Microcomputed Tomography Calibration Using Polymers and Minerals for Enamel Mineral Content Quantitation.

OBJECTIVE: The aim of this paper was to develop calibration standards (CSs) that are readily available for clinical researchers for the quantitation of enamel mineral content. METHOD: Polyethylene terephthalate (PET), acetal, polyphenylene sulfide (PPS), selenite, Egyptian alabaster, aragonite, and fluorite were fashioned into discs, and their densities were measured and stacked for microcomputed tomography examination. Frame averaging, flat-field correction, pre-filtration, and beam-hardening correction were applied. CSs were checked for homogeneity. The linear relationship between the mean greyscale value (GSV) of each disc and its physically calculated density was explored, and reproducibility was tested. A calibration function was established and then validated using a bovine enamel disc and sound enamel of extracted human premolar teeth. RESULTS: Measured densities were PET (ρ = 1.38 g/cm3), acetal (ρ = 1.41 g/cm3), PPS (ρ = 1.64 g/cm3), selenite (ρ = 2.24 g/cm3), Egyptian alabaster (ρ = 2.7 g/cm3), aragonite (ρ = 2.72 g/cm3), and fluorite (ρ = 3.11 g/cm3). Examination of the profile sections of CSs confirmed the uniformity of GSVs with minimal beam-hardening effect. A squared Pearson correlation coefficient of R2 = 0.994 was determined between the mean GSV of each CS and its calculated density and was reproduced at different settings with R2 >0.99. A linear regression equation of density (y) versus GSV (x) was established using the least squares regression equation method. The estimated density of the bovine enamel disc (2.48 g/cm3) showed high accuracy when compared to the physically measured value (2.45 g/cm3). The -relative error was 1.2%. Densities of sound enamel in the extracted human premolar teeth were 2.6-3.1 g/cm3. CONCLUSIONS: This is a simple, valid, and reproducible method to quantitate enamel mineral content. This simple, yet accurate system could be used to expand knowledge in the field of enamel caries research.

Micro-CT imaging: Developing criteria for examining fetal skeletons in regulatory developmental toxicology studies - A workshop report.

During the past two decades the use and refinements of imaging modalities have markedly increased making it possible to image embryos and fetuses used in pivotal nonclinical studies submitted to regulatory agencies. Implementing these technologies into the Good Laboratory Practice environment requires rigorous testing, validation, and documentation to ensure the reproducibility of data. A workshop on current practices and regulatory requirements was held with the goal of defining minimal criteria for the proper implementation of these technologies and subsequent submission to regulatory agencies. Micro-computed tomography (micro-CT) is especially well suited for high-throughput evaluations, and is gaining popularity to evaluate fetal skeletons to assess the potential developmental toxicity of test agents. This workshop was convened to help scientists in the developmental toxicology field understand and apply micro-CT technology to nonclinical toxicology studies and facilitate the regulatory acceptance of imaging data. Presentations and workshop discussions covered: (1) principles of micro-CT fetal imaging; (2) concordance of findings with conventional skeletal evaluations; and (3) regulatory requirements for validating the system. Establishing these requirements for micro-CT examination can provide a path forward for laboratories considering implementing this technology and provide regulatory agencies with a basis to consider the acceptability of data generated via this technology.

Geometric Parameters Estimation and Calibration in Cone-Beam Micro-CT.

The quality of Computed Tomography (CT) images crucially depends on the precise knowledge of the scanner geometry. Therefore, it is necessary to estimate and calibrate the misalignments before image acquisition. In this paper, a Two-Piece-Ball (TPB) phantom is used to estimate a set of parameters that describe the geometry of a cone-beam CT system. Only multiple projections of the TPB phantom at one position are required, which can avoid the rotation errors when acquiring multi-angle projections. Also, a corresponding algorithm is derived. The performance of the method is evaluated through simulation and experimental data. The results demonstrated that the proposed method is valid and easy to implement. Furthermore, the experimental results from the Micro-CT system demonstrate the ability to reduce artifacts and improve image quality through geometric parameter calibration.

Effect of data binning and frame averaging for micro-CT image acquisition on the morphometric outcome of bone repair assessment.

