About

Letian (LT) Zhang is an Associate Professor of Management and Organizations at the Kellogg School of Management, Northwestern University. He is a sociologist who studies organizations and work in both contemporary and historical settings. His research primarily utilizes large-scale archival datasets and often incorporates qualitative interviews, case studies, and increasingly, computational models. LT holds a Ph.D. in Sociology from Harvard University and a B.S. in Mathematics from Stanford University. Prior to joining Kellogg, he was on the faculty at Harvard Business School. His academic work includes courses such as 'Leading at Scale: Power, Design, and Influence in Organizations,' which focuses on how power shapes organizational dynamics and leadership in complex environments.

Research topics

• Materials science
• Geometry
• Orthodontics
• Structural engineering
• Surgery
• Mathematics
• Medicine
• Composite material

Selected publications

• The Implementation and Effectiveness of Progressive Rehabilitation Nursing on Quality of Life, Self-Care Ability, and Psychological Status in Patients with Breast Cancer after Modified Radical Mastectomy.

  PubMed · 2025-05-01

  article

  Objective: To evaluate the implementation and effectiveness of progressive rehabilitation nursing in patients undergoing modified radical mastectomy for breast cancer. Methods: A total of 70 patients undergoing modified radical mastectomy for breast cancer in our hospital were selected as the research subjects, and they were randomly divided into a control group and an observation group, with 35 patients in each group. The control group received routine rehabilitation nursing intervention after surgery, while the observation group received progressive rehabilitation nursing intervention based on the control group's nursing. The quality of life, self-care ability, mental state, and incidence of complications were compared between the two groups. Results: Before the intervention, the two groups had no significant difference in the quality of life (P > .05). After the intervention, the quality of life in the observation group was significantly better than that in the control group (P < .05). Before the intervention, the two groups had no significant difference in the self-care ability (P > .05). After the intervention, the self-care ability in the observation group was significantly better than that in the control group (P < .05). Before the intervention, the two groups had no significant difference in the SAS and SDS scores (P > .05). After the intervention, the SAS and SDS scores in the observation group were significantly lower than those in the control group (P < .05). The incidence of complications in the control group was 22.86%, while that in the observation group was 5.71%. The incidence of complications in the observation group was significantly lower than in the control group (P < .05). Conclusion: Compared with routine nursing intervention, the implementation of progressive rehabilitation nursing intervention can further improve the quality of life, self-care ability, and mental state of patients undergoing modified radical mastectomy for breast cancer and reduce the risk of related complications, which helps promote the recovery process of patients and is worthy of clinical promotion and application.

  Publisher

• Abstract 126: In-bed robot-guided ankle sensory-motor rehabilitation in early subacute stroke survivors: a preliminary clinical trial

  Stroke · 2025-01-30

  articleSenior author

  Introduction: The most commonly observed motor impairment associated with stroke is the weakness of ankle muscles and stiffness of the ankle joint, which severely restricts gait and balance function and limits the performance of many activities of daily living. Stroke survivors have the most potential for motor recovery in their acute and subacute stages. An intensive in-bed robot-guided ankle training may aid in promoting motor recovery in early sub-acute stroke survivors. The purpose of the study was to investigate the feasibility and efficacy of in-bed robot-guided ankle movement training in early subacute stroke survivors. Method: This was a controlled trial. The initial 8 patients were assigned to the study group and the rest patients were randomized to the study and control groups. In total, 44 stroke survivors at the early subacute stage were assigned to either a study group (n=26) or a control group (n=18) during their hospital stay. Individuals in the study group received 45-minutes of in-bed robot-guided ankle movement training, including passive stretching and game-based active movement training; while the control group used the same ankle robot and received passive ankle movement in the mid-range of motion and attempted active ankle movement without robotic assistance. Biomechanical and clinical outcome measures were obtained before and after the intervention. Results: After the training (sessions: 11.3 ± 4.2 sessions), the study group had a significantly larger increase in ankle active range of motion (p=0.002, eta 2 =0.213), maximal voluntary contraction in plantar flexion (p=0.016,eta 2 =0.131) and dorsiflexion (p=0.035,eta 2 =0.102), compared with the control group. Patients in both groups showed a significant increase in Fugl-Meyer assessment lower limb motor score (p&lt;0.001, eta 2 =0.560), Berg Balance Scale (p&lt;0.001, eta 2 =0.503), and a decrease in Modified Ashworth Scale in plantar flexors (p&lt;0.001, eta 2 =0.291), without significant group differences. Conclusions: In-bed robot-guided ankle training is feasible in patients at the early subacute stage. The robotic training including passive stretching and active movement helped the recovery of ankle voluntary muscle contraction and active range of motion. Incorporating an early in-bed robotic ankle rehabilitation is a feasible intervention technique that may help facilitate the ankle volitional control.

