A method and an apparatus for three-dimensional imaging of ultrasound data by reducing speckle artifact data before the acquired data from a volume of interest is projected onto an image plane. An ultrasound scanner collects B-mode or color flow mode images in a cine memory, i.e., for a multiplicity of slices. The data from a respective region of interest for each slice is sent to a master controller, such data forming a volume of interest. The master controller performs an algorithm that iteratively projects the pixel data in the volume of interest onto a plurality of rotated image planes using a ray-casting technique. Prior to projection, the master controller smooths the speckle contained in the pixel data filtering using a convolution filter having a nine-point kernel. Convolution filtering of image data is carried out by defining a desired area of the image, such as an area represented by an array of pixels, by weighting each of the pixels in the array with a respective weighting coefficient, and then by summing the weighted pixels to produce a filtered pixel value which is substituted for the central pixel in the array. The filtered pixel data forms a new data volume which is then projected onto each successive image plane.