Virtual Objects Research Articles

The Neural Correlates of Embodied L2 Learning: Does Embodied L2 Verb Learning Affect Representation and Retention?

Abstract We investigated how naturalistic actions in a highly immersive, multimodal, interactive 3D virtual reality (VR) environment may enhance word encoding by recording EEG in a pre/post-test learning paradigm. While behavior data have shown that coupling word encoding with gestures congruent with word meaning enhances learning, the neural underpinnings of this effect have yet to be elucidated. We coupled EEG recording with VR to examine whether embodied learning improves learning and creates linguistic representations that produce greater motor resonance. Participants learned action verbs in an L2 in two different conditions: specific action (observing and performing congruent actions on virtual objects) and pointing (observing actions and pointing to virtual objects). Pre- and post-training participants performed a match–mismatch task as we measured EEG (variation in the N400 response as a function of match between observed actions and auditory verbs) and a passive listening task while we measured motor activation (mu [8–13 Hz] and beta band [13–30 Hz] desynchronization during auditory verb processing) during verb processing. Contrary to our expectations, post-training results revealed neither semantic nor motor effects in either group when considered independently of learning success. Behavioral results showed a great deal of variability in learning success. When considering performance, low performance learners showed no semantic effect and high performance learners exhibited an N400 effect for mismatch versus match trials post-training, independent of the type of learning. Taken as a whole, our results suggest that embodied processes can play an important role in L2 learning.

Virtual reality modelling for planning of percutaneous first step palliation in a newborn with heterotaxy syndrome.

We report the first-stage percutaneous palliation in a newborn with a rare heterotaxy syndrome variant including interrupted inferior vena cava, partial anomalous pulmonary venous drainage, and restrictive interatrial communication. Virtual reality imaging aided visualisation, decision-making, and planning. Successful atrial septoplasty performed via the internal jugular vein and anomalous pulmonary vein was followed by stenting of ductus arteriosus.

Impact of scatter radiation on spectral quantification performance of first- and second-generation dual-layer spectral computed tomography.

To assess the impact of scatter radiation on quantitative performance of first and second-generation dual-layer spectral computed tomography (DLCT) systems. A phantom with two iodine inserts (1 and 2mg/mL) configured to intentionally introduce high scattering conditions was scanned with a first- and second-generation DLCT. Collimation widths (maximum of 4cm for first generation and 8cm for second generation) and radiation dose levels were varied. To evaluate the performance of both systems, the mean CT numbers of virtual monoenergetic images (MonoEs) at different energies were calculated and compared to expected values. MonoEs at 50 versus 150keV were plotted to assess material characterization of both DLCTs. Additionally, iodine concentrations were determined, plotted, and compared against expected values. For each experimental scenario, absolute errors were reported. An experimental setup, including a phantom design, was successfully implemented to simulate high scatter radiation imaging conditions. Both CT scanners illustrated high spectral accuracy for small collimation widths (1 and 2cm). With increased collimation (4cm), the second-generation DLCT outperformed the earlier DLCT system. Further, the spectral performance of the second-generation DLCT at an 8cm collimation width was comparable to a 4cm collimation on the first-generation DLCT. A comparison of the absolute errors between both systems at lower energy MonoEs illustrates that, for the same acquisition parameters, the second-generation DLCT generated results with decreased errors. Similarly, the maximum error in iodine quantification was less with second-generation DLCT (0.45 and 0.33mg/mL for the first and second-generation DLCT, respectively). The implementation of a two-dimensional anti-scatter grid in the second-generation DLCT improves the spectral quantification performance. In the clinical routine, this improvement may enable additional clinical benefits, for example, in lung imaging.

Low-contrast detectability of photon-counting-detector CT at different scan modes and image types in comparison with energy-integrating-detector CT.

