Presentation Correlation between DWI bi-exponential estimates and PET hypoxia imaging activities in head and neck carcinoma

Imaizumi, Akiko  ,  Obata, Takayuki  ,  Inubushi, Masayuki  ,  Koizumi, Mitsuru  ,  Yoshikawa, Kyosan  ,  Ming-Rong, Zhang  ,  Tanimoto, Katsuyuki  ,  Harada, Rintaro  ,  Uno, Takashi  ,  Saga, Tsuneo

<B>Objective</B><BR>Hypoxic tumor has highly malignant property and resistance to radiotherapy and chemotherapy. Assessment of hypoxia is important for selection of treatment method, including hypoxia-targeting therapy, and prediction of treatment effect. <SUP>18</SUP>F-fluoroazomycin arabinoside (FAZA) positron emission tomography (PET) has been reported to be useful for hypoxia imaging, but it will take some time to become prevalent in clinical practice. Under hypoxia, alteration of cell structure leads to change in water diffusion. This change may be detected by diffusion-weighted magnetic resonance imaging (DWI) by bi-exponential model. The purpose of this study was to evaluate the correlation between DWI bi-exponential estimates and FAZA-PET activities and to investigate the usefulness of MRI for hypoxia imaging of head and neck carcinoma.<BR><B>Materials and Methods</B><BR>Eleven patients with head and neck carcinoma (8 primary tumors and 5 lymph nodes without necrosis) were included. They were the subjects that had this MRI protocol in the previous FAZA study [1]. By bi-exponential model, the diffusion coefficients of fast and slow components (Dfast, Dslow) and their fractions were obtained. Apparent diffusion coefficient (ADC) was also obtained at low and high b-value ranges (lowbADC, highbADC). On FAZA-PET images, tumor-muscle ratios (T/M) were measured for comparison between DWI bi-exponential and FAZA-PET estimates using Spearman’s rank correlation coefficient.<BR><B>Results</B><BR>There was a positive correlation between Dslow and T/M (rs=0.63, p=0.022). Dfast, fraction, lowbADC, or highbADC did not correlate with T/M.<BR><B>Conclusion</B><BR>Among bi-exponential estimates of DWI, only Dslow correlated with FAZA-PET parameter. Dslow might be useful as an indicator of hypoxia.<BR><B>Reference</B><BR>1. Saga, T., et al. ANN 30, 217-224.

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