Publications by authors named "Albert J Shih"

53 Publications

Failure modes and effects analysis of mechanical thrombectomy for stroke discovered in human brains.

J Neurosurg 2021 Jun 4:1-8. Epub 2021 Jun 4.

3Neurosurgery, University of Michigan, Ann Arbor, Michigan.

Objective: Despite advancement of thrombectomy technologies for large-vessel occlusion (LVO) stroke and increased user experience, complete recanalization rates linger around 50%, and one-third of patients who have undergone successful recanalization still experience poor neurological outcomes. To enhance the understanding of the biomechanics and failure modes, the authors conducted an experimental analysis of the interaction of emboli/artery/devices in the first human brain test platform for LVO stroke described to date.

Methods: In 12 fresh human brains, 105 LVOs were recreated by embolizing engineered emboli analogs and recanalization was attempted using aspiration catheters and/or stent retrievers. The complex mechanical interaction between diverse emboli (elastic, stiff, and fragment prone), arteries (anterior and posterior circulation), and thrombectomy devices were observed, analyzed, and categorized. The authors systematically evaluated the recanalization process through failure modes and effects analysis, and they identified where and how thrombectomy devices fail and the impact of device failure.

Results: The first-pass effect (34%), successful (71%), and complete (60%) recanalization rates in this model were consistent with those in the literature. Failure mode analysis of 184 passes with thrombectomy devices revealed the following. 1) Devices loaded the emboli with tensile forces leading to elongation and intravascular fragmentation. 2) In the presence of anterograde flow, small fragments embolize to the microcirculation and large fragments result in recurrent vessel occlusion. 3) Multiple passes are required due to recurrent (15%) and residual (73%) occlusions, or both (12%). 4) Residual emboli remained in small branching and perforating arteries in cases of alleged complete recanalization (28%). 5) Vacuum caused arterial collapse at physiological pressures (27%). 6) Device withdrawal caused arterial traction (41%), and severe traction provoked avulsion of perforating and small branching arteries.

Conclusions: Biomechanically superior thrombectomy technologies should prevent unrestrained tensional load on emboli, minimize intraluminal embolus fragmentation and release, improve device/embolus integration, recanalize small branching and perforating arteries, prevent arterial collapse, and minimize traction.
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http://dx.doi.org/10.3171/2020.11.JNS203684DOI Listing
June 2021

Detecting High-Resolution Intramural Vascular Wall Strain Signals Using DICOM Data.

ASAIO J 2021 May 28. Epub 2021 May 28.

From the Research Service, VA Ann Arbor Healthcare System, Ann Arbor, Michigan, USA Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan Department of Statistics, University of Michigan, Ann Arbor, Michigan Michigan Tech Research Institute, Michigan Technological University, Ann Arbor, Michigan Department of Psychiatry, University of Michigan, Ann Arbor, Michigan Radiology, Weill Cornell Medicine, New York City, New York Radiology, Rocky Vista University, Ivins, Utah Emerge Now Inc., Los Angeles, California Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts Departments of Radiology and Surgery, University of Michigan, Ann Arbor, Michigan.

Maintaining dialysis vascular access is a source of considerable morbidity in patients with end-stage renal disease (ESRD). High-resolution radiofrequency (RF) ultrasound vascular strain imaging has been applied experimentally in the vascular access setting to assist in diagnosis and management. Unfortunately, high-resolution RF data are not routinely accessible to clinicians. In contrast, the standard DICOM formatted B-mode ultrasound data are widely accessible. However, B-mode, representing the envelope of the RF signal, is of much lower resolution. If strain imaging could use open-source B-mode data, these imaging techniques could be more broadly investigated. We conducted experiments to detect wall strain signals with submillimeter tracking resolutions ranging from 0.2 mm (3 pixels) to 0.65 mm (10 pixels) using DICOM B-mode data. We compared this submillimeter tracking to the overall vascular distensibility as the reference measurements to see if high-strain resolution strain could be detected using open-source B-Mode data. We measured the best-fit coefficient of determination between signals, expressed as the percentage of strain waveforms that exhibited a correlation with a p value of 0.05 or less. The lowest percentage was 86.7%, and most were 90% and higher. This indicates high-resolution strain signals can be detected within the vessel wall using B-mode DICOM data.
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http://dx.doi.org/10.1097/MAT.0000000000001490DOI Listing
May 2021

A planar piecewise continuous lumped muscle parameter model for prediction of walking gait.

Gait Posture 2021 Jul 24;88:146-154. Epub 2021 May 24.

Department of Industrial and Operations Engineering, University of Michigan, Ann Arbor, MI, USA; Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.

Goal: This work aims to develop a planar piecewise continuous lumped muscle parameter (PPCLMP) model that can utilize inputs that can be obtained in a clinical or home setting using simple tools (e.g. video cameras and inertial sensors) to predict human walking gait.

Methods: The model characterizes the sagittal-plane movement of the lower limbs during the single stance phase as an inverted pendulum, the double stance phase as a kinematic chain, and the swing phase as a double pendulum. The joint angles and angular velocities at the end of one phase are used as the initial conditions of the next phase. The model predicts the gait cycle based on the initial joint angles and angular velocities via forward dynamics. The errors between the initial and end conditions are minimized by changing the input initial joint angles and angular velocities of the gait cycle.

Results: Sensitivity analysis showed that the errors between the initial and end conditions of a gait cycle were sensitive to the initial joint angles. The step length was sensitive to subject stature. The model only works for a certain range of initial conditions.

Conclusions: The model can predict gait cycles based on forward dynamics and selects initial conditions that minimize the errors between the initial and end conditions of the gait cycle. The model utilizes 2-D representations of lower limbs and simplified representations of joint torques to reduce the required inputs for gait prediction and builds the foundation of gait assessment tools.
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http://dx.doi.org/10.1016/j.gaitpost.2021.05.021DOI Listing
July 2021

Sono-angiography for dialysis vascular access based on the freehand 2D ultrasound scanning.

J Vasc Access 2021 May 10:11297298211015066. Epub 2021 May 10.

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, USA.

