A Novel Patient-Specific Computational Fluid Dynamics Study of the Activation of Primary Collateral Pathways in the Circle of Willis During Vasospasm.

The Circle of Willis (CoW) is a redundant network of blood vessels that perfuses the brain. The ringlike anatomy mitigates the negative effects of stroke by activating collateral pathways that help maintain physiological perfusion. Previous studies have investigated the activation of these pathways during embolic stroke and internal carotid artery occlusion. However, the role of collateral pathways during cerebral vasospasm-an involuntary constriction of blood vessels after subarachnoid hemorrhage-is not well-documented. This study presents a novel technique to create patient-specific computational fluid dynamics (CFD) simulations of the Circle of Willis before and during vasospasm. Computed tomographic angiography (CTA) scans are segmented to model the vasculature, and transcranial Doppler ultrasound (TCD) measurements of blood flow velocity are applied as boundary conditions. Bayesian analysis leverages information about the uncertainty in the measurements of vessel diameters and velocities to find an optimized parameter set that satisfies mass conservation and that is applied in the final simulation. With this optimized parameter set, the diameters, velocities, and flow rates fall within typical literature values. Virtual angiograms modeled using passive scalar transport agree closely with clinical angiography. A sensitivity analysis quantifies the changes in collateral flow rates with respect to changes in the inlet and outlet flow rates. This analysis can be applied in the future to a cohort of patients to investigate the relationship between the locations and severities of vasospasm, the patient-to-patient anatomical variability in the Circle of Willis, and the activation of collateral pathways.

Transesophageal echocardiography simulation: A review of current technology.

Transesophageal echocardiography (TEE) has experienced tremendous increase in interest and demand alongside the rapid growth of transcatheter structural cardiac interventions. TEE instruction prolongs the procedure, increasing the risk of probe malfunction from overheating and patient complications from prolonged sedation. Echocardiographic simulation programs have been developed to hone the procedural skills of novice operators in a time-unrestricted, low-pressure environment before they perform TEEs on real patients. Simulators likely benefit training in interventional TEE for the same reasons. We searched PubMed, basic Google, and Google Scholar for currently marketed TEE simulators, including foreign as well as US companies. We queried the vendors regarding features of the simulators that pertain to effective instructional design for diagnostic TEE. We also queried regarding the simulators' applicability to training in interventional TEE. The vendors' responses are reported here. In addition, we discuss the specific training needs for structural heart interventions, for which echocardiographic simulation could be a powerful educational tool. Lastly, we discuss the role of simulation for formative and summative assessment, and the advances required to improve training in complex procedures within the field of interventional echocardiography.

Focused cardiac ultrasound training in medical students: Using an independent, simulator-based curriculum to objectively measure skill acquisition and learning curve.

BACKGROUND: Using simulators built and validated at the University of Washington (UW), the study sought to test whether medical students can learn the basic skills of focused cardiac ultrasound (FoCUS) from an individually paced, simulator-based curriculum, how skills improve, and the rate at which these skills are acquired. METHODS: The curriculum presented didactic material interspersed with hands-on practice. Psychomotor skill was measured by the angle error of the acquired image view plane relative to the correct image view plane. The rate of learning was assessed at baseline, after 7 practice cases, and after 10 cases. To assess the rate of learning, the same case was repeatedly presented at all three tests. To assess students' ability to apply their learning, a previously unseen post-test was included. RESULTS: A total of 41 students completed the course. Average angle error improved from 43° ± 24 pretraining to 23° ± 16 post-training, with most students falling within one SD of the view angle acquired by sonographers. Regarding learning curve, or the rate of skill acquisition, an angle error of 43 ± 24° (pre) changed to 22 ± 14° (interim test, P < .0001 vs. pretest) and remained at that level for the post-test evaluation on both the repeated case (23 ± 16°) and the new case (26 ± 18°). CONCLUSIONS: This study describes the learning curve and technical skill acquisition in FoCUS. A simulator-based curriculum improved medical student's skills in an objective and quantifiable manner. The individually paced curriculum allowed for independent knowledge and skill attainment, without facilitator oversight.

Simulation for competency assessment in vascular and cardiac ultrasound.

