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\begin{document}

\title{Stepwise manipulation of cardiac computed tomography multi-planar
reconstruction to mimic trans-esophageal echocardiography}



\author[1]{Wei Tsung Lai}%
\author[1]{Ming-Chon Hsiung}%
\author[2]{LUNG-CHUN LIN}%
\author[1]{Wei-Hsian Yin}%
\author[1]{Ching-Hsuan Hsu}%
\author[1]{Kuan-Chih Huang}%
\affil[1]{Cheng Hsin General Hospital}%
\affil[2]{National Taiwan University Hospital}%


\vspace{-1em}



  
  \date{June 14, 2024}


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\selectlanguage{english}
\begin{abstract}
Cardiac computed tomography (CT) is increasingly used to plan
transcatheter structural heart interventions, however, intra-operative
guidance relies on trans-esophageal echocardiography (TEE) and
fluoroscopy. This study sought to develop the methods of stepwise CT
multi-planar reconstruction manipulation to mimic TEE thus bridging the
gap between preoperative planning and intra-operative guidance tools.
This CT manipulation successfully reproduces similar configurations as
TEE views in mid-esophageal left ventricle (LV) views, transgastric LV
2-chamber views for mitral apparatus, and other miscellaneous views.
Stepwise cardiac CT manipulation to mimic TEE is the final piece of the
puzzle in the mental co-registration of these three crucial imaging
modalities. With it, we are enabled to foresee the TEE images and
fluoroscopy projections in a preoperative rehearsal thus improving the
intra-operative accuracy of interventions.%
\end{abstract}%



\sloppy


\textbf{KEYWORDS}

Mental co-registration of imaging modalities, multi-planar
reconstruction, transcatheter structural heart interventions,
interventional echocardiography

\textbf{1 | INTRODUCTION}

Cardiac computed tomography (CT), fluoroscopy and trans-esophageal
echocardiography (TEE) are three major imaging modalities, which support
the increasing complexity of trans-catheter interventions in congenital
and structural heart diseases. \textsuperscript{1--3} These modalities
are based on different mathematical coordinate systems, and are often
demonstrated at different visual perspectives. Multi-planar
reconstruction (MPR) of cardiac CT, commonly used as pre-operative
planning tool, is based on the standard Cartesian coordinate system
(Figure 1A). Although manual adjustment is allowed for plane rotation
and movement of the origin of the coordinate system into the region of
interest (ROI), the re-sliced 2D images can still be intuitively
understood because CT datasets include abundant isotropic details in
cardiac anatomy. Instead of multi-slice imaging, fluoroscopy provides
with the X-ray projection from the visual perspective of the image
intensifier, whose trajectory is clinically described by the spherical
coordinate system (Figure 1B) as right anterior oblique (RAO)/left
anterior oblique (LAO) and cranial (CRA)/caudal (CAU). The coordinate
system of TEE is the most complex so the same structure scanned at
different esophageal levels requires mental co-registration in
understanding (Figure 1C, right). The TEE is basically a cylindrical
coordinate system (Figure 1C, left) and its monitor produces 2D
anatomical information on the polar coordinate reference plane, similar
to the axial and the coronal CT MPR planes for trans-esophageal and
trans-gastric windows, respectively. However, the longitudinal axis
(similar to z-axis in Cartesian system) of such cylindrical coordinate
system is not a straight line, not to mention the anteflex and retroflex
probe manipulation; rather, the longitudinal axis actually means the
esophageal tract. Furthermore, the reference plane is allowed to rotate
around its polar axis (the mid-line of the scanning sector) and the
geometry of flex to the right/left maneuver is even more complex. As a
result, both the acquisition and the understanding of TEE images need
learning curve.

