Comparing deposition characteristics of various embolic particles using an in vitro prostate microvasculature model.

PURPOSE: To compare spatial distributions of radiopaque glass (RG) microspheres, trisacryl gelatin (TAG) microspheres, and polyvinyl alcohol (PVA) foam particles within a planar in vitro microvascular model of the hyperplastic hemiprostate. MATERIALS AND METHODS: A microvascular model simulating hyperplastic hemiprostate was perfused with a water-glycerin mixture. A microcatheter was positioned distal to the model's prostatic artery origin and embolic particles (RG: 50 µm, 100 µm, and 150 µm; TAG: 100-300 µm and 300-500 µm; and PVA: 90-180 µm and 180-300 µm) were administered using a syringe pump. Microscopic imaging and subsequent semantic segmentation were performed to quantify particle distributions within the models. Distal penetrations were quantified statistically via modal analysis of the particle distributions. RESULTS: Maximum distal penetration was observed for RG 50, followed by RG 100 and then TAG 100-300 and RG 150. TAG 300-500, PVA 90-180, and PVA 180-300 particles exhibited the lowest distal penetrations. The distal penetration metrics between groups were significantly different (p < 0.05) except between TAG 100-300 and RG 150 and between PVA 90-180 and PVA 180-300. CONCLUSIONS: Comparing the spatial distributions of embolic particles in an in vitro microvascular model simulating the hyperplastic hemiprostate revealed that noncompressible particles and those with narrower size calibrations and smaller relative diameters exhibited higher degrees of distal packing. The embolization front was less distinct for particles with wider size calibrations, which resulted in smaller, more distal emboli along with larger, more proximal emboli. PVA and TAG 300-500 particles both exhibited relatively low overall distal penetration.

Comparison of Bolus Versus Dual-Syringe Administration Systems on Glass Yttrium-90 Microsphere Deposition in an In Vitro Microvascular Hepatic Tumor Model.

PURPOSE: To utilize an in vitro microvascular hepatic tumor model to compare the deposition characteristics of glass yttrium-90 microspheres using the dual-syringe (DS) and traditional bolus administration methods. MATERIALS AND METHODS: The microvascular tumor model represented a 3.5-cm tumor in a 1,400-cm3 liver with a total hepatic flow of 160 mL/min and was dynamically perfused. A microcatheter was placed in a 2-mm artery feeding the tumor model and 2 additional nontarget arteries. Glass microspheres with a diameter of 20-30 µm were administered using 2 methods: (a) DS delivery at a concentration of 50 mg/mL in either a single, continuous 2-mL infusion or two 1-mL infusions and (b) bolus delivery (BD) of 100 mg of microspheres in a single 3-mL infusion. RESULTS: Overall, the degree of on-target deposition of the microspheres was 85% ± 11%, with no significant differences between the administration methods. Although the distal penetration into the tumor arterioles was approximately 15 mm (from the second microvascular bifurcation of the tumor model) for all the cases, the distal peak particle counts were significantly higher for the DS delivery case (approximately 5 × 105 microspheres achieving distal deposition vs 2 × 105 for the BD case). This resulted in significantly higher deposition uniformity within the tumor model (90% for the DS delivery case vs 80% for the BD case, α = 0.05). CONCLUSIONS: The use of this new in vitro microvascular hepatic tumor model demonstrated that the administration method can affect the deposition of yttrium-90 microspheres within a tumor, with greater distal deposition and more uniform tumor coverage when the microspheres are delivered at consistent concentrations using a DS delivery device. The BD administration method was associated with less favorable deposition characteristics of the microspheres.

Gastric artery embolization: studying the effects of catheter type and injection method on microsphere distributions within a benchtop arterial model.

