Reformations deliver diagnostic CT data

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Cystic peripancreatic lymph node in 41-year-old woman with history of mucinous ovarian carcinoma. Oblique coronal volumetric reformatted image shows enlarged cystic peripancreatic lesion located between pancreatic head and duodenum (D) without local invasion. Findings are consistent with peripancreatic lymph node rather than pancreatic mass. N = node, C = common bile duct, PD = pancreatic duct. Image and caption courtesy of the American Roentgen Ray Society.

Volumetric oblique coronal reformations are a useful noninvasive method to provide diagnostic information about periampullary abnormalities as well as show secondary features important for local staging and management of the ampulla of Vater, according to research published this month in the American Journal of Roentgenology.

According to the authors, a number of different abnormal conditions may affect the ampulla, including obstruction from bile duct stones, localized or generalized inflammatory processes, trauma, and neoplastic diseases—such as periampullary carcinomas.

“Radiographic evaluation of the fine structures of the periampullary region using CT, conventional MRI, and transabdominal sonography is often limited,” noted the team from Stanford University in Stanford, Calif., who conducted the evaluation of 2D and 3D post-processing techniques on CT data.

They noted that although endoscopy is the definitive test for the assessment of the ampulla of Vater, CT is useful for noninvasive evaluation of the structure. The team employed a contrast-enhanced multiphase acquisition as part of their technique.

Immediately before scanning, patients were asked to drink a water-based neutral contrast agent (VoLumen, ACIST Medical Systems) to distend the duodenum. A biphasic breath-hold exam was performed on a Somatom Sensation 64-slice CT (Siemens Healthcare) or a LightSpeed 16-slice CT (GE Healthcare) system after the injection of nonionic contrast material (Isovue, Bracco Diagnostics).

Post-acquisition processing of the CT data was performed on dedicated 3D workstations (Volume Viewer, GE). On transverse CT data sets, volumetric slabs were generated in a 20-degree right coronal oblique plane to optimize visualization of the duodenal sweep and to parallel the common bile duct, the researchers reported.

“The study was reformatted along this plane using a small field of view of approximately 12 cm,” the authors wrote. “Three-dimensional images were generated at 1-mm intervals with the volume anterior to the cut plane visualized on each individual image. This resulted in a slice thickness of 1 mm in the volumetric slab, as prescribed to cover the anatomic area of interest on the transverse images.”

The team noted that their technique generated scrollable 3D data sets focused on the region of interest, which they chose to depict in gray scale. This was done, the authors explained, to “facilitate appreciation of subtle attenuation differences as well as to preserve familiarity for referring clinicians.”

They researchers found that post-acquisition processing to generate volumetric reformations can provide useful diagnostic information about the primary disorder, such as its enhancement characteristics and morphology, as well as show secondary features important for local staging and management, such as direct invasion or associated complications.

“Based on our experience, 3D reformations have also provided a time efficient
reference to show pertinent findings and anatomic relationships with clinicians,” the authors concluded.  “Future prospective studies are warranted to assess the gain in diagnostic usefulness of transverse source data versus additional post-processing
techniques in the evaluation of periampullary disorders.”