Quantitative 3D strain analysis in analogue experiments: Integration of X-ray computed tomography and digital volume correlation techniques

The combination of scaled analogue experiments, material mechanics, X-ray computed tomography (XRCT) and Digital Volume Correlation techniques (DVC) is a powerful new tool not only to examine the 3 dimensional structure and kinematic evolution of complex deformation structures in scaled analogue experiments, but also to fully quantify their spatial strain distribution and complete strain history. Digital image correlation (DIC) is an important advance in quantitative physical modelling and helps to understand non-linear deformation processes. Optical non-intrusive (DIC) techniques enable the quantification of localised and distributed deformation in analogue experiments based either on images taken through transparent sidewalls (2D DIC) or on surface views (3D DIC). X-ray computed tomography (XRCT) analysis permits the non-destructive visualisation of the internal structure and kinematic evolution of scaled analogue experiments simulating tectonic evolution of complex geological structures. The combination of XRCT sectional image data of analogue experiments with 2D DIC only allows quantification of 2D displacement and strain components in section direction. This completely omits the potential of CT experiments for full 3D strain analysis of complex, non-cylindrical deformation structures. In this study, we apply digital volume correlation (DVC) techniques on XRCT scan data of “solid” analogue experiments to fully quantify the internal displacement and strain in 3 dimensions over time. Our first results indicate that the application of DVC techniques on XRCT volume data can successfully be used to quantify the 3D spatial and temporal strain patterns inside analogue experiments. We demonstrate the potential of combining DVC techniques and XRCT volume imaging for 3D strain analysis of a contractional experiment simulating the development of a non-cylindrical pop-up structure. Furthermore, we discuss various options for optimisation of granular materials, pattern generation, and data acquisition for increased resolution and accuracy of the strain results. Three-dimensional strain analysis of analogue models is of particular interest for geological and seismic interpretations of complex, non-cylindrical geological structures. The volume strain data enable the analysis of the large-scale and small-scale strain history of geological structures.

IN-VIVO CT DOSIMETRY DURING VIRTUAL COLONOSCOPY

Virtual colonoscopy (VC) is a minimally invasive means for identifying colorectal polyps and colorectal lesions by insufflating a patient’s bowel, applying contrast agent via rectal catheter, and performing multi-detector computed tomography (MDCT) scans. The technique is recommended for colonic health screening by the American Cancer Society but not funded by the Centers for Medicare and Medicaid Services (CMS) partially because of potential risks from radiation exposure. To date, no in‐vivo organ dose measurements have been performed for MDCT scans; thus, the accuracy of any current dose estimates is currently unknown. In this study, two TLDs were affixed to the inner lumen of standard rectal catheters used in VC, and in-vivo rectal dose measurements were obtained within 6 VC patients. In order to calculate rectal dose, TLD-100 powder response was characterized at diagnostic doses such that appropriate correction factors could be determined for VC. A third-order polynomial regression with a goodness of fit factor of R2=0.992 was constructed from this data. Rectal dose measurements were acquired with TLDs during simulated VC within a modified anthropomorphic phantom configured to represent three sizes of patients undergoing VC. The measured rectal doses decreased in an exponential manner with increasing phantom effective diameter, with R2=0.993 for the exponential regression model and a maximum percent coefficient of variation (%CoV) of 4.33%. In-vivo measurements yielded rectal doses ranged from that decreased exponentially with increasing patient effective diameter, in a manner that was also favorably predicted by the size specific dose estimate (SSDE) model for all VC patients that were of similar age, body composition, and TLD placement. The measured rectal dose within a younger patient was favorably predicted by the anthropomorphic phantom dose regression model due to similarities in the percentages of highly attenuating material at the respective measurement locations and in the placement of the TLDs. The in-vivo TLD response did not increase in %CoV with decreasing dose, and the largest %CoV was 10.0%.