  PublisherDOI

• Loss of Joint Individuation and Abnormal Synergy Post Stroke in Upper Limb Movements

  Neurorehabilitation and neural repair · 2025-06-20

  articleOpen accessSenior authorCorresponding

  BackgroundStroke often leads to long-term impairments in upper extremity motor function, including muscle weakness, spasticity, and abnormal joint synergies, which hinder independent joint control and daily activities.ObjectiveThis study examined multi-joint motor impairments and characterized abnormal synergy patterns post-stroke using a robotic exoskeleton.MethodsThe exoskeleton independently controlled shoulder, elbow, and wrist joints while measuring responses across all joints during horizontal plane movements. Fifty-three stroke survivors and 24 age-matched controls performed single-joint movements under constrained (fixed joints) and unconstrained (free joints) conditions. Coupled range of torques and range of motion at non-instructed joints were calculated relative to instructed joint movements and summarized in a 3 × 3 matrix.ResultsStroke survivors showed significantly higher coupling torques and motions at non-instructed joints compared to controls, with the greatest impairments in isolating distal movements, particularly in a proximal-to-distal gradient. Abnormal synergy patterns were systematically identified, revealing that stroke survivors exhibited two common patterns for shoulder and elbow tasks, marked by excessive coupling at neighboring joints. For wrist movement tasks, four distinct patterns emerged, involving excessive coupling at both shoulder and elbow joints.ConclusionThese findings demonstrate characteristic impairments in joint individuation and synergy following a stroke, providing a framework to understand motor deficits and guide rehabilitation strategies aimed at restoring joint-specific control.

  PublisherOA PDFDOI

• Ultra-high interfacial strength of glass fiber/epoxy composites via semi-interpenetrating networks modified rigid-flexible structures

  Composites Science and Technology · 2025-03-22 · 10 citations

  articleSenior author
  PublisherDOI

• A dual-cup reverse shoulder replacement improves impingement-free motion

  Seminars in Arthroplasty JSES · 2025-01-08

  article
  PublisherDOI

• Coexistent Pulmonary Tuberculosis and Lung Cancer: An Analysis of Incidence Trends, Financial Burdens and Influencing Factors

  Cancer Innovation · 2025-04-07 · 3 citations

  articleOpen access

  ABSTRACT Background Tuberculosis (TB) and lung cancer (LC) are both major global health threats. However, coexistent pulmonary TB and LC (TBLC) is a unique condition for which incidence trends and risk factors have not been fully defined. Methods We retrospectively reviewed the medical records of patients with TBLC and LC alone between 2010 and 2022 at Beijing Chest Hospital, the standard authority for the diagnosis and treatment of TB and LC in China. The cumulative incidence rate (CIR) of TBLC was calculated as the number of new TBLC cases/number of LC cases at risk per 100,000 annually. The comparative incidence rate ratio (IRR) was estimated to be the TB incidence in LC patients/TB incidence in the general population. Logistic regression was used to explore risk factors for TBLC. Results The CIR of TBLC has rapidly increased each year since 2014 and reached 7027 per 100,000 LC patients in 2022. Patients with LC had a higher risk of developing active TB than the general population (IRR = 25.21, 95% confidence interval [CI]: 21.54–29.89). Medical expenditure per patient was 100.60 thousand yuan for those with TBLC and 105.60 thousand yuan for patients with LC ( p = 0.687). Patients with TBLC were older (63.61 ± 10.46 vs. 61.08 ± 10.77, p &lt; 0.001) and had a higher male‐to‐female ratio (2.82 vs. 1.59, p = 0.044) than those with LC alone. A tendency of earlier disease onset was observed in patients with LC rather than TBLC. A majority (44.92%) of TBLC lesions were located in the upper lobes of the lung and had a higher proportion of squamous cell carcinomas than LC alone (32.24% vs. 27.49%, p = 0.002). TBLC also presented more aggressively, with more lymph node involvement and distant metastases. Multivariate analysis revealed that older age, the male sex, mediastinal lymph node invasion, lung/bone metastases, anemia, hypoalbuminemia, malnutrition, pulmonary fibrosis, and chronic obstructive pulmonary disease were risk factors for active TBLC. Conclusions There has been a rise in the incidence of coexistent TBLC and a concomitant increase in its financial burden in China that deserves more awareness and attention.

