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.

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.

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 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.

Method for three-dimensional data registration from disparate imaging modalities in the NOGA Myocardial Viability Trial.

Region-by-region comparison of data concerning left ventricular (LV) status is difficult to perform quantitatively if the data was acquired from disparate imaging modalities. We validated a method for comparing measurements obtained by electromechanical mapping (EMM) catheter with dobutamine stress echocardiography (DSE) via biplane contrast ventriculography, with the assistance of three-dimensional (3-D) echocardiographic data. The ventriculograms were traced and the borders were used to reconstruct the LV in 3-D with the aid of a database of 3-D echocardiographic studies. The 3-D LV was oriented to the EMM data based on the body coordinates and then manually scaled and translated to fit. The EMM data were mapped to the 3-D surface. The 3-D surface was divided into the 16 regions defined for echocardiographic assessment. The mean EMM value for local linear shortening, a parameter of function, was computed in each segment. The EMM and semiquantitative echocardiographic assessments of regional myocardial function were compared by segment, and the volume of the 3-D LV was compared with the volume computed from the ventriculogram. The volume of the 3-D surface correlated closely with that of the ventriculogram (r = 0.97, SEE = 27.4 ml) but with a significant overestimation of 63 +/- 35 ml. There was a highly significant (p < 0.0001) agreement in regional function between EMM and echo. Local linear shortening correlated significantly (p < 0.0001) with echocardiographic severity of wall motion, averaging 9.5 +/- 6.5, 8.1 +/- 5.4, 5.9 +/- 4.8, and 6.2 +/- 3.3 in segments read as normal, hypokinetic, akinetic, and dyskinetic, respectively. The method presented is valid for comparing cardiac parameters derived from disparate image data on a region-by-region basis by employing anatomic landmarks on 3-D reconstructions of the LV endocardial surface.

The severity of functional mitral regurgitation depends on the shape of the mitral apparatus: a three-dimensional echo analysis.

BACKGROUND AND AIMS OF THE STUDY: The relationship between structural abnormalities of the mitral apparatus and severity of functional mitral regurgitation (MR) was examined in patients with non-ischemic dilated cardiomyopathy. METHODS: Three-dimensional (3D) echocardiography was performed in 13 cardiomyopathy patients with mild (n = 5) or moderate to severe (n = 8) MR, and in eight normal volunteers using freehand scanning. The size, shape and function of the left ventricle, and the dimensions of the mitral annulus, chordae tendineae and papillary muscles, were measured. RESULTS: Virtually all parameters differed significantly between normal subjects and cardiomyopathy patients. Annular size, the central angle between the anterior and posterior chordae, and dilatation of the anterior and anterolateral left ventricular (LV) wall were greater in patients with moderate to severe MR than in those with trace to mild MR. Anterior wall dilatation was associated with greater outward displacement of the anterior papillary muscle, and correlated with widening of the central chordal angle, apical displacement of the mitral leaflet coaptation point, and mitral annular dilatation. CONCLUSION: In non-ischemic dilated cardiomyopathy, functional MR is related to both annular dilatation and to dilatation of the anterior and anterolateral LV wall. The latter results in displacement of the anterior papillary muscle, narrowing of the angle of the anterior chorda to the mitral annulus, and widening of the central angle between the anterior and posterior chordae.

Defining normal left ventricular wall motion from contrast ventriculograms.

Sources of variability in defining the normal range for left ventricular (LV) motion from contrast ventriculograms were assessed by comparing the function of 183 normal patients from six sites in three countries. Wall motion was measured using the centreline method at seven regions around the LV contour. The influence of institution, heart rate, age, end diastolic volume, body surface area and gender was evaluated using univariate analysis, and then compared using multivariate regression analysis. Wall motion varied significantly but weakly (/r/ < 0.32 for all) with site, gender and body surface area in some regions. Variability was greater within sites than between sites. Wall motion was most similar in the two sites with the largest patient populations (N = 49 and N = 52). Normal LV wall motion is influenced by many factors. The reliable definition of the normal range requires analysis of a large number of subjects. For wall motion, the normal population should comprise closer to 50 subjects than the 10-20 that are commonly referenced.

Expert visual guidance of ultrasound for telemedicine.

