1. A method for obtaining a three-dimensional volume image of a sample, the method comprising: obtaining, by dark-field microscopy, a plurality of two-dimensional images from the sample, the plurality of images comprising at least one two-dimensional image taken at each of a plurality of equally spaced sample locations along a direction of focus, each two-dimensional image containing both in-focus and out-of-focus light from the sample; inputting the plurality of two-dimensional images to a three-dimensional computational method for determining a location of at least one structure present in the sample; and formulating a three-dimensional volume image of the sample, the three-dimensional image showing the location of the at least one structure present in the sample.