Search PubMed⌕ Search

Biomedical subjects

B Hannaford

Publications and source records attributed to B Hannaford.

At least 19 recordsLinked to original sources
PubMed2001

Markov modeling of minimally invasive surgery based on tool/tissue interaction and force/torque signatures for evaluating surgical skills.

The best method of training for laparoscopic surgical skills is controversial. Some advocate observation in the operating room, while others promote animal and simulated models or a combination of surgery-related tasks. A crucial process in surgical education is to evaluate the level of surgical skills. For laparoscopic surgery, skill evaluation is traditionally performed subjectively by experts grading a video of a procedure performed by a student. By its nature, this process uses fuzzy criteria. The objective of the current study was to develop and assess a skill scale using Markov models (MMs). Ten surgeons [five novice surgeons (NS); five expert surgeons (ES)] performed a cholecystectomy and Nissen fundoplication in a porcine model. An instrumented laparoscopic grasper equipped with a three-axis force/torque (F/T) sensor was used to measure the forces/torques at the hand/tool interface synchronized with a video of the tool operative maneuvers. A synthesis of frame-by-frame video analysis and a vector quantization algorithm, allowed to define F/T signatures associated with 14 different types of tool/tissue interactions. The magnitude of F/T applied by NS and ES were significantly different (p < 0.05) and varied based on the task being performed. High F/T magnitudes were applied by NS compared with ES while performing tissue manipulation and vise versa in tasks involved tissue dissection. From each step of the surgical procedures, two MMs were developed representing the performance of three surgeons out of the five in the ES and NS groups. The data obtained by the remaining two surgeons in each group were used for evaluating the performance scale. The final result was a surgical performance index which represented a ratio of statistical similarity between the examined surgeon's MM and the MM of NS and ES. The difference between the performance index value, for a surgeon under study, and the NS/ES boundary, indicated the level of expertise in the surgeon's own group. Using this index, 87.5% of the surgical procedures were correctly classified into the NS and ES groups. The 12.5% of the procedures that were misclassified were performed by the ES and classified as NS. However in these cases the performance index values were very close to the NS/ES boundary. Preliminary data suggest that a performance index based on MM and F/T signatures provides an objective means of distinguishing NS from ES. In addition, this methodology can be further applied to evaluate haptic virtual reality surgical simulators for improving realism in surgical education.

Algorithms↗
PubMed2001

Effects of geared motor characteristics on tactile perception of tissue stiffness.

Endoscopic haptic surgical devices have shown promise in addressing the loss of tactile sensation associated with minimally invasive surgery. However, these devices must be capable of generating forces and torques similar to those applied on the tissue with a standard endoscopic tool. Geared motors are a possible solution for actuation; however, they possess mechanical characteristics that could potentially interfere with tactile perception of tissue qualities. The aim of the current research was to determine how the characteristics of a geared motor suitable for a haptic surgical device affect a user's perception of stiffness. The experiment involved six blindfolded subjects who were asked to discriminate the stiffness of six distinct silicone rubber samples whose mechanical properties are similar to those of soft tissue. Using a novel testing device whose dimensions approximated those of an endoscopic grasper, each subject palpated 30 permutations of sample pairs for each of three types of mechanical loads; the motor (friction and inertia), a flywheel (with the same inertia as motor), and a control (no significant mechanical interference). One factor ANOVA of the error scores and palpation time showed that no significant difference existed among error scores, but mean palpation time for the control was significantly less than for the other two methods. These results indicated that the mechanical characteristics of a geared motor chosen for application in a haptic surgical device did not interfere with the subjects' perception of the silicone samples' stiffness, but these characteristics may significantly affect the energy expenditure and time required for tissue palpation. Therefore, before geared motors can be considered for use in haptic surgical devices, consideration should be given to factors such as palpation speed and fatigue.

Biomechanical Phenomena↗
PubMed2001

Objective laparoscopic skills assessments of surgical residents using Hidden Markov Models based on haptic information and tool/tissue interactions.

