Andrew H Gee

University of Cambridge, Cambridge, England, United Kingdom

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Publications (175)274.67 Total impact

  • No preview · Article · Apr 2016 · Osteoarthritis and Cartilage
  • [Show abstract] [Hide abstract] ABSTRACT: Background: Teriparatide (TPTD) is an anabolic agent indicated for the treatment of severely osteoporotic patients who are at high risk of fragility fractures. The originally approved duration of TPTD treatment in several regions, including Europe, was 18 months. However, studies of areal bone mineral density (aBMD) showed additional benefit when treatment is continued beyond 18 months, and the drug is currently licenced for 24 months. Improvements in cortical structure at the proximal femur have already been shown in patients given TPTD for 24 months using quantitative computed tomography (QCT). Here, we investigate whether cortical and endocortical trabecular changes differ between an 18- and 24-month treatment. Methods: Since an 18- versus 24-month TPTD study using QCT has not been conducted, we studied combined QCT data from four previous clinical trials. Combined femoral QCT data from three 18-month TPTD studies ('18-month group') were compared with data from a fourth 24-month trial ('24-month group'). Cortical parameters were measured over the entire proximal femur which allowed for a comparison of the mean changes as well as a visual comparison of the colour maps of changes after 18 and 24 months TPTD. Results: For both the combined 18-month group and the 24-month group, overall cortical thickness and endocortical trabecular density increased, while overall cortical bone mineral density decreased. While the changes in the 24-month group were of greater magnitude compared to the 18-month group, the differences were only significant for the endocortical trabecular density (ECTD), corrected for age, weight, femoral neck T-score, total hip T-score and the baseline mean ECTD. Conclusion: Although the combination of data from different clinical trials is not optimal, these data support the concept that the duration of TPTD in the 18-24 month phase is of clinical relevance when considering improvement in hip structure.
    No preview · Article · Feb 2016 · PLoS ONE
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    [Show abstract] [Hide abstract] ABSTRACT: Objective: To assess the relationship between proximal femoral cortical bone thickness and radiological hip osteoarthritis using quantitative 3D analysis of clinical computed tomography (CT) data. Methods: Image analysis was performed on clinical CT imaging data from 203 female volunteers with a technique called cortical bone mapping (CBM). Colour thickness maps were created for each proximal femur. Statistical parametric mapping was performed to identify statistically significant differences in cortical bone thickness that corresponded with the severity of radiological hip osteoarthritis. Kellgren and Lawrence (K&L) grade, minimum joint space width (JSW) and a novel CT-based osteophyte score were also blindly assessed from the CT data. Results: For each increase in K&L grade, cortical thickness increased by up to 25 % in distinct areas of the superolateral femoral head-neck junction and superior subchondral bone plate. For increasing severity of CT osteophytes, the increase in cortical thickness was more circumferential, involving a wider portion of the head-neck junction, with up to a 7 % increase in cortical thickness per increment in score. Results were not significant for minimum JSW. Conclusions: These findings indicate that quantitative 3D analysis of the proximal femur can identify changes in cortical bone thickness relevant to structural hip osteoarthritis. Key points: • CT is being increasingly used to assess bony involvement in osteoarthritis • CBM provides accurate and reliable quantitative analysis of cortical bone thickness • Cortical bone is thicker at the superior femoral head-neck with worse osteoarthritis • Regions of increased thickness co-locate with impingement and osteophyte formation • Quantitative 3D bone analysis could enable clinical disease prediction and therapy development.
