AJR 2001; 176:689-693
© American Roentgen Ray Society
Multidetector CT of the Pancreas and Bile Duct System
Value of Curved Planar Reformations
Matilde Nino-Murcia1,2,
R. Brooke Jeffrey, Jr.1,
Christopher F. Beaulieu1,
King C. P. Li1 and
Geoff D. Rubin1
1
Department of Radiology, Stanford University Medical Center, 300 Pasteur Dr.,
Rm. H1307, Stanford, CA 94305.
2
Department of Radiology, Veterans Administration Palo Alto Health Care System,
3801 Miranda Ave., Palo Alto, CA 94304.
Received June 8, 2000;
accepted after revision August 7, 2000.
Address correspondence to R. B. Jeffrey, Jr.
Introduction
An important feature distinguishing multidetector CT from single-slice
helical CT is the increased speed of scanning that permits routine use of very
thin collimation. With a breath-held acquisition, volumetric data sets are
obtained that may be used to create high-quality multiplanar reformations.
Curved planar reformations are two-dimensional displays that may be used to
trace the course of an anatomic structure through the entire data set. The
purpose of this pictorial essay is to highlight the unique display of
diagnostic information by curved planar reformations of the pancreas, biliary
tract, and peripancreatic vasculature in patients scanned with multidetector
CT.
Technique
Current multidetector CT technology (Light-Speed QX/i; General Electric
Medical Systems, Milwaukee, WI) captures four helical scans of data during a
single 0.8-sec gantry rotation. After an initial digital scout radiograph of
the abdomen has been obtained, a series of unenhanced scans is obtained using
a 10- to 12-sec breath-held acquisition, 10-mm collimation, and a pitch of 6
(high-speed mode). The unenhanced scans are used to define the target volume
that will be scanned during an IV injection of contrast material. The patient
must be instructed to attempt to achieve a similar level of deep inspiration
during all scan acquisitions to ensure that the target volume is not missed.
For a patient referred primarily for pancreatic studies, the target volume is
from the celiac axis to the transverse duodenum. For a patient referred for
biliary scans, the target volume is from approximately 2 cm above the porta
hepatis to the level of the transverse duodenum. Immediately before scanning,
the patient is asked to ingest 941.2 mL of water as a nonopaque intraluminal
contrast agent. After insertion of a 20-gauge catheter into an antecubital
vein, 150 mL of iohexol 300 mg I/mL (Omnipaque; Nycomed, Princeton, NJ)
iodinated contrast material is injected at a rate of 4 mL/sec with a power
injector. Forty seconds after initiation of the injection, 1.25-mm nominal
thickness sections are obtained during a 15- to 20-sec breath-hold through the
target volume using a pitch of 6 (high-speed mode). This late arterial scan
acquisition phase is referred to as the pancreatic phase
[1]. After this acquisition,
the patient is asked to inhale and exhale deeply. Another breath-held
acquisition is obtained during the portal venous phase (i.e., 70 sec after
injection initiation) through the entire liver and upper abdomen using 5-mm
nominal thickness sections and a pitch of 6 (high-speed mode). The images
obtained during the pancreatic phase are reconstructed at 0.5-mm intervals
using a 20-cm field of view. These data are then transferred to a workstation
(Advantage Windows; General Electric Medical Systems).
Curved planar reformations are obtained by interactively placing a cursor
on a stack of axial, sagittal, coronal, or oblique sections along the course
of a specific anatomic structure, typically a tubular lumen. The thickness of
the curved plane is the voxel dimension perpendicular to the curved plane and
depends on the orientation of the section on which it is drawn. The section
thickness of the curved plane will never be larger than the effective section
thickness or smaller than the transverse pixel dimensions. The plane thus
prescribed results in a two-dimensional image that displays the entire course
of the anatomic structure throughout the data set (Fig.
1A,1B).
Two orthogonal curved planes are created through each structure—a curved
transverse and a curved sagittal or coronal reformation. The curved planar
reformations are obtained in our three-dimensional CT laboratory by dedicated
technologists who have been trained by a physician to delineate the biliary
and pancreatic ductal anatomy. The total time for performing the curved planar
reformation is less than 20 min. Curved planar reformations are obtained to
display the course of the pancreatic duct, common bile duct, and
peripancreatic vasculature, including the superior mesenteric artery and
portal venous system (Figs.
2A,2B,2C
and 3).