Mental co-registration of these modalities is the foundation to
facilitate heart-team communication. \textsuperscript{4,5} For quick
switch between imaging modalities with different coordinate systems,
assistive theory and technology have been developed.
Echocardiography-fluoroscopic fusion imaging transforms the coordinate
system of TEE probe to that of the image intensifier so that 2D and 3D
TEE images can be calibrated and projected onto the 2D
fluoroscopy.\textsuperscript{6,7} As a result, images of these two
modalities can be viewed in the same visual perspective
\textsuperscript{4,5,8} with acceptable mean target registration error.
Piazza and colleagues\textsuperscript{9,10} introduced the concept of
optimal projection curve that comprises all the projection angles of
which the X-ray tube-to-image intensifier direction is orthogonal to the
normal vector of the interested anatomical targets. Their method is
applied to minimize the parallax during the deployment of a
quasicylindrical device into an anatomical structure of variable
geometry. However, the bridge between cardiac CT and TEE is lacking.
Adjusting the MPR crosshairs into the center of mitral valve plane and
crossing the third MPR line through the LV apex are the traditional
methods to obtain LV four-chamber, two-chamber and long-axis CT
re-slices without foreshortening.\textsuperscript{11} These views
precisely describe the LV segments and mitral apparatus, but are usually
at a different reference plane from that of TEE imaging. Although TEE
simulator based on CT images has been developed as a valuable teaching
tool, \textsuperscript{12} it sacrifices the wide visual field of CT
scan and loses image quality during datasets transformation. Due to
rapid development of new trans-catheter devices, more and more distinct
imaging requirements are called for. As a result, it is mandatory to
bridge the gap between the pre-operative planning tool and the
intra-operative imaging guidance.

For this purpose, we developed the methods of stepwise cardiac CT MPR
manipulation to mimic trans-esophageal echocardiography. On the other
hand, from the patient-specific information of cardiac CT, we can also
plan the TEE imaging in a preoperative rehearsal to make the desired
standardized TEE views more reproducible.

\textbf{2 | METHOD} (Figure 2)

Since the motion of TEE probe is confined to the esophagus-stomach
tract, it is difficult for TEE sonographers to reproduce the cardiac CT
MPR views used for preoperative plan. By contrast, it is easier to use
CT datasets to simulate TEE imaging. There are three basic MPR planes --
axial, coronal and sagittal -- that are perpendicular to each other. One
can adjust the cross-sectional orientation of the other two planes by
moving and rotating their MPR lines on the selected MPR plane (i.e., we
can adjust coronal and sagittal MPR lines on axial plane and vice
versa). To represent the TEE scanning sector, we imagine a circular
sector with the origin in the MPR crosshairs on the axial plane and the
sector has a line of symmetry as the sagittal MPR line. Once we move the
MPR crosshairs into the esophagus with the following sequential steps,
we can translate basic TEE probe movements into corresponding CT MPR
manipulation with the following steps.

Step 1: Manipulation on the sagittal plane: advance, withdrawal,
anteflex and retroflex

The first step to simulate TEE on CT axial MPR plane is to invert the
z-axis (the coronal MPR line on the sagittal MPR plane), because CT
offers a perspective from a caudal direction on the axial MPR plane but
TEE, the cranial perspective on the reference plane. Next, we simulate
the advance/withdrawal by moving the crosshairs along the esophageal
tract into the gastric space. Moreover, we can simulate the anteflex by
clockwise rotation of the axial MPR line on the sagittal MPR plane and
the retroflex by counterclockwise rotation.

Step 2: Manipulation on the axial plane: turn to the left/right

Because the sector width of TEE is limited, sonographers have to turn
the TEE probe rightward to observe the right-sided structures and vice
versa. We can simulate this maneuver by rotating the sagittal MPR line
on the axial MPR plane. Step1 and Step 2 can be repeated randomly until
satisfactory image is obtained on the axial MPR plane before moving on
to the step 3.

Step 3: Manipulation on the coronal plane: rotation, flex to the
left/right

Since the z-axis has been inverted at the very beginning, the anterior
posterior direction on the coronal MPR plane is reversed, too. As a
result, the counterclockwise rotation of TEE scanning plane will be
simulated by a clockwise rotation of the axial MPR line on the coronal
MPR plane. TEE probe is steerable for delicate adjustment of imaging
orientation. The flexible joint is around 5cm above the scanning center.
To simulate the ``flex to the right,'' two steps have to be taken.
Firstly, we rotate the crosshairs about the flexible joint of TEE probe.
Secondly, a negative rotation with the same degree that the crosshairs
are rotated should be added. Examples of flex to the right at
mid-esophagus level and flex to the left at transgastric level are
illustrated in Figure 3 and Figure 4 respectively.

