Efficient storage of microCT data preserving bone morphometry assessment

Available online 15 July 2015Preclinical micro-computed tomography (microCT) images are of utility for 3D morphological bone evaluation, which is of great interest in cancer detection and treatment development. This work introduces a compression strategy for microCTs that allocates specific substances in different Volumes of Interest (VoIs). The allocation procedure is conducted by the Hounsfield scale. The VoIs are coded independently and then grouped in a single DICOM-compliant file. The proposed method permits the use of different codecs, identifies and transmit data corresponding to a particular substance in the compressed domain without decoding the volume(s), and allows the computation of the 3D morphometry without needing to store or transmit the whole image. The proposed approach reduces the transmitted data in more than 90% when the 3D morphometry evaluation is performed in high density and low density bone. This work can be easily extended to other imaging modalities and applications that work with the Hounsfield scale

RELATIONSHIPS OF LONG-TERM BISPHOSPHONATE TREATMENT WITH MEASURES OF BONE MICROARCHITECTURE AND MECHANICAL COMPETENCE

Oral bisphosphonate drug therapy is a common and effective treatment for osteoporosis. Little is known about the long-term effects of bisphosphonates on bone quality. This study examined the structural and mechanical properties of trabecular bone following 0-16 years of bisphosphonate treatment. Fifty-three iliac crest bone samples of Caucasian women diagnosed with low turnover osteoporosis were identified from the Kentucky Bone Registry. Forty-five were treated with oral bisphosphonates for 1 to 16 years while eight were treatment naive. A section of trabecular bone was chosen from a micro-computed tomography (Scanco µCT 40) scan of each sample for a uniaxial linearly elastic compression simulation using finite element analysis (ANSYS 14.0). Morphometric parameters (BV/TV, SMI, Tb.Sp., etc.) were computed using µCT. Apparent modulus, effective modulus and estimated failure stress were calculated. Biomechanical and morphometric parameters improved with treatment duration, peaked around 7 years, and then declined independently of age. The findings suggest a limit to the benefits associated with bisphosphonate treatment and that extended continuous bisphosphonate treatment does not continue to improve bone quality. Bone quality, and subsequently bone strength, may eventually regress to a state poorer than at the onset of treatment. Treatment duration limited to less than 7 years is recommended

Micro-CT imaging of Thiel-embalmed and iodine-stained human temporal bone for 3D modeling

Introduction This pilot study explores whether a human Thiel-embalmed temporal bone is suitable for generating an accurate and complete data set with micro-computed tomography (micro-CT) and whether solid iodine-staining improves visualization and facilitates segmentation of middle ear structures. Methods A temporal bone was used to verify the accuracy of the imaging by first digitally measuring the stapes on the tomography images and then physically under the microscope after removal from the temporal bone. All measurements were compared with literature values. The contralateral temporal bone was used to evaluate segmentation and three-dimensional (3D) modeling after iodine staining and micro-CT scanning. Results The digital and physical stapes measurements differed by 0.01–0.17 mm or 1–19%, respectively, but correlated well with the literature values. Soft tissue structures were visible in the unstained scan. However, iodine staining increased the contrast-to-noise ratio by a factor of 3.7 on average. The 3D model depicts all ossicles and soft tissue structures in detail, including the chorda tympani, which was not visible in the unstained scan. Conclusions Micro-CT imaging of a Thiel-embalmed temporal bone accurately represented the entire anatomy. Iodine staining considerably increased the contrast of soft tissues, simplified segmentation and enabled detailed 3D modeling of the middle ear

Non-invasive prediction of bone mechanical properties of the mouse tibia in longitudinal preclinical studies

The mouse tibia is a common site to investigate bone remodelling and the effect of treatments preclinically. It can be monitored using in vivo micro-Computed Tomography (microCT) imaging in order to track longitudinal changes in its morphometric and densitometric properties. Additionally, microCT images can be converted into micro-Finite Element (microFE) models for the non-invasive estimation of mechanical properties. Therefore, the combination of in vivo imaging and microFE modelling can provide comprehensive analyses about bone changes over space and time. However, repeated ionizing radiation exposure can have a significant effect on the bone properties; also, microFE models need to be validated against experimental measurements before application. The aim of this PhD project was to provide the best practice for the definition and validation of the in vivo microCT scanning procedure for the mouse tibia in preclinical studies. First, different scanning protocols have been tested by quantifying the accuracy of the image-based measurements against high resolution scans. One of the procedures has been selected as the best compromise between measurement accuracy and nominal radiation dose. Afterwards, microFE predictions of local and structural mechanical properties obtained using the selected scanning protocol have been validated. The experimental data for the validation has been obtained using the Digital Volume Correlation (DVC) approach, the only method which can provide volumetric measurements of local displacements under loading. Good to excellent correlations between the measured and predicted displacements were found. Errors in predictions of structural properties were in the order of 10-15%. Lastly, the protocol has been tested in vivo. The right tibia of 24 mice has been scanned in vivo five times, while the left tibia has been used as non-irradiated control. Non-significant or minimal radiation effects were found on the morphometric, densitometric and mechanical properties of the tibia. In conclusion, a scanning procedure for longitudinal in vivo microCT imaging of the whole mouse tibia has been defined and validated. The protocol will be used in future studies for investigating the effect of bone interventions

Bone-like inducing grafts: in vivo and micro-CT analysis

L'abstract è presente nell'allegato / the abstract is in the attachmen

Toughening mechanisms for the attachment of architectured materials: The mechanics of the tendon enthesis

