3D Distance Map Research Articles

Distance Mapping of Subtalar Joint after Total Ankle Arthroplasty - A Pilot Study

Category: Hindfoot; Ankle Arthritis Introduction/Purpose: Patients with ankle arthritis often present with concomitant subtalar joint deformity, as the subtalar joint may compensate for ankle malalignment. This compensation in the subtalar joint may manifest as joint space narrowing and sinus tarsi impingement. The objective of this study was to use 3D distance maps (DMs) from weightbearing computed tomography (WBCT) images to see if altering alignment of the tibiotalar joint with total ankle arthroplasty alters alignment of the subtalar joint. We hypothesized that, in patients with ankle arthritis, improving alignment of the tibiotalar joint from total ankle arthroplasty would increase the mean distances across the subtalar joint, indicative of improved alignment. Methods: A retrospective review of WBCT data of randomly selected patients who underwent total ankle arthroplasty between February 2022-July 2023 was performed as a pilot study. Using principal components analysis, the calcaneus was divided into 9 regions on the posterior facet, 4 regions in the sinus tarsi, 1 region in the middle facet, and 1 region in the anterior facet of the subtalar joint, as shown in Figure 1. 3D distance technique was used to objectively measure joint space across the subtalar joint. DMs were measured in millimeters, and DMs of the posterior facet and sinus tarsi were also averaged. Descriptive analysis was performed. Results: A total of 15 patients were included – 10 patients with preoperative and 5 patients with postoperative WBCT scans. The mean DMs in all regions increased postoperatively, showing a trend toward improved alignment. The greatest change in mean DM was seen in the middle facet articulation, from 1.78 mm preoperatively to 2.44mm postoperatively. The sinus tarsi was the second highest change, from a mean DM of 2.45 mm preoperatively to 2.80 postoperatively. Conclusion: This pilot study demonstrates that improved tibiotalar alignment through total ankle arthroplasty results in changes in the subtalar joint. Further study with adequate power is warranted to quantify the effect that improved tibiotalar alignment has on subtalar alignment.

3D-2D Distance Maps Conversion Enhances Classification of Craniosynostosis.

Diagnosis of craniosynostosis using photogrammetric 3D surface scans is a promising radiation-free alternative to traditional computed tomography. We propose a 3D surface scan to 2D distance map conversion enabling the usage of the first convolutional neural networks (CNNs)-based classification of craniosynostosis. Benefits of using 2D images include preserving patient anonymity, enabling data augmentation during training, and a strong under-sampling of the 3D surface with good classification performance. The proposed distance maps sample 2D images from 3D surface scans using a coordinate transformation, ray casting, and distance extraction. We introduce a CNNbased classification pipeline and compare our classifier to alternative approaches on a dataset of 496 patients. We investigate into low-resolution sampling, data augmentation, and attribution mapping. Resnet18 outperformed alternative classifiers on our dataset with an F1-score of 0.964 and an accuracy of 98.4 %. Data augmentation on 2D distance maps increased performance for all classifiers. Under-sampling allowed 256-fold computation reduction during ray casting while retaining an F1-score of 0.92. Attribution maps showed high amplitudes on the frontal head. We demonstrated a versatile mapping approach to extract a 2D distance map from the 3D head geometry increasing classification performance, enabling data augmentation during training on 2D distance maps, and the usage of CNNs. We found that low-resolution images were sufficient for a good classification performance. Photogrammetric surface scans are a suitable craniosynostosis diagnosis tool for clinical practice. Domain transfer to computed tomography seems likely and can further contribute to reducing ionizing radiation exposure for infants.

What is the impact of miniscrew-assisted rapid palatal expansion on the midfacial soft tissues? A prospective three-dimensional stereophotogrammetry study

ObjectivesTo evaluate the midfacial soft tissue changes of the face in patients treated with miniscrew-assisted rapid palatal expansion (MARPE).Materials and methods3D facial images and intra-oral scans (IOS) were obtained before expansion (T0), immediately after completion of expansion (T1), and 1 year after expansion (T2). The 3D images were superimposed and two 3D distance maps were generated to measure the midfacial soft tissue changes: immediate effects between timepoints T0 and T1 and overall effects between T0 and T2. Changes of the alar width were also measured and dental expansion was measured as the interpremolar width (IPW) on IOS.ResultsTwenty-nine patients (22 women, 7 men, mean age 25.9 years) were enrolled. The soft tissue in the regions of the nose, left of philtrum, right of philtrum, and upper lip tubercle demonstrated a statistically significant anterior movement of 0.30 mm, 0.93 mm, 0.74 mm, and 0.81 mm, respectively (p < 0.01) immediately after expansion (T0–T1). These changes persisted as an overall effect (T0–T2). The alar width initially increased by 1.59 mm, and then decreased by 0.08 mm after 1 year, but this effect was not significant. The IPW increased by 4.58 mm and remained stable 1 year later. There was no significant correlation between the increase in IPW and alar width (r = 0.35, p = 0.06).ConclusionsOur findings indicate that MARPE results in significant but small changes of the soft tissue in the peri-oral and nasal regions. However, the clinical importance of these findings is limited.Clinical relevanceMARPE is an effective treatment modality to expand the maxilla, incurring only minimal and clinically insignificant changes to the midfacial soft tissues.

