Tissue to background ratio

The tissue to background ratio is a measure of the specificity of radiopharmaceutical uptake within the target organ in a nuclear medicine study. It is also referred to as tumor to background ratio in the literature.

The presence of radiopharmaceutical in the background (tissues external to the target organ) can be secondary to the following:

• low retention rate in target organ, leading to leakage into surrounding tissues
• preferential uptake by other organs (particularly highly vascular structures such as the liver, spleen, gut and kidneys)