Stuart Crozier - Academia.edu (original) (raw)
Papers by Stuart Crozier
Physics in medicine and biology, Jan 21, 2015
To develop an automated approach for 3D quantitative assessment and measurement of alpha angles f... more To develop an automated approach for 3D quantitative assessment and measurement of alpha angles from the femoral head-neck (FHN) junction using bone models derived from magnetic resonance (MR) images of the hip joint.Bilateral MR images of the hip joints were acquired from 30 male volunteers (healthy active individuals and high-performance athletes, aged 18-49 years) using a water-excited 3D dual echo steady state (DESS) sequence. In a subset of these subjects (18 water-polo players), additional True Fast Imaging with Steady-state Precession (TrueFISP) images were acquired from the right hip joint. For both MR image sets, an active shape model based algorithm was used to generate automated 3D bone reconstructions of the proximal femur. Subsequently, a local coordinate system of the femur was constructed to compute a 2D shape map to project femoral head sphericity for calculation of alpha angles around the FHN junction. To evaluate automated alpha angle measures, manual analyses were...
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, Jan 30, 2015
To validate a fully automated scheme to extract biochemical information from the hip joint cartil... more To validate a fully automated scheme to extract biochemical information from the hip joint cartilages using MR T2 mapping images incorporating segmentation of co-registered three-dimensional Fast-Spin-Echo (3D-SPACE) images. Manual analyses of unilateral hip (3 Tesla) MR images of 24 asymptomatic volunteers were used to validate a 3D deformable model method for automated cartilage segmentation of SPACE scans, partitioning of the individual femoral and acetabular cartilage plates into clinically defined sub-regions and propagating these results to T2 maps to calculate region-wise T2 value statistics. Analyses were completed on a desktop computer (∼10 min per case). The mean voxel overlap between automated A and manual M segmentations of the cartilage volumes in the (clinically based) SPACE images was 73% (100×2|A∩M|/[|A|+|M|]). The automated and manual analyses demonstrated a relative difference error <10% in the median "T2 average signal" for each cartilage plate. The a...
Physics in medicine and biology, Jan 7, 2014
Accurate segmentation of hip joint cartilage from magnetic resonance (MR) images offers opportuni... more Accurate segmentation of hip joint cartilage from magnetic resonance (MR) images offers opportunities for quantitative investigations of pathoanatomical conditions such as osteoarthritis. In this paper, we present a fully automatic scheme for the segmentation of the individual femoral and acetabular cartilage plates in the human hip joint from high-resolution 3D MR images. The developed scheme uses an improved optimal multi-object multi-surface graph search framework with an arc-weighted graph representation that incorporates prior morphological knowledge as a basis for segmentation of the individual femoral and acetabular cartilage plates despite weak or incomplete boundary interfaces. This automated scheme was validated against manual segmentations from 3D true fast imaging with steady-state precession (TrueFISP) MR examinations of the right hip joints in 52 asymptomatic volunteers. Compared with expert manual segmentations of the combined, femoral and acetabular cartilage volumes...
Osteoarthritis and Cartilage, 2014
To validate an automatic scheme for the segmentation and quantitative analysis of the medial meni... more To validate an automatic scheme for the segmentation and quantitative analysis of the medial meniscus (MM) and lateral meniscus (LM) in magnetic resonance (MR) images of the knee. We analysed sagittal water-excited double-echo steady-state MR images of the knee from a subset of the Osteoarthritis Initiative (OAI) cohort. The MM and LM were automatically segmented in the MR images based on a deformable model approach. Quantitative parameters including volume, subluxation and tibial-coverage were automatically calculated for comparison (Wilcoxon tests) between knees with variable radiographic osteoarthritis (rOA), medial and lateral joint space narrowing (mJSN, lJSN) and pain. Automatic segmentations and estimated parameters were evaluated for accuracy using manual delineations of the menisci in 88 pathological knee MR examinations at baseline and 12 months time-points. The median (95% confidence-interval (CI)) Dice similarity index (DSI) (2 ∗|Auto ∩ Manual|/(|Auto|+|Manual|)∗ 100) between manual and automated segmentations for the MM and LM volumes were 78.3% (75.0-78.7), 83.9% (82.1-83.9) at baseline and 75.3% (72.8-76.9), 83.0% (81.6-83.5) at 12 months. Pearson coefficients between automatic and manual segmentation parameters ranged from r = 0.70 to r = 0.92. MM in rOA/mJSN knees had significantly greater subluxation and smaller tibial-coverage than no-rOA/no-mJSN knees. LM in rOA knees had significantly greater volumes and tibial-coverage than no-rOA knees. Our automated method successfully segmented the menisci in normal and osteoarthritic knee MR images and detected meaningful morphological differences with respect to rOA and joint space narrowing (JSN). Our approach will facilitate analyses of the menisci in prospective MR cohorts such as the OAI for investigations into pathophysiological changes occurring in early osteoarthritis (OA) development.