We aim to compare the low-contrast detectability of a clinical whole-body photon-counting-detector (PCD)-CT at different scan modes and image types with an energy-integrating-detector (EID)-CT. We used a channelized Hotelling observer (CHO) previously optimized for quality control purposes. An American College of Radiology CT accreditation phantom was scanned on both PCD-CT and EID-CT with 10 phantom positionings. For PCD-CT, images were generated using two scan modes, standard resolution (SR) and ultra-high-resolution (UHR); two image types, virtual monochromatic images at 70keV and low-energy threshold (T3D); both filtered-back-projection (FBP) and iterative reconstruction (IR) reconstruction methods; and three reconstruction kernels. For each positioning, three repeated scans were acquired for each scan mode, image type, and CTDIvol of 6, 12, and 24mGy. For EID-CT, images acquired from scans (10 positionings × 3 repeats × 3 doses) were reconstructed using the closest counterpart FBP and IR kernels. CHO was applied to calculate the index of detectability () on both scanners. With the smooth Br44 kernel, the of UHR was mostly comparable with that of the SR mode (difference: -11.4% to 8.3%, to 0.956), and the T3D images had a higher (difference: 0.7% to 25.6%) than 70keV images on PCD-CT. Compared with the EID-CT, UHR-T3D of PCD-CT had non-inferior (difference: -2.7% to 12.9%) with IR and non-superior (difference: 0.8% to 11.2%) with FBP using the Br44 kernel. PCD-CT produced higher than EID-CT by 61.8% to 247.1% with the sharper reconstruction kernels. The comparison between PCD-CT and EID-CT was significantly influenced by the reconstruction method and kernel. With a smooth kernel that is typically used in low-contrast detection tasks, the PCD-CT demonstrated low-contrast detectability that was comparable to EID-CT with IR and showed no superiority when using FBP. With the use of sharper kernels, the PCD-CT significantly outperformed EID-CT in low-contrast detectability.

Improved noise reduction in photon-counting detector CT using prior knowledge-aware iterative denoising neural network.

We aim to reduce image noise in high-resolution (HR) virtual monoenergetic images (VMIs) from photon-counting detector (PCD) CT scans by developing a prior knowledge-aware iterative denoising neural network (PKAID-Net) that efficiently exploits the unique noise characteristics of VMIs at different energy (keV) levels. PKAID-Net offers two major features: first, it utilizes a lower-noise VMI (e.g., 70keV) as a prior input; second, it iteratively constructs a refined training dataset to improve the neural network's denoising performance. In each iteration, the denoised image from the previous module serves as an updated target image, which is included in the dataset for the subsequent training iteration. Our study includes 10 patient coronary CT angiography exams acquired on a clinical dual-source PCD-CT (NAEOTOM Alpha, Siemens Healthineers). The HR VMIs were reconstructed at 50, 70, and 100keV, using a sharp vascular kernel (Bv68) and thin (0.6mm) slice thickness (0.3mm increment). PKAID-Net's performance was evaluated in terms of image noise, spatial detail preservation, and quantitative accuracy. PKAID-Net achieved a noise reduction of 96% compared to filtered back projection and 65% relative to iterative reconstruction, all while preserving spatial and spectral fidelity and maintaining a natural noise texture. The iterative refinement of PCD-CT data during the training process substantially enhanced the robustness of deep learning-based denoising compared to the original method, which resulted in some spatial detail loss. The PKAID-Net provides substantial noise reduction while maintaining spatial and spectral fidelity of the HR VMIs from PCD-CT.

Interacting with virtual characters, objects and environments: investigating immersive virtual reality in rehabilitation

Purpose This pilot study aimed to (a) investigate opportunities for immersive Virtual Reality (VR) technology in communication, physical, and visual rehabilitation by examining the interaction of people without disabilities in a range of structured virtual environments; and (b) validate research protocols that might be used to evaluate the physical, visual, and verbal interaction of users in virtual worlds, and their safety while using the technology. Methods Thirteen adults identifying as people without disability were exposed to VR via a head-mounted display. A video-review method was used to qualitatively code and analyse each participant’s communication, movement, orientation, and support needs. Results All participants oriented to their virtual environments sufficiently to use applications. Their spoken language was effective for interaction, although unconventional social behaviours were also observed. Two participants reported minor adverse reactions consistent with mild cybersickness. Conclusion The results provide insight into the types of environments and characters that support the greatest communicative, physical, and visual interaction in immersive VR. The tested protocols are useful to assess safety when using VR, and to observe communicative, physical, and visual interaction with virtual environments and characters. Implications for future research and use of VR with people with communication, physical and visual disability are discussed.

Manufacturing reflection holographic couplers for see-through applications recorded in photopolymers without prisms: an experimental validation.

