313
J . CC Vul . 1 s. No . 2 February 1992 311-2n
On-line Assessment of Ventricular Function by Automatic Boundary Detection and Ultrasonic Backscatter Imaging JULIO E . PEREZ, MD, FACC . ALAN D . WAGGGNER, BA, RUMS, BENICO BARZILAI, MD, FACC, H . E . MELTON . JR ., PtoD, JAMES G . MILLER, PHD, BURTON E. SOBEL, MD, FACC St. Louis, Alissoori
To provide an approach suitable for on-line analysis of ventricular function, a conventional two-dimensional ultrasound imaging system was modified to detect and track blood-tissue interfaces in real time based an their quantitative acoustic properties . This modification permitted on-line display of the left ventricular cavity area, fractional area change, volumes and ejection fraction on a beat by beat basis. Images were obtained from 54 patients and 12 normal subjects with broad ranges of ventricular dimensions and systolic function. On-line measurements of cavity areas were compared with off-line measurements of cavity areas (analysis of videotaped conventional
images). Left ventricular easily areas measured on-line from short-axis views correlated closely with off-line views as did areas from apical views. On-line fractional area change correlated well with ejection fraction calculated off-line . More titan 70%5 of patients could be studied adequately with the approach developed . Thus, automatic boundary detection based on quantitative assessment of tissue acoustic properties permits on-line quant!tat(on of ventricular cavity areas and indrxgs of function. (3 Am Cell t,ardiol 1992 ;19:313-20)
Conventional two-dimensional echocardiography is a powerful tool for measuring cardiac chamber dimensions, ventricular wall thickness (it and quantifying left ventricular function with criteria recommended by the American Society of Echocardiography (2) . In clinical practice, however . ventricular function is generally assessed only qualitatively and subjectively because of the impracticality of routine quantitation of off-line video image analysis, which requires computer-assisted systems for off-line digital acquisition of selected frames, meticulous frame by frame assessment of endocardial-blood interfaces, experienced observers and labor-intensive procedures . Accordingly, considerable attention has been devoted to developing automated procedures capable of quantifying ventricular function by echocardiography 13-161 . Most approaches explored have employed off-line computer-ass i sted algorithms for outlining and enhancing the ventricular cavity and endocardial-blood interfaces . We previously equipped a commercially available echocardiegraphic system with circuitry that provides real time
two-dimensional imaging of ultrasonic integrated backccatter along each amplitude (A)-!ine of the field of view . In the present study, we utilized this system and novel software to permit on-line and real time delineation and tracking of the sharply demarcated borders between endocardium and blond based on integrated backscatter imaging . Subsequently . quantification and display of cardiac chamber cavity areas were implemented on-line, permitting serial derivation and display of indexes of ventricular function in real tine . The study was designed to determine whether !he approach developed for on-line imaging, tracking and display of cardiac ultrasonic boundaries would permit quantification of left ventricular systolic function on a beat by beat basis . Results were compared with those obtained by the traditiopal . extensively validated off-line operator-dependent echocardiographic procedures (2) .
From the Cardiovascular Division and Depanmert of Physics . Washing ,on Urivmsily. St. Louis . Missouri. This study was supponcd in pan by Grants HL17646 (SCOR in Coronvy and Vascular Hean Diseases and H1A0302 from the National tsstitute- of Heahh . Sethesda. Maryland . Man min in received April 30 . i591 revised manoscnpl received July In. 1991, sce July 23. 18°l . Address for re riot$: Julio E. H':ez. MD. Cardiovascu)a Division . Washington Un,versity, sS,1-1 of Medi ane. 660 South Euclid Avenue . box 556 . St. Louis. Missouri 63110. 11992
by eFe
American College of Cardaalogy
Mef:tols Backscatter imaging system. The modified echocardiographic system employed for quantitative integrated backscatter imaging was developed in our institution (17-21) and has been validated by others (22-251. The integrated backscatter imaging system employs a relatively long integration time (3 2 µs) over which each radiofrequency A-line is analyzed. Approximately 100 data points of backscatter are collected along each line and the information is sent to the scan converter for on-line construction of the image in real 0e35-109719265 .00
314
t'fREL LT AL . UN-LNF ASSESSMENT OF VENTRICULAR FLNCTION
jACC Vol . 19 . Nn . : February 1 .2.111-2a
Figure 1 . End-systolic conventional four . chamber(Iefrl and automatic real time boundap • detected (right( images . I he reduction in nose (specklel permits the on-line detection and
tracking of the sharply demarcated blood-tissue edges .
time (17,18). The rear iling two-dimensional integrated backscatter image data are therefore considerably smoothed and averaged, resulting in marked reduction of speckle (26) noise in the image . Accordingly, discrimination of the endocardialblood interfaces or boundaries (those with significantly different backscatter or sign :d strength) is facilitated, allowing automatic detection and •racking of these boundaries in real time (Fig . 1). Refinements of previous approaches (8) and the addition of novel software developed for the present study permit the operator to trace a region of interest around the well delineated Mood pool cavity (Fig . 21 . A calculation and graphics software package then computes and displays the area of the cavity within the region of interest instantaneously (in cm) along with the fractional area change (in %) for each beat . Oil the basis of geometric assumptions applicable to the chamber of interest . other variables, such as c wily diastolic and systolic volume . stroke volume and ejection fraction, can be derived readily in real time on a beat by beat basis (Fig . 31 . Normal subjects and patient, studied. After written informed consent was obtained, images were obtained in studies of 12 normal subjects and 54 unselected in-hospital and outpatients in whom a conventional two-dimensional echocardiogram had been ordered for evaluation of ventricular function . diagnosis or assessment of the severity of ischemic heart disease with respect to regional or global will motion abnormalities . evaluation of valvular heart disease or cardiomyopathy (dilated and hypertrophic) or preoperative evaluation of potential lung or heart transphnt recipients or patients with peripheral vascular disease . Procedures . after each conventional two-dimensional echocardiographic view was obtained and recorded (longaxis, short-axis and apical four-chamber views), the respective automatic boundary detection, real time . backscatter
images were obtained from each . To implement the automatic boundary detection image. we first obtained the highest possible quality conventional two-dimensional echocar diogram as defined by the optimal delineation of endocardiat surfaces . Without any change in transducer placement . the backscatter imaging boundary detection algorithm was acti-
Figure 2. End-diastolic frame of a lour chamber automatic boundary-detected image (small sector in upper right turner) with a region of interest (solid white line) drawn amend the left ventricular easily . The top graph shows the cavity area computed and displayed instantaneously with calibration marks tin cm-1 and with the electrocardiogram displayed for timing purposes . Die helium graph displays the on-line computed fractional area chance who calibration marks (in Sf) .
(ACC Vnl 19 . Na 2 Fe:n-, 19 v2 II -11
Figure
3.
