Instrumentation & Measurement Magazine 25-1 - 8

Ultrasound
Signal Model
for Artery
Monitoring
Fig. 2. An illustration of ultrasound signal model for artery monitoring, using (a) WUS emitting pulsed plane-wave
ultrasound and (b) array UTs emitting focusing ultrasound.
layer were grounded through an ultrasonic pulser-receiver
when used for experiments. The resulting WUS is flexible
and lightweight so that it can be attached onto a curved and
deformable body surface without deforming the underlying
soft tissues including the artery or restricting the underlying
tissue motion. Multiple PVDF layers can also be used to design
for a particular ultrasound frequency and to improve the
intensity of the emitted ultrasound [4].
An example of a constructed WUS is presented in Fig. 1b.
It is flexible and lightweight, with an active ultrasonic sensing
area (overlapped electrode size) of 20 mm by 20 mm. The ultrasonic
performance of the WUS was evaluated experimentally
using a 12.3-mm thick Plexiglas plate sample. The WUS was attached
on the top surface of the sample with an ultrasonic gel
couplant, and the ultrasonic signal reflected from the bottom
surface was acquired. The ultrasound center frequency and
bandwidth were estimated to be 5.4 MHz and 6.6 MHz, respectively,
by analyzing the acquired signal.
Fig. 2 illustrates the ultrasound
signal model
for artery monitoring in
the pulse-echo technique
using the WUS with comparison
of the array UTs
employed in clinical ultrasound
imaging probe. The
WUS emits pulsed planewave
ultrasound of which
wavefront size is greater
than the diameter of an artery
as shown in Fig. 2a.
This complicates automatic
measurement of the artery
properties using the WUS
since there is more scattering
echo interference from tissues adjacent to the artery than
the array UTs with focusing ultrasound (Fig. 2b), obscuring the
artery wall echoes in the acquired signals.
Measurement Configuration
The measurement configuration for artery monitoring using
the WUS in the pulse-echo technique is shown in Fig. 3.
The WUS is secured over the common carotid artery (CCA) in
this example. The WUS was positioned to maximize the amplitude
of the ultrasound signals reflected from the CCA. To
prevent the lateral and vertical movements of the WUS that
may cause motion artifacts of the acquired ultrasonic signals
during the data acquisition, the WUS was fixed using adhesive
tape on top of the WUS and skin surface. Ultrasonic gel
couplant was applied between the WUS and skin surface for
the ultrasound transmission. An ultrasonic pulser-receiver
(Model: DPR300, JSR Ultrasonics, Pittsford, NY, USA) was
used to produce short electric pulses with the peak voltage up
Fig. 3. (a) A block diagram of WUS-based measurement configuration for CCA monitoring; (b) A schematic of the pulse-echo technique.
8
IEEE Instrumentation & Measurement Magazine
February 2022

Instrumentation & Measurement Magazine 25-1

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