Patient-specific ascending aortic intervention criteria

OBJECTIVES

Ascending aortic aneurysms pose a different risk to each patient. We aim to provide personalized risk stratification for such patients based on sex, age, body surface area, and aneurysm location (root vs ascending).

METHODS

Root and ascending diameters, and adverse aortic events (dissection, rupture, death) of ascending thoracic aortic aneurysm patients were analyzed. Aortic diameter was placed in context vis-a-vis the normal distribution in the general population with similar sex, age, and BSA, by conversion to z scores. These were correlated of major adverse aortic events, producing risk curves with 'hinge points' of steep risk, constructed separately for the aortic root and mid ascending aorta.

RESULTS

1162 patients were included. Risk curves unveiled generalized thresholds of z = 4 for the aortic root, and z = 5 for the mid ascending aorta. These correspond to individualized thresholds of less than the standard criterion of 5.5 cm in the vast majority of patients. Indicative results include a 75 year-old typical male with 2.1 m2 body surface area, who was found to be at increased risk of adverse events if root diameter exceeds 5.15 cm, or mid ascending exceeds 5.27 cm. An automated calculator is presented which identifies patients at high risk of adverse events based on sex, age, height, weight, and root and ascending size.

CONCLUSIONS

This analysis exploits a large sample of aneurysmal patients, demographic features of the general population, pre-dissection diameter, discrimination of root and supracoronary segments, and statistical tools to extract thresholds of increased risk tailor-made for each patient.

A clinical solution for non-toxic 3D-printed photon blocks in external beam radiation therapy

PURPOSE

A well-known limitation of multi-leaf collimators is that they cannot easily form island blocks. This can be important in mantle region therapy. Cerrobend photon blocks, currently used for supplementary shielding, are labor-intensive and error-prone. To address this, an innovative, non-toxic, automatically manufactured photon block using 3D-printing technology is proposed, offering a patient-specific and accurate alternative.

METHODS AND MATERIALS

The study investigates the development of patient-specific photon shielding blocks using 3D-printing for three different patient cases. A 3D-printed photon block shell filled with tungsten ball bearings (BBs) was designed to have similar dosimetric properties to Cerrobend standards. The generation of the blocks was automated using the Eclipse Scripting API and Python. Quality assurance was performed by comparing the expected and actual weight of the tungsten BBs used for shielding. Dosimetric and field geometry comparisons were conducted between 3D-printed and Cerrobend blocks, utilizing ionization chambers, imaging, and field geometry analysis.

RESULTS

The quality assurance assessment revealed a -1.3% average difference in the mass of tungsten ball bearings for different patients. Relative dose output measurements for three patient-specific blocks in the blocked region agreed within 2% of each other. Against the Treatment Planning System (TPS), both 3D-printed and Cerrobend blocks agreed within 2%. For each patient, 6 MV image profiles taken through the 3D-printed and Cerrobend blocks agreed within 1% outside high gradient regions. Jaccard distance analysis of the MV images against the TPS planned images, found Cerrobend blocks to have 15.7% dissimilarity to the TPS, while that of the 3D-printed blocks was 6.7%.

CONCLUSIONS

This study validates a novel, efficient 3D-printing method for photon block creation in clinical settings. Despite potential limitations, the benefits include reduced manual labor, automated processes, and greater precision. It holds potential for widespread adoption in radiation therapy, furthering non-toxic radiation shielding.

A Novel Method for Secondary Mandible Reconstruction to Re-Achieve a Native Condyle Position Comprising a New Design for Cutting Guides and New Positioning Devices

Secondary mandibular reconstruction using fibular free flaps (FFF) is a technical challenge for surgeons. Appropriate operation planning is crucial for postoperative quality control and is notably necessary for the (re-) achievement of a physiological condylar position, and the sensible expansion and shaping of the transplant. Computer-assisted planning may help to reconstruct mandibular defects in a patient-specific and precise manner. Herein, we present a newly-developed workflow for secondary mandibular reconstruction using FFF; it comprises digital planning and in-house manufacturing to perform precise secondary mandible reconstruction. This method utilizes a newly designed positioning device to ensure the precise positioning of the fibula segments in relation to each other and the mandibular stumps. The presented in-house-printed positioning device made it possible to achieve digital planning with high precision during surgery.

BME-free primary patient-specific organoids obtained with a one-day mimicking method to replicate the corresponding tumor for personalized treatment options

Introduction

In cancer treatment, every minute counts. Due to the unpredictable behavior of cancer cells caused by continuous mutations, each cancer patient has a unique situation and may or may not respond to a specific drug or treatment. The process of finding an effective therapy can be time-consuming, but cancer patients do not have the luxury of time for trial and error. Therefore, a novel technology to fast generate a patient relevant organoid for the therapies selecting is urgently needed.

Methods

Utilizing the new organoid technology by specially dissolving the mesenchyme in tumor tissues acquired from cancer patients, we realized the work of creating patient-specific organoids (PSO) within one day.

Results

PSO properties reflect those of its respective original in vivo tumor tissue and can be utilized to perform various in vitro drug sensitivity tests to identify the most effective clinical treatment for patients. Additionally, PSO can aid in assessing the efficacy of immune cell therapies.

Discussion

Organoid technology has advanced significantly in recent years. However, current cancer organoid methods involve creating 3D tumor tissue from 2D cancer cells or cell clusters, primarily for cancer research purposes aimed at investigating related molecular and cellular mechanisms of tumor development. These methods are research-driven, not tailored towards clinical applications, and cannot provide personalized information for individual patients. PSO filled the gap of clinic-driven and time-saving method for the personalized therapies selecting to the cancer patients.

Patient-specific cognitive profiles in the detection of dementia subtypes: A proposal

Many physicians rely on sum score cognitive screening tests to evaluate patients for cognitive decline. Because the vast majority of cognitively impaired patients never receive more extensive testing, the results of these screening tests impact patients and their family members profoundly. No previous study has examined whether the metrics used by the popular Mini-Mental State Examination, Montreal Cognitive Assessment, and Saint Louis University Mental Status tests reliably identify single-domain deficits or allow clinicians to adequately track disease progression. We compare side by side the metrics used by these three tests to highlight the differences in the ways they measure domain impairments. We then contrast the sum score approach to cognitive screening with brief domain-specific tests that use extended metrics in each domain examined. Last, we suggest that moderate-to-severe domain-specific deficits on these tests should lead physicians to anticipate specific functional problems and alert family members.

Custom designed and 3D-printed titanium pelvic implants for acetabular reconstruction after tumour resection

BACKGROUND

Reconstructive procedure following resection of large pelvic tumours around the hip joint remains a complex challenge.

METHODS

This study presents a retrospective case series of patients presenting with benign or malignant pelvic tumour for which an internal hemipelvectomy including the hip joint and subsequent reconstruction with a custom designed 3-dimensional printed titanium pelvic implant (3DPPI) has been performed between August 2013 and January 2018.

RESULTS

15 consecutive patients with a median age of 33.9 years (IQR 26.4-72.2) and a median BMI of 20.7 kg/m2 (IQR 19.0-33.3) were reviewed after median follow-up of 33.8 months (IQR 24.0-78.1). The majority of patients presented with a malignant tumour as their principal diagnosis (n = 13, 86.7%). The median surgical time was 5.5 hours (IQR 4.5-8.5) and median peri-operative blood loss was 5000 ml (IQR 2000-10000). The median MSTS score at follow-up was 63.3% (IQR 51.7-86.7%). The median NRS in rest was 0.0 (IQR 0.0-5.0), the median NRS during activity was 2.0 (IQR 0.5-7.0) and the median HOOS-PS was 76.6% (IQR 67.9-91.0). 4 patients had implant-specific complications (n = 4, 26.6%); 1 hip dislocation (Henderson type 1a), 3 structural complications (type 3a), 1 deep infection (type 4a) and 1 local tumour recurrence (type 5b). At follow-up, 4 out of 15 implants were classified as a failure, resulting in an implant survival rate of 73.3%.

