Three-D techniques showcase the pancreas and biliary

The advent of multislice CT, advanced computer workstations, and 3D and postprocessing algorithms has allowed for new perspectives from which to view imaging data. These are especially useful for pancreatic cancer and biliary pathology. They can be used by the radiologist for problem solving and facilitated communication between the radiologist and the referring clinician, aiding diagnosis, illustrating disease extent, describing staging clearly, and guiding surgical planning.

Acquisition of suitable source images for postprocessing is vital. We acquire 2.5-mm contiguous images for interpretation and reconstruct them to either 1.25 mm every 0.625 mm or as contiguous 0.625-mm images depending on the capabilities of the particular CT scanner being used for postprocessing.

Images are obtained of the entire abdomen during two phases: the peak pancreatic parenchymal phase of enhancement, to maximize visualization of tumor and arteries, and the portal venous phase for liver metastases, veins, and the pancreatic duct.¹ Using a rapid injection rate of 4 to 5 cc/sec for 30 seconds, we achieve peak pancreatic enhancement at approximately 40 to 45 seconds after the start of contrast injection. The portal venous phase is approximately 60 seconds after the start. Bolus tracking is used to adjust for cardiac circulation time.²

Multiple techniques are available for postprocessing. Coronal multiplanar reconstructions (also known as raysum) using 2.5-mm-thick slices every 2.5 mm provide excellent visualization of the relationship of tumor to adjacent structures. Maximum intensity projection (MIP) images or angiographic technique volume-rendered images created as a rotating coronally oriented 5-cm slab or semithick 10-mm coronal images every 2.5 mm are useful to display vascular anatomy.

Minimum intensity projection (MinIP) images, 15-mm thick every 2.5 mm in the coronal plane, are useful to show hilar and extrahepatic biliary pathology, the pancreatic duct, and, particularly, side branch dilatation and potential communication with cystic lesions. Curved planar reformations can be very helpful in providing a concise summary of findings. In all cases, images should be reviewed by a radiologist to confirm that they convey information accurately, especially if they are ultimately to be viewed by a nonradiologist.

PROBLEM SOLVING

The approach must vary depending on the problem to be solved.

• Pancreas. Axial images are typically sufficient for evaluation of the superior mesenteric artery and, in most cases, the celiac trunk. In our experience, however, coronally oriented images are very useful for showing the relationship of tumor, especially in the pancreatic head, with the common hepatic artery (Figure 1). It is also useful for evaluating the length of the superior mesenteric vein and/or portal vein involvement in cases of potential venous bypass graft placement (Figure 2). These images are also useful for showing the craniocaudal extent of disease. Recent studies have confirmed that postprocessed images can improve the accuracy of staging pancreatic cancer.^3,4

The presence of a vascular variant, particularly an accessory or replaced right hepatic artery, is important to note because it crosses the surgical field of resection and, in our experience, is often at risk for involvement by pancreatic head tumors (Figure 3). Coronally oriented images are also useful for showing dilated pancreatic duct side branches extending from small cystic lesions, which may help in the suggestion of pseudocysts or side branch intraductal papillary mucinous neoplasms.

• Biliary. Surgical planning for resection of hilar cholangiocarcinomas requires precise identification of the degree of involvement of the biliary tree and portal vein branches, particularly if there is evidence of bilateral disease, which typically precludes surgery. This can be aided by coronally oriented images, including raysum, MIP, and MinIP of CT data.

Indeed, CT cholangiopancreatography has been shown to have image quality similar to endoscopic retrograde cholangiopancreatography as well as similar accuracy in identifying the level and cause of obstruction.⁵MR cholangiopancreatography data can also be manipulated using MIP or volume rendering, with selective editing, to provide additional detail regarding the biliary tree. Use of MRCP and MR angiography has been shown to be effective in diagnosing the level of obstruction, arterial ivolvement, and venous invasion.^6-8

More complex techniques, such as segmental volume measurements, are useful when techniques like preoperative portal vein embolization are used to predict if the resultant hypertrophy of nonembolized segments is sufficient to preclude significant postoperative morbidity. ⁹

Postprocessing can also be very helpful in understanding postoperative changes. This approach is especially useful when tumor recurrence, such as in pancreatic cancer, distorts already complex surgical anatomy.

DELIVERY OF INFORMATION

Images can be delivered to the clinician in a variety of ways, including CD, enterprise PACS, dedicated web server with illustrated reports, or even film. The ability to do real-time processing anywhere, such as with thin-client solutions, allows on-demand 3D processing at multidisciplinary conferences to convey complex data to clinicians regarding pancreatic cancer or biliary pathology.

Several postprocessing or 3D techniques allow the radiologist to gain new perspectives from which to view CT and MRI data. These can aid understanding of complex anatomy that would be extremely difficult to obtain from axial images alone, leading to improved diagnosis, staging, and communication of findings.

References

1. Lu DS, Vedantham S, Krasny RM, et al. Two-phase helical CT for pancreatic tumors pancreatic versus hepatic phase enhancement for tumor, pancreas and vascular structures. Radiology 1996;199: 697-701.
2. Kim T, Murakami T, Takahashi S, et al. Pancreatic CT imaging: effects of different injection rates and doses of contrast material. Radiology 1999;212:219-225.
3. Raptopoulos V, Steer ML, Sheiman RG, et al. The use of helical CT and CT angiography to predict vascular involvement from pancreatic cancer: correlation with findings at surgery. AJR 1997;168: 971-977.
4. Baek SY, Sheafor DH, Keogan MT, et al. Two-dimensional multiplanar and three-dimensional volume-rendered vascular CT in pancreatic carcinoma: interobserver agreement and comparison with standard helical techniques. AJR 2001;176:1467-1473.
5. Raptopoulos V, Prassopoulos P, Chuttani R, et al. Multiplanar CT pancreatography and distal cholangiography with minimum intensity projections. Radiology 1998;
207:317-324.
6. Pavone P, Laghi A, Catalano C, et al. MRI of the biliary and pancreatic ducts. Eur Radiol 1999;9:1513-1522.
7. Zech CJ, Schoenberg SO, Reiser M, Helmberger T. Cross-sectional imaging of biliary tumors: current clinical status and future developments. Eur Radiol 2004;14:1174-1187.
8. Lee MG, Park KB, Shin YM, et al. Preoperative evaluation of hilar cholangiocarcinoma with contrast-enhanced three-dimensional fast imaging with steady-state precession magnetic resonance angiography: comparison with intraarterial digital subtraction angiography. World J Surg 2003;27:278-283.
9. Abdalla EK, Barnett CC, Doherty D, et al. Extended hepatectomy in patients with hepatobiliary malignancies with and without preoperative portal vein embolization. Arch Surg 2002;137:675-680; discussion 680-681.