UNLABELLED: Laparoscopic surgical skills evaluation of surgery residents is usually a subjective process, carried out in the operating room by senior surgeons. By its nature, this process is performed using fuzzy criteria. The objective of the current study was to develop and assess an objective laparoscopic surgical skill scale using Hidden Markov Models (HMM) based on haptic information, tool/tissue interactions and visual task decomposition. METHODS: Eight subjects (six surgical trainees: first year surgical residents 2 x R1, third year surgical residents 2 x R3 fifth year surgical residents 2 x R5; and two expert laparoscopic surgeons: 2 x ES) performed laparoscopic cholecystectomy following a specific 7 steps protocol on a pig. An instrumented laparoscopic grasper equipped with a three-axis force/torque sensor located at the proximal end with an additional force sensor located on the handle, was used to measure the forces and torques. The hand/tool interface force/torque data was synchronized with a video of the tool operative maneuvers. A synthesis of frame-by-frame video analysis was used to define 14 different types of tool/tissue interactions, each one associated with unique force/torque (F/T) signatures. HMMs were developed for each subject representing the surgical skills by defining the various tool/tissue interactions as states and the associated F/T signatures as observations. The statistical distance between the HMMs representing residents at different levels of their training and the HMMs of expert surgeons were calculated in order to generate a learning curve of selected steps during laparoscopic cholecystectomy. RESULTS: Comparison of HMM's between groups showed significant differences between all skill levels, supporting the objective definition of a learning curve. The major differences between skill levels were: (i) magnitudes of F/T applied (ii) types of tool/tissue interactions used and the transition between them and (iii) time intervals spent in each tool/tissue interaction and the overall completion time. The objective HMM analysis showed that the greatest difference in performance was between R1 and R3 groups and then decreased as the level of expertise increased, suggesting that significant laparoscopic surgical capability develops between the first and the third years of their residency training. The power of the methodology using HMM for objective surgical skill assessment arises from the fact that it compiles enormous amount of data regarding different aspects of surgical skill into a very compact model that can be translated into a single number representing the distance from expert performance. Moreover, the methodology is not limited to in-vivo condition as demonstrated in the current study. It can be extended to other modalities such as measuring performance in surgical simulators and robotic systems.

Animals↗
PubMed2000

Skills evaluation in minimally invasive surgery using force/torque signatures.

BACKGROUND: One of the more difficult tasks in surgical education is to teach the optimal application of instrument forces and torques necessary to facilitate the conduct of an operation. For laparoscopic surgery, this type of training has traditionally taken place in the operating room, reducing operating room efficiency and potentially affecting the safe conduct of the operation. The objective of the current study was to measure and compare forces and torques (F/T) applied at the tool/hand interface generated during laparoscopic surgery by novice (NS) and experienced (ES) surgeons using an instrumented laparoscopic grasper and to use this data for evaluating the skill level. METHODS: Ten surgeons (five-NS, five-ES) performed a cholecystectomy and Nissen fundoplication in a porcine model. An instrumented laparoscopic grasper with interchangeable standard surgical tips equipped with a three-axis F/T sensor located at the proximal end of the grasper tube was used to measure the F/T at the hand/tool interface. In addition, one axis force sensor located at the grasper's handle was used to measure the grasping force. F/T data synchronized with visual view of the tool operative maneuvers were collected simultaneously via a novel graphic user interface incorporated picture-in-picture video technology. Subsequent frame-by-frame video analysis of the operation allowed a definition of states associated with different tool/tissue interactions within each step of the operation. F/T measured within each state were further analyzed using vector quantization (VQ). The VQ analysis defines characteristic sets of F/T in the database that were defined as F/T signature. RESULTS: The magnitude of F/T applied by NS and ES were significantly different (p < 0.05) and varied based on the task being performed. Higher F/T magnitudes were applied by NS than by ES when performing tissue manipulation, whereas lower F/T magnitudes were applied by NS than by ES during tissue dissection. Furthermore, the time to complete the surgical procedure was longer for NS by a factor of 1.5-4.8 when compared to the time for ES. State analysis suggests that most of this time is consumed in an [idle] state, in which movements of the surgeon make no tissue contact. CONCLUSIONS: Preliminary data suggest that F/T magnitudes associated with the tool/tissue interactions provide an objective means of distinguishing novices from skilled surgeons. Clinical F/T analysis using the proposed technology and methodology may be helpful in training, developing surgical simulators, and measuring technical proficiency during laparoscopic surgery.