\textbf{3 | RESULTS}

\textbf{Mid-esophageal LV views without foreshortening (Figure 2 \& 3)}

After inverting the z-axis and moving the MPR crosshairs into the
esophageal lumen, we simulate ``turn to the left'' by rotating the
sagittal MPR line counterclockwise on the axial MPR plane to make the
sagittal plane cross the LV apex. Then we can easily use the sagittal
plane to discern that at different level of esophagus, different degrees
of retroflex are needed to avoid LV foreshortening. With a LV image
without foreshortening, we can rotate the reference plane on the coronal
MPR plane to obtain LV 4-chamber, 2-chamber, bi-commissural and
long-axis images.

Orthogonal interrogation of ultrasound beams obtains the highest
reflection to deserve the most precise resolution. As a result, by
acquiring the mid-esophageal LV views with the ideal orientation, the
imagers can reconstruct the high-resolution 3D mitral valve en face
views. However, if the LV axis crossing from the center of mitral valve
to LV apex is not contained in the plane of ultrasound scanning beams,
there will be configural differences between TEE and CT imaging. On CT
TEE simulation, we can easily discern such configural differences by
investigating whether the sagittal MPR line on the axial plane crosses
the center of mitral valve or not (Figure 3C). Sometimes a little ``flex
to the right'' can partially ameliorate the configural differences. This
effect can also be easily realized by CT simulation as a parallel
movement of the sagittal line of sector from lateral annulus toward the
center of mitral valve on the axial plane. It is important for the
operators to understand such configural differences or they will be
confused by intraoperative TEE imaging, because the more the configural
differences appear, the higher the possibility that the devices make
out-of-plane motion on TEE imaging.

\textbf{Transgastric LV 2-chamber views for mitral apparatus (Figure 5)}

Mitral apparatus evaluation is the key to both surgical and
transcatheter mitral valve repair. Severity of leaflet tethering by
infarcted myocardium determines the success of mitral repair. During
chordal length determination for artificial chordae implantation, it is
important to have the papillary muscle, measured chordae tendineae and
the edge of mitral valve all be clearly identified simultaneously on a
two-dimensional plane in a systolic phase. Such evaluations could be
performed on the transgastric LV bi-commissural view, which can be
derived from planar rotation from the transgastric LV short axis view at
papillary muscle level (Figure 5). On CT simulation, we can start with a
mid-esophageal foreshortened 4-chamber view, and then move the MPR
crosshairs into the gastric cardia. Next, we simulate anteflex at the
sagittal MPR plane to obtain a short axis view at papillary muscle
level. Finally, we rotate the axial MPR line on the coronal MPR plane to
obtain the transgastric view for mitral apparatus.

\textbf{Transgastric views for LV outflow tract (LVOT) to ascending
aorta (AsAo) (Deep transgastric 5-chamber view and transgastric long
axis view)} (Figure 6)

This is the ideal view to obtain a parallel alignment of Doppler signal
to the LV outflow jet. When there are aortic or mitral prostheses or
calcification, this is the only view to investigate aortic valve cusps
without acoustic shadowing. After transcatheter aortic valve
replacement, this view is the optimal to evaluate paravalvular leakage;
and it is also crucial to estimate the pressure gradient at LVOT and
aortic valve after procedures, such as, mitral valve-in-valve and
transcatheter aortic/mitral valve replacement. More often than not,
there are configural differences between pre-operative CT and
intra-operative TEE images on the aorto-mitral structure. On CT
simulation, we firstly move the MPR crosshairs into the gastric fundus
and then rotate the axial MPR line clockwise toward the aortic valve
(step1). Next, we adjust the sagittal MPR line to cross the aortic valve
on the axial MPR plane (step2). Lastly, we rotate the axial MPR line on
the coronal MPR plane to check the relationship between mitral
structure/device and LVOT (step3).

