258 JACC Vol. 22, No. 1 Juiy 1993:258-70

DONALD L. KING, JR., MS, DONALD L. KING, MD

New York, New York and Danbury, Connecticut

Objectives. We evaluated a threemdi e~io~al echocardio- graphic method for ventricular volume and surface area determim nation that uses polyhedral surface reconstruction. Six to eight nonparallel, unequally spaced, nonintersecting short-axis planes were p&tioned with a line of intersection display to overcome limitations associated with twoqdimensional echocard

~~kg~u~. Twedimensional echocardi Of

ventricular volume and surface area determi by assumptions about ventricular shape snd image plane pa&ion.

ventricular enddiastolic and end-systolic vol- ardiai surface areas determined by three-

dimensional echocardiography and nuclear magnetic resonance

( ) imaging were compared in 15 normal subjects (7 men, 8 women, aged 23 to 41 years, body surface area 1.38 to 2.17 m’). ‘l’een of these subjects also underwent tw~dime~ion~ echocardi- ograpby; and er;:d-oliastoiic and end.systolic volumes were deter- mined by the apical biplane summation of discs meth and compared with results of NMR imaging.

Resuk. Interobserver variability was 5% to 8% for three- dimensiunai echocardiography and 6% to 9% for NMR imaging.

Left ventricular vohme is an important clinical variable to monitor in patients with valvular disease, cardiomyopathy and myocardial infarction. Therefore, an accurate, repeat- able, noninvasive method of determining left ventricular end-diastolic and end-systolic volumes would be useful, but to date this has not been widely available. Determination of endocardia! surface areas would also be useful for quantify- ing infarct size and for studying the effects of ventricular remodeling. Cineangiography has several limitations, the most important of which is a requirement far geometric

..-.- -....-. I ..,, .._.. New _” . . . .

r Hosoital. Danhttrv. (Innnertir~~t

From the Division of Card;ology, Colutnhia Ilniverritv NPW VO;

York: and *DivisionofCardiology. Danburl .__ _r . . .._. _ -_____, , ___.____..__.. This study was presented in part at the 4~ Annual Scicotific Session of the American College of Cardiology, D&s, Texas, Amil 1992.

hk~~~script received July i6, 1992; revised manuscript received Decem- ber 29. 1992, accepted January 7. 1993.

M&&QrJQP n,swndence: Aasha S. Gopal, MD, Columbia University, Division ofCardio!ogy, P&S Building !&Ml,630 West 168 Street, New York, New York 10032.

01993 by the American College of Cardiology

assumptions in the calculation of volume (I). Radisnuclide methods are subject to other problems related to detection of edges and end planes as well as determination of background activity (2).

Attempts to use two-dimensional echocardiography to determine left ventricular volume identified several limita- tions, particularly in patients with regions of asynergy (3-6). The ability to predict absolute volume for a given patient has been hindered by broad variability in results (7,g). Endocar- dial surface area, likewise, can be estimated by two- dimensional echocardiography only with the help of geomet- ric assumptions at the current time (3-i ij. Factors contributing to the low predictive accuracy (6) of two- dimensional echlocardiograpbic volume measurements in- clude geometric assumptions (i2), image plane positioning errors (13,14) and imprecise endocardial boundary demarca- tion.

A variety of three-dimensional echocardiomphic scan- ners have been developed primarily to address the issue of

0735-1097/P3/$6.00

JAW Vol. 22, No. B July !!993:258-70

used an algorithm bas polyhedral surface reconstruc- tion (34-36) of the ven from a series of short-axis cross sections that are neither parallel nor intersecting. Although the accuracy of this a~go~tbrn has been for other organ systems by ultworaogra tomography using para.lleI imajges (37): ventricular volume computati~on iii

our previous in vitro st method for !eR ventricular volu

to validate our three-

end-diastolic and end-systolic volume and surface area de- termination using NMR imaging as a standard of compari-

computer memory a reference

image is moved, the line of intersection moves in bot

GOPAL ET AL. THREE-DIMENSIONAL ECHOCARDIOGRAPHY

JACC Vol. 22, No. 1 July 1593:258-70

Figure 1. Three-dimensional echocardiographic method of ventric- ular volume and surface area determination from unequally spaced, nonparallel, nonintersecting short-axis cross sections. Top left, First parastemal long-axis reference image with guided short-axis cross sections positioned using the line of intersection display. Top right, Second parasternal long-axis reference image, which includes the apex. Bottom left, Real time short-axis image used for boundary tracing with the line of intersection of both reference images shown. Bottom right, Traced boundary of digitized real time short-axis image to be used for calculation of ventricular volume and endocar- dial surface area by polyhedral surface reconstruction.

