. J. Radiat. Oncol. Biol. Phys. 2009; 75, 1209-1215.

47. Remmele, S., Sprinkart, A. M., Muller, A., Traber, F., von Lehe, M., Gieseke, J., Flacke, S., Willinek, W. A., Schild, H. H., Senegas, J., Keupp, J., and Murtz, P. Dynamic and simultaneous MR measurement of R1 and R2*changes during respiratory challenges for the assessment of blood and tissue oxygenation. Magn. Reson. Med. 2013; 70, 136-146.

48. Burrell, J. S., Walker-Samuel, S., Baker, L. C. J., Boult, J. K. R., Jamin, Y., Halliday, J., Waterton, J. C., and Robinson, S. P. Exploring ΔR2* and ΔR1 as imaging biomarkers of tumor oxygenation. J. Magn. Reson. Imaging 2013; 38, 429-434.

49. Beeman, S. C., Shui, Y.-B., Perez-Torres, C. J., Engelbach, J. A., Ackerman, J. J. H., and Garbow, J. R. O2-sensitive MRI distinguishes brain tumor versus radiation necrosis in murine models. Magn. Reson. Med. 2015; n/a-n/a.

50. O'Connor, J. P. B., Rose, C. J., Waterton, J. C., Carano, R. A. D., Parker, G. J. M., and Jackson, A. Imaging Intratumor Heterogeneity: Role in Therapy Response, Resistance, and Clinical Outcome. Clinical Cancer Research 2015; 21, 249-257.

51. Jordan, B. F., Magat, J., Colliez, F., Ozel, E., Fruytier, A.-C., Marchand, V., Mignion, L., Bouzin, C., Cani, P. D., Vandeputte, C., Feron, O., Delzenne, N., Himmelreich, U., Denolin, V., Duprez, T., and Gallez, B. Mapping of oxygen by imaging lipids relaxation enhancement: A potential sensitive endogenous MRI contrast to map variations in tissue oxygenation. Magn. Reson. Med. 2013; 70, 732-744.

52. Colliez, F., Neveu, M. A., Magat, J., Pham, T. T. C., Gallez, B., and Jordan, B. F. Qualification of a Noninvasive Magnetic Resonance Imaging Biomarker to Assess Tumor Oxygenation. Clinical Cancer Research 2014; 20, 5403-5411.

53. Safronova, M. M., Colliez, F., Magat, J., Joudiou, N., Jordan, B. F., Raftopoulos, C., Gallez, B., and Duprez, T. Mapping of global R1 and R2*values versus lipids R1 values as potential markers of hypoxia in human glial tumors: A feasibility study. Magnetic Resonance Imaging 2016; 34, 105-113. 54. Zhang, Z., Hallac, R. R., Peschke, P., and Mason, R. P. A noninvasive tumor oxygenation imaging strategy using magnetic resonance imaging of endogenous blood and tissue water. Magn. Reson. Med. 2014; 71, 561-569.

55. Mürtz, P., Flacke, S., Müller, A., Soehle, M., Wenningmann, I., Kovacs, A., Träber, F., Willinek, W. A., Gieseke, J., Schild, H. H., and Remmele, S. Changes in the MR relaxation rate R2* induced by respiratory challenges at 3.0 T: a comparison of two quantification methods. NMR Biomed. 2010; 23, 1053-1060.

56. Chopra, S., Foltz, W. D., Milosevic, M. F., Toi, A., Bristow, R. G., Menard, C., and Haider, M. A. Comparing oxygen-sensitive MRI (BOLD R2*) with oxygen electrode measurements: A pilot study in men with prostate cancer. Int. J. Radiat. Biol. 2009; 85, 805 - 813.

57. Alonzi, R., Padhani, A. R., Taylor, N. J., Collins, D. J., D'Arcy, J. A., Stirling, J. J., Saunders, M. I., and Hoskin, P. J. Antivascular Effects of Neoadjuvant Androgen Deprivation for Prostate Cancer: an in Vivo Human Study Using Susceptibility and Relaxivity Dynamic Mri. Int. J. Radiat. Oncol. Biol. Phys. 2011; 80, 721-727.

58. Jiang, L., Weatherall, P. T., McColl, R. W., Tripathy, D., and Mason, R. P. Blood oxygenation level-dependent (BOLD) contrast magnetic resonance imaging (MRI) for prediction of breast cancer chemotherapy response: A pilot study. J. Magn. Reson. Imaging 2013; 37, 1083–1092.