Introduction: Dialysis vascular access, preferably an autogenous arteriovenous fistula, remains an end stage renal disease (ESRD) patient's lifeline providing a means of connecting the patient to the dialysis machine. Once an access is created, the current gold standard of care for maintenance of vascular access is angiography and angioplasty to treat stenosis. While point of care 2D ultrasound has been used to detect access problems, we sought to reproduce angiographic results comparable to the gold standard angiogram (fistulogram) using ultrasound data acquired from a conventional 2D ultrasound scanner.

Methods: A 2D ultrasound probe was used to acquire a series of cross sectional images of the vascular access including arteriovenous anastomosis of a subject with a radio-cephalic fistula. These 2D B-mode images were used for 3D vessel reconstruction by binary thresholding to categorize vascular versus non-vascular structures followed by standard image segmentation to select the structure representative of dialysis vascular access and morphologic filtering. Image processing was done using open source Python Software.

Results: The open source software was able to: (1) view the gold standard fistulogram images, (2) reconstruct 2D planar images of the fistula from ultrasound data as viewed from the top, analogous to computerized tomography images, and (3) construct a 2D representation of vascular access similar to the angiogram.

Conclusion: We present a simple approach to obtain an angiogram-like representation of the vascular access from readily available, non-proprietary 2D ultrasound data in the point of care setting. While the sono-angiogram is not intended to replace angiography, it may be useful in providing 3D imaging at the point of care in the dialysis unit, outpatient clinic, or for pre-operative planning for interventional procedures. Future work will focus on improving the robustness and quality of the imaging data while preserving the straightforward freehand approach used for ultrasound data acquisition.
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http://dx.doi.org/10.1177/11297298211015066DOI Listing
May 2021

Novel preclinical method for evaluating the efficacy of a percutaneous treatment in human ex vivo calcified plaque.

Med Biol Eng Comput 2021 Apr 12;59(4):799-811. Epub 2021 Mar 12.

Department of Internal Medicine, University of Michigan Health System at Ann Arbor, 1500 E Medical Center Dr, Ann Arbor, MI, 48109, USA.

The lack of suitable atherosclerotic calcification models and testing strategies inhibits preclinical efficacy testing of existing and novel percutaneous devices. The goal of this study is to develop a preclinical testing method for quantitatively and qualitatively evaluating the efficacy of noncompliant balloon angioplasty (NC BA) treatment in human ex vivo calcified plaque (CP). NC BA using a 3- and 4-mm diameter balloon was performed on an ex vivo tibial calcified vessel obtained from an amputation. Three-dimensional microcomputed tomography (μ-CT) imaging was performed pre- and post-BA to compare crack density in the CP. Comparing the pre- and posttreatment three-dimensional μ-CT images showed a glass-like cracking that occurred in the CP due to the BA procedure. Expansion of the 3-mm balloon showed little tissue deformation and no CP cracking. Although expansion of the 4-mm balloon occurred nonuniformly along balloon length and across the perpendicular projections, the balloon generated cracking throughout the CP, which allowed the surrounding elastic tissue to be dilated. This combined X-ray microscopy and μ-CT technique is a useful preclinical tool for quantifying the efficacy of percutaneous treatments for CP. Because of its nondestructive nature, the CP structure can be visualized pre- and posttreatment to determine the treatment effect.
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http://dx.doi.org/10.1007/s11517-021-02334-wDOI Listing
April 2021

Novel intraperitoneal hemostasis device prolongs survival in a swine model of noncompressible abdominal hemorrhage.

J Trauma Acute Care Surg 2021 05;90(5):838-844

From the Department of Emergency Medicine (B.M.M., M.H.T., C.I.C., D.C.L., N.L.G., K.R.W.), Michigan Center for Integrative Research in Critical Care (B.M.M., M.H.T., C.I.C., D.C.L., N.L.G., J.S.P., A.J.S., K.R.W.), Biomedical Engineering (J.S.P., A.J.S., K.R.W.), and Mechanical Engineering (J.S.P., A.J.S.), University of Michigan, Ann Arbor, Michigan.

Background: Noncompressible torso hemorrhage (NCTH) of the abdomen is a challenge to rapidly control and treat in the prehospital and emergency department settings. In this pilot study, we developed a novel intraperitoneal hemostasis device (IPHD) prototype and evaluated its ability for slowing NCTH and prolonging survival in a porcine model of lethal abdominal multiorgan hemorrhage.

Methods: Yorkshire male swine (N = 8) were instrumented under general anesthesia for monitoring of hemodynamics and blood sampling. Animals were subjected to a 30% controlled arterial hemorrhage followed by lacerating combinations of the liver, spleen, and kidney. The abdomen was closed and after 2 minutes of NCTH, and the IPHD was inserted into the peritoneal cavity via an introducer (n = 5). The balloon was inflated and maintained for 60 minutes. At 60 minutes postdeployment, the balloon was deflated and removed, and blood resuscitation was initiated followed by gauze packing for hemostasis. The remaining animals (n = 3) were used as controls and subjected to the same injury without intervention.

Results: All animals managed with IPHD intervention (5 of 5 swine) survived the duration of the intervention period (60 minutes), while all control animals (3 of 3 swine) died at a time range of 15 to 43 minutes following organ injury (p = 0.0042). Animals receiving IPHD remained hemodynamically stable with a mean arterial pressure range of 44.86 to 55.10 mm Hg and experienced increased cardiac output and decreased shock index after treatment. Controls experienced hemodynamic decline in all parameters until endpoints were met. Upon IPHD deflation and removal, all treated animals began to hemorrhage again and expired within 2 to 132 minutes despite packing.

Conclusion: Our data show that the IPHD concept is capable of prolonging survival by temporarily stanching lethal NCTH of the abdomen. This device may be an effective temporary countermeasure to NCTH of the abdomen that could be deployed in the prehospital environment or as a bridge to more advanced therapy.
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http://dx.doi.org/10.1097/TA.0000000000003091DOI Listing
May 2021

A human brain test bed for research in large vessel occlusion stroke.

J Neurosurg 2021 Jan 22:1-9. Epub 2021 Jan 22.

1Department of Neurosurgery, University of Michigan, Ann Arbor, Michigan.