Expert visual guidance (EVG) is computer assistance that displays to the examiner how the image plane moves towards (or away from) a desired anatomical location as the ultrasound probe is manipulated over the patient's body. We tested whether EVG by a remote expert could assist inexperienced examiners in acquiring abdominal ultrasound images. The inexperienced examiners were 20 medical students, who were randomly assigned to verbal instruction alone (Group 1) or to EVG (Group 2). The examiners were tested on their ability to visualize the abdominal aorta and the right kidney. Group 2 was more successful in identifying specified anatomy in longitudinal and cross-sectional views of the aorta (95 vs. 75%, P = 0.032) and kidney (98 vs. 88%, P = 0.09). The groups succeeded equally well in obtaining a true cross-sectional view of the aorta. Kidney length was also similar when measured by the two groups. The results demonstrate that an inexperienced ultrasonographer can be significantly assisted by EVG compared to verbal instruction alone. This could be useful for tele-mentoring in rural hospitals as well as for teaching, both in person and at a remote site.

Quantitative assessment of regional left ventricular function with cardiac MRI: three-dimensional centersurface method.

OBJECTIVES: The purpose of this study was to provide the first in vivo validation of a three-dimensional (3D) method to quantify regional left ventricular (LV) function with cardiac magnetic resonance (CMR) imaging after myocardial infarction (MI). BACKGROUND: Current cardiac methods to analyze LV function are limited by geometric assumptions and observer biases. METHODS: MI was induced percutaneously by 90-min proximal left circumflex artery balloon occlusion in 25 Yucatan minipigs. Cine and contrast-enhanced (CE) CMR imaging was performed at 5 days (n = 21) and 8 weeks (n = 22) post-MI. Twelve control animals without MI were also imaged. Regional wall thickening was measured orthogonal to the myocardial wall using the centersurface method. The left ventricle was divided into 16 segments (six basal 60 degrees , six middle 60 degrees , four apical 90 degrees ). Normal ranges for segmental wall thickness and wall thickening were defined as mean +/- 2D in control hearts. Hypokinesis was defined as a segmental thickening value below the normal range. RESULTS: Hypokinesis following MI was identified in the inferior, inferolateral and anterolateral segments when compared with controls and corresponded to areas of infarction by CE CMR. The aggregate wall thickening was also expressed as a percentage at 5 days (Infarct zone: 15% +/- 16% vs. NonInfarct zone 33% +/- 20%, P < 0.001) and 8 weeks (Infarct zone 20% +/- 20% vs. NonInfarct zone 32% +/- 22%, P < 0.001). CONCLUSIONS: The centersurface method can quantify regional wall thickening and spatially identify regions of abnormal function in 3D after MI without relying on geometric assumptions. This method may be a valuable tool to quantify regional LV function in the assessment of myocardial viability, ischemia, infarction, and the response to therapeutic interventions.

Evaluation of midwall systolic function in left ventricular hypertrophy: a comparison of 3-dimensional versus 2-dimensional echocardiographic indices.

OBJECTIVE: This study investigated the sensitivity of 3-dimensional (3D) midwall ejection fraction (EF) (3DEF(mw)) to the presence of left ventricular (LV) hypertrophy (LVH) in comparison with conventional echocardiographic indices for systolic function. BACKGROUND: EF and fractional shortening (FS) do not reflect the prognosis of patients with LVH. Midwall mechanics better represent the true function in LVH. However, midwall FS (FS(mw)) interrogates a limited region of LV. We developed a method for determining 3DEF(mw). METHODS: This study compared 3DEF(mw) with 2-dimensional (endocardial EF [EF(endo)], endocardial FS, FS(mw), and systolic tissue velocity) and 3D (3D EF(endo) and mitral annular motion [MAM]) echocardiographic indices in 28 patients with essential hypertension and LV mass index by M-mode greater than 125 g/m(2) versus 21 healthy individuals. RESULTS: Systolic function assessed by EF(endo), endocardial FS, 3D EF(endo), and systolic tissue velocity did not differ between the two groups, but MAM (11.6 vs 14.0 mm), FS(mw) (14.7 vs 18.2%), and 3DEF(mw) (36.6 vs 44.1%) were significantly decreased in LVH compared with normal. Only 3 parameters correlated significantly with both the M-mode and 3D measurements of LV mass index: FS(mw) (r = -0.74 [M-mode]; r = -0.48 [3D]), 3DEF(mw) (r = -0.63 [M-mode]; r = -0.68 [3D]), and MAM (r = -0.43 [M-mode]; r = -0.36 [3D]). Midwall indices FS(mw) (F = 40.4) and 3DEF(mw) (F = 26.5) better discriminated LVH and normal groups than MAM or endocardial indices. CONCLUSIONS: The 3DEF(mw) method discriminates the systolic function of LVH and normal groups, and correlates with the degree of hypertrophy. By avoiding the limitations of FS(mw) or MAM, 3DEF(mw) provides a more comprehensive metric of systolic function in patients with LVH.

