Hypoxia is associated with prostate tumor aggressiveness, local recurrence, and biochemical failure. Magnetic resonance imaging (MRI) offers insight into tumor pathophysiology and recent reports have related transverse relaxation rate (R₂*) and longitudinal relaxation rate (R₁) measurements to tumor hypoxia. We have investigated the inclusion of oxygen-enhanced MRI for multi-parametric evaluation of tumor malignancy. Multi-parametric MRI sequences at 3 Tesla were evaluated in 10 patients to investigate hypoxia in prostate cancer prior to radical prostatectomy. Blood oxygen level dependent (BOLD), tissue oxygen level dependent (TOLD), dynamic contrast enhanced (DCE), and diffusion weighted imaging MRI were intercorrelated and compared with the Gleason score. The apparent diffusion coefficient (ADC) was significantly lower in tumor than normal prostate. Baseline R₂* (BOLD-contrast) was significantly higher in tumor than normal prostate. Upon the oxygen breathing challenge, R₂* decreased significantly in the tumor tissue, suggesting improved vascular oxygenation, however changes in R₁ were minimal. R₂* of contralateral normal prostate decreased in most cases upon oxygen challenge, although the differences were not significant. Moderate correlation was found between ADC and Gleason score. ADC and R₂* were correlated and trends were found between Gleason score and R₂*, as well as maximum-intensity-projection and area-under-the-curve calculated from DCE. Tumor ADC and R₂* have been associated with tumor hypoxia, and thus the correlations are of particular interest. A multi-parametric approach including oxygen-enhanced MRI is feasible and promises further insights into the pathophysiological information of tumor microenvironment.

Purpose: To present a novel imaging strategy for noninvasive measurement of tumor oxygenation using MR imaging of endogenous blood and tissue water.Theory and Methods: The proposed approach for oxygen partial pressure (pO₂) estimation is based on intravoxel incoherent motion diffusion MRI and the dependence of the blood R₂ relaxation rate on the inter‐echo spacing measured using a multiple spin‐echo Carr‐Purcell‐Meiboom‐Gill sequence and weak‐field diffusion model. The accuracy of the approach was validated by comparison with ¹⁹F MRI oximetry.Results: The results in eight rats at 4.7 T showed that tumors have longer T₁ (1980 ± 186 ms) and T₂ (59 ± 9 ms) relaxation times, heterogeneous blood volume fraction (0.23 ± 0.1), oxygen saturation level (Y) (0.53 ± 0.12), and pO₂ (36 ± 15 mmHg) distributions compared with normal muscle (T₁ 1480 ± 86 ms, T₂ 29 ± 2 ms, blood volume fraction 0.22 ± 0.03, Y 0.49 ± 0.06, and pO₂ 39 ± 5 mmHg). pO₂ estimates based on the novel ¹H approach were essentially identical with ¹⁹F observations.Conclusion: The study indicates that noninvasive measurement of tumor pO₂ using ¹H MRI derived multiparametric maps is feasible and could become a valuable tool to evaluate tumor hypoxia. Magn Reson Med 71:561–569, 2014.

Purpose: To assess tumor response to oxygen challenge using quantitative diffusion magnetic resonance imaging (MRI).Materials and Methods: A well‐characterized Dunning R3327‐AT1 rat prostate cancer line was implanted subcutaneously in the right thigh of male Copenhagen rats (n = 8). Diffusion‐weighted images (DWI) with multiple b values (0, 25, 50, 100, 150, 200, 300, 500, 1000, 1500 s/mm²) in three orthogonal directions were obtained using a multishot FSE‐based Stejskal‐Tanner DWI sequence (FSE‐DWI) at 4.7T, while rats breathed medical air (21% oxygen) and with 100% oxygen challenge. Stretched‐exponential and intravoxel incoherent motion (IVIM) models were used to calculate and compare quantitative diffusion parameters: diffusion heterogeneity index (α), intravoxel distribution of diffusion coefficients (DDC), tissue diffusivity (Dt), pseudo‐diffusivity (Dp), and perfusion fraction (f) on a voxel‐by‐voxel basis.Results: A significant increase of α (73.9 ± 4.7% in air vs. 78.1 ± 4.5% in oxygen, P = 0.0198) and a significant decrease of f (13.4 ± 3.7% in air vs. 10.4 ± 2.7% in oxygen, P = 0.0201) were observed to accompany oxygen challenge. Correlations between f and α during both air and oxygen breathing were found; the correlation coefficients (r) were −0.90 and −0.96, respectively. Positive correlations between Dt and DDC with oxygen breathing (r = 0.95, P = 0.0003), f and DDC with air breathing were also observed (r = 0.95, P = 0.0004).Conclusion: Quantitative diffusion MRI demonstrated changes in tumor perfusion in response to oxygen challenge. J. Magn. Reson. Imaging 2015;42:1450–1457.

