#Beam hardening artifact meaning free#

Then, cone beam CT was used to scan the fixed base plate twice. Methods: The 5mm-diameter metal ball and resin ball were fixed on the light-cured resin base plate respectively, while four vitro molars were fixed above and below the ball, on the left and right respectively, which have 10mm distance with the metal ball. Objectives: Based on the pixel gray value measurements, establish a beam-hardening artifacts index of the cone- beam CT tomographic image, and preliminarily evaluate its applicability. Yuan, Fusong Lv, Peijun Yang, Huifang Wang, Yong Sun, Yuchun

#Beam hardening artifact meaning free#

Since the element geometry projections are free from the effect of beam hardening, the nearly linear weighted sum of them, the synthetical geometry projections, are almost free from the effect of beamĪn index of beam hardening artifact for two-dimensional cone- beam CT tomographic images: establishment and preliminary evaluation In a simulation example, the normalized root mean square difference (NRMSD) can be reduced 17.52% compared to a newest algorithm. Several examples demonstrate the proposed approach is efficient in reducing beam hardening artifacts and has satisfactory performance in the term of some general criteria. The image gray values are adjusted according to the attenuation coefficient means to obtain proper CT numbers. The underlying images are obtained using the projections by general reconstruction algorithms such as the filtered back projection (FBP).

In this process, the attenuation coefficients are modified to make Newton-Raphson iterative functions satisfy the convergence conditions of fixed pointed iteration(FPI) so that the solutions will approach the true synthetical geometry projections stably. The solutions are named as the synthetical geometry projections, which are the nearly linear weighted sum of element geometry projections with respect to mean of each attenuation coefficient. Newton-Raphson algorithm is employed to solve the functions. With help of a prior knowledge on spectrum distribution of X-ray beam source and energy-dependent attenuation coefficients, the functions have explicit expressions. According to Lambert-Beer law, the (detected) projections can be expressed as monotonic nonlinear functions of element geometry projections, which are the theoretical projections produced only by the pixel intensities (image grayscale) of certain element (component). An iterative approach is proposed to reduce beam hardening artifact caused by metallic components in polychromatic X-ray CT. The beam hardening artifact is one of most important modalities of metal artifact for polychromatic X-ray computed tomography (CT), which can impair the image quality seriously. Reduce beam hardening artifacts ofÂ polychromatic X-ray computed tomography by an iterative approximation approach. The BHC algorithm could significantly improve image quality in CT scans with metallic screws, whereas MAR algorithm could alleviate artifacts in hip-implants and dentalfillings. Results of the study indicate that beam hardening could be a dominant source of artifact in many spine and extremity fixations, whereas dental and hip implants could be dominant source of photon starvation. Comparison of BHC and MAR on different metallic implants was used to characterize dominant source of the artifacts, and conceivable methods to overcome those. The data included spine fixation screws, hip-implants, dental-filling, and body extremity fixations, covering range of clinically used metal implants. In the MAR algorithm, the corrupted projection samples are replaced by the combination of original projections and in-painted data obtained by forward projecting a prior image. Stainless-steel and Titanium were used to model and correct for metal beam hardening effect.

In this work, a metal beam hardening correction (BHC) and a projection-completion based metal artifact reduction (MAR) algorithms were developed, and applied on phantom and clinical CT scans with various metallic implants. A comparison of CT images obtained with different metallic hardware in various applications, along with acquisition and reconstruction parameters, helps understand methods for reducing or overcoming such artifacts. The cause and occurrence of metal- artifacts are primarily due to beam hardening, scatter, partial volume and photon starvation however, the contribution to the artifacts from each of them depends on the type of hardware. The presence of metal- artifacts in CT imaging can obscure relevant anatomy and interfere with disease diagnosis. Reduction of metal artifacts: beam hardening and photon starvation effects