In the present work, the viability of a novel recording geometry to produce reflection holographic couplers is analyzed. Recalling the idea of previous works, photopolymers are used as the recording material because they have been proven to be well-suited for the intended see-through application: the capability to provide a virtual image without compromising the information about the surrounding environment. Moreover, holography fundamentals give us the proper background to examine the proposed design, where no prisms or microlenses arrays are used. Aiming to support the analysis, we provide experimental evidence that the produced reflection holographic gratings exhibit the correct properties to work as a coupler, where the sensitivity of the material and its properties are studied and examined.

Task-based automatic keV selection: leveraging routine virtual monoenergetic imaging for dose reduction on clinical photon-counting detector CT * *Portions presented at RSNA 2021 and 2022.

Objective. Photon-counting detector (PCD) CT enables routine virtual-monoenergetic image (VMI) reconstruction. We evaluated the performance of an automatic VMI energy level (keV) selection tool on a clinical PCD-CT system in comparison to an automatic tube potential (kV) selection tool from an energy-integrating-detector (EID) CT system from the same manufacturer. Approach. Four torso-shaped phantoms (20–50 cm width) containing iodine (2, 5, and 10 mg cc−1) and calcium (100 mg cc−1) were scanned on PCD-CT and EID-CT. Dose optimization techniques, task-based VMI energy level and tube-potential selection on PCD-CT (CARE keV) and task-based tube potential selection on EID-CT (CARE kV), were enabled. CT numbers, image noise, and dose-normalized contrast-to-noise ratio (CNRd) were compared. Main results. PCD-CT produced task-specific VMIs at 70, 65, 60, and 55 keV for non-contrast, bone, soft tissue with contrast, and vascular settings, respectively. A 120 kV tube potential was automatically selected on PCD-CT for all scans. In comparison, EID-CT used x-ray tube potentials from 80 to 150 kV based on imaging task and phantom size. PCD-CT achieved consistent dose reduction at 9%, 21% and 39% for bone, soft tissue with contrast, and vascular tasks relative to the non-contrast task, independent of phantom size. On EID-CT, dose reduction factor for contrast tasks relative to the non-contrast task ranged from a 65% decrease (vascular task, 70 kV, 20 cm phantom) to a 21% increase (soft tissue with contrast task, 150 kV, 50 cm phantom) due to size-specific tube potential adaptation. PCD-CT CNRd was equivalent to or higher than those of EID-CT for all tasks and phantom sizes, except for the vascular task with 20 cm phantom, where 70 kV EID-CT CNRd outperformed 55 keV PCD-CT images. Significance. PCD-CT produced more consistent CT numbers compared to EID-CT due to standardized VMI output, which greatly benefits standardization efforts and facilitates radiation dose reduction.

Comparing MRI and arthroscopic appearances of common knee pathologies: A pictorial review

Knee pathology, including anterior cruciate ligament (ACL) tears, meniscal tears, articular cartilage lesions, and intra-articular masses or cysts are common clinical entities treated by orthopedic surgeons with arthroscopic surgery. Preoperatively, magnetic resonance imaging (MRI) is now standard in confirming knee pathology, particularly detecting pathology less evident with history and physical examination alone. The radiologist’s MRI interpretation becomes essential in evaluating intra-articular knee structures. Typically, the radiologist that interprets the MRI does not have the opportunity to view the same pathology arthroscopically. Thus, the purpose of this article is to illustratively reconcile what the orthopedic surgeon sees arthroscopically with what the radiologist sees on magnetic resonance imaging when viewing the same pathology. Correlating virtual and actual images can help better understand pathology, resulting in more accurate MRI interpretations. In this article, we present and review a series of MR and correlating arthroscopic images of ACL tears, meniscal tears, chondral lesions, and intra-articular masses and cysts. Short teaching points are included to highlight the importance of radiological signs and pathological MRI appearance with significant clinical and arthroscopic findings.

A clinical-radiomics nomogram based on spectral CT multi-parameter images for preoperative prediction of lymph node metastasis in colorectal cancer.

