Medical Design Briefs - April 2023 - 12

Optimal Coaxial Cables
may interfere with other systems using
the same frequencies, such as Wi-Fi in
the 2.4 GHz band.
InstaBend® 047 is a flexible, coaxial microwave assembly designed for interconnects between RF
circuit cards, modules, and enclosure panels. The cable can be bent very closely behind the connector,
simplifying cable routing. (Credit: Times Microwave)
building blocks are combined from a
material standpoint, from the center
connector and dielectric to the braid
and the outer jacket.
For example, low loss is an essential
requirement for lead cable assembly
due to its long length. A lossy lead cable
can significantly impact power transmission
efficiency. The loss also increases
with frequency, and excessive loss may
cause the cable and ablation antenna's
temperatures to rise, resulting in a large
amount of dissipated heat along the signal
path to the antenna.
Power Handling and Thermal Management.
An ablation device may need
more than 100 W of output power from
the generator to be effective. This presents
a cabling challenge - because longer
cables may be required to connect
the generator and device, and as cable
length increases, so does loss, reducing
the power yield. For example, a lead cable
assembly with 3 dB of insertion loss
will deliver only half of the output power
from the generator. The loss is dissipated
through the cable as heat.
A cable with elevated surface temperature
can be a risk to both the patient and
the physician performing the procedure.
Most medical procedures can only be
safely executed within a controlled temperature
range. Technical standards
such as IEC 60601-1 provide acceptable
temperature requirements.
Managing dissipated heat from cable
loss may require active cooling to keep
cable temperature at an acceptable level.
Some manufacturers use liquid coolant
12
to control the temperature throughout
the cable assembly. Active cooling can be
implemented as a closed-loop system,
circulating fluid through one or several
send and return lines separated from the
electrical components.
Elements in a coaxial cable, such as
metal braid and outer jacket, can aid
thermal dissipation or act as insulators,
preventing the operator and patient
from direct contact with hot surfaces.
The key is ensuring that the exterior device
temperature doesn't exceed a
threshold deemed safe for the patient
and the operator.
Reliability and Safety. Safe, reliable
performance is closely related to power
requirements and heat generation.
The integrity of cable-connector junction
and connector retention is also important
because of the high level of RF
or microwave energy transmitted. Intermittency
or disruption in the
high-power cable or wires connecting
various control circuits would cause a
severe safety hazard during an ablation
procedure.
Electrosurgery applications like RF
and microwave ablation do not tolerate
equipment failure impacting safety.
Therefore, the interconnect system must
be reliable and error-proof, with secure
and keyed connections to provide safe
and efficient power transmission.
Shielding Effectiveness. Shielding effectiveness
describes how well a coaxial
cable assembly is isolated from nearby
electrical devices and/or energy sources.
This is key because high energy levels
www.medicaldesignbriefs.com
Ease of Use and Integration. Microcoaxial
cables used in ablation are typically
integrated into higher-level assemblies
such as a catheter, so ease of use and integration
are essential considerations for
optimizing clinical efficiency and ergonomics.
The careful selection of cables
and connectors can streamline integration
and can ensure optimal performance.
Lightweight and seamless device handling
are needed to facilitate precise
movement and access to treatment
spots, especially those in harder-to-reach
locations. Cable flexibility can also impact
the user's comfort while performing
a procedure. For example, a stiff cable
with pronounced shape memory
makes it difficult to handle and control
the handheld device. Since an ablation
procedure can take hours, fatigue can
become a significant problem.
Cable flexibility is also essential to optimize
device ergonomics. Minimizing
interconnect size and weight helps when
it can be accomplished without negatively
affecting performance, safety, or ergonomics.
The small size also enables procedures
to be as minimally invasive as
possible; smaller openings into the patient's
body help reduce infection risk
and recovery time.
Cabling Recommendations
Hybrid Cable Assemblies. An optimal
lead cable assembly for connecting the
generator to the handpiece must balance
many vital requirements in an ablation
application, including:
* Low insertion loss.
* High flexibility.
* Low surface temperature.
* Lightweight.
* Integration.
* Aesthetics.
Hybrid cable assemblies provide an
integrated solution for power, signal,
and thermal management. This type
of cable combines a high-power cable
for microwave energy delivery, small
signal wires that incorporate low voltage
lines for LEDs, thermocouples,
system control, and fluid lines that circulate
a saline solution for cooling -
in a single assembly. Hybrid cable assemblies
are typically available as a
cable bundle, single-ended assembly,
or double-ended assembly.
Medical Design Briefs, April 2023

http://www.medicaldesignbriefs.com

Medical Design Briefs - April 2023

Table of Contents for the Digital Edition of Medical Design Briefs - April 2023