Tech Briefs Magazine - November 2023 - PIT-9

Laser-based System Achieves Noncontact Medical Ultrasound Imaging
R
Haupt, a Senior Staff Member in Lincoln
Laboratory's Active Optical Systems
Group. Haupt and Senior Staff Member
Charles Wynn are co-inventors of the
technology, with Assistant Group Leader
Matthew Stowe providing technical leadership
and oversight of the NCLUS program.
Rajan Gurjar is the System Integrator
Lead, with Jamie Shaw, Bert Green,
Brian Boitnott (now at Stanford University),
and Jake Jacobsen collaborating on
optical and mechanical engineering and
construction of the system.
Medical Ultrasound in Practice
If your doctor orders an ultrasound, you
can expect a highly trained sonographer to
press and manipulate an array of transducesearchers
from MIT Lincoln
Laboratory and their collaborators
at the Massachusetts General Hospital
(MGH) Center for Ultrasound Research
and Translation (CURT) have developed
a new medical imaging device: the
Noncontact Laser Ultrasound (NCLUS).
This laser-based ultrasound system provides
images of interior body features
such as organs, fat, muscle, tendons, and
blood vessels. The system also measures
bone strength and may have the potential
to track disease stages over time.
" Our patented skin-safe laser system
concept seeks to transform medical ultrasound
by overcoming the limitations associated
with traditional contact probes, "
explains principal investigator Robert
ers, set in a handheld device, onto your
body. As the sonographer pushes the transducer
probe across your skin, high-frequency
acoustic waves (ultrasound waves)
penetrate and propagate through your
body tissue, where they " echo " off different
tissue structures and features. These echoes
manifest from the acoustic impedance, or
change in tissue strength (tissue softness or
rigidity), from fat, muscle, organs, blood
vessels, and bone deep inside the body.
The probe receives the returning echoes,
which are assembled into representational
images of the body's internal features. Specialized
processing schemes (synthetic aperture
processing) are used to construct
the shapes of the tissue features in 2D or
3D, and these constructions are then displayed
on a computer monitor in real time.
Using ultrasound, doctors can noninvasively
" see " inside the body to image diverse
tissues and their geometries. Ultrasound
can also measure blood flow pulsing
through arteries and veins, and can characterize
the mechanical properties (elastography)
of tissues and organs. Ultrasound is
used routinely to assist doctors in evaluating
and diagnosing a variety of health conditions,
diseases, and injuries. For example,
ultrasound can be used to image the anatomy
a developing fetus, detect tumors, and
measure the degree of narrowing or leakage
in heart valves. Ranging from handheld
devices on an iPhone to cart-based
systems, ultrasound is highly portable, relatively
inexpensive, and widely used in
point-of-care and remote-field settings.
Limitations of Ultrasound
Though state-of-the-art medical ultra12 "
8 "
Scan
Mirror
8 "
Scan
Mirror
Scan
Mirror
US
receive
(2 chan)_
US transmit
Patient Skin
*LDV - laser Doppler vibrometer
The NCLUS portable, multiple-degree-of-freedom plane-positioning armature (top) stages an optical
head (bottom left), which houses a miniaturized laser source and receiver, flexible optical fibers, mirrors,
and a camera (bottom right). (Images: Glen Cooper)
Photonics & Imaging Technology, November 2023
sound systems can resolve tissue features
within fractions of a millimeter, the technique
has some limitations. Free hand manipulation
of the probe by sonographers to
obtain the best viewing window into the
body interior leads to imaging errors. More
specifically, as sonographers apply pressure
to the probe by feel, they randomly compress
the local tissue where the probe
makes contact, causing unpredictable
changes in the tissue properties that impact
the travel paths of the ultrasound
waves. This compression distorts tissue-feature
images with some unpredictability,
meaning feature shapes are not accurately
9
Fast frame rate
camera
Pulsed laser
Fiber Optical
2 um
2 channel
LDV
2 Fiber Optic
1um
LDV
Tech Briefs Magazine - November 2023

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