A method for refining shape estimates of detected abnormalities in medical images, particularly for the detection of pulmonary lesions in CT imagery is described. The design provides a high power, ultra-low frequency oval projector having a number of applications, including underwater seismic prospecting and fish mitigation. The method further includes mapping the extracted reference feature information to the graphical representation of the bone, receiving information indicative of a positional landmark associated with the bone, and estimating an intersection between the positional landmark and the mapped reference feature. The apparatus further comprises a data processing device which generates the processed data to obtain an outgoing frequency spectrum wherein a frequency component causing interference with a low frequent component of the markings is suppressed or not present.