Table 1.

Treatment response features. Reprinted, with permission, from ACR [5]

Features	Definitions
Viability	Presence of live tumor cells within or along the margin of a treated lesion. Radiologic viability is not synonymous with pathologic viability as imaging is not sensitive to microscopic or small foci of residual tumor.
Treatment-specific expected enhancement	Expected temporal and spatial pattern of posttreatment enhancement attributable to treatment-related changes in parenchymal perfusion. Posttreatment enhancement patterns may not reliably differentiate viable from nonviable tumor. The most appropriate response category may be LR-TR Equivocal.
No lesional enhancement	Absence of enhancement within or along the margin of a treated lesion. Note: complete disappearance after locoregional treatment is considered equivalent to absence of enhancement.
Posttreatment APHE	Nodular, masslike, or thick and irregular arterial phase hyperenhancement (APHE) contained within or along the margin of a treated lesion suggests posttreatment tumor viability.
Posttreatment “washout”	Nodular, masslike, or thick and irregular washout appearance contained within or along the margin of a treated lesion suggests posttreatment tumor viability.
Posttreatment enhancement similar to pretreatment	Nodular, masslike, or thick and irregular enhancement similar to pretreatment enhancement in all postcontrast phases contained within or along the margin of a treated lesion suggests posttreatment tumor viability, even in the absence of APHE or washout appearance.