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To Enhance or Not to Enhance? ¹⁸F-FDG and CT Contrast Agents in Dual-Modality ¹⁸F-FDG PET/CT

¹ Department of Diagnostic and Interventional Radiology, University Hospital Essen, Essen, Germany
² Department of Nuclear Medicine, University Hospital Essen, Essen, Germany

View larger version (68K): [in a new window]   FIGURE 1. Hepatic metastasis on nonenhanced CT (A) and after application of 100 mL of an iodinated intravenous contrast agent (B). Lesion (arrows) was barely visible on unenhanced image but was clearly delineated after intravenous contrast administration.

View larger version (69K): [in a new window]   FIGURE 2. Image artifact in contrast-enhanced PET/CT studies. Bolus passage of intravenous contrast agent in left subclavian and brachiocephalic veins on CT (A, arrows) led to areas of apparently increased glucose metabolism on corrected PET (B, arrows). On fused PET/CT images, this area of apparently increased glucose metabolism correlated with high-density contrast in venous system on CT (C). PET image reconstruction without attenuation correction demonstrated homogeneous tracer distribution (D), demasking areas of apparently increased glucose metabolism as artificial.

View larger version (77K): [in a new window]   FIGURE 3. (A) Positive oral contrast agent (barium) in stomach on CT image. Area of apparently increased glucose metabolism on PET (B, arrow) corresponded to contrast-enhanced bowel lumen on PET/CT (C). (D) Homogeneous tracer distribution was seen on nonattenuation corrected PET images.

View larger version (27K): [in a new window]   FIGURE 4. Good small-bowel distension on transverse CT image (A) with negative oral contrast agent containing water, 2.5% mannitol, and 0.2% locust bean gum. Both PET (B) and fused PET/CT (C) images were free of contrast-induced artifacts.

View larger version (89K): [in a new window]   FIGURE 5. Split CT protocol to optimize contrast enhancement in each body region. Desired contrast enhancement is arterial in thorax, portal–venous in upper abdomen, venous in pelvis, and late-venous in neck and head. To meet these requirements, PET/CT scanners need to allow whole-body acquisition starting with thorax (scanned in caudocranial direction), followed by abdomen and pelvis (craniocaudal direction), and by neck and head (caudocranial scanning).

View larger version (33K): [in a new window]   FIGURE 6. Hepatic metastasis from uveal melanoma in 58-y-old woman. (A) Contrast-enhanced CT clearly depicted lesion (arrow) in right liver lobe. (B) PET imaging was found to be negative for malignant disease. (C) Diagnosis of metastatic disease was based on CT data when evaluating fused images. Metastatic disease to liver was proven by histopathology.

View larger version (28K): [in a new window]   FIGURE 7. Small lymph node adjacent to thyroid gland. (A) As result of contrast enhancement of thyroid after application of iodine-based intravenous contrast agent, hypodense lymph node (arrow) was clearly distinguished from thyroid parenchyma. Increased 18F-FDG uptake on PET (B) was accurately attributed to this lymph node rather than to thyroid gland (C). Without contrast enhancement, similar densities of parenchymal organs and lymph nodes frequently render differentiation of organ metastasis from adjacent lymph node metastasis difficult.

View larger version (91K): [in a new window]   FIGURE 8. (A and B) On nonenhanced images, differentiation of lymph node from lesion (arrow) within stomach wall was not possible. (C and D) When applying intravenous contrast agents in a different patient, contrast enhancement of stomach wall was clearly distinguished from hypodense lesion adjacent to stomach wall, thus identifying lesion as abdominal lymph node (arrows).

View larger version (84K): [in a new window]   FIGURE 9. Patient (56-y-old man) 1 y after local resection of hepatic metastasis. (A) Two hypodense lesions (arrow and arrowhead) were found on contrast-enhanced CT, but differentiation of viable tumor tissue from postoperative tissue alteration was not possible. (B) PET imaging demonstrated viable tumor tissue but without additional ability to accurately localize lesion within liver. (C) On fused PET/CT, lateral hepatic lesion was identified as local tumor recurrence (arrow), and medial lesion was caused by postoperative tissue alteration (arrowhead). (D–F) Radiofrequency ablation was selectively performed on lateral lesion, and complete tumor ablation was shown on postinterventional follow-up scan.

View larger version (39K): [in a new window]   FIGURE 10. Patient (83-y-old man) with hepatocellular carcinoma of right liver lobe after transarterial chemoembolization. (A) On transverse contrast-enhanced CT image hyperdense chemoembolizing agents were visible, but differentiation of viable tumor tissue from normal liver parenchyma and necrotic tumor areas was difficult. PET image (B) clearly demonstrated residual viable tumor that could be accurately localized based on PET/CT data (C). By providing accurate anatomic localization of remaining tumor tissue, PET/CT aided further interventional planning.

View larger version (80K): [in a new window]   FIGURE 11. Hepatic metastasis in 47-y-old female patient with cancer of unknown primary. (A) Contrast-enhanced CT could not clearly distinguish between viable tumor tissue and normal liver parenchyma. (B) PET imaging demonstrated increased glucose metabolism. (C) Increased tracer uptake was accurately localized based on PET/CT images. (D) Additional manual fusion of PET/CT images with interventional images showed biopsy device to be within viable tumor tissue.

View larger version (37K): [in a new window]   FIGURE 12. Patient (64-y-old man) 2 wk after radiofrequency ablation of pulmonary metastasis in right lower pulmonary lobe. (A) Round area of necrosis and hematoma (arrows) was found postinterventionally on CT. PET imaging demonstrated rim-like area of increased glucose metabolism (B) that correlated with periphery of necrotic zone on PET/CT (C). This increase in tracer uptake in periphery of lesion may have been result of tissue regeneration or viable tumor. Further follow-up in this patient revealed decrease in peripheral tracer uptake over time. Thus, increased peripheral glucose metabolism was found to be result of tissue regeneration rather than residual tumor.