Contrast-Enhanced Mammography
Contrast enhanced mammography shows tumour blood vessels using an iodinated contrast agent and dual energy X-ray images. Cancers develop abnormal new vessels that leak contrast, so they take up the iodine and appear bright, in the same way as on MRI.
After contrast injection, each view is taken with a low energy and a high energy exposure in one compression. The low energy image looks like a normal mammogram. The high energy image is combined with it to remove the normal tissue and leave a map of the iodine.
Iodinated contrast (300 to 370 mg iodine/mL) is given at 1.5 mL/kg, up to 150 mL, at 2 to 3 mL/s through a venous line. Imaging starts 2 minutes after the injection, and all four views are completed within about 10 minutes.
The mean glandular dose is about 1.2 to 1.8 times that of a digital mammogram, and still within the limit set for screening. The total effective dose is about 0.5 to 1 mSv.
Sensitivity is about 90 to 97% and specificity is about 75 to 85%. This is better than mammography and ultrasound, and close to MRI in many studies.
It is faster, cheaper and more tolerable than MRI, which makes it an alternative when MRI is not possible.
Indications.
- Problem solving after an inconclusive mammogram, tomosynthesis or ultrasound.
- Local staging in newly diagnosed cancer, to assess size, extent and multifocal or contralateral disease.
- Monitoring of response to treatment given before surgery.
- Screening of women at intermediate or high risk when MRI is not possible or not tolerated.
- Women with dense breasts and a recall.
- Assessment of an unexplained nipple discharge or of a palpable lump with negative tests.
- Detection of an occult primary tumour when there is a node with cancer.
- Direction of biopsy to lesions seen only after contrast (contrast directed biopsy).
Contraindications and precautions.
- Allergy to iodinated contrast: previous severe reaction is a contraindication, and mild reactions need a prepared plan. Resuscitation equipment must be at hand.
- Renal impairment: the estimated glomerular filtration rate should be over about 30 mL/min (local limits apply). Hydration is used in marginal cases.
- Thyrotoxicosis and recent thyroid treatment: iodine load may worsen thyroid disease.
- Pregnancy: avoided. Breast feeding: continuation is acceptable after the usual advice.
- Metformin: local rules for stopping or continuing apply when renal function is low.
- Extravasation of contrast can cause pain and skin damage. A reliable line is needed.
- Contrast injection and mild compression are uncomfortable. Anxiety and claustrophobia are not issues, unlike with MRI.
- The test is not a replacement for a biopsy.
Preparation and technique.
Renal function and allergy history are checked. No fasting is needed, but oral fluids are encouraged. Consent covers the contrast risks. A venous line is placed in the arm opposite the affected breast if possible.
Contrast is injected with a power injector, and the breast is positioned without compression for 2 minutes. Compression is then applied lightly, and the dual energy exposures are taken for each view, starting with the breast of concern.
Low energy images and recombined images are shown together. Reading compares enhancement with the mammogram and the ultrasound.
Contrast uptake is highest at 2 to 4 minutes and then washes out, so views should be completed within 7 to 10 minutes.