Use of load-bearing materials whose functionality arises from architectured microstructures, so called architectured materials, has been hindered by the challenge of connecting them. A solution in nature is found at the tendon enthesis, a tissue that connects tendon and bone, two vastly different natural architectured materials. The tendon enthesis provides stability and allows for mobility of a joint though effective transfer of muscle forces from tendon to bone, while exhibiting toughness across a wide range of loadings. Unfortunately, many painful and physically debilitating conditions occur at or near this interface when the enthesis architecture is compromised due to injury or degeneration. Surgical and natural repairs do not reconstitute the natural toughening mechanisms of the enthesis and often fail. Hence, understanding the architectural mechanisms by which healthy and pathologic tendon entheses achieve strength and toughness would inform the development of both biological and engineered attachments.Integrating biomechanical analyses, failure characterizations, numerical simulations, and novel imaging, this thesis presents architectural mechanisms of enthesis toughening in a mouse model. Imaging uncovered fibrous architecture within the enthesis, which controlled trade-offs between strength and toughness. Ex vivo enthesis failure modes exhibited nanoscale differences in damage, milliscale differences in fiber load-sharing, and macroscale differences in energy absorption that depended on structure, composition, and the nature of loading. The elastic and failure responses of the tendon enthesis also varied with the direction of loading. This variation was due to the fibrous nature of the tendon enthesis, with a clear role for bony anatomy and fiber recruitment in enthesis toughening behavior. In vivo, , the loss of toughening mechanisms at the enthesis due to pathologic loading was evaluated by either increased (i.e., overuse) loading via downhill treadmill running or decreased (i.e., underuse) loading via botulinum toxin A induced paralysis. These loading environments led to changes in the mineralization and architecture at the tendon enthesis. These micro-architectural adaptations compromised the trade-offs between strength and toughness; overuse loading prompted active reinforcement and stiffening of the underlying trabeculae, leading a maintenance of strength and a compromise in overall toughness, whereas underloading prompted active resorption of the underlying trabecular architecture, leading to a compromise in both strength and toughness. The mouse models of the tendon enthesis failure revealed a correlation between tendon enthesis architecture and injury prevention (i.e., toughening) mechanisms. To test this concept in a clinical setting, an injury classification system was developed for patellar tendinopathy and partial patellar tendon tears. This classification system identified the stages of tear progression and prognosis by tracking changes to patellar tendon architecture. Results revealed a relationship between patellar tendon thickness and likelihood of improvement with nonoperative treatment. Taken together, this dissertation revealed how fibrous architecture can be tailored to toughen attachments between vastly different materials. This understanding can have prognostic value: tracking changes to enthesis architecture can be used as a tool for identifying candidates for various treatment options, as we showed for the patellar tendon clinical example. Furthermore, the toughening mechanisms identified here provide guidance for enhancing enthesis surgical repair and designing enthesis tissue engineered scaffolds, as well as motivating biomimetic approaches for attachment of architectured engineering material systems

The Digital Fish Library: Using MRI to Digitize, Database, and Document the Morphological Diversity of Fish

Museum fish collections possess a wealth of anatomical and morphological data that are essential for documenting and understanding biodiversity. Obtaining access to specimens for research, however, is not always practical and frequently conflicts with the need to maintain the physical integrity of specimens and the collection as a whole. Non-invasive three-dimensional (3D) digital imaging therefore serves a critical role in facilitating the digitization of these specimens for anatomical and morphological analysis as well as facilitating an efficient method for online storage and sharing of this imaging data. Here we describe the development of the Digital Fish Library (DFL, http://www.digitalfishlibrary.org), an online digital archive of high-resolution, high-contrast, magnetic resonance imaging (MRI) scans of the soft tissue anatomy of an array of fishes preserved in the Marine Vertebrate Collection of Scripps Institution of Oceanography. We have imaged and uploaded MRI data for over 300 marine and freshwater species, developed a data archival and retrieval system with a web-based image analysis and visualization tool, and integrated these into the public DFL website to disseminate data and associated metadata freely over the web. We show that MRI is a rapid and powerful method for accurately depicting the in-situ soft-tissue anatomy of preserved fishes in sufficient detail for large-scale comparative digital morphology. However these 3D volumetric data require a sophisticated computational and archival infrastructure in order to be broadly accessible to researchers and educators

Biomechanics of spinal metastases

The lack of suitable models for prediction of the vertebral body (VB) failure load for a variety of pathologies hampers the development of indications for surgical and pharmaceutical interventions and the assessment of novel treatments. Similar models would also be of benefit in a laboratory environment in which predictions of failure load could aid experimental design when using cadaveric tissue. Finite element modelling shows great potential but the expertise required to effectively deploy this technology in a clinical environment precludes its routine use at the present time. Its deployment within the laboratory environment is also time consuming. An alternative approach may be the use of composite beam theory structural analysis that takes into account both vertebral geometry and the bone mineral density (BMD) distribution and they are utilised to predict the loads at which vertebrae will fail. As a part of this work, vertebrae suffering from three distinct pathologies (osteoporosis, multiple myeloma (MM) and metastases) were tested in a wedge compression loading protocol (WCF) as a determinant for vertebroplasty treatment. MM bone was first tested for changes at the bone tissue level by means of depth-sensing micro-indentation testing. In the second part more than one hundred VBs were subjected to a destructive in-vitro WCF experiment, while CT images were used for in-silico structural and morphological assessment. In the last part, two vertebroplasty cements, calcium phosphate and PMMA, were tested. At the tissue level MM bone shows rather moderate changes which are of such small magnitude that alone would not be sufficient to change the overall vertebral strength. Relatively good predictions of VB strength were obtained when using image-based fracture prediction suggesting that bone distribution and pathological alterations to its structure make a significant contribution to overall VB strength. The results of VB reinforcement using either of the cements show increased strength while stiffness was restored only when PMMA cement was injected in lower porosity samples