Cholecystectomy, Laparoscopic↗
PubMed2000

Hidden Markov models of minimally invasive surgery.

A crucial process in surgical education is to evaluate the level of surgical skills. For laparoscopic surgery, skill evaluation is traditionally preformed subjectively by experts grading a video of a procedure performed by a student. By its nature, this process is preformed using fuzzy criteria. The objective of the current study was to develop and assess a skill scale using Discrete Hidden Markov Models (DHMM). Ten surgeons (5 Novice Surgeons--NS; 5 Expert Surgeons--ES) performed a cholecystectomy and Nissen fundoplication in a porcine model. An instrumented laparoscopic grasper equipped with a three-axis force/torque sensor was used to measure the forces/torques at the hand/tool interface synchronized with a video of the tool operative maneuvers. A synthesis of frame-by-frame video analysis and a vector quantization algorithm, defined force/torque signatures for 14 types of tool/tissue interactions. From each step of the surgical procedures, two DHMM were developed representing the performance of 3 surgeons randomly selected from the 5 in the ES and NS groups. The data obtained by the remaining 2 surgeons in each group were used for evaluating the performance scale. The final result was a surgical performance index which represented a ratio of statistical similarity between the examined surgeon's DHMM and the DHMM of NS and ES. The difference between the performance index value, for a surgeon under study, and the NS/ES boundary, was considered to indicate the level of expertise in the surgeon's own group. Using this index, 87.5% of the surgical procedures were correctly classified into the NS and ES groups. The 12.5% of the procedures that were misclassified were preformed by the ES and classified as NS. However, in these cases the performance index values were very close to the NS/ES boundary. Preliminary data suggest that a performance index based on DHMM and force/torque signatures provides an objective means of distinguishing NS from ES. In addition this methodology can be further applied to evaluate haptic virtual reality surgical simulators for improving realism in surgical education.

Animals↗
PubMed1999

Force controlled and teleoperated endoscopic grasper for minimally invasive surgery--experimental performance evaluation.

Minimally invasive surgery generates new user interfaces which create visual and haptic distortion when compared to traditional surgery. In order to regain the tactile and kinesthetic information that is lost, a computerized force feedback endoscopic surgical grasper (FREG) was developed with computer control and a haptic user interface. The system uses standard unmodified grasper shafts and tips. The FREG can control grasping forces either by surgeon teleoperation control, or under software control. The FREG performance was evaluated using an automated palpation function (programmed series of compressions) in which the grasper measures mechanical properties of the grasped materials. The material parameters obtained from measurements showed the ability of the FREG to discriminate between different types of normal soft tissues (small bowel, lung, spleen, liver, colon, and stomach) and different kinds of artificial soft tissue replication materials (latex/silicone) for simulation purposes. In addition, subjective tests of ranking stiffness of silicone materials using the FREG teleoperation mode showed significant improvement in the performance compared to the standard endoscopic grasper. Moreover, the FREG performance was closer to the performance of the human hand than the standard endoscopic grasper. The FREG as a tool incorporating the force feedback teleoperation technology may provide the basis for application in telesurgery, clinical endoscopic surgery, surgical training, and research.

Algorithms↗
PubMed1999

Surgeon-tool force/torque signatures--evaluation of surgical skills in minimally invasive surgery.

The best method of training for laparoscopic surgical skills is controversial. Some advocate observation in the operating room, while others promote animal and simulated models or a combination of surgical related tasks. The mode of proficiency evaluation common to all of these methods has been subjective evaluation by a skilled surgeon. In order to define an objective means of evaluating performance, an instrumented laparoscopic grasper was developed measuring the force/torque at the surgeon hand/tool interface. The measured database demonstrated substantial differences between experienced and novice surgeon groups. Analyzing forces and torques combined with the state transition during surgical procedures allows an objective measurement of skill in MIS. Teaching the novice surgeon to limit excessive loads and improve movement efficiency during surgical procedures can potentially result in less injury to soft tissues and less wasted time during laparoscopic surgery. Moreover the force/torque database measured in this study may be used for developing realistic virtual reality simulators and optimization of medical robots performance.

