title: Pulsed and oscillating gradient MRI for assessment of cell size and extracellular space (POMACE) in mouse gliomas.
abstract: Solid tumor microstructure is related to the aggressiveness of the tumor, interstitial pressure and drug delivery pathways, which are closely associated with treatment response, metastatic spread and prognosis. In this study, we introduce a novel diffusion MRI data analysis framework, pulsed and oscillating gradient MRI for assessment of cell size and extracellular space (POMACE), and demonstrate its feasibility in a mouse tumor model. In vivo and ex vivo POMACE experiments were performed on mice bearing the GL261 murine glioma model (n = 8). Since the complete diffusion time dependence is in general non-analytical, the tumor microstructure was modeled in an appropriate time/frequency regime by impermeable spheres (radius Rcell , intracellular diffusivity Dics ) surrounded by extracellular space (ECS) (approximated by constant apparent diffusivity Decs in volume fraction ECS). POMACE parametric maps (ECS, Rcell , Dics , Decs ) were compared with conventional diffusion-weighted imaging metrics, electron microscopy (EM), alternative ECS determination based on effective medium theory (EMT), and optical microscopy performed on the same samples. It was shown that Decs can be approximated by its long time tortuosity limit in the range [1/(88 Hz)-31 ms]. ECS estimations (44 ± 7% in vivo and 54 ± 11% ex vivo) were in agreement with EMT-based ECS and literature on brain gliomas. Ex vivo, ECS maps correlated well with optical microscopy. Cell sizes (Rcell  = 4.8 ± 1.3 in vivo and 4.3 ± 1.4 µm ex vivo) were consistent with EM measurements (4.7 ± 1.8 µm). In conclusion, Rcell and ECS can be quantified and mapped in vivo and ex vivo in brain tumors using the proposed POMACE method. Our experimental results support the view that POMACE provides a way to interpret the frequency or time dependence of the diffusion coefficient in tumors in terms of objective biophysical parameters of neuronal tissue, which can be used for non-invasive monitoring of preclinical cancer studies and treatment efficacy. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, USA. oli.reynaud@gmail.com.|Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA. oli.reynaud@gmail.com.
authors.forename: Olivier
authors.initials: O
authors.lastname: Reynaud
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, USA.|Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA.
authors.forename: Kerryanne Veronica
authors.initials: KV
authors.lastname: Winters
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, USA.|Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA.
authors.forename: Dung Minh
authors.initials: DM
authors.lastname: Hoang
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, USA.|Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA.
authors.forename: Youssef Zaim
authors.initials: YZ
authors.lastname: Wadghiri
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, USA.|Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA.
authors.forename: Dmitry S
authors.initials: DS
authors.lastname: Novikov
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, USA.|Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA.
authors.forename: Sungheon Gene
authors.initials: SG
authors.lastname: Kim
mesh_terms: D000818:Animals; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology*; D045744:Cell Line, Tumor; D048429:Cell Size; D003198:Computer Simulation; D005110:Extracellular Space; D005240:Feasibility Studies; D005260:Female; D005910:Glioma / Q000000981:diagnostic imaging / Q000473:pathology*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D009991:Oscillometry / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D047368:Tumor Burden
keywords: POMACE; diffusion time dependence; extracellular space; glioma; oscillating gradient spin echo; restrictions