CONCLUSIONS

Acceptable peri-operative outcomes, functional results, complication rates and short-term implant survival can be achieved in a cohort of complex patients undergoing 3DPPI reconstruction after hemipelvectomy including the acetabulum.

Motivational Message Framing Effects on Physical Activity Dynamics in a Digital Messaging Intervention: Secondary Analysis

BACKGROUND

Digital smartphone messaging can be used to promote physical activity to large populations with limited cost. It is not clear which psychological constructs should be targeted by digital messages to promote physical activity. This gap presents a challenge for developing optimal content for digital messaging interventions.

OBJECTIVE

The aim of this study is to compare affectively framed and social cognitively framed messages on subsequent changes in physical activity using dynamical modeling techniques.

METHODS

We conducted a secondary analysis of data collected from a digital messaging intervention in insufficiently active young adults (18-29 years) recruited between April 2019 and July 2020 who wore a Fitbit smartwatch for 6 months. Participants received 0 to 6 messages at random per day across the intervention period. Messages were drawn from 3 content libraries: affectively framed, social cognitively framed, or inspirational quotes. Person-specific dynamical models were identified, and model features of impulse response and cumulative step response were extracted for comparison. Two-way repeated-measures ANOVAs evaluated the main effects and interaction of message type and day type on model features. This early-phase work with novel dynamic features may have been underpowered to detect differences between message types so results were interpreted descriptively.

RESULTS

Messages (n=20,689) were paired with valid physical activity monitoring data from 45 participants for analysis. Received messages were distributed as 40% affective (8299/20,689 messages), 39% social-cognitive (8187/20,689 messages), and 20% inspirational quotes (4219/20,689 messages). There were no statistically significant main effects for message type when evaluating the steady state of step responses. Participants demonstrated heterogeneity in intervention response: some had their strongest responses to affectively framed messages, some had their strongest responses to social cognitively framed messages, and some had their strongest responses to the inspirational quote messages.

CONCLUSIONS

No single type of digital message content universally promotes physical activity. Future work should evaluate the effects of multiple message types so that content can be continuously tuned based on person-specific responses to each message type.

Commissural Alignment With ACURATE neo2 Valve in an Unselected Population

BACKGROUND

Commissural alignment has become an important topic in transcatheter aortic valve replacement (TAVR) because it may improve coronary access, facilitate future valve procedures, and possibly improve valve durability. The efficacy of commissural alignment with ACURATE neo2 has not yet been shown in a large population.

OBJECTIVES

The authors sought to determine the feasibility and success of attempting commissural alignment in an unselected TAVR population treated with the ACURATE neo2 prosthetic heart valve.

METHODS

A total of 170 consecutive patients underwent TAVR with a dedicated implantation technique to align the TAVR valve to the native valve. Using right-left overlap and 3-cusp views, valve orientation was adjusted by rotation of the unexpanded valve at the level of the aortic root. Effectiveness was assessed postprocedure as the degree of misalignment determined by analyzing fluoroscopic valve orientation to corresponding cusp orientation on preprocedural computed tomography. Safety endpoints included mortality, stroke/transient ischemic attack, and additional complications through 30 days.

RESULTS

Of 170 patients, 167 (98.2%) could be analyzed for alignment, and all 170, for safety outcomes. Most patients (97%) had successful alignment (≤ mild misalignment), with 80% with commissural alignment, while the degrees of misalignment were 17% mild, 1.2% moderate, 1.8% severe.

CONCLUSIONS

In this large evaluation of a commissural alignment technique, alignment was achieved in nearly all patients without safety concerns or impact to procedure duration. Commissural alignment appears effective and safe across all patients with this novel technique.

Lower Limb Salvage Using Patent-Specific 3D-Printed Titanium Cage Following Severe Left Ankle Traumatic Partial Amputation: A Pediatric Case Report

BACKGROUND

Patients with large bony defects of the ankle who wish to avoid amputation have limited surgical intervention options for limb salvage. Each of these interventions are technically complex and present significant risk for complications. The use of a patient-specific 3D-printed titanium cage in conjunction with a tibiotalocalcaneal (TTC) arthrodesis using a retrograde nail is another management option. This case adds to the scarce published literature on this technique.

CASE PRESENTATION

This report presents the case of a 16-year-old female who suffered a traumatic partial amputation of her left distal lower extremity following an all-terrain-vehicle accident that resulted in a 10.0 × 10.0 cm skin laceration and a 5-cm subsegmental bony loss of the distal tibia. She was successfully treated using a patient-specific 3D-printed titanium truss cage in conjunction with a TTC arthrodesis using a retrograde nail.

CONCLUSIONS

The decision to amputate or attempt limb salvage in a severely injured lower limb is still a topic of active debate. However, literature has shown that patients who undergo limb salvage surgery have better psychological health outcomes and equivalent functional outcomes as patients who have undergone amputation. Therefore, research on techniques that optimize and advance limb salvage surgery is needed. As the numerous potential benefits and limitations of patient-specific 3D-printed implants are assessed throughout the field of orthopedics, further research and cost-analysis will be required. Cases such as the one presented add to the limited existing literature of patient-specific 3D-printed implant for treatment of large distal lower extremity bony defects.

LEVELS OF EVIDENCE

Level V (Case Report).

Dose coefficients for organ dosimetry in tomosynthesis imaging of adults and pediatrics across diverse protocols

PURPOSE

The gold-standard method for estimation of patient-specific organ doses in digital tomosynthesis (DT) requires protocol-specific Monte Carlo (MC) simulations of radiation transport in anatomically accurate computational phantoms. Although accurate, MC simulations are computationally expensive, leading to a turnaround time in the order of core hours for simulating a single exam. This limits their clinical utility. The purpose of this study is to overcome this limitation by utilizing patient- and protocol-specific MC simulations to develop a comprehensive database of air-kerma-normalized organ dose coefficients for a virtual population of adult and pediatric patient models over an expanded set of exam protocols in DT for retrospective and prospective estimation of radiation dose in clinical tomosynthesis.

MATERIALS AND METHODS

A clinically representative virtual population of 14 patient models was used, with pediatric models (M and F) at ages 1, 5, 10, and 15 and adult patient models (M and F) with body mass index (BMIs) at 10th, 50th, and 90th percentiles of the US population. A graphics processing unit (GPU)-based MC simulation framework was used to simulate organ doses in the patient models, incorporating the scanner-specific configuration of a clinical DT system (VolumeRad, GE Healthcare, Waukesha, WI, USA) and an expanded set of exam protocols, including 21 distinct acquisition techniques for imaging a variety of anatomical regions (head and neck, thorax, spine, abdomen, and knee). Organ dose coefficients (h_n ) were estimated by normalizing organ dose estimates to air kerma at 70 cm (X_70cm ) from the source in the scout view. The corresponding coefficients for projection radiography were approximated using organ doses estimated for the scout view. The organ dose coefficients were further used to compute air-kerma-normalized patient-specific effective dose coefficients (K_n ) for all combinations of patients and protocols, and a comparative analysis examining the variation of radiation burden across sex, age, and exam protocols in DT, and with projection radiography was performed.

RESULTS

The database of organ dose coefficients (h_n ) containing 294 distinct combinations of patients and exam protocols was developed and made publicly available. The values of K_n were observed to produce estimates of effective dose in agreement with prior studies and consistent with magnitudes expected for pediatric and adult patients across the different exam protocols, with head and neck regions exhibiting relatively lower and thorax and C-spine (apsc, apcs) regions relatively higher magnitudes. The ratios (r = K_n /K_{n ,rad} ) quantifying the differences air-kerma-normalized patient-specific effective doses between DT and projection radiography were centered around 1.0 for all exam protocols, with the exception of protocols covering the knee region (pawk, patk).

CONCLUSIONS

This study developed a database of organ dose coefficients for a virtual population of 14 adult and pediatric XCAT patient models over a set of 21 exam protocols in DT. Using empirical measurements of air kerma in the clinic, these organ dose coefficients enable practical retrospective and prospective patient-specific radiation dosimetry. The computation of air-kerma-normalized patient-specific effective doses further enables the comparison of radiation burden to the patient populations between protocols and between imaging modalities (e.g., DT and projection radiography), as presented in this study.