Healthcare providers who use peripheral vascular and cardiac ultrasound require specialized training to develop the technical and interpretive skills necessary to perform accurate diagnostic tests. Assessment of competence is a critical component of training that documents a learner's progress and is a requirement for competency-based medical education (CBME) as well as specialty certification or credentialing. The use of simulation for CBME in diagnostic ultrasound is particularly appealing since it incorporates both the psychomotor and cognitive domains while eliminating dependency on the availability of live patients with a range of pathology. However, successful application of simulation in this setting requires realistic, full-featured simulators and appropriate standardized metrics for competency testing. The principal diagnostic parameter in peripheral vascular ultrasound is measurement of peak systolic velocity (PSV) on Doppler spectral waveforms, and simulation of Doppler flow detection presents unique challenges. The computer-based duplex ultrasound simulator developed at the University of Washington uses computational fluid dynamics modeling and presents real-time color-flow Doppler images and Doppler spectral waveforms along with the corresponding B-mode images. This simulator provides a realistic scanning experience that includes measuring PSV in various arterial segments and applying actual diagnostic criteria. Simulators for echocardiography have been available since the 1990s and are currently more advanced than those for peripheral vascular ultrasound. Echocardiography simulators are now offered for both transesophageal echo and transthoracic echo. These computer-based simulators have 3D graphic displays that provide feedback to the learner and metrics for assessment of technical skill that are based on transducer tracking data. Such metrics provide a motion-based or kinematic analysis of skill in performing cardiac ultrasound. The use of simulation in peripheral vascular and cardiac ultrasound can provide a standardized and readily available method for training and competency assessment.

Numerical Modeling of Flow in the Cerebral Vasculature: Understanding Changes in Collateral Flow Directions in the Circle of Willis for a Cohort of Vasospasm Patients Through Image-Based Computational Fluid Dynamics.

The Circle of Willis (CoW) is a ring-like network of blood vessels that perfuses the brain. Flow in the collateral pathways that connect major arterial inputs in the CoW change dynamically in response to vessel narrowing or occlusion. Vasospasm is an involuntary constriction of blood vessels following subarachnoid hemorrhage (SAH), which can lead to stroke. This study investigated interactions between localization of vasospasm in the CoW, vasospasm severity, anatomical variations, and changes in collateral flow directions. Patient-specific computational fluid dynamics (CFD) simulations were created for 25 vasospasm patients. Computed tomographic angiography scans were segmented capturing the anatomical variation and stenosis due to vasospasm. Transcranial Doppler ultrasound measurements of velocity were used to define boundary conditions. Digital subtraction angiography was analyzed to determine the directions and magnitudes of collateral flows as well as vasospasm severity in each vessel. Percent changes in resistance and viscous dissipation were analyzed to quantify vasospasm severity and localization of vasospasm in a specific region of the CoW. Angiographic severity correlated well with percent changes in resistance and viscous dissipation across all cerebral vessels. Changes in flow direction were observed in collateral pathways of some patients with localized vasospasm, while no significant changes in flow direction were observed in others. CFD simulations can be leveraged to quantify the localization and severity of vasospasm in SAH patients. These factors as well as anatomical variation may lead to changes in collateral flow directions. Future work could relate localization and vasospasm severity to clinical outcomes like the development of infarct.

Echo simulator with novel training and competency testing tools.

We developed and validated an echo simulator with three novel tools that facilitate training and enable quantitative and objective measurement of psychomotor as well as cognitive skill. First, the trainee can see original patient images - not synthetic or simulated images - that morph in real time as the mock transducer is manipulated on the mannequin. Second, augmented reality is used for Visual Guidance, a tool that assists the trainee in scanning by displaying the target organ in 3-dimensions (3D) together with the location of the current view plane and the plane of the anatomically correct view. Third, we introduce Image Matching, a tool that leverages the aptitude of the human brain for recognizing similarities and differences to help trainees learn to perform visual assessment of ultrasound images. Psychomotor competence is measured in terms of the view plane angle error. The construct validity of the simulator for competency testing was established by demonstrating its ability to discriminate novices vs. experts.

Formative Assessment of Performance in Diagnostic Ultrasound Using Simulation and Quantitative and Objective Metrics.