SurfNN: Joint Reconstruction of Multiple Cortical Surfaces from Magnetic Resonance Images.

To achieve fast, robust, and accurate reconstruction of the human cortical surfaces from 3D magnetic resonance images (MRIs), we develop a novel deep learning-based framework, referred to as SurfNN, to reconstruct simultaneously both inner (between white matter and gray matter) and outer (pial) surfaces from MRIs. Different from existing deep learning-based cortical surface reconstruction methods that either reconstruct the cortical surfaces separately or neglect the interdependence between the inner and outer surfaces, SurfNN reconstructs both the inner and outer cortical surfaces jointly by training a single network to predict a midthickness surface that lies at the center of the inner and outer cortical surfaces. The input of SurfNN consists of a 3D MRI and an initialization of the midthickness surface that is represented both implicitly as a 3D distance map and explicitly as a triangular mesh with spherical topology, and its output includes both the inner and outer cortical surfaces, as well as the midthickness surface. The method has been evaluated on a large-scale MRI dataset and demonstrated competitive cortical surface reconstruction performance.

Chopart Peritalar Subluxation in Progressive Collapsing Foot Deformity Assessed by Three- Dimensional Coverage Maps

Category: Hindfoot; Midfoot/Forefoot; Other Introduction/Purpose: Progressive collapsing foot deformity (PCFD) is a complex three-dimensional (3D) deformity characterized by peritalar subluxation (PTS) of the hindfoot through the triple joint complex. In this context, adjacent structures adopt different positions, and bone relations change, producing areas of higher or less contact and stress. The objective of this study was to use 3D distance maps (DMs) and coverage maps (CMs) from weightbearing CT (WBCT) images to assess subluxation across the Chopart joint in PCFD patients. We hypothesized that CMs would show decreased coverage indicative of subluxation through regions of the Chopart joint in PCFD patients when compared to controls. Methods: In this IRB-approved, retrospective case-control study, we analyzed WBCT data of 20 consecutive patients with flexible PCFD and 20 controls. Using principle component analysis, coverage area was divided into six regions on the talar head and 4 on the calcaneal-cuboid articular surface. Novel 3D distance mapping (DM) technique was used to objectively characterize joint coverage across the entire Chopart surface on both talus and calcaneus. Distance maps were measured in millimeters and colored to highlight covered areas. Distances less than 4mm were defined to be covered, while areas with distances greater than 4mm uncovered. Joint coverage was defined as percentage of articular area with DMs lower than 4 mm. Coverage Maps (CM) were built highlighting areas of coverage (teal) versus non-coverage (pink). The Foot and Ankle Offset (FAO) was used as a reference semi-automatic three-dimensional measurement. Comparisons were performed with independent t-tests, assuming unequal variances and p-values &lt;.05 considered significant. Results: Changes in coverage percentages of PCFD cases relative to controls are indicated in the attached figure. The superomedial and the inferomedial regions of the talar head were found to have a 75% and 79% decrease in coverage in PCFD cases relative to the controls (ps&lt;0.003). The medial side of the head had an overall increase in coverage (ps&lt;0.002). On the calcaneus, the calcaneal-cuboid joint plantar region was found to have a significant coverage decrease of 12% relative to the controls (p=0.037), while the lateral quadrant observed a 13% increase (p=0.002). DMs evaluation showed no significant differences in the mean distances for either the calcaneocuboid or the talonavicular (ps&gt;0.05). The FAO was found to be correlated with changes in talar and calcaneal coverages (rs=0.90; R2=0.81). Conclusion: Our results support the hypothesis that significant changes occur at the Chopart joint in early flexible PCFD cases. Increased coverage in the lateral region of the talar head and decreased coverage in the medial and plantar regions point to internal rotation of the talus indicating subluxation through the entire joint. This behavior was also translated in the calcaneal- cuboid, where plantar and medial areas had a decrease in coverage. Coverage 3D mapping enabled objective subluxation quantification through the Chopart joint in early-stage PCFD. These findings may assist clinical assessment of normal joint alignment restoration during PCFD corrections.

