Figure 1

Measurement of ADC metrics from brain metastases on diffusion-weighted MRI scans. A patient with a history of lung adenocarcinoma presents with headache and focal neurological deficit. A. Postcontrast T1-weighted sequence demonstrates a right frontal lesion, which was confirmed as a metastasis after excision. B. An ADC map is generated from B = 0.1000 images using post processing software. On this color map, blue areas represent low ADC and red higher ADC. C. A freehand region of interest is traced around the tumor border using the postcontrast T1-weighted sequence as reference on the axial slice with the largest tumor area and those immediately above and below. The ADCmin is the lowest bin of a histogram of ADC values for all pixels contained within this ROI, averaged over these three slices. Three ROI are placed within the tumor on the axial slice with the largest area, avoiding necrosis, haemorrhage, cyst and the mean taken to give ADCmean. D. To assess change of ADC across the tumor border, four ROI are placed starting just inside the tumor border and extending out into the peritumoral region. The slope of the four ADC values is taken as the “ADC transition coefficient” or ATC. This is repeated in 3 orthogonal directions, avoiding structures such as ventricle or falx and then repeated on two slices above and below, with the ATC being the mean of the 9 readings.