Personalized Virus Load Curves for Acute Viral Infections

We introduce an explicit function that describes virus-load curves on a patient-specific level. This function is based on simple and intuitive model parameters. It allows virus load analysis of acute viral infections without solving a full virus load dynamic model. We validate our model on data from mice influenza A, human rhinovirus data, human influenza A data, and monkey and human SARS-CoV-2 data. We find wide distributions for the model parameters, reflecting large variability in the disease outcomes between individuals. Further, we compare the virus load function to an established target model of virus dynamics, and we provide a new way to estimate the exponential growth rates of the corresponding infection phases. The virus load function, the target model, and the exponential approximations show excellent fits for the data considered. Our virus-load function offers a new way to analyze patient-specific virus load data, and it can be used as input for higher level models for the physiological effects of a virus infection, for models of tissue damage, and to estimate patient risks.

Multimodal Patient-Specific Registration for Breast Imaging Using Biomechanical Modeling with Reference to AI Evaluation of Breast Tumor Change

Background: The strategy to combat the problem associated with large deformations in the breast due to the difference in the medical imaging of patient posture plays a vital role in multimodal medical image registration with artificial intelligence (AI) initiatives. How to build a breast biomechanical model simulating the large-scale deformation of soft tissue remains a challenge but is highly desirable. Methods: This study proposed a hybrid individual-specific registration model of the breast combining finite element analysis, property optimization, and affine transformation to register breast images. During the registration process, the mechanical properties of the breast tissues were individually assigned using an optimization process, which allowed the model to become patient specific. Evaluation and results: The proposed method has been extensively tested on two datasets collected from two independent institutions, one from America and another from Hong Kong. Conclusions: Our method can accurately predict the deformation of breasts from the supine to prone position for both the Hong Kong and American samples, with a small target registration error of lesions.

Three-Dimensional Anatomically Pre-Contoured Locking Plate for Isolated Weber B Type Fracture

We aimed to evaluate the functional and radiographic outcomes of a three-dimensionally (3D) pre-contoured lateral locking plate fixation for isolated Weber B type fractures and to evaluate the necessity of an interfragmentary lag screw in the use of the plate. Patients who underwent surgery for isolated Weber B type fracture were divided into two groups: 41 patients treated with the 3D plate and lag screw (Group A) and 31 patients treated with the 3D plate only (Group B). The included patients were evaluated regarding the functional and radiographic outcomes. According to the McLennan and Ungersma criteria, the majority of patients showed good or fair outcomes in both groups. Comparing the two groups, Group B showed better functional outcomes (p < 0.0046), while no difference between the two groups was found in terms of the radiographic outcomes (p = 0.143). The operation time was significantly shorter in Group B (p < 0.001) and the time to bony union was within 14 months in all patients with no significant difference between the two groups (p = 0.0821). No postoperative complication was observed in both groups. In conclusion, the use of a 3D pre-contoured lateral locking plate fixation for isolated Weber B type fractures demonstrated satisfactory functional and radiographic outcomes, regardless of lag screw insertion.

Comparison of 3D Printed Spherical Implants versus Femoral Head Allografts for Tibiotalocalcaneal Arthrodesis

Successful tibiotalocalcaneal (TTC) arthrodesis can be difficult to achieve in patients with bulk bone defects even with the use of femoral head allograft. Retrograde intramedullary nail placement through custom 3-dimensional (3D) spherical implants is an innovative option for these patients. The purpose of this study was to compare fusion rates, graft resorption, and complication rates between patients undergoing TTC fusion with 3D sphere implants versus femoral head allografts. Patients who underwent TTC arthrodesis with an intramedullary nail along with a 3D spherical implant (n = 8) or femoral head allograft (n = 7) were included in this study. The rate of successful fusion of the tibia, calcaneus, and talar neck to the 3D sphere or femoral head allograft was compared between the groups. The rate of total fused articulations was significantly higher in the 3D sphere group (92%) than the femoral head allograft group (62%; p = .018). The number of patients achieving successful fusion of all 3 articulations was higher in the 3D sphere group (75%) than the femoral head allograft group (42.9%, p = .22). The rate of graft resorption was significantly higher in the femoral head allograft group (57.1%) than the 3D sphere group (0%, p = .016). There were no significant differences between the groups in terms of complications. These data demonstrate that the use of a custom 3D printed sphere implant is safe in patients with severe bone loss undergoing TTC arthrodesis with a retrograde intramedullary nail and may result in improved rates of successful arthrodesis.

Clinical and Radiological Outcomes after Knee Arthroplasty with Patient-Specific versus Off-the-Shelf Knee Implants: A Systematic Review

Customised, patient-specific implants (PSI) manufactured based on computed tomography data are intended to improve the clinical outcome by restoring more natural knee kinematics as well as providing a better fit and a more precise positioning. The aim of this systematic review is to investigate the effect of these PSI on the clinical and radiological outcome compared to standard, off-the-shelf (OTS) implants. Thirteen comparative studies including a total of 2127 knee implants were identified. No significant differences in clinical outcome assessed with the range of motion, the Knee Society Score (KSS), and the Forgotten Joint Score (FJS-12) were found between PSI and OTS implants. PSI showed fewer outliers from the neutral limb axis and a better implant fit and positioning. Whether these radiological differences lead to long-term advantages in terms of implant survival cannot be answered based on the current data. Patients receiving PSI could be discharged home earlier at the same or at an even lower total cost. The effective overall superiority of PSI has yet to be proven in long-term studies.

Complex Bone Tumors of the Trunk-The Role of 3D Printing and Navigation in Tumor Orthopedics: A Case Series and Review of the Literature

The combination of 3D printing and navigation promises improvements in surgical procedures and outcomes for complex bone tumor resection of the trunk, but its features have rarely been described in the literature. Five patients with trunk tumors were surgically treated in our institution using a combination of 3D printing and navigation. The main process includes segmentation, virtual modeling and build preparation, as well as quality assessment. Tumor resection was performed with navigated instruments. Preoperative planning supported clear margin multiplanar resections with intraoperatively adaptable real-time visualization of navigated instruments. The follow-up ranged from 2–15 months with a good functional result. The present results and the review of the current literature reflect the trend and the diverse applications of 3D printing in the medical field. 3D printing at hospital sites is often not standardized, but regulatory aspects may serve as disincentives. However, 3D printing has an increasing impact on precision medicine, and we are convinced that our process represents a valuable contribution in the context of patient-centered individual care.

The biomechanical study of cervical spine: A Finite Element Analysis

The biomechanical study helps us to understand the mechanics of the human cervical spine. A three dimensional Finite Element (FE) model for C3 to C6 level was developed using computed tomography (CT) scan data to study the mechanical behaviour of the cervical spine. A moment of 1 Nm was applied at the top of C3 vertebral end plate and all degrees of freedom of bottom end plate of C6 were constrained. The physiological motion of the cervical spine was validated using published experimental and FE analysis results. The von Mises stress distribution across the intervertebral disc was calculated along with range of motion. It was observed that the predicted results of functional spine units using FE analysis replicate the real behaviour of the cervical spine.

Toward Patient Specific Models of Pediatric IVDs: A Parametric Study of IVD Mechanical Properties

Patient specific finite element (FE) modeling of the pediatric spine is an important challenge which offers to revolutionize the treatment of pediatric spinal pathologies, for example adolescent idiopathic scoliosis (AIS). In particular, modeling of the intervertebral disc (IVD) is a unique challenge due to its structural and mechanical complexity. This is compounded by limited ability to non-invasively interrogate key mechanical parameters of a patient's IVD. In this work, we seek to better understand the link between mechanical properties and mechanical behavior of patient specific FE models of the pediatric lumbar spine. A parametric study of IVD parameter was conducted, coupled with insights from current knowledge of the pediatric IVD. In particular, the combined effects of parameters was investigated. Recommendations are made toward areas of importance in patient specific FE modeling of the pediatric IVD. In particular, collagen fiber bundles of the IVD are found to dominate IVD mechanical behavior and are thus recommended as an area of primary focus for patient specific FE models. In addition, areas requiring further experimental research are identified. This work provides a valuable building block toward the development of patient specific models of the pediatric spine.