Despite the current advances in micro-CT analysis, the influence of some image acquisition parameters on the morphometric assessment outcome have not been fully elucidated. The aim of this study was to determine whether data binning and frame averaging affect the morphometric outcome of bone repair assessment using micro-CT. Four Wistar rats' tibiae with a surgically created bone defect were imaged with micro-CT six times each, frame averaging set to 1 and 2, and data binning set to 1, 2 and 4, for each of the averaging values. Two-way ANOVA followed by Bonferroni tests assessed the significance of frame averaging and data binning on a set of morphometric parameters assessed in the image volumes (p < 0.01). The effect of frame averaging was not significant for any of the assessed parameters. Increased data binning led to larger trabecular thickness. In contrast, smaller bone volume fraction and bone volume were found as data binning increased. Trabeculae number and trabecular separation were not influenced by any of the parameters. In conclusion, the morphometric outcome of bone repair assessment in micro-CT demonstrated dependency upon data binning, but not frame averaging. Therefore, image acquisition of small anatomical structures (e.g., rat trabeculae) should be performed without data binning.

Accuracy of volumetric measurement of teeth in vivo based on cone beam computer tomography.

OBJECTIVES: to evaluate the accuracy of cone beam computed tomography (CBCT) for volumetric measurement of teeth, using micro-computed tomography (Micro-CT) as the reference standard. SETTING AND SAMPLE POPULATION: The Department of Orthodontics at Sichuan University. The sample consisted of 27 maxillary and mandibular premolars of 15 patients, planned to be extracted for orthodontic treatment. MATERIAL AND METHODS: The 27 teeth were subjected to standardized CBCT scanning before extraction and Micro-CT scanning after extraction. From CBCT data, teeth were tissue segmented and then three-dimensionally (3D) reconstructed, while from Micro-CT data, teeth were 3D reconstructed directly. Tooth volumes were then calculated. The intra-observer repeatability and reproducibility of two observers and the overall between-instrument agreement of the measurements were evaluated using intra-class correlation coefficients (ICCs) and concordance correlation coefficient (CCC), respectively. RESULTS: The intra-observer repeatability was high for both observers. ICCs were 0.999 and 0.998, respectively. The reproducibility of the two observers was also high (ICC, 0.740). The overall between-instrument agreement of the measurements was good, and CCC was 0.993 and its lower 95% confidence interval was 0.989. CONCLUSIONS: The accuracy of the CBCT method for volumetric measurement of teeth in vivo is comparable to the Micro-CT method in vitro. The CBCT method has the potential possibility to be applied in studies on root resorption associated with orthodontic force. Further study is needed to prove the sensitivity of the method.

Micro-CT data of early physiological cancellous bone formation in the lumbar spine of female C57BL/6 mice.

Micro-CT provides critical data for musculoskeletal research, yielding three-dimensional datasets containing distributions of mineral density. Using high-resolution scans, we quantified changes in the fine architecture of bone in the spine of young mice. This data is made available as a reference to physiological cancellous bone growth. The scans (n = 19) depict the extensive structural changes typical for female C57BL/6 mice pups, aged 1-, 3-, 7-, 10- and 14-days post-partum, as they attain the mature geometry. We reveal the micro-morphology down to individual trabeculae in the spine that follow phases of mineral-tissue rearrangement in the growing lumbar vertebra on a micrometer length scale. Phantom data is provided to facilitate mineral density calibration. Conventional histomorphometry matched with our micro-CT data on selected samples confirms the validity and accuracy of our 3D scans. The data may thus serve as a reference for modeling normal bone growth and can be used to benchmark other experiments assessing the effects of biomaterials, tissue growth, healing, and regeneration.

Quality control protocol for in vitro micro-computed tomography.

