Iatrogenic spinal cord ischemia: A patient level meta-analysis of 74 case reports and series.

BACKGROUND: We seek to characterize the features of iatrogenic spinal ischemia, determine which spinal levels are affected, and evaluate the efficacy of management strategies. METHODS: We performed a meta-analysis of case reports and series of spinal ischemia in the past 10 years. 343 full-length case reports and case series were screened against predefined inclusion/exclusion criteria. 89 patients were included for our final meta-analysis using PRISMA guidelines. RESULTS: Mean age of patients was 59.62 years (range: 9 months-88 years). 66% of all cases were male. Endovascular surgery (32.6%) and aortic surgery (36.0%) were most common causes of iatrogenic injury, followed by non-aortic surgery (32.6%), and non-surgical procedures (22.47%). A- and B-level ASIA Impairment was found in 66% of all patients. Rehabilitation was the most common management (49.44% of cases), followed by blood pressure management (40.45%). Non-aortic surgeries had the poorest overall outcomes (OR = 0.28, p = 0.016), whereas aortic and endovascular surgeries saw significant improvement in outcomes measured at discharge (OR = 2.6, OR = 2.3, respectively, p < 0.05). Therapeutic surgical infarctions were found to be associated with improved outcomes (OR = 5.33, p = 0.032). Ischemic injury to T4-T7, and T10 were associated with significantly poorer outcomes. Autonomic impairment was associated with a likelihood of infarction at T10 (OR = 4.54, p = 0.0183). CONCLUSIONS: In this paper, we compare outcomes following iatrogenic spinal ischemia. We demonstrate the need for more comprehensive randomized controlled trials to test effective treatment strategies.

Mechanical Design and Modeling of a Manipulator Tool for a Compact Multiple-Tool Single Port Laparoscopic Robot Platform.

Laparoendoscopic single-site surgery (LESS) has been shown to reduce the invasiveness of surgery by requiring only one incision to access the abdominal cavity. However, single-site surgery integrating with a compact robotic surgical platform remains as a unique challenge. To address this challenge, we have designed a comprehensive robotic surgery platform that consists of three 6-DOF manipulators and a laparoscope camera can all be inserted into the operation field through a single 18 mm cannula holding by one 4 degrees of freedom light-weight supporting frame. Each dexterous manipulator is 5+1 degree-of-freedom (DOF), serially inserted and removable, and remotely driven by 12 actuation tendons and is composed of rigid links joined by hybrid flexure hinges. This paper introduces the compact multiple-tool single port laparoscopic robot platform for the first time. Details of the mechanical design of the trocar and manipulator including joint design and tendon routing are presented. The forward and inverse kinematics of the manipulator are also discussed along with an analysis and simulation of the cooperative workspace of two manipulators. A preliminary dynamic model of the manipulator was also constructed to study the effect of tendon-sheath friction forces at various joint configurations. Future work will illustrate the existing supporting frame mechanism for posing tools and trocar.

Vascular decomposition using weighted approximate convex decomposition.

OBJECTIVE: Stroke treatment often requires analysis of vascular pathology evaluated using computed tomography (CT) angiography. Due to vascular variability and complexity, finding precise relationships between vessel geometries and arterial pathology is difficult. A new convex shape decomposition strategy was developed to understand complex vascular structures and synthesize a weighted approximate convex decomposition (WACD) method for vascular decomposition in computer-aided diagnosis. MATERIALS AND METHODS: The vascular tree is decomposed into optimal number of components (determined by an expert). The decomposition is based on two primary features of vascular structures: (i) the branching factor that allows structural decomposition and (ii) the concavity over the vessel surface seen primarily at the site of an aneurysm. Such surfaces are decomposed into subcomponents. Vascular sections are reconstructed using CT angiograms. Next the dual graph is constructed, and edge weights for the graph are computed from shape indices. Graph vertices are iteratively clustered by a mesh decimation operator, while minimizing a cost function related to concavity. RESULTS: The method was validated by first comparing results with an approximate convex decomposition (ACD) method and next on vessel sections (n = 177) whose number of clusters (ground truth) was predetermined by an expert. In both cases, WACD produced promising results with 84.7 % of the vessel sections correctly clustered and when compared with ACD produced a more effective decomposition. Next, the algorithm was validated in a longitudinal study data of 4 subjects where volumetric and surface area comparisons were made between expert segmented sections and WACD decomposed sections that contained aneurysms. The results showed a mean error rate of 7.8 % for volumetric comparisons and 10.4 % for surface area comparisons. CONCLUSION: Decomposition of the cerebral vasculature from CT angiograms into a geometrically optimal set of convex regions may be useful for computer-assisted diagnosis. A new WACD method capable of decomposing complex vessel structures, including bifurcations and aneurysms, was developed and tested with promising results.

