Coupled Active Shape Models for Automated Segmentation and Landmark Localization in High-Resolution CT of the Foot and Ankle

Morphologic analysis of the 1st and 2nd tarsometatarsal joint articular surfaces

Tarsometatarsal joint arthrodesis is used to treat a variety of injuries and deformities in the midfoot. However, the surgical technique has not been optimized, in part due to limited knowledge of morphologic features and variation in the related joints. Previous research has relied primarily on dissection-based anatomical analysis, but quantitative imaging may allow for a more sophisticated description of this complex. Here, we used quantitative micro-CT imaging to examine dimensions, distance maps, and curvature of the four articular surfaces in the first and second tarsometatarsal joints. Image segmentation, articular surface identification, and anatomic coordinate systems were all done with semi or fully automatic methods, and distance and size measurements were all taken utilizing these anatomic planes. Surface curvature was studied using Gaussian curvature and a newly defined measure of curvature similarity on the whole joint and on four subregions of each surface. These data show larger articular surfaces on the cuneiforms, rather than metatarsals, and define the generally tall and narrow articular surfaces seen in these joints. Curvature analysis shows minimally curved opposing convex surfaces. Our results are valuable for furthering knowledge of surgical anatomy in this poorly understood region of the foot.

Computed Tomography: State-of-the-Art Advancements in Musculoskeletal Imaging

ABSTRACT

Although musculoskeletal magnetic resonance imaging (MRI) plays a dominant role in characterizing abnormalities, novel computed tomography (CT) techniques have found an emerging niche in several scenarios such as trauma, gout, and the characterization of pathologic biomechanical states during motion and weight-bearing. Recent developments and advancements in the field of musculoskeletal CT include 4-dimensional, cone-beam (CB), and dual-energy (DE) CT. Four-dimensional CT has the potential to quantify biomechanical derangements of peripheral joints in different joint positions to diagnose and characterize patellofemoral instability, scapholunate ligamentous injuries, and syndesmotic injuries. Cone-beam CT provides an opportunity to image peripheral joints during weight-bearing, augmenting the diagnosis and characterization of disease processes. Emerging CBCT technologies improved spatial resolution for osseous microstructures in the quantitative analysis of osteoarthritis-related subchondral bone changes, trauma, and fracture healing. Dual-energy CT-based material decomposition visualizes and quantifies monosodium urate crystals in gout, bone marrow edema in traumatic and nontraumatic fractures, and neoplastic disease. Recently, DE techniques have been applied to CBCT, contributing to increased image quality in contrast-enhanced arthrography, bone densitometry, and bone marrow imaging. This review describes 4-dimensional CT, CBCT, and DECT advances, current logistical limitations, and prospects for each technique.

Weight-bearing cone-beam CT: the need for standardised acquisition protocols and measurements to fulfill high expectations-a review of the literature

Weight bearing CT (WBCT) of the lower extremity is gaining momentum in evaluation of the foot/ankle and knee. A growing number of international studies use WBCT, which is promising for improving our understanding of anatomy and biomechanics during natural loading of the lower extremity. However, we believe there is risk of excessive enthusiasm for WBCT leading to premature application of the technique, before sufficiently robust protocols are in place e.g. standardised limb positioning and imaging planes, choice of anatomical landmarks and image slices used for individual measurements. Lack of standardisation could limit benefits from introducing WBCT in research and clinical practice because useful imaging information could become obscured. Measurements of bones and joints on WBCT are influenced by joint positioning and magnitude of loading, factors that need to be considered within a 3-D coordinate system. A proportion of WBCT studies examine inter- and intraobserver reproducibility for different radiological measurements in the knee or foot with reproducibility generally reported to be high. However, investigations of test-retest reproducibility are still lacking. Thus, the current ability to evaluate, e.g. the effects of surgery or structural disease progression, is questionable. This paper presents an overview of the relevant literature on WBCT in the lower extremity with an emphasis on factors that may affect measurement reproducibility in the foot/ankle and knee. We discuss the caveats of performing WBCT without consensus on imaging procedures and measurements.

Atlas-based algorithm for automatic anatomical measurements in the knee

We present an algorithm for automatic anatomical measurements in tomographic datasets of the knee. The algorithm uses a set of atlases, each consisting of a knee image, surface segmentations of the bones, and locations of landmarks required by the anatomical metrics. A multistage volume-to-volume and surface-to-volume registration is performed to transfer the landmarks from the atlases to the target volume. Manual segmentation of the target volume is not required in this approach. Metrics were computed from the transferred landmarks of a best-matching atlas member (different for each bone), identified based on a mutual information criterion. Leave-one-out validation of the algorithm was performed on 24 scans of the knee obtained using extremity cone-beam computed tomography. Intraclass correlation (ICC) between the algorithm and the expert who generated atlas landmarks was above 0.95 for all metrics. This compares favorably to inter-reader ICC, which varied from 0.19 to 0.95, depending on the metric. Absolute agreement with the expert was also good, with median errors below 0.25 deg for measurements of tibial slope and static alignment, and below 0.2 mm for tibial tuberosity-trochlear groove distance and medial tibial depth. The automatic approach is anticipated to improve measurement workflow and mitigate the effects of operator experience and training on reliability of the metrics.