RESUMO
Objective. Beam hardening (BH) artifacts in computed tomography (CT) images originate from the polychromatic nature of x-ray photons. In a CT system with a bowtie filter, residual BH artifacts remain when polynomial fits are used. These artifacts lead to worse visuals, reduced contrast, and inaccurate CT numbers. This work proposes a pixel-by-pixel correction (PPC) method to reduce the residual BH artifacts caused by a bowtie filter.Approach. The energy spectrum for each pixel at the detector after the photons pass through the bowtie filter was calculated. Then, the spectrum was filtered through a series of water slabs with different thicknesses. The polychromatic projection corresponding to the thickness of the water slab for each detector pixel could be obtained. Next, we carried out a water slab experiment with a mono energyE= 69 keV to get the monochromatic projection. The polychromatic and monochromatic projections were then fitted with a 2nd-order polynomial. The proposed method was evaluated on digital phantoms in a virtual CT system and phantoms in a real CT machine.Main results. In the case of a virtual CT system, the standard deviation of the line profile was reduced by 23.8%, 37.3%, and 14.3%, respectively, in the water phantom with different shapes. The difference of the linear attenuation coefficients (LAC) in the central and peripheral areas of an image was reduced from 0.010 to 0.003cm-1and 0.007cm-1to 0 in the biological tissue phantom and human phantom, respectively. The method was also validated using CT projection data obtained from Activion16 (Canon Medical Systems, Japan). The difference in the LAC in the central and peripheral areas can be reduced by a factor of two.Significance. The proposed PPC method can successfully remove the cupping artifacts in both virtual and authentic CT images. The scanned object's shapes and materials do not affect the technique.
Assuntos
Artefatos , Processamento de Imagem Assistida por Computador , Imagens de Fantasmas , Tomografia Computadorizada por Raios X , Tomografia Computadorizada por Raios X/métodos , Processamento de Imagem Assistida por Computador/métodos , HumanosRESUMO
RATIONALE AND OBJECTIVES: To compare degradation of the image quality due to beam hardening artifacts in reduced-iodine-dose virtual monochromatic imaging (VMI) between a new fast kVp switching dual-energy computed tomography (CT) scanner (Revolution CT) and the conventional dual-energy scanner (Discovery CT). MATERIALS AND METHODS: First, a phantom study was performed to quantitatively evaluate beam hardening artifacts in images obtained by VMI reconstruction at different energy levels. In the second study, we performed a retrospective evaluation of the images of 28 patients who had undergone reduced-iodine (300 mg/kg) dual-energy scanning in both Revolution CT and Discovery CT. We evaluated each image quantitatively by measuring the contrast-to-noise ratio (CNR) and qualitatively by scoring the artifacts and image quality. We also calculated the modulation transfer function (MTF) and noise power spectrum (NPS) of the two scanners. RESULTS: In the phantom study, VMI reconstruction of the CT images at 40-70 keV was associated with a significantly greater reduction in the severity of the artifacts in the Revolution CT images as compared to the Discovery CT images. In the retrospective study, there were no significant differences in the CT value of the aorta, noise, or CNR between the two scanners, but the scores for image quality were significantly higher in the Revolution CT images as compared to the Discovery CT images. The MTF of Revolution CT was higher than that of Discovery CT, reflecting the better spatial resolution. CONCLUSION: In Revolution CT, beam hardening artifacts were reduced in reduced-iodine VMI at lower energy levels compared to Discovery CT, contributing to better image quality.
Assuntos
Artefatos , Iodo , Humanos , Interpretação de Imagem Radiográfica Assistida por Computador , Estudos Retrospectivos , Razão Sinal-Ruído , Tomografia Computadorizada por Raios XRESUMO
INTRODUCTION: Limited field of view cone-beam computed tomographic (CBCT) imaging has been used to augment clinical testing of vertical root fractures (VRFs); however, the presence of gutta-percha (GP) in the canal space generates substantial imaging artifacts that make fracture detection difficult. The purpose of this study was to evaluate the influence of a zirconium (Zr)-based root filling material with radiologic properties that reduce beam hardening (BH) artifacts using CBCT imaging in the in vitro diagnosis of VRFs. METHODS: One hundred seventy-six single-rooted mandibular premolar teeth were obtained, and half of these teeth were filled with GP or Zr (CPoint; EndoTechnologies, LLC, Shrewsbury, MA). VRFs were induced in 44 decoronated teeth in each group using an Instron (Norwood, MA) Universal Testing Machine. Each root was then placed in a dry human mandible and imaged with the Carestream 9000 3D CBCT system (Carestream Dental, Atlanta, GA). The images were evaluated by 6 oral maxillofacial radiologists (OMRs) and residents. RESULTS: The sensitivity was greater for detecting VRFs in the Zr group than the GP group (P = .035). However, the specificity was greater for the GP group than the Zr group (P = .028). Receiver operating characteristic area under the curve values were greater for the Zr group than the GP group, but these differences were not statistically significant. The OMRs outperformed the residents in the detection of VRFs in the Zr group with respect to specificity (P = .006) and positive predictive value (P = .012). CONCLUSIONS: The reduced BH of the Zr group improved the sensitivity of the detection of artificially induced VRFs. The ability to detect VRFs in the Zr group was further enhanced by clinical experience.
