Thomas M. Link

Advanced imaging of bone macro and micro structure

In the past decade, considerable progress has been made in the development of methods for assessing the skeleton noninvasively so that osteoporosis can be detected early, its progression and response to therapy carefully monitored, or the risk of fracture effectively ascertained. Bone mineral density (BMD) of the peripheral, central, or entire skeleton as well as the trabecular or cortical bone envelopes, can now be evaluated with a high degree of accuracy and precision, and the strength of bone and the propensity to fracture can be reliably estimated. Noninvasive and/or nondestructive techniques are capable of providing macro or micro structural information about bone, beyond simple bone densitometry. While the latter provides important information about osteoporotic fracture risk, numerous studies indicate that bone strength is only partially explained by BMD. Quantitative assessment of macrostructural characteristics such as geometry, and microstructural features such as relative trabecular volume, trabecular spacing, and connectivity, may improve our ability to estimate bone strength. The methods available for quantitatively assessing macrostructure include (besides conventional radiographs, which are not considered in this review) computed tomography and particularly volumetric quantitative computed tomography (vQCT). Methods for assessing microstructure of trabecular bone noninvasively and/or nondestructively include high-resolution computed tomography (hrCT), micro computed tomography (mCT), high-resolution magnetic resonance (hrMR), and micro magnetic resonance (mMR). vQCT, hrCT, and hrMR are generally applicable in vivo, and mCT and mMR are principally applicable in vitro.

Malignant fibrous histiocytoma of bone: conventional X-ray and MR imaging features

Abstract Objective. To evaluate the conventional X-ray and MR imaging features of malignant fibrous histiocytoma (MFH) of bone. Design. MRI examinations and conventional radiographs were reviewed in 39 patients with biopsy-proven MFH. Imaging characteristics were analyzed and the differential diagnoses assessed in a masked fashion by two experienced radiologists. Results. Typical X-ray features included aggressive, destructive tumor growth centrally located in the metaphysis of long bones. Periosteal reactions and expansive growth were rarely seen. On MR images extraosseous tumor spread was frequently noted. On T2-weighted images and contrast-enhanced T1-weighted images most of the tumors displayed an inhomogeneous, nodular signal pattern with peripheral Gd-DTPA enhancement. Conclusions. Although several MR imaging criteria were typical for MFH none of them was specific. X-ray diagnosis of MFH may also prove difficult, with the main differential diagnosis being metastasis in the older and osteosarcoma in the younger population.

Application of the Minkowski Functionals in 3D to high resolution MR Images of trabecular bone: prediction of the biomechanical strength by non-linear topological measures

Multi-dimensional convex objects can be characterized with respect to shape, structure, and the connectivity of their components using a set of morphological descriptors known as the Minkowski functionals. In a 3D Euclidian space, these correspond to volume, surface area, mean integral curvature, and the Euler-Poincaré characteristic. We introduce the Minkowski functionals to medical image processing for the morphological analysis of trabecular bone tissue. In the context of osteoporosis-a metabolic disorder leading to a weakening of bone due to deterioration of micro-architecture-the structure of bone increasingly gains attention in the quantification of bone quality. The trabecular architecture of healthy cancellous bone consists of a complex 3D system of inter-connected mineralised elements whereas in osteoporosis the micro-structure is dominated by gaps and disconnections. At present, the standard parameter for diagnosis and assessment of fracture risk in osteoporosis is the bone mineral density (BMD) - a bulk measure of mineralisation irrespective of structural texture characteristics. With the development of modern imaging modalities (high resolution MRI, micro-CT) with spatial resolutions allowing to depict individual trabeculae bone micro-architecture has successfully been analysed using linear, 2- dimensional structural measures adopted from standard histo-morphometry. The preliminary results of our study demonstrate that due to the complex - i.e. the non-linear - network of trabecular bone structures non-linear measures in 3D are superior to linear ones in predicting mechanical properties of trabecular bone from structural information extracted from high resolution MR image data.

Future Perspective and Significance of Cartilage Imaging and Quantification

Cartilage is one of the most significant structures for joint function and is compromised in degenerative and traumatic joint disease. MR imaging has been established as the standard cartilage imaging modality, and techniques have been developed and optimized to visualize cartilage morphology, to quantify its volume and to analyze its biochemical composition. The substantial amount of research that is invested in the development of these morphologic and quantitative imaging techniques is geared at preventing and treating traumatic and degenerative cartilage disease at the earliest stages.