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Fig. 1A. —64-year-old man with pancreatic carcinoma. Curved planar
reformations are obtained by placing cursors interactively along course of
pancreatic duct. Note plane of curved planar reformation (arrows,
A). Two orthogonal curved planes are created through pancreatic duct,
including curved transverse and curved sagittal coronal reformations. Note in
A curved planar reformation of pancreatic duct. Resulting reformation
in B shows hypodense mass (M) representing carcinoma. There is a subtle
area of extrapancreatic spread of tumor (short arrow, B). In
B, also note dilated proximal duct (long arrow) and atrophy of
tail of pancreas distal to obstructing mass.
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Fig. 1B. —64-year-old man with pancreatic carcinoma. Curved planar
reformations are obtained by placing cursors interactively along course of
pancreatic duct. Note plane of curved planar reformation (arrows,
A). Two orthogonal curved planes are created through pancreatic duct,
including curved transverse and curved sagittal coronal reformations. Note in
A curved planar reformation of pancreatic duct. Resulting reformation
in B shows hypodense mass (M) representing carcinoma. There is a subtle
area of extrapancreatic spread of tumor (short arrow, B). In
B, also note dilated proximal duct (long arrow) and atrophy of
tail of pancreas distal to obstructing mass.
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Fig. 3. —62-year-old man with suspected pancreatic carcinoma and
pancreas divisum. Curved planar reformation shows normal variant of pancreatic
duct (pancreas divisum). Main pancreatic duct enters minor papilla.
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Clinical Applications
Local Staging of Pancreatic Carcinoma
In a patient with known or suspected pancreatic carcinoma, the main value
of curved planar reformations is to provide additional diagnostic information
about the extent of local invasion. Scans obtained during the pancreatic phase
using a 40-sec scan delay improve conspicuity between the normally enhancing
pancreatic parenchyma and the typically lower attenuating pancreatic carcinoma
[1]. Curved planar reformations
of the pancreatic duct may aid in detecting partial obstruction of the
pancreatic duct by hypodense (Figs.
1B and
4) or isodense
(Fig. 5) pancreatic lesions. In
addition, perivascular spread of tumor with encasement of the superior
mesenteric artery, celiac axis, or portal venous system (Figs.
6 and
7) may also be clearly
identified with curved planar reformations of the peripancreatic
vasculature.
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Fig. 4. —54-year-old woman with pancreatic carcinoma. Curved planar
reformation of pancreas reveals small hypodense pancreatic mass (straight
arrow) causing partial obstruction of duct. Note mild dilatation
(curved arrow) of proximal duct.
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Fig. 5. —68-year-old woman with pancreatic carcinoma. Curved planar
reformation through main pancreatic duct shows dilated interrupted main
pancreatic duct resulting from isodense mass (M) in head of pancreas.
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Fig. 6. —71-year-old man with unresectable pancreatic carcinoma
encasing superior mesenteric artery. Curved planar reformation obtained in
plane drawn through central portion of superior mesenteric artery from
sagittal sections shows perivascular spread of tumor (arrows). In
this reformation spine is seen at top of image.
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Fig. 7. —57-year-old woman with unresectable pancreatic carcinoma and
vascular encasement. Curved planar reformation of splenic and portal veins
reveals high-grade obstruction of splenic venous confluence (black
arrow). Note encasement of superior mesenteric artery (white
arrow).
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Curved planar reformations may also aid in the diagnosis of intraductal
pancreatic neoplasms by clarifying the position of low-density lesions
relative to the main pancreatic duct (Figs.
8 and
9). Side-branch
mucin-producing tumors of the pancreatic ductal system are more likely to be
benign and are often caused by epithelial hyperplasia. Tumors involving the
duct of Wirsung (main branch type), however, have a higher incidence of
invasive adenocarcinoma, and patients with such tumors should always undergo
resection. In our experience, curved planar reformations may be used to help
differentiate between intraductal and extraductal tumors.
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Fig. 8. —60-year-old woman with side-branch intraductal
mucin-producting tumor involving uncinate process. Curved planar reformation
shows communication (arrow) between normal uncinate branch and
distended portion of ductal system containing mucin-producing tumor (T).
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Fig. 9. —71-year-old woman with mucinous cystic neoplasm of pancreas.
Curved planar reformation of pancreatic duct shows no communication between
cystic mass (M) and distal pancreatic duct (black arrow). Note marked
atrophy and ductal dilatation of proximal pancreas (white arrow).
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Pancreatitis
In a patient with hemorrhagic pseudocysts or in whom hemorrhagic
pancreatitis is suspected on the basis of unenhanced CT scans, pancreatic
phase images may facilitate the diagnosis of peripancreatic pseudoaneurysms
(Fig.