Uncertainty in model-based treatment decision support: Applied to aortic valve stenosis

Patient outcome in trans-aortic valve implantation (TAVI) therapy partly relies on a patient's haemodynamic properties that cannot be determined from current diagnostic methods alone. In this study, we predict changes in haemodynamic parameters (as a part of patient outcome) after valve replacement treatment in aortic stenosis patients. A framework to incorporate uncertainty in patient-specific model predictions for decision support is presented. A 0D lumped parameter model including the left ventricle, a stenotic valve and systemic circulatory system has been developed, based on models published earlier. The unscented Kalman filter (UKF) is used to optimize model input parameters to fit measured data pre-intervention. After optimization, the valve treatment is simulated by significantly reducing valve resistance. Uncertain model parameters are then propagated using a polynomial chaos expansion approach. To test the proposed framework, three in silico test cases are developed with clinically feasible measurements. Quality and availability of simulated measured patient data are decreased in each case. The UKF approach is compared to a Monte Carlo Markov Chain (MCMC) approach, a well-known approach in modelling predictions with uncertainty. Both methods show increased confidence intervals as measurement quality decreases. By considering three in silico test-cases we were able to show that the proposed framework is able to incorporate optimization uncertainty in model predictions and is faster and the MCMC approach, although it is more sensitive to noise in flow measurements. To conclude, this work shows that the proposed framework is ready to be applied to real patient data.

Using in vivo EPID images to detect and quantify patient anatomy changes with gradient dose segmented analysis

PURPOSE

To investigate the utility of gradient dose segmented analysis (GDSA) in combination with in vivo electronic portal imaging device (EPID) images to predict changes in the PTV mean dose for patient cases. Also, we use the GDSA to retrospectively analyze patients treated in our clinic to assess deviations for different treatment sites and use time-series data to observe any day-to-day changes.

METHODS

In vivo EPID transit images acquired on the Varian Halcyon were analyzed for simulated errors in a phantom, including gas bubbles, weight loss, patient shifts, and an arm erroneously in the field. GDSA threshold parameters were tuned to maximize the coefficient of determination (R² ) between GDSA metrics and the change in the PTV mean dose (D_mean ) as estimated in a treatment planning system (TPS). Similarly for a gamma analysis, the gamma criteria were adjusted to maximize R² between gamma pass rate and the change in the PTV D_mean from the TPS. The predictive accuracy of these models was tested on patient data measuring the mean and standard deviation of the difference in the predicted change in PTV D_mean and the change in PTV D_mean measured in the TPS. This analysis was extended retrospectively for every patient treated over a 23-month period (n = 852 patients) to assess the range of expected deviations that occurred during routine clinical operation, as well as to assess any differences between treatment sites. Grouping patients treated on the same day, a time-series analysis was performed to determine if GDSA metrics could add value in tracking machine behavior over time.

RESULTS

For the phantom data, analyzing the errors, except for shifts, and comparing the change in PTV D_mean and GDSA mean, a maximal R²  = 0.90 was found for a dose threshold of 5% and gradient threshold of 3 mm. For the gamma approach a linear fit between the gamma pass rate for change in the PTV D_mean was assessed for different criteria, using the same image data. A maximal, R²  = 0.84 was found for a gamma criteria of 3%/3 mm, 45% lower dose threshold. For patient data, the predictive accuracy of the change in the PTV D_mean using the GDSA approach and the gamma approach was 0.09 ± 0.98 % and - 0.65 ± 2.21%, respectively. Comparing the two approaches the accuracy did not significantly differ (P = 0.38), whereas the precision of the GDSA prediction is significantly less (P < 0.001). The dosimetric impact of shifts was not detectable with either the GDSA or gamma approach. Analysis of all patients treated over 23 months showed that over 95% of fractions treated deviated from the first fraction by 2% or less. Deviations> 2% occurred most frequently for the later fractions of head-and-neck and lung treatments. Additionally, averaging the GDSA mean metric over all patients on a given treatment day showed that changes in the machine output on the order of 1% could be identified.

CONCLUSIONS

GDSA of in vivo EPID images is a useful technique for monitoring patient changes during the course of treatment, particularly weight loss and tumor shrinkage. The GDSA mean provides a quantitative estimate of the change in the PTV D_mean , giving a simple, quantitative metric by which to flag patients with clinically meaningful deviations in treatment. Averaging the GDSA metric over all patients treated on a given day and tracking daily variations can also provide a flag for any systematic deviations in treatment due to machine performance.

Patient-specific dose quality assurance of single-isocenter multiple brain metastasis stereotactic radiosurgery using PTW Octavius 4D

Purpose

Single‐isocenter multiple brain metastasis stereotactic radiosurgery is an efficient treatment modality increasing in clinical practice. The need to provide accurate, patient‐specific quality assurance (QA) for these plans is met by several options. This study reviews some of these options and explores the use of the Octavius 4D as a solution for patient‐specific plan quality assurance.

Methods

The Octavius 4D Modular Phantom (O4D) with the 1000 SRS array was evaluated in this study. The array consists of 977 liquid‐filled ion chambers. The center 5.5 cm × 5.5 cm area has a detector spacing of 2.5 mm. The ability of the O4D to reconstruct three‐dimensional (3D) dose was validated against a 3D gel dosimeter, ion chamber, and film measurements. After validation, 15 patients with 2–11 targets had their plans delivered to the phantom. The criteria used for the gamma calculation was 3%/1 mm. The portion of targets which were measurable by the phantom was countable. The accompanying software compiled the measured doses allowing each target to be counted from the measured dose distribution.

Results

Spatial resolution was sufficient to verify the high dose distributions characteristic of SRS. Amongst the 15 patients there were 74 targets. Of the 74 targets, 61 (82%) of them were visible on the measured dose distribution. The average gamma passing rate was 99.3% (with sample standard deviation of 0.68%).

Conclusions

The high resolution provided by the O4D with 1000 SRS board insert allows for very high‐resolution measurement. This high resolution in turn can allow for high gamma passing rates. The O4D with the 1000 SRS array is an acceptable method of performing quality assurance for single‐isocenter multiple brain metastasis SRS.

3D printed anatomical (bio)models in spine surgery: clinical benefits and value to health care providers

The applications of three-dimensional printing (3DP) for clinical purposes have grown rapidly over the past decade. Recent advances include the fabrication of patient specific instrumentation, such as drill and cutting guides, patient specific/custom long term implants and 3DP of cellular scaffolds. Spine surgery in particular has seen enthusiastic early adoption of these applications. 3DP as a manufacturing method can be used to mass produce objects of the same design, but can also be used as a cost-effective method for manufacturing unique one-off objects, such as patient specific models and devices. Perhaps the first, and currently most widespread, application of 3DP for producing patient specific devices is the production of patient specific anatomical models, often termed biomodels. The present manuscript focuses on the current state of the art in anatomical (bio)models as used in spinal clinical practice. The biomodels shown and discussed include: translucent and coloured models to aid in identification of extent and margins of pathologies such as bone tumours; dynamic models for implant trial implantation and pre-operative sizing; models that can be disassembled to simulate surgical resection of diseased tissue and subsequent reconstruction. Biomodels can reduce risk to the patient by decreasing surgery time, reducing the probability of the surgical team encountering unexpected anatomy or relative positioning of structures and/or devices, and better pre-operative planning of the surgical workflow including ordered preparation of the necessary instrumentation for multi-step and revision procedures. Conversely, risks can be increased if biomodels are not accurate representations of the anatomy, which can occur if MRI/CT scan data is simply converted into 3DP format without interpretation of what the scan represents in terms of patient anatomy. A review and analysis of the cost-benefits of biomodels shows that biomodels can potentially reduce cost to health care providers if operating room time is reduced by 14 minutes or more.

