MEDICAL DEVICE INNOVATION - Medical Device Daily

MEDICAL DEVICE INNOVATION 2010
New imaging analysis provides
new ‘map’ for tumor survival
By ROB KIMBALL
Medical Device Daily Staff Writer
One of the constant barriers that physicians, and their
patients, seem to encounter is the battle against time. In the
case of tumor treatments and diagnosis, researchers have
published a study that could save time to recovery if a
treatment isn’t working for a patient — via a new way of
observing a standard MRI.
As early as one week after beginning treatment for
brain tumors, a new imaging analysis method was able to
predict which patients would live longer, researchers from
the University of Michigan Comprehensive Cancer
Center (Ann Arbor) have found.
The method uses a standard magnetic resonance imaging
(MRI) protocol to monitor changes over time in tumor
blood volume within individual voxels of the image, rather
than a composite view of average change within the tumor.
This parametric response map (PRM) allowed researchers
to see specific areas in which tumor blood volume
increased or decreased, that may have canceled each other
out when looking at the changes as an average.
Results of the study appear in the advance online edition
of Nature Medicine.
Craig Galban, PhD, assistant professor of radiology at
the U-M Medical School and the study author, told Medical
Device Daily that this could be a “huge paradigm shift” if
clinicians go in this new direction. Galban describes the
potential for this imaging analysis as “adaptive therapy.”
The researchers looked at 44 people with high-grade
glioma, a type of brain tumor, who were treated with
chemotherapy and radiation. Each participant underwent
MRIs before treatment, and one week and three weeks after
starting treatment. The researchers then looked at the relative
cerebral blood volume and the relative cerebral blood
flow of the tumor to analyze voxel-wise changes among
the serial scans.
Looking at standard comparisons using averages, the
scans indicated no change one week and three weeks into
treatment. But, using the parametric response map
approach, the researchers were able to show changes in
the tumor’s blood volume and blood flow after one week
that corresponded to the patient’s overall survival.
“Right now, physicians have to wait until the treatment
is over to determine if it was effective. We are proposing
that we can determine right away if the treatment is effective.
If it is not working, then we can tailor the therapy rapidly
to the individual. We are trying to personalize the care
and get this valuable and accurate information to the clinician
so that they can make a decision on the proper course
of treatment for the patient,” Galban told MDD.
High-grade gliomas have a high-mortality rate, with
139
people surviving only an average of 12 months after diagnosis.
Typically, patients receive six to seven weeks of
treatment, followed by a traditional MRI scan six weeks
after completing therapy to determine if the tumor shrank.
If the cancer did not respond to the treatment, a new
approach may be tried.
A voxel is a volume element, representing a value on a
regular grid in 3-D space, as compared to a pixel which is 2-
D. As with pixels, voxels themselves typically do not contain
their position in space (their coordinates) — but rather,
it is inferred based on their position relative to other voxels
(i.e., their position in the data structure that makes up a
single volume image).
Galban explained the differences in standard imaging
analysis compared to PRM for MDD. “It’s really looking at
voxel-wide changes,” he said. “PRM is measuring the
changes in blood volume in these individual voxels. The
standard way to look at the functional data [such as an MRI
on a tumor] is to take all the information and gather it into
a mean, or average. We are proposing not just to look at the
statistical average of all the voxels and blood volume, but
to examine them discreetly and individually, and determine
spatially how much of the tumor did respond to treatment.
These are highly heterogeneous tumors. Some of the tumor
might have responded well to the treatment, but another
part of the tumor may not. So that’s how BPM differs — it is
really looking at changes in the blood volume in the individual
voxels. We’re interested in how much of that tumor
volume changes. “
The researchers believe this approach might also be
useful with other imaging techniques such as PET and CT
scans.
(This story originally appeared in the April 28, 2009,
edition of Medical Device Daily).
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