Automatic detection of pulmonary nodules in CT images by incorporating 3D tensor filtering with local image feature analysis

Computer-aided detection (CAD) technology has been developed and demonstrated its potential to assist radiologists in detecting pulmonary nodules especially at an early stage. In this paper, we present a novel scheme for automatic detection of pulmonary nodules in CT images based on a 3D tensor filtering algorithm and local image feature analysis. We first apply a series of preprocessing steps to segment the lung volume and generate the isotropic volumetric CT data. Next, a unique 3D tensor filtering approach and local image feature analysis are used to detect nodule candidates. A 3D level set segmentation method is used to correct and refine the boundaries of nodule candidates subsequently. Then, we extract the features of the detected candidates and select the optimal features by using a CFS (Correlation Feature Selection) subset evaluator attribute selection method. Finally, a random forest classifier is trained to classify the detected candidates. The performance of this CAD scheme is validated using two datasets namely, the LUNA16 (Lung Nodule Analysis 2016) database and the ANODE09 (Automatic Nodule Detection 2009) database. By applying a 10-fold cross-validation method, the CAD scheme yielded a sensitivity of 79.3% at an average of 4 false positive detections per scan (FP/Scan) for the former dataset, and a sensitivity of 84.62% and 2.8 FP/Scan for the latter dataset, respectively. Our detection results show that the use of 3D tensor filtering algorithm combined with local image feature analysis constitutes an effective approach to detect pulmonary nodules.     

Combination of dual-energy computed tomography and iterative metal artefact reduction to increase general quality of imaging for radiotherapy patients with high dense materials. Phantom study

PurposeTo evaluate the use of pseudo-monoenergetic reconstructions (PMR) from dual-energy computed tomography, combined with the iterative metal artefact reduction (iMAR) method.MethodsPseudo-monoenergetic CT images were obtained using the dual-energy mode on the Siemens Somatom Definition AS scanner. A range of PMR combinations (70–130 keV) were used with and without iMAR. A Virtual Water™ phantom was used for quantitative assessment of error in the presence of high density materials: titanium, alloys 330 and 600. The absolute values of CT number differences (AD) and normalised standard deviations (NSD) were calculated for different phantom positions. Image quality was assessed using an anthropomorphic pelvic phantom with an embedded hip prosthesis. Image quality was scored blindly by five observers.ResultsAD and NSD values revealed differences in CT number errors between tested sets. AD and NSD were reduced in the vicinity of metal for images with iMAR (p < 0.001 for AD/NSD). For ROIs away from metal, with and without iMAR, 70 keV PMR and pCT AD values were lower than for the other reconstructions (p = 0.039). Similarly, iMAR NSD values measured away from metal were lower for 130 keV and 70 keV PMR (p = 0.002). Image quality scores were higher for 70 keV and 130 keV PMR with iMAR (p = 0.034).ConclusionThe use of 70 keV PMR with iMAR allows for significant metal artefact reduction and low CT number errors observed in the vicinity of dense materials. It is therefore an attractive alternative to high keV imaging when imaging patients with metallic implants, especially in the context of radiotherapy planning.     

Morphological variation among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti)

Living mysticetes (baleen whales) and odontocetes (toothed whales) differ significantly in auditory function in that toothed whales are sensitive to high‐frequency and ultrasonic sound vibrations and mysticetes to low‐frequency and infrasonic noises. Our knowledge of the evolution and phylogeny of cetaceans, and mysticetes in particular, is at a point at which we can explore morphological and physiological changes within the baleen whale inner ear. Traditional comparative anatomy and landmark‐based 3D‐geometric morphometric analyses were performed to investigate the anatomical diversity of the inner ears of extinct and extant mysticetes in comparison with other cetaceans. Principal component analyses (PCAs) show that the cochlear morphospace of odontocetes is tangential to that of mysticetes, but odontocetes are completely separated from mysticetes when semicircular canal landmarks are combined with the cochlear data. The cochlea of the archaeocete Zygorhiza kochii and early diverging extinct mysticetes plot within the morphospace of crown mysticetes, suggesting that mysticetes possess ancestral cochlear morphology and physiology. The PCA results indicate variation among mysticete species, although no major patterns are recovered to suggest separate hearing or locomotor regimes. Phylogenetic signal was detected for several clades, including crown Cetacea and crown Mysticeti, with the most clades expressing phylogenetic signal in the semicircular canal dataset. Brownian motion could not be excluded as an explanation for the signal, except for analyses combining cochlea and semicircular canal datasets for Balaenopteridae. J. Morphol. 277:1599–1615, 2016. © 2016 Wiley Periodicals, Inc.     

