Effect of Statistically Iterative Image Reconstruction on Vertebral Bone Strength Prediction Using Bone Mineral Density and Finite Element Modeling: A Preliminary Study.

Statistical iterative reconstruction (SIR) using multidetector computed tomography (MDCT) is a promising alternative to standard filtered back projection (FBP), because of lower noise generation while maintaining image quality. Hence, we investigated the feasibility of SIR in predicting MDCT-based bone mineral density (BMD) and vertebral bone strength from finite element (FE) analysis. The BMD and FE-predicted bone strength derived from MDCT images reconstructed using standard FBP (FFBP) and SIR with (FSIR) and without regularization (FSIRB0) were validated against experimental failure loads (Fexp). Statistical iterative reconstruction produced the best quality images with regard to noise, signal-to-noise ratio, and contrast-to-noise ratio. Fexp significantly correlated with FFBP, FSIR, and FSIRB0. FFBP had a significant correlation with FSIRB0 and FSIR. The BMD derived from FBP, SIRB0, and SIR were significantly correlated. Effects of regularization should be further investigated with FE and BMD analysis to allow for an optimal iterative reconstruction algorithm to be implemented in an in vivo scenario.

Effect of radiation dose reduction on texture measures of trabecular bone microstructure: an in vitro study.

Osteoporosis is characterized by bone loss and degradation of bone microstructure leading to fracture particularly in elderly people. Osteoporotic bone degeneration and fracture risk can be assessed by bone mineral density and trabecular bone score from 2D projection dual-energy X-ray absorptiometry images. However, multidetector computed tomography image based quantification of trabecular bone microstructure showed significant improvement in prediction of fracture risk beyond that from bone mineral density and trabecular bone score; however, high radiation exposure limits its use in routine clinical in vivo examinations. Hence, this study investigated reduction of radiation dose and its effects on image quality of thoracic midvertebral specimens. Twenty-four texture features were extracted to quantify the image quality from multidetector computed tomography images of 11 thoracic midvertebral specimens, by means of statistical moments, the gray-level co-occurrence matrix, and the gray-level run-length matrix, and were analyzed by an independent sample t-test to observe differences in image texture with respect to radiation doses of 80, 150, 220, and 500 mAs. The results showed that three features-namely, global variance, energy, and run percentage, were not statistically significant ([Formula: see text]) for low doses with respect to 500 mAs. Hence, it is evident that these three dose-independent features can be used for disease monitoring with a low-dose imaging protocol.

Multidetector Computed Tomography Imaging: Effect of Sparse Sampling and Iterative Reconstruction on Trabecular Bone Microstructure.

Multidetector computed tomography-based trabecular bone microstructure analysis ensures promising results in fracture risk prediction caused by osteoporosis. Because multidetector computed tomography is associated with high radiation exposure, its clinical routine use is limited. Hence, in this study, we investigated in 11 thoracic midvertebral specimens whether trabecular texture parameters are comparable derived from (1) images reconstructed using statistical iterative reconstruction (SIR) and filtered back projection as criterion standard at different exposures (80, 150, 220, and 500 mAs) and (2) from SIR-based sparse sampling projections (12.5%, 25%, 50%, and 100%) and equivalent exposures as criterion standard. Twenty-four texture features were computed, and those that showed similar values between (1) filtered back projection and SIR at the different exposure levels and (2) sparse sampling and equivalent exposures and reconstructed with SIR were identified. These parameters can be of equal value in determining trabecular bone microstructure with lower radiation exposure using sparse sampling and SIR.

Early T2 changes predict onset of radiographic knee osteoarthritis: data from the osteoarthritis initiative.

OBJECTIVE: To evaluate whether T2 relaxation time measurements obtained at 3 T MRI predict the onset of radiographic knee osteoarthritis (OA). MATERIALS AND METHODS: We performed a nested case-control study of incident radiographic knee OA in the Osteoarthritis Initiative cohort. Cases were 50 knees with baseline Kellgren-Lawrence (KL) grade of 0 that developed KL grade of 2 or more over a 4-year period. Controls were 80 knees with KL grade of 0 after 4 years of follow-up. Baseline T2 relaxation time measurements and laminar analysis of T2 in deep and superficial layers were performed in all knee compartments. The association of T2 values with incident OA was assessed with logistic regression and differences in T2 values by case-control status with linear regression, adjusting for age, sex, body mass index (BMI) and other covariates. RESULTS: Baseline T2 values in all compartments except the medial tibia were significantly higher in knees that developed OA compared with controls and were particularly elevated in the superficial cartilage layers in all compartments. There was an increased likelihood of incident knee OA associated with higher baseline T2 values, particularly in the patella, adjusted OR per 1 SD increase in T2 (3.37 (95% CI 1.72 to 6.62)), but also in the medial femur (1.90 (1.07 to 3.39)), lateral femur (2.17 (1.11 to 4.25)) and lateral tibia (2.23 (1.16 to 4.31)). CONCLUSIONS: These findings suggest that T2 values assessed when radiographic changes are not yet apparent may be useful in predicting the development of radiological tibiofemoral OA.