three-dimensional echocardiography. Subjects were screened according to the quality of the routine echocardio- graphic study and selected to provide a wide range of chamber size. One subject was excluded owing to poor three-dimensional echocardiographic images. All subjects were voluntary participants and gave verbal informed con- sent before the study. All examinations were easily per- formed it: the left lateral decubrtus position and were of minimal tt:hnical difficulty. High quality images with easy and complete identification of all structures were available in all cases. Images were always acquired at end-expiration using a defined three-dimensional echocardiographic image acquisition protocol. If patient motion occurred during im- age acquisitton, the data set was discarded and the procc- dure repeated. First, two temporary short-axis images, one at the level of the aortic valve and the other at the apex, were

obtained to define the long axis of the ventricle. Adjusting the ~arasterna~ long-axis image such that its line of intersec- tion bisected the temporary short-axis images ensured that the optimal long-axis image had been obtained. This parasternal long-axis image then served as the reference image. However, because it is rarely possible to visualize both the base and the apex using a single parasternal long-axis reference image, a second long-axis reference image that included the apex was opttmally positioned using the line of intersection display and the temporary short-axis image of the apex as a guide. The temporary short-axis images were then discarded, and both long-axis reference images, one excluding the apex and other including it, were used to position real time short-axis images. A series of eight to nine nonparallel real time short-axis images were posi- tioned and acquired in digital format, paying careful atten- tion to the end-plane images and using the line of intersection display to ensure that the image planes did not intersect within the left ventricular cavity (Fig. 1). The first image plane passed through the inferior surface of the aortic valve cusps. The second passed tbrough the center of the mitral anulus. The third was positioned at the posterior mitral anulus at its junction with the posteroi~ferior myocardium. The subsequent image planes were spaced variably in the midventricle and were optimized for endocardial boundary definition. The last image plane was positioned at the endo- cardial ape% without any remaining lumen using the line of

the vemtricle were co struction using traced

was defined between two the same contour and a sin

at is, each tile bo~~da~ was ur element” and by two “spans” Hence, there were 360 triangks area between adjacent cross secttons.

endocardial surface area could be areas of all surface triangles. To ume, a centroid was defined for eat ce, and vectors were

two slices was decomposed into 180 X 3 =

total volume of the ventricle. NueIe tie ance

subjects nt ng o system (GE Medical). One subject was excluded owing to poor NMR images. All subjects were volunteers and gave verbal informed consent before the study, in accordance with Institutional Revieiv Board guidelines. Subjects were connected to telemetered electrocardiographic (ECG) gating with respiratory compensation and then placed oo the imag- ing table in a 30* left anterior oblique (left shoulder down) position. Initial “scout” was obtained using a multislice, single-phase, echo sequence (pulse repetition time [TR] = one mterval; echo delay time [TN = 20 ms). These cotomal images (long axis) were ac&red inroa256 X 128 matrix.The 3coci: imagedisplaying the longest vertical axis of the heart was used to define the location for the subsequent slices used to calculate left ventricular vohrme. Five contiguous siices pei-a:endicutar to

two separate observers without knowle the other observer or of the echsca

Apical two- and four-chamber views, along witb a paraster- nat sho&x& view at the rnidve~t~c~~ar level were ob- tained. Images were digitized into a video display analysis

method as recommended by the guidelines of tbe American §I? of Echocardiography

ysis. Conventions for dimm$.mal echo

vention was chosen for the papillary muscles because the current version of the poiyhedrai surface reconst