Revision of Failed Total Ankle Replacement With a Custom 3-Dimensional Printed Talar Component With a Titanium Truss Cage: A Case Presentation

An innovative technique is presented for salvage of a failed total ankle replacement resulting from talar subsidence with the use of a custom 3-dimensional printed articulating talar component with a titanium truss cage. This introduces a better alternative to an ankle arthrodesis with which ankle joint function and range of motion may be preserved.

Novel 3-dimensionally printed patient-specific guide improves accuracy compared with standard total shoulder arthroplasty guide: a cadaveric study

Background

Patient-specific instrumentation (PSI) systems for total shoulder arthroplasty (TSA) can improve glenoid component placement, but may involve considerable expense and production delays. The purpose of this study was to evaluate a novel technique for in-house production of 3-dimensionally printed, patient-specific glenoid guides. We hypothesized that our PSI guide would improve the accuracy of glenoid guide pin placement compared with a standard TSA guide.

Methods

We randomized 20 cadaveric shoulders to receive pin placement via the PSI guide (n = 10, study group) or standard TSA guide (n = 10, control group). PSI guides were designed to fit each glenoid based on 3-dimensional scapular models constructed from computed tomography scans. A presurgical plan was created for the guide pin trajectory in neutral version and inclination based on individual scapular anatomy. After pin placement, 3-dimensional models from repeated computed tomography scans were superimposed to calculate deviation from the presurgical plan for each specimen.

Results

Inclination deviation was significantly lower in the PSI group than in the standard guide group (1.5° ± 1.6° vs. 6.4° ± 5.0°, P = .009). The glenoid entry site exhibited significantly less deviation in the PSI group (0.8 ± 0.6 mm vs. 2.1 ± 1.2 mm, P = .008). The average production cost and time for the PSI guides were $29.95 and 4 hours 40 minutes per guide, respectively.

Conclusions

The PSI guide significantly improved the accuracy of glenoid pin placement compared with the standard TSA guide. Our PSI guides can be produced in-house, inexpensively, and with substantially reduced time compared with commercially available guides.

Kinematic boundary conditions substantially impact in silico ventricular function

Computational cardiac mechanical models, individualized to the patient, have the potential to elucidate the fundamentals of cardiac (patho-)physiology, enable non-invasive quantification of clinically significant metrics (eg, stiffness, active contraction, work), and anticipate the potential efficacy of therapeutic cardiovascular intervention. In a clinical setting, however, the available imaging resolution is often limited, which limits cardiac models to focus on the ventricles, without including the atria, valves, and proximal arteries and veins. In such models, the absence of surrounding structures needs to be accounted for by imposing realistic kinematic boundary conditions, which, for prognostic purposes, are preferably generic and thus non-image derived. Unfortunately, the literature on cardiac models shows no consistent approach to kinematically constrain the myocardium. The impact of different approaches (eg, fully constrained base, constrained epi-ring) on the predictive capacity of cardiac mechanical models has not been thoroughly studied. For that reason, this study first gives an overview of current approaches to kinematically constrain (bi) ventricular models. Next, we developed a patient-specific in silico biventricular model that compares well with literature and in vivo recorded strains. Alternative constraints were introduced to assess the influence of commonly used mechanical boundary conditions on both the predicted global functional behavior of the in-silico heart (cavity volumes, stroke volume, ejection fraction) and local strain distributions. Meaningful differences in global functioning were found between different kinematic anchoring strategies, which brought forward the importance of selecting appropriate boundary conditions for biventricular models that, in the near future, may inform clinical intervention. However, whilst statistically significant differences were also found in local strain distributions, these differences were minor and mostly confined to the region close to the applied boundary conditions.

Clinical accuracy of a patient-specific femoral osteotomy guide in minimally-invasive posterior hip arthroplasty

INTRODUCTION

Patient specific guides can be a valuable tool in improving the precision of planned femoral neck osteotomies, especially in minimally invasive hip surgery, where bony landmarks are often inaccessible. The aim of our study was to validate the accuracy of a novel patient specific femoral osteotomy guide for THR through a minimally invasive posterior approach, the direct superior approach (DSA).

METHODS

As part of our routine preoperative planning 30 patients underwent low dose CT scans of their arthritic hip. 3D printed patient specific femoral neck osteotomy guides were then produced. Intraoperatively, having cleared all soft tissue from the postero-lateral neck of the enlocated hip, the guide was placed and pinned onto the posterolateral femoral neck. The osteotomy was performed using an oscillating saw and the uncemented hip components were implanted as per routine. Postoperatively, the achieved level of the osteotomy at the medial calcar was compared with the planned level of resection using a 3D/2D matching analysis (Mimics X-ray module, Materialise, Belgium).

RESULTS

A total of 30 patients undergoing uncemented Trinity acetabular and TriFit TS femoral component arthroplasty (Corin, UK) were included in our analysis. All but one of our analysed osteotomies were found to be within 3 mm from the planned height of osteotomy. In one patient the level of osteotomy deviated 5 mm below the planned level of resection.

CONCLUSION

Preoperative planning and the use of patient specific osteotomy guides provides an accurate method of performing femoral neck osteotomies in minimally invasive hip arthroplasty using the direct superior approach.

LEVEL OF EVIDENCE

IV (Case series).

Can a Single-Use and Patient-Specific Instrumentation Be Reliably Used in Primary Total Knee Arthroplasty? A Multicenter Controlled Study

BACKGROUND

The aim of this controlled multicenter study is to evaluate the clinical and radiologic outcomes of primary total knee arthroplasty (TKA) using single-use fully disposable and patient-specific cutting guides (SU) and compare the results to those obtained with traditional patient-specific cutting guides (PSI) vs conventional instrumentation (CI).

METHODS

Seventy consecutive patients had their TKA performed using SU. They were compared to 140 historical patients requiring TKA that were randomized to have the procedure performed using PSI vs CI. The primary measure outcome was mechanical axis as measured on a standing long-leg radiograph using the hip-knee-ankle angle. Secondary outcome measures were Knee Society and Oxford knee scores, operative time, need for postoperative transfusion, and length of hospital stay.

RESULTS

The mean hip-knee-ankle value was 179.8° (standard deviation [SD] 3.1°), 179.2° (SD 2.9°), and 178.3° (SD 2.5°) in the CI, PSI and SU groups, respectively (P = .0082). Outliers were identified in 16 of 65 (24.6%), 15 of 67 (22.4%), and 14 of 70 (20.0%) knees in the CI, PSI, and SU group, respectively (P = .81). There was no significant difference in the clinical results (P = .29 and .19, respectively). Operative time, number of unit transfusion, and length of hospital stay were not significantly different between the 3 groups (P = .45, .31, and 0.98, respectively).

CONCLUSION

The use of an SU in TKA provided similar clinical and radiologic results to those obtained with traditional PSI and CI. The potential economic advantages of single-use instrumentation in primary TKA require further investigation.

Quantification of near-wall hemodynamic risk factors in large-scale cerebral arterial trees

Detailed hemodynamic analysis of blood flow in pathological segments close to aneurysm and stenosis has provided physicians with invaluable information about the local flow patterns leading to vascular disease. However, these diseases have both local and global effects on the circulation of the blood within the cerebral tree. The aim of this paper is to demonstrate the importance of extending subject-specific hemodynamic simulations to the entire cerebral arterial tree with hundreds of bifurcations and vessels, as well as evaluate hemodynamic risk factors and waveform shape characteristics throughout the cerebral arterial trees. Angioarchitecture and in vivo blood flow measurement were acquired from healthy subjects and in cases with symptomatic intracranial aneurysm and stenosis. A global map of cerebral arterial blood flow distribution revealed regions of low to high hemodynamic risk that may significantly contribute to the development of intracranial aneurysms or atherosclerosis. Comparison of pre-intervention and post-intervention of pathological cases further shows large angular phase shift (~33.8°), and an augmentation of the peak-diastolic velocity. Hemodynamic indexes of waveform analysis revealed on average a 16.35% reduction in the pulsatility index after treatment from lesion site to downstream distal vessels. The lesion regions not only affect blood flow streamlines of the proximal sites but also generate pulse wave shift and disturbed flow in downstream vessels. This network effect necessitates the use of large-scale simulation to visualize both local and global effects of pathological lesions.