Reproducibility measurements of three methods for calculating in vivo MR-based knee kinematics.

PURPOSE: To describe three quantification methods for magnetic resonance imaging (MRI)-based knee kinematic evaluation and to report on the reproducibility of these algorithms. MATERIALS AND METHODS: T2 -weighted, fast-spin echo images were obtained of the bilateral knees in six healthy volunteers. Scans were repeated for each knee after repositioning to evaluate protocol reproducibility. Semiautomatic segmentation defined regions of interest for the tibia and femur. The posterior femoral condyles and diaphyseal axes were defined using the previously defined tibia and femur. All segmentation was performed twice to evaluate segmentation reliability. Anterior tibial translation (ATT) and internal tibial rotation (ITR) were calculated using three methods: a tibial-based registration system, a combined tibiofemoral-based registration method with all manual segmentation, and a combined tibiofemoral-based registration method with automatic definition of condyles and axes. Intraclass correlation coefficients and standard deviations across multiple measures were determined. RESULTS: Reproducibility of segmentation was excellent (ATT = 0.98; ITR = 0.99) for both combined methods. ATT and ITR measurements were also reproducible across multiple scans in the combined registration measurements with manual (ATT = 0.94; ITR = 0.94) or automatic (ATT = 0.95; ITR = 0.94) condyles and axes. CONCLUSION: The combined tibiofemoral registration with automatic definition of the posterior femoral condyle and diaphyseal axes allows for improved knee kinematics quantification with excellent in vivo reproducibility.

Changes in MR relaxation times of the meniscus with acute loading: an in vivo pilot study in knee osteoarthritis.

PURPOSE: To prospectively evaluate changes in T1ρ and T2 relaxation times in the meniscal body with acute loading using MRI in osteoarthritic knees and to compare these findings with those of age-matched healthy controls. MATERIALS AND METHODS: Female subjects above 40 years of age with (N1 = 20) and without osteoarthritis (OA) (N2 = 10) were imaged on a 3 Tesla MR scanner using a custom made loading device. MR images were acquired, with the knee flexed at 20°, with and without a compressive load of 50% of the subject's bodyweight. The subjects were categorized based on the radiographic evidence of OA. Three different zones (outer, middle, and inner) of meniscus body were defined (each occupying 1/3rd the width). After adjusting for age and body mass index in the general linear regression model, repeated measures analysis of variance was used to detect significant differences in T1ρ and T2 with and without loading. RESULTS: In the unloaded condition, the average T1ρ and T2 times were elevated in the outer and middle zones of the medial meniscus in OA subjects compared with the controls. In the loaded condition, T1ρ and T2 times of the outer zone of the medial meniscus was significantly elevated in OA subjects compared with controls. Finally the change (from unloaded to loaded) was significantly higher in controls than OA subjects (15.1% versus 8.3%; P = 0.039 for ΔT1ρ , and 11.5% versus 6.9%, P = 0.049 for ΔT2 ). CONCLUSION: These findings suggest that while the OA process appears to affect the relaxation times of all regions within the meniscus, it may affect some regions sooner or to a greater degree. Furthermore, the differences in the change in relaxation times between unloaded and loaded conditions may reveal evidence about load transmission failure of the outer zone of the medial meniscus in subjects with knee OA. It is possible that these metrics (ΔT1ρ and ΔT2 ) may be valuable as an early biomechanical biomarker, which could be used to predict load transmission to the underlying articular cartilage.

Are There Sex Differences in Knee Cartilage Composition and Walking Mechanics in Healthy and Osteoarthritis Populations?

