Hindawi Publishing Corporation
Minimally Invasive Surgery
Volume 2012, Article ID 145381, 10 pages
TransapicalAortic Valve Replacement
Ming Li,DumitruMazilu,and KeithA.Horvath
Cardiothoracic Surgery Research Program, National Heart, Lung, and Blood Institute, National Institutes of Health,
9000 Rockville Pike, Bldg 10, B1D47, Bethesda, MD 20892, USA
Correspondence should be addressed to Ming Li, firstname.lastname@example.org and Keith A. Horvath, email@example.com
Received 8 August 2012; Accepted 21 September 2012
Academic Editor: Babu Kunadian
Copyright © 2012 Ming Li et al. This is an open access article distributedunder the Creative Commons AttributionLicense, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Minimally invasive cardiac surgery is less traumatic and therefore leads to quicker recovery. With the assistance of engineering
technologies on devices, imaging, and robotics, in conjunction with surgical technique, minimally invasive cardiac surgery will
improve clinical outcomes and expand the cohort of patients that can be treated. We used transapical aortic valve implantation as
and engineering technologies. Feasibility studies and long-term evaluation results prove that transapical aortic valve implantation
under MRI guidance is feasible and practical. We are investigating an MRI compatible robotic surgical system to further assist
the surgeon to precisely deliver aortic valve prostheses via a transapical approach. Ex vivo experimentation results indicate that a
robotic system can also be employed in in vivo models.
Traditional cardiac surgery requires a sternotomy, cardiopul-
monary bypass, and cardiac arrest to provide a still and
bloodlessheartand itsvesselsforoperation. Whilenecessary,
these interventions are invasive and traumatic. The morbid-
ity of cardiac surgery can be quite a burden to the patients
In order to reduce the risks associated with open-
heart surgery, minimally invasive approaches have been
investigated [4–7]. Cardiac surgeons operate through small
incisions in the chest, eliminating the need for a sternotomy,
stopping the heart, or requiring a heart-lung machine to be
used. Decreased trauma to tissue and muscle with smaller
incisions typically results in less pain. Avoiding the bypass
machine reduces the risks for neurological complications
and stroke. In general, minimally invasive cardiac surgery, in
comparison to traditional procedures, offers many benefits
including reduction of the chance for postsurgical complica-
tions and leads to shorter hospital stay with a faster return to
Aortic valve replacement is such a cardiac procedure
that can be performed with minimally invasive techniques.
In the last decade, transcatheter aortic valve replacement
(TAVR) has been studied for treating the patients of high
surgical risk. The bioprosthetic valves are delivered through
catheters transfemorally [8–13] or transapically [14–18] and
are implanted within the diseased aortic valve. In current
while the transapical method is only chosen for patients
who have poor vascular access . However, the transapical
aortic valve approach may be more applicable to a wider
range of patients because of the lack of physical anatomic
limitations. Antegrade access avoids possible complication
with retrograde access, which is caused by inability to
cross a stenotic valve. Larger sheath diameters used in the
transapical access lead to less need for crimping of the valves,
which may be translated into better prosthesis longevity
[20, 21]. Early, midterm, clinical, and echocardiographic
despite a significantly higher risk profile in the cohort treated
with the transapical approach .
Typically, the imaging employed for TAVR is primarily
high-resolution fluoroscopy and adjunctive 2-dimensional
M-mode transesophageal echocardiography. The problems
with fluoroscopy guidance include device embolization,
2 Minimally Invasive Surgery
Figure1:Devices:(a)balloon-expandable prosthesis.(b)Self-expanding prosthesis,aMedtronicFreestylevalve sewninsidetheNitinolself-
expanding stent.Asmallstainlesssteelwelded onthesmallroundextensionofdistalendofthestentserves asapassivemarker indicatingthe
orientationofthe prosthesis.Thegrasping member of theproximal end is usedfor retrieve and repositionofthe stent.(c) A CADdrawing of
the delivery device with loop coil and antenna. Sheath with handle (1) protects and retains the prosthesis compressed until the deployment.
Inner rod with handle (2) pushes the prosthesis for deployment. Inner channel of the inner rod provides access for the loop snare wire (4).