Syndesmotic Malreduction Assessment using Three-Dimensional Distance Mapping: A Cadaveric WBCT Study

Category: Sports; Ankle; Ankle Arthritis; Arthroscopy; Trauma Introduction/Purpose: Diagnosing syndesmotic injuries is challenging. Avoiding intra-operative syndesmotic malreduction is even more challenging. Malreduction can be devastating to the long-term health of the ankle joint and has been shown to be more frequent and unforgiving with rigid screw fixation when compared to flexible implants. Syndesmotic position assessment postoperatively is usually performed using bilateral CT. Evaluation is frequently subjective or based on conventional distance, angular, area, and volumetric measurements. Diagnostic accuracy of these measurements is still questionable. The goal of this study was to utilize a 3D Weightbearing CT distance mapping algorithm to objectively assess syndesmotic position in a cadaveric model simulating different patterns of syndesmotic malreduction. We also aimed to evaluate the relative changes in syndesmotic position when fixation was converted from rigid to flexible. Methods: In this cadaveric experimentation, four below-knee specimens were utilized. Specimens were mounted in an external frame simulated weightbearing condition (350N of axial load). Specimens underwent sequential WBCT imaging in four different conditions: native normal ankle, syndesmotic instability, malreduced, and released conditions. In the instability condition, syndesmotic ligaments were surgically released using a conventional limited lateral approach. The malreduced position consisted of controlled 5mm anterior displacement, 5mm posterior displacement, 15o of internal rotation, and over-compressed (160N) states. Fixation was performed with a single implant 20mm proximal to the ankle joint. Implant utilized allowed initial rigid screw- type fixation, followed by implant flexibilization similar to a suture-type fixation (released position). Tibia, fibula, and talus WBCT images were segmented, and syndesmotic incisura and gutter distances were assessed using a 3D distance map algorithm. The syndesmotic position was compared between normal, unstable, malreduced, and released positions. Color-coded representations of the observed differences were presented (Figure). Results: When comparing normal to unstable condition, we observed significant widening of the syndesmotic posterior aspect (average, 13.9%; p=0.004). Overall, all four malreduced positions lead to significantly decreased tibiofibular distances when compared to the unstable state, consistent with syndesmotic over-compression (average, 19.8%; p=0.01), particularly in the posterior aspect of the joint (average, 26.9%; p=0.04). This over-compression was also more pronounced in the anterior displacement (31.5%) and internal rotation malreductions (23.1%). In the released flexible position we found a non-significant trend towards widening of the tibiofibular distances (average, 12%; p=0.08) when compared to the malreduced conditions, indicating partial restoration the syndesmotic relationship. The syndesmotic distances in the released position were also not significantly different from the normal condition. When compared to normal, the lateral gutter demonstrated significant widening in the unstable condition (average 16.7%; p=0.02), narrowing in the malreduced state (average 6.6%; p=0.04), and widening in the released position (average 3.7%; p=0.002). Conclusion: In this study we used 3D WBCT distance mapping to assess syndesmotic position in a cadaveric model simulating syndesmotic instability and multiple syndesmotic malreduction conditions (anterior and posterior displacement, internal rotation and over-compression). We observed significant widening when the syndesmotic ligaments were sectioned, followed by significant tibiofibular narrowing in the malreduced and fixed rigid states. When the implant fixation was released, we observed a trend towards restoration of normal syndesmotic alignment, with relative widening that was however not significantly different from the malreduced rigidly fixed state. Increased sample size cadaveric assessment and clinical studies are necessary to validate our results.

Generative-Adversarial-Network-Based Data Augmentation for the Classification of Craniosynostosis

Abstract Craniosynostosis is a congenital disease characterized by the premature closure of one or multiple sutures of the infant’s skull. For diagnosis, 3D photogrammetric scans are a radiation-free alternative to computed tomography. However, data is only sparsely available and the role of data augmentation for the classification of craniosynostosis has not yet been analyzed. In this work, we use a 2D distance map representation of the infants’ heads with a convolutional-neural-network-based classifier and employ a generative adversarial network (GAN) for data augmentation. We simulate two data scarcity scenarios with 15% and 10% training data and test the influence of different degrees of added synthetic data and balancing underrepresented classes. We used total accuracy and F1-score as a metric to evaluate the final classifiers. For 15% training data, the GAN-augmented dataset showed an increased F1-score up to 0.1 and classification accuracy up to 3 %. For 10% training data, both metrics decreased. We present a deep convolutional GAN capable of creating synthetic data for the classification of craniosynostosis. Using a moderate amount of synthetic data using a GAN showed slightly better performance, but had little effect overall. The simulated scarcity scenario of 10% training data may have limited the model’s ability to learn the underlying data distribution.

