To effectively treat coronary disease, physicians need to see how blood flows
through the arteries and heart. To accomplish this, an intervential cardiologist
injects radiographic material (contrast) into the patient, then views images of
the coronary anatomy on overhead monitors. Acist Medical Systems (Eden Prairie,
MN) claims to have developed the first angiographic-fluid-delivery system to
combine programmable computer and motion-control technology with
physician-interactive control for precise fluid delivery.
While the last decade has seen many breakthroughs in the devices used to
treat coronary artery disease, angiographic-fluid-delivery systems have lagged
behind. Most intervential cardiologists today use a confusing array of
stopcocks, a maze of tubing, and an awkward hand syringe to inject contrast.
Motorized injectors emerged several years ago for use in ventriculargrams that
demand higher contrast volumes and rates. But they don't let the physician
control and vary the flow rate during these injections.
With more than 2 million cardiac angiograms performed in the U.S. every year
(Source: The Cowen Group), the opportunity to find a better method presented
itself to visionary Robert Wilson. A noted University of Minnesota cardiologist,
Dr. Wilson envisioned this new system would overcome the limitations of current
angiography. "My colleagues and I joked about how we would like to perform
angiography as simply as we pump gas in our cars--just squeeze a hand
controller; the more you squeeze, the more you get."
Setting out to use as much off-the-shelf computer technology to semi-automate
the process, Wilson teamed up medical and technical experts and founded Acist
Medical Systems with the goal of providing the cardiologist with total control
over every element of the procedure. "Competitive contrast systems are simply an
on/off switch that delivers the entire amount of contrast programmed, with no
variable control over the injection whatsoever," says Acist's Vice President of
Marketing Mark Gillick.
"Additionally, manual systems have complicated setup requirements that take
longer than our method. Our design simplifies the physician's work using an
interactive, power-assisted control handpiece. The physician controls all
aspects of the procedure with the AngioTouchTM controller while
viewing injection data on the system's control monitor. The system's preset
parameters help facilitate reproducible injection of coronary arteries. And
allow the physician to choose more or less aggressive parameters with the touch
of a finger."
The Acist system injects either contrast or saline fluids at the discretion
of the physician during the cardiac procedure. It automatically aspirates and
purges. "Because the injection process is more precise, shorter imaging times
are possible, which means less radiation exposure for the patient and physician.
And because it is a simpler system to set up and operate, fewer personnel may be
required. It also conserves contrast media, and most important, new built-in
safeguards maximize patient safety," says Gillick.
Sensors for safety. The automatic syringe is equipped with
sensors to monitor the amount of available contrast, and the entire refilling
process--including automatic purging of air--to ensure a continuous,
uninterrupted supply of contrast media. The system automatically detects air as
contrast is dispensed. Other safety features include a backlit automatic syringe
and high-pressure tubing for enhanced visibility in the low light of the cath
lab, along with a hand controller lockout to prevent unintentional actuation of
the hand controller trigger.
Audible indicators alert the user of button depressions, system messages, and
touch screen commands. The ACIST Injection System also provides the ability to
automatically switch between high- and low-pressure ports so that the patient's
blood pressure is monitored any time fluid is not being dispensed.
"Aside from a custom rod-type actuator from Tol-O-Matic (Hamel, MN), we use
mostly off-the-shelf components," explains Acist's Vice President of New Product
Development Doug Duchon. Leveraging technologies already proven in the field cut
development time. "We designed custom electronics, consisting primarily of a
dual-processor logic board and an analog power board, to support the
motion-control hardware." Advanced Motion Controls supplies the AMC BE25A20
servo amplifier that runs in encoder-velocity-feedback mode. And a 2,000-line,
incremental, digital, quadrature encoder system from U.S. Digital supplies
feedback.
After receiving U.S. Food and Drug Administration clearance to market in
December 1997, it was introduced at the March 1998 American College of
Cardiology conference in Atlanta. And most recently, at the Tenth Annual
Symposium on Transcatheter Cardiovascular Therapeutics, an estimated ten
thousand physicians eagerly observed live-case demonstrations via satellite from
hospitals in Washington D.C. and New York.
Injection system overview. The ACIST Injection System
increases the efficiency and control of the cardiac catheterization procedure.
First to combine fully programmable computer technology with
physician-interactive control of fluid delivery into one complete system, it
provides precise control of contrast flow into the coronary arteries while
replacing all of the stopcocks and maze of tubing with a single line and the
patented AngioTouch Hand Controller.
AngioTouch Hand Controller.The hand controller replaces the
manual syringe, and is the only system to offer singlehanded, variable flow-rate
control of all contrast and saline injections. No compromise in visualization
under fluoroscopy is seen when injecting around PTCA balloons or intracoronary
stents, allowing the use of smaller catheters for diagnostic (4 French) or
interventional (6 French) procedures.
Touch screen monitor.Designed to provide precise injection
and procedure information, the touch screen monitor provides a continuously
updated display of total contrast delivered, the actuals of the last injection,
and automatically refills the contrast syringe when needed. Moreover, it offers
default parameters for the left coronary artery, the right coronary artery, or
the left ventricle/aorta, based upon physician preference and patient weight.