AIMS: The objective of the study is to investigate the effect of catheter type and injection method on microsphere distributions, specifically vessel targeting accuracy. MATERIALS AND METHODS: The study utilized three catheter types (a standard end-hole micro-catheter, a Surefire anti-reflux catheter, and an Endobar occlusion balloon catheter) and both manual and computer-controlled injection schemes. A closed-loop, dynamically pressurized surrogate arterial system was assembled to replicate arterial flow for bariatric embolization procedures. Four vessel branches immediately distal to the injection site were targeted for embolization. Embolic microspheres were injected into the model using these  three catheter types and both manual and computer-controlled injections. RESULTS: Across all injection methods, the catheter effect on the proportion of microspheres to target vessels (vs. non-target vessels) was significant (p = 0.005). The catheter effect on the number of non-target vessels embolized was nearly significant (p = 0.059). Across all catheter types, the injection method effect was not statistically significant for either of two outcome measures (percent microspheres to target vessels: p = 0.265, number of non-target vessels embolized: p = 0.148). CONCLUSION: Catheter type had a significant effect on targeting accuracy across all injection methods. The Endobar catheter exhibited a higher targeting accuracy in pairwise comparisons with the other two injection catheters across all injection schemes and when considering the Endobar catheter with the manifold injection method vs. each of the catheters with the manual injection method; the differences were significant in three of four analyses. The injection method effect was not statistically significant across all catheter types and when considering the Endobar catheter/Endobar manifold combination vs. Endobar catheter injections with manual and pressure-replicated methods.

Retraction mechanics of Finochietto-style self-retaining thoracic retractors.

OBJECTIVES: Analyze the mechanics of Finochietto-style retractors, including the responses of thoracic tissues during thoracotomy, with an emphasis on tissue trauma and means for its reduction. METHODS: Mechanical analyses of the retractor were performed, including analysis of deformation under load and kinematics of the crank mechanism. Thoracotomies in a porcine model were performed in anesthetized animals (7) and fresh cadavers (17) using an instrumented retractor. RESULTS: Mechanical analyses revealed that arm motion is a non-linear function of handle rotation, that deformation of the retractor under load concentrates force at one edge of the retractor blade, and that the retractor behaves like a spring, deforming under the load of retraction and continuing to force open the incision long after crank rotation stops. Experimental thoracotomies included retractions ranging from 50 to 112 mm over 30 to 370 s, generating maximum forces of 118 to 470 N (12-50 kgf). Tissue ruptures occurred in 12 of the 24 retractions. These ruptures all occurred at retraction distances wider than 30 mm and at forces greater than 122.5 N. Significant tissue ruptures were observed for nearly all retractions at higher retraction rates (exceeding ½ rotation of the crank per 10 s). CONCLUSIONS: The Finochietto-style retractor can generate large forces and some aspects of its design increase the probability of tissue trauma.

PATH OPTIMIZATION AND CONTROL OF A SHAPE MEMORY ALLOY ACTUATED CATHETER FOR ENDOCARDIAL RADIOFREQUENCY ABLATION.

This paper introduces a real-time path optimization and control strategy for shape memory alloy (SMA) actuated cardiac ablation catheters, potentially enabling the creation of more precise lesions with reduced procedure times and improved patient outcomes. Catheter tip locations and orientations are optimized using parallel genetic algorithms to produce continuous ablation paths with near normal tissue contact through physician-specified points. A nonlinear multivariable control strategy is presented to compensate for SMA hysteresis, bandwidth limitations, and coupling between system inputs. Simulated and experimental results demonstrate efficient generation of ablation paths and optimal reference trajectories. Closed-loop control of the SMA-actuated catheter along optimized ablation paths is validated experimentally.

Design Optimization and Tradeoff Analysis of an Actuated Continuum Probe for Pulmonary Nodule Localization and Resection.

Pulmonary nodules are abnormal tissue masses in the lungs, typically less than 3.0 cm in diameter, commonly detected during imaging of the chest and lungs. While most pulmonary nodules are not cancerous, surgical resection may be required if growth is detected between scans. This resection is typically performed without the benefit of intraoperative imaging, making it difficult for surgeons to confidently provide appropriate margins. To enhance the efficacy of wedge resection, researchers have developed a modified ultrasound imaging approach that utilizes both multiple scattering (MS) and single scattering (SS) to enhance the accuracy of margin delineation. Clinical deployment of this novel ultrasound technology requires a highly maneuverable ultrasound probe, ideally one that could be deployed and actuated with minimal invasiveness. This study details the design optimization and tradeoff analysis of an actuated continuum probe for pulmonary nodule localization and resection. This device, deployed through intercostal ports, would enable the intraoperative imaging and precise mapping of nodules for improved margin delineation and patient outcomes. To achieve this objective, multiple objective genetic algorithms (MOGAs) and a design of experiments (DOE) study are used to explore the design space and quantify key dimensional relationships and their effects on probe actuation.

Tissue-disruptive forces during median sternotomy.