262 GOPAL ET AL. IACC Vol. 22. Na. 1

THREE-DIMENSIONAL ECHOCARDIOGRAPHY July 1993:258-90

algorithm does not accept discontinuous data. The conven- tion for boundary tracing by NMR imaging always included the papiikry suscles as part of the cavity. Using the mean of two observers, left ventrici;!z end-diastolic and end-systolic volumes and en6dAstolic and end-systoiic cr.dncardial sur- face areas, as determined by three-dimensional echocardi- ography and NMR imaging, were compared with one an- other using Pearson’s correlation coefficient and simple regression. The F test was used to test the null hypothesis that NMR imaging and echocardiographic measurements were identical, thus yielding the equation y = x. The regression estimates of the slope and intercept were simul- taneously tested against the values of 1 and 0 (values for the line of identity) by the F test (45). Interobserver variability for selection of images and boundary tracing was determined for each method, as shown below, wheat: s, = values of observer 1; x2 = values of observer 2, a& w = 15:

Statistical analysis was performed using separate compari- sons of two- and three-dimensional echocardiography with NMR imaging (Pearson’s correlation coefficient and simple regression) for the subset of 10 subjects who returned at a later date for a two-dimensional echocardiographic study.

The results for ventricular volumes are shown in Table I. Values for interobserver variability for three-dimensional echocardiographic end-diastolic volume (4.99%) and for three-dimensional echocardiographic end-systolic volume (8.01%) were lower than those obtained for NMR imaging end-diastolic and end-systolic volumes (6.59% and 9.02%, respectively). Excellent (p < 0.001) correlations were ob- tained for both end-diastolic and end-systolic volumes (r = 0.92 and 0.81, respectively), with a low SEE (6.99 and 4.01 ml, respectively). The values for end-diastolic and end-systolic volumes by both methods and their regression equations are plotted in Figures 2 and 3. Three-dimensional echocardiography resulted in systematically higher end- diastolic and end-systolic volumes than those obtained with NMR imaging. The regression equation for end-diastolic volumes did not differ significantly from the line of identity. The regression equation for end-systolic volumes did differ significantly from the line of identity and was associated with a slightly greater spread of values.

The results for ventricular endocardial surface areas are shown in Table 1. Interobserver variability was not deter- mined because the traced boundaries by both methods were used io simu&&neously determine both volume an6 s&ace

ale II. Comparison of Left Ventricular End-Diastolic and End- stolic Volumes and Endocardial Surface

Dimensional Echocard~ogra~hy and Nuciea Resonance Imaging

Interobserver Variability r* SEE p Vaiue

Volume End-diastolic

3D Echo 4.99% 0.92 6.99 ml <: 0.001 NMR imaging 6.5%

End-systolic 3D Echo 8.01% 0.81 4.01 ml NMR imaging 9.02%

Endocardial surface area End-diastolic

3D Echo - 0.84 8.25 cm’ < 0.001 NMR imaging -

End-systolic 3D Echo 0.84 4.89 cm2 c: 0.001 NMR imaging

r* = Pearson’s correlation coefficient. NMR = nuclear magnetic reso- nance; 3D Echo = three-dimensional echocardiography.

area. Once again, excellent I) correlations were obtained for end-diastoli nd-systolic endocardial sur- face areas (r = 0.84 and espectively), with low SEE values (8.25 and 4.89 cm’, respectively). Plots of end- diastolic and end-systolic endocardial surface areas methods, along with their regression equations, are shown in

re 2. End-diastolic volume (EDV) determined by three- dimensional echocardiography (3D ECHO) plotted against end- diastolic volume by nuclear magnetic resonance (NMR) imaging. Dashed lines represent 95% confidence intervals. Interobs. Variab. = interobserver variability.

160

125

E t I

B

3 D ECHO Interobs. Variab. = 4.69Y0

NMR Interobs. Variab. = 6.69%

r = 0.92

SEE = 6.99 ml

p c 0.001

Nwt End-diilic Volume (mu

MAR End-systohc Voiume (ml)

F@mz 3. End-systolic voiume (WV) determines by three- ocardiography (3D ECHO) plotted by nuclear magnetic resonance @I

8 represent 95% confidence intervals. C&he as in Figure 2.

