Quantitative and textural analysis of magnetization transfer and diffusion images in the early detection of brain metastases

Abstract

Purpose: The sensitivity of the magnetization transfer ratio (MTR) and apparent diffusion coefficient (ADC) for early detection of brain metastases was investigated in mice and humans.

Methods: Mice underwent MRI twice weekly for up to 31 days following intra-cardiac injection of the brain-homing breast cancer cell line MDA-MB231-BR. Patients with small cell lung cancer underwent quarterly MRI for a year. MTR and ADC were measured in regions of metastasis and matched contralateral tissue at the final time-point and in registered regions at earlier time-points. Texture analysis and linear discriminant analysis were performed to detect metastasis-containing slices.

Results: Compared with contralateral tissue, mouse metastases had significantly lower MTR and higher ADC at the final time-point. Some lesions were visible at earlier time-points on the MTR and ADC maps: 24% of these were not visible on corresponding T2-weighted images. Texture analysis using the MTR maps showed 100% specificity and 98% sensitivity for metastasis at the final time-point, with 77% sensitivity 2-4 days earlier and 46% 5-8 days earlier. Only 2/16 patients developed metastases, and their penultimate scans were normal.

Conclusion: Some brain metastases may be detected earlier on MTR than conventional T2; however, the small gain is unlikely to justify ‘predictive’ MRI.