Nuclear Medicine, Molecular Imaging and Contrast Media Safety
Nuclear medicine, molecular imaging and contrast media safety tests radiopharmaceutical behaviour, common scan indications and the prevention and management of contrast reactions.
Nuclear medicine essentials
- FDG is a glucose analogue; normal uptake is seen in brain, myocardium, kidneys and bladder. SUV is semiquantitative and is not a stand-alone diagnosis.
- Tc-99m MDP bone scanning detects osteoblastic activity; a superscan shows diffuse uptake with absent renal shadows.
- Ventilation-perfusion scanning is used for suspected pulmonary embolism when CT contrast is contraindicated.
- I-131 is used for thyroid ablation; sentinel node mapping guides breast and melanoma surgery.
Contrast safety
- Iodinated contrast can cause hypersensitivity and contrast-induced nephropathy; iso-osmolar agents and hydration reduce risk in renal impairment.
- Gadolinium: macrocyclic group II agents are preferred in renal failure; linear agents carry the highest risk of nephrogenic systemic fibrosis.
- Metformin should be reviewed around iodinated contrast in renal impairment because of lactic acidosis risk.
- Shellfish allergy is not a specific contraindication to iodinated contrast.
Worked example
A patient with eGFR 25 needs MRI. Use a macrocyclic gadolinium agent at the lowest diagnostic dose, or avoid gadolinium if the study can be done another way. Do not use a linear agent, which is associated with nephrogenic systemic fibrosis.
Traps
- Treating a high SUV as proof of malignancy.
- Missing a pregnancy check before contrast or radiopharmaceutical administration.
- Withholding contrast from every patient with a shellfish allergy.