Objective: Endovascular removal of emboli causing large vessel occlusion (LVO)-related stroke utilizing suction catheter and/or stent retriever technologies or thrombectomy is a new standard of care. Despite high recanalization rates, 40% of stroke patients still experience poor neurological outcomes as many cases cannot be fully reopened after the first attempt. The development of new endovascular technologies and techniques for mechanical thrombectomy requires more sophisticated testing platforms that overcome the limitations of phantom-based simulators. The authors investigated the use of a hybrid platform for LVO stroke constructed with cadaveric human brains.

Methods: A test bed for embolic occlusion of cerebrovascular arteries and mechanical thrombectomy was developed with cadaveric human brains, a customized hydraulic system to generate physiological flow rate and pressure, and three types of embolus analogs (elastic, stiff, and fragment-prone) engineered to match mechanically and phenotypically the emboli causing LVO strokes. LVO cases were replicated in the anterior and posterior circulation, and thrombectomy was attempted using suction catheters and/or stent retrievers.

Results: The test bed allowed radiation-free visualization of thrombectomy for LVO stroke in real cerebrovascular anatomy and flow conditions by transmural visualization of the intraluminal elements and procedures. The authors were able to successfully replicate 105 LVO cases with 184 passes in 12 brains (51 LVO cases and 82 passes in the anterior circulation, and 54 LVO cases and 102 passes in the posterior circulation). Observed recanalization rates in this model were graded using a Recanalization in LVO (RELVO) scale analogous to other measures of recanalization outcomes in clinical use.

Conclusions: The human brain platform introduced and validated here enables the analysis of artery-embolus-device interaction under physiological hemodynamic conditions within the unmodified complexity of the cerebral vasculature inside the human brain.
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http://dx.doi.org/10.3171/2020.7.JNS202278DOI Listing
January 2021

Gastroesophageal resuscitative occlusion of the aorta: Physiologic tolerance in a swine model of hemorrhagic shock.

J Trauma Acute Care Surg 2020 12;89(6):1114-1123

From the Department of Emergency Medicine (M.H.T., B.M.M., C.I.C., D.C.L., N.L.G., K.R.W.), Michigan Center for Integrative Research in Critical Care (M.H.T., B.M.M., C.I.C., J.S.P., D.C.L., N.L.G., S.C.W., A.J.S., J.L.E., K.R.W.), Biomedical Engineering (J.S.P., A.J.S., K.R.W.), Mechanical Engineering (J.S.P., A.J.S.), and Department of Surgery (J.S.P., S.C.W., J.L.E.), University of Michigan, Ann Arbor, Michigan.

Background: Resuscitative endovascular balloon occlusion of the aorta (REBOA) has been shown to be effective for management of noncompressible torso hemorrhage. However, this technique requires arterial cannulation, which can be time-consuming and not amendable to placement in austere environments. We present a novel, less invasive aortic occlusion device and technique designated gastroesophageal resuscitative occlusion of the aorta (GROA). In this study, we aimed to characterize the physiological tolerance and hemodynamic effects of a prototype GROA device in a model of severe hemorrhagic shock and resuscitation and compare with REBOA.

Methods: Swine (N = 47) were surgically instrumented for data collection. A 35% controlled arterial hemorrhage was followed by randomizing animals to 30-minute, 60-minute, or 90-minute interventions of GROA, REBOA, or control. Following intervention, devices were deactivated, and animals received whole blood and crystalloid resuscitation. Animals were monitored for an additional 4 hours.

Results: All animals except one GROA 90-minute application survived the duration of their intervention periods. Survival through resuscitation phase in GROA, REBOA, and control groups was similar in the 30-minute and 60-minute groups. The 90-minute occlusion groups exhibited deleterious effects upon device deactivation and reperfusion with two GROA animals surviving and no REBOA animals surviving. Mean (SD) arterial pressure in GROA and REBOA animals increased across all groups to 98 (31.50) mm Hg and 122 (24.79) mm Hg, respectively, following intervention. Lactate was elevated across all GROA and REBOA groups relative to controls during intervention but cleared by 4 hours in the 30-minute and 60-minute groups. Postmortem histological examination of the gastric mucosa revealed mild to moderate inflammation across all GROA groups.

Conclusion: In this study, the hemodynamic effects and physiological tolerance of GROA was similar to REBOA. The GROA device was capable of achieving high zone II full aortic occlusion and may be able to serve as an effective method of aortic impingement.
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http://dx.doi.org/10.1097/TA.0000000000002867DOI Listing
December 2020

Standardized Fabrication Method of Human-Derived Emboli with Histologic and Mechanical Quantification for Stroke Research.

J Stroke Cerebrovasc Dis 2020 Nov 7;29(11):105205. Epub 2020 Aug 7.

Department of Neurosurgery, University of Michigan, Ann Arbor, Michigan, USA; Department of Neurosurgery, Mayo Clinic, Rochester, Minnesota, USA. Electronic address:

Background: As access to patient emboli is limited, embolus analogs (EAs) have become critical to the research of large vessel occlusion (LVO) stroke and the development of thrombectomy technology. To date, techniques for fabricating standardized human blood-derived EAs are limited in the variety of compositions, and the mechanical properties relevant to thrombectomy are not quantified.

Methods: EAs were made by mixing human banked red blood cells (RBCs), plasma, and platelet concentrate in 10 different volumetric percentage combinations to mimic the broad range of patient emboli causing LVO strokes. The samples underwent histologic analysis and tensile testing to mimic the pulling action of thrombectomy devices, and were compared to patient emboli.

Results: EAs had histologic compositions of 0-96% RBCs, 0.78%-92% fibrin, and 2.1%-22% platelets, which can be correlated with the ingredients using a regression model. At fracture, EAs elongated from 81% to 136%, and the ultimate tensile stress ranged from 16 to 949 kPa. These EAs' histologic compositions and tensile properties showed great similarity to those of emboli retrieved from LVO stroke patients, indicating the validity of such EA fabrication methods. EAs with lower RBC and higher fibrin contents are more extensible and can withstand higher tensile stress.

Conclusions: EAs fabricated and tested using the proposed new methods provide a platform for stroke research and pre-clinical development of thrombectomy devices.
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http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2020.105205DOI Listing
November 2020

Tissue mimicking materials for imaging and therapy phantoms: a review.

Phys Med Biol 2020 Sep 30. Epub 2020 Sep 30.