Patient-specific multiscale computational fluid dynamics assessment of embolization rates in the hybrid Norwood: effects of size and placement of the reverse Blalock-Taussig shunt

The hybrid Norwood operation is performed to treat hypoplastic left heart syndrome. Distal arch obstruction may compromise flow to the brain. In a variant of this procedure, a synthetic graft (reverse Blalock-Taussig shunt) is placed between the pulmonary trunk and innominate artery to improve upper torso blood flow. Thrombi originating in the graft may embolize to the brain. In this study, we used computational fluid dynamics and particle tracking to investigate the patterns of particle embolization as a function of the anatomic position of the reverse Blalock-Taussig shunt. The degree of distal arch obstruction and position of particle origin influence embolization probabilities to the cerebral arteries. Cerebral embolization probabilities can be reduced by as much as 20% by optimizing graft position, for a given arch geometry, degree of distal arch obstruction, and particle origin. There is a tradeoff, however, between cerebral pulmonary and coronary embolization probabilities.

A framework for designing patient-specific bioprosthetic heart valves using immersogeometric fluid-structure interaction analysis

Numerous studies have suggested that medical image derived computational mechanics models could be developed to reduce mortality and morbidity due to cardiovascular diseases by allowing for patient-specific surgical planning and customized medical device design. In this work, we present a novel framework for designing prosthetic heart valves using a parametric design platform and immersogeometric fluid-structure interaction (FSI) analysis. We parameterize the leaflet geometry using several key design parameters. This allows for generating various perturbations of the leaflet design for the patient-specific aortic root reconstructed from the medical image data. Each design is analyzed using our hybrid arbitrary Lagrangian-Eulerian/immersogeometric FSI methodology, which allows us to efficiently simulate the coupling of the deforming aortic root, the parametrically designed prosthetic valves, and the surrounding blood flow under physiological conditions. A parametric study is performed to investigate the influence of the geometry on heart valve performance, indicated by the effective orifice area and the coaptation area. Finally, the FSI simulation result of a design that balances effective orifice area and coaptation area reasonably well is compared with patient-specific phase contrast magnetic resonance imaging data to demonstrate the qualitative similarity of the flow patterns in the ascending aorta.

Physically consistent data assimilation method based on feedback control for patient-specific blood flow analysis

This paper presents a novel data assimilation method for patient-specific blood flow analysis based on feedback control theory called the physically consistent feedback control-based data assimilation (PFC-DA) method. In the PFC-DA method, the signal, which is the residual error term of the velocity when comparing the numerical and reference measurement data, is cast as a source term in a Poisson equation for the scalar potential field that induces flow in a closed system. The pressure values at the inlet and outlet boundaries are recursively calculated by this scalar potential field. Hence, the flow field is physically consistent because it is driven by the calculated inlet and outlet pressures, without any artificial body forces. As compared with existing variational approaches, although this PFC-DA method does not guarantee the optimal solution, only one additional Poisson equation for the scalar potential field is required, providing a remarkable improvement for such a small additional computational cost at every iteration. Through numerical examples for 2D and 3D exact flow fields, with both noise-free and noisy reference data as well as a blood flow analysis on a cerebral aneurysm using actual patient data, the robustness and accuracy of this approach is shown. Moreover, the feasibility of a patient-specific practical blood flow analysis is demonstrated.

Generation of patient specific human neural stem cells from Niemann-Pick disease type C patient-derived fibroblasts

Niemann-Pick disease type C (NPC) is a neurodegenerative and lysosomal lipid storage disorder, characterized by the abnormal accumulation of unesterified cholesterol and glycolipids, which is caused by mutations in the NPC1 genes. Here, we report the generation of human induced neural stem cells from NPC patient-derived fibroblasts (NPC-iNSCs) using only two reprogramming factors SOX2 and HMGA2 without going through the pluripotent state. NPC-iNSCs were stably expandable and differentiated into neurons, astrocytes, and oligodendrocytes. However, NPC-iNSCs displayed defects in self-renewal and neuronal differentiation accompanied by cholesterol accumulation, suggesting that NPC-iNSCs retain the main features of NPC. This study revealed that the cholesterol accumulation and the impairments in self-renewal and neuronal differentiation in NPC-iNSCs were significantly improved by valproic acid. Additionally, we demonstrated that the inhibition of cholesterol transportation by U18666A in WT-iNSCs mimicked the impaired self-renewal and neuronal differentiation of NPC-iNSCs, indicating that the regulation of cholesterol homeostasis is a crucial determinant for the neurodegenerative features of NPC. Taken together, these findings suggest that NPC-iNSCs can serve as an unlimited source of neural cells for pathological study or drug screening in a patient specific manner. Furthermore, this direct conversion technology might be extensively applicable for other human neurodegenerative diseases.

Patient specific methods for room-mounted x-ray imagers for monoscopic/stereoscopic prostate motion monitoring

PURPOSE

To investigate the improvement of combined monoscopic/stereoscopic prostate motion monitoring with room-mounted dual x-ray systems by adopting patient specific methods.

METHODS

The linac couch was used as a motion stage to simulate 40 highly dynamic real patient prostate trajectories. For each trajectory, 40 s pretreatment and 120 s treatment periods were extracted to represent a typical treatment fraction. Motion was monitored via continuous stereoscopic x-ray imaging of a single gold fiducial and images were retrospectively divided into periods of stereoscopic and monoscopic imaging to simulate periodic blocking of the room-mounted system by the gantry during arc-based therapy. The accuracy of the combined motion monitoring was assessed by comparison with the linac couch log files. To estimate 3-D marker position during monoscopic imaging, the use of population statistics was compared to both maximum likelihood estimation and stereoscopic localization based estimation of individualized prostate probability density functions (PDFs) from the pretreatment period. The inclusion of intrafraction updating was compared to pretreatment initialization alone.

RESULTS

Combined mono/stereoscopic localization was successfully implemented. During the transitions from stereoscopic to monoscopic imaging, fiducial localization exhibits sharp discontinuities when population PDFs were employed. Patient specific PDFs successfully reduced the localization error when estimated from stereoscopic localizations, whereas maximum likelihood estimation (MLE) was too unstable in the room-mounted geometry. Intrafraction stereoscopic updating provided further increases in accuracy. Residual error tended to decrease throughout the treatment fraction, as the patient-specific PDFs became more refined.

CONCLUSIONS

This is the first demonstration of toggled monoscopic/stereoscopic localization using room-mounted dual x-ray imagers, enabling continuous intrafraction motion monitoring for these systems. We showed that both pretreatment individualization and intrafraction updating should be used to provide the most accurate motion monitoring.

Automated, patient-specific estimation of regional imparted energy and dose from tube current modulated computed tomography exams across 13 protocols

Currently, computed tomography (CT) dosimetry relies on surrogates for dose, such as CT dose index and size-specific dose estimates, rather than dose per se. Organ dose is considered as the gold standard for radiation dosimetry. However, organ dose estimation requires precise knowledge of organ locations. Regional imparted energy and dose can also be used to quantify radiation burden and are beneficial because they do not require knowledge of organ size or location. This work investigated an automated technique to retrospectively estimate the imparted energy from tube current-modulated (TCM) CT exams across 13 protocols. Monte Carlo simulations of various head and body TCM CT examinations across various tube potentials and TCM strengths were performed on 58 adult computational extended cardiac-torso phantoms to develop relationships between scanned mass and imparted energy normalized by dose length product. Results from the Monte Carlo simulations indicate that normalized imparted energy increases with increasing both scanned mass and tube potential, but it is relatively unaffected by the strength of the TCM. The automated algorithm was tested on 40 clinical datasets with a 98% success rate.

