- Email: [email protected]
Accurate Fully Automated 4D Segmentation of Osteoarthritic Knee MRI
Abstracts / Osteoarthritis and Cartilage 25 (2017) S76eS444
untreated. Therapy by soft Pavlik harness in infancy is highly successful in most patients, but because the mechanism of effect is not well understood, it is unclear which patients will fail therapy or develop complications such as avascular necrosis (AVN). The harness places the dysplastic joint into a stable abducted position, which modifies loading so that cartilaginous remodeling into more mechanically favorable geometry can occur. Since the cartilage remodeling can be hypothesized to be influenced by articular contact pressures (CP), study of CP during Pavlik harness treatment can advance our understanding of this process of cartilage remodeling and articular development. This could ultimately lead to improved strategies to prevent osteoarthritis. Here, we performed finite element modeling (FEM) simulation of the load environment in Pavlik harness for normal and dysplastic hips through a clinically relevant range of abduction. We assessed the peak contact pressures, contact area, and distribution of pressures in each hip. To use patient-specific finite element (FE) modeling to investigate CP in normal and dysplastic infant hip joints in Pavlik harness. Methods: In ethics-approved study we performed non-sedated coronal gradient echo MRI (1 mm slice thickness) in a 17-week-old boy with normal hips and a 5-week-old girl with a moderately dysplastic left hip (as per orthopedic clinical assessment). 3D geometric hip models were reconstructed using manual segmentation of the joint components (Figure 1aeb). Each FEM (Figure 1ced) consisted of bone, cartilage and adductor muscles (represented by non-linear springs). Bone and cartilage were modeled as rigid and linear-elastic materials respectively, with frictionless articular contact mechanism. Models simulated hip behaviour at 90 flexion/40 , 60 and 80 abduction. At 40 abduction the leg weight is partly held by the harness’s upper strap and partly by the adductors. At 60 abduction, the leg is in natural force equilibrium of its weight and passive action of the adductors. At 80 abduction, a tight strap harness causes adduction beyond natural equilibrium. Model output was articular surface CP. Results: In each position of harness treatment (Figure 2a), CP on articular surfaces varied between normal (Figure 2b) and dysplastic (Figure 2c) hip models. CP increased substantially in both models with increase in abduction angle. The peak CP values in the dysplastic hip were more than twice those of the normal hips for all abduction angles. Narrow-band stress concentrations appeared on the inner edge of the posterior surface of the acetabulum and along the corresponding lateral surface of femoral head, especially at 80 abduction of the normal hip, and at 60 and 80 abduction of the dysplastic hip. Conclusions: FEM of infant normal and dysplastic hips in Pavlik harness in different degrees of abduction is feasible and demonstrates different distributions and magnitudes of CP in normal and dysplastic hips. The pressures observed on the anterior acetabular wall may contribute to desired therapeutic remodeling. Conversely, the elevated and concentrated CP observed posteriorly / laterally in the dysplastic hip model
S227
Fig 2. at 80 forced abduction may explain the development of avascular necrosis (AVN) as a complication. FEM of infant hips may improve our understanding of the biomechanics of hip dysplasia and its treatment to prevent OA while bones are still developing.
