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Brief Rapid Communications
New Three-Dimensional Echocardiographic System Using
Digital Radiofrequency Data—Visualization and
Quantitative Analysis of Aortic Valve Dynamics
With High Resolution
Methods, Feasibility, and Initial Clinical Experience
Michael Handke, MD; Cosima Jahnke, MD; Gudrun Heinrichs, PhD; Jörg Schlegel, PhD;
Clemens Vos, PhD; Daniel Schmitt, PhD; Christoph Bode, MD; Annette Geibel, MD
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Background—Common 3D systems have only limited spatial and temporal resolution (frame rate of 25 Hz). Thin
structures such as cardiac valves are not imaged exactly; rapid movement patterns cannot be precisely recorded. The
objective of the present project was to achieve radiofrequency (RF) data transmission to the 3D workstation to improve
image resolution.
Methods and Results—A commercially available echocardiographic system (5-MHz transesophageal echocardiography
probe) with an integrated raw data interface enables transmission of RF data (up to 40 megabytes per second). A 3D
data set may contain up to 3 gigabytes, so that all of the high-resolution ultrasound information of the 2D image is
available. Frame rates of up to 168 Hz result in temporal resolution 6 times that of standard 3D systems. The
applicability of the system and the image quality were tested in 10 patients. The structure of the aortic valve and the
dynamic changes were depicted by volume rendering. The changes in the orifice areas were measured in frame-by-frame
planimetry. The mean number of frames recorded per cardiac cycle was 122⫾16. The improved structural resolution
enabled a detailed imaging of the morphology of the aortic cusps. The rapid systolic movement patterns were recorded
with up to 51 frames. The high number of frames enabled creation of precise area-time diagrams. Thus, the individual
phases of aortic valve movement (rapid opening, slow valve closing, and rapid valve closing) could be analyzed
quantitatively.
Conclusion—A 3D system based on RF data enables high-resolution imaging of cardiac movement patterns. This offers
new perspectives for qualitative and quantitative analyses, especially of cardiac valves. (Circulation. 2003;107:28762879.)
Key Words: echocardiography, 3D 䡲 valve, aortic 䡲 imaging
T
he impetus for the technical development of 3D echocardiography was its greater diagnostic potential than
that of 2D examinations.1,2 The spatial imaging of cardiac
structures is especially important in the planning and performance of surgical and catheter interventional procedures.3,4
In addition, new possibilities of quantitative analysis, such as
the determination of ventricular size and function, are also
offered.5,6 Establishing 3D echocardiography as a clinical
routine procedure requires, however, further technical improvements in spatial and temporal image resolution.
The rationale for the technical realization of radiofrequency (RF) data transmission from the ultrasound unit to the
3D workstation via a raw data interface is the attendant
considerable improvement in spatial and temporal image
resolution. In this article, we present a system in which the
frame rate has been increased 6 times to 168 Hz. Practical
applicability and image quality of the system were tested
under clinical conditions.
Methods
Data Acquisition Setup
The investigations were performed using a PowerVision 6000
ultrasound system (Toshiba Corp) equipped with a 5-MHz multiplane transesophageal echocardiography (TEE) probe and a digital
Original received January 9, 2003; de novo received March 14, 2003; accepted May 6, 2003.
From the Department of Cardiology and Angiology, Albert-Ludwigs-University, Freiburg (M.H., C.J., G.H., C.B., A.G.), Germany; TomTec GmbH,
Unterschleissheim (C.V.), Germany; Center of Competence for Biomedical Microdevices, Fraunhofer Institute, St Ingbert (D.S.), Germany; and Toshiba
Corporation, Otawara-shi, Japan (J.S.).
Movies are available in the online-only Data Supplement at http://www.circulationaha.org.
Correspondence to Michael Handke, MD, Department of Cardiology and Angiology, Albert-Ludwigs-University, Hugstetter-Strasse 55, 79106
Freiburg, Germany. E-mail [email protected]
© 2003 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
DOI: 10.1161/01.CIR.0000077909.54159.B4
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Handke et al
3D Echocardiography Using Radiofrequency Data
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Figure 1. Data flow of 3D system. PC indicates personal computer; IO, input/output.
RF data output. A 3D system with modified Echo-Scan software
(TomTec GmbH) was used as a control unit. RF data were acquired
at a data rate of 40 megabytes per second using a parallel input/
output interface. RF data were directly transmitted to a data acquisition unit. Bidirectional serial command lines were used to automatically detect the ultrasound system settings as well as to control
data acquisition from the remote computer and to acknowledge
execution of commands (Figure 1).