To develop a clinical-radiomics nomogram based on spectral CT multi-parameter images for predicting lymph node metastasis in colorectal cancer. A total of 76 patients with colorectal cancer and 156 lymph nodes were included. The clinical data of the patients were collected, including gender, age, tumor location and size, preoperative tumor markers, etc. Three sets of conventional images in the arterial, venous, and delayed phases were obtained, and six sets of spectral images were reconstructed using the arterial phase spectral data, including virtual monoenergetic images (40keV, 70keV, 100keV), iodine density maps, iodine no water maps, and virtual non-contrast images. Radiomics features of lymph nodes were extracted from the above images, respectively. Univariate analysis and least absolute shrinkage and selection operator (LASSO) regression were used to select features. A clinical model was constructed based on age and carcinoembryonic antigen (CEA) levels. The radiomics featuresselected were used to generate a composedradiomics signature (Com-RS). A nomogram was developed using age, CEA, and theCom-RS. The models' prediction efficiency, calibration, and clinical application value were evaluated by the area under the receiver operating characteristic curve (AUC), calibration curve, and decision curve analysis, respectively. The nomogram outperforms the clinical model and the Com-RS (AUC = 0.879, 0.824). It is well calibrated and has great clinical application value. This study developed a clinical-radiomics nomogram based on spectral CT multi-parameter images, which can be used as an effective tool for preoperative personalized prediction of lymph node metastasis in colorectal cancer.

Advanced Imaging of Total Knee Arthroplasty.

The prevalence of total knee arthroplasty (TKA) is increasing with the aging population. Although long-term results are satisfactory, suspected postoperative complications often require imaging with the implant in place. Advancements in computed tomography (CT), such as tin prefiltration, metal artifact reduction algorithms, dual-energy CT with virtual monoenergetic imaging postprocessing, and the application of cone-beam CT and photon-counting detector CT, allow a better depiction of the tissues adjacent to the metal. For magnetic resonance imaging (MRI), high bandwidth (BW) optimization, the combination of view angle tilting and high BW, as well as multispectral imaging techniques with multiacquisition variable-resonance image combination or slice encoding metal artifact correction, have significantly improved imaging around metal implants, turning MRI into a useful clinical tool for patients with suspected TKA complications.

Update on Renal Cell Carcinoma Diagnosis with Novel Imaging Approaches.

This review highlights recent advances in renal cell carcinoma (RCC) imaging. It begins with dual-energy computed tomography (DECT), which has demonstrated a high diagnostic accuracy in the evaluation of renal masses. Several studies have suggested the potential benefits of iodine quantification, particularly for distinguishing low-attenuation, true enhancing solid masses from hyperdense cysts. By determining whether or not a renal mass is present, DECT could avoid the need for additional imaging studies, thereby reducing healthcare costs. DECT can also provide virtual unenhanced images, helping to reduce radiation exposure. The review then provides an update focusing on the advantages of multiparametric magnetic resonance (MR) imaging performance in the histological subtyping of RCC and in the differentiation of benign from malignant renal masses. A proposed standardized stepwise reading of images helps to identify clear cell RCC and papillary RCC with a high accuracy. Contrast-enhanced ultrasound may represent a promising diagnostic tool for the characterization of solid and cystic renal masses. Several combined pharmaceutical imaging strategies using both sestamibi and PSMA offer new opportunities in the diagnosis and staging of RCC, but their role in risk stratification needs to be evaluated. Although radiomics and tumor texture analysis are hampered by poor reproducibility and need standardization, they show promise in identifying new biomarkers for predicting tumor histology, clinical outcomes, overall survival, and the response to therapy. They have a wide range of potential applications but are still in the research phase. Artificial intelligence (AI) has shown encouraging results in tumor classification, grade, and prognosis. It is expected to play an important role in assessing the treatment response and advancing personalized medicine. The review then focuses on recently updated algorithms and guidelines. The Bosniak classification version 2019 incorporates MRI, precisely defines previously vague imaging terms, and allows a greater proportion of masses to be placed in lower-risk classes. Recent studies have reported an improved specificity of the higher-risk categories and better inter-reader agreement. The clear cell likelihood score, which adds standardization to the characterization of solid renal masses on MRI, has been validated in recent studies with high interobserver agreement. Finally, the review discusses the key imaging implications of the 2017 AUA guidelines for renal masses and localized renal cancer.

Measurement method of virtual image distance for a head-mounted display based on a variable-focus liquid lens

The distance from the virtual image to the human eye is an important factor in measuring the comfort of a head-mounted display (HMD). However, accurately measuring their distance is challenging due to the dynamic changes in virtual presence and distance. In this paper, we proposed a virtual image distance measurement prototype based on a variable-focus liquid lens and derived a virtual image distance calculation model. We built a variable-focus liquid lens experimental platform to verify the method’s correctness. In addition, we proposed an improved optimization algorithm that can efficiently and accurately search for the optimal focal length corresponding to the maximum sharpness moment of the virtual image within the focal length value space. Verified in an experimental scene of 0.5 m to 3.5 m, we observed that the error between the object image distance and the virtual image distance at the same focal length is about 5 cm. The proposed virtual image distance measurement method can accurately measure the distance value of the virtual image in the HMD. This method can be widely used in virtual and augmented reality, especially in the task of constructing realistic scenes.

