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Liver PET/MRI
Thomas Hope, MD, Miguel Pampaloni, MD, PhD, Michael Ohliger, MD, Spencer Behr, MD, Vahid Ravanfar, RT, Henry VanBrocklin, PhD,
James Slater, RPh, PhD, Carina Mari Aparici, MD, Judy Yee, MD, Eric Nakakura, MD, Emily Bergsland, MD, Carlos Corvera, MD,
Daniel Vigneron, PhD, and Sharmila Majumdar, PhD
Hepatic imaging benefits greatly from the use of MRI compared
to CT. In addition to contrast dynamics you can investigate
T2 signal intensity and diffusion weighted imaging that
can help detect and characterize hepatic lesions in ways
that are not possible on CT. PET/MRI promises to provide
a significant advance in clinical staging compared to PET/
CT for hepatic lesions.
Imaging using FDG
Fluorodeoxyglucose (FDG) is the most common PET
radiotracer used in clinical medicine. There are numerous
clinical indications for imaging hepatic metastatic disease,
although FDG PET is used infrequently to evaluate primary
liver malignancy. Combining focused liver MRI has
demonstrated an ability to increase the detection of small
hepatic metastases that can change patient care. This is
particularly relevant in patients with colorectal cancer being
treated with curative resection. In addition to metastatic
disease, there may be a role in the setting of hepatocellular
carcinoma. Well-differentiated HCCs are typically not
FDG avid, but poorly differentiated and infiltrative lesions
are frequently hypermetabolic. Particularly in the setting of
infiltrative HCC, FDG PET/MRI can help delineate the margins
of the malignancy, which can aid in surgical resection
(Figure 1).
How to solve the issue of motion
Motion is a significant issue with hepatic imaging, which is
exacerbated in the setting of PET/MRI. In addition to the
respiratory blurring seen with PET/CT, there is respiratory
ghosting due to the numerous breath-holds performed
during the simultaneous PET and MRI acquisitions. Many
solutions have been proposed, which frequently depend
on acquiring an MR-based motion tracker throughout the
PET acquisition. This approach is limited as it interferes with
the acquisition of the diagnostic liver imaging sequences.
Therefore we decided to use respiratory bellows to provide
a gating signal, allowing for continuous acquisition of
MR sequences. Using this approach we remove all data
associated with breath-holds and restrict PET data to that
Figure 1 Example
of FDG PET/MRI in a
patient with infiltrative
HCC demonstrating the
utility of FDG to help
discriminate between
possible vascular
shunting (A, arrow
heads) associated with
portal vein thrombus
(B, white arrow) and
(C) metabolically
active infiltrative tumor.
Fused imaging (D)
demonstrates that the
entire right lobe of the
liver has been replaced
by infiltrative HCC.
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