Automated manifold. The system's automated manifold
eliminates the need for a completely separate system for injecting coronary
arteries or the left ventricle. Aspiration of contrast injection and saline
flushing is controlled automatically and the system deposits waste material in a
disposable bag. The system automatically switches the pressure transducer
off/on, both before and after each injection, to support patient safety and
physician control over the injections.
The pressure waveform signal instantly reappears once the injection is
completed. This gives the physician total control of the procedure, and provides
immediate access to the patient's vital signs without having to look down at the
table to manipulate manifolds, stopcocks, etc.
"The physicians who have used the ACIST Injection System have been extremely
impressed with the control they have over the entire angiographic procedure,"
explains Acist Vice President Mark Gillick. "Rather than looking down at the
table to manipulate manifolds and stopcocks, physicians can now focus their full
attention on the diagnosis and treatment, allowing them to deliver contrast at
the touch of a button and accurately place a balloon or stent without ever
taking their eyes off the monitor."
"ACIST moves beyond the limitations of both manual and motorized devices to
set new standards for catheterization performance," says Gillick. The system's
modular design easily fits various cath-lab configurations. It simplifies
delivery of contrast media into the patient's arteries, while increasing the
procedure's efficiency, productivity, and patient management. ACIST offers
single-hand control, touch screen convenience, complete procedure monitoring,
and continuous optimal/variable fluid-injection control.
That was then, this is now...
Manual and Power Injections
Continuous turning of stopcocks for injecting, refilling, or monitoring
pressures
ACIST Injection System
Total physician control over the entire procedure
Rod-type actuator frees physician's hands
Key to Acist's fluid-injection control is Tol-O-Matic's electrically powered,
screw-drive actuator. "While the actuator's design is straightforward," explains
Acist's VP of R&D Doug Duchon, "Tol-O-Matic's ability to prototype rapidly
and give us exactly what we needed made the choice easy. Moreover, because we
are a small company, many of the firms we contacted gave us a "lukewarm"
reception, while Tol-O-Matic engineers expressed genuine interest in the task at
hand. In fact, Tol-O-Matic actually built a custom extrusion for this actuator."
It was evident when Acist design engineers started developing early
prototypes of the system that a custom actuator was needed. Enter Tol-O-Matic
engineers, with new and exclusive electric linear-actuator products and a
willingness to provide customization as needed on challenging projects. "We
looked at using a standard Tol-O-Matic BC3 cylinder body and a standard lead
screw and ball nut for the actuator," said Derek Wise, Tol-O-Matic design
engineer, "but because of Acist's special requirements, we needed to work off a
clean sheet of paper to build a prototype with all of the special features they
wanted.
Acist's engineers defined the requirements of the actuator and the design
evolved as the system developed. Design targets included:
A rugged and reliable design
The cylinder body is a custom aluminum extrusion which allows component
mounting from all four sides. This configuration accommodated design changes
along the way, plus it furnished a versatile design platform for future product
models which Acist is planning for radiology and ultrasound applications.
Unlike many actuator applications where carrying and moving a load are the
primary requirements, the Tol-O-Matic rod-type actuator carries no load, but is
designed to provide movement and thrust force to a syringe in the injection
system. As a result, the actuator was more compact because it uses no radial
bearings. A custom-designed, stainless-steel rod end transmits the actuator's
motion and force to the syringe plunger and provides consistently smooth
straight-line motion.
To power the actuator, Acist specifies Electrocraft (Eden Prairie, MN)
brushless-dc servo motors. The NEMA-34 frame (E3629) servo motor ships directly
from Electrocraft to Tol-O-Matic, where it's mounted onto the backing plate of
the actuator. It provides a peak torque of 575 inch-oz.
Tol-O-Matic integrates another ten-turn, boron-wound, precision potentiometer
supplied by Riverside, CA-based Bourns Inc., for extra safety. Mounted in the
drive area, it provides position feedback data, and shuts the system down in the
event of problems such as a broken belt. "To insure high accuracy, Tol-O-Matic
calibrates each unit individually prior to shipment," explains Wise.
Two gears drive the potentiometer system. Originally designed of aluminum,
one gear was redesigned with an aluminum/acetal composite to reduce the
possibility of system contamination due to wear and to operate with less noise.
And hard-coat, anodized belt pulleys reduce system contamination due to belt
wear.
The actuator lead nut incorporates special Delrin AF antirotation keys. A new
design feature for Tol-O-Matic actuators, these keys prevent the thrust rod from
rotating, and they also actuate micro-switches which provide position data to
the system controller. These switches shut the system down to prevent the unit
from travel past end of stroke. The actuator motor mounting plate has a special
access port which allows easy drive-system removal and adjustment when
calibrating the actuator and performing maintenance. Finally, actuator
components include special finishes such as nickel plating some steel
components, and anodizing all aluminum components.
In addition to assembling the actuator and motor components for Acist,
Tol-O-Matic provides three separate operating tests of the final assembly. A
runout test verifies system tolerances. A second test with a dynamometer
confirms current stability so there is no potential for electrical surges. A
final test checks the potentiometer gears for system backlash.
"Even with all of the modifications, the final actuator design is relatively
simplistic," says Wise, "but the best designs are straightforward and easy to
operate. We liked it so much that we just released the RSA series of rod screw
actuators. With six new sizes, we've got all kinds of new applications lined up
including: third axis in gantry systems, indexers, platform tables, and others."
Other Applications
Servo-fluid injection
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