  PublisherOA PDFDOI

• Predicting the efficacy of first-line therapy for patients with colorectal cancer liver metastases using CT imaging and clinical data

  2025-07-14

  article

  Colorectal cancer (CRC) patients are highly prone to liver metastasis (CRLM), which often becomes the leading cause of death in this population. Predicting the efficacy of first-line therapies is crucial for clinicians to develop personalized treatment strategies for CRLM patients. In this paper, we propose a novel multimodal cross-attention model that integrates contrast-enhanced liver CT imaging and clinical data to predict the therapeutic efficacy of first-line treatment in CRLM patients. Our approach utilizes the nnUNetv2 model to segment liver and intratumoral regions from CT scans. Radiomics features are extracted from the segmented tumor regions, followed by a feature selection process to identify key predictors of treatment efficacy. In parallel, highly correlated clinical variables are identified and preprocessed. The selected radiomic features and clinical variables are processed through two separate branches with identical structures, each incorporating a multi-head cross-attention module to enable efficient exchange and alignment of multimodal information. The fused multimodal features are subsequently used to predict therapeutic outcomes. Experiments conducted on a dataset of 177 patients demonstrate that our multimodal learning model outperforms uni-modal models and existing deep learning methods, achieving an AUC of 0.7195. This approach highlights the potential of integrating imaging and clinical data for improved treatment efficacy prediction in CRLM.Clinical relevance- This study highlights the importance of integrating contrast-enhanced liver CT imaging and clinical data for predicting the efficacy of first-line therapies in CRLM patients.

  PublisherDOI

• EgoFall: Real-time Privacy-Preserving Fall Risk Assessment with a Single On-Body Tracking Camera

  IEEE Transactions on Neural Systems and Rehabilitation Engineering · 2025-01-01

  articleOpen access

  Falls are a leading cause of injury among older adults, with research indicating that they often fall due to certain individual biomechanical factors. Therefore, real-time individual fall risk assessment is essential for designing more effective fall prevention programs and developing advanced home-based training solutions. However, existing methods for fall risk assessment either raise privacy concerns due to sensors installed in the environment or require multiple wearable devices, limiting their practicality for home-based applications and long-term monitoring. In this paper, we introduce EgoFall, a real-time privacy-preserving fall risk assessment system. EgoFall utilizes a chest-mounted commercial tracking camera and a carefully designed data pre-processing pipeline to acquire the ego-body motion data of the subject. The data is then fed to a lightweight CNN-Transformer model for fall risk assessment. To evaluate the proposed method, we establish the EgoWalk dataset, which includes four walking patterns: normal, anterior-posterior instability, medial-lateral instability, and combined instability. Experimental results show that EgoFall achieves an accuracy exceeding 95% on the EgoWalk dataset, outperforming baseline methods while maintaining low computational complexity. Additionally, a series of ablation studies explore the impact of fine-tuning data and error analysis, further highlighting EgoFall's practicality in real-world applications.

  PublisherDOI

• Functional Electrical Stimulation of the Lateral Knee Muscles Can Reduce Peak Knee Adduction Moment during Stepping: A Pilot Study

  Bioengineering · 2024-08-30 · 3 citations

  articleOpen accessSenior authorCorresponding

  Knee osteoarthritis (KOA) is an age-dependent disease dominantly affected by mechanical loading. Balancing the forces acting on the medial knee compartment has been the focus of KOA interventions. This pilot study investigated the effects of functional electrical stimulation (FES) of the biceps femoris and lateral gastrocnemius on reducing peak knee adduction moment (pKAM) in healthy adults and individuals with medial KOA while stepping on an instrumented elliptical system. Sixteen healthy individuals and five individuals with medial KOA stepped on the robotic stepping system, which measured footplate-reaction forces/torques and ankle kinematics and calculated 3-D knee moments in real time using inverse dynamics. Participants performed four different tasks: regular stepping without FES as the baseline condition, stepping with continuous FES of the lateral gastrocnemius (FESLG), biceps femoris (FESBF), and simultaneous FES of both lateral gastrocnemius and biceps femoris (FESLGBF), throughout the elliptical cycle. The 3-D knee moments, tibia kinematics, and footplate-reaction forces were compared between the baseline and the three FES stepping conditions. Healthy participants demonstrated lower pKAM during each of the three FES conditions compared to baseline (FESLG (p = 0.041), FESBF (p = 0.049), FESLGBF (p = 0.048)). Participants with KOA showed a trend of lower pKAM during FES, which was not statistically significant given the small sample available. Incorporating elliptical + FES as a training strategy is feasible and may help to enhance selective force generation of the targeted muscles and reduce the medial knee compartment loading.