End spacer with dimension protection (3) protects the end valve and ensures the exact dimension for the loop snare wire. The loop coil
antenna (5) is fixed into the groove cut on exterior tube of valve delivery system. The delivery device is made of nylon and delrin.
coronary obstruction, low or high placement, misalignment,
landmark loss (after ballooning the valve the calcium
pattern used by fluoroscopy to identify the leaflets/annulus
is changed), perivalvular leaks, need for rapid ventricular
pacing, radiation exposure, and intravenous contrast toxic-
ities. All of these are imaging related and may be improved
with better imaging; hence our desire is to pursue magnetic
resonance imaging guidance.
MRI provides excellent visualization particularly in its
ability to provide high-resolution images of blood-filled
structures without additional risk of radiation or contrast
reaction. Vascular as well as soft tissue visualization can
easily be performed simultaneously. MRI also provides
the ability to assess ventricular and valvular function and
myocardial perfusion. New generations of open, wide, and
short bore MR scanners and real-time sequences made
MRI not only cardiovascular diagnostics but also minimally
invasive cardiac surgery possible.
The confined physical space of the MRI scanner, even
with a wider and shorter bore, can be a challenging envi-
ronment in which valve replacement is performed. During
the procedure, the surgeon must manipulate the different
components of the delivery device and other tools through
simultaneously. In order to deliver the prosthesis properly,
a coordinated effort between the surgeon and the team is
critical in the noisy MRI environment while contending
with respiratory and cardiac motion during a beating heart
procedure. The use of a robotic assistance can potentially
alleviate the need of this level of coordination and provide
dexterous manipulation of the interventional tools inside the
Our group has focused on magnetic resonance imaging-
(MRI-) guided transapical aortic valve replacement [24–27].
In this paper, we report our work on this beating-heart
procedure: surgical techniques, medical imaging, medical
devices, feasibility of the procedure, and long-term results.
We also report on our work with robotic assistance for this
2.1. MR Imaging System. Magnetom Espree (Siemens Medi-
This 1.5-T magnet design, with short (120cm) and wide
(70cm) bore, gives a clearanceof up to 30cmabove the chest
of the supine patient and makes surgical access to the patient
ing. This system comprises an interactive user interface, an
operating room large-screen display, gated pulse sequences,
and image reconstruction software. Multiple oblique slices
can be obtained in rapid succession and can be simultane-
ously displayed in a 3D rendering to provide optimal 3D
anatomic information. Image contrast, image plane orienta-
tions, acquisition speed, 3D rendering, and device tracking
can be readily adjusted as needed during scanning .
2.2. Stents and Devices. A new self-expanding stent was desi-
gned to accommodate conventional stentless aortic bio-
prostheses (Toronto SPV, St. Jude Medical, Minneapolis,
MN, or Freestyle, Medtronic Inc., Minneapolis, MN) 
(Figure 1). The stent is made of a biocompatible nickel-
titanium alloy (nitinol), which assumes a “preprogrammed”
final configuration upon release from the delivery system
and exposure to body temperature. The stent has nine rods,
three of which are aligned with the valve commissures, and
a chevron repeating pattern along the length of the cylinder
Minimally Invasive Surgery3
Figure 2: (a) Passive marker showing black signal in MRI. (b) Active marker showing bright signal and highlighted in green. These markers
are used to indicate the orientation of the prosthesis in an MRI-guided aortic valve implantation procedure.
and expanded status prevents stress on the bioprosthetic
valve especially at suturing area. The chevron geometry
also prevents migration of stent at systole (high blood
pressure) because of the self-anchoring properties of the
chevron spikes. The structure of the stent also makes it easily
retractable into a delivery device. Adjustment of the position
during valve placement is therefore possible.
We also implanted balloon-expandable bioprostheses.
A stentless bioprosthesis (Toronto SPV or Freestyle) was
mounted on a commercially available platinum-iridium
stent (Cheatham Platinum, NuMed, Hopkinton, NY)
(Figure 1). The stented prosthesis was then circumferentially
compressed over a balloon-tipped catheter (NuMed, 25–
30mm OD, 50mm long). The expansion of the balloon
expanded the stented prosthesis to its proper shape.