Application of virtual endoscopic imaging to parapelvic cyst incision by flexible ureteroscopy: a multicenter retrospective cohort study.

A three-dimensional (3D) reconstruction of the kidney, parapelvic cyst and the collecting system was conducted using the 3D Slicer software. The reconstructed image was used to form a virtual endoscope to assist flexible ureteroscopic incision and drainage was performed with a holmium laser for treating parapelvic cysts. The effectiveness of this assistive technique was assessed. This was a retrospective cohort study. The clinical information of 59 patients undergoing flexible ureteroscopic incision and drainage for parapelvic cysts in two medical centers was collected. 3D Slicer software reconstruction and virtual endoscopic imaging were performed for 28 cases. Before the operation, the best point for incision on the collecting system's mucosa was assessed by virtual endoscope imaging. Propensity score matching was adopted for the reconstructive and non-reconstructive groups. After matching, the reconstructive group and non-reconstructive group both had 21 cases each. The operation time in the reconstructive and non-reconstructive groups was 38.81±5.01 and 51.00±18 minutes, respectively. Statistically significant differences existed between the two groups (t=7.024, P<0.001). No statistical significance was found in postoperative fever, immediate postoperative C reactive protein (CRP), length of postoperative hospital stay and cyst diameter three months after the operation. The operator was provided with a more direct and real vision when 3D Slicer software reconstruction was adopted via virtual endoscopic imaging to assist flexible ureteroscopic parapelvic cyst incision. This helped reduce the operation time. Further follow-ups and observations are required to assess the long-term efficacy of flexible ureteroscopic parapelvic cyst incision.

The Assessment of Airway Compression Due to Cervical Fusion in Klippel-Feil Syndrome Patients: A Report of Two Cases.

In general anesthesia for Klippel-Feil syndrome (KFS) patients, there is a potential risk of difficult intubation. However, airway assessment to predict difficult intubation for KFS patients is not known. In Patient 1, cervical spine computed tomography (CT) revealed airway compression due to cervical fusion. For airway assessment, bronchofiberscopy, three-dimensional (3-D) CT, and virtual bronchoscopic image (VBI) construction were performed. Based on these images, fiberoptic nasotracheal awake intubation was performed. In Patient 2, magnetic resonance imaging and bronchofiberscopy showed no airway compression due to cervical fusion; therefore, tracheal intubation was performed using a video laryngoscope after anesthetic administration. Airway compression due to cervical fusion is considered one of the risk factors for difficult intubation in KFS patients.

Electron density dual-energy CT can improve the detection of lumbar disc herniation with higher image quality than standard and virtual non-calcium images.

To compare the diagnostic performance and image quality of dual-energy computed tomography (DECT) with electron density (ED) image reconstruction with those of DECT with standard CT (SC) and virtual non-calcium (VNCa) image reconstructions, for diagnosing lumbar disc herniation (L-HIVD). A total of 59 patients (354 intervertebral discs from T12/L1 to L5/S1; mean age, 60 years; 30 women and 29 men) who underwent DECT with spectral reconstruction and 3-T MRI within 2 weeks were enrolled between March 2021 and February 2022. Four radiologists independently assessed three image sets of randomized ED, SC, and VNCa images to detect L-HIVD at 8-week intervals. The coefficient of variance (CV) and the Weber contrast of the ROIs in the normal and diseased disc to cerebrospinal fluid space (NCR-normal/-diseased, respectively) were calculated to compare the image qualities of the noiseless ED and other series. Overall, 129 L-HIVDs were noted on MRI. In the detection of L-HIVD, ED showed a higher AUC and sensitivity than SC and VNCa; 0.871 vs 0.807 vs 833 (p = 0.002) and 81% vs 70% vs 74% (p = 0.006 for SC), respectively. CV was much lower in all measurements of ED than those for SC and VNCa (p < 0.001). Furthermore, NCR-normal and NCR-diseased were the highest in ED (ED vs SC in NCR-normal and NCR-diseased, p = 0.001 and p = 0.004, respectively; ED vs VNCa in NCR-diseased, p = 0.044). Compared to SC and VNCa images, DECT with ED reconstruction can enhance the AUC and sensitivity of L-HIVD detection with a lower CV and higher NCR. To our knowledge, this is the first study to quantify the image quality of noiseless ED images. ED imaging may be helpful for detecting L-HIVD in patients who cannot undergo MRI. ED images have diagnostic potential, but relevant quantitative analyses of image quality are limited. ED images detect disc herniation, with a better coefficient of variance and normalized contrast ratio values. ED images could detect L-HIVD when MRI is not an option.