Measurement of right ventricular volume from biplane contrast ventriculograms: validation by cast and three-dimensional echo.

We compared six models for measuring right ventricular (RV) volume from biplane ventriculograms in the 30 degrees right anterior oblique and 60 degrees left anterior oblique projections in adult and dilated RVs. We used 27 casts of normal RVs plus 37 three-dimensional (3D) echocardiographic RV reconstructions that we rotated to the oblique projections for contour extraction. Biplane volumes were computed using published formulas. RV volumes ranged from 18.9 to 322.4 ml. Both sets of volumes correlated similarly to true volume and were combined. Simpson's method with 50 slices yielded the lowest absolute error (19.5 +/- 28.9 ml); Simpson's with 20 slices yielded the lowest bias (1.3 +/- 35.7 ml). The prism and area-length models performed within this range. The Simpson's method provides the most accurate measurement of RV volume from biplane contrast ventriculograms recorded in oblique projections. Volume validation can be performed using 3D echo data.

Three-dimensional assessment of two-dimensional technique for evaluation of right ventricular function by tricuspid annulus motion.

BACKGROUND: Measurement of tricuspid annulus motion (TAM) is an easy way to estimate right ventricular ejection fraction (RVEF). However the accuracy of two-dimensional (2-D) methods for analyzing the three-dimensional (3-D) structure of the tricuspid annulus has not been evaluated. OBJECTIVE: This study evaluated the accuracy with which 2-D measurements of TAM reflect RVEF using 3-D reconstructions of the heart at end diastole (ED) and end systole (ES). METHODS: 2-D echocardiographic studies were performed on 12 subjects and used to reconstruct the RV and tricuspid annulus in 3-D at ED and ES. Measurements of TAM from medial and lateral positions on the annulus were selected from the standard echocardiographic apical four-chamber view. The minimum and maximum possible TAM values, RV volumes, and movement of the apex of the heart along the trajectory of TAM were calculated from the 3-D reconstructions. RESULTS: TAM correlated highly with RVEF (r > or = 0.90). Values found by 2-D and 3-D techniques were not significantly different. Correcting TAM for apex motion did not improve correlation. Summation of medial and lateral TAM data increased correlation values slightly relative to lateral TAM alone. Regional aberrant contractility degraded the predictive value of TAM. CONCLUSION: Estimation of RVEF from 2-D echo measurement of TAM is accurate, especially when medial and lateral TAM are summed, except in patients with severe apical RV dysfunction.

Three-dimensional echocardiographic measurement of left and right ventricular mass and volume: in vitro validation.

INTRODUCTION: Three-dimensional (3D) echocardiography has been shown to offer highly accurate measurements of left ventricular (LV) volume and mass. The present study evaluated the accuracy of 3D surface reconstruction by the piecewise smooth subdivision method in measuring volume and mass not only in the LV but also in the more complexly shaped right ventricle (RV). METHODS: 3D echo scans were obtained of in vitro LV's (n = 15) and RVs (n = 10). From digitized images, ventricular borders were traced and used in surface reconstructions. Mass and volume determined from the reconstructions were compared to true volume and mass determined prior to imaging. Additionally casts of two RVs were made and laser-scanned. Distances between the laser-identified points on the RV surface and the corresponding 3D echo reconstructions were measured. RESULTS: 3D LV volume agreed well with the true volume (y = 0.99x + 1.73, r = 0.99, SEE = 3.35 ml, p < 0.0001), as did 3D LV mass (y = 0.99x - 4.71, r = 0.99, SEE = 9.85 g, p < 0.0001). 3D RV volume overestimated true volume (y = 1.11x + 1.77, r = 0.99, SEE = 3.36 ml, p < 0.001) by 6.23+/-3.70 ml (p < 0.0001). 3D mass agreed well with RV mass (y = 0.78x + 17.32, r2 = 0.93, SEE = 3.54 g, p < 0.0001). 3D echo reconstructions matched the laser-scanned RV closely with residual distances of 1.1+/-0.9 and 1.4+/-1.2 mm, respectively. CONCLUSIONS: 3D echo using freehand scanning combined with surface reconstruction by the piecewise smooth subdivision surface method enables accurate determination of LV mass and volume, of RV mass and volume, and of the RV's complex shape.