Ultrasound
Holograms
of the heart
Dynamic 3D
echocardiography in virtual reality
By Annemien E van den Bosch, Jackie S McGhie, Folkert J Meijboom and
Maarten L Simoons of the Department of Cardiology, Erasmus MC University
Hospital, Rotterdam, The Netherlands; Anton HJ Koning and Peter J van
der Spek, Bioinformatics, Erasmus MC University; and Ad JJC Bogers,
Cardiothoracic surgery, Erasmus MC University Hospital
ABSTRACT
Background
This pilot study was
performed to evaluate
whether virtual reality is
applicable for three-dimensional
echocardiography and
if three-dimensional echocardiographic
'holograms' have
the potential to become a
clinically useful tool.
Methods
Three-dimensional echocardiographic
data sets from 2
normal subjects and from 4
patients with a mitral valve
pathological condition were
included in the study. The
three-dimensional data sets
were acquired with the
Philips Sonos 7500 echosystem
and transferred to the
BARCO (Barco N.V., Kortrijk,
Belgium) I-space. Ten independent
observers assessed
the 6 three-dimensional data
sets with and without mitral
valve pathology. After 10
minutes' instruction in the ISpace,
all of the observers
could use the virtual pointer
that is necessary to create cut
planes in the hologram.
Results
The 10 independent observers
correctly assessed the normal
and pathological mitral valve
in the holograms (analysis time
approximately 10 minutes).
Conclusion
This report shows that
dynamic holographic
imaging of three-dimensional echocardiographic
data is feasible. However,
the applicability and usefullness
of this technology
in clinical practice is still
limited.
INTRODUCTION
Evaluation of intracardiac
anatomy from multiple twodimensional
echocardiographic
images requires a
mental conceptualisation
process that is complicated
by cardiac dynamics [1-3].
Currently, real-time 3D
echocardiographic images
of the heart do no longer
demand this difficult and
individually variable
conceptualisation processes,
by offering an equivocal
presentation of cardiac
anatomy throughout the
cardiac cycle.
However, the
full 3D potential of these
imaging modalities cannot
be appreciated, since the 3D
data are presented on a flat
2D screen. Virtual dynamic
systems, known as virtual
reality, can assist with the
interpretation of 3D data of
the heart in space and
makes it possible to 'dive'
into the 3D model of the
heart (4-8).
This study is an attempt in
the technological process of
the future to evaluate
whether virtual reality is
feasible for 3D echocardiography
and if 3D echocardiographic
images in a virtual
reality can advance to a clinically
useful tool.
Methods
Data sets from normal
subjects and from patients
with mitral valve disease,
referred for a diagnostic
echocardiogram, were
selected with the aim of gathering
a representative series
of mitral valve pathological
conditions with sufficient
image quality.
For this feasibility study, we
selected 3D data sets of clinical
conditions which have
advantage of 3D perspective:
(1) two patients with a
normal mitral valve, (2) a
patient with a mitral valve
prolaps of the P2 segment of
the posterior leaflet, (3) a
patient with mitral valve
stenosis, (4) a patient with
hypertrophic obstructive
cardiomyopathy and systolic
anterior motion of the mitral
valve, and (5) a patient with
an atrioventricular septal
defect (AVSD) where there is
a commissure present
between the superior and
inferior bridging leaflets. Ten
observers (5 cardiologist, 3
cardiologist-in-training and 2
cardiothoracic surgeons),
who were blinded for the
type of mitral valve
morphology, were instructed
to assess mitral valve
anatomy/pathology and
function.
Three-dimensional echocardiographic data
acquisition
The 3D data sets were acquired with the Philips Sonos 7500 echo system
(Philips Medical Systems,
Andover, MA, USA)
equipped with a 3D data
acquisition software package.
Real-time 3D echocardiographic
(RT-3DE) acquisition
was done with ECG gating
and in an end-expiratory
breath-hold, lasting 6 to 8
seconds (depending on the
heart rate). The 3D image
data was stored on CD-ROM
in DICOM 3.0 format and
transferred to the computer
(SGI Onyx4 Ultimate Vision,
Silicon Graphics, Inc.,
Mountain View, CA, USA)
driving the I-space.
Visualisation in a virtual
reality environment
The BARCO (Barco N.V.,
Kortrijk, Belgium) I-space
installed at the ErasmusMC,
is a so-called four-walled
CAVE(tm)-like virtual reality
system (figure 1). In the Ispace
researchers are
surrounded by computer generated
stereo images,
which are projected by 4
high quality DLP-projectors
on three walls and the floor
of a small "room".
The virtual reality system
has a resolution of 1280 by
1024 pixels per projector.
This is comparable to or
greater than the resolution of
the CRT monitors and LCD
flat panels used in ultrasound
systems and with
workstations. The CAVORE
(CAve VOlume REnderer)
volume rendering application
is used to investigate 3D
ultrasound images during
the cardiac cycle [9].