BACKGROUND: We developed simulator-based tools for assessing provider competence in transthoracic echocardiography (TTE) and vascular duplex scanning. METHODS: Psychomotor (technical) skill in TTE image acquisition was calculated from the deviation angle of an acquired image from the anatomically correct view. We applied this metric for formative assessment to give feedback to learners and evaluate curricula.Psychomotor skill in vascular ultrasound was measured in terms of dexterity and image plane location; cognitive skill was assessed from measurements of blood flow velocity, parameter settings, and diagnosis. The validity of the vascular simulator was assessed from the accuracy with which experts can measure peak systolic blood flow velocity (PSV). RESULTS: In the TTE simulator, the skill metric enabled immediate feedback, formative assessment of curriculum efficacy, and comparison of curriculum outcomes. The vascular duplex ultrasound simulator also provided feedback, and experts' measurements of PSV deviated from actual PSV in the model by <10%. CONCLUSIONS: Skill in acquiring diagnostic ultrasound images of organs and vessels can be measured using simulation in an objective, quantitative, and standardized manner. Current applications are provision of feedback to learners to enable training without direct faculty oversight and formative assessment of curricula. Simulator-based metrics could also be applied for summative assessment.

Analysis of Factors Influencing Accuracy of Volume Flow Measurement in Dialysis Access Fistulas Based on Duplex Ultrasound Simulation.

OBJECTIVE: We developed a duplex ultrasound simulator and used it to assess accuracy of volume flow measurements in dialysis access fistula (DAF) models. METHODS: The simulator consists of a mannequin, computer, and mock transducer. Each case is built from a patient's B-mode images that are used to create a 3-dimensional surface model of the DAF. Computational fluid dynamics is used to determine blood flow velocities based on model vessel geometry. The simulator displays real-time B-mode and color-flow images, and Doppler spectral waveforms are generated according to user-defined settings. Accuracy was assessed by scanning each case and measuring volume flow in the inflow artery and outflow vein for comparison with true volume flow values. RESULTS: Four examiners made 96 volume flow measurements on four DAF models. Measured volume flow deviated from the true value by 35 ± 36%. Mean absolute deviation from true volume flow was lower for arteries than veins (22 ± 19%, N = 48 vs. 58 ± 33%, N = 48, p < 0.0001). This finding is attributed to eccentricity of outflow veins which resulted in underestimating true cross-sectional area. Regression analysis indicated that error in measuring cross-sectional area was a predictor of error in volume flow measurement (ß = 0.948, p < 0.001). Volume flow error was reduced from 35 ± 36% to 9 ± 8% (p < 0.000001) by calculating vessel area as an ellipse. CONCLUSIONS: Duplex volume flow measurements are based on a circular vessel shape. DAF inflow arteries are circular, but outflow veins can be elliptical. Simulation-based analysis showed that error in measuring volume flow is mainly due to assumption of a circular vessel.

Three-dimensional shape analysis of right ventricular remodeling in repaired tetralogy of Fallot.

Understanding of right ventricular (RV) remodeling is needed to elucidate the mechanism of RV dysfunction in the overloaded right ventricle, but is hampered by the chamber's complex shape. We imaged 15 patients with repaired tetralogy of Fallot (TOF) and 8 normal subjects by magnetic resonance imaging in long- and short-axis views. We reconstructed the right ventricles in 3 dimensions using the piecewise smooth subdivision surface method. Shape was analyzed from cross-sectional contours generated by intersecting the right ventricle with 20 planes evenly spaced from apex to tricuspid annulus. Patients with TOF had dilated right ventricles compared with normal (end-diastolic volume index 216 +/- 99 vs 81 +/- 16 ml/m(2), p <0.001) but near-normal function (ejection fraction 40 +/- 9% vs 48 +/- 12%, respectively, p = NS). RV shape in patients with TOF differed from normal subjects in several ways. First, the right ventricle had a larger normalized cross-sectional area in patients with TOF (p <0.01 in apical planes). Second, the cross-sectional shape was rounder in patients with TOF (p <0.05 in apical planes). Also, the interventricular septum underwent relatively less enlargement so that it comprised only 27 +/- 4% of total RV surface area in patients with TOF, compared with 33 +/- 2% in normal subjects (p = 0.0001). In addition, the right ventricle in patients with TOF exhibited bulging basal to the tricuspid valve (4 +/- 4% of total RV length), unlike normals (1 +/- 2%, p <0.001). This basal bulging was amplified by tilting of the tricuspid annulus (29 +/- 11 degrees vs 15 +/- 7 degrees , respectively, p <0.005). In conclusion, the right ventricle remodels in several directions rather than following a shape continuum. Characterization of RV remodeling from 3-dimensional reconstructions provides novel insights.

