Christos Mitrogiannis

Two dimensional polymer-embedded quasi-distributed FBG pressure sensor for biomedical applications

We report on the development of a flexible 2D optical fiber-based pressure sensing surface suitable for biomedical applications. The sensor comprises of highly-sensitive Fiber Bragg Grating elements embedded in a thin polymer sheet to form a 2x2 cm(2) sensing pad with a minimal thickness of 2.5mm, while it is easily expandable in order to be used as a building block for larger surface sensors. The fabricated pad sensor was combined with a low physical dimension commercially available interrogation unit to enhance the portability features of the complete sensing system. Sensor mechanical properties allow for matching human skin behavior, while its operational performance exhibited a maximum fractional pressure sensitivity of 12 MPa(-1) with a spatial resolution of 1x1cm(2) and demonstrated no hysteresis and real time operation. These attractive operational and mechanical properties meet the requirements of various biomedical applications with respect to human skin pressure measurements, including amputee sockets, shoe sensors, wearable sensors, wheelchair seating-system sensors, hospital-bed monitoring sensors.

Patient-specific knee joint finite element model validation with high-accuracy kinematics from biplane dynamic Roentgen stereogrammetric analysis

Little is known about in vivo menisci loads and displacements in the knee during strenuous activities. A new method that combines high-speed kinematics measured with biplane dynamic Roentgen stereogrammetric analysis (DRSA) and a subject-specific finite element (FE) model for studying in vivo meniscal behavior is presented here. Further model calibration in a very controlled uniaxial low and high-rate compression loading condition is presented by comparing the model behavior against the measured high-accuracy menisci DRSA kinematics and direct tibio-femoral pressure measurement from a K-scan sensor. It is apparent that certain model aspects such as removing of the pressure sensor from the model can result in relatively large errors (14%) in contact parameters that are not reflected in the change of the measured meniscal kinematics. Changing mesh size to 1mm by 1mm elements increased the magnitude of all but one of the contact variables by up to 45%. This local validation using accurate localized patient-specific geometry and meniscal kinematics was needed to enhance model fidelity at the level of contact between menisci and cartilage.

Assessment of amputee socket–stump–residual bone kinematics during strenuous activities using Dynamic Roentgen Stereogrammetric Analysis

The design, construction, and fitting of artificial limbs remain to this day an art, dependent on the accumulated expertise of the practitioner/prosthetist. Socket fitting is cost ineffective, time consuming, and a source of inconvenience for the amputee. Stump-skin slippage within the socket can cause discomfort, internal limb pain, and eventually skin ulcers as a result of excessive pressure and shear within the socket. This study presents a new method of assessment of three-dimensional (3D) socket-stump kinematics/slippage of strenuous activities using Biplane Dynamic Roentgen Stereogrammetric Analysis instrumentation. Ten below knee amputees participated in the study. A more holistic representation of the downward slippage trend of all proximal side skin markers with respect to the socket, and an even more characteristic and of higher magnitude downward-and anterioposterior slippage (maximum slippage: 151 mm for the fast-stop task and 19 mm for the step-down task) between the distal markers after impact, was possible for both tasks for all amputees. Displacement between skin-to-skin marker pairs reached maximum values of approximately 10mm for the step-down trials and up to 24 mm for the fast stop trials. Maximum skin strain was dependent on the position of the skin markers. Distally positioned skin marker pairs demonstrated mainly anterioposterior displacement between each other (maximum relative strain: 13-14%). Maximum relative strain for the proximal markers was 8-10%. This highly accurate, in-vivo, patient-specific, unobtrusive dynamic information, presented using 3D visualization tools that were up to now unavailable to the clinician-prosthetist, can significantly impact the iterative cycle of socket fitting and evaluation.

Assessment of Internal and External Prosthesis Kinematics during Strenuous Activities Using Dynamic Roentgen Stereophotogrammetric Analysis