Multi-head attention-based U-Nets for predicting protein domain boundaries using 1D sequence features and 2D distance maps

The information about the domain architecture of proteins is useful for studying protein structure and function. However, accurate prediction of protein domain boundaries (i.e., sequence regions separating two domains) from sequence remains a significant challenge. In this work, we develop a deep learning method based on multi-head U-Nets (called DistDom) to predict protein domain boundaries utilizing 1D sequence features and predicted 2D inter-residue distance map as input. The 1D features contain the evolutionary and physicochemical information of protein sequences, whereas the 2D distance map includes the structural information of proteins that was rarely used in domain boundary prediction before. The 1D and 2D features are processed by the 1D and 2D U-Nets respectively to generate hidden features. The hidden features are then used by the multi-head attention to predict the probability of each residue of a protein being in a domain boundary, leveraging both local and global information in the features. The residue-level domain boundary predictions can be used to classify proteins as single-domain or multi-domain proteins. It classifies the CASP14 single-domain and multi-domain targets at the accuracy of 75.9%, 13.28% more accurate than the state-of-the-art method. Tested on the CASP14 multi-domain protein targets with expert annotated domain boundaries, the average per-target F1 measure score of the domain boundary prediction by DistDom is 0.263, 29.56% higher than the state-of-the-art method.

Three-Dimensional Distance Mapping Method to Evaluate Mandibular Symmetry and Morphology of Adults with Unilateral Premolar Scissors Bite

(1) Objective: This study aimed to evaluate the association between unilateral premolar scissors bite and mandibular symmetry of adults via the 3D distance mapping method. (2) Methods: A total of 53 cone-beam computed tomography (CBCT) images of adults with unilateral premolar scissors bite were set as study samples. A total of 53 age- and sex-matched samples without scissors bite were in the control group. Three-dimensional mandibular models and seven mandibular functional units, including condylar process (Co), coronoid process (Cr), mandibular ramus (Ra), mandibular angle (Ma), alveolar process (Ap), mandibular body (Mb), and chin process (Ch) were constructed and mirrored. After superimposition of the original and the mirrored models, 3D distance maps and deviation analysis were performed to evaluate the mandibular symmetry and morphology. (3) Results: In the study group, the matching percentages of the entire mandible (50.79 ± 10.38%), Ap (67.00 ± 12.68%), Mb (66.62 ± 9.44%), Ra (62.52 ± 11.00%), Ch (80.75 ± 9.86%), and Co (62.78 ± 13.56) were lower than that of the entire mandible (58.60 ± 5.52) (p &lt; 0.01), Ap (73.83 ± 8.88%) (p &lt; 0.01), Mb (72.37 ± 8.69%) (p &lt; 0.01), Ra (68.60 ± 7.56%) (p &lt; 0.01), Ch (85.23 ± 6.80%) (p &lt; 0.01), and Co (67.58 ± 10.32%) (p &lt; 0.05) in the control group. However, Cr and Ma showed no significant difference (p &gt; 0.05). (4) Conclusions: The 3D distance mapping method provided a qualitative and quantitative mandibular symmetry and morphology assessment. Mandibular asymmetry was found in adults with unilateral premolar scissors bites. Mandibular functional units, including the alveolar process, mandibular body, mandibular ramus, chin process, and condylar process, showed significant differences, while no significant difference was observed in the coronoid process and mandibular angle.

Surgical Correction of Peritalar Subluxation and Patient-Reported Outcomes: A Prospective Comparative Outcome Study in Flexible Progressive Collapsing Foot Deformity