The aim of this work was to present and discuss a quality control protocol for in vitro micro-computed tomography (microCT), based on the adaptation of the quality control protocols for medical computed tomography. The importance of establishing a quality control protocol is related to the opportunity to identify problems on time comparing the microCT images acquired in different time points, and in this way to verify the performance of the device. The proposed quality control protocol was applied for a long-time monitoring period to verify the stability of the micro-tomographic system over time. The protocol proposed in this study was applied to the histomorphometric characterization of bone tissue, but it can be used on a wide range of in vitro microCT applications. Noise and uniformity tests, taken and adapted to micro-tomographic system by medical standard guidelines of quality control, were performed by the use of a water phantom. An accuracy test was designed and performed by the use of a morphometric calibrated phantom. All these tests were performed during a long-time monitoring period to control the stability of the system. Specific control charts and monitoring parameters for each test were used to represent the monthly measures collected during 20 months and an out of control condition was defined. The reference values (baseline), calculated to control the stability of micro-tomographic system over time, were calculated during acceptance/status test. During the period, no out of control conditions in noise, uniformity and accuracy tests were recorded. However, a changing condition was found in noise test, as showed by using statistical C (P < 0.01) and Kruskal-Wallis (P < 0.05) tests. In particular, a Wilcoxon rank sum test with Bonferroni correction (P < 0.0125) was applied in noise test to investigate which of the comparisons among first five acquisitions of year 2004 (group B.L.) and each group was significant (P < 0.0125). The noise showed a slight but significant increase over the years compared to baseline value; however, no out of control conditions were recorded. Nonetheless, a maintenance service to control the performance of mechanical components of microCT was required and performed.

The value of digital volume tomography in assessing the position of cochlear implant arrays in temporal bone specimens.

OBJECTIVES: Radiological evaluation of the position of cochlear implant (CI) devices is an upcoming method for quality control after CI surgery. First, results of imaging of the middle and inner ear with digital volume tomography (DVT) show considerable advantages such as exceptional image quality, thin slice thickness, and low radiation dose. The aim of this study was to evaluate whether DVT is an appropriate method for postoperative imaging of CI patients and to identify the exact position of the implant array within the cochlear by multiple measurements. DESIGN: Thirteen formalin-fixed temporal bone specimens were implanted with a CI array and scanned in DVT. To determine the exact electrode position, these specimens were ground and stained for microscopic measurements. The measurements on grindings acted as a referee and were compared with the measurements in DVT scans. The statistical analysis between the two measurement protocols was performed using the Bland-Altman method. RESULTS: Best achievable agreement between DVT scans and histological reference was shown. Mean differences between DVT and grindings from -1.55 to -65.40 microm were calculated. All means are within the region of accuracy. General positioning of the implant into the cochlea could be verified in all specimens. The exact position of the implanted array within the cochlear scalae could be recognized correctly in 11 of 13 cases in DVT. It was possible to identify shiftings between the tympanic and vestibular scalae in all cases. CONCLUSION: DVT seems to be a convenient technique for postoperative position control after cochlear implantation.

Standardization of Microcomputed Tomography for Tracheal Tissue Engineering Analysis.

Tracheal tissue engineering has become an active area of interest among clinical and scientific communities; however, methods to evaluate success of in vivo tissue-engineered solutions remain primarily qualitative. These evaluation methods have generally relied on the use of photographs to qualitatively demonstrate tracheal patency, endoscopy to image healing over time, and histology to determine the quality of the regenerated extracellular matrix. Although those generally qualitative methods are valuable, they alone may be insufficient. Therefore, to quantitatively assess tracheal regeneration, we recommend the inclusion of microcomputed tomography (µCT) to quantify tracheal patency as a standard outcome analysis. To establish a standard of practice for quantitative µCT assessment for tracheal tissue engineering, we recommend selecting a constant length to quantify airway volume. Dividing airway volumes by a constant length provides an average cross-sectional area for comparing groups. We caution against selecting a length that is unjustifiably large, which may result in artificially inflating the average cross-sectional area and thereby diminishing the ability to detect actual differences between a test group and a healthy control. Therefore, we recommend selecting a length for µCT assessment that corresponds to the length of the defect region. We further recommend quantifying the minimum cross-sectional area, which does not depend on the length, but has functional implications for breathing. We present empirical data to elucidate the rationale for these recommendations. These empirical data may at first glance appear as expected and unsurprising. However, these standard methods for performing µCT and presentation of results do not yet exist in the literature, and are necessary to improve reporting within the field. Quantitative analyses will better enable comparisons between future publications within the tracheal tissue engineering community and empower a more rigorous assessment of results. Impact statement The current study argues for the standardization of microcomputed tomography (µCT) as a quantitative method for evaluating tracheal tissue-engineered solutions in vivo or ex vivo. The field of tracheal tissue engineering has generally relied on the use of qualitative methods for determining tracheal patency. A standardized quantitative evaluation method currently does not exist. The standardization of µCT for evaluation of in vivo studies would enable a more robust characterization and allow comparisons between groups within the field. The impact of standardized methods within the tracheal tissue engineering field as presented in the current study would greatly improve the quality of published work.