PEREZ CT AL . uN.l-IFF ASSESSMENT OF VENTRICULAR FUNCTION
315
End-diastolic frame of a (our-chamber auto-
matic heonderg-detected image r, .all rector in loner left corner) with the region of into e, ; drmsn around the left ventricular cav try . S he graphs ea the right demonstrate from tap m bottom The instantaneously nwa,urcd and displayed cavity area (calibrated IT. emi t . cavity volume
rcalibrated in cm'l and ejection fraction computed beat by heal calibrated In cm! 'k
vsted . In most patients, minor adjustments in the time-gain compensation settings and transmit-gain control were required as bright gray dotted lines were automatically in scribed and superimposed in a tracking fashion (diastof_ to systole) over the endocardial blood interface deieeted by the algorithrrt . The compression and postprocessiag controls are not operational with the boundary detection imaging mode . and the preprocessing control was not changed from Jtat used for acquisition of the conventional images . Once a suitable stable image was obtained . a cursor crosshair was g ted within the teal time boundary-detected image . The trackball of the system was used by the operator to position the cursor and draw a line through the mid-myocardial echoes and around the left ventricular cavity to select a region of interest containing all portions of end-diastolic and end-systolic cavity areas- Graphics mere then displayed in real time with a software package providing a menu (area . fractional area change) . Backwater images were recorded on 0 .5 in . (1 .27 cmt videotape as well . In addition to area and fractional area change graphics, displays of cavity volume curves from the four-chamber view were used to provide an estimate of stroke volume and ejection fraction on a heat by heat basis . Relations between on-line measurements obtained from automated processing of the backseatter image and results of offtine conventional anaysis of images recorded on videotape . To evaluate the accuracy of the automated system and algorithms for measurement of cavity areas, displayed left ventricular areas (end-diastolic at the peak of the area tracing and end-systolic at the nadir of the tracing) defined by the on-line automated backscatter boupdary detection system (at least 3 beatslpatient ; mean - 3O) were compared with the off-line measurement of the same boundary detection images recorded on videotape . The off-line measurements were performed independently by two of the investigators using the trackball of the imaging system and with
iu the recorded video images, In the initial studies, those cardiac ,ycles used for on-line measurements were not the same as those analyzed off-line from the video recordings because the grapt,cc displays had to be turned off so that the full screen image with the boundary detection algorithm display could he obtained for off-line analysis . Thus, in the initial studies . comparisons of on-line and off-line data were obtained with sets of cycles obtained within tit s of each other . Mean values (C SD) of diastolic and systolic cavity areas for the on-line and off-line methods were compared statistically by regres ;sr a^°t7° :e. We then compared end-diastolic and end-systolic left ventricular cavity areas detected by the automatic backscatter image boundary detection algorithm with the corresponding cavity areas measured off-line from conventional twodimensional echocardiugraphic images (with the boundary detection algorithm of the system turned off) using the trackball of the imaging sysicm . Again, the two sets of data being compared were obtained from sets of cardiac cycles within 10 s of each other (oonsimultaneous beats) . Simultaneous on-line data and conventional images . Additional software added to the system after the study had been initiated permitted simultaneous real time display of the conventional two-dimensional echocardiogram (with the automatic boundary detection algorithm engaged but not contributing to the display) and the cavity area data computed by the algorithm in real time . The echocardiographic image was displayed as two-thirds of the standard full size screen (Fig . 4t. permitting comparison of the conventional image area (measured off-line with the trackball( with the simultaneous automated computation of area for the same cardiac cycle . Comparisons of this type were performed in 23 patients in both the short-a ;tis a :td four-chamber views . Fractional area change. Comparisons were also made between the mean values of fractional area change calcu-
off-line calibration based on the centimeter scale
316
YEREZ ET AL Oft-LINE ASSESSMENT
'15 "EN
1ACC Vol. Iv. Na . I F0 nuury 10x2'311211
F.ICULARFUNC77 ;N Table 1 . Validation of Algorithm r Value Nomimullaneou, heals LV area. WS asi, -On-line EL v, . nlt-hoe ED n v5 Oe'line ES vs. nn-lire ES 11 .70 LV area. shun a.i, cmw Dn-line ED vs . nfLl ee ED 0 vs Dn-tine ES vs en tine Es O .W LV area. In., chamber lieu; On-tine ED vs . entire ED 097 On-l-ESvs offlirnES Ow. ED = end-diastole : ES = end-ss,o,le : IN
SEL
ICm'1
No .
R 2 0
IS
2 8
10 10
2
15 Is
= let
vemnculer .
and correlation coefficients were obtained for each comparison . Ejection fraction on-line . With novel software that was added to the system to permit estimation of the cavity volumes (in ml) based on the area measurements in real time . ejection fraction was displayed as well [Fig . 3). The, estimation of ventricular volumes was based on the assumption that volume cann be estimated by the ratio of the area of the ventricle in the shorl-axis view to that in the apical fourchamber view. Our purpose was not to validate this approach for calculation of volume itself. It was simply to compare one estimate of ejection fraction (on-line) with another established estimate of ejection fraction calculated off-line .
Results
Figure 4. A, Stop Frame of a shor :axis autonatic boundarydeteeled image displayed in the lop two-thirds ef(he screen . with the on-line instantaneous cavity area graph displayed below . The image displays the circular region of interest drawn through the midmyocardial echoes (white bright line) . B, Stop frame obtained I s after A, aow with the automatic boundary-detected image engaged but concealed from the image. Thus, the image does not show the borders (concealed). although the graph on the bottom continues to depict the algorithm-detected and computed cavity area fin em' ;. The larger (two-thirds of screen size) image without the border, shown is recorded cn tape and the cavity measured off-line with use of the trckbail. Results are compared with the algorithm-detected areas as displayed and recorded in the same cardiac cycle . latcd on-line (from each of the echocardiograpi -tic views) and corresponding values obtained off-line . The fractional area change obtained on-line front the apical four-chamber view was compared with the ejection fraction determined off-line by either the area-length method (2) or the method of Quinones et al . (27) (both methods were used in 44 patients)
We obtained satisfactory studies with automatic boundary detection in 48 (727) of 66 patients and subjects, with detection and [racking of the endocardial-blood interfaces sufficient to permit analysis of cavity area in at least one of the three echocardiographic views . In addition to these criteria, we considered a study as satisfactory when, while turning the borders on and off during the study, we could ensure that a close estimate of the true endocardiunn was obtained by the automatic boundary detection method . Of these 48 patients, 13 had global left ventricular dysfunction and 8 had segmental dysfunction. The performance of automatic boundary detection in a single view (shoe-axis or four-chamber) added approximately 3 to 5 min to the study. Off-line analysis on videotaped data took approximately 10 min per view (se!ccl :cn . freeze iiame and analysis) . Validation of the algorithm (Table 1). Results with the algorithm and real time boundary detection system compared with off-line results from recordings of the same boundary-detected images in comparable views are shown in Table I . The correiations between the two sets of results were r-lose with small standard errors . Thus, the algorithm displayed cavity areas (in cm °) accurately as imaged. Validation of the method ( .able 2). Comparisons between left ventricular cavity areas (end-diastolic and end-systolic)
)ACC Vol. 19 . Nu. . Fehrrar. I'or : )li- 2 o
ON .LINI . ASSLSSMENT
OF
PEREZ ET AL . VENTRICULAR FUNCTION
317
Table 2. Autoluatic &nmdars Detection Image On-line Verru, Loftenuonai - I - we-Dimensional Off-line Measurements Mean Nomimulteiir bear, t .v ,re . , h° I anti „e,. 40)) sn- .a e I-.I) MA i,11 ED ARU nn-t is Ls 21) u lLire 1 S I.V
s . U .~,
oIt
No .