Category:Hindfoot; Midfoot/ForefootIntroduction/Purpose:Peritalar subluxation (PTS) of the hindfoot is a critical finding in Progressive Collapsing Foot Deformity (PCFD). Subluxation of the middle facet and sinus tarsi recently been shown to represent essential markers of pronounced and potentially progressive deformity. Weightbearing CT (WBCT) imaging and three-dimensional (3D) distancing coverage maps (CM) allow a complete and accurate assessment of PTS markers across the entire peritalar surface. This prospective comparative study aimed to assess the effectiveness of joint-sparing realignment surgical treatment for flexible PCFD in reducing PTS and to correlate the improvement with patient-reported outcomes (PROs). We hypothesized that would significantly improve PTS markers, mainly decreasing sinus tarsi coverage/impingement and middle facet subluxation, and that this improvement would correlate with increased PROs.Methods:In this IRB-approved prospective and comparative study, we enrolled patients with flexible PCFD, no prior surgeries, and failed conservative treatment. Included females/3 males, mean age 57.2, range 37-74) underwent joint-sparing surgical realignment procedure by a single surgeon. Standing weightbearing CT (WBCT) was complete 3-months postoperatively.Following automatic bone segmentation, 3D distance maps (DMs) of the entire peritalar surface were generated, and coverage of the subtalar joint (anterior, middle, and posterior) and sinus tarsi were assessed as markers of PTS. Joint coverage was defined as the percentage of articular space where DMs were <5 mm. CM were built highlighting areas of adequate joint interaction (blue), joint subluxation (pink), and impingement (red). PROs were evaluated preoperatively and at the latest follow-up between preop/postop measurements and PROs were assessed by independent t-tests/Wilcoxon and bivariate analysis. P-values <.05 were considered significant.Results:The overall follow-up was 8.2 months (6-13 months). Medial displacement calcaneal osteotomies, lateral column lengthening, and first ray realignment procedure osteotomy or Lapidus) were performed in all patients. Foot and Ankle Offset significantly improved from 10.6% preoperatively to 3.1% postoperatively (p=0.0005), on averaged improvement was also observed in anterior facet joint coverage (61.6%), as well as a reduction in sinus tarsi coverage/impingement (-43.2%) (both p<0.001). Middle posterior facet joint coverage (3.5%, p=0.06) also demonstrated improvements, however not significant. PROs improved significantly on average postoperatively, with the E Ankle Surgery (EFAS) Score increasing from 3.1 to 7.3 (p=0.02) and the Foot Function Index (FFI) improving from 71.5 to 48.7 (p=0.01). Improvements in EFAS scores and FFI s with improvements in middle facet coverage (R2 0.89, p=0.0154) and anterior facet coverage (R2 0.80, p=0.04), respectively.Conclusion:Our study was the first to evaluate WBCT 3D distance mapping's role in the assessment of surgical correction of PTS in patients with PCFD. We found significant subtalar joint anterior facet coverage and sinus tarsi impingement following surgical reconstruction, with a trend to significant improvements in middle and posterior facet j importantly, improvements in middle and anterior facet coverage correlated significantly with improved PROs (EFAS score and FFI, respectively).Significance/Clinical Relevance: Based on our study results, optimization of subtalar joint coverage and reduction of PTS should be goals of surgical treatment of PC

Surgical Correction of Peritalar Subluxation and Patient Reported Outcomes: A Prospective Comparative Outcome Study in Flexible Progressive Collapsing Foot Deformity

Category:Ankle; Hindfoot; OtherIntroduction/Purpose:Peritalar subluxation (PTS) of the hindfoot is a critical finding in Progressive Collapsing Foot Deformity (PCFD). Subluxation of the middle facet and sinus tarsi impingement have recently been shown to represent essential markers of pronounced and potentially progressive deformity. Weightbearing CT (WBCT) imaging and three-dimensional (3D) distance (DM) and coverage maps (CM) allow a complete and accurate assessment of PTS markers across the entire peritalar surface. This prospective comparative study aimed to assess the effectiveness of joint-sparing realignment surgical treatment for flexible PCFD in reducing PTS and to correlate the improvement with patient-reported outcomes (PROs). We hypothesized that surgical treatment would significantly improve PTS markers, mainly decreasing sinus tarsi coverage/impingement and middle facet subluxation, and that this improvement would correlate with increased PROs.Methods:In this IRB-approved prospective and comparative study, we enrolled patients with flexible PCFD, no prior surgeries, and failed conservative treatment. Included patients (n=10, 7 females/3 males, mean age 57.2, range 37-74) underwent joint-sparing surgical realignment procedure by a single surgeon. Standing weightbearing CT (WBCT) was completed preoperatively and 3- months postoperatively. Following automatic bone segmentation, 3D distance maps (DMs) of the entire peritalar surface were generated, and coverage of the subtalar joint articular facets (anterior, middle, and posterior) and sinus tarsi were assessed as markers of PTS. Joint coverage was defined as the percentage of articular space where DMs were <5 mm. Coverage Maps (CM) were built highlighting areas of adequate joint interaction (blue), joint subluxation (pink), and impingement (red). PROs were evaluated preoperatively and at the latest follow-up. Differences between preop/postop measurements and PROs were assessed by independent t-tests/Wilcoxon and bivariate analysis. P-values <.05 were considered significant.Results:The overall follow-up was 8.2 months (6-13 months). Medial displacement calcaneal osteotomies, lateral column lengthening, and first ray realignment procedures (either Cotton osteotomy or Lapidus) were performed in all patients. Foot and Ankle Offset significantly improved from 10.6% preoperatively to 3.1% postoperatively (p=0.0005), on average. Significant averaged improvement was also observed in anterior facet joint coverage (61.6%), as well as a reduction in sinus tarsi coverage/impingement (-43.2%) (both p<0.001). Middle (19.5%, p=0.08) and posterior facet joint coverage (3.5%, p=0.06) also demonstrated improvements, however not significant. PROs improved significantly on average postoperatively, with the European Foot and Ankle Surgery (EFAS) Score increasing from 3.1 to 7.3 (p=0.02) and the Foot Function Index (FFI) improving from 71.5 to 48.7 (p=0.01). Improvements in EFAS scores and FFI significantly correlated with improvements in middle facet coverage (R2 0.89, p=0.0154) and anterior facet coverage (R2 0.80, p=0.04), respectively.Conclusion:Our study was the first to evaluate WBCT 3D distance mapping's role in the assessment of surgical correction of PTS in patients with PCFD. We found significant improvements in subtalar joint anterior facet coverage and sinus tarsi impingement following surgical reconstruction, with a trend to significant improvements in middle and posterior facet joint coverage. More importantly, improvements in middle and anterior facet coverage correlated significantly with improved PROs (EFAS score and FFI, respectively). Based on our study results, optimization of subtalar joint coverage and reduction of PTS should be goals of surgical treatment of PCFD patients.

