What is 18F-FDG?
18F-FDG is Fluorine-18 fluoro-2-deoxy-D-glucose, an injected radiopharmaceutical. It is a glucose analogue, with t1/2 =110min. It demonstrates the increased glycolysis in malignant cells, but also in infection, inflammation, autoimmune and granulomatous diseases by overexpression of glucose transporter (GLUT) isotypes and by an overproduction of glycolytic enzymes. Quantitative uptake is measured by the standard uptake value (SUV).
FDG is the most widely used radiopharmaceutical in PET imaging, however other radiopharmaceuticals are being developed and utilized to overcome its limitations.
There are important causes of physiologic uptake of FDG, some of which are summarized in the table below, and illustrated in cases on this website.
What is PET-CT?
PET-CT is dual image acquisition in a single imaging episode (15-30min) through combined PET (Positron-emission) and CT (computerised tomography) gantries. This modality adds to conventional imaging through the combined benefits of PET and CT. PET provides qualitative and quantitative metabolic information, allowing assessment of disease extent and early detection of disease that may appear morphologically normal on CT. CT provides anatomic and morphologic information, allowing accurate localization and clarification of physiologic uptake.
PET-CT is a particularly useful application in oncology- for diagnosis, staging, monitoring response during treatment and detection of recurrence. Its clinical utility is expected to continue rising.
There are many causes for false positive and false negative interpretation in the assessment of malignancy using PET-CT, as well as many causes of artifacts. Some of these are summarized in the table below, and illustrated in cases on this website.
Pitfalls
| Organ |
Uptake |
| Stomach |
Non-focal, more homogeneous |
| Small bowel |
Variable, usually low grade |
| Colon |
May be quite avid, especially caecum/ ascending colon, diffuse, changes on delayed imaging |
| Urinary tract (any part) |
Increased along urinary tract |
| Liver |
Mildly intense, mottled |
| Spleen |
Less than liver |
| Adrenal |
Malignant>> Liver activity > Benign |
| Endometrium |
Pre-menopausal: Biphasic peaks- during Ovulation, and Menstruation |
| Ovary |
Pre-menopausal: Physiologic Uptake |
| Brown Fat |
Neck
Supraclavicular
Paraspinal
Periadrenal |
| Disease process |
example |
| Granulomatous disease |
Tuberculosis |
| Inflammation |
Gastritis, Diverticulitis, Arteriosclerosis |
Surgical change, foreign body reaction
Abscess |
|
| Benign tumors |
Colonic Adenomas Fibroids |
| Pancreas |
Chronic Active Pancreatitis
Autoimmune Pancreatitis
Irradiated Tissue
Inflammed Parenchyma
Haemorrhagic Pseudocyst
Peripancreatic Lymph Nodes
Retroperitoneal Fibrosis |
| Portal Vein Thrombosis |
|
| Adrenal |
Adrenal Hyperplasia |
| Bone Marrow |
Colony Stimulating Factors
Paget's disease
fibrous dysplasia |
| Metallic implants |
|
| Contrast medium |
|
| Disease process |
example |
| Small Tumours |
|
| Non-FDG-Avid Tumours |
Some Neuroendocrine Tumors
Renal Cell Carcinoma
Certain types of low-grade Lymphoma
Some Mucinous Tumours
Cystic Tumours
Low-grade Tumors
HCC- poorly avid
Prostate Carcinoma |
| High neighboring background activity |
|
| Miliary peritoneal disease |
|
| Process |
Example |
| Misregistration Artifact |
Peristalsis
Patient motion
Breathing |
| Respiratory artifact |
Liver dome |
| truncation artifact |
Discrepancy between CT (50cm) and PET (70cm) field-of-view
Streaking artifact
|
References
- Dahnert W. Radiology Review Manual. 2003. Lippincott Williams & Wilkins. Philadelphia.
- Ho CL. Clinical PET imaging--an Asian perspective. Ann Acad Med Singapore. 2004;33(2):155-65.
- Kumar V. Abbas A. Fausto N. Robbins and Cotran Pathologic Basis of Disease. 2005. Elselvier. Pennsylvania.
- Lin EC, Alavi A. PET and PET-CT.2009. Thieme Medical Publishers Inc. New York.
- Von Shulthess G. Molecular Anatomic Imaging. 2007. Lippincott Williams & Willkins. Philadelphia.