National Physical Laboratory, Teddington, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND.

Tissue mimicking materials (TMMs), typically contained within phantoms, have been used for many decades in both imaging and therapeutic applications. This review investigates the specifications that are typically being used in development of the latest TMMs. The imaging modalities that have been investigated focus around CT, mammography, SPECT, PET, MRI and ultrasound. Therapeutic applications discussed within the review include radiotherapy, thermal therapy and surgical applications. A number of modalities were not reviewed including optical spectroscopy, optical imaging and planar x-rays. The emergence of image guided interventions and multimodality imaging have placed an increasing demand on the number of specifications on the latest TMMs. Material specification standards are available in some imaging areas such as ultrasound. It is recommended that this should be replicated for other imaging and therapeutic modalities. Materials used within phantoms have been reviewed for a series of imaging and therapeutic applications with the potential to become a testbed for cross-fertilization of materials across modalities. Deformation, texture, multimodality imaging and perfusion are common themes that are currently under development.
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http://dx.doi.org/10.1088/1361-6560/abbd17DOI Listing
September 2020

Ultrasound speckle tracking to detect vascular distensibility changes from angioplasty and branch ligation in a radio-cephalic fistula: Use of novel open source software.

J Vasc Access 2020 Sep 26:1129729820959910. Epub 2020 Sep 26.

VA Ann Arbor Healthcare System, Ann Arbor, MI, USA.

We used novel open source software, based on an ultrasound speckle tracking algorithm, to examine the distensibility of the vessel wall of the inflow artery, anastomosis, and outflow vein before and after two procedures. An 83-year-old white man with a poorly maturing radio-cephalic fistula received an angioplasty at the anastomosis followed by branch ligation 28 days later. Duplex Doppler measurements corroborated the blood flow related changes anticipated from the interventions. The experimental distensibility results showed that it is technically feasible to measure subtle vessel wall motion changes with high resolution (sub-millimeter) using standard Digital Imaging and Communications in Medicine (DICOM) ultrasound data, which are readily available on conventional ultrasound scanners. While this methodology was originally developed using high resolution radiofrequency from ultrasound data, the goal of this study was to use DICOM data, which makes this technology accessible to a wide range of users.
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http://dx.doi.org/10.1177/1129729820959910DOI Listing
September 2020

Construction of a comprehensive endovascular test bed for research and device development in mechanical thrombectomy in stroke.

J Neurosurg 2020 Apr 3;134(3):1190-1197. Epub 2020 Apr 3.

Departments of1Neurosurgery and.

Objective: The development of new endovascular technologies and techniques for mechanical thrombectomy in stroke has greatly relied on benchtop simulators. This paper presents an affordable, versatile, and realistic benchtop simulation model for stroke.

Methods: A test bed for embolic occlusion of cerebrovascular arteries and mechanical thrombectomy was developed with 3D-printed and commercially available cerebrovascular phantoms, a customized hydraulic system to generate physiological flow rate and pressure, and 2 types of embolus analogs (elastic and fragment-prone) capable of causing embolic occlusions under physiological flow.

Results: The test bed was highly versatile and allowed realistic, radiation-free mechanical thrombectomy for stroke due to large-vessel occlusion with rapid exchange of geometries and phantom types. Of the transparent cerebrovascular phantoms tested, the 3D-printed phantom was the easiest to manufacture, the glass model offered the best visibility of the interaction between embolus and thrombectomy device, and the flexible model most accurately mimicked the endovascular system during device navigation. None of the phantoms modeled branches smaller than 1 mm or perforating arteries, and none underwent realistic deformation or luminal collapse from device manipulation or vacuum. The hydraulic system created physiological flow rate and pressure leading to iatrogenic embolization during thrombectomy in all phantoms. Embolus analogs with known fabrication technique, structure, and tensile strength were introduced and consistently occluded the middle cerebral artery bifurcation under physiological flow, and their interaction with the device was accurately visualized.

Conclusions: The test bed presented in this study is a low-cost, comprehensive, realistic, and versatile platform that enabled high-quality analysis of embolus-device interaction in multiple cerebrovascular phantoms and embolus analogs.
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http://dx.doi.org/10.3171/2020.1.JNS192732DOI Listing
April 2020

Analysis of human emboli and thrombectomy forces in large-vessel occlusion stroke.

J Neurosurg 2020 Feb 28;134(3):893-901. Epub 2020 Feb 28.

Departments of3Neurosurgery and.

Objective: This study's purpose was to improve understanding of the forces driving the complex mechanical interaction between embolic material and current stroke thrombectomy devices by analyzing the histological composition and strength of emboli retrieved from patients and by evaluating the mechanical forces necessary for retrieval of such emboli in a middle cerebral artery (MCA) bifurcation model.

Methods: Embolus analogs (EAs) were generated and embolized under physiological pressure and flow conditions in a glass tube model of the MCA. The forces involved in EA removal using conventional endovascular techniques were described, analyzed, and categorized. Then, 16 embolic specimens were retrieved from 11 stroke patients with large-vessel occlusions, and the tensile strength and response to stress were measured with a quasi-static uniaxial tensile test using a custom-made platform. Embolus compositions were analyzed and quantified by histology.

Results: Uniaxial tension on the EAs led to deformation, elongation, thinning, fracture, and embolization. Uniaxial tensile testing of patients' emboli revealed similar soft-material behavior, including elongation under tension and differential fracture patterns. At the final fracture of the embolus (or dissociation), the amount of elongation, quantified as strain, ranged from 1.05 to 4.89 (2.41 ± 1.04 [mean ± SD]) and the embolus-generated force, quantified as stress, ranged from 63 to 2396 kPa (569 ± 695 kPa). The ultimate tensile strain of the emboli increased with a higher platelet percentage, and the ultimate tensile stress increased with a higher fibrin percentage and decreased with a higher red blood cell percentage.

Conclusions: Current thrombectomy devices remove emboli mostly by applying linear tensile forces, under which emboli elongate until dissociation. Embolus resistance to dissociation is determined by embolus strength, which significantly correlates with composition and varies within and among patients and within the same thrombus. The dynamic intravascular weakening of emboli during removal may lead to iatrogenic embolization.
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http://dx.doi.org/10.3171/2019.12.JNS192187DOI Listing
February 2020

Hollow Notched K-Wires for Bone Drilling With Through-Tool Cooling.