During the TEE manipulation, an important tip to acquire the
transgastric LVOT-AsAo view is to add some ``flex to the left.'' The in
vitro motion of TEE probe during ``flex to the left'' deviates somewhat
for there is to the certain extent ``anteflex'' and it becomes, instead,
more like a ``turn to the left'' (i.e., counterclockwise rotation of the
TEE probe, Figure 4). However, due to the resistance of the esophageal
tract and accumulated torque at esophagogastric junction (EGJ), there
will be an in vivo disproportional loss of rotation at the TEE probe to
that added by imager. As a result, the ``flex to the left'' will be a
more suitable method to control the TEE probe in the gastric fundus to
achieve better contact and a more predictable and controllable rotation.
In patients with dilated LV chamber or horizontal AsAo, it is more
difficult to acquire the deep transgastric 5-chamber view because the
scanning sector cannot simultaneously include the LVOT and LV chamber
even with the ``flex to the left.'' In that case, the transgastric long
axis view may catch the LVOT-AsAo structure in the right side. If the
axial MPR plane cannot produce the ideal deep transgastric 5-chamber
view after the step 2 mentioned earlier, (i.e., only AsAo and atria but
limited LV chamber), the transgastric long axis view may become a more
suitable intraoperative choice (Figure 4). As a result, CT simulation
can provide with a quick check for the difficulty in TEE acquisition.

\textbf{Distal esophageal views for tricuspid valve (Figure 7)}

At the mid-esophageal level, septal leaflet is prone to be attenuated by
the acoustic shadowing from interatrial septum; however, such
attenuation can be avoided at the distal esophageal level, and 3D en
face views reconstructed at this level can be used for delicate
investigation in the etiology of tricuspid regurgitation. Although
aortic valve disappears sometimes, the anatomical landmarks such as
ostium of coronary sinus, Eustachian valve, and rough part of right
atrium, can still help determine the orientation in TEE views at the
distal esophageal level. On CT simulation, we firstly move the MPR
crosshairs into the distal esophageal level, near the EGJ and then
rotate the axial MPR line clockwise toward the aortic valve. Next, we
simulate ``turn to the right'' by rotating the sagittal MPR line
clockwise on the axial MPR plane to cross the tricuspid valve. Finally,
we rotate the axial MPR line on the coronal MPR plane to evaluate the
relationship between leaflets.

\textbf{Transgastric RV inflow views for tricuspid apparatus (Figure 8)}

Transgastric views for right heart give details about moderator band,
papillary muscles for anterior and posterior leaflets (RV inlet view),
and the only 2D view for simultaneous visualization of all 3 tricuspid
leaflets (RV basal view). On CT simulation, we firstly move the MPR
crosshairs into the gastric cardia and then rotate the axial MPR line
clockwise toward the aortic valve. Next, we simulate ``turn to the
right'' by rotating the sagittal MPR line clockwise on the axial MPR
plane to cross the RV. Finally, we rotate the axial MPR line on the
coronal MPR plane to produce the RV in-out view and the short axis view
of tricuspid leaflets.

Examples of left atrial appendage, short-axis view of aortic valve, and
bicaval view of interatrial septum are illustrated in Figure 9.

\textbf{4 | DISCUSSION}

TEE is the primary image guidance modality used for trans-catheter
structural heart intervention technologies because of its better
real-time visualization of cardiac anatomical structures. However, its
limited sector width and complex probe orientation prolong the learning
curve to comprehend the spatial configuration of procedural TEE imaging.
Although CT has been widely used as a preoperative planning tool for
trans-catheter structural heart interventions, the created 2D CT images
are usually taken from different visual perspectives of intraoperative
TEE images. This creates issues in positioning, docking and taking other
specific key steps of these image-guided interventions, because the
procedural TEE imaging may fail to reproduce the same prerequisite
patterns as the CT based preoperative planning. Compared to the high
degree of freedom in the CT MPR slices, the motion of TEE probe is
rather limited. Therefore, the methodology which we propose here is
capable of carrying out a preoperative plan by CT MPR to simulate the
intraoperative TEE rather than applying the TEE to acquire images
conforming to what is showed on CT slices. In this article, we
demonstrate a stepwise CT MPR manipulating method to simulate the TEE
probe motion and preview the procedural TEE images on a different
imaging modality. This reduces somewhat the differences in deciding the
size of devices from these two imaging modalities. Besides validating
this method in different TEE views, we also applied it on dynamic CT to
mimic TEE videos. This concept has not previously been introduced in a
systematic fashion.