Evaluating tool-artery interaction force during endovascular neurosurgery for developing haptic engine.

Endovascular neurosurgery has gained acceptance as the best method of treatment of vascular abnormalities like cerebral aneurysms. However, the procedure is associated with difficulties in tool/tissue manipulation. Navigation of stent, catheter and, guide wire through complex arteries without any force information often causes stent snagging, plaque dislocations and formation of thrombosis caused by the damage of the arterial wall. Currently, there is no haptic device available which can provide the surgeons with the force information, related to stent placement procedure. The goal of this work is to create a data base for a fast synthetic endovascular force simulator, which will provide the surgeon with force information during tool-artery interaction, based on the various combinations of tool sizes and vessel complexity, [1, 2] to facilitate better preoperative planning, safer interventions, and advanced training of new surgeons.

Parametric modeling and simulation of trocar insertion.

Trocar insertion, the first step to most micro surgery procedures is a difficult procedure to learn and practice because procedure is carried out almost entirely without any visual feedback of the organs underlying the tissue being punctured. A majority of injuries is attributed to the excessive use of force by the surgeon. This paper looks at developing a haptic based trocar insertion simulator which will assist in training and skill advancement in carrying out this procedure. Different issues regarding development of force model and and trocar-tissue interaction is studied.

3D Real-time FEM based guide wire simulator with force feedback.

Minimally invasive surgical techniques using catheter is now used in many procedures. Development of surgical training of such procedures requires real-time simulation of tool-organ interaction. In such processes, each subsequent step of interaction would be based on the current configuration of the surgical tool (guidewire in this case), leading to development of techniques to solve and visualize the configuration of tool at every time step. This paper presents a Finite Element (FEM) based approach to simulate the tool-organ interaction.

The haptic kymograph: a diagnostic tele-haptic device for sensation of vital signs.

The kymograph is device for measuring and presenting pressure-based signals, such as human heart beat and artery volume pressure. The Haptic Kymograph is a haptically-enhanced tele-medicine system which is used to acquire human vital signs and then to transform these signs into sensible, scalable and ubiquitous media so that a user can easily comprehend subtle and ambiguous signals in a remote place. In an experiment setup a patient's artery pressure pulse was captured at 200 Hz of sampling rate, transmitted via TCP/IP network, and replicated in a remote place using a PHANToM haptic device coupled with a real-time visual interface. In this paper we report our recent progresses in developing a low-cost input system, network interfaces and haptic replication of the human artery volume pulse signal.

Development of a method for surface and subsurface modeling using force and position sensors.

Subsurface modeling of deformable objects, such as soft tissues and organs, involves the use of non-destructive methods of determining the properties of an object encased by a material. Some of the properties that can be determined from subsurface modeling include: shape, hardness, texture and possibly material. The ability to determine these properties is based on the accuracy of the method used and the properties of the surface encasing the object. As computers become more powerful and are able to produce even more realistic graphics, it will be possible to store and re-create precise duplicates of the original for later analysis. This paper will present a method of approximately modeling both the surface and an object below the surface of the skin by a method of palpation and then present this data in an interactive 3-D model.

Real-time volume haptic rendering of non-linear viscoelastic behavior of soft tissue through dynamic atomic unit approach.