In the I-space, this result in
an animated "hologram" of
the dataset being visualised,
floating in space in front of
the viewers. The viewers
wear a pair of lightweight
glasses with polarising lenses
that allows seeing the hologram
with depth. Interaction
with this "hologram" is by
means of a virtual pointer
and makes it possible to
assess the interior of the
heart.
The observers were
instructed to create several
cut plane in the hologram.
For the analysis of the mitral
valve, two opposite views
were reconstructed: 1) a view
from the left atrium towards
the atrioventricular junction,
allowing a "surgical view" of
the mitral valve, and 2) a
view from the left ventricular
apex toward the mitral valve.
The observers were asked
to assess in these views, the
anterior and posterior
leaflets, and subvalvular
apparatus for possible
pathology.
Results
The 3D data sets of the 6
patients with normal or
abnormal mitral valve
anatomy were transformed
to 3D holographic heart
models. Once the transformation
method had been
developed, the time required
to create a hologram from
the 3D data set varied from 1
to 3 minutes. Figure 2
demonstrates the reviewer
inside the I-space creating the
necessary cut planes in a
hologram.
After 10 minutes instruction
in the I-Space, all
observers could use the
virtual pointer and make the
necessary cut planes. The 10
independent observers
correctly assessed the normal
and pathological mitral valve
in holograms with analysis
time of approximately 10
minutes for each study.
Visualisation of the mitral
valve in virtual reality
In the generated 3D hologram
of a normal mitral
valve, the mitral valve is best
visualised from the apex of
the left ventricle (LV) looking
upwards to the crux of the
heart.
The anatomy of the mitral
valve can clearly be
discerned. Mitral valve
motion becomes more
apparent when the hologram
is tilted up or down
and can be stopped in any
desired phase of the cardiac
cycle.
In the patient with localised prolaps of the
posterior leaflet, this prolaps
was best seen when looking
down from the left atrium
towards the mitral valve. In
early systole, the mitral valve
closes and the localised
prolaps of the posterior
mitral valve leaflet starts to
become visible.
With the time progression
during systole, the extent of
the prolaps is seen to
increase to its maximum late
in systole.
The additional
structures of the mitral valve
apparatus (chordae, papillary
muscles and valve leaflets)
were visualised and identified
by all observers.
In figure 3, the left-sided
atrioventricular (AV) valve of
a heart with an atrioventricular
septal defect is
displayed, visualised from
the apex of the LV.
All
observers correctly identified
the commissure between the
superior and inferior
bridging leaflets.
Discussion
This report presents a novel
approach for visualisation of
dynamic 3D echocardiographic
data, known as
virtual reality.
The 3D echocardiographic
data sets generated by a
commercial available echo
machine can be visualised as
a dynamic hologram inside
the I-Space. Until now, the
3D echocardiographic reconstructions
could only be seen
on a 2D screen, but virtual
reality makes it possible to
'dive' into the actual 3D
anatomy of the heart.
We show that professionals,
familiar with intracardiac
anatomy, can learn
how to handle the technique
and cut through these holograms
within 10 minutes.
Subsequently, they were all
able to correctly diagnose the
intracardiac anatomy or
pathology of the mitral
valve.
At the moment, I-Space
technology is only available
in a few dedicated research centres throughout the
world. Therefore, the combination
of the 3D echocardiography
and virtual reality is
very uncommon and the
applicability and usefulness in clinical practice is still
limited.
However, in our opinion,
it has potential and one can
think of possible applications
in the future.
Virtual reality provides a
unique resource for education
of intracardiac anatomy
in general and/or specific
cardiac structures.
Especially for all professionals
for whom detailed
knowledge of the intracardiac
anatomy is essential,
virtual reality might lead to
a better understanding of
the intracardiac anatomy.
With the growth of
minimal invasive cardiac
surgery and interventional
procedures, the interest for
simulation of the heart
hologram as a training tool
has increased.
We believe that dynamic
3D echocardiography in
virtual reality has t
he potential
for wider applicability in
providing a preview of real intracardiac anatomy.
With the I-Space technology,
the complex
anatomy, pathology and
dynamic changes of the heart
are appropriately visualised
in a virtual heart model,
which increases the accessibility
and availability of
virtual reality for clinical
practice. In order to be integrated
into clinical practice,
this application should be
able to run on smaller virtual
reality systems, either based
on a single projection
surface, or on a monitor (CRT
or LCD).
Credit:
This Open Access article was
originally published in
Cardiovascular Ultrasound
2005, 3:37 doi:
10.1186/1476-7120-3-37©
2005 van den Bosch et al;
licensee BioMed Central Ltd.
The electronic version of this article is the complete one and can be
found online at:
www.cardiovascularultrasound.com/content/3/1/3
A short MPEG video to
demonstrate virtual reality in
the I-Space is available
online.