On the other hand, such a learning curve is also steep for
interventional echocardiographers to precisely offer the
procedure-specific imaging needs in every patient.
\textsuperscript{13}Although basic acquisition protocols of TEE have
been introduced by Hahn and colleagues, \textsuperscript{13--16} many
patient-specific anatomical conditions, such as
clockwise/counterclockwise rotation of the heart, trajectory of
esophageal tract, geometry of gastric space and its relative position
with cardiac structures all lead to significant differences in the
spatial configuration of procedural TEE imaging. As a result, the TEE
imaging is of large variability and highly technique dependent.
Sometimes, it is even impossible to obtain the ideal procedure-specific
views in patients of challenging anatomy. In the application of a
traditional method, interventional echocardiographers discern not the
feasibility of those procedure-specific views until TEE probe is
inserted. Fortunately, in our simulation, the CT datasets in nature
contain all the anatomical information, and thus broaden the vision of
interventional echocardiographers beyond the scanning sector, offer the
spatial orientation between esophagus and the interested cardiac
structure, and thus enable us to foresee whether the desired
procedure-specific imaging is feasible or not since each step in our
method can be translated back into a patient-specific TEE acquisition
protocol. If the procedure-specific imaging is not feasible, the
heart-team can promptly use our method to seek surrogate TEE views at
other esophageal or transgastric levels. This assists interventional
echocardiographers and operators reach to a consensus in the
preoperative rehearsal and may even shorten the procedure time and
fluoroscopic time.

In this era of echocardiography-fluoroscopic and CT-fluoroscopic fusion
imaging, one might underestimate the importance in comprehending the 3D
orientation of 2D TEE images. Nevertheless, it is important for
transcatheter interventionists to extend their proprioception all the
way to the catheter tip and nearby structures. Proprioception needs
visual assistance to become precise perception; however, unlike the
electroanatomical mapping systems of the ablation catheters, current
devices for structural heart diseases are still unable to work on
precise targeting or tracking in the 3D space but only projecting to the
fluoroscopy where essential spatial resolution is lacking. In fact,
simply putting all modalities onto a cine fluoroscopy produces nothing
more than confusions because there are either just static segmentations
or mere artificial intelligence based modeling rather than imaging.
Although fusion imaging with high-resolution TEE images is feasible
nowadays, anatomical details are still discernible only when the image
intensifier is at the correct projection angles to spread the 2D images.
Our method allows patient-specific fluoroscopic viewing angles to be
generated simultaneously during the MPR manipulation. In combination
with the concept of the optimal projection curve and the
projection-slice relationship, \textsuperscript{9,10} CT MPR can enhance
a better understanding of the spatial orientation of
echocardiography-fluoroscopic fusion imaging.

\textbf{5 | CONCLUSION}

Stepwise cardiac computed tomography manipulation to mimic
trans-esophageal echocardiography is the last piece of the puzzle to
achieve mental co-registration of the three important imaging
modalities. With a high quality electrocardiogram gated cardiac CT, we
are enabled to foresee the fluoroscopy projections and TEE images in a
preoperative rehearsal to decide the interventional fluoroscopy
projection angles according to the patient-specific conditions, and to
assist the interventional echocardiographer to plan the imaging.

\textbf{HIGHLIGHTS}

MPR manipulation of the cardiac CT can integrate different imaging
modalities in evaluating structural heart diseases and set up the
procedural imaging plan in the preoperative rehearsal.

The steps of MPR manipulation of the cardiac CT can be translated back
into TEE probe manipulation protocols and thus shorten the learning
curve for novices.

Adjusting images of different modalities to similar reference planes and
configurations may reduce the discrepancies which appear during device
sizing.

\textbf{CONFLICTS OF INTEREST}

The authors have no conflicts of interest to disclose.