BACKGROUND: Acute and chronic pain after median sternotomy is common and often underestimated. The mechanical retractors used for median sternotomy exert significant forces on the skeletal cage. We hypothesized that instrumented retractors could be developed to enable real-time monitoring and control of retraction forces, functions that may provide equivalent exposure with significantly reduced forces and tissue damage, and thus, less postoperative pain. METHODS: We developed a novel instrumented retractor designed to enable real-time force monitoring during surgical retraction and then tested it by performing median sternotomies on 16 mature sheep. For 8 of these median sternotomies, retraction was performed to 7.5 cm at a standard "clinical pace" of 7.25 +/- 0.97 minutes without real-time monitoring of retraction forces. For the other 8 median sternotomies, we performed retraction to the same exposure using real-time visual force feedback and, consequently, a more deliberate pace of 12.05 +/- 1.73 minutes (P <.001). Retraction forces, blood pressure, and heart rate were monitored throughout the procedure. RESULTS: Full retraction resulted in an average force of 102.99 +/- 40.68 N at the standard clinical pace, compared to 64.68 +/- 17.60 N with force feedback (a 37.2% reduction, P = .021). Standard retraction produced peak forces of 368.79 +/- 133.61 N, whereas force feedback yielded peak forces of 254.84 +/- 75.77 N (a 30.9% reduction, P = .1152). Heart rate was significantly higher during standard clinical retraction (P = .025). CONCLUSIONS: Use of the novel instrumented retractor resulted in lower average and peak retraction forces during median sternotomy. Moreover, these reduced retraction forces correlated to a reduction in animal stress, as documented by heart rate.

Solid Tumor Embolotherapy in Hepatic Arteries with an Anti-reflux Catheter System.

Unresectable hepatoma accounts for the majority of malignant liver tumor cases for which embolization therapy is considered a viable treatment option. However, the potential risk of aberrant particle deposition in non-target regions could cause severe side-effects, alongside diminished efficacy. A computational model has been developed to analyze the particle-hemodynamics before and after deployment of an FDA-approved anti-reflux catheter. The catheter features a retractable, porous cone-like tip designed to allow forward blood flow while preventing microsphere reflux. A patient-specific hepatic artery system, with different daughter branches connected to a liver tumor, was chosen as a representative test bed. In vitro as well as in vivo measurements were used to validate the computer simulation model. The model captures the effect of tip-deployment on blood perfusion and pressure drop in an interactive manner under physiologically realistic conditions. A relationship between the pressure drop and embolization level was established, which can be used to provide clinicians with real-time information on the best infusion-stop point. However, the results show that the present procedure for embolization of downstream vessels which feed a tumor is quite arbitrary. Nevertheless, a method to recycle aberrant particles captured by the deployed tip was proposed to minimize side-effects.

Adaptive system identification applied to the biomechanical response of the human trunk during sudden loading.

Epidemiological evidence indicates that sudden loading of the torso is a risk factor for low back injury. Accurately quantifying the time-varying loading of the spine during sudden loading events and how these loading profiles are affected by workplace factors such as fatigue, expectation, and training can potentially lead to intervention strategies that can reduce these risks. Electromyographic and trunk motion data were collected from six male participants who performed a series of sudden loading trials with varying levels of expectation (no preview, 300-ms audible preview), fatigue (no fatiguing exertion preceding sudden load, short duration/high intensity fatiguing exertion preceding sudden load), and training (untrained, trained). These data were used as inputs to an adaptive system identification model wherein time-varying lower back stiffness, torque, work, and impulse magnitudes were calculated. Results indicated that expectation significantly increased peak and average stiffness by 70% and 113%, respectively, and significantly decreased peak torque, work, and impulse magnitudes by 36%, 50%, and 45%, respectively. Training significantly decreased peak torque and work by 25% and 34%, respectively. The results also showed a significant interaction between expectation and training wherein training had a positive effect during the trials with preview but no effect during the trials with no preview (increased peak stiffness by 17% and decreased impulse magnitude by 43%).

Innovation in catheter design for intra-arterial liver cancer treatments results in favorable particle-fluid dynamics.