Evaluation of deformable image registration for improved 4D CT-derived ventilation for image guided radiotherapy

Recent treatment planning studies have demonstrated the use of physiologic images in radiation therapy treatment planning to identify regions for functional avoidance. This image-guided radiotherapy (IGRT) strategy may reduce the injury and/or functional loss following thoracic radiotherapy. 4D computed tomography (CT), developed for radiotherapy treatment planning, is a relatively new imaging technique that allows the acquisition of a time-varying sequence of 3D CT images of the patient's lungs through the respiratory cycle. Guerrero et al. developed a method to calculate ventilation imaging from 4D CT, which is potentially better suited and more broadly available for IGRT than the current standard imaging methods. The key to extracting function information from 4D CT is the construction of a volumetric deformation field that accurately tracks the motion of the patient's lungs during the respiratory cycle. The spatial accuracy of the displacement field directly impacts the ventilation images; higher spatial registration accuracy will result in less ventilation image artifacts and physiologic inaccuracies. Presently, a consistent methodology for spatial accuracy evaluation of the DIR transformation is lacking. Evaluation of the 4D CT-derived ventilation images will be performed to assess correlation with global measurements of lung ventilation, as well as regional correlation of the distribution of ventilation with the current clinical standard SPECT. This requires a novel framework for both the detailed assessment of an image registration algorithm's performance characteristics as well as quality assurance for spatial accuracy assessment in routine application. Finally, we hypothesize that hypo-ventilated regions, identified on 4D CT ventilation images, will correlate with hypo-perfused regions in lung cancer patients who have obstructive lesions. A prospective imaging trial of patients with locally advanced non-small-cell lung cancer will allow this hypothesis to be tested. These advances are intended to contribute to the validation and clinical implementation of CT-based ventilation imaging in prospective clinical trials, in which the impact of this imaging method on patient outcomes may be tested.

Lung cancer screening with CT: evaluation of radiologists and different computer assisted detection software (CAD) as first and second readers for lung nodule detection at different dose levels

OBJECTIVES To find the best pairing of first and second reader at highest sensitivity for detecting lung nodules with CT at various dose levels. MATERIALS AND METHODS An anthropomorphic lung phantom and artificial lung nodules were used to simulate screening CT-examination at standard dose (100 mAs, 120 kVp) and 8 different low dose levels, using 120, 100 and 80 kVp combined with 100, 50 and 25 mAs. At each dose level 40 phantoms were randomly filled with 75 solid and 25 ground glass nodules (5-12 mm). Two radiologists and 3 different computer aided detection softwares (CAD) were paired to find the highest sensitivity. RESULTS Sensitivities at standard dose were 92%, 90%, 84%, 79% and 73% for reader 1, 2, CAD1, CAD2, CAD3, respectively. Combined sensitivity for human readers 1 and 2 improved to 97%, (p1=0.063, p2=0.016). Highest sensitivities--between 97% and 99.0%--were achieved by combining any radiologist with any CAD at any dose level. Combining any two CADs, sensitivities between 85% and 88% were significantly lower than for radiologists combined with CAD (p<0.03). CONCLUSIONS Combination of a human observer with any of the tested CAD systems provide optimal sensitivity for lung nodule detection even at reduced dose at 25 mAs/80 kVp.

Liver Remnant Regeneration in Donors After Living Donor Liver Transplantation: Long-Term Follow-Up Using CT and MR Imaging

Purpose: To assess liver remnant volume regeneration and maintenance, and complications in the long-time follow-up of donors after living donor liver transplantation using CT and MRI. Materials and Methods: 47 donors with a mean age of 33.5 years who donated liver tissue for transplantation and who were available for follow-up imaging were included in this retrospective study. Contrast-enhanced CT and MR studies were acquired for routine follow-up. Two observers evaluated pre- and postoperative images regarding anatomy and pathological findings. Volumes were manually measured on contrast-enhanced images in the portal venous phase, and potential postoperative complications were documented. Pre- and postoperative liver volumes were compared for evaluating liver remnant regeneration. Results: 47 preoperative and 89 follow-up studies covered a period of 22.4 months (range: 1 - 84). After right liver lobe (RLL) donation, the mean liver remnant volume was 522.0 ml (± 144.0; 36.1 %; n = 18), after left lateral section (LLS) donation 1,121.7 ml (± 212.8; 79.9 %; n = 24), and after left liver lobe (LLL) donation 1,181.5 ml (± 279.5; 72.0 %; n = 5). Twelve months after donation, the liver remnant volume were 87.3 % (RLL; ± 11.8; n = 11), 95.0 % (LS; ± 11.6; n = 18), and 80.1 % (LLL; ± 2.0; n = 2 LLL) of the preoperative total liver volume. Rapid initial regeneration and maintenance at 80 % of the preoperative liver volume were observed over the total follow-up period. Minor postoperative complications were found early in 4 patients. No severe or late complications or mortality occurred. Conclusion: Rapid regeneration of liver remnant volumes in all donors and volume maintenance over the long-term follow-up period of up to 84 months without severe or late complications are important observations for assessing the safety of LDLT donors. Key Points: Liver remnant volumes of LDLT donors rapidly regenerated after donation and volumes were maintained over the long-term follow-up period of up to 84 months without severe or late complications.