For a saabset of 1 three-d~rne~sio~~~ ech

imaging values (Table 2). dimensional echocardio agmg were ag-

echocardiography and aging (r = 0.48, SEE = 20.5 ml. p = NS for en volume; r = 0.70, SEE = 5.6 ml, p < 0.025 for end-systolic volume).

left ventricular end-diastolic and

are possible by the elimhatr,.. ‘QF~ or geometric assumptions and image plane positionhg error. Larger end-diastolic and

r two reasons.

between corresponding systolic

designed to minimize sources of error in ~~trasol~~d SYS~CCII%

264 GOPALETAL. .'ACC Vol. 22, No. 1 THREE-DIMENSIONAL ECHOCARDIOGRAPHY July 1993:258-70

NMR End-systolic Endocardial Sutface Area (cm2,

Figure 5. End-systolic endocardial surface area (ESSA) determined 4l. three-dimensional echocardiography (3D ECHO) plotted against end-systolic endocardial surface area by nuclear magnetic reso- nance !NMR) imaging. Dashed lines represent 95% confidence intervals.

utilized parallel imaging planes and yielded a mean error of 1.6% (0.64 + 0.72 ml) (35). The capability of the polyhedral surface reconstruction algorithm to utilize nonparallel, un- equally spaced, nonintersecting short-axis image planes for volume computation was validated using nonuniform bal- loon phantoms and the results were compared with true volumes by water displacement and volumes obtained by NMR imaging. We obtained the following results for three- dimensional echocardiography: accuracy = 2.27%. inter- observer variability = 4.33%, r = 0.999, SEE = 2.45 ml; p -C 0.0001. Those for magnetic resonance imaging were accuracy = 8.01%, interobserver variability = 13.78%, r = 0.995, SEE = 7.01 ml; p < 0.001. There was no statistically

Table 2. Comparison of Two- ar.d Thret-Dimensional Ventricular Volumes With Nuclear Magnetic Resonance Imaging

r SEE Value (ml) D Value

2D Echo vs.NMR imaging

EDV ESV

3D Echo vs. NMR imaging

EDV

0.48 20.5 NS 0.70 5.6 < 0.025

0.90 7.0 <O.nnl “.“_” ESV 0.88 3.1 <G.oOi

-.-

E;iV = end-diastolic volume: ESV = end-systolic volume: 2D Echo =

two-dimensional echocardiography; other abbr&ttbr,s as in Table 1.

significant difference between the two met of this study indicated that by eliminating g tions and image plane positiooi~g error, high accuracy and reproducibility for volume computation were achievable in vitro and that NMR imaging wo~!d serve as an in vivo standard of comparison (40). The ability of the technique to accurately predict true volume (r = 0.99, SEE = 2.72 ml; p < O.OOOl) in the presence of irregular endocardial borders with regions of echo dropout was further demonstrate glutaraldehyde-fixed sheep and pig hcartts (46).

Lower correlations between two-dimensional cc R imaging were observed in this

ose in previous two- ensio in ies (5-7); however, severa if-

ferences in study design make corn~a~~so~s di of cineangiography as a reference standard in previous studies has inherent geometric assumptions in the cakula- tion of volume and thus the result cannot be strictly com- pared with those in a study of this kind, ac :!,hich a standard free of geometric assumptions was used. Another important difference between previous studies and the current study is related to the range of volumes studied. The inclusion of patients with wall motion abnormalities in previous studies provided a greater ra higher correlation co study, which include was particularly true for end-systolic volumes and surface areas, which varied over a relatively narrow range.

Results obtained for surface area are also very encourag ing and confirm our p vious in vitro results. Once again,, three-dimensional e ocardiographic values for end- diastolic and end-systolic endocardial surface areas were higher than NMR imaging values, largely owing to inclusion of the mitral anulus and left ventricular outflow tract in the three-dimensional echocardiographic method. The in vitro model used to validate the three-dimensional echocardio- graphic method for total endocardial surface area and infarct surface area was a pin model, in which pinheads mounted in three parallel arcs served as the acoustic targets. K’his study revealed values for intraobserver and interobserver variabil- ity and accuracy to be 0.54%, 0.4% and 1.36%, respectively, for total surface area; the same values for infarct area were I .40%, 1.27% and 2.13%, respectively. Interobserver vari- ability in vitro was primarily due to boundary tracing error, not to imaging (49). This finding indicates that the three- dimensional echocardiographic system is robust and per- forms as inktied, accurately computing volume from non- parallel data presented to the system. We believe that errors that might result from use of the system will arise from the presentation of incorrect data to it by the operator, not from the three-dimensional echocardiographic system itself.