BACKGROUND: Liver tumors are increasingly treated with radioembolization. Here, we present first evidence of catheter design effect on particle-fluid dynamics and downstream branch targeting during microsphere administrations. MATERIALS AND METHODS: A total of 7 experiments were performed in a bench-top model of the hepatic arterial vasculature with recreated hemodynamics. Fluorescent microspheres and clinically used holmium microspheres were administered with a standard microcatheter (SMC) and an anti-reflux catheter (ARC) positioned at the same level along the longitudinal vessel axis. Catheter-related particle flow dynamics were analyzed by reviewing video recordings of UV-light illuminated fluorescent microsphere administrations. Downstream branch distribution was analyzed by quantification of collected microspheres in separate filters for two first-order branches. Mean deviation from a perfectly homogenous distribution (DHD) was used to compare the distribution homogeneity between catheter types. RESULTS: The SMC administrations demonstrated a random off-centered catheter position (in 71 % of experiments), and a laminar particle flow pattern with an inhomogeneous downstream branch distribution, dependent on catheter position and injection force. The ARC administrations demonstrated a fixed centro-luminal catheter position, and a turbulent particle flow pattern with a more consistent and homogenous downstream branch distribution. Quantitative analyses confirmed a significantly more homogeneous distribution with the ARC; the mean DHD was 40.85 % (IQR 22.76 %) for the SMC and 15.54 % (IQR 6.46 %) for the ARC (p = 0.047). CONCLUSION: Catheter type has a significant impact on microsphere administrations in an in-vitro hepatic arterial model. A within-patient randomized controlled trial has been initiated to investigate clinical catheter-related effects during radioembolization treatment.

INDIRECT INTELLIGENT SLIDING MODE CONTROL OF A SHAPE MEMORY ALLOY ACTUATED FLEXIBLE BEAM USING HYSTERETIC RECURRENT NEURAL NETWORKS.

This paper introduces an indirect intelligent sliding mode controller (IISMC) for shape memory alloy (SMA) actuators, specifically a flexible beam deflected by a single offset SMA tendon. The controller manipulates applied voltage, which alters SMA tendon temperature to track reference bending angles. A hysteretic recurrent neural network (HRNN) captures the nonlinear, hysteretic relationship between SMA temperature and bending angle. The variable structure control strategy provides robustness to model uncertainties and parameter variations, while effectively compensating for system nonlinearities, achieving superior tracking compared to an optimized PI controller.

Experimental microsphere targeting in a representative hepatic artery system.

Recent work employing the computational fluid-particle modeling of the hepatic arteries has identified a correlation between particle release position and downstream branch distribution for direct tumor-targeting in radioembolization procedures. An experimental model has been constructed to evaluate the underlying simulation theory and determine its feasibility for future clinical use. A scaled model of a generalized hepatic system with a single inlet and five outlet branches was fabricated to replicate the fluid dynamics in the hepatic arteries of diseased livers. Assuming steady flow, neutrally buoyant microspheres were released from controlled locations within the inlet of the model and the resulting output distributions were recorded. Fluid and particle transport simulations were conducted with identical parameters. The resulting experimentally and simulation-derived microsphere distributions were compared. The experimental microsphere distribution exhibited a clear dependence on injection location that correlated very strongly with the computationally predicted results. Individual branch targeting was possible for each of the five outputs. The experimental results validate the simulation methodology for achieving targeted microsphere distributions in a known geometry under constant flow conditions.

A novel shape memory alloy annuloplasty ring for minimally invasive surgery: design, fabrication, and evaluation.

A novel annuloplasty ring with a shape memory alloy core has been developed to facilitate minimally invasive mitral valve repair. In its activated (austenitic) phase, this prototype ring has comparable mechanical properties to commercial semi-rigid rings. In its pre-activated (martensitic) phase, this ring is flexible enough to be introduced through an 8-mm trocar and easily manipulated with robotic instruments within the confines of a left atrial model. The core is constructed of 0.50 mm diameter NiTi, which is maintained below its martensitic transition temperature (24 °C) during deployment and suturing. After suturing, the ring is heated above its austenitic transition temperature (37 °C, normal human body temperature) enabling the NiTi core to attain its optimal geometry and stiffness characteristics indefinitely. This article summarizes the design, fabrication, and evaluation of this prototype ring. Experimental results suggest that the NiTi core ring could be a viable alternative to flexible bands in robot-assisted minimally invasive mitral valve repair.

A dynamic heart system to facilitate the development of mitral valve repair techniques.