The aim of computer haptics is to enable the user to touch, feel and maneuver virtual objects using a haptic interface. As the user "feels" the virtual object by applying force through the interface, complex calculations have to be done in real-time to generate a feedback force appropriate to the material properties of the object being "touched". In this paper we propose a method for modeling soft bodies, which incorporate non-linear, viscoelastic, anisotropic behavior that will enable real-time user interaction and still satisfy the high force-feedback frequency requirements. In this paper, we restrict the user interaction with virtual objects to palpation.

A prototype virtual reality system for preoperative planning of neuro-endovascular interventions.

This paper describes our efforts at creating a system with real time acquisition and geometric processing of the patients vascular anatomy, supplemented by a framework to simulate catheter vasculature interaction. Our system uses biplane angiograms coupled with an algorithm for generation of 3D vascular trees for patient data acquisition. Surface reconstruction and processing of this data is performed to provide novel decision aids to the interventionalist. The processed data can be loaded in a virtual environment to simulate guidance of the catheter through the patient's vasculature. With our combination of techniques, a patient specific visualization and simulation environment can be prepared within the narrow time window available for this procedure.

Utilization of virtual reality for endotracheal intubation training.

Tracheal intubation is performed for urgent airway control in injured patients. Current methods of training include working on cadavers and manikins, which lack the realism of a living human being. Work in this field has been limited due to the complex nature of simulating in real-time, the interactive forces and deformations which occur during an actual patient intubation. This study addressed the issue of intubation training in an attempt to bridge the gap between actual and virtual patient scenarios. The haptic device along with the real-time performance of the simulator give it both visual and physical realism. The three-dimensional viewing and interaction available through virtual reality make it possible for physicians, pre-hospital personnel and students to practice many endotracheal intubations without ever touching a patient. The ability for a medical professional to practice a procedure multiple times prior to performing it on a patient will both enhance the skill of the individual while reducing the risk to the patient.

Development of an interactive teaching system based on motion synchrony between physical and virtual models.

In advancing our capabilities in the realm of virtual reality, the development of haptic technology has been a rate-limiting factor in producing tactile sensations directly onto the human hands. The Living Anatomy Program seeks to obviate the need for such technology by designing physical objects based on anatomic components that feel realistic to the touch. Furthermore, synchronizing motion between physical and related virtual objects infinitely expands visual design options and provides a profound level of immersion into content.

A virtual environment for esophageal intubation training.

Esophageal intubations are performed for urgent airway control in injured patients. Current methods of training include working on cadavers and mannequins, which lack the realism of a living human being. Work in this field has been limited due to the complex nature of simulating in real-time the interactive forces and deformations which occur during an actual patient intubation. This study addressed the issue of intubation training in an attempt to bridge the gap between actual and virtual patient scenarios. The two haptic devices along with the real-time performance of the simulator give it both visual and physical realism. The three dimensional viewing and interaction available through virtual reality make it possible for physicians, pre-hospital personnel and students to practice many esophageal intubations without ever touching a patient. The ability for a medical professional to practice a procedure multiple times prior to performing it on a patient will both enhance the skill of the individual while reducing the risk to the patient.

Material property determination of sub-surface objects in a viscoelastic environment.

Modeling human organs and soft tissue or anatomic regions for the purpose of medical training and simulation is a relatively new area. The data presented here is the groundwork for our ongoing development of a real-time haptic virtual environment for abdominal soft tissue palpation. The purpose of modeling the human abdomen is twofold. First, to provide a mathematical description of soft tissue and organs and second, to simulate the behavior of realistic interactions in real-time within a virtual environment. We have developed a, non-invasive, system that will allow us to determine mathematical functions that model the deformation of individual layers of soft tissue within the human abdomen. This system has been tested, experimentally, with a viscoelastic polyester foam model. We have been able to determine the stiffness and force/displacement function of an object beneath two layers of foam having different material characteristics. These experimental results correlate well with known polyester foam material characteristics. In general, the calculated stiffness constants were within 5% of the actual value. The data presented in this study shows that this system may be a viable tool for accurate measurement of human soft tissue properties and behavioral response to palpation.