J Orthop Res 2019 11 1;37(11):2297-2306. Epub 2019 Aug 1.

Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan.

Kirschner wire (K-wire) is a common tool in clinical orthopedic surgery for bone fracture fixation. A significant amount of heat is generated in bone drilling using K-wires, causing bone thermal necrosis and osteonecrosis. To minimize the temperature rise, a hollow notched K-wire in a modified surgical hand drill with through-tool cooling was developed to study the bone temperature, debris evacuation, and material removal rate. The hollow notched K-wire was fabricated by grinding and micro-milling on a stainless steel tube. Bone drilling tests were conducted to evaluate its performance against the solid K-wires. Results showed that compared with solid K-wires, hollow notched K-wire drilling without cooling reduced the peak bone temperature rise, thrust force, and torque by 42%, 59%, and 62% correspondingly. The through-tool compressed air reduced the peak bone temperature rise by 48% with the forced air convection and better debris evacuation. The through-tool water cooling decreased the bone temperature by only 26% due to accumulation and blockage of bone debris in the groove and channel. This study demonstrated the benefit of using the hollow notched K-wire with through-tool compressed air to prevent the bone thermal necrosis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2297-2306, 2019.
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http://dx.doi.org/10.1002/jor.24419DOI Listing
November 2019

Evaluation of Heat Generation in Unidirectional Versus Oscillatory Modes During K-Wire Insertion in Bone.

J Orthop Res 2019 09 31;37(9):1903-1909. Epub 2019 May 31.

Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan.

Heat generation during insertion of Kirschner wires (K-wires) may lead to thermal osteonecrosis and can affect the construct fixation. Unidirectional and oscillatory drilling modes are options for K-wire insertion, but understanding of the difference in heat generation between the two modes is lacking. The goal of this study was to compare the temperature rise during K-wire insertion under these two modes and provide technical guidelines for K-wire placement to minimize thermal injury. Ten orthopedic surgeons were instructed to drill holes on hydrated ex vivo bovine bones under two modes. The drilling trials were evaluated in terms of temperature, thrust force, torque, drilling time, and tool wear. The analysis of variance showed that the oscillatory mode generated significantly lowered peak bone temperature rise (13% lower mean value, p = 0.036) over significantly longer drilling time (46% higher mean time, p < 0.001) than the unidirectional mode. Drilling time had significant effect on peak bone temperature rise under both modes (p < 0.001) and impact of peak thrust force was significant under oscillatory mode (p < 0.001). These findings suggest that the drilling mode choice is a compromise between peak temperature and bone exposure time. Shortening the drilling time was the key under both modes to minimize temperature rise and thermal necrosis risk. To achieve faster drilling, technique analysis found that "shaky" and intermittent drilling with moderate thrust force are preferred techniques by small vibration of the drill about the K-wire axis and slight lift-up of the K-wire once or twice during drilling. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1903-1909, 2019.
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http://dx.doi.org/10.1002/jor.24345DOI Listing
September 2019

Continuous Inferior Vena Cava Diameter Tracking through an Iterative Kanade-Lucas-Tomasi-Based Algorithm.

Ultrasound Med Biol 2018 12 11;44(12):2793-2801. Epub 2018 Sep 11.

Department of Emergency Medicine, University of Michigan, Ann Arbor, Michigan, USA; Michigan Center for Integrative Research in Critical Care (MCIRCC), University of Michigan, Ann Arbor, Michigan, USA.

Ultrasound assessment of the respiratory-induced change in size of the inferior vena cava is a useful technique in the evaluation and management of critically ill patients. We have developed an automated technique based on the Kanade-Lucas-Tomasi feature tracker and pyramidal segmentation to continuously track the diameter of the inferior vena cava during ultrasound. To test the accuracy of this automated process, the inferior vena cava of 47 spontaneously breathing patients were measured by trained ultrasound physicians and compared against the results obtained via the automated tracking. Good agreement between the techniques was found, with intra-class correlation coefficients for maximum vessel diameter, minimum diameter and caval index of 0.897, 0.967 and 0.975, respectively. More than 95% of the difference between physicians and automated measurements agreed to within 10% of the inferior vena cava collapse. Furthermore a phenomenon of cardiac collapsibility index variability was observed and reported. The accuracy and precision of this algorithmic technique provide a foundation for future automated measures for critical care ultrasound.
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http://dx.doi.org/10.1016/j.ultrasmedbio.2018.07.022DOI Listing
December 2018

3D Printed composite for simulating thermal and mechanical responses of the cortical bone in orthopaedic surgery.

Med Eng Phys 2018 11 1;61:61-68. Epub 2018 Sep 1.

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, United States.

Synthetic bones made of polyurethane (PU) foams or glass-fiber reinforced epoxy are often used in surgical training, planning, and tool analysis, but these materials cannot be 3D printed for a patient-specific design. This paper introduces a new type of bone-mimicking material made by the binder jetting technology and a post-strengthening process with epoxy, namely 3D polymer-infiltrated composite (3DPIC). 3DPIC has been previously evaluated by surgeons as a proper alternative to commercial synthetic bones, but no quantitative testing data is available. Therefore, a series of experiments are conducted in this study to verify the use of 3DPIC. The first part of experiments includes the measurement of mechanical properties using the four-point bending and the measurement of thermal properties. The second part of experiments is to test drilling haptic and thermal responses of 3DPIC as compared to the cortical bone. The results show that 3DPIC has a comparable elastic modulus but a lower strength than the cortical bone. 3DPIC can produce realistic drilling force and torque as well as representative temperature change in drilling operations, but the bone debris tends to be more ductile and continuous than that of the cortical bone. Applications and limitations of 3DPIC are discussed based on these results.
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http://dx.doi.org/10.1016/j.medengphy.2018.08.004DOI Listing
November 2018

Computational Fluid Dynamics Modeling of the Burr Orbital Motion in Rotational Atherectomy with Particle Image Velocimetry Validation.

Ann Biomed Eng 2018 Apr 24;46(4):567-578. Epub 2018 Jan 24.

