Akiko Imaizumi^{1,2}, Takayuki Obata^{1}, Yasuhiko Tachibana^{1}, Masayuki Inubushi^{3}, Mitsuru Koizumi^{4}, Kyosan Yoshikawa^{5}, Ming-Rong Zhang^{6}, Katsuyuki Tanimoto^{7}, Rintaro Harada^{8}, Takashi Uno^{8}, and Tsuneo Saga^{9}

To investigate the usefulness of diffusion-weighted imaging (DWI) for visualizing hypoxia of head and neck carcinoma, the correlation between DWI parameter estimates and ^{18}F-fluoroazomycin arabinoside (FAZA) positron emission tomography (PET) activity was evaluated.
The diffusion coefficients and fractions of the fast and slow compartments according to the 2-compartment model (D_{fast}, D_{slow} and F_{fast}, F_{slow}) were estimated. The diffusional kurtosis (K) and the corrected diffusion coefficient (D) were also obtained according to the diffusional kurtosis imaging (DKI) method.
Amongst the DWI estimates, D_{slow} and K were significantly correlated with FAZA-PET activity, which suggests they might be useful as indicators of hypoxia.

Purpose

Hypoxic tumors of the head and neck are highly malignant and have high resistance to radiotherapy and chemotherapy. An assessment of hypoxia is important for selecting a suitable treatment method (eg hypoxia-targeting therapy), and to predict its efficacy.Methods

Eleven patients with head and neck carcinoma (8 primary tumors and 5 lymph nodes without necrosis) were included in this retrospective study. DWI and FAZA-PET images were available as a part of a previous FAZA studyResults

A significant positive correlation between DDiscussion

The 2-compartment model divides the diffusing water molecules into fast and slow diffusion compartments. The slow compartment is thought to correspond to intracellular water molecules that interact highly with the cell membrane. Thus, destruction of cell membrane and increases in cell diameter may both contribute to elevate the diffusion coefficient of the slow compartment (DConclusion

The DWI parameters D1. Saga T, Inubushi M, Koizumi M, et al. Prognostic value of PET/CT with (18)F-fluoroazomycin arabinoside for patients with head and neck squamous cell carcinomas receiving chemoradiotherapy. Ann Nucl Med. 2016;30(3):217-224.

2. Tachibana Y, Obata T, Yoshida M, et al. Analysis of normal-appearing white matter of multiple sclerosis by tensor-based two-compartment model of water diffusion. Eur Radiol. 2015;25(6):1701-1707.

3. Kumar V, Abbas AK, Fausto N, Mitchell RN. Robbins basic pathology 8th edition. Chapter 1. Cell injury, cell death, and adaptations. Philadelphia, PA: Saunders Elsevier; 2007.

4. Tachibana Y, Obata T, Tsuchiya H, et al. Diffusion-tensor-based method for robust and practical estimation of axial and radial diffusional kurtosis. Eur Radiol. 2016;26(8):2559-2566.

Figure 1: Correlation between the tumor-muscle ratio (T/M) of ^{18}F-fluoroazomycin arabinoside positron emission tomography and diffusion-weighted imaging (DWI) parameter estimates. There was a positive correlation with significance between T/M and D_{slow} ( ρ=0.63, P=0.022) (a), and a negative correlation with significance between T/M and K ( ρ=-0.56, P=0.046) (b).