Assuntos
Tomografia Computadorizada de Feixe Cônico , Radiografia Dentária , Materiais Restauradores do Canal Radicular/uso terapêutico , Fraturas dos Dentes/etiologia , Raiz Dentária/lesões , Zircônio/uso terapêutico , Artefatos , Humanos , Fraturas dos Dentes/diagnóstico por imagem , Raiz Dentária/diagnóstico por imagem , Microtomografia por Raio-XRESUMO
INTRODUCTION: The beam hardening (BH) artifact produced by root filling materials in cone-beam computed tomographic (CBCT) images is influenced by their radiologic K absorption edge values. The purpose of this study was to describe a novel technique to characterize BH artifacts in CBCT images produced by 3 root canal filling materials and to evaluate the effects of a zirconium (Zr)-based root filling material with a lower K edge (17.99 keV) on the production of BH artifacts. METHODS: The palatal root canals of 3 phantom model teeth were prepared and root filled with gutta-percha (GP), a Zr root filling material, and calcium hydroxide paste. Each phantom tooth was individually imaged using the CS 9000 CBCT unit (Carestream, Atlanta, GA). The "light" and "dark" components of the BH artifacts were quantified separately using ImageJ software (National Institutes of Health, Bethesda, MD) in 3 regions of the root. Mixed-design analysis of variance was used to evaluate differences in the artifact area for the light and dark elements of the BH artifacts. RESULTS: A statistically significant difference in the area of the dark portion of the BH artifact was found between all fill materials and in all regions of the phantom tooth root (P < .05). GP generated a significantly greater dark but not light artifact area compared with Zr (P < .05). Moreover, statistically significant differences between the areas of both the light and dark artifacts were observed within all regions of the tooth root, with the greatest artifact being generated in the coronal third of the root (P < .001). CONCLUSIONS: Root canal filling materials with lower K edge material properties reduce BH artifacts along the entire length of the root canal and reduce the contribution of the dark artifact.
Assuntos
Tomografia Computadorizada de Feixe Cônico/métodos , Radiografia Dentária/métodos , Artefatos , Cavidade Pulpar/diagnóstico por imagem , Humanos , Imagens de Fantasmas , Materiais Restauradores do Canal RadicularRESUMO
Conventional computed tomography (CT) uses a polychromatic energy beam to offer superb anatomic detail of the head and spine. However, technical challenges remain that can degrade the diagnostic image quality of these examinations. Dual-energy CT analyzes the changes in attenuation of soft tissues at different energy levels, from which different reconstructions can be made to yield the optimal contrast-to-noise ratio, reduce beam-hardening artifact, or evaluate tissue composition. In this article, selective applications of the dual energy CT technique are discussed, highlighting a powerful tool in the diagnostic CT evaluation of the head, neck, and spine.
Assuntos
Artefatos , Neoplasias de Cabeça e Pescoço/diagnóstico por imagem , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Imagem Radiográfica a Partir de Emissão de Duplo Fóton/métodos , Doenças da Coluna Vertebral/diagnóstico por imagem , Humanos , Tomografia Computadorizada por Raios X/métodosRESUMO
PURPOSE: The aim of this study was to evaluate the image quality of hand tendons using dual-energy computed tomographic gemstone spectral imaging (DECT GSI) compared with conventional CT images. MATERIALS AND METHODS: Forty patients scanned with GSI mode on DECT were enrolled. The 65-keV optimal contrast-to-noise ratio for viewing hand tendons was selected. The image quality of monochromatic GSI images (65 keV) and conventional CT images was compared with two different methods including a subjective method and an objective method by two radiologists, respectively. RESULTS: In the subjective method, the image quality in GSI images was superior to conventional CT images (P<.05). And in the objective method, the beam-hardening artifacts in the phalanges of finger space were reduced markedly, with hand tendons displaying more clearly in GSI images (P<.05). There was no significant difference between the two radiologists in both methods, with good correlation (kappa=0.75, kappa=0.85). CONCLUSION: DECT GSI with the optimal 65-keV monochromatic images could reduce the artifacts and increase image quality significantly in hand tendons imaging. It might be very useful in detecting tendon diseases in routine work.