Optimal performance of artificial limbs is still largely dependent on the accurate evaluation of their biomechanical behavior. The accumulated expertise of the prosthetist and indirect measurements of socket and joint kinematics are currently used in a trial and error format for prosthesis-socket performance maximization. The accurate direct unobtrusive assessment of residual limb-skin slippage within the socket during dynamic high-speed activities remains an unresolved challenge till date. This assessment is further complicated in the case of transtibial amputees who have previously undergone joint arthroplasty surgery. This study uses a new method of assessment of the combination of three-dimensional (3D) total knee prosthesis kinematics and socket-residual limb kinematics/slippage during high-speed strenuous activities using Biplane Dynamic Roentgen Stereogrammetric Analysis (DRSA) instrumentation. Marker-based assessment of dynamic socket-residual limb and residual bone telescoping motion with as much as 0.03-mm translational and 1.3 degrees rotational accuracy was demonstrated. The in-vivo dynamic accuracy for the model-based (markerless) tracking (MBT) method to track the joint prosthesis was further improved from that reported previously. Quantitatively, measurement bias between DRSA and the MBT methods ranged from −0.012 to −0.11 mm (depending on coordinate axis) for the femoral prosthesis and from 0.004 to 0.048 mm for the socket. The results from this transtibial case study indicated that maximum 3D slippage for some socket-skin-marker pairs reached values of up to 16 mm for the fast-stop task and up to 8 mm for the step-down task. Maximum “deformation” of up to 12.5% is observed for the fast-stop trials and step-down trials between skin-to-skin marker pairs. The respective deformation between skin-to-socket marker pairs reached maximum values of almost 22%. The deformation between femur/tibia edges and skin/socket marker pairs reached maximum values of almost 100%. Relative skin strain calculated from skin-marker pairs reached values that range between 0.01 and 0.1 for step-down and fast-stop trials, respectively. The relative engineering shear (γ) between selected skin-marker clusters that form orthonormal meshes ranged between 81.5 and 129 degrees. This in-vivo, patient-specific, unobtrusive dynamic information is highly accurate and allows socket-residual limb interactions to be presented using 3D visualization tools that were until recently unavailable to the clinician prosthetist. These methods can significantly impact the iterative cycle of socket fitting and evaluation.

Assessment of Vacuum-assisted trans-tibial amputee socket dynamics

Daily volume loss of the residual limp is reported as one of the greatest challenges in socket fitting. Assisted vacuum socket systems were developed to prevent stumps volume loss and maintain sufficient socket fit. There is however very little quantitative biomechanical research for the evaluation of below knee sockets with assisted vacuum systems. Highly accurate in-vivo measurements became recently available using high-speed, high resolution Biplane Dynamic Rontgen Stereogrammetric Analysis (DRSA) instrumentation. This study presents the first effort to evaluate the efficiency of the vacuum assisted liner socket using DRSA. This in-vivo patient specific information is highly accurate and can significantly influence the iterative cycle of trans-tibial socket fitting and evaluation.

Development of a new bed system with improved decubitus prophylaxis for bed-ridden patients

An adaptable bedding surface for the prophylaxis and treatment of decubitus ulcers was developed and evaluated in a number of preclinical studies. The new bed reduced the average contact pressure peaks in prolonged supine bed rest while significantly decelerating the onset and progression of pressure sores. A special advantage of the surface is its discrete, independently-mobile pin elements that allow localized implementation of sensors and diagnostic tools in the bed structure. The bed is currently being evaluated in clinical trials with at series of different patient populations with different pressure ulcer pathologies. The systems overall ability to prevent the conditions that contribute to the onset of ulcers as indicated by improvements on the ulcer incidence rate is presented here.

Dynamic Radiography Imaging as a Tool in the Design and Validation of a Novel Intelligent Amputee Socket

It is apparent that socket fit is the most common source of dissatisfaction in amputees and part of a growing medical and socioeconomic problem. Even the most up to date trans-tibial socket designs are not capable of coping with the issue of continuous stump volume change that is apparent within a day, week, month or season of socket use. Intelligent sockets integrating variable volume (VVSS) with elevated vacuum (EV) systems hold that promise but have yet to reach completion in feasibility studies. This is mainly due to delays in the relevant technological maturity, cost and poor assessment methodologies. These challenges can be overcome by current advantages in dynamic radiography imaging. These advantages are presented with an example of a novel socket design as: a) solutions to problems of direct socket-stump motion measurement, and b) as tools for calibrating socket control hardware and computer aided socket design. Imaging can therefore be integrated as part of an expert clinical system for imaging-driven computer-aided socket design and evaluation (cost-labor effective).

Accuracy assessment of a photoimaging and scanner-based wound diagnostics method

The new Wound Diagnostics Tool (WDT) software package presented here aims to produce wound progress statistics that have clinical significance by linking digital image-based and three-dimensional (3D) geometry maps of the ulcer with existing traditional risk assessment techniques and other wound progress tracking information. All this information is then combined in a detailed electronic report that can be integrated with additional patient progress information in a picture archives communication system or web based database. This study presents data from early clinical trials supporting the increased accuracy and efficiency of the new photoimaging and scanner-based wound diagnostics method.

Validation of 3D radiographical image distortion correction and calibration algorithms

Dynamic Roentgen Stereogrammetric Analysis (DRSA) provides a highly accurate research and clinical tool in human movement sciences. Essential for the respective DRSA measurements is proper alignment and calibration of the device. An improved method for determining the sufficiency of those preparations is introduced and discussed.