At Senology Unit of the AOU Careggi, Florence, we introduced CEDM into clinical practice since September 2016. From September 2016 to September 2019 more than 1300 CEDM examinations were performed. We used a mammography system, which has the capability of performing FFDM, tomosynthesis and CEDM examinations. 

We retrospectively analyzed our radiological database and evaluated the artefacts encountered during our work. [6] 

The most common artifacts found in our clinical practice were:

1. Artefacts visible in both CEDM and FFDM images

Based on previous literature, it has already been validated that the LE images are comparable to FFDM images [3]. Therefore, some artefacts that are seen in FFDM can also be visualised in CEDM images. The most commomn were:

• Motion artefacts

With the current CEDM process, motion artefacts have been significantly minimized due to the brief interval of time between the LE and HE exposures. However, CEDM images are still more prone to motion artefacts compared to FFDM because dual-energy acquisition requires longer exposure and compression times. In the recombined images, motion artefacts appear as blurring of the margins of lesions (Fig. 1). Adequate compression can reduce motion artefacts. [7] 

• Air-trapping artefacts

Air-trapping is a common artefact causedby partial contact between the skin and the detector or compression paddle [1;8]. This leads to the presence of air, which creates a dark artefact in the configuration of the area of incomplete contact, possibly hiding underlying abnormalities (Fig. 2).

2.  Contrast Related Factors

• Contrast splatter

It is critical to pay close attention to the technique during contrast administration to prevent contrast contamination. When detaching the tubing from the power injector, the contrast media may accidentally splatter onto the adjacent equipment or skin, resulting in the appearance of small white dots on both recombined and LE images, which may be confused with suspicious enhancement areas or microcalcifications. (Fig. 3) 

However, it should be noted that that while calcifications are white on FFDM and LE CEDM images, they appear black on CEDM recombined images. 

To avoid this artefact from occurring, nurses or doctors must administer contrast media away from the mammography unit. [9]. Carefully cleaning the region to be examined and the detector of the mammography unit prior to subsequent acquisitions can resolve this artefact.

3. CEDM Related Factors

This category includes artefacts that are unique to CEDM.

• Post biopsy markers

Markers of different composition and materials can demonstrate a variable appearance. On the recombined CEDM images, all markers appear as high attenuation structures, however a surrounding dark halo is occasionally seen with some types of these markers. (Fig. 4)

• Breast implant artefacts

Breast implants tend to produce significant artefacts on CEDM recombined images, which may obscure an underlying pathology. (Fig. 5) Therefore, MRI continues to be the imaging modality of choice in women with breast implants and the presence of implants represents a CEDM's contraindication.

• Negative contrast enhancement

In recombined CEDM images, cysts, calcifications or post-biopsy hematomas demonstrate an area of rim enhancing hypodensity in relation to the surrounding background giving it a “negative contrast enhancement” appearance which is also referred to as the “eclipse sign”. This phenomenon is actually not a true artefact, but is in fact a natural consequence of the acquisition technique. (Fig.6)

• Ripple Artefact

Ripple artefacts are very commonly visible on recombined images as alternating black and white lines. (Figs. 7) Dromain et al. [10] suggested that this may be attributed to patient motion, due to the short interval between the low and high-energy exposures. However there are some authors [4] who attribute it to cardiac pulsations transmitted through the chest wall as it more commonly seen in the lower quadrants of MLO projections of the left breast. Reducing patient anxiety might reduce this artefact; however, it does not compromise the image quality.

• Misregistration artefacts

Misregistration artefacts are commonly observed in relation to surgical clips, vessels, and calcifications. It is seen as alternating bright and dark lines, illustrating a “zebra artefact” seen exclusively on recombined images. (Fig. 8) Even minimal motion between the LE and HE images causes misalignment of the images, resulting in imprecise subtraction. 

• Skin-line enhancement and enhancing skin lesions

The skin doesn’t usually demonstrate enhancement in recombined images; however, it may show a thin rim of enhancement. This artefact may be caused by non-uniform scatter radiation and difference in skin thickness throughout the breast and is also known as “skyline artefact”. It is necessary to check the skin thickness in the LE images, to verify that the skin is not truly affected by a disease.

Moreover, some vascular skin formations, such as skin angiomas, may show contrast enhancement, mimicking the presence of suspicious lesions. (Fig. 9) A careful clinical examination of the patient's skin may be necessary. 

4. Quality-control (QC) Artefacts

These artefacts can severely compromise the image quality.It is important to train all technologists and schedule specific times for the daily QC processes and specific days for the weekly QC processes. 

Other artifacts we encountered are summarized in Table 1. (Fig. 10)