Small austenitic stainless steel fragments (0.5mm) were
welded on the side of both the balloon-expandable and self-
as a dark signal in the MRI and is used to indicate the
orientation of the stented prosthesis (Figure 2(a)).
A delivery device was developed for holding and deliv-
ering the stented prosthesis (Figure 1). The delivery device
consists of a straight plastic rod, outside of which is a sheath
protecting the stented prosthesis before it is deployed. The
diameter of the delivery device is 9.5mm and fits into a
10mm trocar. The inner rod has a central channel for a
guide wire, balloon catheter, and/or stent retrieving device.
A small rubber gasket is used to prevent blood leakage from
the central channel. The plastic rod can move back and forth
inside the sheath. An active guide wire is embedded in a
groove on the sheath. This active guide wire is shown as a
bright signal in the MRI and is also used to indicate the
orientation of the stented prosthesis (Figure 2(b)). There is
a handle on the inner rod and the sheath, respectively, for the
surgeon to hold and manipulate the delivery device.
2.3. Valve Replacement Procedure. We chose Yucatan pigs
(45–57kgs) as the animal model for the preclinical studies.
The principle reasons for this choice are the similarity to
the cardiac anatomy of humans and suitability for long-term
studies because growth is somewhat limited compared to
domestic strains over the 6 months of followup.
After the large animal was intubated and anesthetized,
the physician placed the trocar into the apex of the heart.
Specifically using standard titanium surgical instruments via
a 6-cm subxiphoid incision, the pericardium was opened
and the apex of the heart was exposed. Two concentric
purse strings were placed around the apex, through which
a 10-mm trocar was inserted into the left ventricle. Typical
time to complete this part of the procedure was 15 to 20
minutes. Standard MR sequences were performed to obtain
the orientation of the heart, evaluate ventricular and valve
function, and locate the native valve annulus and the origin
of the coronary arteries. Prescanning also allows setting up
scan planes to be used for real-time imaging during valve
implantation and followup myocardial perfusion and aortic
flow imaging. Three imaging planes were prescribed for real-
time imaging during implantation. Two of these planes were
positioned to provide long-axis views of the left ventricle,
showing the right coronary artery and left main coronary
artery origins, respectively. The other plane provided an
axial view of the aortic valve. The coronary ostia and aortic
annulus location were digitally marked. These digital marks
remained visible at all times in the 3D rendering and were
used for anatomic reference.
Based on the preoperative image, an appropriate sized
prosthesis was selected. The prosthesis was then compressed
and placed inside the outer sheath at the distal end of the
delivery device. The prosthesis was aligned with the active
guide wire in the sheath of the delivery device.
The surgeon viewed the real-time imaging on a pro-
jection screen while manipulating the deployment device
within the animal in the magnet (Figure 3). The prosthetic
valve and delivery system were advanced through the trocar.
During implantation, the axial slice was shifted as needed
to visualize the device and guide proper orientation of
commissures with the help of the passive and active markers.
The long-axis views were interactively modified to show
the path of the delivery device, while keeping the coronary
origins in view. Both the active wire and the passive marker
4 Minimally Invasive Surgery
Figure 3: Using real-time MRI as projected onto the screen, the
surgeon advances the delivery device into the LV. He can then
precisely position the prosthetic valve for deployment.
were used to identify the location and orientation of the
prosthesis. The surgeon was in direct contact with the
(Magnacoustics, Atlantic Beach, NY) to request changes in
the imaging planes as needed.
During the procedure, the animals were monitored with
an electrocardiogram, oxygen saturation, end-tidal carbon
dioxide, systemic and left ventricular blood pressure, and
arterial blood gas analysis.
In a procedure using the self-expanding prosthesis, the
loaded delivery device was first advanced into the ascending
aorta. Upon release of the stent by retraction of the outer
sheath, the chevron-like Nitinol cylinder together with bio-
prosthetic valve expanded to its preprogrammed diameter.
