• Apparent diffusion coefficient
• Correlation of functional parameters
• Diffusion-weighted MR imaging
• Head and neck squamous cell carcinoma
• PET/CT

Background: The relationship between imaging functional parameters in squamous cell carcinoma of the upper aerodigestive tract (SCUAT) is of increasing interest because could have clinical implications such as in earlier diagnosis, prediction of treatment responses, evaluation of treatment outcome and guidance for treatment planning.
Purpose: To analyze the relationship between tumor biologic characteristics derived from 18F-FDG PET/CT and diffusion weighted imaging-MRI (DWI-MRI) in untreated and treated patients with SCUAD.
Material and methods: In 32 untreated and 20 treated enrolled patients, we correlate primary (SUVmax, SUVmin, SUVpeak) and secondary (SUVmean, TLV, MTV) semi-quantitative uptake values with apparent diffusion coefficient (ADC) functional parameters (ADCmin, ADCmean, ADCsd, ADCskewness and ADCkurtosis) in both primary lesion and lymph nodes, with regard to therapy (before and after chemo-radiotherapy).
Results: In treated patients, non-parametric Spearman test revealed a moderately strong inverse correlation between SUVmax and ADCmean (P = 0.000, r = -0.528), SUVmin and both ADCmin and ADCmean (P = 0.001, r = -0.427; P = 0.000, r = -0.483), SUVpeak and both ADCmin and ADCmean (P = 0.001, r = -0.419; P = 0.000, r = -0.580), SUVmean and ADCmean (P = 0.000, r = -0.514), ADCsd and SUVmax (P = 0.000, r = -0.501), SUVpeak (P = 0.000, r = -0.542), SUVmean (P = 0.000, r = -0.460), MTV (P = 0.000, r = -0.459) and TLG (P = 0.000, r = 0.525), respectively.

Conclusion: The demonstrated relationships suggest complex interactions between biological characteristics of tumor. These diagnostic techniques might play a complementary role in the assessment of SCUAT.