Simultaneous achievement of accurate CT number and image quality improvement for myocardial perfusion CT at 320-MDCT volume scanning

PurposeTo investigate differences in image-to-image variations between full- and half-scan reconstruction on myocardial CT perfusion (CTP) study.MethodsUsing a cardiac phantom we performed ECG-gated myocardial CTP on a second-generation 320-multidetector CT volume scanner. The heart rate was set at 60 bpm; once per second for a total of 24 s were performed. CT images were acquired at 80- and 120 kVp and subjected to full- and half-scan reconstruction. On images acquired at the same slice level we then measured image-to-image variations, coefficients of variance (CV), and image noise.ResultsThe image-to-image variations with full- and half-scan reconstruction were 1.3 HU vs. 27.2 HU at 80 kVp (p < 0.001) and 0.70 HU vs. 9.3 HU at 120 kVp (p < 0.001) even though the mean HU value was almost the same for both reconstruction methods. The CV of 80- and 120-kVp images of the left ventricular cavity decreased by 0.16% and 0.17%, respectively, with full-scan reconstruction; with half-scan reconstruction it decreased by 3.34% and 2.30%, respectively. Compared with half-scan reconstruction, the image noise was reduced by 27.2% at 80 kVp and by 28.0% at 120 kVp with full-scan reconstruction.ConclusionMyocardial CTP with full-scan reconstruction substantially decreased image-to-image variations and provided accurate CT attenuation.     

The development of cephalic armor in the tokay gecko (Squamata: Gekkonidae: Gekko gecko)

Armored skin resulting from the presence of bony dermal structures, osteoderms, is an exceptional phenotype in gekkotans (geckos and flap-footed lizards) only known to occur in three genera: Geckolepis, Gekko, and Tarentola. The Tokay gecko (Gekko gecko LINNAEUS 1758) is among the best-studied geckos due to its large size and wide range of occurrence, and although cranial dermal bone development has previously been investigated, details of osteoderm development along a size gradient remain less well-known. Likewise, a comparative survey of additional species within the broader Gekko clade to determine the uniqueness of this trait has not yet been completed. Here, we studied a large sample of gekkotans (38 spp.), including 18 specimens of G. gecko, using X-rays and high-resolution computed tomography for visualizing and quantifying the dermal armor in situ. Results from this survey confirm the presence of osteoderms in a second species within this genus, Gekko reevesii GRAY 1831, which exhibits discordance in timing and pattern of osteoderm development when compared with its sister taxon, G. gecko. We discuss the developmental sequence of osteoderms in these two species and explore in detail the formation and functionality of these enigmatic dermal ossifications. Finally, we conducted a comparative analysis of endolymphatic sacs in a wide array of gekkotans to explore previous ideas regarding the role of osteoderms as calcium reservoirs. We found that G. gecko and other gecko species with osteoderms have highly enlarged endolymphatic sacs relative to their body size, when compared to species without osteoderms, which implies that these membranous structures might fulfill a major role of calcium storage even in species with osteoderms.     