Femoroacetabular impingement and hip OsteoaRthritis Cohort (FORCe): protocol for a prospective study

markdownabstractIntroduction: Femoroacetabular impingement syndrome is a common cause of hip-related pain in active young adults. It comprises a triad of imaging findings, symptoms and signs, and is usually characterised by extra bone formation at the femoral head-neck junction known as ‘cam morphology’. Cam morphology is theorised to create hip impingement in hip flexion activities, place stress on hip joint structures, and increase the risk of hip osteoarthritis over time.

The Locally Adapted Scaling Vector Method: A New Tool for Quantifying Anisotropic Structures in Bone Images

Osteoporosis is a metabolic bone disorder in which bones become brittle and prone to fracture. According to the World Health Organization, it is characterized by the loss of bone mineral density and the deterioration of the bone micro-architecture (Prevention and Management of Osteoporosis, 2003). One of the most important factors in determining the risk of fracture is the bone strength. In clinical practice, the risk of fracture and the effects of drug therapy are assessed using only densitometric techniques as a quantitative measure (Kanis, 2002; Kanis, 2007). Modern high-resolution imaging modalities like High-Resolution Computer Tomography (HRCT) and High-Resolution Magnetic Resonance Imaging (HRMRI) open up new possibilities to improve diagnostic techniques of osteoporosis since they are able to depict the architecture of trabecular bone. In particular, recent advances in MRI technology allow us to obtain images with in-plane spatial resolution as high as 50 μm in vitro and 150 μm in vivo, and a slice thickness of 128 μm in vitro and 280 μm in vivo (Link, et al., 1999; Carballido-Gamio et al., 2006; Wehrli, 2007; Krug et al., 2006). These figures should be compared with the actual thickness of the trabeculae, which ranges from 80 to 200 μm with an average size of approximately 120 μm. It has been shown that these imaging modalities enable the assessment of image data with respect to textural properties to detect structural differences (Boutry et al., 2003; Majumdar et al., 1996; Vieth et al., 2001). HRCT is the preferred methodology to image bones. In contrast to MRI scans, CT scans can easily be calibrated using phantoms, thus rendering images with a standardize grey level distribution. In addition, CT images of the bone are free from the susceptibility artifacts and, in case of in vivo applications, have a less stringent requirement for patients to remain absolutely motionless during the scan as compared to MRI.

MR T2 Relaxation Time Measurements for Cartilage and Menisci

Magnetic Resonance Imaging (MRI) can be used not only for morphologic but also for quantitative assessment of knee cartilage. Quantitative T1rho and T2 relaxation time measurements and dGEMRIC (delayed Gadolinium enhanced MRI of the cartilage) have emerged as potential cartilage biomarkers to assess early degenerative disease. This chapter focuses on the T2-technique and clinical applications of hyaline cartilage and meniscal T2 relaxation time measurements in particular at the knee.

Nicht-lineare Texturmaße basierend auf den Minkowski-Funktionalen in 3D: Vorhersage der Bruchlast trabekulärer Knochenpräparate durch Strukturanalyse hochauflösender MR-Aufnahmen

Die Topologie multi-dimensionaler, konvexer Objekte kann mit Hilfe der Minkowski-Funktionale (MF) eindeutig charakterisiert werden. Im 3-dimensionalen euklidischen Raum sind diese proportional dem Volumen, der Oberflache, der mittleren integralen Krummung und der Euler-Poincare-Charakteristik. In unserer Arbeit wird mittels nicht-linearer Strukturmase, die auf den MF in 3D basieren, aus hochauflosenden MRT-Bilddaten menschlicher spinaler und femoraler Knochenpraparate die mechanische Bruchfestigkeit (MCS) vorherbestimmt. Die pradiktive Wertigkeit der neuen Parameter in vitro wird der Wertigkeit der Knochenmineralsalzdichte (BMD), gemessen durch quantitative Computertomographie (QCT), sowie der Wertigkeit linearer Strukturmasse gegenuber gestellt.