Test of simulator-based assessment of psychomotor skill in transthoracic echo.

BACKGROUND: We developed a transthoracic echo simulator that measures technical skill in image acquisition in terms of the deviation angle between an acquired image and the anatomically correct plane for that view. We studied whether this metric reflects the clinical experience of providers. METHODS: Attendees at an echo course or at the annual meeting of the Swedish Heart Association were invited to test themselves on the simulator by scanning a mannequin and acquiring four views in 15 min: parasternal long axis (pLAX) in patient 1, apical four chamber and apical long axis (aLAX) in patient 2 and pLAX in patient 3. Their experience with echo was assessed from duration in years and procedure volume in the past year. Image acquisition error was assessed from the deviation angle. RESULTS: Of 61 participants, there were 37 physicians and 24 non-physicians (22 sonographers and two nurses). Non-physicians had higher procedure volume than physicians (850 ± 599 versus 312 ± 393 tests year-1 , P<0·001); both had similar duration of experience (9 ± 8 versus 12 ± 11 years, P = NS). The deviation angle for aLAX (55 ± 37 degrees) was higher than for any other view (P<0·00001). aLAX was the only view whose deviation angle correlated significantly with experience and only with procedure volume (r = -0·357, P = 0·008). CONCLUSIONS: These results demonstrate that deviation angle, a novel metric of technical skill in image acquisition, reflects clinical experience. Simulator-based testing provides objective and quantitative assessment that may be of value in the certification of trainees and for maintenance of certification.

Integrating Scaffolding and Deliberate Practice Into Focused Cardiac Ultrasound Training: A Simulator Curriculum.

Introduction: Focused cardiac ultrasound (FoCUS) is widely used for the point-of-care evaluation of basic cardiac pathology, and there is a need for efficient and consistent training in this modality. We designed a simulator-based FoCUS curriculum that integrates instructional scaffolding and deliberate practice to create a directed, self-regulated learning experience for novices. The goal of this strategy was to guide the novice's learning efforts more efficiently and moderate cognitive load while retaining the benefits of independent learning. Methods: The complex task of learning cardiac ultrasound is broken into discrete steps, with focused didactic information immediately followed by targeted simulator practice for each module. The practice complexity increases through successive modules, and learners ultimately apply their skills by completing unassisted simulator cases. Immediate visual and quantitative feedback is provided by the simulator whenever an ultrasound image was captured during practice. The entire curriculum is self-guided. Results: Sixteen nurse practitioners and resident physicians completed this FoCUS curriculum. In comparison to a previously validated, lecture-before-practice-style curriculum, the average time to completion decreased from 8.0 ± 2.5 hours to 4.7 ± 1.9 hours (p < .0001). There was no difference in posttraining cognitive or psychomotor outcomes between the curricula as measured by a simulator posttest. Discussion: A curriculum integrating scaffolding and deliberate practice provides a more efficient, but equally effective, means of teaching psychomotor and cognitive skills in FoCUS. These instructional design principles may translate to other operational learning tasks and allow novices to build skills and reach basic competency more rapidly.

Evaluation of Examiner Performance Using a Duplex Ultrasound Simulator. Flow Velocity Measurements in Dialysis Access Fistula Models.

We developed a duplex ultrasound simulator for training and assessment of scanning skills. We used the simulator to test examiner performance in the measurement of flow velocities in dialysis access fistulas. Test cases were created from 3-D ultrasound scans of two dialysis access fistulas by reconstructing 3-D blood vessel models and simulating blood flow velocity fields within the lumens. The simulator displays a 2-D B-mode or color Doppler image corresponding to transducer position on a mannequin; a spectral waveform is generated according to Doppler sample volume location and system settings. Examiner performance was assessed by comparing the measured peak systolic velocity (PSV) with the true PSV provided by the computational flow model. The PSV measured by four expert examiners deviated from the true value by 7.8 ± 6.1%. The results indicate the ability of the simulator to objectively assess an examiner's measurement accuracy in complex vascular targets.