Three-Dimensional Coverage Maps in the Assessment of Chopart Subluxation in Progressive Collapsing Foot Deformity

Category:Basic Sciences/Biologics; Hindfoot; Midfoot/ForefootIntroduction/Purpose:Progressive collapsing foot deformity (PCFD), formerly termed Adult-Acquired Flatfoot Deformity (AAFD), is a complex 3D deformity characterized by peritalar subluxation (PTS) of the hindfoot through the triple joint complex. In this context, adjacent structures may adopt different positions and boney relations can change, producing areas increased contact or subluxation. The objective of this study was to use 3D distance maps (DMs) and coverage maps (CMs) from weightbearing CT (WBCT) images to assess subluxation across the Chopart joint in PCFD patients. We hypothesized that CMs would show decreased coverage indicative of subluxation through certain regions of the Chopart joint in PCFD patients when compared to the controls.Methods:In this IRB-approved, retrospective case-control study, we analyzed WBCT data of 18 consecutive patients with flexible PCFD and 10 controls. Using principle component analysis, candidate coverage area was divided into nine regions on the talar head and 4 regions on the calcaneal-cuboid (CC) articular surface. Novel 3D distance mapping (DM) technique was used to objectively characterize joint coverage across the entire Chopart joint surface on both the talus and calcaneus. Distance maps were measured in millimeters and colored to highlight covered areas. Areas with distances less than 4mm were defined to be covered, while areas with distances greater than 4mm were considered to be uncovered. Joint coverage was defined as percentage of articular area with DMs lower than 4 mm. Coverage Maps (CM) were created to highlight areas of coverage (teal) versus non- coverage (pink). Comparisons were performed with independent t-tests, assuming unequal variances. P values <.05 were considered significant.Results:Changes in coverage percentages of PCFD cases relative to controls are indicated in attached figure 1. The middle lateral region of the talar head was found to have a 9% increase in coverage in PCFD cases relative to the controls (p = 0.011). The plantar region of the calcaneal-cuboid joint was found to have a 18% decrease in coverage compared to the controls. Except for the dorsal medial regions, the medial side of the talar head saw overall decreases in coverage. However, these values were not statistically significant. On the calcaneus, the plantar region of the calcaneal-cuboid joint was found to have a significant coverage decrease of 18% relative to the controls (p = 0.017). There was also a decrease in coverage observed in the medial region of the calcaneal-cuboid joint and an increase in the dorsal and lateral areas.Conclusion:Our results support the occurrence of significant Chopart joint changes in early flexible PCFD. Increased lateral and decreased medial/plantar talar head coverage point to internal rotation and plantarflexion of the talus. Associated dorsal migration of the cuboid where plantar and medial areas have decreased coverage indicate subluxation through the entirety of the Chopart joint. Novel 3D coverage mapping enabled objective quantification of subluxation though the Chopart joint in early stage PCFD. These findings may assist clinical decision making regarding the restoration of normal joint alignment during PCFD corrections. Further studies are needed to establish thresholds of change associated with degeneration.

Development of an Automated Mass-Customization Pipeline for Knee Replacement Surgery Using Biplanar X-Rays

Abstract For standard “off-the-shelf” knee replacement procedures, surgeons use X-ray images to aid implant selection from a limited number of models and sizes. This can lead to complications and the need for implant revision due to poor implant fit. Customized solutions have been shown to improve results but require increased preoperative assessment (Computed Tomography or Magnetic Resonance Imaging), longer lead times, and higher costs which have prevented widespread adoption. To attain the benefits of custom implants, whilst avoiding the limitations of currently available solutions, a fully automated mass-customization pipeline, capable of developing customized implant designs for fabrication via additive manufacturing from calibrated X-rays, is proposed. The proof-of-concept pipeline uses convolutional neural networks to extract information from biplanar X-ray images, point depth, and statistical shape models to reconstruct the anatomy, and application programming interface scripts to generate various customized implant designs. The pipeline was trained using data from the Korea Institute of Science and Technology Information. Thirty subjects were used to test the accuracy of the anatomical reconstruction, ten from this data set, and a further 20 independent subjects obtained from the Osteoarthritis Initiative. An average root-mean-squared error of 1.00 mm was found for the femur test cases and 1.07 mm for the tibia. Three-dimensional (3D) distance maps of the output components demonstrated these results corresponded to well-fitting components, verifying automatic customization of knee replacement implants is feasible from 2D medical imaging.