360 ACCURATE FULLY AUTOMATED OSTEOARTHRITIC KNEE MRI
4D
SEGMENTATION
OF
S. Kashyap, H. Zhang, M. Sonka. The Univ. of Iowa, Iowa City, IA, USA
Fig 1.Ă
Purpose: A method for 4D (3Dþtime) segmentation of bone and cartilage surfaces of the knee joint imaged by magnetic resonance (MR) is reported. Accurate segmentation is necessary to understand osteoarthritis (OA) disease processes and quantify the efficacy of DMOAD (disease-modifying OA drug) drug trials. Manual segmentation is tedious, time-consuming (several hours per joint) and irreproducible. We have previously reported an automated 3D approach based on layered optimal graph segmentation of multiple objects and surfaces (LOGISMOS). This study extends 3D LOGISMOS to 3Dþtime (4D) LOGISMOS to simultaneously segment four cartilage and bone surfaces (femur, tibia) in longitudinal sequences of follow-up MRI's. The key benefit of using our automated 4D LOGISMOS method is that information from all time points of the temporal sequence contributes to the single optimal solution that utilizes temporal and spatial context between adjacent time points. Methods: Our 4D LOGISMOS approach consists of two major steps: a) Constraining topological relationships between identical pre-segmentation meshes between time-points using rigid registration, and b) enforcing physiologically permissible maximum changes between time-points by introducing inter-time point graph arcs that longitudinally link the temporally corresponding locations of the respective bones and cartilages of the femur and tibia. Robust hierarchical random-forest classifiers were used to derive cartilage cost functions trained using segmentation examples. Once segmented, automated
S228
Abstracts / Osteoarthritis and Cartilage 25 (2017) S76eS444
sub-plate analysis was used to identify segmentation accuracy in medial/lateral regions of the femur (cMF/cLF) and tibia (cMT/cLT). To assess segmentation accuracy, 54 patients at baseline and 12-month follow-up visits from the OAI (Osteoarthritis Initiative) progressive cohort were analyzed (108 3D MR DESS datasets) and compared with the manually-traced independent standard (IS). To assess the temporal consistency of the segmentations, a large sub-cohort of 399 patients with five yearly follow-ups (baseline, 12, 24, 36, 48 month; 1,995 DESS MRI’s) were analyzed to show the benefits of 4D over 3D analysis. Since no independent standard was available for this cohort, consistency assessment was based on a hypothesis that cartilage thickness losses over the five-year period would be monotonically decreasing and that this hypothesis can be tested using longitudinal cartilage thickness correlation coefficient R. Higher occurrence of analyses satisfying this hypothesis indicates a larger success rate e histograms of R-values were analyzed to determine whether 4D LOGISMOS outperformed the 3D approach. Results: Tables show signed and unsigned cartilage border positioning errors using the 4D and 3D methods at baseline and 12 months with green boxes representing significant improvement while red boxes indicate a worsened performance. Analyzing histograms of R-values for different sub-plates showed a significantly (p<0.05) better performance of the 4D LOGISMOS when compared to that of 3D.
Table 1 Baseline signed and unsigned cartilage surface positioning errors between 4D and 3D LOGISMOS on the major femoral and tibial sub-plates.
Table 2 12-month signed and unsigned cartilage surface positioning errors comparison between 4D and 3D LOGISMOS on the major femoral and tibial sub-plates.
Conclusions: The proposed 4D LOGISMOS segmentation algorithm outperformed the 3D approach and demonstrated the benefits of using temporal contextual information in studies with multiple follow-up MRIs. Temporal-context aware image segmentation techniques offer a significant improvement of segmentation performance in hard-toanalyze longitudinal studies of OA progression. 361 ASSOCIATIONS BETWEEN INFRA-PATELLAR FAT PAD VOLUME AND KNEE JOINT STRUCTURE IN YOUNG ADULTS AT 2e3 YEARS AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION AND HEALTHY CONTROLS: A CROSS-SECTIONAL ANALYSIS A. Van Ginckel y, K. Fortin y, K.L. Bennell y, X. Wang y, T.V. Wrigley y, Y. Wang z, F.M. Cicuttini z, D.J. Lloyd x, D.J. Saxby x, A.L. Bryant y. y The Univ. of Melbourne, Melbourne, Australia; z Monash Univ., Melbourne, Australia; x Griffith Univ., Gold Coast, Australia Purpose: Infra-patellar fat pad (IPFP) pathology, particularly Hoffasynovitis, has been associated with increased risks for the onset of radiographic and/or symptomatic knee osteoarthritis. By contrast, greater IPFP size has been related to less symptomatic and/or slowed structural decline in both people with and without clinical knee osteoarthritis, suggesting a protective, instead of deleterious, role in disease onset. People after anterior cruciate ligament (ACL) injury and/or reconstruction (ACLR) are at a higher risk of osteoarthritis onset. The IPFP in these patients may also show a range of abnormalities (e.g. scarring and fibrosis, synovitis, edema or tears). As such, studying the IPFP could provide additional insights into potential factors affecting the structural longevity of the knee in this population. The aim of this cross-sectional study was to investigate the association between IPFP volume in people at 2e3 years after ACLR and healthy controls, and outcomes of knee joint structure. Methods: Baseline data of 130 participants (100 ACLR patients, 30 controls) from a 2-year prospective cohort study were analysed. Briefly, eligible ACLR patients (mean (SD) age¼ 30.4 (6.4) years, mean (SD) BMI¼25.2 (3.5) kg/m2, 62 (67%) males) had a semitendinosus and gracilis (hamstring) autograft ACLR performed 2e3 years prior to testing, with a diagnosis of an acute ACL tear within 6 months of injury and International Cartilage Repair Society (ICRS) cartilage defects grade <¼ 2 at time of ACLR. Healthy participants (mean (SD) age¼28.3 (5.2) years, mean (SD) body mass index¼23.2 (3.3) kg/m2, 19 (63%) males) had no prior knee surgery or known lower limb injury. Tibial cartilage volumes (mm3) (and corresponding subchondral bone area (mm2)) as well as IPFP volumes (mm3) were measured through manual segmentation of medial/lateral tibial cartilage plates and the IPFP, respectively, from sagittal T1-weighted 3D gradient-echo recall MRI sequences. Prevalence of medial/lateral tibiofemoral cartilage defects and bone marrow lesions (BMLs) was assessed from sagittal/coronal proton density-weighted fat-suppressed turbo-spin echo sequences. A prevalent cartilage defect was defined as an ICRS score of 2 at any site. BMLs were evaluated in 10 subregions of the tibiofemoral joint using the MRI Osteoarthritis Knee Score (MOAKS) and were deemed prevalent when grade 1 was recorded for any of the subregions. Within patients and controls, associations between IPFP volume and structural outcomes were investigated using logistic regression analysis for dichotomous dependent variables (prevalence of cartilage defects or BMLs) or linear regression for continuous dependent variables of cartilage volume, each adjusted for body mass index and gender (as known correlates of IPFP volume), concomitant meniscal pathology (in patients only), MRI scanner and subchondral bone area (when regressed onto cartilage volumes). Results: In both ACLR patients and controls, no significant associations were found between IPFP volumes and prevalence of cartilage defects, BMLs, or medial tibial cartilage volume. However, in ACLR patients, but not controls, a greater IPFP volume was significantly and positively associated with lateral tibial cartilage volume (B¼0.06 (95% CI: 0.032, 0.088), b: 0.64, p<0.001, Figure 1).
untreated. Therapy by soft Pavlik harness in infancy is highly successful in most patients, but because the mechanism of effect is not well understood, it is unclear which patients will fail therapy or develop complications such as avascular necrosis (AVN). The harness places the dysplastic joint into a stable abducted position, which modifies loading so that cartilaginous remodeling into more mechanically favorable geometry can occur. Since the cartilage remodeling can be hypothesized to be influenced by articular contact pressures (CP), study of CP during Pavlik harness treatment can advance our understanding of this process of cartilage remodeling and articular development. This could ultimately lead to improved strategies to prevent osteoarthritis. Here, we performed finite element modeling (FEM) simulation of the load environment in Pavlik harness for normal and dysplastic hips through a clinically relevant range of abduction. We assessed the peak contact pressures, contact area, and distribution of pressures in each hip. To use patient-specific finite element (FE) modeling to investigate CP in normal and dysplastic infant hip joints in Pavlik harness. Methods: In ethics-approved study we performed non-sedated coronal gradient echo MRI (1 mm slice thickness) in a 17-week-old boy with normal hips and a 5-week-old girl with a moderately dysplastic left hip (as per orthopedic clinical assessment). 3D geometric hip models were reconstructed using manual segmentation of the joint components (Figure 1aeb). Each FEM (Figure 1ced) consisted of bone, cartilage and adductor muscles (represented by non-linear springs). Bone and cartilage were modeled as rigid and linear-elastic materials respectively, with frictionless articular contact mechanism. Models simulated hip behaviour at 90 flexion/40 , 60 and 80 abduction. At 40 abduction the leg weight is partly held by the harness’s upper strap and partly by the adductors. At 60 abduction, the leg is in natural force equilibrium of its weight and passive action of the adductors. At 80 abduction, a tight strap harness causes adduction beyond natural equilibrium. Model output was articular surface CP. Results: In each position of harness treatment (Figure 2a), CP on articular surfaces varied between normal (Figure 2b) and dysplastic (Figure 2c) hip models. CP increased substantially in both models with increase in abduction angle. The peak CP values in the dysplastic hip were more than twice those of the normal hips for all abduction angles. Narrow-band stress concentrations appeared on the inner edge of the posterior surface of the acetabulum and along the corresponding lateral surface of femoral head, especially at 80 abduction of the normal hip, and at 60 and 80 abduction of the dysplastic hip. Conclusions: FEM of infant normal and dysplastic hips in Pavlik harness in different degrees of abduction is feasible and demonstrates different distributions and magnitudes of CP in normal and dysplastic hips. The pressures observed on the anterior acetabular wall may contribute to desired therapeutic remodeling. Conversely, the elevated and concentrated CP observed posteriorly / laterally in the dysplastic hip model
S227
Fig 2. at 80 forced abduction may explain the development of avascular necrosis (AVN) as a complication. FEM of infant hips may improve our understanding of the biomechanics of hip dysplasia and its treatment to prevent OA while bones are still developing.
