Pictorial Essay. Multidetector CT of the Pancreas and Bile Duct System: Value of Curved Planar Reformations

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1 Downloaded from by on 02/03/18 from IP address Copyright RRS. For personal use only; all rights reserved n 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 Multidetector CT of the Pancreas and ile Duct System: Value of Curved Planar Reformations Matilde Nino-Murcia 1,2, R. rooke Jeffrey, Jr. 1, Christopher F. eaulieu 1, King C. P. Li 1, Geoff D. Rubin 1 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. fter 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 ml of water as a nonopaque intraluminal contrast agent. fter 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]. fter this acquisition, the patient is asked to inhale and exhale deeply. nother Pictorial Essay 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 (dvantage 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. 1). Two orthogonal curved planes are created through each structure a curved transverse and a curved sagittal or coronal Received June 8, 2000; accepted after revision ugust 7, Department of Radiology, Stanford University Medical Center, 300 Pasteur Dr., Rm. H1307, Stanford, C ddress correspondence to R.. Jeffrey, Jr. 2 Department of Radiology, Veterans dministration Palo lto Health Care System, 3801 Miranda ve., Palo lto, C JR 2001;176: X/01/ merican Roentgen Ray Society JR:176, March

2 Nino-Murcia et al. Downloaded from by on 02/03/18 from IP address Copyright RRS. For personal use only; all rights reserved 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. 2 and 3). Clinical pplications 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. 1 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. 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. 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. 10) requiring embolization. Other vascular complications of pancreatitis, such as portal venous Fig year-old man with pancreatic carcinoma. and, Curved planar reformations are obtained by placing cursors interactively along course of pancreatic duct. Note plane of curved planar reformation (arrows, ). Two orthogonal curved planes are created through pancreatic duct, including curved transverse and curved sagittal coronal reformations. Note in curved planar reformation of pancreatic duct. Resulting reformation in shows hypodense mass (M) representing carcinoma. There is a subtle area of extrapancreatic spread of tumor (short arrow, ). In, also note dilated proximal duct (long arrow) and atrophy of tail of pancreas distal to obstructing mass. C Fig. 2. Curved planar reformations in 47-year-old woman with normal pancreas, superior mesenteric artery, and common bile duct., Normal caliber pancreatic duct throughout entire course., Superior mesenteric artery. C, Normal common bile duct through entire course. 690 JR:176, March 2001

3 CT of the Pancreas and ile Duct System Downloaded from by on 02/03/18 from IP address Copyright RRS. For personal use only; all rights reserved 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). iliary Tract bnormalities Curved planar reformations may be helpful in depicting biliary tract lesions such as Fig 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. 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 Fig 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. Fig 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. duct dilatation to the level of the ampulla (Fig. 14). 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 Fig 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. Fig 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). 6 7 JR:176, March

4 Nino-Murcia et al. Downloaded from by on 02/03/18 from IP address Copyright RRS. For personal use only; all rights reserved 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. Fig year-old woman with side-branch intraductal mucin-producing 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). However, a variety of other three-dimensional and two-dimensional reformations may be of value in assessing the pancreas and biliary tract [3 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. current limitation of the curved planar reformtions 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. lthough 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 Fig 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). Fig year-old man with acute pancreatitis, gastrointestinal hemorrhage, and prior cystic gastrostomy for pancreatic pseudocyst., Curved planar reformation of left hepatic artery () shows pseudoaneurysm (arrow)., Maximum-intensity-projection image shows pseudoaneurysm (straight arrow) and residual undrained pseudocyst (curved arrow). 692 JR:176, March 2001

5 CT of the Pancreas and ile Duct System Fig year-old man with necrotizing pancreatitis and occlusion of splenic vein. Curved planar reformation reveals occlusion of splenic vein posterior to mid body of pancreas (arrow). Downloaded from by on 02/03/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig 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). Fig 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. Fig 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). short time to accomplish this training. ccurate 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. lthough 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. cknowledgments We thank Laura Logan and Marc Sofilos for their excellent work in processing our cases. References 1. O Malley ME, oland GW, Wood J, Fernandez-del Castillo C, Warshaw L, Mueller PR. denocarcinoma of the head of the pancreas: determination of surgical unresectability with thin-section pancreaticphase helical CT. JR 1999;173: Rubin GD, Dake MD, Semba C. Current status of three-dimensional spiral CT scanning for imaging the vasculature. Radiol Clin North m 1995;33: Takeshita K, Furui S, Yamauchi T, et al. Minimum intensity projection image and curved reformation image of the main pancreatic duct obtained by helical CT in patients with main pancreatic duct dilation [in Japanese]. Nippon Igaku Hoshasen Gakkai Zasshi 1999;59: Raptopoulos V, Prassopoulos P, Chuttani R, McNicholas MM, McKee JD, Kressel HY. Multiplanar CT pancreatography and distal cholangiography with minimum intensity projections. Radiology 1998;207: Fishman EK, Wyatt SH, Ney DR, Kuhlmann JE, Siegelman SS. Spiral CT of the pancreas with multiplanar display. JR 1992;159: JR:176, March