Physics in medicine and biology, Jan 22, 2015
We present a statistical shape model approach for automated segmentation of the proximal humerus ... more We present a statistical shape model approach for automated segmentation of the proximal humerus and scapula with subsequent bone-cartilage interface (BCI) extraction from 3D magnetic resonance (MR) images of the shoulder region. Manual and automated bone segmentations from shoulder MR examinations from 25 healthy subjects acquired using steady-state free precession sequences were compared with the Dice similarity coefficient (DSC). The mean DSC scores between the manual and automated segmentations of the humerus and scapula bone volumes surrounding the BCI region were 0.926 ± 0.050 and 0.837 ± 0.059, respectively. The mean DSC values obtained for BCI extraction were 0.806 ± 0.133 for the humerus and 0.795 ± 0.117 for the scapula. The current model-based approach successfully provided automated bone segmentation and BCI extraction from MR images of the shoulder. In future work, this framework appears to provide a promising avenue for automated segmentation and quantitative a...
Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, 2007
ABSTRACT
Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, 2010
ABSTRACT
Diffusion weighted (DW) MRI-and in particular the apparent diffusion coefficient (ADC)-shows pote... more Diffusion weighted (DW) MRI-and in particular the apparent diffusion coefficient (ADC)-shows potential for improving the characterization and classification of enhancing breast lesions identified using dynamic contrast-enhanced (DCE) MRI. Nevertheless, to date there does not exist a well defined and objective method for computing a representative ADC value for such lesions. Typically an average ADC is computed for a manually selected region of interest (ROI) [1]. This is problematic for two reasons. Firstly the choice of ROI is subjective. Differences in ROI selection between individuals, as well as the reproducibility of selection for a given individual, can lead to variation in the mean ADC. In addition ROIs are often defined to be circular or elliptical which imposes an arbitrary geometry on the ROI [2]. Secondly, given the heterogeneity in breast lesions, an ensemble average of ADC may not provide a truly representative value. It is assumed that a representative ADC will be present in the area of neovascularisation, as indicated by rapid contrast enhancement. In order to improve the objectivity, reproducibility and efficiency of representative ADC computation, we propose an automated method based on the selection of hypo-intense areas on the ADC map corresponding to regions of greatest initial contrast enhancement identified in the DCE-MRI data. We also present an evaluation of the method using routine clinical data.
Anziam Journal, Sep 15, 2007
The design of gradient coils within Magnetic Resonance Imaging equipment is considered. These coi... more The design of gradient coils within Magnetic Resonance Imaging equipment is considered. These coils produce linear magnetic fields in each of the three orthogonal directions in physical space. In addition, they are turned on and off repeatedly to enhance the clarity of the image, but this produces a great deal of noise within the coil, as its shape distorts under the influence of Lorentz forces. We present a method for calculating the movement of the coil in the background magnetic field, and estimating the consequent noise levels. This involves solving for the current density in the coil coupled with equations for its elastic deformation, along with acoustic equations for the pressure in the surrounding air. Winding patterns are designed to minimize the noise produced by the Magnetic Resonance Imaging coil.
Trakic, Adnan, Liu, Feng, Wang, Hua and Crozier, Stuart (2007). TFSF-FDTD Numerical Computational... more Trakic, Adnan, Liu, Feng, Wang, Hua and Crozier, Stuart (2007). TFSF-FDTD Numerical Computational Method for Evaluation of Transient Eddy Currentsin MRI. In: , Proceedings International Society for Magnetic Resonance in Medicine (ISMRM) Workshop on Advances in High Field MRI. ...
Introduction Conventional RF technology struggles to provide safe, uniform B1 fields for high-fie... more Introduction Conventional RF technology struggles to provide safe, uniform B1 fields for high-field MRI [1]. Additional tissue-heating, caused by field interactions and/or a RF energy misbalance, can be ameliorated by employing adequate numbers of arrays to tailor the ...
A new concept relating to a fast mechanically rotating radio-frequency (RRF) transceive coil and ... more A new concept relating to a fast mechanically rotating radio-frequency (RRF) transceive coil and method for application in MRI is presented. The introduction of controlled RF system rotation as additional degree of freedom during imaging facilitates the use of (at least) one coil sensitivity pattern to effectively emulate a conventional RF coil array over time. This approach aims to substantially diminish the number of coil elements and channels, lumped circuit components and tedious mutual decoupling while preserving the benefits of very large RF coil arrays. This feasibility study presents and discusses first experimental results of the RRF system in in-vitro imaging and spatially selective excitation.