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\textbf{FIGURE LEGEND}

\textbf{FIGURE 1} Mathematical coordinate system for different imaging
modalities

\textbf{(A)} Computed tomography multi-planar reconstruction is based on
Cartesian coordinate system. \textbf{(B)} Fluoroscopy is the projection
in the direction of image intensifier, which is of spherical coordinate
system. Spider view of left coronary artery is yielded from the left
anterior oblique (LAO)/ caudal (CAU) projection.
\textbf{(C)}Trans-esophageal echocardiography imaging reference plane is
similar to the polar coordinate plane in the cylindrical coordinate
system. 1-3\textbf{=} spatial orientation of different TEE sectors (1
\textbf{=}Transgastric left ventricular short axis view; 2\&3 \textbf{=}
Two orthogonal mid-esophageal views); Blue circle \textbf{=}
mid-esophageal level; Orange circle \textbf{=} transgastric level; AsAo
= ascending aorta; DsAo = descending aorta; LA = left atrium; LAD = left
anterior descending artery; LCX = left circumflex artery; LM = left main
trunk; LV = left ventricle; LV = left ventricular outflow tract; RV =
right ventricle.

\textbf{FIGURE 2} Methods of stepwise multi-planar reconstruction (MPR)
to simulate trans-esophageal echocardiography (TEE) from cardiac
computed tomography (CT)

LEFT: Step 1: Invert the z-axis. Eye symbols and colored human models
describe the visual perspectives of the CT slices. After obtaining top
visual perspective, crosshairs are moved into the esophageal lumen
(shorter yellow arrow). Step 2: Turn to the left. On the axial MPR plane
(red box), sagittal MPR line is rotated to cross the center of mitral
valve. Slight retroflex is added to avoid foreshortening on 4-chamber
view (blue box). Steps 3: Rotate. On coronal MPR plane (green box),
axial MPR line is rotated to obtain 2-chamber and 3-chamber (long-axis)
view. RIGHT: Similarity in configuration is examined by overlaying the
yielded CT slices with the corresponded TEE views. ALPM = anterolateral
papillary muscle; AsAo = ascending aorta; AV = aortic valve; DsAo =
descending aorta; LA = left atrium; LV = left ventricle; MV = mitral
valve; PMPM = posteromedial papillary muscle; RA = right atrium; RSPV =
right superior pulmonary vein; RV = right ventricle; RVOT = right
ventricular outflow tract.

\textbf{FIGURE 3} Flex to the right

\textbf{(A)} Orange box: Decomposition of trans-esophageal
echocardiography (TEE) probe ``flex to the right'' movement into
displacement and negative rotation of the Cartesian coordinate
system.\textbf{(B)} Effect of ``flex to the right'' on mid-esophageal
left ventricle 4-chamber view: the left ventricular outflow tract (LVOT)
is revealed due to the ``negative rotation'' component, and is offset
with a compensatory positive rotation. \textbf{(C)} Cardiac tomography
multi-planar reconstruction simulation. Without ``flex to the right'',
the line of symmetry of the TEE scanning sector is close to the lateral
mitral annulus. As a result, the rotation-yielded bi-commissural view is
compromised (left lower green box). With ``flex to the right'', the line
of symmetry of the TEE scanning sector is displaced toward the center of
mitral valve, and the LVOT is again revealed due to the ``negative
rotation'' component. Compensatory positive rotation and rotated degree
for bi-commissural view are illustrated with the right lower green box,
and better bi-commissural view is obtained. AsAo \textbf{=} ascending
aorta; DsAo \textbf{=} descending aorta; Eso = esophagus; LA
\textbf{=}left atrium; LV \textbf{=} left ventricle; LV \textbf{=} left
ventricle outflow tract; RA \textbf{=} right atrium; RV \textbf{=} right
ventricle; RVOT \textbf{=} right ventricular outflow tract; S = spine.