Monte Carlo dose in a prosthesis phantom based on exact geometry vs streak artefact contaminated CT data as benchmarked against Gafchromic film measurements

PurposeIn radiotherapy, accurate calculation of patient radiation dose is very important for good clinical outcome. In the presence of metallic implants, the dose calculation accuracy could be compromised by metal artefacts generated in computed tomography (CT) images of patients. This study investigates the influence of metal-induced CT artefacts on MC dose calculations in a pelvic prosthesis phantom.MethodsA pelvic phantom containing unilateral Ti prosthesis was CT-scanned and accurate Hounsfield unit (HU) values were assigned to known materials of the phantom as opposed to HU values produced through the artefact CT images of the phantom. Using the DOSXYZnrc MC code, dose calculations were computed in the phantom model constructed from the original CT images containing the artefacts and artefact-free images made from the exact geometry of the phantom with known materials. The dose calculations were benchmarked against Gafchromic EBT3 film measurements using 15 MeV electron and 10 MV photon beams.ResultsThe average deviations between film and MC dose data decreased from 3 ± 2% to 1 ± 1% and from about 6 ± 2% to 3 ± 1% for the artefact and artefact-free phantom models against film data for the electron and photon fields, respectively.ConclusionsFor the Ti prosthesis phantom, the presence of metal-induced CT artefacts could cause dose inaccuracies of about 3%. Construction of an artefact-free phantom model made from the exact geometry of the phantom with known materials to overcome the effect of artefacts is advantageous compared to using CT data directly of which the exact tissue composition is not well-known.     

Monte Carlo-based assessment of the trade-off between spatial resolution,field-of-view and scattered radiation in the variable resolution X-ray CT scanner

ObjectiveThe purpose of this work is to evaluate the impact of optimization of magnification on performance parameters of the variable resolution X-ray (VRX) CT scanner.MethodsA realistic model based on an actual VRX CT scanner was implemented in the GATE Monte Carlo simulation platform. To evaluate the influence of system magnification, spatial resolution, field-of-view (FOV) and scatter-to-primary ratio of the scanner were estimated for both fixed and optimum object magnification at each detector rotation angle. Comparison and inference between these performance parameters were performed angle by angle to determine appropriate object position at each opening half angle.ResultsOptimization of magnification resulted in a trade-off between spatial resolution and FOV of the scanner at opening half angles of 90°–12°, where the spatial resolution increased up to 50% and the scatter-to-primary ratio decreased from 4.8% to 3.8% at a detector angle of about 90° for the same FOV and X-ray energy spectrum. The disadvantage of magnification optimization at these angles is the significant reduction of the FOV (up to 50%). Moreover, magnification optimization was definitely beneficial for opening half angles below 12° improving the spatial resolution from 7.5 cy/mm to 20 cy/mm. Meanwhile, the FOV increased by more than 50% at these angles.ConclusionIt can be concluded that optimization of magnification is essential for opening half angles below 12°. For opening half angles between 90° and 12°, the VRX CT scanner magnification should be set according to the desired spatial resolution and FOV.     

Evaluation of mesh- and binary-based contour propagation methods in 4D thoracic radiotherapy treatments using patient 4D CT images

Based on four dimensional (4D) computed tomography (CT) images, mesh- and binary-based contour propagation algorithms for 4D thoracic radiotherapy treatments were evaluated. Gross tumor volumes (GTVs), lungs, hearts and spinal cords on the CT images at the end-exhale and end-inhale phases for six patients were delineated by the physician. All volumes of interest (VOIs) were automatically propagated from the end-exhale phase to the end-inhale phase using two propagation methods. The propagated VOIs were quantitatively compared with the VOIs contoured at the end-inhale phase by the physician using Dice Similarity Coefficient (DSC), Mean Slicewise Hausdorff Distance (MSHD), Center Of Mass (COM) displacement and volume difference. A two-sided Student’s t test was implemented to examine the significance of the differences between the results obtained from the two algorithms. For GTVs, statistically significant differences between the two algorithms were not observed. For all the other VOIs, the mesh-based method showed higher mean DSCs for the heart, left lung, right lung and spinal cord, lower mean MSHD for the spinal cord, lower mean COM displacement for the heart, and lower mean volume differences for the left lung, right lung and spinal cord with statistically significant differences than the binary-based method. The running time for propagation was approximately 3 s and 3 min for the mesh- and binary-based methods, respectively. Collectively, the mesh-based algorithm provides superiorities in running time and reliability for contour propagation in 4D radiotherapy.     