Retracting and repositioning of the prosthesis were possible
before the stent was fully advanced outside of the sheath
In a procedure using the balloon-expandable prosthesis,
the balloon is first partially inflated by using normal saline
mixed 100:1 with an MR contrast agent Gd-DTPA (Magne
vist, Berlex Inc., Montville, NJ); the position is reconfirmed
to be ideal and the balloon is then fully expanded and the
After placement of the valve, the trocar was removed
and the apex closed with the purse-string sutures. After-
placement images were acquired to confirm the positions of
the prostheses and the valvular and heart function. Gated
cine-MRI was used to assess mitral valve function and
myocardial function. Phase contrast cine-MRI was used to
identifyflow throughthenew valveaswellasdetectingintra-
or paravalvular regurgitation. An MR first-pass perfusion
scan was performed during intravenous injection of Gd-
DTPA contrast agent to confirm that myocardial blood flow.
2.4. Long-Term Evaluation. The animals were allowed to
survive for long-term followup. At 1 and 3 months postoper-
atively, followup MRI scans and transthoracic echocardiog-
raphy were acquired while at 6 months postoperatively MRI
scans and confirmatory 2D and 3D transesophageal echocar-
diography were acquired. Retrospectively gated CINE MR,
phase contrast CINE MR, and MR first-pass perfusion
scanning during intravenous injection of Gd-DTPA contrast
agent were repeated at those time points to confirm the
position of the prostheses and the valvular and heart
function. After 6 months the animals were sacrificed, and the
histopathologic analyses were performed.
2.5. Robotic Assistance System. Based on the results seen
with a surgeon and human assistant manual approach, we
developed an MRI compatible robotic surgical assistant sys-
tem that could more precisely deliver aortic valve prostheses
[29–32]. The robotic system consists of an MRI compatible
robotic arm, a valve delivery module, and user interfaces for
the surgeon to plan the procedure and manipulate the robot.
The CAD sketch of the 9 degree of freedom (DOF) robotic
system which operates in the confined space between the
MRI bore and the supine patient is shown in Figure 4.
heim, Germany) was employed to hold the robotic module
and move the valve delivery device on its planned trajectory.
The robotic arm has a remote center of motion structure
and its configuration fits into a standard closed MRI scanner.
A robotic module was designed for manipulating a delivery
module comprises two linear joints: the translation joint
and the insertion joint, as well as a rotational joint. The
operations of the linear joints and the rotational joint are
independent. Two linear joints can be independently or
simultaneously controlled. The translation joint provides
linear displacement of the delivery device along its axis.
The rotation joint allows the delivery device rotating around
its axis to change the orientation of the prosthesis relative
to coronary ostia before it is deployed. The insertion joint
moves only the inner rod of the delivery device. Sole motion
of the insertion joint moves only the inner rod of the delivery
device, driving the balloon-expandable prosthesis out of the
protecting sheath to the desired position. Simultaneously
retracting the translation joint and advancing the insertion
joint at the same velocity keep the inner rod of the delivery
device at its location and retracts the protecting sheath back
to expose the prosthesis. This simultaneous motion will let
the crimped self-expanding prosthesis expand and affix to
the desired position.
To maintain image quality and prevent local heating
in the proximity of the patient, the prototype module was
made from nonconductive plastic materials, MR compatible
pneumatic actuators (Airpel, Norwalk, CT), and magneto-
translucent fiber-optical encoders (Innomedic, Herxheim,
Germany). The control PC that was placed outside of the
MR room communicated with the electronic devices that
control pneumatic valves and read encoder signals via the
Different interfaces—cooperative adjustment, operative
plan, and interactive GUI adjustments—were implemented
to suit the needs at the different phases of the procedure
(Figure 4) . After the physician places the trocar into
the subject’s heart, the Innomotion robotic arm is then
mounted on the MRI table and adjusted such that its end
effector is close to the trocar port. The robotic module with
a fiducial rod attached is mounted on the Innomotion arm.
Minimally Invasive Surgery5
MR images (S2 and S3 )
Figure 4: (a) A CAD sketch of the robotic system with patient inside an MRI bore. (b) Diagram showing connections between different
subsystems and interactions of the physician with the system.