Department of Mechanical Engineering, University of Michigan, 2350 Hayward, Ann Arbor, MI, 48109, USA.

Rotational atherectomy (RA) uses a high-speed rotating burr introduced via a catheter through the artery to remove hardened atherosclerotic plaque. Current clinical RA technique lacks consensus on burr size and rotational speed. The rotating burr orbits inside the artery due to the fluid force of the blood. Different from a common RA technique of upsizing burrs for larger luminal gain, a small burr can orbit to treat a large lumen. A 3D computational fluid dynamics (CFD) model was developed to simulate the burr motion and study the fluid flow and force in RA. A particle image velocimetry experiment was conducted to measure and validate the flow field including the radial and axial velocities and a pair of counter-rotating vortices near the burr equator in CFD. The hydraulic force on the burr and the contact force between the burr and the arterial wall were estimated by CFD. The contact force can be reduced by using smaller burr and lower rotational speed. Utilizing the small burr orbital motion has the potential to be an improved RA technique.
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http://dx.doi.org/10.1007/s10439-018-1984-zDOI Listing
April 2018

An experimental study and finite element modeling of head and neck cooling for brain hypothermia.

J Therm Biol 2018 Jan 4;71:99-111. Epub 2017 Nov 4.

Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.

Reducing brain temperature by head and neck cooling is likely to be the protective treatment for humans when subjects to sudden cardiac arrest. This study develops the experimental validation model and finite element modeling (FEM) to study the head and neck cooling separately, which can induce therapeutic hypothermia focused on the brain. Anatomically accurate geometries based on CT images of the skull and carotid artery are utilized to find the 3D geometry for FEM to analyze the temperature distributions and 3D-printing to build the physical model for experiment. The results show that FEM predicted and experimentally measured temperatures have good agreement, which can be used to predict the temporal and spatial temperature distributions of the tissue and blood during the head and neck cooling process. Effects of boundary condition, perfusion, blood flow rate, and size of cooling area are studied. For head cooling, the cooling penetration depth is greatly depending on the blood perfusion in the brain. In the normal blood flow condition, the neck internal carotid artery temperature is decreased only by about 0.13°C after 60min of hypothermia. In an ischemic (low blood flow rate) condition, such temperature can be decreased by about 1.0°C. In conclusion, decreasing the blood perfusion and metabolic reduction factor could be more beneficial to cool the core zone. The results also suggest that more SBC researches should be explored, such as the optimization of simulation and experimental models, and to perform the experiment on human subjects.
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http://dx.doi.org/10.1016/j.jtherbio.2017.10.022DOI Listing
January 2018

Influence of non-invasive blood pressure measurement intervals on the occurrence of intra-operative hypotension.

J Clin Monit Comput 2018 Aug 30;32(4):699-705. Epub 2017 Sep 30.

Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA.

The American Society of Anesthesiologists Standards for Basic Monitoring recommends blood pressure (BP) measurement every 5 min. Research has shown distractions or technical factors can cause prolonged measurement intervals exceeding 5 min. We investigated the relationship between prolonged non-invasive BP (NIBP) measurement interval and the incidence of hypotension, detected post-interval. Our secondary outcome was to determine independent predictors of these prolonged NIBP measurement intervals. Retrospective data were analyzed from 139,509 general anesthesia cases from our institution's Anesthesia Information Management System (AIMS). Absolute hypotension (AH) was defined a priori as a systolic BP < 80 mmHg and relative hypotension (RH) was defined as a 40% decrease in systolic BP from the preoperative baseline. Odds ratios (OR) with 95% confidence intervals and Pearson's Chi square Test reported the association of prolonged NIBP measurement intervals on hypotension detected post-NIBP measurement interval. Logistic regression models were developed to determine independent predictors of NIBP measurement intervals. The analysis revealed that NIBP measurement intervals greater than 6 and 10 min are associated with an approximately four times higher incidence of a patient transitioning into hypotension (AH/RH > 6 min OR 4.0 / 3.6; AH/RH > 10 min OR 4.3 / 3.9; p < 0.001). A key finding was that the "> 10-minute AH model" indicated that age 41-80, increased co-morbidity profile, obesity and turning (repositioning) of the operative room table were significant predictors of prolonged NIBP measurement intervals (p < 0.001). While we do not suggest NIBP measurement intervals cause hypotension, intervals greater than 6 and 10 min are associated with a fourfold increase in the propensity of an undetected transition into both RH or AH. These data support current monitoring guidelines.
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http://dx.doi.org/10.1007/s10877-017-0065-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6138874PMC
August 2018

An Open-Source Ultrasound Software for Diagnosis of Fistula Maturation.

ASAIO J 2018 Jan/Feb;64(1):70-76

Vascular access is essential for hemodialysis patients. The mature native arteriovenous fistula has been the preferred vascular access for hemodialysis, because it has greater longevity than synthetic grafts. However, once surgically created, fistulas often fail to develop (mature) into viable points of vascular access, requiring surgical or radiologic interventions before their use. Because maturation depends on vascular mechanics (e.g., distensibility and wall shear), we developed open-source ultrasound software to investigate these metrics clinically. We demonstrated in a single patient the ability of the software for consistent measurements from various locations within a cardiac cycle and between different cardiac cycles. We further assessed the ability of the software to identify changes in distensibility of a patient's fistula from 1 to 6 weeks postoperation. The routine frame rates of clinical machines demonstrated high fidelity tracking within cardiac cycles (coefficient of variation [CV] = 2.4% ± 0.011) and between cardiac cycles (CV = 2.4% ± 0.004). The distensibility of the patient's fistula from 1 to 6 weeks postoperation increased from 4% to 7% in the arterial inflow and from 3% to 4% in the postarterial anastomotic segment (PAAS). In contrast, the distensibility of the outflow vein decreased from 4% to 2%. These results corroborate that in addition to diameter changes, the mechanical properties of the vascular segments changed during fistula maturation. This demonstrates that our software-based approach may allow ultrasound-based mechanical measurements to become more accessible for wider clinical research.
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http://dx.doi.org/10.1097/MAT.0000000000000590DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5677585PMC
July 2018

Effects of geometry and material on the insertion of very small neural electrode.

