Dynamic breast MR imaging: is parametric mapping superior to image subtraction in lesion detection?

We compared the detection of malignant lesions in two different methods of parametric-guided analysis to the widely used early subtraction images. The parametric colour-coded overlays were defined by the increase of signal intensity after contrast injection and the course of the time signal intensity curve. Exams of 30 patients with histopathological evidence of 32 invasive breast carcinomas were evaluated. Five hundred five areas of additional enhancing tissue were found in the early subtraction images. The sensitivity was 100 in the subtraction images and 100 and 93.8 in the parametric images, respectively, the specificity 67.5, 84.2 and 88.7, respectively. On average 4.4 ROI-measurements were needed to find the highest increase of signal intensity in the subtraction series compared to 1.9 in the parametric images. Properly selected thresholds in parametric imaging may be helpful in the differentiation of enhancing tissue. Furthermore the parametric image-guided ROI selection significantly speeds up the analysis and makes it safer as a lower rate of ROI-measurements is needed to find the strongest enhancement.