BACKGROUND: Women are at a greater risk for knee osteoarthritis (OA), but reasons for this greater risk in women are not well understood. It may be possible that differences in cartilage composition and walking mechanics are related to greater OA risk in women. QUESTIONS/PURPOSES: (1) Do women have higher knee cartilage and meniscus T1ρ than men in young healthy, middle-aged non-OA and OA populations? (2) Do women exhibit greater static and dynamic (during walking) knee loading than men in young healthy, middle-aged non-OA and OA populations? METHODS: Data were collected from three cohorts: (1) young active (<35 years) (20 men, 13 women); (2) middle-aged (≥35 years) without OA (Kellgren-Lawrence [KL] grade < 2) (43 men, 65 women); and (3) middle-aged with OA (KL>1) (18 men, 25 women). T1ρ and T2 relaxation times for cartilage in the medial knee, lateral knee, and patellofemoral compartments and medial and lateral menisci were quantified with 3.0-T MRI. A subset of the participants underwent three-dimensional motion capture during walking for calculation of peak knee flexion and adduction moments, flexion and adduction impulses, and peak adduction angle. Differences in MR, radiograph, and gait parameters between men and women were compared in the three groups separately using multivariate analysis of variance. RESULTS: Women had higher lateral articular cartilage T1ρ (men=40.5 [95% confidence interval {CI}, 38.8-42.3] ms; women=43.3 [95% CI, 41.9-44.7] ms; p=0.017) and patellofemoral T1ρ (men=44.4 [95% CI, 42.6-46.3] ms; women=48.4 [95% CI, 46.9-50.0] ms; p=0.002) in the OA group; and higher lateral meniscus T1ρ in the young group (men=15.3 [95% CI, 14.7-16.0] ms; women=16.4 [95% CI, 15.6-17.2] ms; p=0.045). The peak adduction moment in the second half of stance was lower in women in the middle-aged (men=2.05 [95% CI, 1.76-2.34] %BW*Ht; women=1.66 [95% CI, 1.44-1.89] %BW*Ht; p=0.037) and OA (men=2.34 [95% CI, 1.76-2.91] %BW*Ht; women=1.42 [95% CI, 0.89-1.94] %BW*Ht; p=0.022) groups. Static varus from radiographs was lower in women in the middle-aged (men=178° [95% CI, 177°-179°]; women=180° [95% CI, 179°-181°]; p=0.002) and OA (men=176° [95% CI, 175°-178°]; women=180° [95% CI, 179°-181°]; p<0.001) groups. Women had lower varus during walking in all three groups (young: men=4° [95% CI, 3°-6°]; women=2° [95% CI, 0°-3°]; p=0.013; middle-aged: men=2° [95% CI, 1°-3°]; women=0° [95% CI, -1° to 1°]; p=0.015; OA: men=4° [95% CI, 2°-6°]; women=0° [95% CI, -2° to 2°]; p=0.011). Women had a higher knee flexion moment (men=4.24 [95% CI, 3.58-4.91] %BW*Ht; women 5.40 [95% CI, 4.58-6.21] %BW*Ht; p=0.032) in the young group. CONCLUSIONS: These data demonstrate differences in cartilage composition and gait mechanics between men and women in young healthy, middle-aged healthy, and OA cohorts. Considering the cross-sectional nature of the study, longitudinal research is needed to investigate if these differences in cartilage composition and walking mechanics are associated with a greater risk of lateral tibiofemoral or patellofemoral OA in women. Future studies should also investigate the relative risk of lateral versus medial patellofemoral cartilage degeneration risk in women compared with men. LEVEL OF EVIDENCE: Level III, retrospective study.

Magnetic resonance analysis of loaded meniscus deformation: a novel technique comparing participants with and without radiographic knee osteoarthritis.

