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In Practice
PET/MR Increases Sensitivity
of Lesion Detection in Drug
Refractory Epilepsy Patients
Epilepsy is the fourth most common neurological disorder—following
migraines, stroke, and Alzheimer’s—with approximately 50 million people
affected worldwide. Treating patients suffering from epilepsy is most
effective when the origin of their seizures can be localized to one or
more regions of the brain.1,2
The Mayo Clinic (Rochester, MN) is a
the country. This preeminence extends
world renowned leader in healthcare
to multiple diseases and care areas,
PET/MR Executive Chair, Mayo did scan
and medical research, ranked as the top
including epilepsy.
epilepsies with PET/CT. However, upon
overall hospital in the US by U.S. News
& World Report, as well as #1 in more
specialties than any other hospital in
Since January 2016, Mayo has been
utilizing PET/MR (SIGNA™ PET/MR,
GE Healthcare) for epilepsy cases.
According to Robert J. Witte, MD,
acquisition of the new PET/MR system,
the Mayo Clinic has increased the
number of PET studies in epilepsy.
“When you have a high-quality PET scan,
you can see the abnormalities more
clearly,” says Geoffrey B. Johnson, MD,
PhD, Nuclear Medicine Division Chair.
Robert J. Witte, MD,
“The MR scan is key; but having more
is PET/MR Executive Chair and Associate
Professor of Radiology at Mayo Clinic in
Rochester, MN.
GEHEALTHCARE.COM/MR
than one dataset, such as the PET data,
helps guide the radiologist’s eye.”
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In Practice
Dr. Geoffrey B. Johnson,
MD, PhD,
is Nuclear Medicine Division Chair and
Assistant Professor of Radiology at
Mayo Clinic in Rochester, MN.
Dr. Witte shares a statement from
Jeffrey W. Britton, MD, Epilepsy
Division Chair: “PET/MR has increased
our utilization of FDG in epilepsy. Its
primary niche is in the evaluation of
patients with intractable focal epilepsy,
“
That’s the whole point of what we are doing with PET/MR;
we spend a lot of time on the MR side adding sequences to
discover the pathology. If by combining these together we can
decrease that imaging time by a quarter or a third, then that’s
a big win where we can make significant improvements in the
patient workup.
„
with whom the routine MR is negative.
Dr. Robert J. Witte
In these patients, pre-scheduling of
imaging and other testing is important
In some of these cases, Dr. Witte adds,
Further, Dr. Witte sees potential
for efficient evaluation and expedited
PET/MR has been helpful in imaging
clinical and workflow benefits from the
decision making. Many of our patients
areas of the brain for targeted surgery.
have intractable epilepsy and have
undergone MR imaging prior to coming
to Mayo. In such cases, the chance that
our epilepsy MR protocol will reveal an
abnormality not seen by prior centers
is low.
“In select cases, we are moving our
practice to pre-schedule PET/MR as
our initial imaging modality instead
of just using our usual MR protocol.
We have a few cases where PET/MR
pointed to an area of the brain that fit
with the patient’s other localization
data and allowed further scrutiny of
MR, which revealed relevant subtle
structural abnormalities not previously
appreciated.”
Overall, Dr. Johnson and Dr. Witte have
been very happy with the initial results.
They found PET/CT was not especially
useful and in general the resolution of
PET has not been sufficient. However,
the combination of the new PET
with MR in a single exam is making
a difference.
simultaneous acquisition—and that
could also impact cost by reducing the
number of MR sequences. He explains
that Mayo has two MR protocols for
epilepsy. One MR protocol can take
up to 40 minutes to complete. If the
addition of PET-FDG can help the
clinician target and scrutinize the
important area(s) to investigate, then
there is the potential to decrease
“A busy practice with a high volume will
need to evaluate patients in a timely
fashion,” Dr. Witte says. While fusing
MR and PET has historically been an
option, there are more benefits with a
simultaneous scan. “This is especially
true for small lesions, such as 1 cm focal
cortical dysplasia where we require
optimal fusion and co-localization.”
the MR imaging time for the patient,
he says.
“That’s the whole point of what we are
doing with PET/MR; we spend a lot of
time on the MR side adding sequences
to discover the pathology,” Dr. Witte
says. “If by combining these together
we can decrease that imaging time by
a quarter or a third, then that’s a big
win where we can make significant
improvements in the patient workup.”