Comparison of systemic right ventricular function in transposition of the great arteries after atrial switch and congenitally corrected transposition of the great arteries.

In patients with transposition of the great arteries corrected by interatrial baffle (TGA) and those with congenitally corrected transposition of the great arteries (ccTGA) the right ventricle (RV) is subjected to systemic pressure and fails prematurely. Previous studies have demonstrated RV dysfunction may be more pronounced in patients with TGA. The present study sought to compare patients with TGA and ccTGA using three-dimensional (3D) techniques to comprehensively analyze the shape, volume, global and regional function in the systemic RV. We compared RV size, shape, and regional and global function in 25 patients with TGA, 17 patients with ccTGA, and 9 normal subjects. The RVs were reconstructed from cardiac Magnetic Resonance Images for 3D analyses. Compared to normal, the RV in TGA and ccTGA was dilated, rounded, and reduced in function. Compared to each other, TGA and ccTGA patients had similar RV size and shape. Global RV function was lower in TGA than ccTGA when assessed from ejection fraction (EF) (30 ± 7 vs. 35 ± 7, p = 0.02) and from normalized tricuspid annular systolic plane excursion (TAPSE) (0.10 ± 0.04 vs. 0.18 ± 0.04, p < 0.01). Basilar RV function was poorer in the TGA patients when compared to ccTGA. The systemic RVs in both TGA and ccTGA are dilated, spherical, and poorly functioning. Compared to ccTGA, TGA RVs have reduced TAPSE and worse basilar hypokinesis.

Quantitative Feedback Facilitates Acquisition of Skills in Focused Cardiac Ultrasound.

INTRODUCTION: With the development of portable, affordable ultrasound machines with good image quality, many physicians have adopted focused cardiac ultrasound (FoCUS). To facilitate acquisition of these skills, we developed a simulator-based, self-taught curriculum for FoCUS that provides immediate feedback for rapid performance improvement. METHODS: Twenty-two first-year residents participated in the study. The curriculum consisted of instructive modules teaching image acquisition and interpretation of standard echocardiography views and common cardiac pathology, 7 practice cases in which participants scanned a mannequin using a mock transducer, acquired specified views with feedback provided by visual guidance technology, and interpreted these images. Trainees were tested pretraining and posttraining on different cases, without visual guidance assistance or feedback. Previously validated metrics were used to assess psychomotor skill in terms of the angle error in degrees between the planes of the optimal view, defined anatomically, and of the acquired view, as well as cognitive skill in image interpretation. RESULTS: The average error in image acquisition decreased from a median of 81 degrees at the pretest to 28 degrees after training (P < 0.0001). Cognitive skill improved by 29% (21%, P < 0.0001). There was a significant correlation between cognitive and psychomotor skill (r = 0.64, P < 0.001). DISCUSSION: A novel, simulator-based curriculum that provides immediate feedback was effective in teaching both psychomotor and cognitive skills in FoCUS without need for direct expert oversight of the learner. The curriculum's components provide a useful tool that can be applied to improve, assess, and monitor physician skill in FoCUS.

Development of a Duplex Ultrasound Simulator and Preliminary Validation of Velocity Measurements in Carotid Artery Models.