Elim~~at~~n of geamdric assumptions. The three- dimensional echocardiographic method of volume computa- tion spatially registers images and is therefore free of any geometric assumptions of left ventricular shape or image relation. This represents a significant improvement over a

JACC Vol. 22. No. I July 1993:256-70

ventricular volume cm isn assumes an 0

because operators must rely on image tive sense and a ~~0w~edge Of t the correct image position. A

study of two-d~me~sio~a~ echocardi rn~~at~On by Erbej et al. (13) sho two-chamber views were displaced to the apex, resulting in a fores~o~e~i~g of the ventricular image and underestimation of ventricular volume. study using our three-dimensional echocardiogra ner, we showed that approximately 50% of standard two- dimensional echocardiographic imaging views by experi- enced operators are not optimally positioned (32). Tracing improperly positioned short-axis images will contribute to errors in volume computation. The line of intersection display allows Operators to accurately and re position image planes for volume com~~tatio reference image to provide additional land otherkse nonvisualized dimension. Using this nirsue, we were able to improve the regroduc ,-~~sae positkning appximately threefold (32), in turn lead- ing ‘:o a threefold improvement in reprOduCibility of left ventricular end-diastolic dimension (33).

lane

the polyhedral surface reccdnstruc-

usly c~eC~~~~ the acsuracy Of the ycle of data ac~~is~t~o~, the lengths

angles formed by the three soimd emi

standards results in automatic rejection bf the data and repetitiCn of image acquisition until satisfacto~ data at-e obtained. $%rm random measurement variation may Occur

266 GOPAL ET AL. THREE-DIMENSIONAL ECHOCARDIt%RAPHY

becgdse echocardiographic and NMR images are acquired over a seties of respiratory cycles. Accurate image position- ing using the line of intersection display also has been tested by measuring distances between defined image planes on the pin model phantom. The results show that errors fioin ihe ;iue of intersection display ‘are ~0.4% of the distance be- tween image planes (35). The polyhedral suifacc reconstruc- tion algorithm slightly underestimates the true vohme Of

convex structures such as the left ventricle because the surface is reconstructed from rhfirAn r.lV.UJ drh-i~n between points on the boundary contours. These chords lie inside the arc defining the convex surface and thus omit from the calcula- tion a very small volume found between the chord and the arc, Similarly, the calculation of surface area is slightly underestimated because each triangle of the polyhedral reconstructed surface is a flat surface. The mag;:iiude of this omission is minimized by choosing a large number of points on the boundary contours and by increasing the frequency of spacing of the cross sections. In the current study, 360 triangles/slice were used to approximate the surface. The average distance between images or average slice thickness depends on the depth. It is estimated that the mean distance between images at the midventricular level was -1 cm. The accuracy of the polyhedral surface reconstruction algorithm for volume and surface area computation has been validated by us (40,46,49) and by Cook et al. (37). Additionally, operator-dependent errors may occur owing to interpretive factors. In addition to identifying the first and last cross sections of an object, the operator must space sections close together when the surface curvature is changing rapidly. If the slices are too thick relative to the changing surface curvature, sigr ificant volume may be excluded by the poly- hedral surface reconstruction algorithm. The use of eight or nine short-axis images in this study was based on the work of Weiss et al. (3) and ou our in vitro validation studies (40,46,49). We believe that all of these errors associated with the three-dimensional echocardiographic method are negli- gible compared with inherent errors of two-dimensional echocardiographic systems.

ndary tracing error. Boundary tracing errors of two- dimensional echocardiographic systems are also a persistent major source of volume computation error in three- dimensional echocardiographic systems by presenting im- precise data. These errors are caused prim&y by inade- quate definition of the boundary and by relatively poor lateral resolution of the ultrasound beam within the image plane and perpendicular to it. Furthermore, lateral resolu- tion errors are exaggerated by using more than the minimal necessary amplification. Curvilinear geometry and irregular trabeculation of the ventricle produce echo boundaries of the

chamber that are spatially Lmbiguous. Typically, an echo composed of a large number of pixels represents a single point in the chamber boundary. Selecting the correct bound- arY pixel is very difficult and almost invariably results in some volume computation error. This problem was ad- dressed in the present study by using the minimal amplifica-

tion necessary to visualize the boundary and by using t three-dimensional ecbocardiogra~bic line ofi~tersectio~ dls- play to direct the image plane or ~~traso~~d beam as nearly perpendicular to the endocardia! scrface as possibi nonparallel cross sections permitted the seleciion axis images that were optimized for endocard~a~ b definition, Precise boundary tracing, however, difficult problem that may be addressed in the future by computer-based semiautcmaied boundary recognition pro-

specific objective of validate the three-d and surface area computation another tomographic me studies have been judged

niques may require geometric assumptions or other limitations and do not serve as ideal comparison.

