No abstract

This study aims to quantify the heterogeneity of tumour enhancement in dynamic contrast-enhanced MRI (DCE-MRI) using texture analysis methods. The suitability of the coherence and the fractal dimension to monitor tumour response was evaluated in 18 patients with limb sarcomas imaged by DCE-MRI pre- and post-treatment. According to the histopathology, tumours were classified into responders and non-responders. Pharmacokinetic (K(trans)) and heuristic model-based parametric maps (slope, max enhancement, AUC) were computed from the DCE-MRI data. A substantial correlation was found between the pharmacokinetic and heuristic model-based parametric maps: ρ = 0.56 for the slope, ρ = 0.44 for maximum enhancement, and ρ = 0.61 for AUC. From all four parametric maps, the enhancing fraction, and the heterogeneity features (i.e. coherence and fractal dimension) were determined. In terms of monitoring tumour response, using both pre- and post-treatment DCE-MRI, the enhancing fraction and the coherence showed significant differences between the response group and the non-response group (i.e. the highest sensitivity (91%) for K(trans), and the highest specificity (83%) for max enhancement). In terms of treatment prediction, using solely the pre-treatment DCE-MRI, the enhancing fraction and coherence discriminated between responders and non-responders. For prediction, the highest sensitivity (91%) was shared by K(trans), slope and max enhancement, and the highest specificity (71%) was achieved by K(trans). On average, tumours that responded showed a high enhancing fraction and high coherence on the pre-treatment scan. These results suggest that specific heterogeneity features, computed from both pharmacokinetic and heuristic model-based parametric maps, show potential as a biomarker for monitoring tumour response.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) using macromolecular contrast media enables assessments of the tumor vasculature based on the differential distribution of the contrast agent within normal and pathologic tissues. Quantitative assays of both morphologic and functional properties can provide useful diagnostic insight into tissue angiogenesis. The use of MRI enhanced with macromolecular agents for the characterization of tumor microvessels has been experimentally demonstrated in a range of malignant tumor types. Kinetic analysis of DCE-MRI data can be used to estimate microvascular permeability and tumor blood volume. By measuring these functional tumor properties, an accurate, noninvasive, and quantitative description of the microcirculation of individual tumors can be acquired, improving the specificity of imaging examinations for cancer diagnosis and for treatment and follow up. The noninvasive MRI assessment of tumor angiogenesis can be applied in the diagnostic differentiation between benign and malignant tumors and can also provide means for in vivo monitoring of antitumor therapy. In this review, the potential clinical applications and limitations of various macromolecular contrast agents applied for evaluations of tumor angiogenesis, with and without drug interventions, are discussed.