Appendix E1

Percent enhancement (E) is a measure of the uptake of contrast material in a lesion calculated by obtaining pre- and postcontrast signal levels,

,

where E₁ is the initial percent enhancement, E_peak is the peak percent enhancement, S₁ is the signal intensity in the ROI at the first postcontrast point, S_peak is the peak signal intensity, and S₀ is the precontrast signal intensity in the ROI. 

Time to peak enhancement (T_peak) is the time in seconds between the injection of contrast material and the peak of the signal intensity–versus-time curve.

The parameter used to quantify washout is the signal enhancement ratio (SER), which is a measure of the relative signal intensity decrease from the first postcontrast time point to the final postcontrast point:

,

where S_last is the signal intensity in the ROI at the last postcontrast time point.  We can use the SER parameter to quantify washout by choosing threshold values.  A SER value of less than 0.9 means that the final signal intensity increases relative to the first postcontrast time point (persistent increase); a SER value between 0.9 and 1.1 indicates that the final signal intensity is comparable to the first postcontrast time point (plateau); and a SER greater than 1.1 indicates that the final signal intensity decreases relative to the first postcontrast time point (washout).

SER measures washout relative to the first postcontrast time point, whereas the BI-RADS assessment of delayed phase can involve any part of the kinetic curve.  SER values greater than 1.1 correspond to washout relative to the first postcontrast time point.  Therefore, any curves with SER greater than 1.1 that are classified as “plateau” or “persistent” are inconsistent.  SER values between 0.9 and 1.1 correspond to a plateau relative to the first postcontrast time point.  Therefore, any curves with 0.9 < SER < 1.1 that are classified as “persistent” are inconsistent.  Note that these plateau curves could be classified as “washout” curves; the curve may peak at the second postcontrast time point, for example, and wash out from then on but still be classified as a plateau curve relative to the first postcontrast time point.  SER values less than 0.9 correspond to a persistent signal increase relative to the first postcontrast time point.  Note that these persistent curves could be classified as “plateau” or “washout” as well, depending on the curve data at other time points.