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

Color-coded maps in 2 different patients with OPSCC (same patients as in Fig 1) illustrating changes in ADC pixel values and distribution caused by the choice of b-values. T2 images and corresponding b=1000 images with tumor ROIs (in yellow) are shown on the left. The upper 2 rows on the right show the color-coded ADC maps of the HPV+ OPSCC, while the lower 2 rows show the respective maps of the HPV– OPSCC. For all images, the same color map with the same quantitative scale (0–3000 ×10⁻⁶mm²/s) was used to display the original gray levels. Note the clearly visible difference between HPV+ versus HPV– OPSCC on the ADC maps with b=0, with HPV+ OPSCC having lower ADCs and less ROI heterogeneity than HPV– OPSCC. This difference disappears on maps calculated with higher b-values only, and the distinction between the 2 tumor types is visually hardly possible on maps calculated with b ≥ 500. The 2 readers correctly identified the HPV+ and the HPV– OPSCC on the first 7 ADC maps; they failed, however, to correctly distinguish between the 2 tumor types on the last 2 ADC maps.