The physician uses cooperative hands-on interface  to
adjust the Innomotion arm to insert the fiducial rod into
the trocar. Once the fiducial rod is in place, the user input
sensor is detached and the robot is moved into the bore. In
the preoperative phase, the patient undergoes another MRI
scan for the physician to plan the trajectory of the delivery
device. At the same time, another MR sequence is used for
system registration. The Innomotion arm is moved to the
planned trajectory, under image guidance. The fiducial rod
is then replaced with the delivery device. Thus, direct access
to the aortic annulus is created. In the intraoperative phase,
the physician uses the visual feedback from the rtMRI and
interactively adjusts and deploys the prosthesis using the
robotic module via a GUI.
3.Results and Discussion
3.1. MRI Guidance. A steady-state free precession (SSFP)
sequence was used with following scanning parameter: TR =
436.4ms, TE = 1.67ms, echo spacing = 3.2ms, bandwidth =
1000Hz/pixel, flip angle = 45◦, slice thickness = 4.5mm,
FOV = 340 × 283mm, and matrix = 192 × 129. The active
wires were a superb indicator of the valve orientation in
MRI. The passive markers on the stents also help to identify
the valve orientation. These markers were somewhat difficult
to visualize via MRI when the stents were fully crimped
but became more apparent as the stents were deployed.
Finally digital markers were placed on the images to identify
landmarks and provide surgical references (e.g., light blue
dots in Figure 2(a)).
6 Minimally Invasive Surgery
Figure 5: After-procedure evaluation. (a) Short-axis frames from a cine-phase contrast scan depict the blood flow through the aorta and
atria after trocar removal and chest closure. These scans are used to confirm adequate valve opening and blood flow through the prosthetic
valve and identify intra- or paravalvular regurgitation. Left: diastole. Right: systole. (b) A first-pass perfusion scan was performed during
intravenous injection of Gd-DTPA contrast agent to confirm that myocardial blood flow was intact to all segments of the myocardium. From
left to right the progression of time after venous injection of Gd-DTPA is represented.
Postplacement gated cine MRI revealed excellent
myocardial function after valve implantation in both
long- and short-axis views for animals in whom the valves
valve leaflet opening and no evidence of turbulence, diastolic
regurgitant flow, or paravalvular leak (Figure 5(a)). First-
pass perfusion studies demonstrated adequacy of myocardial
cessful deployment. The perfusion results confirmed ade-
positioning with respect to the coronary ostia (Figure 5(b)).
eriments wereconductedin which42 animals weresacrificed
after valve placement and assessment by MRI. Following the
acute studies, 34 animals were enrolled in chronic studies, 11
were implanted with a self-expanding prosthesis.
Total procedure time was 37 and 31 minutes for using
balloon-expandable prosthesis and self-expanding prosthe-
sis, respectively. They were not significantly different (P =
0.12). The time from introduction of the prosthesis into the
(mean ± std. dev.), respectively. This deployment time was
significantly shorter for the self-expanding prosthesis (P =
0.027). The procedures using balloon-expandable prosthesis
the ballooninflation and the difficulty in orienting the valve
knowing that once the balloon was completely inflated there
was no margin to allow for adjustment.
3.3. Long-Term Result. The prostheses were successfully
deployed in all of the chronic studies. Twenty-one of these
survived for 6 months and were sacrificed per protocol.
Postmortem pathologic analysis, after sacrifice at 6 months,
verified that the implanted prostheses appeared in place in
Minimally Invasive Surgery7
NIH number 167
NIH number 167
Figure 6: Radiographs (a) and necropsy results (b) of the hearts with the self-expanding prosthesis 6-months postimplantation. Both
anterior and lateral views of the heart show an intact self-expanding stent frame without any fractures. The bottom row shows inferior and
superior views of the self-expanding prosthetic aortic prosthesis; note that the entire stent frame crowns are covered as well as the annulus of
the prosthetic valve is covered by opaque white tissue without pannus formation extending into the valve bases. The anterior mitral leaflet is
unremarkable. The superior view of the aortic prosthetic valve shows good coaptation of the free edges of the valve leaflets. VS-ventricular
septum, AML-anterior mitral leaflet.
the aortic root. The prosthetic commissures were incorpo-
rated with neointimal growth continuous with the native
leaflet commissures. Representative radiographs and autopsy
confirmation of the self-expanding prosthesis after 6 months
implantation are shown in Figures 6(a) and 6(b).