Left ventricular volume computation by N irnag~~~ has been validated in vitro and in vivo previousl ,39) and is believed to be the best available clinical modality for quantitative study of the ve e that is free of assumptions (51). The use e cross sections previously validated for in vivo volume and mass c (39,52), and increasing the number of slices further adds to the imaging time, with little improvement in technique. The method for surface area determination has not been formally validated; however, the calculation is based on measure- ments of circumference that have been validated previously and thus should be a reasonable first approximation.

The limitations of N imaging with regard to patient movement and the disti on between the blood pool and the myocardium, particularly in conditions of slow flow, are well known. In this study, one subject was excluded because of suboptimal images resulting from patient movement. To eliminate the majority of the slow-flowing bloodlendocardial interface artifact, saturation pulses were applied outside the z selected slice just before each acquisition. Other sources of error include slice thickness-dependent partial volume ef- fects and variable end-slice positioning in addition to bound- ary tracing error.

Study limitations. Three-dimensional echocardiography and NMR imaging have important differehlces in the algo- rithms used for volume and surface area computation. Meth- odologic differences involved in the computation of left ventricular volumes are due to inclusion of the left ular outflow tract by three-dimcnsiomal echocardi and exclusion of this volume by NMR imaging. This limita- tion was recognized at the outset of the study; however, the objective of the study was to compare the volume meawre- ment by three-dimensional echocard~ogra~hy with the roost accurate tomographic method available as it is used clini- cally. Our intent was not to closely match the two techniques but, rather, to develop a clinically practical threy-

three-dimensional echocardiography at the lower end of the

face area by tbree- ens~ona~ echoca lower end of the scale is innately 75% J~ger than the corresponding value by imaging. This discrepancy involving the y intercepts of the volume and surface area regression equations is du diBerences in tbe algorithms used by the two methods. ce, the discrepancy is due to methodologic bias rather than to random meas!~rc~e~t vari- ation. Random errors of true measuremenr would have

ducer position limits t transthoracic windows. lanes are often acqui

is ca

268 GOPALETAL. THIW,E-DIMENSIONAL ECI%.?CAPU)IOGRAP~Y

unnecessary boundary tracing. Thr: concept of using inter- gz&g images to calculate image plane position has been

P revio&y used by Geiser et al. (19). Our system continu- ously displays the three-dimensional spatial information encoded in the acoustic spatial locater data so that it can he used in an on-line, interactive, prospective fashion to guide and orient image plane positioning in real time (28). This permits optimal endocardial boundary definition while still acquiring the minhmal necessary short-axis images to ade- quately represent the ventricle. The volume aigotithm used in this study differs from that of Siu et al. (16) and from Moritz et al. (25) in that areas where the endocardial boundary is poorly defined, manual rather than computer interpolation is required.

implications. The three-dimensional echocardio- graphic method described in this study offers an excellent, repeatable, noninvasive clinical method of left ventricular end-diastolic and end-systolic volume cietermination free of geometric assumptions. Tedious boundary tracing may be minimized by carefully guiding and selecting a representa- tive set of image planes using the line of intersection display. This method may be of enormous value in closely monitoring patients with valvuiar heart disease and cardiomyopathy and after myocardial infarction. The method can also be ex- tended to compute myocardiai mass (46) free of geometric assumptions and may be especially important in monitoring the effects of hypertension, antihypertensive therapy and ventricular remodeling after myocardiai infarction. The method also offers a direct measurement of total endocardial surface area and infarct surface area without geometric assumptions (49). as well as the possibility of analyzing wall motion in a much more systematic and quantitative fashion. Both of these may be of great value in the thrombolytic era.

Conclusions. Three-dimensional echocardiography using the line of intersection display for glJidance of image posi- tioning and the polyhedral surface reconstruction algorithm is an excellent method for determining left vent;ricuhr end- diastolic and end-systolic volume as well as endocardial surface area computation in vivo. The results compare favorably with NMR imaging and seem to be superior to the two-dimensional echocardiographic apical biplane summa- tion of discs method of volume determination. A good correlation with NMR imaging is achieved through the elimination of geometric assumptions and image plane posi- tioning error.

