Volume measurement in sequential freehand 3-D ultrasound

It has previously been demonstrated that using 3-D rather than 2-D ultrasound can increase the accuracy of volume measurements. Unfortunately, the time required to produce them is also increased. While freehand 3-D ultrasound allows complete freedom of movement during scanning. the resulting B-scans are generally resampled onto a low resolution, regular voxel array before subsequent processing - increasing the time even further. In contrast, sequential freehand 3-D ultrasound does not require a voxel array, and hence both the data resolution and the processing times are improved. Such a system is presented here, incorporating three novel algorithms, each operating directly on non-parallel B-scans. Volume is measured using Cubic planimetry, which requires fewer planes than step-section planimetry for a given accuracy. Maximal disc guided interpolation can be used to interpolate non-parallel cross-sections. Regularised marching tetrahedra can then be used to provide a regular triangulation of the zero iso-surface of the interpolated data. The first of these algorithms is presented in detail in this paper.