Convolution-based estimation of organ dose in tube current modulated CT

Estimating organ dose for clinical patients requires accurate modeling of the patient anatomy and the dose field of the CT exam. The modeling of patient anatomy can be achieved using a library of representative computational phantoms (Samei et al 2014 Pediatr. Radiol. 44 460-7). The modeling of the dose field can be challenging for CT exams performed with a tube current modulation (TCM) technique. The purpose of this work was to effectively model the dose field for TCM exams using a convolution-based method. A framework was further proposed for prospective and retrospective organ dose estimation in clinical practice. The study included 60 adult patients (age range: 18-70 years, weight range: 60-180 kg). Patient-specific computational phantoms were generated based on patient CT image datasets. A previously validated Monte Carlo simulation program was used to model a clinical CT scanner (SOMATOM Definition Flash, Siemens Healthcare, Forchheim, Germany). A practical strategy was developed to achieve real-time organ dose estimation for a given clinical patient. CTDIvol-normalized organ dose coefficients ([Formula: see text]) under constant tube current were estimated and modeled as a function of patient size. Each clinical patient in the library was optimally matched to another computational phantom to obtain a representation of organ location/distribution. The patient organ distribution was convolved with a dose distribution profile to generate [Formula: see text] values that quantified the regional dose field for each organ. The organ dose was estimated by multiplying [Formula: see text] with the organ dose coefficients ([Formula: see text]). To validate the accuracy of this dose estimation technique, the organ dose of the original clinical patient was estimated using Monte Carlo program with TCM profiles explicitly modeled. The discrepancy between the estimated organ dose and dose simulated using TCM Monte Carlo program was quantified. We further compared the convolution-based organ dose estimation method with two other strategies with different approaches of quantifying the irradiation field. The proposed convolution-based estimation method showed good accuracy with the organ dose simulated using the TCM Monte Carlo simulation. The average percentage error (normalized by CTDIvol) was generally within 10% across all organs and modulation profiles, except for organs located in the pelvic and shoulder regions. This study developed an improved method that accurately quantifies the irradiation field under TCM scans. The results suggested that organ dose could be estimated in real-time both prospectively (with the localizer information only) and retrospectively (with acquired CT data).

Improvements resulting from respiratory-swallow phase training visualized in patient-specific computational analysis of swallowing mechanics

The aim of this study was to visualize improved swallowing mechanics resulting from respiratory-swallow phase training using patient specific computational analysis of Modified Barium Swallow (MBS) videofluoroscopic images. Imaging from a single subject showing improved MBSImP^™© scores in 17 of 18 pre- to post-treatment swallows was selected for analysis. Using a semi-automated MATLAB tracker tool, a frame-by-frame annotation of 10 coordinates mapping muscle functional groups was performed during oropharyngeal swallowing. Computational analysis of coordinate shape change was executed using MorphoJ software to determine differences in swallowing mechanics associated with multiple independent variables. Canonical variant analysis indicated significant differences in mechanics associated with respiratory-swallow phase training (D=1.92,p<.0001). Vectors allowed for visualization of changes in swallowing mechanics associated with respiratory-swallow phase training. A regression of shape associated with laryngeal vestibular closure on respiratory-swallow phase training was highly significant (p<.0001) and accounted for 94.1% of the variance.

Determination of contrast media administration to achieve a targeted contrast enhancement in computed tomography

Contrast enhancement is a key component of computed tomography (CT) imaging and offers opportunities for optimization. The design and optimization of techniques, however, require orchestration with the scan parameters and, further, a methodology to relate contrast enhancement and injection function. We used such a methodology to develop a method, the analytical inverse method, to predict the required injection function to achieve a desired contrast enhancement in a given organ by incorporation of a physiologically based compartmental model. The method was evaluated across 32 different target contrast enhancement functions for aorta, kidney, stomach, small intestine, and liver. The results exhibited that the analytical inverse method offers accurate performance with error in the range of 10% deviation between the predicted and desired organ enhancement curves. However, this method is incapable of predicting the injection function based on the liver enhancement. The findings of this study can be useful in optimizing contrast medium injection function as well as scan timing to provide more consistency in the way contrast-enhanced CT examinations are performed. To our knowledge, this work is one of the first attempts to predict the contrast material injection function for a desired organ enhancement curve.

Planning the Surgical Correction of Spinal Deformities: Toward the Identification of the Biomechanical Principles by Means of Numerical Simulation

In decades of technical developments after the first surgical corrections of spinal deformities, the set of devices, techniques, and tools available to the surgeons has widened dramatically. Nevertheless, the rate of complications due to mechanical failure of the fixation or the instrumentation remains rather high. Indeed, basic and clinical research about the principles of deformity correction and the optimal surgical strategies (i.e., the choice of the fusion length, the most appropriate instrumentation, and the degree of tolerable correction) did not progress as much as the implantable devices and the surgical techniques. In this work, a software approach for the biomechanical simulation of the correction of patient-specific spinal deformities aimed to the identification of its biomechanical principles is presented. The method is based on three-dimensional reconstructions of the spinal anatomy obtained from biplanar radiographic images. A user-friendly graphical user interface allows for the planning of the desired deformity correction and to simulate the implantation of pedicle screws. Robust meshing of the instrumented spine is provided by using consolidated computational geometry and meshing libraries. Based on a finite element simulation, the program is able to predict the loads and stresses acting in the instrumentation as well as those in the biological tissues. A simple test case (reduction of a low-grade spondylolisthesis at L3–L4) was simulated as a proof of concept, and showed plausible results. Despite the numerous limitations of this approach which will be addressed in future implementations, the preliminary outcome is promising and encourages a wide effort toward its refinement.

Current Controversies of Alignment in Total Knee Replacements

Total knee replacement is an increasingly popular operation for end stage knee arthritis. In the majority it alleviates pain and improves function. However up to 20% of patients remain dissatisfied, even with well-aligned and secure implants.

Restoration of a neutral mechanical axis has traditionally been strived for, to improve both function and implant survival and there is historical data to support this. More recently this view has been questioned and some surgeons are trying to improve the function and outcomes by moving away from standard alignment principles in an attempt to reproduce the kinematics of the pre-arthritic knee of that individual. Others are using computers, robots and patient specific guides to improve accuracy. This article aims to review the traditional alignment concept and the newer techniques, along with the evidence behind it.

The effect of radial head implant shape on radiocapitellar kinematics during in vitro forearm rotation

BACKGROUND

A number of radial head implants are in clinical use for the management of radial head fractures and their sequelae. However, the optimal shape of a radial head implant to ensure proper tracking relative to the capitellum has not been established. This in vitro biomechanical study compared radiocapitellar joint kinematics for 3 radial head implant designs as well as the native head.

METHODS

Eight cadaveric upper extremities were tested using a forearm rotation simulator with the elbow at 90° of flexion. Motion of the radius relative to the capitellum was optically tracked. A stem was navigated into a predetermined location and cemented in place. Three unipolar implant shapes were tested: axisymmetric, reverse-engineered patient-specific, and population-based quasi-anatomic. The patient-specific and quasi-anatomic implants were derived from measurements performed on computed tomography models.

RESULTS

Medial-lateral and anterior-posterior translation of the radial head with respect to the capitellum varied with forearm rotation and radial head condition. A significant difference in medial-lateral (P = .03) and anterior-posterior (P = .03) translation was found between the native radial head and the 3 implants. No differences were observed among the radial head conditions except for a difference in medial-lateral translation between the axisymmetric and patient-specific implants (P = .04).

CONCLUSIONS

Radiocapitellar kinematics of the tested radial head implants were similar in all but one comparison, and all had different kinematics from the native radial head. Patient-specific radial head implants did not prove advantageous relative to conventional implant designs. The shape of the fixed stem unipolar radial head implants had little influence on radiocapitellar kinematics when optimally positioned in this testing model.