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A
C
B
Figure 1. (A) BRAVO T1-weighted, (B) FRFSE T2-weighted,
(C) PET TOF, (D) Fused PET/BRAVO T1-weighted. A
32-year-old with a history of epilepsy referred to PET/MR.
(C, D) FDG hypometabolism is seen on the prefontal left
lobe, complementing (A, B) MR images. CortexID Suite
helps with the quantification of the lowered FDG uptake
in the prefrontal lateral left region with a z-score of -4.08.
D
Advancements in technology
There are several clinical advantages
resulting from advancements in PET/MR
you don’t have the bone properly
attenuated,” Dr. Johnson adds.
“With MR, we are doing an entire brain
Dose reduction and
MR sequences
Patient dose may also be reduced when
technology. Certainly, higher PET
scan and during that time we are also
using PET/MR compared to PET/CT. MR
resolution is helpful, Dr. Johnson says,
picking up PET data. We are getting
has no ionizing radiation, but with the
however, “The combination of a Silicon
more data; one, because of the Silicon
high sensitivity of Mayo’s SIGNA PET/MR,
PhotoMultiplier with Time-of-Flight
PhotoMultiplier and how sensitive it
the injected FDG dose has also decreased
capability is a significant advantage.
is and two, because of the 25 cm PET
from 12 mCi down to 5 mCi. “We are
Also, having a bone atlas—the skull in
detector that is taking up more photons
getting superb images with the tracer,
attenuation correction—is essential.”
due to the geometry. What that means
and the lower injected dose may lead to
clinically is that we are more capable of
more noisy images, but this is the best
seeing subtle changes on the PET scan
trade off especially for our pediatric
He explains that without the bone
in the attenuation correction map,
there can be variable and decreased
metabolic activity next to the bone in
the area(s) being evaluated for cortical
brain defects. “That is critical. I think
there is the risk of having abnormal
decreased metabolic activity in the
in the brain cortex. We can see areas
patients,” says Dr. Johnson. “We’ve
of decreased activity that are not just
decreased patient dose by 60% going
random—they may be physiologically
from PET/CT to PET/MR.”
relevant—and then we can look on
the MR and be confident that is the
area of interest.”
At Mayo, several MR sequences are key
in an epilepsy patient workup. Double
inversion recovery is the primary 3D
cortex of the brain with PET because
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“
„
Dr. Geoffrey B. Johnson
volumetric sequence while MPRAGE,
pre-surgical workup for localization
localization of the epileptogenic
a T1w gray matter differentiation
of the epileptogenic zone. The exam
zone. In these cases, the clinician
sequence, is most often utilized.
includes a video EEG recording
may also implant intracortical
Mayo also frequently applies FLAIR.
and neurological examination
electrodes (stereo-EEG) to verify this
supplemented by the patient’s clinician
hypothesis followed by a cortectomy,
history. The patient then undergoes a
or the removal of a specific area of the
structural MR exam to help the clinician
cerebral cortex.
What is most important is the patient
outcome. “If we can identify a lesion
that can be resected, then the patient
has a much better chance of being
seizure free,” says Dr. Witte. Currently
determine if the epilepsy is the result of
a lesion that could be resected.
“(Simultaneous) PET/MR increases
the sensitivity of both scans,” she
many epilepsy patients undergo EEG
According to Dr. Marie-Odile Habert,
adds. “There is often information
monitoring. Dr. Witte believes that
MD, a nuclear medicine physician,
we can use from the scans to help
PET/MR can help reduce that portion
there are two clinical protocols utilized
the neurosurgeon remove only what
of the patient evaluation and workup.
at Hospital Pitié-Salpêtrière before
is needed.”
“If we see an abnormality on MR, then
we can go directly to PET/MR and
maybe that patient doesn’t have to go
through epilepsy monitoring,” he adds.
an eventual surgical resection. If the
patient has mesial temporal lobe
epilepsy, they undergo a PET/MR
to determine if there is mesial
temporal sclerosis associated with
This is particularly important in drug
temporal hypometabolism. In cases
refractory patients, Dr. Johnson adds.
with positive findings, the patient then
“The question becomes, how confident
undergoes surgical resection—either
are we that the lesion causing the
an anterior temporal lobectomy or
seizures can be removed? If all the
an amygdalohippocampectomy. At
Fusing two separate scans—the
PET and MR—is more complicated
and time consuming, she adds. One
simultaneous PET/MR scan is more
comfortable for the patient, but a real
clinical benefit is the ability to localize a
lesion on a structural MR scan initially
considered as normal, thanks to focal
hypometabolism on a PET scan.
data lines up and we can localize
Hospital Pitié-Salpêtrière, more than
Further improvements in PET/MR
that abnormality, then that helps the
80% of patients with mesial temporal
imaging of epilepsy patients could be
patient. These patients suffer and their
lobe epilepsy improve after surgery,
accomplished with the development
lives are altered by epilepsy—we are
Dr. Habert says.
of more specific radiotracers,
very excited about the potential for
PET/MR to help us help our patients.”
