Simple beam hardening correction method (2DCalBH) based on 2D linearization

Abstract

Objective: The polychromatic nature of the X-ray spectrum in CT leads to two types of artifacts in the reconstructed image: cupping in homogeneous areas and dark bands between dense parts, such as bones. This fact, together with the energy dependence of the mass attenuation coefficients of the tissues, results in erroneous values in the reconstructed image. Many post-processing correction schemes previously proposed require either knowledge of the X-ray spectrum or the heuristic selection of some parameters that have been shown to be suboptimal for correcting different slices in heterogeneous studies. In this study, we propose and validate a method to correct the beam hardening artifacts that avoids such restrictions and restores the quantitative character of the image. Approach: Our approach extends the idea of the water-linearization method. It uses a simple calibration phantom to characterize the attenuation for different soft tissue and bone combinations of the X-ray source polychromatic beam. The correction is based on the bone thickness traversed, obtained from a preliminary reconstruction. We evaluate the proposed method with simulations and real data using a phantom composed of PMMA and aluminum 6082 as materials equivalent to water and bone. Main results: Evaluation in simulated data showed a correction of the artifacts and a recovery of monochromatic values similar to that of post-processing techniques used for comparison, while it outperformed them on real data. Significance: The proposed method corrects beam hardening artifacts and restores monochromatic attenuation values with no need of spectrum knowledge or heuristic parameter tuning, based on the previous acquisition of a very simple calibration phantom.

Modeling CT images in the presence of beam hardening

“…This could not be done in previous similar methods (see e.g. [6], [8], [9], [11], [12]), since they were unable to reliably estimate the attenuation parameters.…”

“…These can be divided into several categories [1]. In this work, we consider the modeling and correction of artifacts which appear because of a physical phenomenon known as beam hardening [1], [6], [7], [8], [9], [10], [11]. This phenomenon occurs, because the attenuation properties of a material also depend on the energy level of the photons which make up the X-ray beams.…”

“…The correction of beam hardening artifacts is an intensively studied problem [6], [7], [8], [9], [10], [11], [12]. The most popular existing methods can be divided into two main categories.…”

“…In contrast, software based correction methods usually consider artifact removal as a post processing step of CT imaging [6], [7], [8], [9], [10], [11]. These approaches can be divided into three large subcategories: linearization [6], [9], dual energy [7], [10] and iterative methods [8], [11], [13]. Each of these approaches have their advantages, however iterative methods can be applied in more general settings (see e.g.…”

Simplified Beam Hardening Correction for Ultrafast X-ray CT Imaging of Binary Granular Mixtures

“…For the special case of single-material applications, a simple calibration with different material thicknesses can be applied. Theoretically, this approach can be extended to more materials [24], but with an exponentially growing effort on calibration data generation and storage, as each material length combination needs to be measured in advance. In general, however, more sophisticated methods are required.…”