Physics in medicine and biology, Jan 21, 2015
To develop an automated approach for 3D quantitative assessment and measurement of alpha angles f... more To develop an automated approach for 3D quantitative assessment and measurement of alpha angles from the femoral head-neck (FHN) junction using bone models derived from magnetic resonance (MR) images of the hip joint.Bilateral MR images of the hip joints were acquired from 30 male volunteers (healthy active individuals and high-performance athletes, aged 18-49 years) using a water-excited 3D dual echo steady state (DESS) sequence. In a subset of these subjects (18 water-polo players), additional True Fast Imaging with Steady-state Precession (TrueFISP) images were acquired from the right hip joint. For both MR image sets, an active shape model based algorithm was used to generate automated 3D bone reconstructions of the proximal femur. Subsequently, a local coordinate system of the femur was constructed to compute a 2D shape map to project femoral head sphericity for calculation of alpha angles around the FHN junction. To evaluate automated alpha angle measures, manual analyses were...
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, Jan 30, 2015
To validate a fully automated scheme to extract biochemical information from the hip joint cartil... more To validate a fully automated scheme to extract biochemical information from the hip joint cartilages using MR T2 mapping images incorporating segmentation of co-registered three-dimensional Fast-Spin-Echo (3D-SPACE) images. Manual analyses of unilateral hip (3 Tesla) MR images of 24 asymptomatic volunteers were used to validate a 3D deformable model method for automated cartilage segmentation of SPACE scans, partitioning of the individual femoral and acetabular cartilage plates into clinically defined sub-regions and propagating these results to T2 maps to calculate region-wise T2 value statistics. Analyses were completed on a desktop computer (∼10 min per case). The mean voxel overlap between automated A and manual M segmentations of the cartilage volumes in the (clinically based) SPACE images was 73% (100×2|A∩M|/[|A|+|M|]). The automated and manual analyses demonstrated a relative difference error <10% in the median "T2 average signal" for each cartilage plate. The a...
Physics in medicine and biology, Jan 7, 2014
Accurate segmentation of hip joint cartilage from magnetic resonance (MR) images offers opportuni... more Accurate segmentation of hip joint cartilage from magnetic resonance (MR) images offers opportunities for quantitative investigations of pathoanatomical conditions such as osteoarthritis. In this paper, we present a fully automatic scheme for the segmentation of the individual femoral and acetabular cartilage plates in the human hip joint from high-resolution 3D MR images. The developed scheme uses an improved optimal multi-object multi-surface graph search framework with an arc-weighted graph representation that incorporates prior morphological knowledge as a basis for segmentation of the individual femoral and acetabular cartilage plates despite weak or incomplete boundary interfaces. This automated scheme was validated against manual segmentations from 3D true fast imaging with steady-state precession (TrueFISP) MR examinations of the right hip joints in 52 asymptomatic volunteers. Compared with expert manual segmentations of the combined, femoral and acetabular cartilage volumes...
Osteoarthritis and Cartilage, 2014
To validate an automatic scheme for the segmentation and quantitative analysis of the medial meni... more To validate an automatic scheme for the segmentation and quantitative analysis of the medial meniscus (MM) and lateral meniscus (LM) in magnetic resonance (MR) images of the knee. We analysed sagittal water-excited double-echo steady-state MR images of the knee from a subset of the Osteoarthritis Initiative (OAI) cohort. The MM and LM were automatically segmented in the MR images based on a deformable model approach. Quantitative parameters including volume, subluxation and tibial-coverage were automatically calculated for comparison (Wilcoxon tests) between knees with variable radiographic osteoarthritis (rOA), medial and lateral joint space narrowing (mJSN, lJSN) and pain. Automatic segmentations and estimated parameters were evaluated for accuracy using manual delineations of the menisci in 88 pathological knee MR examinations at baseline and 12 months time-points. The median (95% confidence-interval (CI)) Dice similarity index (DSI) (2 ∗|Auto ∩ Manual|/(|Auto|+|Manual|)∗ 100) between manual and automated segmentations for the MM and LM volumes were 78.3% (75.0-78.7), 83.9% (82.1-83.9) at baseline and 75.3% (72.8-76.9), 83.0% (81.6-83.5) at 12 months. Pearson coefficients between automatic and manual segmentation parameters ranged from r = 0.70 to r = 0.92. MM in rOA/mJSN knees had significantly greater subluxation and smaller tibial-coverage than no-rOA/no-mJSN knees. LM in rOA knees had significantly greater volumes and tibial-coverage than no-rOA knees. Our automated method successfully segmented the menisci in normal and osteoarthritic knee MR images and detected meaningful morphological differences with respect to rOA and joint space narrowing (JSN). Our approach will facilitate analyses of the menisci in prospective MR cohorts such as the OAI for investigations into pathophysiological changes occurring in early osteoarthritis (OA) development.
