Lymph glands, lymphatics and tumours

Published on 01/04/2015 by admin

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Last modified 01/04/2015

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Chapter 11 Lymph glands, lymphatics and tumours

Positron Emission Tomography Imaging

Positron emission tomography (PET) imaging is a technique used to detect and accurately stage malignant disease, to differentiate benign and malignant tissue, and to assess response to treatment. Until recently, PET imaging availability was restricted due to high capital cost and logistics of radiopharmaceutical supply. It uses short-lived cyclotron-produced radionuclides such as 18Fluorine, 11Carbon, 13Nitrogen and 15Oxygen with half-lives of 110, 20, 10 and 2 min respectively. 18Fluorine is the only one of these that has a half-life long enough to allow it to be produced off-site. This does permit 2-[18F]fluoro-2-deoxy-d-glucose (18F-FDG), the single most important PET radiopharmaceutical, to be used by sites without their own cyclotron.

The widespread acceptance of PET as a major advance is due to two major factors:

Normal physiological uptake is seen in organs that are hypermetabolic and big glucose users especially the brain and the heart, or active or recently active skeletal muscle. Variable uptake is seen in the gut and there is normal excreted urinary activity in the urinary tract. One confounding factor for interpretation may be normal physiological uptake in brown fat – particularly in the neck and paraspinal regions. Differentiation of this normal activity from pathology is greatly aided by the co-registration afforded by combined PET CT scanners.

However, FDG is not specific for cancer cells as any hypermetabolic cell such as those in sites of inflammation or infection will show increased uptake of FDG, so interpretation with reference to full clinical details and other imaging is important to avoid false-positive scans.

As the only PET tracer likely to be widely available in the near future, this section is restricted to FDG imaging. Discussion is also limited to the role of PET in oncological patients.


Indications (oncology)

Gallium Radionuclide Tumour Imaging

This is rarely used, having almost entirely been superseded by cross-sectional techniques and PET scanning.1 The main disadvantages are the high radiation dose, the extended nature of the investigation, its non-specific nature, and difficulties in interpretation in the abdomen due to normal bowel activity.