r Value
34
0 .83
4 .6
(a
0,91
3.9
SCE
lentil
18.9 .94 2 :1-nn
5a 46
L_' - 411
t_i'
I' .7 r 9'7
-7-46
$I3 III : rgll ~ u ~
IM-ht
76
sirs
'911' II I '- u - to I
I'_-a I I-a3
36
11111,
Ia5
3'-u ,
I3
0.99
13
(1.99
0 .6
Il-an
Sembn n
ARID un-Imc I ..D 21
SO mRanpe kill
In, ED
ABD on
line ES 2D oil lure I c Simuitanenu . heat, LVAtan area..•h on-:un 0 lire FD 2D off-line ED ABD online FS
'-rdl 5 .2
,rc„ Ii I - "7
Ill-796
"O Iin 3-s
are:, .loutchunlber,ieu ABD "name ED 2D u0-line ED AUC omlmc ES
LV
2D offline ES ABU =
amonmtic boundan
dear, ie. 21)
1
29
0 .93
2-
24 5
Ill ,
7t
'17
Il3
s : :_11 _^
20
0,98
21
2I5
10 0
In %- .(,6
Srcdoemionulech :cardi.ivaphi mhttahhrevralionrasinT'ahlel .
analyzed on-line and off-line and measurements of corresponding areas calculated off-line from videotaped consentional echocardiographic images (short-axis and apicai fourchamber views) are shown in 'Table 2 . Correlations were close. considering that the data were obtained from different cardiac cycles and v-ithout control for the respiration cycle cr preclusion of patient motion that n ay have influenced the two sets of data acquisition differentially . Additional measurements obtained in the 23 patients with a fn-mat that displayed conventional echocardiographic images simultaneously with the computed area tracing obtained with the automatic boundary detection system in the same cardiac cycle are shown 1n 'fable 2 and figure 5 . They illustrate the accuracy of the method when the same cardiac cycle is employed for on-line (automated) and conventional off-line measurements (trackball caliper procedure) . Fractional area change . Percent change in fractional area was displayed on-line with the automatic boundary detection system for end-diastolic and end-systolic areas from each view . This functional index is derived from the areas directly without any needed assm .gnions of cavity geometry . We first compared the fractional area change derived on-line by arbitrarily Cawing a icgion of interest on parasternallongaxis views in a group of 15 patients with that obtained by off-line planimetry of .orrespondmg areas . The correlation was close (29.4 x 12 .4% compared with 30 .1 . 13 .2% : r 0 .93, SEE 4.7% : different cardiac cycles) . Fractional area change derived from the automatic boundary detection measurements of areas in short-axis views was somewhat lower (41 .3 t 16.7%) than that derived from the off-line trackballmeasured areas (47 .1 * 18 .1% ; n = 34: p = 0.1 ; different
cardiac cycles) and the correlation was less close (r - 0.75) . Fractional area change derived on-line by the boundary Jetection algorithm from apical foul-chamber eiews was significantly lower than that from off-line conventional image measurements (22 .9 t 11 .2% vs . 31 . 12 .9% : n = 36; p < 0 .006) . Thus . despite reasonable correlation (r = 0 .77), the automated boundary detection measurements underestimated fractional area change when different cardiac cycles were employed for comparisons . Comparison with ejection fraction estimated off-line . Online fractional area change (parasternal long-axis views) corelated closely with left ventricular ejection fraction estimated off-line by the method of Quinones et al . (27) (r = (1 .84 : SEE = S% : n = 25 patients) . On-line fractional area change (short-axis view) correlated less closely with election fraction estimated off-line by the method of Quinones et al . (27 i (r - 0 .63 ; SEE = 13% ; n - 33 patients) . However, the correlation was closer when the fractional area change derived on-line from the apical four-chamber views was compared with ejection fraction estimated off-line by the method of Quinones et al . (27) (r = 0 .83 ; SEE = 7 .0% ; n 37 paucnlsj . Ejection fraction estimated on-line. The automatic boundary detection on-line-measured chamber cavity areas were used 'o extrapolate volumes and ejection fraction as previously described (Fig . 3) . The boundary detection on-line measurements of ejection fraction were compared with estimates of ejection fraction off-line . The on-line estimates from the four-chamber view 140 .4 15 .1%) were not significantly different (p = 0.06) from estimates off-line calculated by the method of Quinones et al . (27) (46 .6 17%) in 48
318
PEREZ ET AL . ON-LINE ASSESSMENT OF VENTRICULAR FUNCTION
IACC Vol. W. No.2 Fcbn,sry 1492'.510-20
•a
5EE
1
1. 2a an eo fin LV APICa1 Ena-OiantaUv Area (AM) (emrl
A
W
L1_'l
I 20 70
p
Er 4
i 50 BB .0
I
an rH ra 6a Be
Bp Bo 4
60 r
al) --
50 ==qt
W ~'
D
-$007
20 c
30 a
_a LO
0
B
10 Figure e0
B
SEE
20
30
n0
W Aroal EnmSysidic Ana (ABU)
50
60
121 2 )
N
6 . A, Comparison
aB 6B 0 FF py ABU e
•e sn
I r 1n 60 eo
between left ventricular ejection fraction
(EF) determined by the on-line autumade boundary detection IABDI method (abscissa) and that determined oft-line from conventional images by the method of Quinones et al . (27) (ordinate) in 48
Figure 5 . Comparisonn of left ventricular (LVI end-diastolic (upper
patients and subjects (nonsimuitaneous heats) . B, Comparison be-
panel) and end-systolic (bottom pencil cavity areas (apical fourchamber views) measured by both the on-line automatic boundary
tween left ventricular ejection fraction determined by the on-line
detection (ABD) algorithm and the off-line trackball operator-traced
chamber view and tha single-plane area-length method computed off-line from recopied conventional echocardiographic images (non-
method (Conventional) in the same cardiac cycle (simultaneous method) .
automatic foundary detection method Iabsien) from apical four-
simultaneous beats) ir .44 patients and subjects .
in freeze frames of video recordings and the impracticality of patients and the correlation was close (r = 0 .86: SEE = 8.8%) (Fig . 6A) . The on-line estimates (40 .6 . 15.6%) were
rapid acquisition of results .
not significantly different (n = 44 . p = 0 .061 from values
results demonstrate the feacih'dily of performing measure-
determined off - .me by the single plane area-length method . (47 .6 17%c) and the correlation was close (r = 0 .87 : SEE _
ments on-line under clinical conditions in normal stibiects
8.5%) (FSg . 6i3) .
dimensions and compromise of ventricular function . The
Current implementation of on-line measurements. Our
and unselected patients with e wide range of cardiac cavity
algorithm accurately depicts ventricular cavity area (in cm) analogous to a volume curve as evident from the close Discussion
correlations of algorithm-acquired area estimates with offNeed fur quantimdon in echocardiography . Real time
line measurements of the recorded boundary-detected image
automatic detection of the tissue cavitary-blood boundary
(Table I). In addition, it characterizes chamber size accu-
has been an objective of research in trio-dimensional echo-
rately . as
cardiography for more than a decade (3-16). Approaches
on-line estimates based on cavity areas and off-line estimates
based on statistical estimation of the brightness of the
measured in different cardiac cycles . Even higher correla-
borders in conventional echocardiograms have been em-
tions were obtainable when the areas were measured from
ployed for off-line smoothing and approximation of edges to
the same cardiac cycle by both methods in 23 subjects and
quantify wall motion. The approach we developed is predi-
patients (Table 2) . In the present study, we 10Th a conser4-
cated on the quantitative power of measuremeiu of acoustic
ative approach and analyzed function on the basis of com-
is evident from the high correlations between
properties of the tissue in real time . It results in reduction of
parisons between on-line and off-line data from different
speckles in the % .wage, permitting detection and improved
cardiac cycles obtained within 10 s without control for
tracking of the tissue-blood interface . The algorithm we
respiratory motion. patient motion or transducer location
employed is promising for clinical applications and may
and angulation . Despite the impact of these variables, the
obviate difficulties encountered with the labor-intensive .
correlations are close enough to support the view that the
time-consuming, off-line method. That method, which we
on-line method will be a clinically useful alternative to the
used as a standard for comparison has not gained wide
current tedious off-line analysis or simple subjective inter-
clinical acceptance because of degradation of image quality
pretation of ventricular function front analysis of conven-
IACC Vel.i9 .Na .2 Fe6m1vy 1112 M12.
tional
PfREZ FT a L. ON-LINE ASSESSMENT OF 'IENTRICULAR FUNCTION
two-dimensional echocardiograms
(28).