Physics in medicine and biology, Jan 22, 2015
We present a statistical shape model approach for automated segmentation of the proximal humerus ... more We present a statistical shape model approach for automated segmentation of the proximal humerus and scapula with subsequent bone-cartilage interface (BCI) extraction from 3D magnetic resonance (MR) images of the shoulder region. Manual and automated bone segmentations from shoulder MR examinations from 25 healthy subjects acquired using steady-state free precession sequences were compared with the Dice similarity coefficient (DSC). The mean DSC scores between the manual and automated segmentations of the humerus and scapula bone volumes surrounding the BCI region were 0.926 ± 0.050 and 0.837 ± 0.059, respectively. The mean DSC values obtained for BCI extraction were 0.806 ± 0.133 for the humerus and 0.795 ± 0.117 for the scapula. The current model-based approach successfully provided automated bone segmentation and BCI extraction from MR images of the shoulder. In future work, this framework appears to provide a promising avenue for automated segmentation and quantitative a...
Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, 2007
ABSTRACT
Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, 2010
ABSTRACT
Diffusion weighted (DW) MRI-and in particular the apparent diffusion coefficient (ADC)-shows pote... more Diffusion weighted (DW) MRI-and in particular the apparent diffusion coefficient (ADC)-shows potential for improving the characterization and classification of enhancing breast lesions identified using dynamic contrast-enhanced (DCE) MRI. Nevertheless, to date there does not exist a well defined and objective method for computing a representative ADC value for such lesions. Typically an average ADC is computed for a manually selected region of interest (ROI) [1]. This is problematic for two reasons. Firstly the choice of ROI is subjective. Differences in ROI selection between individuals, as well as the reproducibility of selection for a given individual, can lead to variation in the mean ADC. In addition ROIs are often defined to be circular or elliptical which imposes an arbitrary geometry on the ROI [2]. Secondly, given the heterogeneity in breast lesions, an ensemble average of ADC may not provide a truly representative value. It is assumed that a representative ADC will be present in the area of neovascularisation, as indicated by rapid contrast enhancement. In order to improve the objectivity, reproducibility and efficiency of representative ADC computation, we propose an automated method based on the selection of hypo-intense areas on the ADC map corresponding to regions of greatest initial contrast enhancement identified in the DCE-MRI data. We also present an evaluation of the method using routine clinical data.
Anziam Journal, Sep 15, 2007
The design of gradient coils within Magnetic Resonance Imaging equipment is considered. These coi... more The design of gradient coils within Magnetic Resonance Imaging equipment is considered. These coils produce linear magnetic fields in each of the three orthogonal directions in physical space. In addition, they are turned on and off repeatedly to enhance the clarity of the image, but this produces a great deal of noise within the coil, as its shape distorts under the influence of Lorentz forces. We present a method for calculating the movement of the coil in the background magnetic field, and estimating the consequent noise levels. This involves solving for the current density in the coil coupled with equations for its elastic deformation, along with acoustic equations for the pressure in the surrounding air. Winding patterns are designed to minimize the noise produced by the Magnetic Resonance Imaging coil.
Trakic, Adnan, Liu, Feng, Wang, Hua and Crozier, Stuart (2007). TFSF-FDTD Numerical Computational... more Trakic, Adnan, Liu, Feng, Wang, Hua and Crozier, Stuart (2007). TFSF-FDTD Numerical Computational Method for Evaluation of Transient Eddy Currentsin MRI. In: , Proceedings International Society for Magnetic Resonance in Medicine (ISMRM) Workshop on Advances in High Field MRI. ...
Introduction Conventional RF technology struggles to provide safe, uniform B1 fields for high-fie... more Introduction Conventional RF technology struggles to provide safe, uniform B1 fields for high-field MRI [1]. Additional tissue-heating, caused by field interactions and/or a RF energy misbalance, can be ameliorated by employing adequate numbers of arrays to tailor the ...
A new concept relating to a fast mechanically rotating radio-frequency (RRF) transceive coil and ... more A new concept relating to a fast mechanically rotating radio-frequency (RRF) transceive coil and method for application in MRI is presented. The introduction of controlled RF system rotation as additional degree of freedom during imaging facilitates the use of (at least) one coil sensitivity pattern to effectively emulate a conventional RF coil array over time. This approach aims to substantially diminish the number of coil elements and channels, lumped circuit components and tedious mutual decoupling while preserving the benefits of very large RF coil arrays. This feasibility study presents and discusses first experimental results of the RRF system in in-vitro imaging and spatially selective excitation.