OBJECTIVE: Duplex ultrasound scanning with B-mode imaging and both color Doppler and Doppler spectral waveforms is relied upon for diagnosis of vascular pathology and selection of patients for further evaluation and treatment. In most duplex ultrasound applications, classification of disease severity is based primarily on alterations in blood flow velocities, particularly the peak systolic velocity (PSV) obtained from Doppler spectral waveforms. We developed a duplex ultrasound simulator for training and assessment of scanning skills. METHODS: Duplex ultrasound cases were prepared from 2-dimensional (2D) images of normal and stenotic carotid arteries by reconstructing the common carotid, internal carotid, and external carotid arteries in 3 dimensions and computationally simulating blood flow velocity fields within the lumen. The simulator displays a 2D B-mode image corresponding to transducer position on a mannequin, overlaid by color coding of velocity data. A spectral waveform is generated according to examiner-defined settings (depth and size of the Doppler sample volume, beam steering, Doppler beam angle, and pulse repetition frequency or scale). The accuracy of the simulator was assessed by comparing the PSV measured from the spectral waveforms with the true PSV which was derived from the computational flow model based on the size and location of the sample volume within the artery. RESULTS: Three expert examiners made a total of 36 carotid artery PSV measurements based on the simulated cases. The PSV measured by the examiners deviated from true PSV by 8% ± 5% (N = 36). The deviation in PSV did not differ significantly between artery segments, normal and stenotic arteries, or examiners. CONCLUSION: To our knowledge, this is the first simulation of duplex ultrasound that can create and display real-time color Doppler images and Doppler spectral waveforms. The results demonstrate that an examiner can measure PSV from the spectral waveforms using the settings on the simulator with a mean absolute error in the velocity measurement of less than 10%. With the addition of cases with a range of pathologies, this duplex ultrasound simulator will be a useful tool for training health-care providers in vascular ultrasound applications and for assessing their skills in an objective and quantitative manner.

The effect of blockade of the CD11/CD18 integrin receptor on infarct size in patients with acute myocardial infarction treated with direct angioplasty: the results of the HALT-MI study.

OBJECTIVE: The purpose of this study was to determine whether Hu23F2G (LeukoArrest), an antibody to the CD11/CD18 integrin receptors, would reduce infarct size in patients undergoing primary angioplasty for an acute myocardial infarction. BACKGROUND: Reperfusion injury in acute myocardial infarction has been shown experimentally to be related to neutrophil accumulation. Inhibitors of the CD11/CD18 or CD18 integrin receptors have been shown to reduce infarct size in experimental models. METHODS: Patients within 6 h of onset of chest pain with ST-segment elevation were randomized to receive either 0.3 mg/kg or 1.0 mg/kg of Hu23F2G or placebo just before angioplasty of occluded arteries (Thrombolysis in Myocardial Infarction TIMI flow grade 0 or 1). The primary end point was infarct size as measured by sestamibi single-photon emission computed tomography (SPECT) scan five to nine days later. RESULTS: Four-hundred and twenty patients were enrolled and received a placebo or the study drug. The groups did not differ in baseline or angiographic characteristics or angioplasty results. Infarct size was 16%, 17.2% and 16.6%, for placebo, 0.3 mg/kg and 1.0 mg/kg, respectively, of the left ventricle (p = NS). No differences were evident in those patients with anterior myocardial infarction or those presenting within 2 h of onset of chest pain. Corrected TIMI frame count was also not different between groups. Clinical events at 30 days were very low, with a mortality of 0.8%, 1.4% and 3.3%, respectively. The drug was well tolerated, with a slight increase in minor infections in the high dose group. CONCLUSIONS: The results of this multicenter, double-blind, placebo-controlled, randomized clinical trial demonstrated that an antibody to CD11/CD18 leukocyte integrin receptor did not reduce infarct size in patients who underwent primary angioplasty.

Validation of viability assessment by electromechanical mapping by three-dimensional reconstruction with dobutamine stress echocardiography in patients with coronary artery disease.

We evaluated the ability of electromechanical mapping (EMM) to discriminate between normal, viable, and nonviable (scarred) myocardium in patients with coronary artery disease versus dobutamine stress echocardiography (DSE) when the correspondence between the test and reference data sets is established via a common 3-dimensional reconstruction of the left ventricle. We studied 21 patients with coronary artery disease who underwent angiography, biplane ventriculography, and EMM within 1 month of DSE. A 3-dimensional left ventricular (LV) reconstruction was prepared from the ventriculogram and spatially aligned with EMM. EMM measurements of unipolar voltage, bipolar voltage, and local linear shortening were projected onto the three-dimensional left ventricle, averaged in each of 16 segments, and compared with DSE viability (normal, viable, scar) assessed at a core laboratory. All of the EMM measurements varied significantly (p <0.001) between the normal, viable, and scarred myocardium as assessed by DSE. Local linear shortening for normal, viable, and scarred segments was 10.4 +/- 6.5%, 7.8 +/- 5.6%, and 4.8 +/- 4.4%, respectively. In discriminating between these 3 groups, local linear shortening was more powerful than unipolar voltage or bipolar voltage (F = 20.765, F = 10.655, F = 4.795, respectively). Local linear shortening correlated best with viability, perhaps because it shares the same cognitive function as DSE. Three-dimensional analysis provides an anatomic framework that enables direct comparison of data from multiple imaging modalities rather than assuming segmental correspondence. Our results show that EMM provides significant on-line, diagnostic information on myocardial viability assessed by DSE on a segment-by-segment basis.