Countering Calcium Blooming With Personalized Contrast Media Injection Protocols: The 1-2-3 Rule for Photon-Counting Detector CCTA.

Photon-counting detector computed tomography (PCD-CT) enables spectral data acquisition of CT angiographies allowing for reconstruction of virtual monoenergetic images (VMIs) in routine practice. Specifically, it has potential to reduce the blooming artifacts associated with densely calcified plaques. However, calcium blooming and iodine attenuation are inversely affected by energy level (keV) of the VMIs, creating a challenge for contrast media (CM) injection protocol optimization. A pragmatic and simple rule for calcium-dependent CM injection protocols is investigated and proposed for VMI-based coronary CT angiography with PCD-CT. A physiological circulation phantom with coronary vessels including calcified lesions (maximum CT value >700 HU) with a 50% diameter stenosis was injected into at iodine delivery rates (IDRs) of 0.3, 0.5, 0.7, 1.0, 1.5, 2.0, 2.5, and 3.0 g I/s. Images were acquired using a first-generation dual-source PCD-CT and reconstructed at various VMI levels (between 45 and 190 keV). Iodine attenuation in the coronaries was measured at each IDR for each keV, and blooming artifacts from the calcified lesions were assessed including stenosis grading error (as % overestimation vs true lumen). The IDR to achieve 300 HU at each VMI level was then calculated and compared with stenosis grading accuracy to establish a general rule for CM injection protocols. Plaque blooming artifacts and intraluminal iodine attenuation decreased with increasing keV. Fixed windowing (representing absolute worst case) resulted in stenosis overestimation from 77% ± 4% at 45 keV to 5% ± 2% at 190 keV, whereas optimized windowing resulted in overestimation from 29% ± 3% at 45 keV to 4% ± 1% at 190 keV. The required IDR to achieve 300 HU showed a strong linear correlation to VMI energy (R2 = 0.98). Comparison of this linear plot versus stenosis grading error and blooming artifact demonstrated that multipliers of 1, 2, and 3 times the reference IDR for theoretical clinical regimes of no, moderate, and severe calcification density, respectively, can be proposed as a general rule. This study provides a proof-of-concept in an anthropomorphic phantom for a simple pragmatic adaptation of CM injection protocols in coronary CT angiography with PCD-CT. The 1-2-3 rule demonstrates the potential for reducing the effects of calcium blooming artifacts on overall image quality.

Fast kV-switching and dual-layer flat-panel detector enabled cone-beam CT joint spectral imaging