A

Accuracy of Discrete Method qf ata Acquisition

It has been suggested in a report published after acceptance of this study that the method of data acquisition used in our investigation is subject to potential inaccuracies that will not be found in an alternative form of data acquisition (53). The method of data acquisition used in our study is to place and

JACC Vat. 22, No. 1 July 19!3.3:258-70

hold the imaging transducer ir! a desired location, ae single, discrete set of spatial quent@ acquire a series of 16 o images over the next second. The single spatial data set is assigne The alternative method is to coordinate data during image a of spatial data to each video image as it is acquired. It is asserted that the latter continuous method overcomes a

data acquisition (53). This assertion is both methods, in the absence of respi

data from these cau

a acquisition is discrete or continuous. The same authors (53) also suggest that the discrete

method of acquisition is subject to error due to transducer motion occurring during the l-s acquisition frames. We performed a study to determine if ity, in fact, produced significant error. Typically, the 16 captured video frames encompass two ventricular systoles and the diastolic interval between them. On the same 15 subjects reported in the present inve tion, we c uted end-diastolic volume twice, using first end tslic image of each data set and then the second end-diastolic image of the data set. We hypothesized that if the significant error due to transducer motion during the of discrete acquisition then there would be a si difference between the first and secon For the 15 subjects the first and second volumes traced by a single observer were compared using the paired t test. Fci end-diastoie f = -0.16 and p = 0.87. First and second volumes for end-systole were also computed. For these, I = 0.55 and p = 0.59. The results of the paired t test show that there is no significant difference between the first and second volume determinations. From these results we infer that the possibility of error by transducer motion during image ac- quisition by the discrete method does not introduce a signif- icant error into the results of volume computation. We believe that three-dimensional echocardiography signifi- cantly reduces volume computation errors by eliminating geometric assumptions and reducing image plane position errors and that the most significant errors for volume com- putation using three-dimensional echocardiography are in- troduced by manual tracing of endocardial boundaries.

Dodge HT, Sandler H, Baxley WA, Hawley RR. Us’efulness and limita- tions of radiographic methods for determining left ventricular volume. Am J Cardiol 1966;18:10-24. Maurer AH, Siegel JA. Denenberg BS, et ai. Absolute left ventricular volume from gated blood pool imaging with use of esophageal transmis- sion measurement. Am J Cardiol 1983;51:853-8. Weiss JL, Eaton LW. Kallman CH, Maughan WL. Accuracy of volume

JACC Vol. 22, No. I July 1993258-70

4. L, Meerbaum S, Feng MB<, Gueret P, Corday E. Cross-sectional echocardiography. III. Analysis of mathemakic models for qtoanbifying volume of symmetric and asymme!ric left ventric&es. Am Heart J BYSO: 1OO:821-8.

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Scbnittger 1. Fitzgerald PJ, DaugbPers GT, e; al. Ein;iretions ofcompar& left ventrtcular volumes by two-dimensional echocardiography, myocar- dial markers and c~~~~~~o~~a~~y. Am J Cardiol 1982;50:512-9.

Foiiand ED, Parisi AF. Moynihan PF, Jones DR. Feldman CL, Tow DE. Assessment of left ventricular ejection fraction and volumes by real-time t#o Qmensionai ecbocardiography. A comparison of ci~ea~g~~~a~b~c

7. s. Circulation 1979;60:760-6.

Schiller NB, Acquate’i , Ports TA. et al. Left ventricular volume from paired biplane two-d+nensional echocardiography. Circulation 1979;60: 547-55.

8. Gueret P, Meerbaum S, Wq’;iit Hk, Uchiyama T, Lang T, Corday E. Two-~irne~s~o~a~ ec~~ocar~iogra~bic ~~ant~ta~~o~ of left ientricular vol- umes and eiection fraction. Circulation 1980:62:1308-18.

Guyer DE,bibson Tc”, Gillam LD, et al. A new ecbocard~og~a~~~c model for quantifying three-dimensional endocardiai surface area. .I Am Coil Cardiol 1986:8:819-29.

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