OBJECTIVE: To establish a novel method of quantifying meniscal deformation using loaded MRI. More specifically, the goals were to evaluate the (1) accuracy, (2) inter-rater reliability, (3) intra-rater reliability, and (4) scan-rescan reliability. The secondary purpose of this experiment was to evaluate group differences in meniscal deformation in participants with and without radiographic knee OA. MATERIALS AND METHODS: Weight-bearing 3-T MRIs of the knee in full extension and 30° of flexion were processed to create 3D models of meniscal deformation. Accuracy was assessed using a custom-designed phantom. Twenty-one participants either with or without signs of OA were evaluated, and another six participants (14 knees, one subject was scanned twice) underwent repeated imaging to assess scan-rescan reproducibility. Intraclass correlation coefficient (ICC), root-mean squared error (RMSE), and root-mean-square percent coefficient-of-variation (RMS%CV) analyses were performed. Exploratory comparisons were made between those with and without OA to evaluate potential group differences. RESULTS: All variables were found to be accurate with RMSE ranging from 0.08 to 0.35 mm and 5.99 to 14.63 mm(2). Reproducibility of peak anterior-posterior meniscal deformation was excellent (ICC > 0.821; p < 0.013) with RMS%CV for intra-rater ranging from 0.06 to 1.53 % and 0.17 to 1.97 %, inter-rater ranging from 0.10 to 7.20 % and 3.95 to 18.53 %, and scan-rescan reliability ranging from 1.531 to 7.890 % and 4.894 to 9.142 %, for distance and area metric, respectively. Participants with OA were found to have significantly greater anterior horn movement of both the medial (p = 0.039) and lateral meniscus (p = 0.015), and smaller flexed medial meniscus outer area (p = 0.048) when compared to controls. CONCLUSIONS: MRI-based variables of meniscus deformation were found to be valid in participants with and without OA. Significant differences were found between those with and without radiographic OA; further study is warranted.

Automated unsupervised multi-parametric classification of adipose tissue depots in skeletal muscle.

PURPOSE: To introduce and validate an automated unsupervised multi-parametric method for segmentation of the subcutaneous fat and muscle regions to determine subcutaneous adipose tissue (SAT) and intermuscular adipose tissue (IMAT) areas based on data from a quantitative chemical shift-based water-fat separation approach. MATERIALS AND METHODS: Unsupervised standard k-means clustering was used to define sets of similar features (k = 2) within the whole multi-modal image after the water-fat separation. The automated image processing chain was composed of three primary stages: tissue, muscle, and bone region segmentation. The algorithm was applied on calf and thigh datasets to compute SAT and IMAT areas and was compared with a manual segmentation. RESULTS: The IMAT area using the automatic segmentation had excellent agreement with the IMAT area using the manual segmentation for all the cases in the thigh (R(2): 0.96) and for cases with up to moderate IMAT area in the calf (R(2): 0.92). The group with the highest grade of muscle fat infiltration in the calf had the highest error in the inner SAT contour calculation. CONCLUSION: The proposed multi-parametric segmentation approach combined with quantitative water-fat imaging provides an accurate and reliable method for an automated calculation of the SAT and IMAT areas reducing considerably the total postprocessing time.

Measuring discomfort-An objective method for quantifying peak pressure discomfort and improved fit in adults with transtibial amputation.

BACKGROUND: Prosthetic socket coupling with the residual limb should be comfortable without causing skin breakdown or excessive pressure. However, users report socket discomfort, and there is a scarcity of objective measurements available to assess this feeling of discomfort. Quantifying the specific pressure may enable clinicians and users to determine and improve comfort levels objectively. OBJECTIVES: (1) To evaluate if a peak pressure reduction assists in resolving wounds, redness, and pain inside prosthetic sockets in people with transtibial amputation. (2) To determine if peak pressures measured inside the prosthetic socket due to external forces could be used to quantify the level of improvement in socket discomfort. DESIGN: In this cohort study, we used a pressure sensor to quantify and facilitate adjustments to the prosthetic socket, correlating this information to the user's socket comfort. SETTING: Outpatient clinic in a tertiary hospital in Singapore. PARTICIPANTS: People (N = 16) with unilateral transtibial lower limb amputation using a prosthesis. INTERVENTIONS: NA. MAIN OUTCOME MEASURES: Peak pressure and socket comfort score (SCS). RESULTS: The peak pressure value showed a statistically significant reduction across all participants following adjustments at a 50% delta change in pressure (p = .001). This was achieved with a mean number of 2.6 ± 1.4 adjustments per participant. Following the adjustments, the paired t-test results showed a mean increase between the first SCS and final SCS was 2.6 (p = .001). CONCLUSION: The wound, redness, and pain resolved in 15 of 16 participants regardless of diabetic status following socket adjustments. Although the peak pressures values did not correlate to the SCS score, the reduction in peak pressure saw significant improvement to the SCS. The use of a portable sensor is a fast and efficient means to quantify adjustments inside the prosthetic socket and could potentially be considered as part of future care delivery.

Mapping lines of non-extension in persons with lower limb amputation to aid comfort-driven prosthetic socket design.

