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X-ray microtomography: three-dimensional reconstruction methods for x-ray microscopy of biological samples

Biological soft x-ray microscopy using x-ray optics and synchrotron sources has made possible quantitative, element-specific imaging of whole cells in aqueous media at significantly higher resolutions than those of conventional visible light methods. Tomographic reconstruction has been proposed as a means to realize the full potential of the method for viewing thick objects whose structures would otherwise be superimposed in single view projections. The authors present an iterative tomographic reconstruction algorithm, using a regularized weighted least squares objective function, accelerated with the conjugate gradient approach, and modified for the problem of transmission tomography with correction of blurring by an instrumental point spread function. The non-negativity constraint is implemented using a preconditioner. We show by computer simulations that reconstructions that meet realistic and acceptable goals for spatial and density resolution should be achievable at doses compatible with the structural integrity of biological samples at the specific resolution.