    Preview · Article · Oct 2015 · European Radiology
  • [Show abstract] [Hide abstract] ABSTRACT: MicroabstractThe aim of this study was to examine the effects of denosumab versus placebo on cortical bone using clinical CT. We used cortical bone mapping to study the hips of women with osteoporosis treated during the FREEDOM clinical trial. We found that cortical mass surface density and thickness increased rapidly during denosumab therapy, particularly in the hip trochanteric region.Women with osteoporosis treated for 36 months with twice-yearly injections of denosumab sustained fewer hip fractures compared with placebo. Treatment might improve femoral bone at locations where fractures typically occur. To test this hypothesis, we used 3D cortical bone mapping of postmenopausal women with osteoporosis, to investigate the timing and precise location of denosumab versus placebo effects in the hips.We analysed clinical CT scans from 80 female participants in FREEDOM, a randomised trial, wherein half of the study participants received subcutaneous denosumab 60mg twice-yearly and the others received placebo. Cortical 3D bone thickness maps of both hips were created from scans at baseline, 12, 24 and 36 months. Cortical mass surface density maps were also created for each visit. After registration of each bone to an average femur shape model followed by statistical parametric mapping, we visualised and quantified statistically significant treatment effects. The technique allowed us to pinpoint systematic differences between denosumab and control, and display the results on a 3D average femur model.Denosumab treatment led to an increase in femoral cortical mass surface density and thickness, already evident by the third injection (12 months). Overall, treatment with denosumab increased femoral cortical mass surface density by 5.4% over three years. One third of the increase came from increasing cortical density, and two thirds from increasing cortical thickness, relative to placebo. After 36 months, cortical mass surface density and thickness had increased by up to 12%, at key locations such as the lateral femoral trochanter, versus placebo. Most of the femoral cortex displayed a statistically significant relative difference by 36 months.Osteoporotic cortical bone responds rapidly to denosumab therapy, particularly in the hip trochanteric region. This mechanism may be involved in the robust decrease in hip fractures seen in denosumab treated women at increased risk of fracture. © 2014 American Society for Bone and Mineral Research
    No preview · Article · Jul 2015 · Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research
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    [Show abstract] [Hide abstract] ABSTRACT: Within each sex, there is an association between hip fracture risk and the size of the proximal femur, with larger femurs apparently more susceptible to fracture. Here, we investigate whether the thickness and density of the femoral cortex play a role in this association: might larger femurs harbour focal, cortical defects? To answer this question, we used cortical bone mapping to measure the distribution of cortical mass surface density (CMSD, mg/cm(2)) in cohorts of 308 males and 125 females. Principal component analysis of the various femoral surfaces led to a measure of size that is linearly independent from shape. After mapping the data onto a canonical femur surface, we used statistical parametric mapping to identify any regions where CMSD depends on size, allowing for other confounding covariates including shape. Our principal finding was a focal patch on the superior femoral neck, where CMSD is reduced by around 1% for each 1% increase in proximal-distal size (p<0.000005 in the males, p<0.001 in the females). This finding appears to be consistent with models of functional adaptation, and may help with the design of interventional strategies for reducing fracture risk. Copyright © 2015. Published by Elsevier Inc.
    Preview · Article · Jul 2015 · Bone
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    [Show abstract] [Hide abstract] ABSTRACT: Hip fracture risk is known to be related to material properties of the proximal femur, but fracture prediction studies adding richer quantitative computed tomography (QCT) measures to dual energy X-ray (DXA)-based methods have shown limited improvement. Fracture types have distinct relationships to predictors, but few studies have sub-divided fracture into types, since this necessitates regional measurements and more fracture cases. This work makes use of cortical bone mapping (CBM) to accurately assess, with no prior anatomical presumptions, the distribution of properties related to fracture type. CBM uses QCT data to measure the cortical and trabecular properties, accurate even for thin cortices below the imaging resolution. The osteoporotic fractures in men (MrOS) study is a predictive case-cohort study of men over 65: we analyse 99 fracture cases (44 trochanteric and 55 femoral neck) compared