Identifying the extent of involvement of the vessel and nerve, particularly in regard to preoperative evaluation and precise localization of the tumor and its relation to the structures of the extremities, has important applications for advancing the treatment of lower extremity diseases. To review the technical feasibility of simultaneous visualization of nerves and vessels of the lower extremities by using magnetization-prepared susceptibility-weighted magnetic resonance (MR) imaging (MP-SWI) at 3.0T. Ten healthy volunteers and 10 patients were studied. Optimized MP-SWI, MR neurography (MRN) based on 3D diffusion-weighted steady-state free precession imaging and contrast-enhanced MR angiography (CE-MRA) sequences were performed for each subject. The means of signal-to-noise ratio (SNR)n, SNRv, SNRm, contrast-to-noise ratio (CNR)n,m and CNRv,m were calculated and the certainty of identifying nerves and vessels was determined. CNRn,m between MP-SWI and MRN, and CNRv,m between MP-SWI and CE-MRA were compared. MP-SWI provides slightly poorer CNRv,m than CE-MRA, whereas MP-SWI provides a better CNRn,m than MRN. In thin-slice-thickness maximum-intensity projection arbitrary planes, the sciatic nerve and its branches were clearly identified (score 1 or 2 of 2) in 17 subjects (85%); the femoral artery and the main branches were identified (score 1 or 2 of 2) in all 20 subjects (100%). The nerves are isointense to slightly hypointense to muscle, and the vessels show a more obvious hyperintense signal than muscle in MP-SWI. The proposed MP-SWI demonstrates the feasibility of simultaneously visualizing nerves and vessels of the lower extremities without using an exogenous contrast agent. It may enable straightforward localization of a disease process to a specific nerve and vessel.

Purpose: To assess tumor response to oxygen challenge using quantitative diffusion magnetic resonance imaging (MRI).Materials and Methods: A well‐characterized Dunning R3327‐AT1 rat prostate cancer line was implanted subcutaneously in the right thigh of male Copenhagen rats (n = 8). Diffusion‐weighted images (DWI) with multiple b values (0, 25, 50, 100, 150, 200, 300, 500, 1000, 1500 s/mm²) in three orthogonal directions were obtained using a multishot FSE‐based Stejskal‐Tanner DWI sequence (FSE‐DWI) at 4.7T, while rats breathed medical air (21% oxygen) and with 100% oxygen challenge. Stretched‐exponential and intravoxel incoherent motion (IVIM) models were used to calculate and compare quantitative diffusion parameters: diffusion heterogeneity index (α), intravoxel distribution of diffusion coefficients (DDC), tissue diffusivity (Dt), pseudo‐diffusivity (Dp), and perfusion fraction (f) on a voxel‐by‐voxel basis.Results: A significant increase of α (73.9 ± 4.7% in air vs. 78.1 ± 4.5% in oxygen, P = 0.0198) and a significant decrease of f (13.4 ± 3.7% in air vs. 10.4 ± 2.7% in oxygen, P = 0.0201) were observed to accompany oxygen challenge. Correlations between f and α during both air and oxygen breathing were found; the correlation coefficients (r) were −0.90 and −0.96, respectively. Positive correlations between Dt and DDC with oxygen breathing (r = 0.95, P = 0.0003), f and DDC with air breathing were also observed (r = 0.95, P = 0.0004).Conclusion: Quantitative diffusion MRI demonstrated changes in tumor perfusion in response to oxygen challenge. J. Magn. Reson. Imaging 2015;42:1450–1457.