Dual Layer CT

Vlassenbroek, Alain

doi:10.1007/174_2010_56

Cited by 30 publications

(31 citation statements)

References 11 publications

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“…The high noise of the ratio map propagates to the final material specific images, and can be observed by the modest-sized error bars of Figures 4, 7 and 9. This is a well-known problem for dual-energy imaging (22), and while various noise reduction techniques have been proposed (32, 33), evaluation of those techniques were beyond the scope of our proof-of-concept work. A second disadvantage with DSCT is the slightly lower temporal resolution due to the 90° offset of the two sources (34).…”

Section: Discussionmentioning

confidence: 99%

“…For the CMEP, unlike MD, the binary intervals that correspond to pure materials remain independent of the other materials chosen for extraction. Probabilistic definition of the regions between known ratio values has been proposed as an alternative to the gradient regions (22), however these preclude the existence of multiple materials within a given voxel. A final limitation is the CT number dependency of the final extracted images on the E3 image chosen.…”

Section: Discussionmentioning

confidence: 99%

“…Dual-energy ratios tend to be independent of concentration for a given material (18), and as a result of this robust behavior have received attention recently for screening the separability of different elements for MD (18, 19), and for evaluation of DECT source filtration options (20, 21). Despite their conceptual simplicity and utility, dual-energy ratios have only been used on a limited scale, including separation of iodine from calcium (22), bone removal (23), and determination of different kidney stone compositions (24). …”

Section: Introductionmentioning

confidence: 99%

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An Image-Domain Contrast Material Extraction Method for Dual-Energy Computed Tomography

et al. 2017

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Objectives Conventional material decomposition techniques for dual-energy CT (DECT) assume mass or volume conservation, where the CT number of each voxel is fully assigned to predefined materials. We present an image-domain contrast material extraction process (CMEP) method that preferentially extracts contrast-producing materials while leaving the remaining image intact. Materials and Methods Image processing freeware (Fiji) is used to perform consecutive arithmetic operations on a dual-energy ratio map to generate masks, which are then applied to the original images to generate material-specific images. First, a low-energy image is divided by a high-energy image to generate a ratio map. The ratio map is then split into material-specific masks. Ratio intervals known to correspond to particular materials (e.g. iodine, calcium) are assigned a multiplier of 1, while ratio values in between these intervals are assigned linear gradients from 0 to 1. The masks are then multiplied by an original CT image to produce material-specific images. The method was tested quantitatively at Dual-Source (DSCT) and Rapid kVp-Switching CT (RSCT) with phantoms using pure and mixed formulations of tungsten, calcium and iodine. Errors were evaluated by comparing the known material concentrations with those derived from the CMEP material-specific images. Further qualitative evaluation was performed in vivo at RSCT with a rabbit model using identical CMEP parameters to the phantom. Orally administered tungsten, vascularly administered iodine, and skeletal calcium were used as the three contrast materials. Results All five material combinations; tungsten, iodine and calcium, and mixtures of tungsten-calcium and iodine-calcium, showed distinct dual-energy ratios, largely independent of material concentration at both DSCT and RSCT. The CMEP was successful in both phantoms and in vivo. For pure contrast materials in the phantom, the maximum error between the known and CMEP-derived material concentrations was 0.9 mg/mL, 24.9 mg/mL and 0.4 mg/mL for iodine, calcium and tungsten respectively. Mixtures of iodine and calcium showed the highest discrepancies, which reflected the sensitivity of iodine to the image-type chosen for the extraction of the final material-specific image. The rabbit model was able to clearly show the three extracted material phases, vascular iodine, oral tungsten and skeletal calcium. Some skeletal calcium was misassigned to the extracted iodine image, however this did not impede the depiction of the vasculature. Conclusions The CMEP is a straightforward, image domain approach to extract material signal at dual-energy CT. It has particular value for separation of experimental high-Z contrast elements from conventional iodine contrast or calcium, even when the exact attenuation coefficient profiles of desired contrast materials may be unknown. The CMEP is readily implemented in the image-domain within freeware, and can be adapted for use with images from multiple vendors.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An Image-Domain Contrast Material Extraction Method for Dual-Energy Computed Tomography

et al. 2017

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“…This on the one hand provides a low‐ and high‐energy dataset, but on the other hand has its limitations with respect to conventional imaging. The main limitation for kV switching is that both energy scans are limited to the same filtration, and therefore have a relatively high overlap of the energy spectra, and for dual X‐ray sources the main limitations are a reduced field‐of‐view and cross scattering . These limitations may be acceptable, because the benefits of DECT imaging may outweigh the limitations in certain diagnostic examinations.…”

Section: Introductionmentioning

confidence: 99%

“…The top layer is more sensitive to the low‐energy photons, whereas the bottom detector layer absorbs more of the high‐energy photons. This essentially separates a single X‐ray beam into two components . The use of a dual‐layer detector enables retrospective dual‐energy analysis on every recorded dataset acquired at high tube voltage (e.g.…”