Annu Int Conf IEEE Eng Med Biol Soc 2016 Aug;2016:2784-2788

For neural probes to be used chronically for years in the human body, they must provoke minimal scarring. Recently, a number of groups have reported substantially reduced scar tissue using cellular scale electrodes below 15 μm in size. This size scale is accessible to manufacturing techniques, but can be very difficult to insert in the brain for most common electrode materials. In this study, we explore the design space available to cellular scale electrodes that will self-insert into the brain. First a mathematical model is developed using beam buckling equations for different materials and geometries. Buckling mode was found to be one fixed and one hinged end resulting in a mode conditional constant of, n, 2.045. Model predicts insertion success between 90-100% for a 6.8 μm diameter electrode and was used to approximate applied force as 750 μN which is close to reference data of 780 μN [1]. Second, we developed a PVC phantom that mimics the brain's elastic modulus. This phantom was matched to insertion success data obtained from carbon fiber arrays [1]. Overall, these results enable studies to be conducted on other proposed cellular scale electrodes prior to animal testing or large scale fabrication.
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http://dx.doi.org/10.1109/EMBC.2016.7591308DOI Listing
August 2016

Simulator and 2 tools: Validation of performance measures from a novel neurosurgery simulation model using the current Standards framework.

Surgery 2016 09 27;160(3):571-9. Epub 2016 May 27.

Department of Neurosurgery, University of Michigan, Ann Arbor, MI.

Background: Ventriculostomy is a common neurosurgical procedure with a relatively steep learning curve. A low-cost, high-fidelity simulator paired with procedure-specific performance measures would provide a safe environment to teach ventriculostomy procedural skills. The same validated simulation model could also allow for assessment of trainees' proficiencies with measures that align with Accreditation Council for Graduate Medical Education milestones. This study extends previous work to evaluate validity evidence from the simulator, its newly developed performance assessment, the Ventricolostomy Procedural Assessment Tool, and the Objective Structured Assessment for Technical Skills.

Methods: After Institutional Review Board exemption, performance data were collected from 11 novice and 3 expert neurosurgeons (n = 14). Participants self-reported their ability to perform tasks on the simulator using the Ventricolostomy Procedural Assessment Tool, an 11-item, step-wise instrument with 5-point rating scales ranging from 1 (unable to perform) to 5 (performs easily and smoothly). De-identified operative performances were videotaped and independently rated by 3 neurosurgeons, using the Ventricolostomy Procedural Assessment Tool and Objective Structured Assessment for Technical Skills. We evaluated multiple sources of validity evidence (2014 Standards) to examine psychometric quality of the measures and to test our assumption that the tools could discriminate between novice and expert performances adequately. We used a multifacet Rasch model and traditional indices, such as Cronbach alpha, intraclass correlation, and Wilcoxon signed-rank test estimates.

Results: Validity evidence relevant to test content and response processes was supported adequately. Evidence of internal structure was supported by high interitem consistency (n = 0.95) and inter-rater agreement for most Ventricolostomy Procedural Assessment Tool items (Intraclass correlation coefficient = [0.00, 0.91]) and all Objective Structured Assessment for Technical Skills items (Intraclass correlation coefficient = [0.80, 0.93]). Overall, novices performed at a lower level than experts on both scales (P < .05), supporting evidence relevant to relationships to other variables. Deeper analysis of novice/expert ratings indicated novices attained lower performances ratings for all Ventricolostomy Procedural Assessment Tool and Objective Structured Assessment for Technical Skills items, but statistical significance was only achieved for the Objective Structured Assessment for Technical Skills items (P < .01). Rater bias estimates were favorable, supporting evidence relevant to consequences of testing.

Conclusion: Despite a small sample, favorable evidence using current Standards supports the use of the novel simulator and both tools combined for skills training and performance assessment, but challenges (potential threats to validity) should be considered prior to implementation.
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http://dx.doi.org/10.1016/j.surg.2016.03.035DOI Listing
September 2016

Experimental investigation of the abrasive crown dynamics in orbital atherectomy.

Med Eng Phys 2016 07 6;38(7):639-647. Epub 2016 May 6.

Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA; Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA. Electronic address:

Orbital atherectomy is a catheter-based minimally invasive procedure to modify the plaque within atherosclerotic arteries using a diamond abrasive crown. This study was designed to investigate the crown motion and its corresponding contact force with the vessel. To this end, a transparent arterial tissue-mimicking phantom made of polyvinyl chloride was developed, a high-speed camera and image processing technique were utilized to visualize and quantitatively analyze the crown motion in the vessel phantom, and a piezoelectric dynamometer measured the forces on the phantom during the procedure. Observed under typical orbital atherectomy rotational speeds of 60,000, 90,000, and 120,000rpm in a 4.8mm caliber vessel phantom, the crown motion was a combination of high-frequency rotation at 1000, 1500, and 1660.4-1866.1Hz and low-frequency orbiting at 18, 38, and 40Hz, respectively. The measured forces were also composed of these high and low frequencies, matching well with the rotation of the eccentric crown and the associated orbital motion. The average peak force ranged from 0.1 to 0.4N at different rotational speeds.
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http://dx.doi.org/10.1016/j.medengphy.2016.04.006DOI Listing
July 2016

Dynamic Limb Bioimpedance and Inferior Vena Cava Ultrasound in Patients Undergoing Hemodialysis.

ASAIO J 2016 Jul-Aug;62(4):463-9

From the *Department of Emergency Medicine, †Department of Biomedical Engineering, ‡Division of Nephrology, Department of Internal Medicine, §Department of Mechanical Engineering, and ¶Michigan Center for Integrative Research in Critical Care (MCIRCC), University of Michigan, Ann Arbor, Michigan.