Algorithms↗
PubMed1998

Computerized endoscopic surgical grasper.

We report a computerized endoscopic surgical grasper with computer control and a force feedback (haptic) user interface. The system uses standard unmodified grasper shafts and tips. The device can control grasping forces either by direct surgeon control, via teleoperation, or under software control. In this paper, we test an automated palpation function in which the grasper measures mechanical properties of the grasped tissue by applying a programmed series of squeezes. Experimental results show the ability to discriminate between the normal tissues of small bowel, lung, spleen, liver, colon, and stomach. We anticipate applications in telesurgery, clinical endoscopic surgery, surgical training, and research.

Endoscopes↗
PubMed1997

Study of human forearm posture maintenance with a physiologically based robotic arm and spinal level neural controller.

The goals of this research are: (1) to apply knowledge of human neuro-musculo-skeletal motion control to a biomechanically designed, neural controlled, 'anthroform' robotic arm system, (2) to demonstrate that such a system is capable of responses that match those of the human arm reasonably well in comparable experiments, and (3) to utilize the anthroform arm system to study some controversial issues and to predict new phenomena of the human motion control system. A physiologically analogous artificial neural network controller and an anatomically accurate robotic testing elbow are applied in this study. In order to build the physical elbow system to have mechanical properties as close as possible to the human arm, McKibben pneumatic artificial muscles, force sensors, and mechanical muscle spindles are integrated in the system with anatomically accurate muscle attachment points. A physiologically analogous, artificial neural network controller is used to emulate the behavior of spinal segmental reflex circuitry including Ia and Ib afferent feedbacks. Systematic experiments of elbow posture maintenance are performed and compared with physiological experimental data. New experiments are performed in which responses to torque perturbation are measured when selected afferent pathways are blocked. A 'covariance diagram' is introduced. And a linear model is used to help to analyze the roles of system components. The results show that muscle co-contraction and Ia afference with gamma dynamic motoneuron excitation are two efficient ways to increase joint stiffness and damping, which in turn reduces the mechanical sensitivity of the joint to external perturbation and shortens the settling time of the system.

Afferent Pathways↗
PubMed1997

The design of a ferrofluid magnetic pipette.

An electromagnetic pipette using a ferrofluid was designed to sample liquid volumes smaller than 0.2 microliter. Submicroliter sample sizes are desirable for reducing the amount of costly reagents and reducing sample requirement for large-scale analysis. The pipette consists of four electromagnets arranged such that air-gaps are aligned to accommodate a tube. A light-hydrocarbon-based ferrofluid is contained in the tube and acts as a plunger. The position of the ferrofluid in the tube was controlled to within 0.2 mm by combining adjacent air-gap magnetic fields. The position of the ferrofluid as a function of time and magnetic pressure as a function of position was measured in one electromagnet air-gap from the device. Maximum pressure measured was 770 Pa which corresponds to a maximum velocity of 0.9 cm/s. The assembled pipette weighs approximately 25 g, and it measures 4 cm long, 1 cm wide, and 3 cm high.

Biochemistry↗
PubMed1994

A study and model of the role of the Renshaw cell in regulating the transient firing rate of the motoneuron.

This study sought to investigate the role of the Renshaw cell with respect to transient motoneuron firing. By studying the cat motoneuron and Renshaw cell, several low-order lumped parameter models were developed that simulate the known characteristics of the injected input current vs. firing rate. The neuron models in the Renshaw cell inhibition configuration were tuned to fit experimental data from cat motoneurons. Models included both linear versions and those with sigmoidal nonlinearities. Results of the simulation indicate that the motoneuron itself provides the adaptation seen in its firing rate and that the Renshaw cell's role is primarily to fine-tune the motoneuron's adaptation process.

Action Potentials↗
PubMed1994

Technique for mechanical measurements using optical scattering from a micropipette.