The auto-
319
because it is based on multiple linear dimensions and their
mated procedure should facilitate longitudinal assessments
change with systole, integrated from all cardiac views, rather
of ventriculat function in serial studies in patients With
than on geometric assumptions for ventricular shape . The
vaivular . congenital and coronary heart disease .
closc correlations obtained when the single-plane aiea-
Compazison with previous recommendations . Measure .
length method (recommended by the American Society
of
ment of ie t ventricular cavity areas and changes in fractional
Echocardiography) (21 was used further confirm the validity
area from the short-axis views has been recommended by
ui
the American Society of Echocardiography
(2)
iae
to quantify
automated approach .
Conclusions. Our results indicate that quantification
of
vennMular tunetion . With the automatic boundary detection
tissue acoustic properties in real time permits detection and
method described here, estimates of diastolic and systolic
tracking
areas are somewhat, lower in absolute terms . 'the method
'u :mtification
outlines the papillary muscles and excludes their area from
development of this approach should provide assessment of
the measurement of cavitary areas . whereas the conven-
segmental ventricular function under conditions of stress
tional method ignores space occupied by the papillary mus-
:cho:ardlugraphy and serial monitoring of ventricular per-
cles, resulting in, a higher salue for the area. However .
formance in an individual patient in settings such as the
values for fractional area change correlate quite well with the
coronary care unit and operating room (transesophageal
two methods .
imagingl. i n which changes must be detected promptly so
On-line ejection fraction . In the present study . We utilized a first-step approach to derive estimates of ejection fraction
of
the endocardial-blood interfaces, facilitating of ventricular function on-line . Continued
that appropriate adjustments in treatment can be made without delay .
on-line from estimates of ventricular vo'arles based on a simple approximation of short-axislfour-chamber area ratio .
We are grateful to Debbie Taylor for excellent secrcarial assistance.
The close correlation. between ejection fraction estimated on-line and that measured off-line in patients exhibiting mild to profound ventricular dysfunction of diverse etiologies suggests that the on-line estimation
of
useful information, even at an early stage
area change derived from parasternal long-axis views corre-
ejection
~mhran H . F.chaerdiog;aphy. Philadelphia : Lea I27-87.
development .
On-line fractional area change . The on-line fractional
lated well with global
References
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of its
a
`cUiger. 1986 :
2 . Shah PM . Crawford M. Deiana A . et al. Recommendations for gnantinotian at the left vemdde by Iwo .dimensional echocardiography . I Am Son Echn 1989 ;2:358-67
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4.
E.
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5.
oreurs in the minor axis, Obviously, patients with apical hypakincsia, akinesia or dyskinesia will require a thorough evaluation
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'w. Levy R. Garcia E . c1 ai . Validation of a compumnud edge Jerea~,n algorithm for itnecu alive twodimenvonot echocardiogaphy. CircuiaL,n 1983 :68:1127-35 . Bode AJ. Skip Ff . Meyer CR, et .1 -pole, P--mig of
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probably l4i
so the beam.
facilitating detection and tracking. We
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anisotropy (291 of
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:as
and normal subjects .
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SM . Skunun D3. Geisr• CA . It al . Computer-aesisled edge nintwo-dimenvunalecnocardiograpny :c ,. . . .f de a,Am J Cardin] 1994 :53 :1380-7 . ii . GratcE .RacksA .Back, .LudericoB .AatomatischeKontarerkennurg 0 wcidimensionalen Echskardiogramm .Untersuchongen an oirom e0gemeinen Palientenkollcktiv . Z Kardial ;985:74 :445-52. I.
Concua 13A . Geiser EA . Olive, I.H . Miller An . Cone CR. Reproducibil . its of left ventricular area and volume measurements sing a computer cordial edge-detection atgeotbca in normal subject, :4m 3 Card :al 1988.% :947-52 .
meticulous attention to the
transmit-gain and time-gam compensation controls t0 ensure that the endocardial edges visualized on conventional images
13 . Chu WW. Lao LMT. Task-allocation and precedence relations for dlstvbuted real-time systems. IEEE Compel 1987 :36:667-79 . 14. Geiser EA. Oliver LH. Gardin 1M . Clmoai validation of an edge detection algorithm for iwodimensional echacardiogaphic shun axis
are being detected and tracked by the novel algorithm . fraction. The method of Quinones
nag,, . l Am Son Echo 1988 :1 :410-21 . 15, Gesso EA .. Came DA . Limorher MC, Ostlund Slocklon V . Oliver LH,
for determining ejection fraction was employed
tones B . A second generation camporer-based edge detection algorithm
Validation of et at.
(27)
ejection
320
PEFEZ El' AL. ON LINE ASSESSMENT OE VENFRILULAB FLNCTr'iN
(or short ash, two-dimensional eckinnrdiographic images : accuracy and improvement in interohserver variahiloy . 1 Am Soc Echo I99t1 :1 :19-91J . 16. Geiser E .A . Wilson 0C, Gibby GL . Applications of cans correlation techniques to the quaniilatmn of wall motion m shoe a dimensional echacandiographic images . I Am Sac Echo I99J .3 :766-71. I7, Vercd Z. Barzilai B . Mohr GA, ei al . Quantitative ultrasonic tissue characterization with real-lmn, imegmted backsedtter imaging in normal human sublecrs an patens will ddaled cardiomyopalhy. Circulation 1987,'4 :1067-73 . I9 . Thomas LI III . Barzilai B . Perez JE. Sobe; BE . Wi,kline SA . MA.. 1G . Quantitative real-time imaging of myocardium based on ultrasonic mtee grated backronner . IEEE Franc tlltroc e Ferroetecir Frequency Control 1969.36 :466-70. 19 . Vered Z . Mohr GA. Barzdat B . el al. Ultrasound integratetei huckscatter tissue charadrrivation of remote myocardial infarction in human sub jecls J Am Cull Cordial 1999 :11 :94-91 . 20 . Mil-ski MR . Canter CE, fcickline SA, Sahel BE . Miller JG, Perez JE . Card : ac cyciedependem variation of integrated backseatter is not dis toned by abnormal myocardial wall motion in human subjects with parad .rbal septa) motion . U:tm,a,nd Fled Bial 1989 :15311-7. 21 . MilunsL MR . Malt GA, Perez JE . el al . Ultrasonic tissue characleriza . Lion with integrated backseatter : acute myocardial ischen,ia, reperfusien, and slunned myocardium in patients. Circulation 1969 :80 :491-503. 22 . Masuyama T, Nellessen U . Schnitigcr ., Tye T . Haskeil WE. Popp RE. Ultrasonic tissue characterization with a real time integrated back-ale,
.19 No .2 1 V,, IACC . February 195!:111-20
imaging system is normal and aging human beans . J Am Cull Cardiol 1969 :14:1702-6 . 23 . Ma tiyarna T, Valanline HA . Gibbonn B. Schnillger 1. Popp BE Serial s of integrated ultrasonic backseatter in human cardiac allograftsnlort the recognition of acme rejeciion .Orculatioa 1999 .91 :e2939. 14 . Vandonboe6 OF . Ruth I . ShouplA Gerber RE . Collins SM, Shaman 0J Cyclic variation of ultrasound backseatter in normal myaardium is ew-0ependeal clinical studies wall a rechrime tsmkscmler imaging system . I 4m Soc Echo 1989 :2-308-14, 25 . Vanderra,rg BF, Swhlmuller )E. Bath I ., et al . Diagnosis o1 re myocardial mlarctmn wnh quamiiative backvcauer imaging . preliminary studies . I Am Soc Feb . 1991 :4 .10-8. 26 . Skartan Dl, Miller JG. Wickline SA . Borzilai B . Collins SM, Perez JE . Ultrasonic cimracmrizatian of cardiovascular tissue . In Mmra M . Schelben HR. Station 1)1 . Wolf G . eds . Cardiac Imaging : Principles and Practice. Ph adelphia : WO Sounders, 19991:539-56 . 27 . Quirones MA. Waggoner AD . Red.,. LA . et al. A new . stmpl hrd and curare method for delermirsng ejection (rectton with tmo-dimensiom l echscaedwgtaphy . Circulation 19619( :745-a3 . 28 . Wong kl. Brace S . toseph D . Lkoiy H, Estimating left ve dculor ejectioi, Ira' lion from two dimensional echocardiogram nazi and earn polerprocessed interpmtatioos. Echcuardiographv 1991,6 :1-7 . 29 . MmLras El . Per,, lE . Nobel BE . Miler JIG. Anisotrory of ultrasonic backscalleroGnyocardaltissue.11 . Measurements in ivo .IAccustSoc Am 1996 :63(762-9.