360 ACCURATE FULLY AUTOMATED OSTEOARTHRITIC KNEE MRI
4D
SEGMENTATION
OF
S. Kashyap, H. Zhang, M. Sonka. The Univ. of Iowa, Iowa City, IA, USA
Fig 1.Ă
Purpose: A method for 4D (3Dþtime) segmentation of bone and cartilage surfaces of the knee joint imaged by magnetic resonance (MR) is reported. Accurate segmentation is necessary to understand osteoarthritis (OA) disease processes and quantify the efficacy of DMOAD (disease-modifying OA drug) drug trials. Manual segmentation is tedious, time-consuming (several hours per joint) and irreproducible. We have previously reported an automated 3D approach based on layered optimal graph segmentation of multiple objects and surfaces (LOGISMOS). This study extends 3D LOGISMOS to 3Dþtime (4D) LOGISMOS to simultaneously segment four cartilage and bone surfaces (femur, tibia) in longitudinal sequences of follow-up MRI's. The key benefit of using our automated 4D LOGISMOS method is that information from all time points of the temporal sequence contributes to the single optimal solution that utilizes temporal and spatial context between adjacent time points. Methods: Our 4D LOGISMOS approach consists of two major steps: a) Constraining topological relationships between identical pre-segmentation meshes between time-points using rigid registration, and b) enforcing physiologically permissible maximum changes between time-points by introducing inter-time point graph arcs that longitudinally link the temporally corresponding locations of the respective bones and cartilages of the femur and tibia. Robust hierarchical random-forest classifiers were used to derive cartilage cost functions trained using segmentation examples. Once segmented, automated
S228
Abstracts / Osteoarthritis and Cartilage 25 (2017) S76eS444
sub-plate analysis was used to identify segmentation accuracy in medial/lateral regions of the femur (cMF/cLF) and tibia (cMT/cLT). To assess segmentation accuracy, 54 patients at baseline and 12-month follow-up visits from the OAI (Osteoarthritis Initiative) progressive cohort were analyzed (108 3D MR DESS datasets) and compared with the manually-traced independent standard (IS). To assess the temporal consistency of the segmentations, a large sub-cohort of 399 patients with five yearly follow-ups (baseline, 12, 24, 36, 48 month; 1,995 DESS MRI’s) were analyzed to show the benefits of 4D over 3D analysis. Since no independent standard was available for this cohort, consistency assessment was based on a hypothesis that cartilage thickness losses over the five-year period would be monotonically decreasing and that this hypothesis can be tested using longitudinal cartilage thickness correlation coefficient R. Higher occurrence of analyses satisfying this hypothesis indicates a larger success rate e histograms of R-values were analyzed to determine whether 4D LOGISMOS outperformed the 3D approach. Results: Tables show signed and unsigned cartilage border positioning errors using the 4D and 3D methods at baseline and 12 months with green boxes representing significant improvement while red boxes indicate a worsened performance. Analyzing histograms of R-values for different sub-plates showed a significantly (p<0.05) better performance of the 4D LOGISMOS when compared to that of 3D.
Table 1 Baseline signed and unsigned cartilage surface positioning errors between 4D and 3D LOGISMOS on the major femoral and tibial sub-plates.
Table 2 12-month signed and unsigned cartilage surface positioning errors comparison between 4D and 3D LOGISMOS on the major femoral and tibial sub-plates.