59. Ding, Y., Mason, R. P., McColl, R. W., Yuan, Q., Hallac, R. R., Sims, R. D., and Weatherall, P. T. Simultaneous measurement of tissue oxygen level-dependent (TOLD) and blood oxygenation level-dependent (BOLD) effects in abdominal tissue oxygenation level studies. J. Magn. Reson. Imaging 2013; 38, 1230-1236.

60. Remmele, S., Mason, R. P., and O’Connor, J. B. P. (2014) MRI Hypoxia Measurements. In Functional Imaging in Oncology (Luna, A., ed), Springer-Verlag, Heidelberg

61. Hallac, R. R., Ding, Y., Yuan, Q., McColl, R. W., Lea, J., Sims, R. D., Weatherall, P. T., and Mason, R. P. Oxygenation in cervical cancer and normal uterine cervix assessed using blood oxygenation level-dependent (BOLD) MRI at 3T. NMR Biomed 2012; 25, 1321–1330.

62. Rakow-Penner, R., Daniel, B., and Glover, G. H. Detecting Blood Oxygen Level-Dependent (BOLD) Contrast in the Breast. J. Magn. Reson. Imaging 2010; 32, 120-129.

63. Zhao, D., Pacheco-Torres, J., Hallac, R. R., White, D., Peschke, P., Cerdán, S., and Mason, R. P. Dynamic oxygen challenge evaluated by NMR T1 and T2* – insights into tumor oxygenation. NMR Biomed. 2015; 28, 937–947.

64. Loncaster, J. A., Carrington, B. M., Sykes, J. R., Jones, A. P., Todd, S. M., Cooper, R., Buckley, D. L., Davidson, S. E., Logue, J. P., Hunter, R. D., and West, C. M. L. Prediction of radiotherapy outcome using dynamic contrast enhanced MRI of carcinoma of the cervix. Int. J. Radiat. Oncol. Biol. Phys. 2002; 54, 759-767.

65. Egeland, T. A. M., Gulliksrud, K., Gaustad, J. V., Mathiesen, B., and Rofstad, E. K. Dynamic contrast-enhanced-MRI of tumor hypoxia. Magn. Reson. Med. 2012; 67, 519-530.

66. Gulliksrud, K., Ovrebo, K. M., Mathiesen, B., and Rofstad, E. K. Differentiation between hypoxic and non-hypoxic experimental tumors by dynamic contrast-enhanced magnetic resonance imaging. Radiother. Oncol. 2011; 98, 360-364.

67. Ovrebo, K. M., Hompland, T., Mathiesen, B., and Rofstad, E. K. Assessment of hypoxia and radiation response in intramuscular experimental tumors by dynamic contrast-enhanced magnetic resonance imaging. Radiother. Oncol. 2012; 102, 429-435.

Figures

Figure 1 Dynamic quantitative oximetry using 19F MRI. pO2 maps of R3327-AT1 rat tumor obtained using FREDOM showing heterogeneity of tumor oxygenation and response to challenge. Trace shows pO2 at 4 locations chosen as initially hypoxic or well oxygenated. Data generated with Drs. Jiang and Zhao (17).

Figure 2 Oxygen enhanced MRI. Response of (A) T2* (BOLD)- and (B) T1 (TOLD)-weighted image signal intensity to carbogen challenge in a small R3327-HI rat tumor. C) Comparison of mean response for multiple HI and AT1 tumors. Data generated with Drs. Pacheco-Torres and Zhao (63).

Figure 3 Changes in tumor oxygenation in response to oxygen breathing. A) Mean changes in BOLD (red), TOLD (black), %ΔT2* (green) for two R3327-AT1 prostate tumors exhibiting very different response to O2 challenge. B) Corresponding mean changes in pO2 based on FREDOM. Data generated with Drs. Hallac and Zhou (45).

Figure 4 MR Oximetry (MOXI) of R3327-MAT-Lu tumor. a) T2-weighted image; b) pO2 map; c) pO2 distribution; d) BOLD and e) TOLD responses to O2-challenge for regions selected as more (pO2 = 15 Torr) or less (pO2 = 6 Torr) well-oxygenated based on MOXI. Data generated with Dr. Zhang (54).

Table Comparison of oximetry techniques



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)