This communication proposes an optical method using forward light scattering to measure the deflection of a micropipette from a normal contact force with a small elastic solid, and the damping coefficient of a small fluid sample through a dynamic interaction with the pipette. An analytical and experimental study of this sensor is performed and described for each property. Topics covered include: 1) forward light scattering technique for determining the diameter of a micropipette (using exact and simplified geometric interference theories); 2) deflection measurement and analysis on the pipette-sample system using the finite element method; and 3) equivalent damping coefficient and resonant frequency measurement of the pipette-fluid system and its numerical solution derived from the finite element model. A comparison of the experimental results and the analytical results is included to provide the means for analyzing the potential of this new method.

Computer Simulation↗
PubMed1992

Dual stable point model of muscle activation and deactivation.

Two dynamic models of muscle activation and deactivation based on the concepts of ion transport, reaction rates, and muscle mechanics are proposed. Storage release and uptake of calcium by the sarcoplasmic reticulum, and a two-step chemical reaction of calcium and troponin are included in the first model. This is a concise version of the complex chemical reactions of muscle activation and deactivation in sarcoplasm. The second model is similar to the first, but calcium-troponin reactions are simplified into two nonlinear rates functions. Due to these nonlinear dynamics, the second model can explain the catch-like enhancement of isometric force response. Simulation results which match experimental data are shown. Also, two new phenomena which need further experiment to verify are predicted by the second model.

Animals↗
PubMed1990

A nonlinear model of the phasic dynamics of muscle activation.

This paper presents a phasic excitation-activation (PEXA) model of the process of motoneuron excitation and the resultant activation and force development of a motor unit. The model input is an amount of depolarizing current (as when injected with an intracellular electrode) and the model output is muscle force. The model includes dynamics and nonlinearities similar to phenomena discovered experimentally by others: the firing rate response of motoneurons to steps of depolarizing current and the "catch-like enhancement" of force produced by overlapping motor neuron action potentials. The parameter values used in this model are derived from experimentally measured data and expressed in physical units, and model predictions extend to published data beyond those used in generating the model parameter values.

Action Potentials↗
PubMed1987

Late agonist activation burst (PC) required for optimal head movement: a simulation study.

Fast as possible (time optimal) single joint movements throughout the body are characterized by the triphasic (3 pulse) pattern of activation in the agonist and antagonist muscles. Simulation studies using a sixth order, non-linear model were undertaken to determine the relationship between time optimal movement and three pulse control. Exhaustive exploration of the multidimensional space formed by descriptive parameters of the control signal yielded control signals which drove the model to produce optimal movements. The result of these one to two week computer simulation runs was that if the limb is required to stay close to the target immediately after the end of the control signal, the fastest movements are produced by a three pulse control signal.

Biomechanical Phenomena↗
PubMed1986

An intrinsic mechanism for the oscillatory contraction of muscle.

A new model based on the theory of dynamical systems is proposed for the intrinsic random or systems is proposed for the intrinsic random or pseudo-random mechanism underlying certain types of muscular tremor. The active length-tension curve of the individual sarcomere, in conjunction with the passive length-tension relation is a map from length to tension with an observed time delay between length change and resulting tension change. The passive length tension relation is assumed to instantaneously relate this tension change back to a change in length. The stability properties of this iterated interval map are investigated by means of computer simulation and computation of the Lyapunov exponent and the bifurcation tree. The resulting analysis is related to experimental tremor data in the literature in terms of period doubling, bifurcation points, and "chaotic" behavior. The model appears to have its most fruitful application in understanding the insect type and isometric mammalian types of tremor.

Animals↗
PubMed1985

Roles of the elements of the triphasic control signal.

In fast (time-optimal) movements about many joint systems, the triphasic EMG pattern has been observed. Although the first agonist burst obviously initiates the movement, the roles of the second and third bursts, appearing in the antagonist and agonist respectively, have been less clear. In this study, the timing of experimentally measured EMG signals led to construction of a three-pulse control signal that produced an accurate simulation of experimentally measured time-optimal head rotations using a sixth-order nonlinear model in conjunction with an optimization algorithm. By ablating pulses from the model control signal and observing the resulting dynamics, the roles of the three pulses can be assessed. As a result, the pulses can be designated PA, the action pulse (for the first agonist burst), PB, the braking pulse (for the antagonist burst), and PC, the clamping pulse (for the second agonist burst). Comparison of dynamic parameters from the simulated movements revealed strategies used to generate control signals for movements of various speeds.

Electromyography↗