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Why Nearly All PET of Abdominal and Pelvic Cancers Will Be Performed as PET/CT

Division of Nuclear Medicine, Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland

View larger version (72K): [in a new window]   FIGURE 1. (B) PET image (emission image, CT-corrected for attenuation) showed intense tracer activity in posterior stomach region. (A) CT showed very dense contrast (CTHU >3,000) in same area as result of high-grade partial gastric outlet obstruction. Patient had ingested barium several days before. (C) Nonattenuation-corrected image did not show this "gastric tracer uptake." Uptake in stomach was artifactual from inaccurate attenuation correction in presence of very dense barium. Nonattenuation-corrected images can help resolve such a case. (Reprinted with permission from [13]).

View larger version (90K): [in a new window]   FIGURE 2. (A) Example of respiratory artifact that can be seen on PET/CT images obtained when patients breathe quietly. Moderate-sized "cold" area (above liver) was curvilinear and resulted from mismatch of top of liver on PET (free tidal breathing) (B) and CT (more full inspiration in this case). Cold area was actually part of liver, not lung. (Image courtesy of M. Olman).

View larger version (82K): [in a new window]   FIGURE 3. Mislocalization of liver metastasis. (B) Focal intense area on emission PET image appeared to be in right lung but, in fact, was liver metastasis. This artifact resulted from vigorous inspiration during CT scan (A) and from tidal breathing during PET. Lesion was clearly hepatic on MRI (C). (Reprinted with permission from (26)).

View larger version (74K): [in a new window]   FIGURE 4. Recurrent colorectal cancer. (B) Intense focal uptake was seen in anterior abdomen on PET. It was unclear whether this was in bowel or peritoneum. CT (A) and fused image (C) showed bowel to be opacified by oral contrast and that focus of intense activity was just anterior to bowel. Focus was peritoneal metastasis and not atypical normal bowel uptake. Scar just anterior to focal uptake was normal in appearance and intensity of uptake. (Courtesy of C. Cohade, MD).

View larger version (12K): [in a new window]   FIGURE 5. Relationship between HU on CT (x axis) and apparent radioactivity level (y axis) in phantoms filled with both iodinated contrast and 18F-FDG. At low HU, CT (upper 2 curves) and 68Ge attenuation maps gave identical results. At higher HU, CT results were markedly elevated. This indicated that high levels of iodinated contrast could result in miscorrection (overcorrection) of PET data and in hot spots. Thus, contrast must be used cautiously in patients to avoid this problem. (Reprinted with permission from (13)).

View larger version (43K): [in a new window]   FIGURE 6. (B) PET image showed 2 foci of increased tracer uptake. It is not clear whether medial lesion was in left lobe of liver or left-most lesion in spleen or bowel. CT (A) and fused images (C) showed medial activity was normal stomach wall, whereas lesion in left upper abdomen was within spleen. Patient had non-Hodgkin’s lymphoma, and lesion in spleen was consistent with recurrent tumor.

View larger version (85K): [in a new window]   FIGURE 7. (B) PET image showed several foci of intense activity. Paired structures posteriorly were most consistent with renal activity, but it was difficult to pinpoint anterior lesion to determine if it was adrenal, nodal, or hepatic. (C) On fused images, it was apparent that lesion was extrahepatic and in lymph nodes in this case of metastatic colorectal cancer. Kidneys were also seen clearly. (Courtesy of C. Cohade, MD [17]).

View larger version (45K): [in a new window]   FIGURE 8. (B) Multiple FDG-avid foci were seen on PET image. Most anterior lesions appeared to be anterior to liver, whereas posterior lesions could be hepatic, adrenal, or nodal, based on PET only. With CT (A) and fusion (C), it was apparent that anterior lesion was in liver, as was posterior lesion. Two posterior foci, however, were adrenal metastases. These findings resulted from metastatic lung cancer to abdomen. Metastatic lung cancer is common cause of hepatic findings on PET. (Courtesy of P. Patel, MD)

View larger version (64K): [in a new window]   FIGURE 9. (B) PET image showed 2 foci of increased tracer uptake. In general, paired 18F-FDG-containing structures in retroperitoneum are ureters. However, examinations of CT (B) and in particular fused PET/CT (C) images showed lesion on left to clearly medial to left ureter and corresponded to <1-cm lymph node (normal size). Right focus was ureter. Left focus was in metastatic lymph node from colorectal cancer, and only PET/CT resolved this finding. (Courtesy of C. Cohade, MD)

View larger version (56K): [in a new window]   FIGURE 10. (B) Pelvic lesion imaged with PET. Pelvic lesion seen on PET could be intrapelvic, nodal, osseous, or extra pelvic. Implications for lesions in varying locations were considerable. (C) Fusion showed metastatic lesion to bone in patient with stage IV melanoma metastatic to pelvic bone.

View larger version (70K): [in a new window]   FIGURE 11. CT (A) was normal, but PET (B) and fused images (C) showed clear focus of intense tracer activity in left peritoneal cavity just anterior to stomach (on fused image but clearly not involving rib, as might be suspected from PET alone). This was focus of ovarian carcinoma. (Image courtesy C. Cohade and H. Pannu)

View larger version (37K): [in a new window]   FIGURE 12. CT (A), PET (B), and fused images (C) in patient with history of cancer. On first examination of PET image alone, possibility of peritoneal or bowel metastasis existed. Examination of CT and fused image showed lesion was actually lytic bone metastasis, in this case from thyroid cancer. This example illustrates how PET/CT helped differentiate peritoneal or bowel disease from disease in bone of pelvis.

View larger version (63K): [in a new window]   FIGURE 13. Primary pancreatic cancer on PET/CT. Image courtesy of M. Tatsumi.