To Improve Protein Sequence Profile Prediction through Image Captioning on Pairwise Residue Distance Map.

Protein sequence profile prediction aims to generate multiple sequences from structural information to advance the protein design. Protein sequence profile can be computationally predicted by energy-based or fragment-based methods. By integrating these methods with neural networks, our previous method, SPIN2, has achieved a sequence recovery rate of 34%. However, SPIN2 employed only one-dimensional (1D) structural properties that are not sufficient to represent three-dimensional (3D) structures. In this study, we represented 3D structures by 2D maps of pairwise residue distances and developed a new method (SPROF) to predict protein sequence profiles based on an image captioning learning frame. To our best knowledge, this is the first method to employ a 2D distance map for predicting protein properties. SPROF achieved 39.8% in sequence recovery of residues on the independent test set, representing a 5.2% improvement over SPIN2. We also found the sequence recovery increased with the number of their neighbored residues in 3D structural space, indicating that our method can effectively learn long-range information from the 2D distance map. Thus, such network architecture using a 2D distance map is expected to be useful for other 3D structure-based applications, such as binding site prediction, protein function prediction, and protein interaction prediction. The online server and the source code is available at http://biomed.nscc-gz.cn and https://github.com/biomed-AI/SPROF , respectively.

SMASHing the LMC: A Tidally Induced Warp in the Outer LMC and a Large-scale Reddening Map

Abstract We present a study of the three-dimensional (3D) structure of the Large Magellanic Cloud (LMC) using ∼2.2 million red clump (RC) stars selected from the Survey of the MAgellanic Stellar History. To correct for line-of-sight dust extinction, the intrinsic RC color and magnitude and their radial dependence are carefully measured by using internal nearly dust-free regions. These are then used to construct an accurate 2D reddening map (165 deg2 area with ∼10′ resolution) of the LMC disk and the 3D spatial distribution of RC stars. An inclined disk model is fit to the 2D distance map, yielding a best-fit inclination angle degrees with random errors of ±0.°19 and line-of-nodes position angle degrees with random errors of ±0.°49. These angles vary with galactic radius, indicating that the LMC disk is warped and twisted likely due to the repeated tidal interactions with the Small Magellanic Cloud (SMC). For the first time, our data reveal a significant warp in the southwestern part of the outer disk starting at ρ ∼ 7° that departs from the defined LMC plane up to ∼4 kpc toward the SMC, suggesting that it originated from a strong interaction with the SMC. In addition, the inner disk encompassing the off-centered bar appears to be tilted up to 5°–15° relative to the rest of the LMC disk. These findings on the outer warp and the tilted bar are consistent with the predictions from the Besla et al. simulation of a recent direct collision with the SMC.

Fully automatic detection of renal cysts in abdominal CT scans.

Simple renal cysts are a common benign finding in abdominal CT scans. However, since they may evolve in time, simple cysts need to be reported. With an ever-growing number of slices per CT scan, cysts are easily overlooked by the overloaded radiologist. In this paper, we address the detection of simple renal cysts as an incidental finding in a real clinical setting. We propose a fully automatic framework for renal cyst detection, supported by a robust segmentation of the kidneys performed by a fully convolutional neural network. A combined 3D distance map of the kidneys and surrounding fluids provides initial candidates for cysts. Eventually, a second convolutional neural network classifies the candidates as cysts or non-cyst objects. Performance was evaluated on 52 abdominal CT scans selected at random in a real radiological workflow and containing over 70 cysts annotated by an experienced radiologist. Setting the minimal cyst diameter to 10 mm, the algorithm detected 59/70 cysts (true-positive rate=84.3%) while producing an average of 1.6 false-positive per case. The obtained results suggest the proposed framework is a promising approach for the automatic detection of renal cysts as incidental findings of abdominal CT scans.

Three-dimensional quantitative assessment of ablation margins based on registration of pre- and post-procedural MRI and distance map.