to a cohort of 308, randomly selected from 5,994. To our knowledge, this is the largest QCT-based predictive hip fracture study to date, and the first to incorporate CBM analysis into fracture prediction. We demonstrate that both cortical mass surface density, and endocortical trabecular BMD, show significant difference in fracture cases vs. cohort, in regions appropriate to fracture type. We incorporate these regions into predictive models using Cox proportional hazards regression to estimate hazard ratios, and logistic regression to estimate area under the receiver operating characteristic curve (AUC). Adding CBM to DXA-based BMD leads to a small but significant (p < 0.005) improvement in model prediction for any fracture, with AUC increasing from 0.78 to 0.79, assessed using leave-one-out cross-validation. For specific fracture types, the improvement is more significant (p < 0.0001), with AUC increasing from 0.71 to 0.77 (trochanteric fractures) and 0.76 to 0.82 (femoral neck fractures). In contrast, adding DXA-based BMD to a CBM-based predictive model does not result in any significant improvement. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Preview · Article · May 2015 · Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research
  • [Show abstract] [Hide abstract] ABSTRACT: Regular exercisers have lower fracture risk, despite modest effects of exercise on BMC. Exercise may produce localised cortical and trabecular bone changes that affect bone strength independently of BMC. We previously demonstrated that brief, daily unilateral hopping exercises increased femoral neck BMC in the exercise leg versus the control leg of older men. This study evaluated the effects of these exercises on cortical and trabecular bone and its 3D distribution across the proximal femur, using clinical computed tomography (CT). Fifty healthy men had pelvic CT scans before and after the exercise intervention. We used hip QCT analysis to quantify BMC in traditional regions of interest and estimate biomechanical variables. Cortical bone mapping localised cortical mass surface density and endocortical trabecular density changes across each proximal femur, which involved registration to a canonical proximal femur model. Following statistical parametric mapping, we visualised and quantified statistically significant changes of variables over time in both legs, and significant differences between legs. Thirty-four men aged 70 (4) years exercised for 12-months, attending 92% of prescribed sessions. In traditional ROIs, cortical and trabecular BMC increased over time in both legs. Cortical BMC at the trochanter increased more in the exercise than control leg, whilst femoral neck buckling ratio declined more in the exercise than control leg. Across the entire proximal femur, cortical mass surface density increased significantly with exercise (2.7%; P < 0.001), with larger changes (>6%) at anterior and posterior aspects of the femoral neck and anterior shaft. Endocortical trabecular density also increased (6.4%; P < 0.001), with localised changes of >12% at the anterior femoral neck, trochanter and inferior femoral head. Odd impact exercise increased cortical mass surface density and endocortical trabecular density, at regions that may be important to structural integrity. These exercise-induced changes were localised rather than being evenly distributed across the proximal femur. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    No preview · Article · Mar 2015 · Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research
  • [Show abstract] [Hide abstract] ABSTRACT: Combining anti-resorptive and anabolic drugs for osteoporosis may be a useful strategy to prevent hip fractures. Previous studies comparing the effects of alendronate and teriparatide alone, combined or sequentially using Quantitative Computed Tomography (QCT) in postmenopausal women have not distinguished cortical bone mineral density (CBMD) from cortical thickness (CTh) effects, nor assessed the distribution and extent of more localised changes. In this study a validated bone mapping technique was used to examine the cortical and endocortical trabecular changes in the proximal femur resulting from an 18 month course of alendronate or teriparatide. Using QCT data from a different clinical trial, the global and localised changes seen following a switch to teriparatide after an 18 month alendronate treatment or adding teriparatide to the alendronate treatment were compared.CTh increased (4.8%, p < 0.01) and CBMD decreased (-4.5%, p < 0.01) in the teriparatide group compared to no significant change in the alendronate group. A large CTh increase could be seen for the switch group (2.8%, p < 0.01) compared to a significantly smaller increase for the add group (1.5%, p < 0.01). CBMD decreased significantly for the switch group (-3.9%, p < 0.01) and was significantly different from no significant change in the add group. CTh increases were shown to be significantly greater for the switch group compared to the add group at the load bearing regions.This study provides new insights into the effects of alendronate and teriparatide combination therapies on the cortex of the proximal femur and supports the hypothesis of an increased bone remodelling by teriparatide being mitigated by alendronate. This article is protected by copyright. All rights reserved
