Three-dimensional (3-D) image reconstruction algorithms from plane integral projection data by Lauterbur and later by Shopp are described and the improved version which has better efficiency in computation, is proposed. Experiment was performed with the KAIS NMR TOMOGRAPH and sets of 3-D NMR tomograms of a human head were obtained. These show the high signal-to-noise ratio images of various orientations. Further study on the optimization of angular sampling scheme applicable to any kinds of the 3-D projection reconstruction methods was carried out and the results are presented.