OBJECTIVE: This study aimed to develop a new technique to map the strain field for persons with lower-limb amputations to use for the design of comfortable prostheses. METHODS: Using a DSLR camera with stenciled 2D markers, we demonstrated a technique to measure skin strain around the residual limb of persons with lower limb amputations. We used open-source software programs to reconstruct a series of cloud points derived from the pictures of the marked residual limb into 3D models, then calculated the minimum, maximum, and non-extension lines from directional strain fields. RESULTS: A DSLR camera was successful in capturing 2D markers. The maximum mean principal strain was 68% ± 14%, observed around the patella. The minimum compressive mean principal strain of -31% ± 4% was observed posteriorly in the popliteal region of the knee. Although lines of non-extension (LoNE) appear separate in different participants, they are anatomically located in regions that could be generalized for the design of prostheses. CONCLUSIONS: Marker locations extracted from the video of different poses can be compared to calculate strains from which the position of LoNE can be generated. The use of LoNE could be valuable in reducing discomfort at the socket interface and informing future socket design.

Long-term reproducibility of opportunistically assessed vertebral bone mineral density and texture features in routine clinical multi-detector computed tomography using an automated segmentation framework.

Background: To investigate reproducibility of texture features and volumetric bone mineral density (vBMD) extracted from trabecular bone in the thoracolumbar spine in routine clinical multi-detector computed tomography (MDCT) data in a single scanner environment. Methods: Patients who underwent two routine clinical thoraco-abdominal MDCT exams at a single scanner with a time interval of 6 to 26 months (n=203, 131 males; time interval mean, 13 months; median, 12 months) were included in this observational study. Exclusion criteria were metabolic and hematological disorders, bone metastases, use of bone-active medications, and history of osteoporotic vertebral fractures (VFs) or prior diagnosis of osteoporosis. A convolutional neural network (CNN)-based framework was used for automated spine labeling and segmentation (T5-L5), asynchronous Hounsfield unit (HU)-to-BMD calibration, and correction for the intravenous contrast medium phase. Vertebral vBMD and six texture features [varianceglobal, entropy, short-run emphasis (SRE), long-run emphasis (LRE), run-length non-uniformity (RLN), and run percentage (RP)] were extracted for mid- (T5-T8) and lower thoracic (T9-T12), and lumbar vertebrae (L1-L5), respectively. Relative annual changes were calculated in texture features and vBMD for each vertebral level and sorted by sex, and changes were checked for statistical significance (P<0.05) using paired t-tests. Root mean square coefficient of variation (RMSCV) and root mean square error (RMSE) were calculated as measures of variability. Results: SRE, LRE, RLN, and RP exhibited substantial reproducibility with RMSCV-values below 2%, for both sexes and at all spine levels, while vBMD was less reproducible (RMSCV =11.9-16.2%). Entropy showed highest variability (RMSCV =4.34-7.69%) due to statistically significant increases [range, mean ± standard deviation: (4.40±5.78)% to (8.36±8.66)%, P<0.001]. RMSCV of varianceglobal ranged from 1.60% to 3.03%. Conclusions: Opportunistic assessment of texture features in a single scanner environment using the presented CNN-based framework yields substantial reproducibility, outperforming vBMD reproducibility. Lowest scan-rescan variability was found for higher-order texture features. Further studies are warranted to determine, whether microarchitectural changes to the trabecular bone may be assessed through texture features.

Patient-Specific Finite Element Modeling of the Whole Lumbar Spine Using Clinical Routine Multi-Detector Computed Tomography (MDCT) Data-A Pilot Study.

(1) Background: To study the feasibility of developing finite element (FE) models of the whole lumbar spine using clinical routine multi-detector computed tomography (MDCT) scans to predict failure load (FL) and range of motion (ROM) parameters. (2) Methods: MDCT scans of 12 subjects (6 healthy controls (HC), mean age ± standard deviation (SD): 62.16 ± 10.24 years, and 6 osteoporotic patients (OP), mean age ± SD: 65.83 ± 11.19 years) were included in the current study. Comprehensive FE models of the lumbar spine (5 vertebrae + 4 intervertebral discs (IVDs) + ligaments) were generated (L1−L5) and simulated. The coefficients of correlation (ρ) were calculated to investigate the relationship between FE-based FL and ROM parameters and bone mineral density (BMD) values of L1−L3 derived from MDCT (BMDQCT-L1-3). Finally, Mann−Whitney U tests were performed to analyze differences in FL and ROM parameters between HC and OP cohorts. (3) Results: Mean FE-based FL value of the HC cohort was significantly higher than that of the OP cohort (1471.50 ± 275.69 N (HC) vs. 763.33 ± 166.70 N (OP), p < 0.01). A strong correlation of 0.8 (p < 0.01) was observed between FE-based FL and BMDQCT-L1-L3 values. However, no significant differences were observed between ROM parameters of HC and OP cohorts (p = 0.69 for flexion; p = 0.69 for extension; p = 0.47 for lateral bending; p = 0.13 for twisting). In addition, no statistically significant correlations were observed between ROM parameters and BMDQCT- L1-3. (4) Conclusions: Clinical routine MDCT data can be used for patient-specific FE modeling of the whole lumbar spine. ROM parameters do not seem to be significantly altered between HC and OP. In contrast, FE-derived FL may help identify patients with increased osteoporotic fracture risk in the future.