Three-dimensional imaging of mitochondrial cristae complexity using cryo-soft X-ray tomography.

Mitochondria are dynamic organelles that change morphology to adapt to cellular energetic demands under both physiological and stress conditions. Cardiomyopathies and neuronal disorders are associated with structure-related dysfunction in mitochondria, but three-dimensional characterizations of the organelles are still lacking. In this study, we combined high-resolution imaging and 3D electron density information provided by cryo-soft X-ray tomography to characterize mitochondria cristae morphology isolated from murine. Using the linear attenuation coefficient, the mitochondria were identified (0.247 ± 0.04 µm-1) presenting average dimensions of 0.90 ± 0.20 µm in length and 0.63 ± 0.12 µm in width. The internal mitochondria structure was successfully identified by reaching up the limit of spatial resolution of 35 nm. The internal mitochondrial membranes invagination (cristae) complexity was calculated by the mitochondrial complexity index (MCI) providing quantitative and morphological information of mitochondria larger than 0.90 mm in length. The segmentation to visualize the cristae invaginations into the mitochondrial matrix was possible in mitochondria with MCI ≥ 7. Altogether, we demonstrated that the MCI is a valuable quantitative morphological parameter to evaluate cristae modelling and can be applied to compare healthy and disease state associated to mitochondria morphology.

Ultrafast high-resolution in vivo volume-CTA of mice cerebral vessels.

BACKGROUND AND PURPOSE: Animal models developed in rats and mice have become indispensable in preclinical cerebrovascular research. Points of interest include the investigation of the vascular bed and the morphology and function of the arterial, capillary, and venous vessels. Because of their extremely small caliber, in vivo examination of these vessels is extremely difficult. In the present study we have developed a method to provide fast 3D in vivo analysis of cerebral murine vessels using volume computed tomography-angiography (vCTA). METHODS: Using an industrial X-ray inspection system equipped with a multifocus cone beam X-ray source and a 12-bit direct digital flatbed detector, high-speed vCTA (180 degrees rotation in 40 s. at 30 fps) was performed in anesthetized mice. During the scan an iodinated contrast agent was infused via a tail vein. Images were reconstructed using a filtered backprojection algorithm. Image analysis was performed by maximum intensity projection (MIP) and 3D volume reconstruction. RESULTS: All mice tolerated i.v. injection of the iodinated contrast agent well. Smallest achievable voxel size of raw data while scanning the whole neurocranium was 16 mum. Anatomy of cerebral vessels was assessable in all animals, and anatomic differences between mouse strains could easily be detected. Mean vessel diameter was measured in C57BL/6 and BALBc mice. Changes of vessel caliber were assessable by repeated vCTA. CONCLUSIONS: Ultra fast in vivo vCTA of murine cerebral vasculature is feasible at resolutions down to 16 mum. The technique allows the assessment of vessel caliber changes in living mice, thus providing an interesting tool to monitor different features such as vasospasm or vessel patency.

Comments on 'Ionization chamber volume determination and quality assurance using micro-CT imaging'.

The authors of a recent paper (McNiven et al 2008 Phys. Med. Biol. 53 5029-43) measured the volume of a particular type of a small ionization chamber using CT images. Using four Exradin A1SL chambers, they find that the volume measured using CT imaging is, on average, 4.3% larger than the value derived from the chamber calibration coefficient. Although they point out that the effective chamber volume is defined by electric field lines between the collector and the chamber body, they do not estimate how the mechanical volume might differ from the effective volume. We have used a commercial software package to calculate the electric field in the cavity and we show that the field lines define a volume that is about 11% smaller than the mechanical volume. We also show that the effective volume is very sensitive to small changes in the chamber geometry near the base of the collector. We conclude that simply determining the mechanical volume without careful consideration of the electric field lines within the cavity is not a useful dosimetric technique.