Postprocessing and Volume Reconstruction
The acquired RF data correspond directly to the beam-formed
backscatter signals received by the ultrasonic transducer. In a first
step, image lines are created from the RF data by means of echo
processor software. Subsequently, 2D ultrasonic images equal to
those displayed on the ultrasound system monitor are generated
using scan converter software. Each data set contains ⬇130 frames
(average heart rate, 80 bpm; frame rate, 168 frames per second). An
angle increment of 5° was chosen to acquire the 3D data resulting in
36 scanning positions to cover the entire 180° rotation range of the
multiplanar TEE probe. Individual images are created for each frame
in all 36 angle positions, resulting in a total number of 4680 images
per data set. To equalize the number of frames per angle position, the
minimal number of frames over all angles is determined and applied
to all other positions.
All data sets are stored in a file format complying with the
standard file format normally used in the video acquisition setup.
This enables us to apply the Echo-View software (TomTec) directly
for volume reconstruction.
Despite the narrow sector angle (45°) used, each data set aggregates to ⬇3 gigabytes. Applicable review data sets were generated
by selecting a region of interest. Thus, the average data set size was
reduced to ⬇1.2 gigabytes.
Clinical Examinations
The clinical applicability of the system was tested in 10 patients (3
women, 7 men; mean age, 54⫾13 years). The aortic valve was
examined with the maximum frame rate (168 Hz). Multiplane data
recording was performed in 5-degree increments. The study was
approved by the local Ethics Committee. An individual examination
was performed after the patient had granted informed consent.
Results
Data Acquisition
A mean time of 6.5⫾0.5 minutes was required for the
acquisition (5.8 to 7.5 minutes). Depending on the patient’s
heart rate, between 102 and 149 frames per cardiac cycle
could be recorded (mean, 122⫾16 frames).
Structural Image Resolution of the Aortic Valve
Figure 2A shows an aortic valve generated from video signal
data. The edges of the cusps appear too thick as a result of the
low structural resolution. The use of RF data, by contrast,
leads to good structural image resolution in the 3D data set
(Figure 2B). Compared with the 2D echocardiographic image, the cusp edges in the 3D anyplane mode are recorded
with almost the same detail. This is a prerequisite for a
high-resolution spatial image of the valve in the 3D volumerendered mode.
Dynamic Changes of the Aortic Valve During the
Cardiac Cycle
The systolic changes of an aortic valve are shown in Figure
3A in high temporal resolution. The valve opening begins
with a separation of the cusps; then there is a very rapid
increase in the orifice area. The maximum orifice is attained
already in the early systole. Valve closing proceeds in 2
Figure 2. A, Cross section of aortic valve recorded
with standard 3D technique (video signal, 25 Hz).
Because of poor structural resolution, valve edges
appear too thick. B, Left, 2D echocardiographic
cross section of aortic valve. Middle, Using digital
RF data, edges of cusps are almost as well
imaged in 3D anyplane image as in 2D image. This
good structural resolution within the 3D data set is
prerequisite for excellent spatial imaging of the
valve in the 3D volume-rendered mode (right).
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Circulation
June 17, 2003
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Figure 3. A, Dynamic changes in aortic valve during systole (48 frames). B, Corresponding area-time diagram. High number of images
at frame rate of 168 Hz makes quantitative determination of valve movement parameters possible.1, Phase of opening; duration 54 ms,
mean velocity 49 cm2/s. 2, Slow closing; duration 184 ms, mean velocity 3.8 cm2/s. 3, rapid valve closing; duration 48 ms, mean velocity 41 cm2/s. As a comparison, a recording at a frame rate of 50 Hz is also shown. It is clear that especially the phase of rapid valve
opening is less precisely recorded. At a frame rate of 25 Hz, as in common systems, no meaningful depiction of aortic valve movement
is possible. AOA indicates aortic orifice area; A1, maximum AOA; A2, difference between maximum AOA and AOA at the end of the
slow closing movement; A3, AOA at the end of the slow closing movement; T1, time to maximum valve orifice; T2, time of slow closing
movement; T3, time of rapid closing movement; V1, velocity of rapid valve opening; V2, velocity of slow closing movement; and V3,
velocity of rapid closing movement.
phases; after the maximum orifice has been attained, the
valve begins a slow closing movement. Toward the end of the
systole, there is a rapid valve closing movement. The course
of the orifice area over time is shown in Figure 3B. The 3
phases of systolic opening are recorded in detail and can be
quantitatively analyzed. The mean orifice area after the rapid
opening was 2.80⫾1.05 cm2; at the end of the slow valve
closing, 1.83⫾0.91 cm2. The mean velocities for rapid valve
opening and for slow and rapid closing were 64.1⫾22.0,
5.4⫾3.8, and 57.6⫾33.1 cm2/s, respectively. The mean time
required for planimetry of the orifice areas was 13⫾2
minutes.