    No preview · Article · Jan 2015 · Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research
  • G M Treece · A.H. Gee
    [Show abstract] [Hide abstract] ABSTRACT: The local structure of the proximal femoral cortex is of interest since both fracture risk, and the effects of various interventions aimed at reducing that risk, are associated with cortical properties focused in particular regions rather than dispersed over the whole bone. Much of the femoral cortex is less than 3mm thick, appearing so blurred in clinical CT that its actual density is not apparent in the data, and neither thresholding nor full-width half-maximum techniques are capable of determining its width. Our previous work on cortical bone mapping showed how to produce more accurate estimates of cortical thickness by assuming a fixed value of the cortical density for each hip. However, although cortical density varies much less over the proximal femur than thickness, what little variation there is leads to errors in thickness measurement. In this paper, we develop the cortical bone mapping technique by exploiting local estimates of imaging blur to correct the global density estimate, thus providing a local density estimate as well as more accurate estimates of thickness. We also consider measurement of cortical mass surface density and the density of trabecular bone immediately adjacent to the cortex. Performance is assessed with ex vivo clinical QCT scans of proximal femurs, with true values derived from high resolution HRpQCT scans of the same bones. We demonstrate superior estimation of thickness than is possible with alternative techniques (accuracy 0.12±0.39mm for cortices in the range 1-3mm), and that local cortical density estimation is feasible for densities >800mg/cm(3). Copyright © 2014 Elsevier B.V. All rights reserved.
    No preview · Article · Dec 2014 · Medical Image Analysis
  • Andrew H Gee · Graham M Treece
    [Show abstract] [Hide abstract] ABSTRACT: Spatial normalisation is a key element of statistical parametric mapping and related techniques for analysing cohort statistics on voxel arrays and surfaces. The normalisation process involves aligning each individual specimen to a template using some sort of registration algorithm. Any misregistration will result in data being mapped onto the template at the wrong location. At best, this will introduce spatial imprecision into the subsequent statistical analysis. At worst, when the misregistration varies systematically with a covariate of interest, it may lead to false statistical inference. Since misregistration generally depends on the specimen's shape, we investigate here the effect of allowing for shape as a confound in the statistical analysis, with shape represented by the dominant modes of variation observed in the cohort. In a series of experiments on synthetic surface data, we demonstrate how allowing for shape can reveal true effects that were previously masked by systematic misregistration, and also guard against misinterpreting systematic misregistration as a true effect. We introduce some heuristics for disentangling misregistration effects from true effects, and demonstrate the approach's practical utility in a case study of the cortical bone distribution in 268 human femurs.
    No preview · Article · Feb 2014 · Medical image analysis
  • No preview · Conference Paper · Feb 2014
  • No preview · Conference Paper · Feb 2014
  • No preview · Article · Jul 2013 · Journal of Clinical Densitometry
  • No preview · Article · May 2013
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    Preview · Article · Apr 2013 · Osteoarthritis and Cartilage
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    [Show abstract] [Hide abstract] ABSTRACT: An ultrasound image is created from backscattered echoes originating from both diffuse and directional scattering. It is potentially useful to separate these two components for the purpose of tissue characterization. This article presents several models for visualization of scattering fields on 3-dimensional (3D) ultrasound imaging. By scanning the same anatomy from multiple directions, we can observe the variation of specular intensity as a function of the viewing angle. This article considers two models for estimating the diffuse and specular components of the backscattered intensity: a modification of the well-known Phong reflection model and an existing exponential model. We examine 2-dimensional implementations and also propose novel 3D extensions of these models in which the probe is not constrained to rotate within a plane. Both simulation and experimental results show that improved performance can be achieved with 3D models.