Optimal dose levels in screening chest CT for unimpaired detection and volumetry of lung nodules, with and without computer assisted detection at minimal patient radiation

OBJECTIVES The aim of this phantom study was to minimize the radiation dose by finding the best combination of low tube current and low voltage that would result in accurate volume measurements when compared to standard CT imaging without significantly decreasing the sensitivity of detecting lung nodules both with and without the assistance of CAD. METHODS An anthropomorphic chest phantom containing artificial solid and ground glass nodules (GGNs, 5-12 mm) was examined with a 64-row multi-detector CT scanner with three tube currents of 100, 50 and 25 mAs in combination with three tube voltages of 120, 100 and 80 kVp. This resulted in eight different protocols that were then compared to standard CT sensitivity (100 mAs/120 kVp). For each protocol, at least 127 different nodules were scanned in 21-25 phantoms. The nodules were analyzed in two separate sessions by three independent, blinded radiologists and computer-aided detection (CAD) software. RESULTS The mean sensitivity of the radiologists for identifying solid lung nodules on a standard CT was 89.7% ± 4.9%. The sensitivity was not significantly impaired when the tube and current voltage were lowered at the same time, except at the lowest exposure level of 25 mAs/80 kVp [80.6% ± 4.3% (p = 0.031)]. Compared to the standard CT, the sensitivity for detecting GGNs was significantly lower at all dose levels when the voltage was 80 kVp; this result was independent of the tube current. The CAD significantly increased the radiologists' sensitivity for detecting solid nodules at all dose levels (5-11%). No significant volume measurement errors (VMEs) were documented for the radiologists or the CAD software at any dose level. CONCLUSIONS Our results suggest a CT protocol with 25 mAs and 100 kVp is optimal for detecting solid and ground glass nodules in lung cancer screening. The use of CAD software is highly recommended at all dose levels.

Anatomic pathways of peripancreatic fluid draining to mediastinum in recurrent acute pancreatitis: visible human project and CT study

BACKGROUND In past reports, researchers have seldom attached importance to achievements in transforming digital anatomy to radiological diagnosis. However, investigators have been able to illustrate communication relationships in the retroperitoneal space by drawing potential routes in computerized tomography (CT) images or a virtual anatomical atlas. We established a new imaging anatomy research method for comparisons of the communication relationships of the retroperitoneal space in combination with the Visible Human Project and CT images. Specifically, the anatomic pathways of peripancreatic fluid extension to the mediastinum that may potentially transform into fistulas were studied. METHODS We explored potential pathways to the mediastinum based on American and Chinese Visible Human Project datasets. These drainage pathways to the mediastinum were confirmed or corrected in CT images of 51 patients with recurrent acute pancreatitis in 2011. We also investigated whether additional routes to the mediastinum were displayed in CT images that were not in Visible Human Project images. PRINCIPAL FINDINGS All hypothesized routes to the mediastinum displayed in Visible Human Project images, except for routes from the retromesenteric plane to the bilateral retrorenal plane across the bilateral fascial trifurcation and further to the retrocrural space via the aortic hiatus, were confirmed in CT images. In addition, route 13 via the narrow space between the left costal and crural diaphragm into the retrocrural space was demonstrated for the first time in CT images. CONCLUSION This type of exploration model related to imaging anatomy may be used to support research on the communication relationships of abdominal spaces, mediastinal spaces, cervical fascial spaces and other areas of the body.

