MGH Martinos Center for Biomedical Imaging 2016 | Page 12

advances in imaging technology

New Optical Imaging Tool Could Enable Portable
Neuromonitoring
The optical imaging technique diffuse correlation spectroscopy (DCS)
has shown tremendous promise for
neuromonitoring in infants and
children—offering a means to measure cerebral blood flow in, for example, the neonatal intensive care
unit. But translating it for use in
adults has presented a much greater
challenge.
In a paper published in August
2016 in the journal Optica, a team
of researchers at the MGH Martinos
Center described an advance that,
for the first time, has made this possible.
Like its sister technique, near-infrared spectroscopy (NIRS), DCS suffers limitations when operating with
a continuous-wave laser. Namely: It
can’t provide the information needed to separate out the signal from
the skull and the scalp, which can
contaminate the signal you actually want to see. (Continuous-wave
is less problematic in infants and
children because their skulls are
generally thinner; the extracerebral
contribution is larger in adults and,
for this reason, the sensitivity to the
brain is reduced.)
As with NIRS, using either frequency-domain or time-domain
techniques—where you can extract
more information from the signal
by varying the amplitude or duration of the laser—could help to

overcome these limitations. But for
assorted, often esoteric reasons, this
is much more difficult with DCS
than it is with NIRS.

employed specialized detectors developed by a lab in Milan, Italy.

One of the advantages of the instrument they ultimately described is
“Nobody believed you could do it,” that users can perform both timesaid Maria Angela Franceschini, an domain DCS and time-domain
investigator in the Optics Division NIRS using the same laser source
of the Martinos Center, an Associ- and the same detectors—“so from a
ate Professor of Radiology at Har- single measurement you can obtain
vard Medical School, and the senior both tissue optical properties and
author of the Optica paper. “We blood flow,” Franceschini said.
decided to try because there was a
chance we could.”
The ability to measure these two parameters, simultaneously and directIt turned out they were right. In the ly in the brain, could yield a number
study, Franceschini and colleagues of benefits—especially in the clinic,
describe an elegant solution to a where doctors need to know when
seemingly intractable problem with changes in cerebral blood flow are
DCS in the time domain: the limited putting patients at risk.
coherence that results from the use
of a pulsed laser.
Among the possible applications:
monitoring of the brain at bedThey were able to address this by side in stroke or trauma patients
reimagining their approach and in- or other patients in neurointensive
corporating ideas from other tech- care. Also, surgeons could use the
niques. But even after they sorted technology in the operating room,
out the conceptual issues, they had to track responses to anesthesia or
practical matters to attend to. One to keep an eye on perfusion during
example: The laser they needed cardiac procedures that involve bydidn’t exist; because there was no pass.
real demand for a laser particularly
suited to DCS in the time doma in, Authors of the Optica paper include
manufacturers hadn’t yet made one. the Martinos Center’s Bernhard
Undeterred by this, Jason Sutin, Zimmerman, Danil Tyulmankov,
a graduate student in the Center, Davide Tamborini, Kuan Cheng
built the laser himself. Similarly, the (Tony) Wu, Juliette Selb and David
detectors typically used with DCS Boas, as well as Franceschini and
weren’t stable enough to work in the Sutin.
time domain, so the investigators