Contrast-enhanced MR images are widely used to confirm the adequacy of ablation margin after liver ablation for early prediction of local recurrence. However, quantitative assessment of the ablation margin by comparing pre- and post-procedural images remains challenging. We developed and tested a novel method for three-dimensional quantitative assessment of ablation margin based on non-rigid image registration and 3D distance map. Our method was tested with pre- and post-procedural MR images acquired in 21 patients who underwent image-guided percutaneous liver ablation. The two images were co-registered using non-rigid intensity-based registration. After the tumor and ablation volumes were segmented, target volume coverage, percent of tumor coverage, and Dice similarity coefficient were calculated as metrics representing overall adequacy of ablation. In addition, 3D distance map around the tumor was computed and superimposed on the ablation volume to identify the area with insufficient margins. For patients with local recurrences, the follow-up images were registered to the post-procedural image. Three-dimensional minimum distance between the recurrence and the areas with insufficient margins was quantified. The percent tumor coverage for all nonrecurrent cases was 100%. Five cases had tumor recurrences, and the 3D distance map revealed insufficient tumor coverage or a 0-mm margin. It also showed that two recurrences were remote to the insufficient margin. Non-rigid registration and 3D distance map allow us to quantitatively evaluate the adequacy of the ablation margin after percutaneous liver ablation. The method may be useful to predict local recurrences immediately following ablation procedure.

Accuracy of three-dimensional soft tissue simulation in bimaxillary osteotomies

The purpose of this study was to evaluate the accuracy of an algorithm based on the mass tensor model (MTM) for computerized 3D simulation of soft-tissue changes following bimaxillary osteotomy, and to identify patient and surgery-related factors that may affect the accuracy of the simulation. Sixty patients (mean age 26.0 years) who had undergone bimaxillary osteotomy, participated in this study. Cone beam CT scans were acquired pre- and one year postoperatively. The 3D rendered pre- and postoperative scans were matched. The maxilla and mandible were segmented and aligned to the postoperative position. 3D distance maps and cephalometric analyses were used to quantify the simulation error. The mean absolute error between the 3D simulation and the actual postoperative facial profile was 0.81 ± 0.22 mm for the face as a whole. The accuracy of the simulation (average absolute error ≤2 mm) for the whole face and for the upper lip, lower lip and chin subregions were 100%, 93%, 90% and 95%, respectively. The predictability was correlated with the magnitude of the maxillary and mandibular advancement, age and V-Y closure. It was concluded that the MTM-based soft tissue simulation for bimaxillary surgery was accurate for clinical use, though patients should be informed of possible variation in the predicted lip position.

Three-Dimensional Facial Simulation in Bilateral Sagittal Split Osteotomy: A Validation Study of 100 Patients

Three-dimensional (3D) virtual planning of orthognathic surgery in combination with 3D soft tissue simulation allows the surgeon and the patient to assess the 3D soft tissue simulation. This study was conducted to validate the predictability of the mass tensor model soft tissue simulation algorithm combined with cone-beam computed tomographic (CBCT) imaging for patients who underwent mandibular advancement using a bilateral sagittal split osteotomy (BSSO). One hundred patients were treated with a BSSO according to the Hunsuck modification. The pre- and postoperative CBCT scans were matched and the mandible was segmented and aligned. The 3D distance maps and 3D cephalometric analyses were used to calculate the differences between the soft tissue simulation and the actual postoperative results. Other study variables were age, gender, and amount of mandibular advancement or rotation. For the entire face, the mean absolute error was 0.9 ± 0.3 mm, the mean absolute 90th percentile was 1.9 mm, and for all 100 patients the absolute mean error was less than or equal to 2 mm. The subarea with the least accuracy was the lower lip area, with a mean absolute error of 1.2 ± 0.5 mm. No correlation could be found between the error of prediction and the amount of advancement or rotation of the mandible or age or gender of the patient. Overall, the soft tissue prediction algorithm combined with CBCT imaging is an accurate model for predicting soft tissue changes after mandibular advancement. Future studies will focus on validating the mass tensor model soft tissue algorithm for bimaxillary surgery.

A Bayesian Recursive Algorithm for Freespace Estimation Using a Stereoscopic Camera System in an Autonomous Wheelchair

This paper proposes a Bayesian Recursive (BR) algorithm for detecting freespace for people with severe disability operating an autonomous wheelchair with a stereoscopic camera system. Based on the left and right images captured from the camera system, the Sum of Absolute Differences (SAD) algorithm is used to produce a stereo disparity map. In short, a three-dimensional (3D) point map is converted to a two-dimensional (2D) distance map. This is generated from the disparity map using a geometric projection. Being based on uncertain information captured from the camera system, the BR algorithm for freespace estimation is developed as a recursive expression for the posterior probability function. The average probability values are calculated for the height and width of the freespace, and these assist to plan a power wheelchair pathway. Based on the average probability of the estimated height and width of the freespace, a Bayesian decision for the power wheelchair to autonomously navigate through the freespace is made. Moreover, Obstacle avoidance problem based on 2D map is considered in this paper. As further support for the method, experimental results indicate the effectiveness of the proposed algorithm.