Assessment of volume status in critically ill patients poses a challenge to clinicians. Measuring changes in the inferior vena cava (IVC) diameter using ultrasound is becoming a standard tool to assess volume status. Ultrasound requires physicians with significant training and specialized expensive equipment. It would be of significant value to be able to obtain this measurement continuously without physician presence. We hypothesize that dynamic changes in limb's bioimpedance in response to respiration could be used to predict changes in IVC. Forty-six subjects were tested a hemodialysis session. Impedance was measured via electrodes placed on the arm. Simultaneously, the IVC diameter was assessed by ultrasound. Subjects were asked to breathe spontaneously and perform respiratory maneuvers using a respiratory training device. Impedance (dz) was determined and compared with change in IVC diameter (dIVC; r = 0.76, p < 0.0001). There was significant relationship between dz and dIVC (p< 0.0001). Receiver-operator curves for dz at thresholds of dIVC (20% to70%) demonstrated high predictive power with areas under the curves (0.87-0.99, p < 0.0001). This evaluation suggests that real-time dynamic changes in limb impedance are capable of tracking a wide range of dynamic dIVC. This technique might be a suitable surrogate for monitoring real-time changes in dIVC to assess intravascular volume status.
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http://dx.doi.org/10.1097/MAT.0000000000000355DOI Listing
November 2017

Two-Finger Tightness: What Is It? Measuring Torque and Reproducibility in a Simulated Model.

J Orthop Trauma 2016 May;30(5):273-7

*Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, MI;†Department of Mechanical Engineering, Texas A&M University, College Station, TX;‡Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI.

Objectives: Residents in training are often directed to insert screws using "two-finger tightness" to impart adequate torque but minimize the chance of a screw stripping in bone. This study seeks to quantify and describe two-finger tightness and to assess the variability of its application by residents in training.

Methods: Cortical bone was simulated using a polyurethane foam block (30-pcf density) that was prepared with predrilled holes for tightening 3.5 × 14-mm long cortical screws and mounted to a custom-built apparatus on a load cell to capture torque data. Thirty-three residents in training, ranging from the first through fifth years of residency, along with 8 staff members, were directed to tighten 6 screws to two-finger tightness in the test block, and peak torque values were recorded. The participants were blinded to their torque values.

Results: Stripping torque (2.73 ± 0.56 N·m) was determined from 36 trials and served as a threshold for failed screw placement. The average torques varied substantially with regard to absolute torque values, thus poorly defining two-finger tightness. Junior residents less consistently reproduced torque compared with other groups (0.29 and 0.32, respectively).

Conclusions: These data quantify absolute values of two-finger tightness but demonstrate considerable variability in absolute torque values, percentage of stripping torque, and ability to consistently reproduce given torque levels. Increased years in training are weakly correlated with reproducibility, but experience does not seem to affect absolute torque levels. These results question the usefulness of two-finger tightness as a teaching tool and highlight the need for improvement in resident motor skill training and development within a teaching curriculum. Torque measuring devices may be a useful simulation tools for this purpose.
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http://dx.doi.org/10.1097/BOT.0000000000000506DOI Listing
May 2016

A physical simulator for endoscopic endonasal drilling techniques: technical note.

J Neurosurg 2016 Mar 4;124(3):811-6. Epub 2015 Sep 4.

Learning Health Sciences, University of Michigan, Ann Arbor, Michigan.

In this paper, the authors present a physical model developed to teach surgeons the requisite drilling techniques when using an endoscopic endonasal approach (EEA) to the skull base. EEA is increasingly used for treating pathologies of the ventral and ventrolateral cranial base. Endonasal drilling is a unique skill in terms of the instruments used, the long reach required, and the restricted angulation, and gaining competency requires much practice. Based on the successful experience in creating custom simulators, the authors used 3D printing to build an EEA training model from post-processed thin-cut head CT scans, formulating the materials to provide realistic haptic feedback and endoscope handling. They performed a preliminary assessment at 2 institutions to evaluate content validity of the simulator as the first step of the validation process. Overall results were positive, particularly in terms of bony landmarks and haptic response, though minor refinements were suggested prior to use as a training device.
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http://dx.doi.org/10.3171/2015.3.JNS1552DOI Listing
March 2016

Numerical evaluation of sequential bone drilling strategies based on thermal damage.

Med Eng Phys 2015 Sep 7;37(9):855-61. Epub 2015 Jul 7.

Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, United States ; Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, United States.

Sequentially drilling multiple holes in bone is used clinically for surface preparation to aid in fusion of a joint, typically under non-irrigated conditions. Drilling induces a significant amount of heat and accumulates after multiple passes, which can result in thermal osteonecrosis and various complications. To understand the heat propagation over time, a 3D finite element model was developed to simulate sequential bone drilling. By incorporating proper material properties and a modified bone necrosis criteria, this model can visualize the propagation of damaged areas. For this study, comparisons between a 2.0 mm Kirschner wire and 2.0 mm twist drill were conducted with their heat sources determined using an inverse method and experimentally measured bone temperatures. Three clinically viable solutions to reduce thermally-induced bone damage were evaluated using finite element analysis, including tool selection, time interval between passes, and different drilling sequences. Results show that the ideal solution would be using twist drills rather than Kirschner wires if the situation allows. A shorter time interval between passes was also found to be beneficial as it reduces the total heat exposure time. Lastly, optimizing the drilling sequence reduced the thermal damage of bone, but the effect may be limited. This study demonstrates the feasibility of using the proposed model to study clinical issues and find potential solutions prior to clinical trials.
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http://dx.doi.org/10.1016/j.medengphy.2015.06.002DOI Listing
September 2015

Development of a 3D-printed external ventricular drain placement simulator: technical note.

J Neurosurg 2015 Oct 26;123(4):1070-6. Epub 2015 Jun 26.

Neurosurgery, and.

In this paper, the authors present a physical model developed to simulate accurate external ventricular drain (EVD) placement with realistic haptic and visual feedbacks to serve as a platform for complete procedural training. Insertion of an EVD via ventriculostomy is a common neurosurgical procedure used to monitor intracranial pressures and/or drain CSF. Currently, realistic training tools are scarce and mainly limited to virtual reality simulation systems. The use of 3D printing technology enables the development of realistic anatomical structures and customized design for physical simulators. In this study, the authors used the advantages of 3D printing to directly build the model geometry from stealth head CT scans and build a phantom brain mold based on 3D scans of a plastinated human brain. The resultant simulator provides realistic haptic feedback during a procedure, with visualization of catheter trajectory and fluid drainage. A multiinstitutional survey was also used to prove content validity of the simulator. With minor refinement, this simulator is expected to be a cost-effective tool for training neurosurgical residents in EVD placement.
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http://dx.doi.org/10.3171/2014.12.JNS141867DOI Listing
October 2015
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