Hospital Pitié-Salpêtrière
In cases where the patient has
Dr. Habert adds.
extratemporal epilepsy and the lesion
References
visualized on MR is not consistent with
1. Epilepsy Foundation. Available at http://www.epilepsy.com/
learn/epilepsy-statistics.
EEG findings, the patient undergoes
2. World Health Organization. Available at http://www.who.int/
mediacentre/factsheets/fs999/en/.
At the Public Hospital of Paris, Hospital
interictal PET-FDG and ictal SPECT,
Pitié-Salpêtrière, patients with
if possible, to help hypothesize the
refractory partial epilepsy undergo a
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In Practice
We are getting superb images with the tracer, and the lower injected dose
may lead to more noisy images, but this is the best trade off especially for
our pediatric patients. We’ve decreased patient dose by 60% going from
PET/CT to PET/MR.
Case 1
Patient with a case of suspected occipital lobe epilepsy.
Findings
Structural MR is normal: No structural lesion detected with FLAIR sequence or
asymmetric perfusion 3D ASL. Right occipital ictal hyperperfusion localized on
subtraction ictal SPECT co-registered MR (SISCOM). Patient underwent PET/MR,
which demonstrated right temporo-occipital hypometabolism in interictal PET/MR,
that is much more widely distributed than as depicted on the SISCOM image.
Utility of hybrid PET/MR
T1
Co-registered SPECT and T1-weighted MR
CBF/T1
PET/T1
Images and case courtesy of Hospital Pitié-Salpêtrière.
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Case 2
Patient with temporal lobe epilepsy.
Findings
MR initially interpreted as normal. Patient underwent PET/MR, which enabled
In Practice
direct comparison of structural MR with metabolic PET information.
PET/MR demonstrated mild hypometabolism in the left mesial and anterior
temporal areas, allowing the identification of a subtle left parahippocampal
hyperintensity on T2 images (arrow) consistent with a focal cortical dysplasia.
In this case, PET/MR increased the sensitivity of lesion detection.
Utility of hybrid PET/MR
T2
PET/T1
Images and case courtesy of Hospital Pitié-Salpêtrière.
Robert J. Witte, MD, is PET/MR Executive Chair and Associate Professor of Radiology at Mayo Clinic in Rochester, MN. He completed his MD at the University
of Nebraska, College of Medicine; finished his fellowship in neuroradiology at Froedtert & The Medical College of Wisconsin; and completed his residency in
radiology at the Nebraska Medical Center. He’s board-certified in Nuclear Medicine, Diagnostic Radiology, and Neuroradiology.
Geoffrey B. Johnson, MD, PhD, is Nuclear Medicine Division Chair and Assistant Professor of Radiology at Mayo Clinic in Rochester, MN. He received his
MD/PhD in Immunology, completed his fellowship in Nuclear Radiology, and finished his residency in Diagnostic Radiology at the Mayo School of Graduate
Medical Education. He’s certified by the American Board of Radiology and the American Board of Nuclear Medicine.
Mayo Clinic is a nonprofit medical practice and medical research group based in Rochester, MN, with additional campuses in Scottsdale and Phoenix, AZ,
and Jacksonville, FL. The health system employs more than 4,500 physicians and scientists and 57,100 allied health staff. Founded in 1889, Mayo Clinic
is committed to clinical practice, education and research, providing expert, whole-person care to everyone who needs healing.
Marie-Odile Habert, MD, is a nuclear medicine physician and senior lecturer at the Public Hospital of Paris, Hospital Pitié-Salpêtrière in Paris, France.
The Hospital Pitié-Salpêtrière is a renowned teaching hospital in Paris, France, and part of the Assistance publique – Hôpitaux de Paris (AP-HP), the largest
hospital system in Europe and one of the largest in the world. The system is comprised of 15,800 physicians working across 44 hospitals, offering services in
52 branches of medicine, serving more than 5 million patients annually.
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