    Preview · Article · Apr 2013 · Journal of ultrasound in medicine: official journal of the American Institute of Ultrasound in Medicine
  • No preview · Conference Paper · Apr 2013
  • [Show abstract] [Hide abstract] ABSTRACT: Hip fracture is the leading cause of acute orthopaedic hospital admission amongst the elderly, with around a third of patients not surviving one year post-fracture. Although various preventative therapies are available, patient selection is difficult. The current state-of-the-art risk assessment tool (FRAX) ignores focal structural defects, such as cortical bone thinning, a critical component in characterizing hip fragility. Cortical thickness can be measured using CT, but this is expensive and involves a significant radiation dose. Instead, Dual-Energy X-ray Absorptiometry (DXA) is currently the preferred imaging modality for assessing hip fracture risk and is used routinely in clinical practice. Our ambition is to develop a tool to measure cortical thickness using multi-view DXA instead of CT. In this initial study, we work with digitally reconstructed radiographs (DRRs) derived from CT data as a surrogate for DXA scans: this enables us to compare directly the thickness estimates with the gold standard CT results. Our approach involves a model-based femoral shape reconstruction followed by a data-driven algorithm to extract numerous cortical thickness point estimates. In a series of experiments on the shaft and trochanteric regions of 48 proximal femurs, we validated our algorithm and established its performance limits using 20 views in the range 0°-171°: estimation errors were 0:19 +/- 0:53mm (mean +/- one standard deviation). In a more clinically viable protocol using four views in the range 0°-51°, where no other bony structures obstruct the projection of the femur, measurement errors were -0:07 +/- 0:79 mm.
    No preview · Article · Feb 2013 · Proceedings of SPIE - The International Society for Optical Engineering
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    [Show abstract] [Hide abstract] ABSTRACT: Most quasi-static ultrasound elastography methods image only the axial strain, derived from displacements measured in the direction of ultrasound propagation. In other directions, the beam lacks high resolution phase information and displacement estimation is therefore less precise. However, these estimates can be improved by steering the ultrasound beam through multiple angles and combining displacements measured along the different beam directions. Previously, beamsteering has only considered the 2D case to improve the lateral displacement estimates. In this paper, we extend this to 3D using a simulated 2D array to steer both laterally and elevationally in order to estimate the full 3D displacement vector over a volume. The method is tested on simulated and phantom data using a simulated 6-10MHz array, and the precision of displacement estimation is measured with and without beamsteering. In simulations, we found a statistically significant improvement in the precision of lateral and elevational displacement estimates: lateral precision 35.69μm unsteered, 3.70μm steered; elevational precision 38.67μm unsteered, 3.64μm steered. Similar results were found in the phantom data: lateral precision 26.51μm unsteered, 5.78μm steered; elevational precision 28.92μm unsteered, 11.87μm steered. We conclude that volumetric 3D beamsteering improves the precision of lateral and elevational displacement estimates.
    Preview · Article · Nov 2012 · Ultrasonics
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    [Show abstract] [Hide abstract] ABSTRACT: Objective: This work is concerned with the creation of three-dimensional (3D) extended-field-of-view ultrasound from a set of volumes acquired using a mechanically swept 3D probe. 3D volumes of ultrasound data can be registered by attaching a position sensor to the probe; this can be an inconvenience in a clinical setting. A position sensor can also cause some misalignment due to patient movement and respiratory motion. We propose a combination of three-degrees-of-freedom image registration and an unobtrusively integrated inertial sensor for measuring orientation. The aim of this research is to produce a reliable and portable ultrasound system that is able to register 3D volumes quickly, making it suitable for clinical use. Method: As part of a feasibility study we recruited 28 pregnant females attending for routine obstetric scans to undergo 3D extended-field-of-view ultrasound. A total of 49 data sets were recorded. Each registered data set was assessed for correct alignment of each volume by two independent observers. Results: In 77-83% of the data sets more than four consecutive volumes registered. The successful registration relies on good overlap between volumes and is adversely affected by advancing gestational age and foetal movement. Conclusion: The development of reliable 3D extended-field-of-view ultrasound may help ultrasound practitioners to demonstrate the anatomical relation of pathology and provide a convenient way to store data.
    Preview · Article · Oct 2012 · The British journal of radiology