Uncertainties of synchrotron microCT-based digital volume correlation bone strain measurements under simulated deformation.

Digital Volume Correlation (DVC) is used to measure internal displacements and strains in bone. Recent studies have shown that Synchrotron radiation micro-computed tomography (SR-microCT) can improve the accuracy and precision of DVC. However, only zero-strain or virtually-moved test have been used to quantify the DVC uncertainties, leading to potential underestimation of the measurement errors. In this study, for the first time, the uncertainties of a global DVC approach have been evaluated on repeated SR-microCT scans of bovine cortical bone (voxel size: 1.6 µm), which were virtually deformed for different magnitudes and along different directions. The results showed that systematic and random errors of the normal strain components along the deformation direction were higher than the errors along unstrained directions. The systematic percentage errors were smaller for larger virtual deformations. The random percentage error was in the order of 10% of the virtual deformation. However, higher errors were localized at the boundary of the volumes of interest, perpendicular to the deformation direction. When only the central region of the samples was considered (100 µm layers removed from the borders where the deformation was applied), the errors in the direction of virtual deformation were comparable to the errors in the unstrained directions. In conclusion, the method presented to estimate the uncertainties of DVC is suitable for testing anisotropic specimens as cortical bone. The good agreement between the uncertainties in measurements of strain components obtained with this approach and with the simpler zero-strain-test suggests that the latter is adequate in the tested deformation scenarios.

Investigation on the validity of 3D micro-CT imaging in the fish brain.

BACKGROUND: Micro-computed tomography (CT) is a non-invasive technique that is used to obtain three-dimensional (3D) images of tissue structure in small animals. Compared with extensive mammal studies, few 3D imaging studies of fish have been conducted using micro-CT. An optimized method for imaging fish tissue structure is necessary, because they have adapted to diverse environments via functional and structural specialization. NEW METHOD: Brains of three species with different sizes and habitats were fixed in 4% paraformaldehyde and immersed in non-ionic iodinated contrast agent (Iopamiron). We examined the relationship between Iopamiron concentration and immersion time to determine universally optimal conditions for use in fish. RESULTS: We reconstructed 3D images of whole fish brains from cross-sections of brains from the Malabar grouper (Epinephelus malabaricus), bastard halibut (Paralichthys olivaceus), and threespot wrasse (Halichoeres trimaculatus). Developmental changes in brain structure were observed in the bastard halibut. Most brain regions of the threespot wrasse were distinguishable, although inner regions of the brain were less visible. COMPARISON WITH EXISTING METHODS: Histological techniques are typically used to observe fish brain structure, despite its drawbacks in terms of tissue sample preparation (shrinkage and distortion) and image capture (3D image constriction). The technique examined in the present study solves these problems and allows for the simultaneous handling of multiple specimens. CONCLUSION: Micro-CT imaging is suitable for observing the surfaces and inner structures of fish of various species.

Ultrasonic cartilage thickness measurement is accurate, reproducible, and reliable-validation study using contrast-enhanced micro-CT.

BACKGROUND: Ultrasonography is a fast and patient-friendly modality to assess cartilage thickness. However, inconsistent results regarding accuracy have been reported. Therefore, we asked what are (1) the accuracy, (2) reproducibility, and (3) reliability of ultrasonographic cartilage thickness measurement using contrast-enhanced micro-CT for validation? METHODS: A series of 50 cartilage-bone plugs were harvested from fresh bovine and porcine joints. Ultrasonic cartilage thickness was determined using an A-mode, 20-MHz hand-held ultrasonic probe with native (1580 m/s) and adjusted speed of sound (1696 m/s). All measurements were performed by two observers at two different occasions. Angle of insonation was controlled by tilting the device and recording minimal thickness. Retrieval of exact location for measurement was facilitated by aligning the circular design of both cartilage-bone plug and ultrasonic device. There was no soft tissue interference between cartilage surface and ultrasonic probe. Ground truth measurement was performed using micro-CT with iodine contrast agent and a voxel size of 16 µm. The mean cartilage thickness was 1.383 ± 0.402 mm (range, 0.588-2.460 mm). RESULTS: Mean accuracy was 0.074 ± 0.061 mm (0.002-0.256 mm) for native and 0.093 ± 0.098 mm (0.000-0.401 mm) for adjusted speed of sound. Bland-Altman analysis showed no systematic error. High correlation was found for native and adjusted speed of sound with contrast-enhanced micro-CT (both r = 0.973; p < 0.001). A perfect agreement for reproducibility (intraclass correlation coefficient [ICC] 0.992 and 0.994) and reliability (ICC 0.993, 95% confidence interval 0.990-0.995) was found. CONCLUSIONS: Ultrasonic cartilage thickness measurement could be shown to be highly accurate, reliable, and reproducible. The A-mode ultrasonic cartilage thickness measurement is a fast and patient-friendly modality which can detect early joint degeneration and facilitate decision making in joint preserving surgery.