Section: Introductionmentioning

confidence: 99%

Image quality of conventional images of dual‐layer SPECTRAL CT: A phantom study

et al. 2018

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Purpose: Spectral CT using a dual layer detector offers the possibility of retrospectively introducing spectral information to conventional CT images. In theory, the dual-layer technology should not come with a dose or image quality penalty for conventional images. In this study, we evaluate the influence of a dual-layer detector (IQon Spectral CT, Philips Healthcare) on the image quality of conventional CT images, by comparing these images with those of a conventional but otherwise technically comparable single-layer CT scanner (Brilliance iCT, Philips Healthcare), by means of phantom experiments. Methods: For both CT scanners, conventional CT images were acquired using four adult scanning protocols: (a) body helical, (b) body axial, (c) head helical, and (d) head axial. A CATPHAN 600 phantom was scanned to conduct an assessment of image quality metrics at equivalent (CTDI) dose levels. Noise was characterized by means of noise power spectra (NPS) and standard deviation (SD) of a uniform region, and spatial resolution was evaluated with modulation transfer functions (MTF) of a tungsten wire. In addition, contrast-to-noise ratio (CNR), image uniformity, CT number linearity, slice thickness, slice spacing, and spatial linearity were measured and evaluated. Additional measurements of CNR, resolution and noise were performed in two larger phantoms. Results: The resolution levels at 50%, 10%, and 5% MTF of the iCT and IQon showed small, but significant differences up to 0.25 lp/cm for body scans, and up to 0.2 lp/cm for head scans in favor of the IQon. The iCT and IQon showed perfect CT linearity for body scans, but for head scans both scanners showed an underestimation of the CT numbers of materials with a high opacity. Slice thickness was slightly overestimated for both scanners. Slice spacing was comparable and reconstructed correctly. In addition, spatial linearity was excellent for both scanners, with a maximum error of 0.11 mm. CNR was higher on the IQon compared to the iCT for both normal and larger phantoms with differences up to 0.51. Spatial resolution did not change with phantom size, but noise levels increased significantly. For head scans, IQon had a noise level that was significantly lower than the iCT, on the other hand IQon showed noise levels significantly higher than the iCT for body scans. Still, these differences were well within the specified range of performance of iCT scanners. Conclusions: At equivalent dose levels, this study showed similar quality of conventional images acquired on iCT and IQon for medium-sized phantoms and slightly degraded image quality for (very) large phantoms at lower tube voltages on the IQon. Accordingly, it may be concluded that the introduction of a dual-layer detector neither compromises image quality of conventional images nor increases radiation dose for normal-sized patients, and slightly degrades dose efficiency for large patients at 120 kVp and lower tube voltages.

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Dual-Layer Spectral–Computed Tomography Enhances the Separability of Calcium-Based Implant Material from Bone: An Ex Vivo Quantitative Imaging Study

Peña

Shaul²,

Müller

et al. 2020

Journal of Bone and Mineral Research

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Local treatment of bone loss with an injection of a resorbable, calcium-based implant material to replace bone has a long history of clinical use. The in vivo discrimination of changes in bone versus implant is challenging with standard computed tomography (CT). However, spectral-CT techniques enable the separation between tissues of similar densities but different chemical compositions. Dual-layer spectral-CT imaging and postprocessing analysis methods were applied to investigate the separability of AGN1 (a triphasic calcium-based implant) and bone after AGN1 injection in n = 10 male cadaveric femurs ex vivo. Using the area under the curve (AUC) from receiver-operating characteristic (ROC) analyses, the separability of AGN1 from bone was assessed for AGN1 (postoperatively) versus compact and versus femoral neck cancellous bone (both preoperatively). CT techniques included conventional Hounsfield (HU) and density-equivalent units (BMD, mg hydroxyapatite [HA]/cm 3 ) and spectral-CT measures of effective atomic number (Zeff ) and electron density (ED). The samples had a wide range of femoral neck BMD (55.66 to 241.71 mg HA/cm 3 ). At the injection site average BMD, HU, Zeff, and ED increased from 69.5 mg HA/cm 3 , 109 HU, 104.38 EDW, and 8.30 Zeff in the preoperative to 1233 mg HA/cm 3 , 1741 HU, 181.27 EDW, and 13.55 Zeff in the postoperative CT scan, respectively. For compact bone at the femoral shaft the preoperative values were 1124.15 mg HA/cm 3 , 1648 HU, 177 EDW, and 13.06 Zeff and were maintained postoperatively. Zeff showed substantially sharper distributions and significantly greater separability compared to ED, BMD, and HU (all p < 0.002, for both regions) with average AUCs for BMD, HU, ED, and Zeff of 0.670, 0.640, 0.645, and 0.753 for AGN1 versus compact and 0.996, 0.995, 0.994, and 0.998 for AGN1 versus femoral neck cancellous sites, respectively. Spectral-CT permits better discrimination of calciumbased implants like AGN1 from bone ex vivo. Our results warrant application of spectral-CT in patients undergoing procedures with similar implants.

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Dual Layer CT

Cited by 30 publications

References 11 publications

An Image-Domain Contrast Material Extraction Method for Dual-Energy Computed Tomography

An Image-Domain Contrast Material Extraction Method for Dual-Energy Computed Tomography

Image quality of conventional images of dual‐layer SPECTRAL CT: A phantom study

Dual-Layer Spectral–Computed Tomography Enhances the Separability of Calcium-Based Implant Material from Bone: An Ex Vivo Quantitative Imaging Study

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