Diffusion-Weighted Imaging to Assess HPV-Positive versus HPV-Negative Oropharyngeal Squamous Cell Carcinoma: The Importance of b-Values
Vincent Lenoir, Bénédicte M. A. Delattre, Yacine M’Rad, Claudio De Vito, Thomas de Perrot, Minerva Becker
Abstract
<h3>BACKGROUND AND PURPOSE:</h3> 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. <h3>MATERIALS AND METHODS:</h3> 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/mm<sup>2</sup>). Monoexponentially calculated perfusion-sensitive (including <i>b</i>=0 s/mm<sup>2</sup>) and perfusion-insensitive/true diffusion ADC maps (with b ≥ 100 s/mm<sup>2</sup> as the lowest b-value) were generated using Matlab. The choice of b-values included 2 b-values (ADC<sub>b0–1000</sub>, ADC<sub>b100–1000</sub>, ADC<sub>b500–1000</sub>, ADC<sub>b750–1000</sub>) and 3–6 b-values (ADC<sub>b0–750–1000</sub>, ADC<sub>b0–500–750–1000</sub>, ADC<sub>b0–50–100–1000</sub>, ADC<sub>b0–50–100–750–1000</sub>, ADC<sub>b0–50–100–500–750–1000</sub>). Readers blinded to the HPV– status contoured all tumors. ROIs were then copied onto ADC maps, and their histograms were compared. <h3>RESULTS:</h3> 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 ADC<sub>b0–1000,</sub> ADC<sub>b0–750–1000</sub>, and ADC<sub>b0–500–750–1000</sub> (<i>P</i> < .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 (ADC<sub>b500–1000</sub> and ADC<sub>b750–1000</sub>). Among all b-value combinations, kurtosis on ADC<sub>b0–1000</sub> 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. <h3>CONCLUSIONS:</h3> 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 ADC<sub>b0–1000</sub> map.