J . CC Vul . 1 s. No . 2 February 1992 311-2n
On-line Assessment of Ventricular Function by Automatic Boundary Detection and Ultrasonic Backscatter Imaging JULIO E . PEREZ, MD, FACC . ALAN D . WAGGGNER, BA, RUMS, BENICO BARZILAI, MD, FACC, H . E . MELTON . JR ., PtoD, JAMES G . MILLER, PHD, BURTON E. SOBEL, MD, FACC St. Louis, Alissoori
To provide an approach suitable for on-line analysis of ventricular function, a conventional two-dimensional ultrasound imaging system was modified to detect and track blood-tissue interfaces in real time based an their quantitative acoustic properties . This modification permitted on-line display of the left ventricular cavity area, fractional area change, volumes and ejection fraction on a beat by beat basis. Images were obtained from 54 patients and 12 normal subjects with broad ranges of ventricular dimensions and systolic function. On-line measurements of cavity areas were compared with off-line measurements of cavity areas (analysis of videotaped conventional
images). Left ventricular easily areas measured on-line from short-axis views correlated closely with off-line views as did areas from apical views. On-line fractional area change correlated well with ejection fraction calculated off-line . More titan 70%5 of patients could be studied adequately with the approach developed . Thus, automatic boundary detection based on quantitative assessment of tissue acoustic properties permits on-line quant!tat(on of ventricular cavity areas and indrxgs of function. (3 Am Cell t,ardiol 1992 ;19:313-20)
Conventional two-dimensional echocardiography is a powerful tool for measuring cardiac chamber dimensions, ventricular wall thickness (it and quantifying left ventricular function with criteria recommended by the American Society of Echocardiography (2) . In clinical practice, however . ventricular function is generally assessed only qualitatively and subjectively because of the impracticality of routine quantitation of off-line video image analysis, which requires computer-assisted systems for off-line digital acquisition of selected frames, meticulous frame by frame assessment of endocardial-blood interfaces, experienced observers and labor-intensive procedures . Accordingly, considerable attention has been devoted to developing automated procedures capable of quantifying ventricular function by echocardiography 13-161 . Most approaches explored have employed off-line computer-ass i sted algorithms for outlining and enhancing the ventricular cavity and endocardial-blood interfaces . We previously equipped a commercially available echocardiegraphic system with circuitry that provides real time
two-dimensional imaging of ultrasonic integrated backccatter along each amplitude (A)-!ine of the field of view . In the present study, we utilized this system and novel software to permit on-line and real time delineation and tracking of the sharply demarcated borders between endocardium and blond based on integrated backscatter imaging . Subsequently . quantification and display of cardiac chamber cavity areas were implemented on-line, permitting serial derivation and display of indexes of ventricular function in real tine . The study was designed to determine whether !he approach developed for on-line imaging, tracking and display of cardiac ultrasonic boundaries would permit quantification of left ventricular systolic function on a beat by beat basis . Results were compared with those obtained by the traditiopal . extensively validated off-line operator-dependent echocardiographic procedures (2) .
From the Cardiovascular Division and Depanmert of Physics . Washing ,on Urivmsily. St. Louis . Missouri. This study was supponcd in pan by Grants HL17646 (SCOR in Coronvy and Vascular Hean Diseases and H1A0302 from the National tsstitute- of Heahh . Sethesda. Maryland . Man min in received April 30 . i591 revised manoscnpl received July In. 1991, sce July 23. 18°l . Address for re riot$: Julio E. H':ez. MD. Cardiovascu)a Division . Washington Un,versity, sS,1-1 of Medi ane. 660 South Euclid Avenue . box 556 . St. Louis. Missouri 63110. 11992
by eFe
American College of Cardaalogy
Mef:tols Backscatter imaging system. The modified echocardiographic system employed for quantitative integrated backscatter imaging was developed in our institution (17-21) and has been validated by others (22-251. The integrated backscatter imaging system employs a relatively long integration time (3 2 µs) over which each radiofrequency A-line is analyzed. Approximately 100 data points of backscatter are collected along each line and the information is sent to the scan converter for on-line construction of the image in real 0e35-109719265 .00
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t'fREL LT AL . UN-LNF ASSESSMENT OF VENTRICULAR FLNCTION
jACC Vol . 19 . Nn . : February 1 .2.111-2a
Figure 1 . End-systolic conventional four . chamber(Iefrl and automatic real time boundap • detected (right( images . I he reduction in nose (specklel permits the on-line detection and
tracking of the sharply demarcated blood-tissue edges .
time (17,18). The rear iling two-dimensional integrated backscatter image data are therefore considerably smoothed and averaged, resulting in marked reduction of speckle (26) noise in the image . Accordingly, discrimination of the endocardialblood interfaces or boundaries (those with significantly different backscatter or sign :d strength) is facilitated, allowing automatic detection and •racking of these boundaries in real time (Fig . 1). Refinements of previous approaches (8) and the addition of novel software developed for the present study permit the operator to trace a region of interest around the well delineated Mood pool cavity (Fig . 21 . A calculation and graphics software package then computes and displays the area of the cavity within the region of interest instantaneously (in cm) along with the fractional area change (in %) for each beat . Oil the basis of geometric assumptions applicable to the chamber of interest . other variables, such as c wily diastolic and systolic volume . stroke volume and ejection fraction, can be derived readily in real time on a beat by beat basis (Fig . 31 . Normal subjects and patient, studied. After written informed consent was obtained, images were obtained in studies of 12 normal subjects and 54 unselected in-hospital and outpatients in whom a conventional two-dimensional echocardiogram had been ordered for evaluation of ventricular function . diagnosis or assessment of the severity of ischemic heart disease with respect to regional or global will motion abnormalities . evaluation of valvular heart disease or cardiomyopathy (dilated and hypertrophic) or preoperative evaluation of potential lung or heart transphnt recipients or patients with peripheral vascular disease . Procedures . after each conventional two-dimensional echocardiographic view was obtained and recorded (longaxis, short-axis and apical four-chamber views), the respective automatic boundary detection, real time . backscatter
images were obtained from each . To implement the automatic boundary detection image. we first obtained the highest possible quality conventional two-dimensional echocar diogram as defined by the optimal delineation of endocardiat surfaces . Without any change in transducer placement . the backscatter imaging boundary detection algorithm was acti-
Figure 2. End-diastolic frame of a lour chamber automatic boundary-detected image (small sector in upper right turner) with a region of interest (solid white line) drawn amend the left ventricular easily . The top graph shows the cavity area computed and displayed instantaneously with calibration marks tin cm-1 and with the electrocardiogram displayed for timing purposes . Die helium graph displays the on-line computed fractional area chance who calibration marks (in Sf) .