The average strut fractures for the platinum iridium
balloon-expandable stent were 5.0 ± 3.1 (mean ± std. dev.),
while the average fractures for the self-expanding stent were
1.6 ± 2.5 (mean ± std. dev.) (P = 0.046). There was no
particular pattern of strut fractures observed. The fractures
are due to the stent material fatigue and the expansion,
contraction, torsion between the aorta and the stent.
3.4. Robotic Assistance. The MR compatibility of the entire
robotic system was evaluated using a 16-cm cylindrical MR
phantominside a1.5TSiemens Espreescanner.This imaging
protocol was similar to the one we used for the cardiac
intervention. The imaging series were taken with (1) phan-
tom only and (2) robotic system placed in the magnet and
running during imaging. The presence and motion of the
robotic system inside the scanner were found to have no
noticeable disturbance in the image. The observed SNR loss
was 8.2% for the entire robotic system placed in the scanner
and in motion.
tom for self-expanding prosthesis deployment (Figure 7(a)).
The phantom was designed to emulate the dimensions of
the valve replacement situation for testing the feasibility of
the robotic system. It consisted of a plastic tube with 25-mm
diameter, which served as the aorta. The diameter of the tube
on one side of a 200 × 100 × 100 mm water tank. A spherical
8 Minimally Invasive Surgery
Figure 7: (a) Setup for system level evaluation on a phantom. The prototype of robotic valve deliver module is mounted on an Innomotion
arm. (b) Sequence of MR images showing the progress of using our robotic system to place prosthesis under MRI guidance. First row shows
the orientation adjustment of the prosthesis. Second row shows the position adjustment of the prosthesis. Third row shows the deployment
of the self-expanding prosthesis.
joint mounted on a flexible, elastic membrane located on
the opposite side of the tank served as the apex. A 12–15-
mm trocar was inserted into the spherical joint. The distance
from spherical joint to the end of the plastic tube was 50
mm, which is the typical distance from the heart apex to the
insertion point had some compliance due to the mounting
The self-expanding prosthesis requires coordinated
motion between two coupled pneumatic joints, thus making
it a more challenging scenario. We aimed to deploy the self-
expanding prosthesis such that its proximal edge is on the
edge of the tube under rtMRI guidance using robotic system.
Figure 7(b) shows the progress of the orientation adjustment
and the position adjustment of the prosthesis, as well as
the progress of the deployment of the prosthesis. After the
prosthesis was deployed, we measured the distance between
the edge of the tube and the edge of the prosthesis. The
average of absolute system level error over seven trials was
1.14 ± 0.33 mm.
Despite the requirement of a minithoracotomy, transapical
aortic valve implantation is a relatively easy, safe, and
straightforward technique. The short and direct access route
allows excellent alignment between the prosthesis and the
aortic root. With the assistance of the visualization of the
active and passive markers on the devices in the MRI, the
orientation and positioning of the implanted valve are more
precise and predictable.
Real-time MRI with proper parameter values provides
excellent visualization for intraoperative guidance of aortic
valve replacement on the beating heart. It provides better
image quality and a complete view of the entire volume
of interest more than other competing imaging methods,
such as fluoroscopy/angiography, in which some anatomic
structures are not visible, and echocardiography, in which
the field of view is small and can be obscured by calcification
which is frequently the source of the valvular problem. MRI-
guided surgery also allows direct functional assessments to
be made before, during, and immediately after valve implan-
However, the presence of a strong magnetic field of MRI
scanner demands all the devices used must be MRI safe and
Both self-expanding and balloon-expandable prostheses
are used in TAVR. In our experience, self-expanding stents
were easier to position and deploy thus leading to fewer
complications during transapical aortic valve replacement.
The intrinsic radial force of the self-expanding stent allows
for even expansion of the prosthesis. As a result, the
orientation of the implanted valve is more predictable.