Evaluation of four-dimensional cone beam computed tomography ventilation images acquired with two different linear accelerators at various gantry speeds using a deformable lung phantom

We evaluated four-dimensional cone beam computed tomography (4D-CBCT) ventilation images (VI_CBCT) acquired with two different linear accelerator systems at various gantry speeds using a deformable lung phantom.The 4D-CT and 4D-CBCT scans were performed using a computed tomography (CT) scanner, an X-ray volume imaging system (Elekta XVI) mounted in Versa HD, and an On-Board Imager (OBI) system mounted in TrueBeam. Intensity-based deformable image registration (DIR) was performed between peak-exhale and peak-inhale images. VI_CBCT- and 4D-CT-based ventilation images (VI_CT) were derived by DIR using two metrics: one based on the Jacobian determinant and one on changes in the Hounsfield unit (HU). Three different DIR regularization values (λ) were used for VI_CBCT. Correlations between the VI_CBCT and VI_CT values were evaluated using voxel-wise Spearman’s rank correlation coefficient (r).In case of both metrics, the Jacobian-based VI_CBCT with a gantry speed of 0.6 deg/sec in Versa HD showed the highest correlation for all the gantry speeds (e.g., λ = 0.05 and r = 0.68). Thus, the r value of the Jacobian-based VI_CBCT was greater or equal to that of the HU-based VI_CBCT. In addition, the ventilation accuracy of VI_CBCT increased at low gantry speeds.Thus, the image quality of VI_CBCT was affected by the change in gantry speed in both the imaging systems. Additionally, DIR regularization considerably influenced VI_CBCT in both the imaging systems. Our results have the potential to assist in designing CBCT protocols, incorporating VI_CBCT imaging into the functional avoidance planning process.     

Generation of clinical 177Lu SPECT/CT images based on Monte Carlo simulation with GATE

PurposePatient-specific dosimetry in MRT relies on quantitative imaging, pharmacokinetic assessment and absorbed dose calculation. The DosiTest project was initiated to evaluate the uncertainties associated with each step of the clinical dosimetry workflow through a virtual multicentric clinical trial. This work presents the generation of simulated clinical SPECT datasets based on GATE Monte Carlo modelling with its corresponding experimental CT image, which can subsequently be processed by commercial image workstations.MethodsThis study considers a therapy cycle of 6.85 GBq ¹⁷⁷Lu-labelled DOTATATE derived from an IAEA-Coordinated Research Project (E23005) on “Dosimetry in Radiopharmaceutical therapy for personalised patient treatment”. Patient images were acquired on a GE Infinia-Hawkeye 4 gamma camera using a medium energy (ME) collimator. Simulated SPECT projections were generated based on experimental time points and validated against experimental SPECT projections using flattened profiles and gamma index. The simulated projections were then incorporated into the patient SPECT/CT DICOM envelopes for processing and their reconstruction within a commercial image workstation.ResultsGamma index passing rate (2% − 1 pixel criteria) between 95 and 98% and average gamma between 0.28 and 0.35 among different time points revealed high similarity between simulated and experimental images. Image reconstruction of the simulated projections was successful on HERMES and Xeleris workstations, a major step forward for the initiation of a multicentric virtual clinical dosimetry trial based on simulated SPECT/CT images.ConclusionsRealistic ¹⁷⁷Lu patient SPECT projections were generated in GATE. These modelled datasets will be circulated to different clinical departments to perform dosimetry in order to assess the uncertainties in the entire dosimetric chain.