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Initial Experience with Oral Contrast in PET/CT: Phantom and Clinical Studies

¹ Division of Nuclear Medicine, Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins Hospital, Baltimore, Maryland
² Department of Environmental Health Sciences, Johns Hopkins School of Public Health, Baltimore, Maryland
³ Diagnostic Imaging Section, Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins Hospital, Baltimore, Maryland

View larger version (58K): [in a new window]   FIGURE 1. Sixty-year-old man with rising CA19-9 level and history of pancreatic cancer after therapy was evaluated by 18F-FDG PET for suspected tumor. Patient had ingested barium for upper gastrointestinal study 1 week before PET/CT study without additional contrast being administered. CT (A; arrow) showed residual, dense barium in distended stomach consistent with high-grade gastric outlet stenosis. CT attenuation-corrected PET emission images (B; arrow) showed area of increased activity in stomach corresponding to barium retention on CT (max CT Hounsfield units = 3,071). However, no increased uptake was seen in gastric lumen in nonattenuation-corrected images (C; arrow). SUVLEAN for high-activity gastric artifact was 5.31 maximum and 3.81 mean.

View larger version (19K): [in a new window]   FIGURE 2. Phantom with syringes filled with variable concentrations of gastrografin, plotted as measured emission data activity (in Bq/mL) versus measured contrast density by CT (in Hounsfield units [HU]). Maximum () and mean () measured activity with CT attenuation correction, and maximum () and mean () measured activity with 68Ge attenuation correction are displayed. Drop in measured activity is observed for high-density contrast. In this region, "real density" is >3,071 HU, but the PET/CT system plateaus at this level. Thus, overcorrection in presence of high-density contrast also has plateau corresponding to 3,071 HU density. However, because of increased true attenuation as result of increasing "real" density, measured counts decrease, resulting in drop in curve.

View larger version (73K): [in a new window]   FIGURE 3. Example of clinical value of oral contrast in patient with resected colorectal carcinoma evaluated with 18F-FDG PET for suspected recurrence. (A) Transverse CT image shows transverse colon with contrast (white arrow) and soft-tissue- density lesion adjacent to anterior abdominal wall (black arrow). (B) PET images with CT attenuation correction show focus of intense uptake in anterior abdomen (white arrow). (C) Fused PET/CT image shows that focus of uptake corresponds to soft-tissue mass (white arrow) and not to bowel. Diagnosis of peritoneal tumor implant was made. Patient underwent chemotherapy.