The self-expanding stent can be retrieved and repositioned
before it is fully expanded; this aids precise placement and
diminishes the risk and embolization. The self-expanding
stent, with its specific geometric design, handles torsion
better, while the balloon-expandable stent has no elasticity
and the material is relatively soft leading to more frequent
Robot assistance can reduce the cognitive load on the
physician with improved accuracy and repeatability in trans-
apical valve replacement under MRI guidance. The high
magnetic field and the confined space of an MR scanner
present many technical challenges. The mechatronic com-
ponents including actuators, sensors, and controllers must
be able to work in an accurate, stable, and robust way in
an MR environment. Materials used for a robotic system
should have low magnetic susceptibilities (comparable with
air, water, or human tissue), low electrical conductibility,
adequate mechanical strength, and good manufacturing
The robotic system has been tested on a stable phantom.
This phantom is not an ideal replica of the beating heart; but
with proper anatomical dimension between the aortic annu-
Minimally Invasive Surgery9
the coordinated working of the different components of the
integrated system before preclinical experimentation.
The control strategy and the human machine interface
for MRI compatible robot systems for medical interventions
need to be studied. In the engineering of robots for medical
applications, detailed analyses of the functions of the entire
gle entity, are arguably more important than the individual
performance of the subsystems (robot, surgeon, interfaces,
and application, separately). Thus, having a combination of
more than one interface such as; an image-guided interface,
console guided interface, or hands-on interface based on the
specific application might yield a higher performance from
the entire system.
Minimally invasive cardiac surgery reduces trauma and
speeds recovery of the patient. It allows a cohort of patients
considered to be at prohibitively high risk for undergoing
standard surgical cardiac operation to potentially realize the
benefits of a better functioning heart without the morbidity
and mortality of a conventional operation.
However, minimally invasive cardiac surgical proce-
dures can be technically demanding and more constrained
than open procedures. Restricted vision, the complexity
of instrument manipulation, and difficulty with hand-eye
coordination are frequent barriers to the implementation of
minimally invasive procedures. We used transapical aortic
valve implantation as an example; demonstrated minimally
invasive cardiac surgery can be implemented with the inte-
gration of surgical techniques, the technologies of medical
images, medical devices, and robotics. The feasibility of the
implantation of the transapical aortic valve under real-time
interactive MRI guidance was successfully demonstrated.
The long-term survival experiments further confirm that
this minimally invasive surgical technique is safe and robust,
ready for translation to a clinical trial.
MRI provides real-time viewing to allow guidance of
procedures in the blood-filled heart without requiring car-
diopulmonary bypass and cardiac arrest. Real-time nonin-
vasive MR imaging that can provide both anatomic details
and functional assessments enables the use of minimally
invasive cardiac approaches that may provide patients with
a less morbid and more durable solution to structural heart
disease. The ability to measure cardiac function online is also
an advantage to performing the minimally invasive surgery
MRI has not been widely implemented in all centers. MRI
equipment is expensive to purchase, maintain, and operate.
A single MRI scanner can cost over 1.5 million dollars.
tools. Devices that are used during interventions, such as
catheters, are usually not designed to be MR visible or
compatible as they often contain ferromagnetic materials or
long electrical conductors.
Robotics augments the dexterity and accuracy of instru-
ment manipulation in a confined space. The marriage of a
medical imaging system and a robot makes the benefit of
minimally invasive interventions substantial. An MRI com-
patible robotic assistant system was developed for assisting
in transapical aortic valve replacement. Different interfaces
were implemented to suit the needs at the different phases
of TAVR procedure. The experimental results show that this
robotic system can assist to smoothly deliver the prosthesis
under real-time MRI guidance with high accuracy. The
presence and motion of the robotic system inside the MRI
scanner were found to have no noticeable disturbance to
the image. The performance of using interactive interface to
control the robotic system in a beating heart is under further
evaluation in an animal study.
nologies such as medical imaging, surgical navigation, and
robotic devices, more cardiac surgeries can be performed in
a minimally invasive fashion. We believe minimally invasive
cardiac technique development is a long evolutionary pro-
cess; it requires collaborative efforts of physicians and engi-
neers to work cooperatively to fill in the technological gaps.
The authors are supported through the Intramural Research
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