Quantification of pleural effusion from single area measurements on CT

The objective of this study was to determine if area measurements of pleural fluid on computed tomography (CT) reflect the actual pleural fluid volume (PEvol) as measured at autopsy, to establish a formula to estimate the volume of pleural effusion (PEest), and to test the accuracy and observer reliability of PEest.132 human cadavers, with pleural effusion were divided into phase 1 (n = 32) and phase 2 (n = 100). In phase 1, PEvol was compared to area measurements on axial (axA), sagittal (sagA), and coronal (corA) CT images. Linear regression analysis was used to create a formula to calculate PEest. In phase 2, intra-class correlation (ICC) was used to assess inter-reader reliability and determine the agreement between PEest and PEvol. PEvol correlated to a higher degree to axA (r s mean = 0.738; p < 0.001) than to sagA (r s mean = 0.679, p < 0.001) and corA (r s mean = 0.709; p < 0.001). PEest can be established with the following formula: axA × 0.1 = PEest. Mean difference between PEest and PEvol was less than 40 mL (ICC = 0.837-0.874; p < 0.001). Inter-reader reliability was higher between two experienced readers (ICC = 0.984-0.987; p < 0.001) than between an inexperienced reader and both experienced readers (ICC = 0.660-0.698; p < 0.001). Pleural effusions may be quantified in a rapid, reliable, and reasonably accurate fashion using single area measurements on CT.

Pitfalls in post-mortem CT-angiography--intravascular contrast induces post-mortem pericardial effusion

We present a case where multi-phase post-mortem computed tomography angiography (PMCTA) induced a hemorrhagic pericardial effusion during the venous phase of angiography. Post-mortem non-contrast CT (PMCT) suggested the presence of a ruptured aortic dissection. This diagnosis was confirmed by PMCTA after pressure controlled arterial injection of contrast. During the second phase of multi-phase PMCTA the presence of contrast leakage from the inferior cava vein into the pericardial sac was noted. Autopsy confirmed the post-mortem nature of this vascular tear. This case teaches us an important lesson: it underlines the necessity to critically analyze PMCT and PMCTA images in order to distinguish between artifacts, true pathologies and iatrogenic findings. In cases with ambiguous findings such as the case reported here, correlation of imaging findings with autopsy is elementary.

The Forensic Reference Phantom-a new tool for quality assurance of attenuation measurements in forensic radiology

Introduction The purpose of this paper is to present the technical specifications of the Forensic Reference Phantom (FRP), to test its behavior relative to organic test materials, and discuss potential applications of the phantom in forensic radiology. Materials and method The FRP prototype is made of synthetic materials designed to simulate the computed tomography (CT) attenuation of water. It has six bore holes that accommodate multiuse containers. These containers were filled with test materials and scanned at 80 kVp, 120 kVp, and 140 kVp. X-ray attenuation was measured by two readers. Intra- and inter-reader reliability was assessed using the intra-class correlation coefficient (ICC). Significance levels between mean CT numbers at 80 kVp, 120 kVp, and 140 kVp were assessed with the Friedman-test. The T-test was used to assess significance levels between the FRP and water. Results Overall mean CT numbers ranged from −3.0–3.7HU for the FRP; −1000.3–−993.5HU for air; −157.7– −108.1HU for oil; 35.5–42.0HU for musle tissue; and 1301.5–2354.8HU for cortical bone. Inter-reader and intra-reader reliability were excellent (ICC>0.994; and ICC=0.999 respectively). CT numbers were significantly different at different energy levels. There was no significant difference between the attenuation of the FRP and water. Conclusions The FRP is a new tool for quality assurance and research in forensic radiology. The mean CT attenuation of the FRP is equivalent to water. The phantom can be scanned during routine post-mortem CT to assess the composition of unidentified objects. In addition, the FRP may be used to investigate new imaging algorithms and scan protocols in forensic radiology.