\textbf{FIGURE 4} Flex to the left with anteflexed echo probe

\textbf{(A)} Orange box: Decomposition of trans-esophageal
echocardiography (TEE) probe ``flex to the left during anteflex''
movement into rotation about the esophagogastric junction and positive
rotation of the Cartesian coordinate system. The right colored human
models explain the visual perspective of coronal multi-planar
reconstruction plane (green box). \textbf{(B)} Effect of ``flex to the
left during anteflex'' on transgastric mitral apparatus view: the left
ventricular outflow tract (LVOT) is revealed on the right side. The
generated view serves as surrogate image to estimate pressure gradient
at LVOT when transgastric LVOT views are not feasible. ALPM
\textbf{=}anterolateral papillary muscle; AsAo \textbf{=} ascending
aorta; AV\textbf{=} aortic valve; EG junction = esophagogastric
junction; LA\textbf{=} left atrium; LAA \textbf{=} left atrial
appendage; LPV = left pulmonary vein; LV \textbf{=} left ventricle; LVOT
\textbf{=} left ventricular outflow tract; MDCT = multi-detector
computed tomography; MPA \textbf{=} main pulmonary artery; MPR =
multi-planar reconstruction; MV \textbf{=} mitral valve; PMPM \textbf{=}
posteromedial papillary muscle.

\textbf{FIGURE 5} Mitral apparatus

Blue box: advance and anteflex of the trans-esophageal echocardiography
probe to obtain the transgastric left ventricle short-axis view (blue
arrow). Green box: Rotation of the multi-planar reconstruction (MPR)
line on the coronal MPR plane to obtain the transgastric 2-chamber view
for mitral apparatus (green arrow). ALPM = anterolateral papillary
muscle; DsAo \textbf{=} descending aorta; LA = left atrium; LAA = left
atrial appendage; LCX = left circumflex artery; LPV = left pulmonary
vein; LV = left ventricle; MV = mitral valve; PMPM = posteromedial
papillary muscle; RA = right atrium; RV = right ventricle.

\textbf{FIGURE 6} Left ventricular outflow tract

UPPER: Standard deep transgastric 5-chamber view without rotation (0
degree). LOWER: Rotation at 135 degree: from computed tomography
orientation cube, we can easily understand the orientation is almost to
be that from anterior perspective. AML = anterior mitral leaflet;
AsAo\textbf{=} ascending aorta; AV = aortic valve; LA = left atrium; LAA
= left atrial appendage; LV = left ventricle; LVOT \textbf{=} left
ventricular outflow tract; PA = pulmonary artery; RA = right atrium; RAA
= right atrial appendage; RV = right ventricle.

\textbf{FIGURE 7} Tricuspid leaflets

Interatrial septum avoided at deep esophageal level (yellow box), and
tricuspid leaflets investigated without acoustic shadowing. Tricuspid
valve and its nearby orientations of nearby cardiac structures are
highly variable. As a result, preview with computed tomography
multi-planar reconstruction slices can help interventional sonographer
to understand better the spatial orientation during procedural
trans-esophageal echocardiography imaging. AsAo = ascending aorta; CS =
coronary sinus; DsAo = descending aorta; Eso = esophagus; EV =
Eustachian valve; IVC = inferior vena cava; LA = left atrium; LV = left
ventricle; MB = moderator band; PB = parietal band; RA = right atrium;
RCA = right coronary artery; RPV = right pulmonary vein; RV = right
ventricle.

\textbf{FIGURE 8} Tricuspid apparatus

Papillary muscle of anterior tricuspid leaflet is continuous with MB.
Several small papillary muscles arising from the diaphragmatic right
ventricle wall support the posterior tricuspid leaflet. Ant = anterior
tricuspid leaflet; CT = chordae tendineae; D = diaphragmatic right
ventricle wall; MB = moderator band; PM = papillary muscle; Post =
posterior tricuspid leaflet; RA = right atrium; RV = right ventricle;
RVOT = right ventricular outflow tract.

\textbf{FIGURE 9} Left atrial appendage, aortic valve and interatrial
septum

AsAo = ascending aorta; BAV = bicuspid aortic valve; CS = coronary
sinus; DsAo = descending aorta; FO = foramen ovale; IAS = interatrial
septum; IVC = inferior vena cava; LA = left atrium; LAA = left atrial
appendage; PA = pulmonary artery; Pec. m. = pectinate muscles; RA =
right atrium; RV = right ventricle; RVOT = right ventricular outflow
tract; SVC = superior vena cava; TV = tricuspid valve.\selectlanguage{english}
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