(ACC Vnl 19 . Na 2 Fe:n-, 19 v2 II -11
Figure
3.
PEREZ CT AL . uN.l-IFF ASSESSMENT OF VENTRICULAR FUNCTION
315
End-diastolic frame of a (our-chamber auto-
matic heonderg-detected image r, .all rector in loner left corner) with the region of into e, ; drmsn around the left ventricular cav try . S he graphs ea the right demonstrate from tap m bottom The instantaneously nwa,urcd and displayed cavity area (calibrated IT. emi t . cavity volume
rcalibrated in cm'l and ejection fraction computed beat by heal calibrated In cm! 'k
vsted . In most patients, minor adjustments in the time-gain compensation settings and transmit-gain control were required as bright gray dotted lines were automatically in scribed and superimposed in a tracking fashion (diastof_ to systole) over the endocardial blood interface deieeted by the algorithrrt . The compression and postprocessiag controls are not operational with the boundary detection imaging mode . and the preprocessing control was not changed from Jtat used for acquisition of the conventional images . Once a suitable stable image was obtained . a cursor crosshair was g ted within the teal time boundary-detected image . The trackball of the system was used by the operator to position the cursor and draw a line through the mid-myocardial echoes and around the left ventricular cavity to select a region of interest containing all portions of end-diastolic and end-systolic cavity areas- Graphics mere then displayed in real time with a software package providing a menu (area . fractional area change) . Backwater images were recorded on 0 .5 in . (1 .27 cmt videotape as well . In addition to area and fractional area change graphics, displays of cavity volume curves from the four-chamber view were used to provide an estimate of stroke volume and ejection fraction on a heat by heat basis . Relations between on-line measurements obtained from automated processing of the backseatter image and results of offtine conventional anaysis of images recorded on videotape . To evaluate the accuracy of the automated system and algorithms for measurement of cavity areas, displayed left ventricular areas (end-diastolic at the peak of the area tracing and end-systolic at the nadir of the tracing) defined by the on-line automated backscatter boupdary detection system (at least 3 beatslpatient ; mean - 3O) were compared with the off-line measurement of the same boundary detection images recorded on videotape . The off-line measurements were performed independently by two of the investigators using the trackball of the imaging system and with
iu the recorded video images, In the initial studies, those cardiac ,ycles used for on-line measurements were not the same as those analyzed off-line from the video recordings because the grapt,cc displays had to be turned off so that the full screen image with the boundary detection algorithm display could he obtained for off-line analysis . Thus, in the initial studies . comparisons of on-line and off-line data were obtained with sets of cycles obtained within tit s of each other . Mean values (C SD) of diastolic and systolic cavity areas for the on-line and off-line methods were compared statistically by regres ;sr a^°t7° :e. We then compared end-diastolic and end-systolic left ventricular cavity areas detected by the automatic backscatter image boundary detection algorithm with the corresponding cavity areas measured off-line from conventional twodimensional echocardiugraphic images (with the boundary detection algorithm of the system turned off) using the trackball of the imaging sysicm . Again, the two sets of data being compared were obtained from sets of cardiac cycles within 10 s of each other (oonsimultaneous beats) . Simultaneous on-line data and conventional images . Additional software added to the system after the study had been initiated permitted simultaneous real time display of the conventional two-dimensional echocardiogram (with the automatic boundary detection algorithm engaged but not contributing to the display) and the cavity area data computed by the algorithm in real time . The echocardiographic image was displayed as two-thirds of the standard full size screen (Fig . 4t. permitting comparison of the conventional image area (measured off-line with the trackball( with the simultaneous automated computation of area for the same cardiac cycle . Comparisons of this type were performed in 23 patients in both the short-a ;tis a :td four-chamber views . Fractional area change. Comparisons were also made between the mean values of fractional area change calcu-
off-line calibration based on the centimeter scale
316
YEREZ ET AL Oft-LINE ASSESSMENT
'15 "EN
1ACC Vol. Iv. Na . I F0 nuury 10x2'311211
F.ICULARFUNC77 ;N Table 1 . Validation of Algorithm r Value Nomimullaneou, heals LV area. WS asi, -On-line EL v, . nlt-hoe ED n v5 Oe'line ES vs. nn-lire ES 11 .70 LV area. shun a.i, cmw Dn-line ED vs . nfLl ee ED 0 vs Dn-tine ES vs en tine Es O .W LV area. In., chamber lieu; On-tine ED vs . entire ED 097 On-l-ESvs offlirnES Ow. ED = end-diastole : ES = end-ss,o,le : IN
SEL
ICm'1
No .
R 2 0
IS
2 8
10 10
2
15 Is
= let
vemnculer .
and correlation coefficients were obtained for each comparison . Ejection fraction on-line . With novel software that was added to the system to permit estimation of the cavity volumes (in ml) based on the area measurements in real time . ejection fraction was displayed as well [Fig . 3). The, estimation of ventricular volumes was based on the assumption that volume cann be estimated by the ratio of the area of the ventricle in the shorl-axis view to that in the apical fourchamber view. Our purpose was not to validate this approach for calculation of volume itself. It was simply to compare one estimate of ejection fraction (on-line) with another established estimate of ejection fraction calculated off-line .
Results
Figure 4. A, Stop Frame of a shor :axis autonatic boundarydeteeled image displayed in the lop two-thirds ef(he screen . with the on-line instantaneous cavity area graph displayed below . The image displays the circular region of interest drawn through the midmyocardial echoes (white bright line) . B, Stop frame obtained I s after A, aow with the automatic boundary-detected image engaged but concealed from the image. Thus, the image does not show the borders (concealed). although the graph on the bottom continues to depict the algorithm-detected and computed cavity area fin em' ;. The larger (two-thirds of screen size) image without the border, shown is recorded cn tape and the cavity measured off-line with use of the trckbail. Results are compared with the algorithm-detected areas as displayed and recorded in the same cardiac cycle . latcd on-line (from each of the echocardiograpi -tic views) and corresponding values obtained off-line . The fractional area change obtained on-line front the apical four-chamber view was compared with the ejection fraction determined off-line by either the area-length method (2) or the method of Quinones et al . (27) (both methods were used in 44 patients)
We obtained satisfactory studies with automatic boundary detection in 48 (727) of 66 patients and subjects, with detection and [racking of the endocardial-blood interfaces sufficient to permit analysis of cavity area in at least one of the three echocardiographic views . In addition to these criteria, we considered a study as satisfactory when, while turning the borders on and off during the study, we could ensure that a close estimate of the true endocardiunn was obtained by the automatic boundary detection method . Of these 48 patients, 13 had global left ventricular dysfunction and 8 had segmental dysfunction. The performance of automatic boundary detection in a single view (shoe-axis or four-chamber) added approximately 3 to 5 min to the study. Off-line analysis on videotaped data took approximately 10 min per view (se!ccl :cn . freeze iiame and analysis) . Validation of the algorithm (Table 1). Results with the algorithm and real time boundary detection system compared with off-line results from recordings of the same boundary-detected images in comparable views are shown in Table I . The correiations between the two sets of results were r-lose with small standard errors . Thus, the algorithm displayed cavity areas (in cm °) accurately as imaged. Validation of the method ( .able 2). Comparisons between left ventricular cavity areas (end-diastolic and end-systolic)
)ACC Vol. 19 . Nu. . Fehrrar. I'or : )li- 2 o
ON .LINI . ASSLSSMENT
OF
PEREZ ET AL . VENTRICULAR FUNCTION
317
Table 2. Autoluatic &nmdars Detection Image On-line Verru, Loftenuonai - I - we-Dimensional Off-line Measurements Mean Nomimulteiir bear, t .v ,re . , h° I anti „e,. 40)) sn- .a e I-.I) MA i,11 ED ARU nn-t is Ls 21) u lLire 1 S I.V
s . U .~,
oIt
No .