Assessment of Transverse Isotropy in Clinical-Level CT Images of Trabecular Bone Using the Gradient Structure Tensor

The aim of this study was to develop a GST-based methodology for accurately measuring the degree of transverse isotropy in trabecular bone. Using femoral sub-regions scanned in high-resolution peripheral QCT (HR-pQCT) and clinical-level-resolution QCT, trabecular orientation was evaluated using the mean intercept length (MIL) and the gradient structure tensor (GST) on the HR-pQCT and QCT data, respectively. The influence of local degree of transverse isotropy (DTI) and bone mineral density (BMD) was incorporated into the investigation. In addition, a power based model was derived, rendering a 1:1 relationship between GST and MIL eigenvalues. A specific DTI threshold (DTI thres) was found for each investigated size of region of interest (ROI), above which the estimate of major trabecular direction of the GST deviated no more than 30° from the gold standard MIL in 95% of the remaining ROIs (mean error: 16°). An inverse relationship between ROI size and DTI thres was found for discrete ranges of BMD. A novel methodology has been developed, where transversal isotropic measures of trabecular bone can be obtained from clinical QCT images for a given ROI size, DTI thres and power coefficient. Including DTI may improve future clinical QCT finite-element predictions of bone strength and diagnoses of bone disease.

Whole genome scan identifies several chromosomal regions linked to equine sarcoids.

Despite the evidence for a genetic predisposition to develop equine sarcoids (ES), no whole genome scan for ES has been performed to date. The objective of this explorative study was to identify chromosome regions associated with ES. The studied population was comprised of two half-sibling sire families, involving a total of 222 horses. Twenty-six of these horses were affected with ES. All horses had been previously genotyped with 315 microsatellite markers. Quantitative trait locus (QTL) signals were suggested where the F statistic exceeded chromosome-wide significance at P < 0.05. The QTL analyses revealed significant signals reaching P < 0.05 on equine chromosome (ECA) 20, 23 and 25, suggesting a polygenic character for this trait. The candidate regions identified on ECA 20, 23 and 25 include genes regulating virus replication and host immune response. Further investigation of the chromosome regions associated with ES and of genes potentially responsible for the development of ES could form the basis for early identification of susceptible animals, breeding selection or the development of new therapeutic targets.

CT myelography for diagnosis of brachial plexus avulsion in small animals

Avulsion of nerve roots of the brachial plexus can be diagnosed clinically, neurologically, radiographically and by electromyography. But like the myelography these techniques are inprecise for determination of the severity (partial or complete disruption) and the localization of the lesion. In human medicine the combination of computerized tomography with myelography shows high accuracy. Veterinary reports of experience in this field are not yet known. The aim of the present study was to demonstrate nerve root avulsions using myelography and computerized tomography. Three dogs and one cat with traumatic lesions of the brachial plexus were examined. The lesion could be seen in all patients. Thus CT-myelography results in an improved prognostic assessment of brachial plexus paralysis. Moreover, this technique could become one of the most important diagnostic methods for brachial plexus lesions involving nerve root reinsertion--neurotizations in veterinary medicine.

Characterization and differentiation of body fluids, putrefaction fluid, and blood using Hounsfield unit in postmortem CT

The purpose of the present study was to evaluate the ranges of Hounsfield unit (HU) found in body fluids, putrefaction fluids, and blood on postmortem CT and how these ranges are affected by postmortem interval, temperatures, and CT beam energy. Body fluids, putrefaction fluids, and blood from a total of 53 corpses were analyzed to determine the ranges of HU values from postmortem CT images that were taken prior to autopsy. The fluids measured in CT images were obtained at autopsy and examined in terms of macroscopic and microscopic appearances. Body fluids and blood were also collected in plastic bottles, which were subjected to CT scans at different beam energies (80-130 kV) and at various fluid temperatures (4 to 40 °C). At a postmortem interval of 1 to 4 days, the ranges of HU values of the serous fluids (13-38 HU) and the nonsedimented blood (40-88 HU) did not overlap. In the sedimented blood, the upper serum layer exhibited HU value ranges that overlapped with those of the serous fluids. The putrefaction fluids exhibited a range of HU values between 80 and -130 HU. Elevated HU values were observed in fluids with accretive cell impurities. HU values decreased slightly with increasing temperature and CT beam energy. We concluded that serous fluids and blood in fresh corpses can be characterized and differentiated from each other based on HU value ranges. In contrast, body fluids in decomposed corpses cannot be differentiated by their HU value ranges. Different beam energies and corpse temperatures had only minor influences on HU value ranges and therefore should not be obstacles to the differentiation and characterization of body fluids and blood.