Accurate imaging of the hepatic and extrahepatic abdomen is an
important component of the management of many patients with cancer.
Historically, clinicians have relied on computed tomography (CT). The
use of intravenous (IV) and oral contrast agents, coupled with
dual-phase, helical CT scanning protocols, have made CT the
workhorse at many institutions.
Recent advances in magnetic resonance imaging (MRI) have challenged
this approach, however. The improved resolution of MRI, along with
physician education and acceptance of this imaging modality, have
added a new tool to the arsenal of treating physicians. Information
provided in this supplement should assist readers in gaining a
practical knowledge of MRI and an understanding of how this
technology may influence the clinical management of patients with
Screening With MRI
The use of MRI as a screening modality in patients at high risk for
developing primary liver cancer has not been thoroughly evaluated.
Overall, the relatively low incidence of primary hepatic tumors in
the United States makes routine hepatic screening impractical.
However, because the incidence of hepatocellular carcinoma (HCC) is
markedly elevated in patients with cirrhosis, hepatic screening may
be of value in this setting. Moreover, a dramatic rise in the number
of people in the United States infected with hepatitis C may result
in an increased incidence of multinodular cirrhosis and subsequent HCC.
Magnetic resonance imaging of the extrahepatic abdomen has long been
hampered by motion artifact and poor resolution. However, ultrafast
image acquisition, the use of oral and IV contrast agents, and better
computer software have markedly improved image quality. Using these
techniques, pancreatic, biliary, renal, adrenal, peritoneal,
gastrointestinal, and osseous imaging can be achieved. The quality of
the resulting images may rival or even surpass those obtained with
helical CT (see the article by Low).
Current screening programs commonly rely on focused hepatic
ultrasound and serial serum alpha-fetoprotein (AFP) levels to make a
diagnosis. Unfortunately, ultrasound has a limited capability for
differentiating HCC from regenerating nodules in the setting of
multinodular cirrhosis, and AFP is often misleading. Thus, MRI may
offer a reasonable screening alternative for this select group of
patients, although further investigation is needed (see the article
by Gogel et al).
Goals of Imaging
Because the curative management of primary and metastatic hepatic
tumors relies heavily on surgical resection and/or ablation, precise
imaging of the liver is essential. Important imaging goals include
tumor detection, tumor characterization, tumor distribution, and the
anatomic relationship of tumor deposits to the hepatic vasculature.
The poor sensitivity of CT in detecting hepatic tumors less than 1 cm
often left additional disease unidentified until the time of surgery,
while the limited specificity of CT arterial portography frequently
overestimated the extent of disease. Thus, changes in management were
not uncommon at the time of surgery, including findings that rendered
patients unresectable or nonablatable.
Fortunately, recent advances in MRI, such as ultrafast breath-hold
techniques, liver-specific IV contrast agents, oral contrast agents,
and multiplanar imaging, have markedly improved image resolution and
lesion detection. Compared to CT, MRI appears to better identify and
characterize hepatic tumors (see the article by Earls).
The improved overall sensitivity of MRI in imaging hepatic tumors,
particularly lesions less than 1 cm, has been demonstrated. This
information can greatly influence preoperative treatment decisions,
often determining whether a curative or palliative approach should be
taken, and can markedly reduce the rate of intraoperative procedures.
In addition, a relative cost advantage has been noted in patients
with suspected hepatic tumors who were imaged with MRI, dispelling
the misconception that MRI will increase the cost of care delivered
in this group of patients (see the article by Schultz
et al). Thus, it appears that MRI offers inherent advantages
over CT when imaging patients with suspected primary or metastatic
tumors of the liver.
The addition of MRI to the imaging modalities used in evaluating and
managing cancer patients can improve diagnostic and therapeutic
accuracy. Also, in the near future, identification and subsequent
characterization of hepatic tumors should be improved by the next
generation of liver-specific contrast agents soon to be approved (see
article by Mintorovitch et al). Most
importantly, hepatic and extrahepatic MRI of intra-abdominal
malignancy can provide useful information to clinicians and patients.
The data provided in this supplement should prove useful to
clinicians interested in obtaining high-resolution intra-abdominal
MRIs for their oncology population.