MicroCT imaging dose to mouse organs using a validated Monte Carlo model of the small animal radiation research platform (SARRP).

The goal of this work was to establish imaging dose to mouse organs with a validated Monte Carlo (MC) model of the image-guided Small Animal Radiation Research Platform (SARRP) and to investigate the effect of scatter from the internal walls on animal therapy dose determination. A MC model of the SARRP was built in the BEAMnrc code and validated with a series of homogeneous and heterogeneous phantom measurements. A segmented microCT scan of a mouse was used in DOSXYZnrc to determine mouse organ microCT imaging doses to 15-35 g mice for the SARRP pancake (mouse lying on couch) and standard (mouse standing on couch) imaging geometries for 40-80 kVp tube voltages. Imaging dose for off-center positioning shifts and maintaining image noise across tube voltages were also calculated. Half-value layer (HVL) measurements for the 220 kVp therapy beam in the presence of the SARRP shielding cabinet were modeled in BEAMnrc and compared to the 100 cm source-to-detector distance (SDD) in the scatter free, narrow-beam geometry recommended by the American Association of Physicists in Medicine Task Group 61 (AAPM TG-61). For a 60 kVp, 0.8 mA, and 60 s scan protocol, maximum mean organ imaging doses to boney and non-boney structures were 10.5 cGy and 3.5 cGy, respectively, for an average size 20 g mouse. Current-exposure combinations above 323, 203, 147, 116, and 95 mAs for 40-80 kVp tube voltages, respectively, will increase body doses above 10 cGy. MicroCT mean body dose was 18% lower in pancake compared to standard imaging geometry. An 11% difference in measured HVL at a 50 cm SDD was found compared to MC simulated HVL for the AAPM TG-61 recommended scatter free geometry at a 100 cm SDD. This change in HVL resulted in a 0.5% change in absorbed dose to water calculations for the treatment beam.

Quantification of voxel values in micro computed tomography using multiple porosity hydroxyapatite blocks.

Microfocus X-ray computed tomography (micro-CT) has been applied as a method for the nondestructive and detailed assessment of trabecular bone patterns and tooth structure. Voxel values obtained from micro-CT are not absolute values. Therefore, voxel values were assessed using hydroxyapatite (HA) blocks with a different vesicle rate to quantify voxel values of micro-CT images in the present investigation.HA blocks with 4 levels of porosity and a block with a soft tissue-equivalent density were used, and the voxel values of each block were measured. Correlations between voxel values of micro-CT and HA densities were analyzed. Also, black and white binary images were produced, and the ratios of white pixels to pixels in regions of interest (ROIs) were calculated. The relationship between voxel values of micro-CT and HA densities could be regressed using a linear equation, and the correlation coefficient was high. Also, there were no significant differences in the regression equations between the first and second times. Voxel values of micro-CT might be convertible to HA densities using a regression equation.

Evaluation of Threshold Values for Root Canal Filling Voids in Micro-CT and Nano-CT Images.