Finite Element Analysis of Osteoporotic and Osteoblastic Vertebrae and Its Association With the Proton Density Fat Fraction From Chemical Shift Encoding-Based Water-Fat MRI - A Preliminary Study.

Purpose: Osteoporosis is prevalent and entails alterations of vertebral bone and marrow. Yet, the spine is also a common site of metastatic spread. Parameters that can be non-invasively measured and could capture these alterations are the volumetric bone mineral density (vBMD), proton density fat fraction (PDFF) as an estimate of relative fat content, and failure displacement and load from finite element analysis (FEA) for assessment of bone strength. This study's purpose was to investigate if osteoporotic and osteoblastic metastatic changes in lumbar vertebrae can be differentiated based on the abovementioned parameters (vBMD, PDFF, and measures from FEA), and how these parameters correlate with each other. Materials and Methods: Seven patients (3 females, median age: 77.5 years) who received 3-Tesla magnetic resonance imaging (MRI) and multi-detector computed tomography (CT) of the lumbar spine and were diagnosed with either osteoporosis (4 patients) or diffuse osteoblastic metastases (3 patients) were included. Chemical shift encoding-based water-fat MRI (CSE-MRI) was used to extract the PDFF, while vBMD was extracted after automated vertebral body segmentation using CT. Segmentation masks were used for FEA-based failure displacement and failure load calculations. Failure displacement, failure load, and PDFF were compared between patients with osteoporotic vertebrae versus patients with osteoblastic metastases, considering non-fractured vertebrae (L1-L4). Associations between those parameters were assessed using Spearman correlation. Results: Median vBMD was 59.3 mg/cm3 in osteoporotic patients. Median PDFF was lower in the metastatic compared to the osteoporotic patients (11.9% vs. 43.8%, p=0.032). Median failure displacement and failure load were significantly higher in metastatic compared to osteoporotic patients (0.874 mm vs. 0.348 mm, 29,589 N vs. 3,095 N, p=0.034 each). A strong correlation was noted between PDFF and failure displacement (rho -0.679, p=0.094). A very strong correlation was noted between PDFF and failure load (rho -0.893, p=0.007). Conclusion: PDFF as well as failure displacement and load allowed to distinguish osteoporotic from diffuse osteoblastic vertebrae. Our findings further show strong associations between PDFF and failure displacement and load, thus may indicate complimentary pathophysiological associations derived from two non-invasive techniques (CSE-MRI and CT) that inherently measure different properties of vertebral bone and marrow.

Associations of Texture Features of Proton Density Fat Fraction Maps between Lumbar Vertebral Bone Marrow and Paraspinal Musculature.

Chemical shift encoding-based water−fat MRI (CSE-MRI)-derived proton density fat fraction (PDFF) has been used for non-invasive assessment of regional body fat distributions. More recently, texture analysis (TA) has been proposed to reveal even more detailed information about the vertebral or muscular composition beyond PDFF. The aim of this study was to investigate associations between vertebral bone marrow and paraspinal muscle texture features derived from CSE-MRI-based PDFF maps in a cohort of healthy subjects. In this study, 44 healthy subjects (13 males, 55 ± 30 years; 31 females, 39 ± 17 years) underwent 3T MRI including a six-echo three-dimensional (3D) spoiled gradient echo sequence used for CSE-MRI at the lumbar spine and the paraspinal musculature. The erector spinae muscles (ES), the psoas muscles (PS), and the vertebral bodies L1-4 (LS) were manually segmented. Mean PDFF values and texture features were extracted for each compartment. Features were compared between males and females using logistic regression analysis adjusted for age and body mass index (BMI). All texture features of ES except for Sum Average were significantly (p < 0.05) different between men and women. The three global texture features (Variance, Skewness, Kurtosis) for PS as well as LS showed a significant difference between male and female subjects (p < 0.05). Mean PDFF measured in PS and ES was significantly higher in females, but no difference was found for the vertebral bone marrow's PDFF. Partial correlation analysis between the texture features of the spine and the paraspinal muscles revealed a highly significant correlation for Variance(global) (r = 0.61 for ES, r = 0.62 for PS; p < 0.001 respectively). Texture analysis using PDFF maps based on CSE-MRI revealed differences between healthy male and female subjects. Global texture features in the lumbar vertebral bone marrow allowed for differentiation between men and women, when the overall PDFF was not significantly different, indicating that PDFF maps may contain detailed and subtle textural information beyond fat fraction. The observed significant correlation of Variance(global) suggests a metabolic interrelationship between vertebral bone marrow and the paraspinal muscles.

