ABSTRACT The non-invasive, cost-effective and radiation-free methodology of ultrasound imaging procedures makes it a convenient tool for the detection of tumours. But, usually, the diagnosis efficiency and accuracy of detection is affected by speckle, intensity inhomogeneities and low contrast. For tumour detection, identifying and segmenting the tumour region is vital. In this proposed work, active contours based segmentation is employed with the initial contour achieved using a thresholding method involving a novel concept of phase gradients. Initially, the raw US image is de-speckled and enhanced using the neutrosophic transformation concept. This pre-processed US image is then thresholded using adaptive constraints derived from the mean, texture (using Gabor filters), gradient, phase information and phase gradient of the image. Then the obtained thresholded image is used as the initial mask/contour for segmentation based on active contours using localized image energies. The proposed methodology gave improved tumour boundary delineations even for challenging tumour echogenicities.