r Value
34
0 .83
4 .6
(a
0,91
3.9
SCE
lentil
18.9 .94 2 :1-nn
5a 46
L_' - 411
t_i'
I' .7 r 9'7
-7-46
$I3 III : rgll ~ u ~
IM-ht
76
sirs
'911' II I '- u - to I
I'_-a I I-a3
36
11111,
Ia5
3'-u ,
I3
0.99
13
(1.99
0 .6
Il-an
Sembn n
ARID un-Imc I ..D 21
SO mRanpe kill
In, ED
ABD on
line ES 2D oil lure I c Simuitanenu . heat, LVAtan area..•h on-:un 0 lire FD 2D off-line ED ABD online FS
'-rdl 5 .2
,rc„ Ii I - "7
Ill-796
"O Iin 3-s
are:, .loutchunlber,ieu ABD "name ED 2D u0-line ED AUC omlmc ES
LV
2D offline ES ABU =
amonmtic boundan
dear, ie. 21)
1
29
0 .93
2-
24 5
Ill ,
7t
'17
Il3
s : :_11 _^
20
0,98
21
2I5
10 0
In %- .(,6
Srcdoemionulech :cardi.ivaphi mhttahhrevralionrasinT'ahlel .
analyzed on-line and off-line and measurements of corresponding areas calculated off-line from videotaped consentional echocardiographic images (short-axis and apicai fourchamber views) are shown in 'Table 2 . Correlations were close. considering that the data were obtained from different cardiac cycles and v-ithout control for the respiration cycle cr preclusion of patient motion that n ay have influenced the two sets of data acquisition differentially . Additional measurements obtained in the 23 patients with a fn-mat that displayed conventional echocardiographic images simultaneously with the computed area tracing obtained with the automatic boundary detection system in the same cardiac cycle are shown 1n 'fable 2 and figure 5 . They illustrate the accuracy of the method when the same cardiac cycle is employed for on-line (automated) and conventional off-line measurements (trackball caliper procedure) . Fractional area change . Percent change in fractional area was displayed on-line with the automatic boundary detection system for end-diastolic and end-systolic areas from each view . This functional index is derived from the areas directly without any needed assm .gnions of cavity geometry . We first compared the fractional area change derived on-line by arbitrarily Cawing a icgion of interest on parasternallongaxis views in a group of 15 patients with that obtained by off-line planimetry of .orrespondmg areas . The correlation was close (29.4 x 12 .4% compared with 30 .1 . 13 .2% : r 0 .93, SEE 4.7% : different cardiac cycles) . Fractional area change derived from the automatic boundary detection measurements of areas in short-axis views was somewhat lower (41 .3 t 16.7%) than that derived from the off-line trackballmeasured areas (47 .1 * 18 .1% ; n = 34: p = 0.1 ; different
cardiac cycles) and the correlation was less close (r - 0.75) . Fractional area change derived on-line by the boundary Jetection algorithm from apical foul-chamber eiews was significantly lower than that from off-line conventional image measurements (22 .9 t 11 .2% vs . 31 . 12 .9% : n = 36; p < 0 .006) . Thus . despite reasonable correlation (r = 0 .77), the automated boundary detection measurements underestimated fractional area change when different cardiac cycles were employed for comparisons . Comparison with ejection fraction estimated off-line . Online fractional area change (parasternal long-axis views) corelated closely with left ventricular ejection fraction estimated off-line by the method of Quinones et al . (27) (r = (1 .84 : SEE = S% : n = 25 patients) . On-line fractional area change (short-axis view) correlated less closely with election fraction estimated off-line by the method of Quinones et al . (27 i (r - 0 .63 ; SEE = 13% ; n - 33 patients) . However, the correlation was closer when the fractional area change derived on-line from the apical four-chamber views was compared with ejection fraction estimated off-line by the method of Quinones et al . (27) (r = 0 .83 ; SEE = 7 .0% ; n 37 paucnlsj . Ejection fraction estimated on-line. The automatic boundary detection on-line-measured chamber cavity areas were used 'o extrapolate volumes and ejection fraction as previously described (Fig . 3) . The boundary detection on-line measurements of ejection fraction were compared with estimates of ejection fraction off-line . The on-line estimates from the four-chamber view 140 .4 15 .1%) were not significantly different (p = 0.06) from estimates off-line calculated by the method of Quinones et al . (27) (46 .6 17%) in 48
318
PEREZ ET AL . ON-LINE ASSESSMENT OF VENTRICULAR FUNCTION
IACC Vol. W. No.2 Fcbn,sry 1492'.510-20
•a
5EE
1
1. 2a an eo fin LV APICa1 Ena-OiantaUv Area (AM) (emrl
A
W
L1_'l
I 20 70
p
Er 4
i 50 BB .0
I
an rH ra 6a Be
Bp Bo 4
60 r
al) --
50 ==qt
W ~'
D
-$007
20 c
30 a
_a LO
0
B
10 Figure e0
B
SEE
20
30
n0
W Aroal EnmSysidic Ana (ABU)
50
60
121 2 )
N
6 . A, Comparison
aB 6B 0 FF py ABU e
•e sn
I r 1n 60 eo
between left ventricular ejection fraction
(EF) determined by the on-line autumade boundary detection IABDI method (abscissa) and that determined oft-line from conventional images by the method of Quinones et al . (27) (ordinate) in 48
Figure 5 . Comparisonn of left ventricular (LVI end-diastolic (upper
patients and subjects (nonsimuitaneous heats) . B, Comparison be-
panel) and end-systolic (bottom pencil cavity areas (apical fourchamber views) measured by both the on-line automatic boundary
tween left ventricular ejection fraction determined by the on-line
detection (ABD) algorithm and the off-line trackball operator-traced
chamber view and tha single-plane area-length method computed off-line from recopied conventional echocardiographic images (non-
method (Conventional) in the same cardiac cycle (simultaneous method) .
automatic foundary detection method Iabsien) from apical four-
simultaneous beats) ir .44 patients and subjects .
in freeze frames of video recordings and the impracticality of patients and the correlation was close (r = 0 .86: SEE = 8.8%) (Fig . 6A) . The on-line estimates (40 .6 . 15.6%) were
rapid acquisition of results .