Conclusions: The proposed 4D LOGISMOS segmentation algorithm outperformed the 3D approach and demonstrated the benefits of using temporal contextual information in studies with multiple follow-up MRIs. Temporal-context aware image segmentation techniques offer a significant improvement of segmentation performance in hard-toanalyze longitudinal studies of OA progression. 361 ASSOCIATIONS BETWEEN INFRA-PATELLAR FAT PAD VOLUME AND KNEE JOINT STRUCTURE IN YOUNG ADULTS AT 2e3 YEARS AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION AND HEALTHY CONTROLS: A CROSS-SECTIONAL ANALYSIS A. Van Ginckel y, K. Fortin y, K.L. Bennell y, X. Wang y, T.V. Wrigley y, Y. Wang z, F.M. Cicuttini z, D.J. Lloyd x, D.J. Saxby x, A.L. Bryant y. y The Univ. of Melbourne, Melbourne, Australia; z Monash Univ., Melbourne, Australia; x Griffith Univ., Gold Coast, Australia Purpose: Infra-patellar fat pad (IPFP) pathology, particularly Hoffasynovitis, has been associated with increased risks for the onset of radiographic and/or symptomatic knee osteoarthritis. By contrast, greater IPFP size has been related to less symptomatic and/or slowed structural decline in both people with and without clinical knee osteoarthritis, suggesting a protective, instead of deleterious, role in disease onset. People after anterior cruciate ligament (ACL) injury and/or reconstruction (ACLR) are at a higher risk of osteoarthritis onset. The IPFP in these patients may also show a range of abnormalities (e.g. scarring and fibrosis, synovitis, edema or tears). As such, studying the IPFP could provide additional insights into potential factors affecting the structural longevity of the knee in this population. The aim of this cross-sectional study was to investigate the association between IPFP volume in people at 2e3 years after ACLR and healthy controls, and outcomes of knee joint structure. Methods: Baseline data of 130 participants (100 ACLR patients, 30 controls) from a 2-year prospective cohort study were analysed. Briefly, eligible ACLR patients (mean (SD) age¼ 30.4 (6.4) years, mean (SD) BMI¼25.2 (3.5) kg/m2, 62 (67%) males) had a semitendinosus and gracilis (hamstring) autograft ACLR performed 2e3 years prior to testing, with a diagnosis of an acute ACL tear within 6 months of injury and International Cartilage Repair Society (ICRS) cartilage defects grade <¼ 2 at time of ACLR. Healthy participants (mean (SD) age¼28.3 (5.2) years, mean (SD) body mass index¼23.2 (3.3) kg/m2, 19 (63%) males) had no prior knee surgery or known lower limb injury. Tibial cartilage volumes (mm3) (and corresponding subchondral bone area (mm2)) as well as IPFP volumes (mm3) were measured through manual segmentation of medial/lateral tibial cartilage plates and the IPFP, respectively, from sagittal T1-weighted 3D gradient-echo recall MRI sequences. Prevalence of medial/lateral tibiofemoral cartilage defects and bone marrow lesions (BMLs) was assessed from sagittal/coronal proton density-weighted fat-suppressed turbo-spin echo sequences. A prevalent cartilage defect was defined as an ICRS score of 2 at any site. BMLs were evaluated in 10 subregions of the tibiofemoral joint using the MRI Osteoarthritis Knee Score (MOAKS) and were deemed prevalent when grade 1 was recorded for any of the subregions. Within patients and controls, associations between IPFP volume and structural outcomes were investigated using logistic regression analysis for dichotomous dependent variables (prevalence of cartilage defects or BMLs) or linear regression for continuous dependent variables of cartilage volume, each adjusted for body mass index and gender (as known correlates of IPFP volume), concomitant meniscal pathology (in patients only), MRI scanner and subchondral bone area (when regressed onto cartilage volumes). Results: In both ACLR patients and controls, no significant associations were found between IPFP volumes and prevalence of cartilage defects, BMLs, or medial tibial cartilage volume. However, in ACLR patients, but not controls, a greater IPFP volume was significantly and positively associated with lateral tibial cartilage volume (B¼0.06 (95% CI: 0.032, 0.088), b: 0.64, p<0.001, Figure 1).