Computer-aided volume measurement of choroidal melanomas.

Using a combination of conventional B-scan ultrasonography, standard video techniques, computer image digitization and area analysis, it is possible to measure the volume of choroidal melanomas by area calculation of successive ultrasound image slices, allowing the monitoring of such tumors. The design of a combined water-bath and linear tracking B-scan transducer is presented, together with a description of the instrumentation and computer software required. The results of volume measurements performed upon eye models demonstrated that melanomas of volume greater than 100 mm3 could be measured with an average error of 6%. The problems associated with linear calibration of the system from scan-head to analysed image, resolution of the digitised image, reproducibility of the measurements, sources of error and assumptions made in formulating the measurement procedure are discussed.