OBJECTIVE: The development of a novel surgical tool or technique for mitral valve repair can be hampered by cost, complexity, and time associated with performing animal trials. A dynamically pressurized model was developed to control pressure and flowrate profiles in intact porcine hearts in order to quantify mitral regurgitation and evaluate the quality of mitral valve repair. METHODS: A pulse duplication system was designed to replicate physiological conditions in explanted hearts. To test the capabilities of this system in measuring varying degrees of mitral regurgitation, the output of eight porcine hearts was measured for two different pressure waveforms before and after induced mitral valve failure. Four hearts were further repaired and tested. Measurements were compared with echocardiographic images. RESULTS: For all trials, cardiac output decreased as left ventricular pressure was increased. After induction of mitral valve insufficiencies, cardiac output decreased, with a peak regurgitant fraction of 71.8%. Echocardiography clearly showed increases in regurgitant severity from post-valve failure and with increased pressure. CONCLUSIONS: The dynamic heart model consistently and reliably quantifies mitral regurgitation across a range of severities. Advantages include low experimental cost and time associated with each trial, while still allowing for surgical evaluations in an intact heart.

Evaluation of a shape memory alloy reinforced annuloplasty band for minimally invasive mitral valve repair.

PURPOSE: An in vitro study using explanted porcine hearts was conducted to evaluate a novel annuloplasty band, reinforced with a two-phase, shape memory alloy, designed specifically for minimally invasive mitral valve repair. DESCRIPTION: In its rigid (austenitic) phase, this band provides the same mechanical properties as the commercial semi-rigid bands. In its compliant (martensitic) phase, this band is flexible enough to be introduced through an 8-mm trocar and is easily manipulated within the heart. EVALUATION: In its rigid phase, the prototype band displayed similar mechanical properties to commercially available semi-rigid rings. Dynamic flow testing demonstrated no statistical differences in the reduction of mitral valve regurgitation. In its flexible phase, the band was easily deployed through an 8-mm trocar, robotically manipulated and sutured into place. CONCLUSIONS: Experimental results suggest that the shape memory alloy reinforced band could be a viable alternative to flexible and semi-rigid bands in minimally invasive mitral valve repair.

A novel instrumented retractor to monitor tissue-disruptive forces during lateral thoracotomy.

OBJECTIVE: Acute and chronic pain after thoracotomy, post-thoracotomy pain syndrome, is well documented. The mechanical retractors used for the thoracotomy exert significant forces on the skeletal cage. Our hypothesis was that instrumented retractors could be developed to enable real-time monitoring and control of retraction forces. This would provide equivalent exposure with significantly reduced forces and tissue damage and thus less post-thoracotomy pain. METHODS: A novel instrumented retractor was designed and fabricated to enable real-time force monitoring during surgical retraction. Eight mature sheep underwent bilateral thoracotomy. One lateral thoracotomy was retracted at a standard clinical pace of 5.93 +/- 0.80 minutes to 7.5 cm without real-time monitoring of retraction forces. The other lateral thoracotomy was retracted to the same exposure with real-time visual force feedback and a consequently more deliberate pace of 9.87 +/- 1.89 minutes (P = .006). Retraction forces, blood pressure, and heart rate were monitored throughout the procedure. RESULTS: Full lateral retraction resulted in an average force of 102.88 +/- 50.36 N at the standard clinical pace, versus 77.88 +/- 38.85 N with force feedback (a 24.3% reduction, P = .006). Standard retraction produced peak forces of 450.01 +/- 129.58 N, whereas force feedback yielded peak forces of 323.99 +/- 127.79 N (a 28.0% reduction, P = .009). Systolic blood pressure was significantly higher during standard clinical retraction (P = .0097), and rib fracture occurrences were reduced from 5 to 1 with force feedback (P = .04). CONCLUSIONS: Use of the novel instrumented retractor resulted in significantly lower average and peak retraction forces during lateral thoracotomy. Moreover, these reduced retraction forces were correlated with reductions in animal stress and tissue damage, as documented by lower systolic blood pressures and fewer rib fractures.

An adaptive system identification model of the biomechanical response of the human trunk during sudden loading.

Sudden loading injuries to the low back are a concern. Current models are limited in their ability to quantify the time-varying nature of the sudden loading event. The method of approach used six males who were subjected to sudden loads. Response data (EMG and kinematics) were input into a system identification model to yield time-varying torso stiffness estimates. The results show estimates of system stiffness in good agreement with values in the literature. The average root mean square error of the model's predictions of sagittal motion was equal to 0.1 deg. In conclusion, system identification can be implemented with minimal error and used to gain more insight into the time-dependent trunk response to sudden loads.