While several materials and techniques have been used to assess the quality of root canal fillings in micro-CT images, the lack of standardization in scanning protocols has produced conflicting results. Hence, the aim of this study was to determine a cutoff voxel size value for the assessment of root canal filling voids in micro-CT and nano-CT images. Twenty freshly extracted mandibular central incisors were used. Root canals were prepared with nickel titanium files to an ISO size 40/0.06 taper and then filled with a single cone (40/0.06 taper) and AH Plus sealer. The teeth were scanned with different voxel sizes with either micro-CT (5.2, 8.1, 11.2, and 16.73 µm) or nano-CT (1.5 and 5.0 µm) equipment. Images were reconstructed and analyzed with the NRecon and CTAn software. Void proportion and void volume were calculated for each tooth in the apical, middle, and coronal thirds of the root canal. Kruskal-Wallis and post hoc Mann-Whitney U tests were performed with a significance level of 5%. In micro-CT images, significantly different results were detected among the tested voxel sizes for void proportion and void volume, whereas no such differences were found in nano-CT images (p > 0.05). Micro-CT images showed higher void numbers over the entire root length, with statistically significant differences between the voxel size of 16.73 µm and the other sizes (p < 0.05). The values of the different nano-CT voxel sizes did not significantly differ from those of the micro-CT (5.2, 8.1, and 11.2 µm), except for the voxel size of 16.73 µm (p < 0.05). All tested voxel sizes enabled the detection of root canal filling voids except for the voxel size of 16.73 µm. Bearing in mind the limitations of this study, it seems that a voxel size of 11.2 µm can be used as a reliable cutoff value for the assessment of root canal filling voids in micro-CT imaging.

Quantitative assessment of paravalvular leakage after transcatheter aortic valve replacement using a patient-specific pulsatile flow model.

BACKGROUND: Quantitative assessment of post-transcatheter aortic valve replacement (TAVR) aortic regurgitation (AR) remains challenging. We developed patient-specific anatomical models with pulsatile flow circuit and investigated factors associated with AR after TAVR. METHODS: Based on pre-procedural computed tomography (CT) data of the six patients who underwent transfemoral TAVR using a 23-mm SAPIEN XT, anatomically and mechanically equivalent aortic valve models were developed. Forward flow and heart rate of each patient in two days after TAVR were duplicated under mean aortic pressure of 80mmHg. Paravalvular leakage (PVL) volume in basal and additional conditions was measured for each model using an electromagnetic flow sensor. Incompletely apposed tract between the transcatheter and aortic valves was examined using a micro-CT. RESULTS: PVL volume in each patient-specific model was consistent with each patient's PVL grade, and was affected by hemodynamic conditions. PVL and total regurgitation volume increased with the mean aortic pressure, whereas closing volume did not change. In contrast, closing volume increased proportionately with heart rate, but PVL did not change. The minimal cross-sectional gap had a positive correlation with the PVL volumes (r=0.89, P=0.02). The gap areas typically occurred in the vicinity of the bulky calcified nodules under the native commissure. CONCLUSIONS: PVL volume, which could be affected by hemodynamic conditions, was significantly associated with the minimal cross-sectional gap area between the aortic annulus and the stent frame. These data may improve our understanding of the mechanism of the occurrence of post-TAVR PVL.

Reliable landmarks for precise topographical analyses of pathological structural changes of the ovine tibial plateau in 2-D and 3-D subspaces.

Selecting identical topographical locations to analyse pathological structural changes of the osteochondral unit in translational models remains difficult. The specific aim of the study was to provide objectively defined reference points on the ovine tibial plateau based on 2-D sections of micro-CT images useful for reproducible sample harvesting and as standardized landmarks for landmark-based 3-D image registration. We propose 5 reference points, 11 reference lines and 12 subregions that are detectable macroscopically and on 2-D micro-CT sections. Their value was confirmed applying landmark-based rigid and affine 3-D registration methods. Intra- and interobserver comparison showed high reliabilities, and constant positions (standard errors < 1%). Spatial patterns of the thicknesses of the articular cartilage and subchondral bone plate were revealed by measurements in 96 individual points of the tibial plateau. As a case study, pathological phenomena 6 months following OA induction in vivo such as osteophytes and areas of OA development were mapped to the individual subregions. These new reference points and subregions are directly identifiable on tibial plateau specimens or macroscopic images, enabling a precise topographical location of pathological structural changes of the osteochondral unit in both 2-D and 3-D subspaces in a region-appropriate fashion relevant for translational investigations.