There are 2 types of contrast-enhanced mammography examination – temporal subtraction and dual-energy.
Initial work in the early 2000s used temporal subtraction, but artifacts due to patient movement during prolonged compression limited its diagnostic usefulness. Travieso et al produced a useful comparison table of the 2 techniques in their 2014 paper 5.
Commercially available contrast mammography equipment now utilizes the dual-energy technique, also known as contrast-enhanced spectral mammography (CESM).
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Technique
A typical digital mammogram uses the energy of ~28 kVp. As the K edge of iodine is 33.2 keV, injecting iodinated contrast and performing standard mammography would result in a low signal intensity, indistinguishable from background tissue. CESM is based on dual-energy acquisition – a low energy spectrum, using standard mammography kV (28-32 kVp) and filtration (molybdenum), and higher energy (above the K-edge of iodine, 45-49 kVp), with stronger filtration (copper) 6.
The process is straightforward - iodinated contrast is given (a typical dose is 100 ml of iopamidol 300 at 3 mls/second) via a cannula in the antecubital fossa. Approximately 2 minutes later, the first images are acquired. Standard views are obtained – CC and MLO of each breast. Dual-energy images are acquired between 2 to 10 minutes window period after contrast administration because after 10 minutes the contrast will begin to washout 6. The dual-energy exposure occurs during one compression (the exposure is a little longer than a standard examination), so the technique is otherwise identical to an ordinary mammogram.
Two images are produced from each compression: low-energy – equivalent to a standard digital mammogram; and recombined - background breast tissue is suppressed to highlight areas of contrast uptake by subtracting low energy image from high energy image 6.
Applications
Previously described as complementary imaging, CESM is now being used instead of a standard digital mammogram in certain situations, e.g. high clinical suspicion of breast cancer. It is also a useful alternative to MRI for problem-solving, or where MRI is contraindicated (e.g. gadolinium allergy or claustrophobia) for staging, or follow-up post-treatment. Research is underway to evaluate its potential use in personalised screening.
Whilst standard digital mammography has a sensitivity of up to 80%, this is lower in dense breasts. CESM has an extremely high sensitivity for invasive breast cancer – up to 98%1. Although false-positives do occur (benign lesions can also enhance), the specificity of CESM is generally higher than that of breast MRI2.