Purpose. Fast kV-switching (FKS) and dual-layer flat-panel detector (DL-FPD) technologies have been actively studied as promising dual-energy spectral imaging solutions for FPD-based cone-beam computed tomography (CT). However, cone-beam CT (CBCT) spectral imaging is known to face challenges in obtaining accurate and robust material discrimination performance. That is because the energy separation by either FKS or DL-FPD, alone, is still limited, along with apparently unpaired signal levels in the effective low- and high-energy projections in real applications, not to mention the x-ray scatter in cone-beam scan which will make the material decomposition almost impossible if no correction is applied. To further improve CBCT spectral imaging capability, this work aims to promote a source-detector joint multi-energy spectral imaging solution which takes advantages of both FKS and DL-FPD, and to conduct a feasibility study on the first tabletop CBCT system with the joint spectral imaging capability developed. Methods. For CBCT, development of multi-energy spectral imaging can be jointly realized by using an x-ray source with a generator whose kilo-voltages can alternate in tens of Hertz (i.e. FKS), and a DL-FPD whose top- and bottom-layer projections corresponds to different effective energy levels. Thanks to the complimentary characteristics inherent in FKS and DL-FPD, the overall energy separation will be significantly better when compared with FKS or DL-FPD alone, and the x-ray photon detection efficiency will be also improved when compared with FKS alone. In this work, a noise performance analysis using the Cramér–Rao lower bound (CRLB) method is conducted. The CRLB for basis material after a projection-domain material decomposition is derived, followed by a set of numerical calculations of CRLBs, for the FKS, the DL-FPD and the joint solution, respectively. To compensate for the slightly angular mismatch between low- and high- projections in FKS, a dual-domain projection completion scheme is implemented. Afterwards material decomposition from the complete projection data is carried out by using the maximum-likelihood method, followed by reconstruction of basis material and virtual monochromatic images (VMI). In this work, the first FKS and DL-FPD jointly enabled multi-energy tabletop CBCT system, to the best of our knowledge, has been developed in our laboratory. To evaluate its spectral imaging performance, a set of physics experiments are conducted, where the multi-energy and head phantoms are scanned using the 80/105/130 kVp switching pairs and projection data are collected using a prototype DL-FPD, whose both top and bottom layer of panels are composed of 550 μm of cesium iodine (CsI) scintillators with no intermediate metal filter in-between. Results. The numerical simulations show that the joint spectral imaging solution can lead to a significant improvement in energy separation and lower noise levels in most of material decomposition cases. The physics experiments confirmed the feasibility and superiority of the joint spectral imaging, whose CNRs in the selected regions of interest of the multi-energy phantom were boosted by an average improvement of 21.9%, 20.4% for water basis images and 32.8%, 62.8% for iodine images when compared with that of the FKS and DL-FPD, respectively. For the head phantom case, the joint spectral imaging can effectively reduce the streaking artifacts as well, and the standard deviation in the selected regions of interest are reduced by an average decrement of 19.5% and 8.1% for VMI when compared with that of the FKS and DL-FPD, respectively. Conclusions. A feasibility study of the joint spectral imaging solution for CBCT by utilizing both the FKS and DL-FPD was conducted, with the first tabletop CBCT system having such a capability being developed, which exhibits improved CNR and is more effective in avoiding streaking artifacts as expected.

Hotel booking intentions in the TikTok era: the role of online celebrity brand equity

PurposeThis study aims to explore the pathway of increasing hotel booking intentions by mapping the linkage mechanism between the antecedents and components of brand equity to ultimately drive followers’ hotel booking intention. In addition, the role of over-endorsement as a moderating variable is also evaluated.Design/methodology/approachThe conceptual model and research hypotheses were each assessed using covariance-based structural equation modeling. Paper-based and online surveys were used to collect data from 443 respondents who are TikTok users and follow at least one TikTok online celebrity, while that online celebrity must have reviewed at least one type of accommodation.FindingsExcept for the relationship between virtual interactivity and online celebrity brand image, the results confirmed the relationships between research concepts.Research limitations/implicationsFurther studies are needed to validate the results in other cultural contexts, generalize findings and broaden the range of target respondents.Originality/valueThis study contributes to the hotel literature by illustrating how online celebrity brand equity (OCBE) drives hotel booking intentions. The study highlights the importance of antecedent factors – follower-centered drivers (e.g. lifestyle congruence, friendship) and online celebrity-led drivers (e.g. virtual interactivity, expertise) – to achieve a hierarchical relationship between OCBE components and followers’ booking intentions.

Overmodulation and phase correction of virtual images propagated by holographic curved waveguide for near-eye display

Generally, current type of waveguide used for near-eye displays is planar waveguide, which belongs to flat panel display. Compared to display system in three-dimensional space, flat panel display limits people's view of the 3-D world and is not conducive to the integration of virtual and reality. This paper proposes a holographic curved waveguide system for near-eye display. In order to analyze the propagation process of light beam in waveguide, an iterative algorithm is established based on angular spectrum theory to get the intensity distribution from each total internal reflection point. According to the simulation results and experimental phenomenon, we have developed phase compensation measures for overmodulation during beam propagation in the waveguide. The research shows that using curved waveguide can achieve beam transmission with less aberration after introducing an appropriate phase compensation in a distance, and it can also achieve beam transmission with lossless energy within a large radius range. Experiments have proven that the final coupling effect is basically consistent with the simulation results, this means that our proposal about curved waveguide has potential application value in near-eye display systems.