  PublisherOA PDFDOI

• Determining Individualized Foot Progression Angle for Reduction of Knee Medial Compartment Loading during Stepping

  Medicine & Science in Sports & Exercise · 2024-08-23 · 2 citations

  articleOpen accessSenior authorCorresponding

  PURPOSE: Modifying foot progression angle (FPA), the angle between the line from the heel to the second metatarsal head and the line of progression, can reduce peak knee adduction moment (pKAM). However, determining the optimal FPA that minimizes pKAM without inducing unnatural walking patterns can be challenging. This study investigated the FPA-pKAM relationship using a robotic stepping trainer to assess the feasibility of determining the optimal FPA based on this relationship. In addition, it examined knee moments during stepping with three different FPAs, as stepping is a recommended exercise for knee osteoarthritis rehabilitation. METHODS: Twenty-six asymptomatic individuals stepped on a robotic stepping trainer, which measured six-axis footplate-reaction forces/torques and three-dimensional ankle kinematics to determine external knee moments. The robot rotated the footplates slowly (~0.5 deg·s -1 ) between 10°-toe-out and 10°-toe-in while participants stepped continuously, unaware of the footplate rotations. The slope of pKAM-FPA relationship during continuous stepping was determined. Peak three-dimensional knee moments were compared between the 10°-toe-in, 0°-FPA, and 10°-toe-out FPAs with repeated-measures ANOVA. Multiple linear regression determined the covariates that predicted pKAM during stepping. RESULTS: Eighteen participants had lower pKAM and KAM impulse with 10°-toe-in than 10°-toe-out ( P < 0.001) and 0°-FPA ( P < 0.001 and P = 0.008, respectively; called toe-in responders). Conversely, eight participants reduced pKAM and KAM impulse with 10°-toe-out compared with 0°-FPA ( P < 0.001, P = 0.017) and 10°-toe-in ( P = 0.026, P = 0.004; called toe-out responders). A linear pKAM-FPA relationship was determined for each individual, and its slope (the pKAM rate with FPA) was positive for toe-in responders ( P < 0.01) and negative for toe-out responders ( P = 0.02). Regression analysis revealed that smaller pKAM with toe-in, in toe-in responders, was explained by increased tibia medial tilt, tibia internal rotation, footplate-reaction lateral force, footplate-reaction anterior force, and decreased footplate-reaction internal rotation torque. CONCLUSIONS: Individuals may exhibit different responses to FPA modification during stepping. The slope and intercept of the linear pKAM-FPA relationship can be determined for individual subjects. This allows for a targeted pKAM reduction through guided FPA positioning and potentially offers subject-specific precision knee osteoarthritis rehabilitation.

  PublisherOA PDFDOI

Recent grants

• NIH Grant R01HD044295

  NIH · $940k · 2009

• NIH Grant R01AR045634

  NIH · $597k · 2004

• NIH Grant R42HD043664

  NIH · $748k · 2008

• NIH Grant R41HD043664

  NIH · $100k · 2004

• Modeling and Identification of multi-joint arm dynamics post stroke

  NSF · $291k · 2009–2014

Frequent coauthors

• Yupeng Ren

  Jiangxi University of Science and Technology

  113 shared

• Elliot J. Roth

  45 shared

• Kyung Koh

  University of Maryland, Baltimore

  44 shared

• Song Joo Lee

  Korea University of Science and Technology

  44 shared

• Yi‐Ning Wu

  41 shared

• Deborah Gaebler‐Spira

  38 shared

• Sang Hoon Kang

  Ulsan National Institute of Science and Technology

  37 shared

• William Z. Rymer

  Shirley Ryan AbilityLab

  36 shared

Labs

• Management & OrganizationsPI

Education

• PhD, Biomedical Engineering

  Vanderbilt University

  1990

• MS, Biomedical Engineering

  Vanderbilt University

  1988

Awards & honors

• Faculty Teaching Awards