10A,10B)
requiring embolization. Other vascular complications of pancreatitis, such as
portal venous occlusion or stenosis (Fig.
11), may also be well delineated on curved planar reformations. In
a patient suspected of having a pancreas divisum, these reformations can
confirm the diagnosis by clearly depicting the entire pancreatic duct with its
opening in the minor papilla (Fig.
3).
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Fig. 10A. —49-year-old man with acute pancreatitis, gastrointestinal
hemorrhage, and prior cystic gastrostomy for pancreatic pseudocyst. Curved
planar reformation of left hepatic artery (A) shows pseudoaneurysm
(arrow).
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Fig. 10B. —49-year-old man with acute pancreatitis, gastrointestinal
hemorrhage, and prior cystic gastrostomy for pancreatic pseudocyst.
Maximum-intensity-projection image shows pseudoaneurysm (straight
arrow) and residual undrained pseudocyst (curved arrow).
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Biliary Tract Abnormalities
Curved planar reformations may be helpful in depicting biliary tract
lesions such as cholangiocarcinoma (Fig.
12), periductal masses, and fluid collections
(Fig. 13). Displaying the
entire length of the common bile duct provides an overview of the length of
tumor involvement and shows the position of the ductal thickening and
intraductal masses relative to the hilar confluence. Lesions of the ampulla of
Vater characteristically produce a double-duct sign. Curved planar
reformations reveal both pancreatic duct and common bile duct dilatation to
the level of the ampulla (Fig.
14).
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Fig. 12. —49-year-old man with hilar confluence cholangiocarcioma.
Curved planar reformation through common bile duct and common hepatic duct
shows focal mural thickening of bile duct (straight arrows) at hilar
confluence. Note tumor extension into proximal left hepatic duct (curved
arrow).
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Fig. 13. —44-year-old man with acute pancreatitis. Curved planar
reformation through common bile duct (straight arrow) reveals
periductal fluid collection (curved arrow) extending along
hepatoduodenal ligament.
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Fig. 14. —62-year-old man with painless jaundice caused by ampullary
carcinoma. Curved planar reformation through common bile duct shows marked
dilatation of bile duct due to ampullary mass (arrows).
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Discussion
To date, curved planar reformations have usually been obtained to evaluate
vascular abnormalities in conjunction with CT angiography
[2]. Our current application of
this technique to the pancreatic and biliary ductal systems extends the
potential diagnostic usefulness of these unique anatomic reformations. One
clear advantage of multidetector CT over single-slice helical CT is its
ability to scan large regions with very thin collimation. This technique
generates numerous axial images, particularly when overlapping reconstructions
are obtained. Curved planar reformations cannot be viewed as a substitute for
careful review of all axial source images. However, it is time-consuming for
referring clinicians to review large numbers of images in great detail. Thus,
curved planar display offers a potential solution to this dilemma that takes
advantage of the volumetric data sets obtained with multidetector CT and
delineates the entire course of an anatomic structure in a single
two-dimensional display. We currently use this technique for staging
pancreatic and biliary tract neoplasms and in selected patients with
pancreatitis if we suspect vascular complications. Our referring clinicians
and surgeons have expressed their enthusiasm for these types of images because
of the quick anatomic overview of key structures and parenchymal organs that
they provide.
However, a variety of other three-dimensional and two-dimensional
reformations may be of value in assessing the pancreas and biliary tract
[3,4,5].
These other reformations include both maximum-intensity and minimum-intensity
images, volume-rendering, and sagittal and coronal reformations. In any given
patient, these other reformations may also provide important additional
information.
A current limitation of the curved planar reformations is that a trained
individual is needed to trace the course of a structure or blood vessel
through an entire volume of the data set. Although the time required for the
reformations is moderate (<20 min), trained personnel and a
three-dimensional workstation are necessary. We found that trained CT
technologists can quickly acquire the skills to obtain high-quality curved
planar reformations and that a physician usually needs only a short time to
accomplish this training. Accurate tracing of the course of the anatomic
structure through the volume of the data set is critical in preventing
artifactual distortion of the structure in the curved planar reformatted
image.
In summary, multidetector CT with thin collimation can be used to create
high-quality curved planar reformations of the common bile duct, pancreatic
duct, and peripancreatic vasculature. Although further studies will be
required to delineate the specific additional value of these displays, our own
experience clearly is that these types of displays help portray unique
anatomic information, highlighting critical anatomic and pathologic
relationships.
Acknowledgments
We thank Laura Logan and Marc Sofilos for their excellent work in
processing our cases.
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Introduction
Technique