Design and development of a novel 3D-printed non-metallic self-locking prosthetic arm for a forequarter amputation.

BACKGROUND: Upper limb, in particular forequarter amputations, require highly customised devices that are often expensive and underutilised. OBJECTIVES: The objective of this study was to design and develop a comfortable 3D-printed cosmetic forequarter prosthetic device, which was lightweight, cool to wear, had an elbow that could lock, matched the appearance of the contralateral arm and was completely free of metal for a specific user's needs. STUDY DESIGN: Device design. TECHNIQUE: An iterative user-centred design approach was used for digitising, designing and developing a functional 3D-printed prosthetic arm for an acquired forequarter amputation, while optimising the fit and function after each prototype. RESULTS: The cost of the final arm was 20% less expensive than a traditionally-made forequarter prostheses in Singapore. The Quebec User Evaluation of Satisfaction with Assistive Technology (QUEST) 2.0 survey was administered, with results indicating that the 3D-printed arm was preferred due to its overall effectiveness, accurate size, ease of use and suspension. However, durability had a lower score, and the weight of the arm was 100 g heavier than the user's current prosthesis. The technique described resulted in a precise fitting and shaped forequarter prosthesis for the user. Using the user's feedback in the iterations of the design resulted in improved QUEST survey results indicating the device was effective, easy to use, perceived as lighter and more secure than the user's traditionally-made device. CONCLUSION: A fully customised cosmetic forequarter prosthesis was designed and developed using digital scanning, computer-aided design modelling and 3D printing for a specific user. These technologies enable new avenues for highly complex prosthetic design innovations.

MDCT-Based Finite Element Analysis for the Prediction of Functional Spine Unit Strength-An In Vitro Study.

(1) Objective: This study aimed to analyze the effect of ligaments on the strength of functional spine unit (FSU) assessed by finite element (FE) analysis of anatomical models developed from multi-detector computed tomography (MDCT) data. (2) Methods: MDCT scans for cadaveric specimens were acquired from 16 donors (7 males, mean age of 84.29 ± 6.06 years and 9 females, mean age of 81.00 ± 11.52 years). Two sets of FSU models (three vertebrae + two disks), one with and another without (w/o) ligaments, were generated. The vertebrae were segmented semi-automatically, intervertebral disks (IVD) were generated manually, and ligaments were modeled based on the anatomical location. FE-predicted failure loads of FSU models (with and w/o ligaments) were compared with the experimental failure loads obtained from the uniaxial biomechanical test of specimens. (3) Results: The mean and standard deviation of the experimental failure load of FSU specimens was 3513 ± 1029 N, whereas of FE-based failure loads were 2942 ± 943 N and 2537 ± 929 N for FSU models with ligaments and without ligament attachments, respectively. A good correlation (ρ = 0.79, and ρ = 0.75) was observed between the experimental and FE-based failure loads for the FSU model with and with ligaments, respectively. (4) Conclusions: The FE-based FSU model can be used to determine bone strength, and the ligaments seem to have an effect on the model accuracy for the failure load calculation; further studies are needed to understand the contribution of ligaments.

Non-anatomical placement adversely affects the functional performance of the meniscal implant: a finite element study.

