Strain processing of intraoperative ultrasound images of brain tumours: initial results

The purpose of the study was to investigate a method for strain calculation and its ability to discriminate between brain tumour and normal brain. During surgery of a low-grade astrocytoma and a metastasis, we acquired ultrasound (US) radiofrequency (RF) data with a hand-held probe at the dura mater. Using cross-correlation and phase-sensitive processing, we quantified the tissue displacements between consecutive US images and, subsequently, the local strain. In the elastograms, the tumour lesions were associated with lower strain levels than those found in the surrounding normal tissue. For both investigated cases, the strain images showed good agreement with the B-mode images. However, the results also indicated that the tumour interpretation might be different in the two modalities. An important finding was that the tissue motion caused by arterial pulsation is sufficient for generating elastograms. Requiring no specialised equipment or changes to acquisition procedures, strain data can be obtained as easily as conventional US imaging.