Diffusion-Weighted Imaging to Assess HPV-Positive versus HPV-Negative Oropharyngeal Squamous Cell Carcinoma: The Importance of b-Values.

BACKGROUND AND PURPOSE: Controversy exists as to whether ADC histograms are capable to distinguish human papillomavirus-positive (HPV+) from human papillomavirus-negative (HPV-) oropharyngeal squamous cell carcinoma. We investigated how the choice of b-values influences the capability of ADC histograms to distinguish between the two tumor types. MATERIALS AND METHODS: Thirty-four consecutive patients with histologically proved primary oropharyngeal squamous cell carcinoma (11 HPV+ and 23 HPV-) underwent 3T MR imaging with a single-shot EPI DWI sequence with 6 b-values (0, 50, 100, 500, 750, 1000 s/mm2). Monoexponentially calculated perfusion-sensitive (including b=0 s/mm2) and perfusion-insensitive/true diffusion ADC maps (with b ≥ 100 s/mm2 as the lowest b-value) were generated using Matlab. The choice of b-values included 2 b-values (ADCb0-1000, ADCb100-1000, ADCb500-1000, ADCb750-1000) and 3-6 b-values (ADCb0-750-1000, ADCb0-500-750-1000, ADCb0-50-100-1000, ADCb0-50-100-750-1000, ADCb0-50-100-500-750-1000). Readers blinded to the HPV- status contoured all tumors. ROIs were then copied onto ADC maps, and their histograms were compared. RESULTS: ADC histogram metrics in HPV+ and HPV- oropharyngeal squamous cell carcinoma changed significantly depending on the b-values. The mean ADC was lower, and skewness was higher in HPV+ than in HPV- oropharyngeal squamous cell carcinoma only for ADCb0-1000, ADCb0-750-1000, and ADCb0-500-750-1000 (P < .05), allowing distinction between the 2 tumor types. Kurtosis was significantly higher in HPV+ versus HPV- oropharyngeal squamous cell carcinoma for all b-value combinations except 2 perfusion-insensitive maps (ADCb500-1000 and ADCb750-1000). Among all b-value combinations, kurtosis on ADCb0-1000 had the highest diagnostic performance to distinguish HPV+ from HPV- oropharyngeal squamous cell carcinoma (area under the curve = 0.893; sensitivity = 100%, specificity = 82.6%). Acquiring multiple b-values for ADC calculation did not improve the distinction between HPV+ and HPV- oropharyngeal squamous cell carcinoma. CONCLUSIONS: The choice of b-values significantly affects ADC histogram metrics in oropharyngeal squamous cell carcinoma. Distinguishing HPV+ from HPV- oropharyngeal squamous cell carcinoma is best possible on the ADCb0-1000 map.