Region-of-interest tomography using filtered backprojection: assessing the practical limits

Abstract

SummaryThere are many cases where it is desirable to reconstruct at high resolution a small volume from a larger sample. Here we describe the outcomes of a reconstruction trial based on real samples aimed at delineating the practical limits to which a small region of interest can be viewed from a large sample. Our approach has been to artificially truncate the sinograms of whole sample scans to simulate region of interest tomography. A simple filtered back projection algorithm has been applied, with the sinograms extended laterally in a simple manner to make up for the truncated portions. The impact of the degree of truncation (from 0% down to 99%), the number of projections used, as well as the position of the region of interest, on the faithfulness of the reconstruction is evaluated for a range of sample types. We have assessed the nature of, and extent to which, artefacts are introduced and the degree to which simple strategies can minimize them to an acceptable level without the need for complex reconstruction algorithms, projection stitching strategies or very large detectors. It is found that for a wide range of objects the effect of truncation on feature detection is negligible and that excellent images can be reconstructed if the number of projections is calculated not on the basis of the number of pixels on the camera, but on the number of pixels that would be required to scan the whole sample at the chosen pixel resolution. This paper demonstrates that in many cases more sophisticated reconstruction strategies are not necessary.

A practical local tomography reconstruction algorithm based on a known sub-region

“…For many applications, constant extrapolation provides acceptable results (Kyrieleis et al, 2011), although cupping artifact makes the segmentation challenging.…”

“…The Filtered Backprojection (FBP) with sinogram extrapolation is widely used in local tomography because it is both simple and gives satisfactory results in general (Kyrieleis et al, 2011). Theoretical investigations found that FBP provides a reconstructed function bearing the same discontinuities as the reference function (Bilgot et al, 2009) , although the cupping effect can make the segmentation challenging.…”

Challenges in imaging and predictive modeling of rhizosphere processes

“…A drawback with this method is that it requires very accurate registration of the two sets of radiographs (Kyrieleis et al 2011).…”

“…2). If this padding is carried out by extending the pixel values at the outer edges of each sinogram, and the number of projections is based not on the ROI diameter, but the diameter of the entire sample, the suppression of artifacts can be highly satisfactory (Kyrieleis et al 2011).…”

High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications

“…To avoid severe imaging artefacts, this volume should have similar size as the complete sample (Kyrieleis et al, 2011). For technological and computational reasons, is usually limited to several thousands of pixels, which sets a limit to the achievable voxel size as a function of the sample size.…”