not significantly different (n = 44 . p = 0 .061 from values
results demonstrate the feacih'dily of performing measure-
determined off - .me by the single plane area-length method . (47 .6 17%c) and the correlation was close (r = 0 .87 : SEE _
ments on-line under clinical conditions in normal stibiects
8.5%) (FSg . 6i3) .
dimensions and compromise of ventricular function . The
Current implementation of on-line measurements. Our
and unselected patients with e wide range of cardiac cavity
algorithm accurately depicts ventricular cavity area (in cm) analogous to a volume curve as evident from the close Discussion
correlations of algorithm-acquired area estimates with offNeed fur quantimdon in echocardiography . Real time
line measurements of the recorded boundary-detected image
automatic detection of the tissue cavitary-blood boundary
(Table I). In addition, it characterizes chamber size accu-
has been an objective of research in trio-dimensional echo-
rately . as
cardiography for more than a decade (3-16). Approaches
on-line estimates based on cavity areas and off-line estimates
based on statistical estimation of the brightness of the
measured in different cardiac cycles . Even higher correla-
borders in conventional echocardiograms have been em-
tions were obtainable when the areas were measured from
ployed for off-line smoothing and approximation of edges to
the same cardiac cycle by both methods in 23 subjects and
quantify wall motion. The approach we developed is predi-
patients (Table 2) . In the present study, we 10Th a conser4-
cated on the quantitative power of measuremeiu of acoustic
ative approach and analyzed function on the basis of com-
is evident from the high correlations between
properties of the tissue in real time . It results in reduction of
parisons between on-line and off-line data from different
speckles in the % .wage, permitting detection and improved
cardiac cycles obtained within 10 s without control for
tracking of the tissue-blood interface . The algorithm we
respiratory motion. patient motion or transducer location
employed is promising for clinical applications and may
and angulation . Despite the impact of these variables, the
obviate difficulties encountered with the labor-intensive .
correlations are close enough to support the view that the
time-consuming, off-line method. That method, which we
on-line method will be a clinically useful alternative to the
used as a standard for comparison has not gained wide
current tedious off-line analysis or simple subjective inter-
clinical acceptance because of degradation of image quality
pretation of ventricular function front analysis of conven-
IACC Vel.i9 .Na .2 Fe6m1vy 1112 M12.
tional
PfREZ FT a L. ON-LINE ASSESSMENT OF 'IENTRICULAR FUNCTION
two-dimensional echocardiograms
(28).
The auto-
319
because it is based on multiple linear dimensions and their
mated procedure should facilitate longitudinal assessments
change with systole, integrated from all cardiac views, rather
of ventriculat function in serial studies in patients With
than on geometric assumptions for ventricular shape . The
vaivular . congenital and coronary heart disease .
closc correlations obtained when the single-plane aiea-
Compazison with previous recommendations . Measure .
length method (recommended by the American Society
of
ment of ie t ventricular cavity areas and changes in fractional
Echocardiography) (21 was used further confirm the validity
area from the short-axis views has been recommended by
ui
the American Society of Echocardiography
(2)
iae
to quantify
automated approach .
Conclusions. Our results indicate that quantification
of
vennMular tunetion . With the automatic boundary detection
tissue acoustic properties in real time permits detection and
method described here, estimates of diastolic and systolic
tracking
areas are somewhat, lower in absolute terms . 'the method
'u :mtification
outlines the papillary muscles and excludes their area from
development of this approach should provide assessment of
the measurement of cavitary areas . whereas the conven-
segmental ventricular function under conditions of stress
tional method ignores space occupied by the papillary mus-
:cho:ardlugraphy and serial monitoring of ventricular per-
cles, resulting in, a higher salue for the area. However .
formance in an individual patient in settings such as the
values for fractional area change correlate quite well with the
coronary care unit and operating room (transesophageal
two methods .
imagingl. i n which changes must be detected promptly so
On-line ejection fraction . In the present study . We utilized a first-step approach to derive estimates of ejection fraction
of
the endocardial-blood interfaces, facilitating of ventricular function on-line . Continued
that appropriate adjustments in treatment can be made without delay .
on-line from estimates of ventricular vo'arles based on a simple approximation of short-axislfour-chamber area ratio .
We are grateful to Debbie Taylor for excellent secrcarial assistance.
The close correlation. between ejection fraction estimated on-line and that measured off-line in patients exhibiting mild to profound ventricular dysfunction of diverse etiologies suggests that the on-line estimation
of
useful information, even at an early stage
area change derived from parasternal long-axis views corre-
ejection
~mhran H . F.chaerdiog;aphy. Philadelphia : Lea I27-87.
development .
On-line fractional area change . The on-line fractional
lated well with global
References
function provides
of its
a
`cUiger. 1986 :
2 . Shah PM . Crawford M. Deiana A . et al. Recommendations for gnantinotian at the left vemdde by Iwo .dimensional echocardiography . I Am Son Echn 1989 ;2:358-67
fraction estimated by the
method of Quinones et al . (27). This observation suggests
3 . trekins RE . Gain- 18, Automatic contouring for twodimensional radiography . Johns Hopkins APL Technical Digest 1980 :1139-43 . (arc',,
that in many patients . ejection fraction can be estimated
4.
E.
quickly from the lone axis fractional area change because most of the shrinkage of the left ventricle during systole
5.
oreurs in the minor axis, Obviously, patients with apical hypakincsia, akinesia or dyskinesia will require a thorough evaluation
of the
'w. Levy R. Garcia E . c1 ai . Validation of a compumnud edge Jerea~,n algorithm for itnecu alive twodimenvonot echocardiogaphy. CircuiaL,n 1983 :68:1127-35 . Bode AJ. Skip Ff . Meyer CR, et .1 -pole, P--mig of
apical v iews. a s is the case in conventional
echocardiographic examirations . Limisafons . The tracking accuracy
of
the endocardial-
blood interface detection appea.-s to he more efficient with the parasternal long-axs than with the short-axis
probably l4i
so the beam.
facilitating detection and tracking. We
often encountered difficulties in detecting and tracking boundaries in the parasternal shop-axis view . particularly in anter,lateral and posteroseptal regions . and in the apical view (lateral wall) perhaps because
of
anisotropy (291 of
myocardium in these zones . The difficulties occurred with similar frequency is pa :
:as
and normal subjects .
The acquisition of quantitative data using automatic boundary detection
requires
8.
view.
because the septum and posterior wall boundaries
of the region of interest in the long-axis view lie perpendic-
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Concua 13A . Geiser EA . Olive, I.H . Miller An . Cone CR. Reproducibil . its of left ventricular area and volume measurements sing a computer cordial edge-detection atgeotbca in normal subject, :4m 3 Card :al 1988.% :947-52 .
meticulous attention to the
transmit-gain and time-gam compensation controls t0 ensure that the endocardial edges visualized on conventional images
13 . Chu WW. Lao LMT. Task-allocation and precedence relations for dlstvbuted real-time systems. IEEE Compel 1987 :36:667-79 . 14. Geiser EA. Oliver LH. Gardin 1M . Clmoai validation of an edge detection algorithm for iwodimensional echacardiogaphic shun axis
are being detected and tracked by the novel algorithm . fraction. The method of Quinones
nag,, . l Am Son Echo 1988 :1 :410-21 . 15, Gesso EA .. Came DA . Limorher MC, Ostlund Slocklon V . Oliver LH,
for determining ejection fraction was employed
tones B . A second generation camporer-based edge detection algorithm
Validation of et at.
(27)
ejection
320
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