Non-anatomical placement may occur during the surgical implantation of the meniscal implant, and its influence on the resulting biomechanics of the knee joint has not been systematically studied. The purpose of this study was to evaluate the biomechanical effects of non-anatomical placement of the meniscal implant on the knee joint during a complete walking cycle. Three-dimensional finite element (FE) analyses of the knee joint were performed, based on the model developed from magnetic resonance images and the loading conditions derived from the gait pattern of a healthy male subject, for the following physiological conditions: (i) knee joint with intact native meniscus, (ii) medial meniscectomized knee joint, (iii) knee joint with anatomically placed meniscal implant, and (iv) knee joint with the meniscal implant placed in four different in vitro determined non-anatomical locations. While the native menisci were modeled using the nonlinear hyperelastic Holzapfel-Gasser-Ogden (HGO) constitutive model, the meniscal implant was modeled using the isotropic hyperelastic neo-Hookean model. Placement of the meniscal implant in the non-anatomical lateral-posterior and lateral-anterior locations significantly increased the peak contact pressure in the medial compartment. Placement of the meniscal implant in non-anatomical locations significantly altered the tibial rotational kinematics and increased the total force acting at the meniscal horns. Results suggest that placement of the meniscal implant in non-anatomical locations may restrain its ability to be chondroprotective and may initiate or accelerate cartilage degeneration. In conclusion, clinicians should endeavor to place the implant as closest as possible to the anatomical location to restore the normal knee biomechanics.

A deep learning approach to the screening of malaria infection: Automated and rapid cell counting, object detection and instance segmentation using Mask R-CNN.

Accurate and early diagnosis is critical to proper malaria treatment and hence death prevention. Several computer vision technologies have emerged in recent years as alternatives to traditional microscopy and rapid diagnostic tests. In this work, we used a deep learning model called Mask R-CNN that is trained on uninfected and Plasmodium falciparum-infected red blood cells. Our predictive model produced reports at a rate 15 times faster than manual counting without compromising on accuracy. Another unique feature of our model is its ability to generate segmentation masks on top of bounding box classifications for immediate visualization, making it superior to existing models. Furthermore, with greater standardization, it holds much potential to reduce errors arising from manual counting and save a significant amount of human resources, time, and cost.

Gender-, Age- and Region-Specific Characterization of Vertebral Bone Microstructure Through Automated Segmentation and 3D Texture Analysis of Routine Abdominal CT.

Purpose: To identify long-term reproducible texture features (TFs) of spinal computed tomography (CT), and characterize variations with regard to gender, age and vertebral level using our automated quantification framework. Methods: We performed texture analysis (TA) on baseline and follow-up CT (follow-up duration: 30-90 days) of 21 subjects (8 females, 13 males, age at baseline 61.2 ± 9.2 years) to determine long-term reproducibility. TFs with a long-term reproducibility error Δrel<5% were further analyzed for an association with age and vertebral level in a cohort of 376 patients (129 females, 247 males, age 62.5 ± 9.2 years). Automated analysis comprised labeling and segmentation of vertebrae into subregions using a convolutional neural network, calculation of volumetric bone mineral density (vBMD) with asynchronous calibration and TF extraction. Varianceglobal measures the spread of the gray-level distribution in an image while Entropy reflects the uniformity of gray-levels. Short-run emphasis (SRE), Long-run emphasis (LRE), Run-length non-uniformity (RLN) and Run percentage (RP) contain information on consecutive voxels of a particular grey-level, or grey-level range, in a particular direction. Long runs (LRE) represent coarse texture while short runs (SRE) represent fine texture. RLN reflects similarities in the length of runs while RP reflects distribution and homogeneity of runs with a specific direction. Results: Six of the 24 extracted TFs had Δrel<5% (Varianceglobal, Entropy, SRE, LRE, RLN, RP), and were analyzed further in 4716 thoracolumbar vertebrae. Five TFs (Varianceglobal,SRE,LRE, RLN,RP) showed a significant difference between genders (p<0.001), potentially being caused by a finer and more directional vertebral trabecular microstructure in females compared to males. Varianceglobal and Entropy showed a significant increase from the thoracic to the lumbar spine (p<0.001), indicating a higher degree and earlier initiation of trabecular microstructure deterioration at lower spinal levels. The four higher-order TFs showed significant variations between spine regions without a clear directional gradient (p ≤ 0.001-0.012). No TF showed a clear age dependence. vBMD differed significantly between genders, age groups and spine regions (p ≤ 0.001-0.002). Conclusion: Long-term reproducible CT-based TFs of the thoracolumbar spine were established and characterized in a predominantly older adult study population. The gender-, age- and vertebral-level-specific values may serve as foundation for osteoporosis diagnostics and facilitate future studies investigating vertebral microstructure.