1. A method for 3-D volume image reconstruction of a subject, comprising: obtaining a plurality of 2-D projection images over a range of scan angles using partial scan cone-beam computed tomography; identifying, by a computer processor, one or more truncated projected images along a horizontal direction in one or more truncated images across all of the view of the plurality of 2-D projection images; forming, by the computer processor, from each of the one or more truncated projected images, a corrected truncated projection image by a repeated process comprising: (i) adaptively assigning an extension length for the rows that are truncated in the current truncated projection images; (ii) identifying the truncated projection view that has the largest extended length; (iii) recalculating the scanning fan angle based on the largest extended length calculated in step (i); (iv) applying an adjusted weighting factor based on the recalculated scanning fan angle; (v) extending the truncated projection image data for the rows that are truncated in the current truncated projection image by applying a cosine function to each value in the extension length; and reconstructing, by the computer processor, the 3-D volume image incorporating the corrected truncated projection images; wherein forming the corrected truncated projected image further comprises adjusting a weighting factor by increasing an x-ray fan angle value to calculate weighting coefficients for an increased range of angles; and wherein the cosine function is a first cosine function and wherein assigning the extension length comprises applying a second cosine function according to row location in the projected image.