Posterior cruciate ligament reconstruction with "all-inside" technique: a technical note

INTRODUCTION

posterior cruciate ligament (PCL) injuries are an increasingly recognized cause of knee instability in the practice of orthopaedic surgery and sports medicine. Clinical interest in these injuries has been increasing over the last several decades as knowledge and understanding of the biomechanical consequences and surgical reconstruction options have progressed. These injuries can be extremely challenging for the treating physician as substantial controversy exists regarding the optimal management of this problem. There has also been increasing interest and recognition of the importance of secondary stabilizing structures, including the posterolateral and posteromedial corner injuries as well as the issues with malalignment that must also be addressed at the time of PCL surgery to optimize results. Thanks to the continuous research for a correct anatomical placement and new systems of fixation, we can now perform the tibial and femoral bone tunnel more easily and safely by retrograde out-in approach with a special "drill-pin".

CONCLUSION

this technique provides a graduated precise execution of the tunnels. New methods were also developed to determine the so-called "second-generation cortical suspensory fixations" that have the feature of being "Adjustable": shortens implant by pulling on strands to allow cinching graft passing and tensioning button to regulate their length after fixation and then to create tension in the new graft, once introduced into the joint.

Accuracy of patient-specific guided glenoid baseplate positioning for reverse shoulder arthroplasty

BACKGROUND

The accuracy of reproducing a surgical plan during shoulder arthroplasty is improved by computer assistance. Intraoperative navigation, however, is challenged by increased surgical time and additional technically difficult steps. Patient-matched instrumentation has the potential to reproduce a similar degree of accuracy without the need for additional surgical steps. The purpose of this study was to examine the accuracy of patient-specific planning and a patient-specific drill guide for glenoid baseplate placement in reverse shoulder arthroplasty.

METHODS

A patient-specific glenoid baseplate drill guide for reverse shoulder arthroplasty was produced for 14 cadaveric shoulders based on a plan developed by a virtual preoperative 3-dimensional planning system using thin-cut computed tomography images. Using this patient-specific guide, high-volume shoulder surgeons exposed the glenoid through a deltopectoral approach and drilled the bicortical pathway defined by the guide. The trajectory of the drill path was compared with the virtual preoperative planned position using similar thin-cut computed tomography images to define accuracy.

RESULTS

The drill pathway defined by the patient-matched guide was found to be highly accurate when compared with the preoperative surgical plan. The translational accuracy was 1.2 ± 0.7 mm. The accuracy of inferior tilt was 1.2° ± 1.2°. The accuracy of glenoid version was 2.6° ± 1.7°.

CONCLUSION

The use of patient-specific glenoid baseplate guides is highly accurate in reproducing a virtual 3-dimensional preoperative plan. This technique delivers the accuracy observed using computerized navigation without any additional surgical steps or technical challenges.

A multi-planar CT-based comparative analysis of patient-specific cutting guides with conventional instrumentation in total knee arthroplasty

Patient specific guides (PSGs) are postulated to improve the alignment of components in total knee arthroplasty. Three hundred consecutive total knee arthroplasties performed with either conventional (CON) (n = 185) or Visionaire PSG (n = 115) were evaluated with a CT protocol for coronal limb alignment, coronal and sagittal alignment of individual components and femoral component rotation. There was no statistically significant difference between the two groups in any of the above parameters. In addition, no difference was found in total operative time. PSGs do not offer any benefit over conventional guides in terms improving the coronal alignment of the limb or alignment of individual components.

An algorithm for seizure onset detection using intracranial EEG

This article addresses the problem of real-time seizure detection from intracranial EEG (IEEG). One difficulty in creating an approach that can be used for many patients is the heterogeneity of seizure IEEG patterns across different patients and even within a patient. In addition, simultaneously maximizing sensitivity and minimizing latency and false detection rates has been challenging as these are competing objectives. Automated machine learning systems provide a mechanism for dealing with these hurdles. Here we present and evaluate an algorithm for real-time seizure onset detection from IEEG using a machine-learning approach that permits a patient-specific solution. We extract temporal and spectral features across all intracranial EEG channels. A pattern recognition component is trained using these feature vectors and tested against unseen continuous data from the same patient. When tested on more than 875 hours of IEEG data from 10 patients, the algorithm detected 97% of 67 test seizures of several types with a median detection delay of 5 seconds and a median false alarm rate of 0.6 false alarms per 24-hour period. The sensitivity was 100% for 8 of 10 patients. These results indicate that a sensitive, specific, and relatively short-latency detection system based on machine learning can be employed for seizure detection from EEG using a full set of intracranial electrodes to individual patients. This article is part of a Supplemental Special Issue entitled The Future of Automated Seizure Detection and Prediction.

euHeart: personalized and integrated cardiac care using patient-specific cardiovascular modelling

The loss of cardiac pump function accounts for a significant increase in both mortality and morbidity in Western society, where there is currently a one in four lifetime risk, and costs associated with acute and long-term hospital treatments are accelerating. The significance of cardiac disease has motivated the application of state-of-the-art clinical imaging techniques and functional signal analysis to aid diagnosis and clinical planning. Measurements of cardiac function currently provide high-resolution datasets for characterizing cardiac patients. However, the clinical practice of using population-based metrics derived from separate image or signal-based datasets often indicates contradictory treatments plans owing to inter-individual variability in pathophysiology. To address this issue, the goal of our work, demonstrated in this study through four specific clinical applications, is to integrate multiple types of functional data into a consistent framework using multi-scale computational modelling.

Patient-specific reconstructed anatomies and computer simulations are fundamental for selecting medical device treatment: application to a new percutaneous pulmonary valve

Nowadays, percutaneous pulmonary valve implantation is a successful alternative to surgery for patients requiring treatment of pulmonary valve dysfunction. However, owing to the wide variety of implantation site morphology, size and dynamics, only about 15 per cent of cases are suitable for current devices. In order to increase the number of patients who could benefit from minimally invasive procedures, a new valved stent graft for percutaneous implantation has been designed recently. In this study, patient-specific computational analyses have been applied to investigate the suitability of new device designs, using real data from 62 patients who had undergone surgical pulmonary valve replacement. Magnetic resonance images of these patients before surgery were elaborated using imaging post-processing software to reconstruct the three-dimensional volume of each patient's implantation site. Three stent designs were created and tested in these patient outflow tracts using finite-element simulations: stent graft SG1 resembles the first device tested in animals; stent graft SG2 is a custom device tailored for a specific patient morphology; and stent graft SG3 represents a hypothetical larger device. The three devices showed an implantation success rate of 37 per cent, 42 per cent and 63 per cent, respectively. Using patient-specific simulations, we have shown that a percutaneous approach with these new devices may be possible for many patients who are currently referred for surgery. Furthermore, when the new devices become available, the methodologies described may help clinicians in the decision-making process, by enabling virtual implantation prior to the actual procedure.

Unicompartmental knee resurfacing: enlarged tibio-femoral contact area and reduced contact stress using novel patient-derived geometries

Advances in imaging technology and computer-assisted design (CAD) have recently enabled the introduction of patient-specific knee implant designs that hold the potential to improve functional performance on the basis of patient-specific geometries, namely a patient-specific sagittal and coronal curvature, as well as enhanced bone preservation. The objective of this study was to investigate the use of a novel implant design utilizing a patient specific sagittal J-curve on the femoral component combined with a novel constant, patient-derived femoral coronal curvature and to assess tibio-femoral contact area and contact stress on a femur matched curved tibial polyethylene insert. Mean contact area and standard deviations were 81+/-5, 96+/-5 and 74+/-4 mm(2) for the heel strike, toe off and mid-stance positions, respectively. Mean contact stress and standard deviations were 23.83+/-1.39, 23.27+/-1.14 and 20.78+/-0.54 MPa for the heel strike, toe off and mid-stance positions, respectively. Standard deviations of the measurements were small, not exceeding 6-7% confirming the consistency of loading conditions across different flexion angles. The results were comparable to those reported for standard, off-the-shelf fixed-bearing implants with paired femoral and tibial geometries. These data show that a constant coronal curvature can be applied to a patient-specific implant by measuring coronal curvatures across the femoral condyle in each patient and by deriving an average curvature. This novel approach combines unique benefits of patient-specific geometry with proven design concepts for minimizing polyethylene wear.