Discussion
Improvement in 3D echocardiographic image resolution is
mandatory for expanded scientific and broad clinical applications. The present study demonstrates that the use of digital
RF data improves the image quality and also brings decisive
improvement in the possibility of quantitative analysis.
Handke et al
3D Echocardiography Using Radiofrequency Data
Current 3D Echocardiographic Imaging Techniques
Only low frame rates of ⬇25 Hz can be achieved using
commercially available 3D systems based on multiplane
examination. In a further development of the multiplane
technique, the temporal image resolution could be doubled to
50 Hz by modification of the acquisition software.
This opened new possibilities for 3D echocardiographic
analysis of cardiac dynamics.7,8 An alternative procedure is
3D echocardiography with phased-array real-time volumetric
systems (RT3DE).6 RT3DE enables rapid data acquisition
during a cardiac cycle, and the latest developments also
enable real-time generation of the 3D image. However,
RT3DE, in addition to limited spatial resolution, offers only
a poor temporal image resolution (⬇20 Hz).
Clinical Applicability of the New System
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The ultrasound unit used is a commercially available system,
which was technically modified. A commercially available
TEE probe can be used for 3D acquisition. This will facilitate
integration into clinical routine. Because greater quantities of
data are processed, the acquisition time is somewhat longer
than in common systems, despite improved computer performance. The examinations were performed in small angle
increments of 5 degrees, to obtain good structural resolution
of the aortic valve. We required a mean time of 6 to 7 minutes
for an acquisition. This is acceptable under clinical
conditions.
New Perspectives for 3D Echocardiography
Real-time generation of 3D images and markedly improved
image resolution are the 2 most important advances for broad
clinical application of 3D echocardiography. The system that
we are presenting is limited by the multiplane technique
(longer acquisition time and offline analysis), but thanks to its
good spatial and temporal image resolution, it opens new
diagnostic possibilities for 3D echocardiography. It is therefore a measure for the requirements for future real-time
systems. Compared with the usual systems, the transfer of RF
data enables a considerably greater data flow to the 3D
workstation. This means that complete 2D ultrasound information is available for 3D reconstruction. Thus, the morphology of cardiac structures can be reconstructed in more detail.
Especially in thin structures such as cardiac valves, good
structural resolution is decisive for the quality of the reconstruction and quantification of the orifice area.9 A high
temporal resolution creates new possibilities for quantitative
analyses. Knowledge of aortic valve function has been
obtained primarily from experimental studies in animals,
because no imaging procedure has been able to record rapid
movement patterns in humans with sufficient accuracy.10,11 In
a recent study (using a system with a 50-Hz image rate), we
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could show for the first time in addition to the normal
function how aortic valve movement is influenced by myocardial and valvular factors.8 The further increase in frame
rate to 168 Hz especially improves diagnosis with respect to
the short phase of valve opening, which occurs at a high
speed.
A new 3D system with a high frame rate can thus
contribute to improved understanding of aortic valve function. Possible clinical applications are analyses of the function of aortic valve bioprostheses, diagnostics of valve
function after valve-preserving surgery, or examinations of
function and progression of stenosed aortic valves.
Conclusion
A 3D system based on RF data enables high-resolution
imaging of cardiac movement patterns. This offers new
perspectives for qualitative and quantitative analyses, especially of cardiac valves.
Acknowledgment
Supported by the Deutsche Forschungsgemeinschaft (German Research Foundation).
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New Three-Dimensional Echocardiographic System Using Digital Radiofrequency Data−−
Visualization and Quantitative Analysis of Aortic Valve Dynamics With High Resolution:
Methods, Feasibility, and Initial Clinical Experience
Michael Handke, Cosima Jahnke, Gudrun Heinrichs, Jörg Schlegel, Clemens Vos, Daniel
Schmitt, Christoph Bode and Annette Geibel
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Circulation. 2003;107:2876-2879; originally published online June 2, 2003;
doi: 10.1161/01.CIR.0000077909.54159.B4
Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 2003 American Heart Association, Inc. All rights reserved.
Print ISSN: 0009-7322. Online ISSN: 1524-4539
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Data Supplement (unedited) at:
http://circ.ahajournals.org/content/suppl/2003/06/12/01.CIR.0000077909.54159.B4.DC1
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