Monitoring change in the three-dimensional shape of the human left ventricle.

BACKGROUND: Characterizing left ventricular (LV) remodeling after myocardial infarction or LV shape change resulting from LV shape-restoration operation can yield valuable prognostic information. However, current methods measure only global parameters of LV shape. METHODS: We developed and validated a method for measuring change in regional LV shape by aligning a patient's follow-up 3-dimensional LV surface reconstruction to baseline surface. We tested the diagnostic power of 6 distance functions to detect a known shape deformation. To create the test data, the LV endocardial surface of a control subject was reconstructed using 3-dimensional echocardiographic techniques. The surface was deformed 9 different ways to model LV dilation (3 different locations and severities). Normal shape variability was defined from 18 serial studies of 6 control subjects. The severity of regional dilation was computed as the orthogonal distance between the aligned baseline and deformed LV surfaces. Deformation was quantified according to regional location using the 16-segment map of the LV. RESULTS: Normal LV shape variability was 3.38 mm. The LV deformations ranged from 2.95 to 8.02 mm. Gaussian distance function produced the highest accuracy for measuring deformation distances (P <.005 by analysis of variance). In addition, the gaussian function correctly identified the location of the maximum deformation in 6 of the 9 distorted surfaces. In the 3 remaining surfaces, the gaussian alignment selected an adjacent basal segment with a similar deformation distance (mean error: 0.2 +/- 0.17 mm). The gaussian function's accuracy in pinpointing the deformation equaled or exceeded the performance of the other 5 functions tested. CONCLUSION: This new method of aligning 3-dimensional LV surfaces in space facilitates detecting, measuring, and localizing regional shape change in the human LV independent of anatomic landmarks or geometric references. Potential applications include quantitative monitoring of change in regional LV shape after a pathologic process and/or surgical procedure to document efficacy of treatment and to assess prognosis.

Three-dimensional visual guidance improves the accuracy of calculating right ventricular volume with two-dimensional echocardiography.

Three-dimensional guidance programs have been shown to increase the reproducibility of 2-dimensional (2D) left ventricular volume calculations, but these systems have not been tested in 2D measurements of the right ventricle. Using magnetic fields to identify the probe location, we developed a new 3-dimensional guidance system that displays the line of intersection, the plane of intersection, and the numeric angle of intersection between the current image plane and previously saved scout views. When used by both an experienced and an inexperienced sonographer, this guidance system increases the accuracy of the 2D right ventricular volume measurements using a monoplane pyramidal model. Furthermore, a reconstruction of the right ventricle, with a computed volume similar to the calculated 2D volume, can be displayed quickly by tracing a few anatomic structures on 2D scans.

Three-dimensional echocardiographic measurement of left ventricular wall thickness: In vitro and in vivo validation.

INTRODUCTION: Three-dimensional (3D) echocardiography has been shown to accurately measure left ventricular (LV) volume and mass. This study evaluated the accuracy of 3D echocardiography and the CenterSurface method for measuring LV wall thickness in vitro and in vivo. METHOD: Three-dimensional echocardiography scans, obtained from 7 LV phantoms and subjects having healthy (n = 5) or diseased (n = 8) hearts, were digitized. Endocardial and epicardial borders were outlined and used in 3D LV reconstruction. In vitro wall thickness was compared with true micrometer measurements. Three-dimensional in vivo wall thickness was compared with 2-dimensional (2D) thickness measured by the centerline method. RESULTS: The in vitro 3D echocardiography measurements agreed closely with true wall thickness (P <.0001), as did in vivo measurements (P <.0001). CONCLUSION: Three-dimensional echocardiography reconstruction has previously been shown to provide accurate representation of LV shape in addition to volume and mass. This study demonstrates that the CenterSurface method provides accurate quantification of wall thickness.