Analog mammography involves the use of hard copy films and, hence, is associated with related artifacts due to technical errors in processing, film handling, and storage (Minigh 2009).

These refer to mammography machine-related artifacts. These artifacts may be due to incorrect collimation, incomplete grid motion, Bucky failure, and compression system failure (Ikeda 2004). Remedies for prevention of these artifacts include mandatory regular quality control tests of the equipment. Equipment-related errors need to be detected and fixed by the service engineers. Identifying the sources of the artifacts often requires investigation with the phantoms.

Various materials located in or on patients may cause artifacts, e.g., deodorants, talc powder, clothing, tattoos, pacemaker, or foreign bodies (charm needles). Motion artifacts are caused by patient breathing and pulling. Poor positioning artifacts may be due to patient-derived artifacts such as hair, chin, nose, axillary–thoracic skinfold, and superimposition of the belly fold. Achieving an optimal mammographic image requires full patient cooperation. Patient-related artifacts, positioning as well as motion artifacts, occur more frequently in older age group. The aged loose skin is easily trapped in the compression paddle, causing the skinfold artifact. A poor or noncooperative patient who has difficulty in understanding is often unable to follow instructions that are required to attain appropriate position. Poorly mobile or wheelchair-bound patients are often not able to achieve and maintain adequate position, which leads to the positioning artifacts and artifacts caused by breast motion, uncontrollable breathing, and insufficient compression. Remedies for patient-related artifacts include reduction of patient motion by optimizing patient’s comfort and careful explanation which helps alleviate the anxiety of examination and may improve their cooperation.

Full-field digital mammography (FFDM) is a new type of mammographic equipment which uses digital technology and X-rays to acquire and store images of the breasts (Pisano 2004). Computed radiography involves use of cassettes with photostimulable phosphor screens to record images which are scanned with a reader device in the workstation to produce a soft copy image. Digital radiography uses flat plane detectors for image acquisition. The equipment-related artifacts that occur in analog mammography can occur in digital mammography (Ikeda 2004; Lewin et al. 2004; Rothenberg et al. 2004; Bloomquist et al. 2006; Yaffe et al. 2006). Detector miscalibration artifacts are the most common artifacts in digital mammography. Fixed digital detector systems use calibration or gain correction to remove differences in sensitivity and nonuniformities of the X-rays. Sometimes, the calibration may cause persistent artifacts. Recalibration of the gain correction will remove persistent artifacts. If recalibration is made too soon after the exposure, a ghosting artifact can be introduced in form of lighter or darker areas on image. This remains and will appear on each subsequent image.

Filtration artifacts occur as mottled background across the entire image. Bad pixel artifact is seen as a white or black isolated dot. Several bad pixels in the group can cause appearance of black or white cluster artifacts. A column or row of bad pixels would introduce a line artifact. Improper collimation and improper detector alignment or damaged detector will cause black or white bands at the margins of the detector. Pre- or post-processing algorithm artifacts can occur. Dust artifacts may be seen as minus density specks on every image. The dust can the collect on top of the digital detector, breast support tray, and compressing paddle, mirror, or filter. Grid artifacts appear similar to those seen in analog mammography.

Patient-related artifacts are similar to those that occur in analog mammography and have an increased frequency in older group of women. Positioning artifacts such as belly fold (Fig. 19.2), chest skinfold (Fig. 19.3), inferior skinfold artifact (Fig. 19.4a, b), and chin artifact (Fig. 19.5) are more common phenomena in this age group as the loose skin is easier to be trapped in the compression paddle. Motion artifacts are caused by breathing or movement during acquisition. Foreign material artifacts may be due to deodorant/talc powder (Fig. 19.6), clothing tattoos, free silicone injection, and charm needles (Fig. 19.7). Patients with difficulty in understanding instructions and who are poorly mobile or wheelchair bound may not be able to stay in the required position and cooperate, which lead to considerable patient-related artifacts. The blurring caused by breast motion appears most commonly because of uncontrollable motion of breathing.

Other artifacts can be related to either laser printers or to image display monitors. Laser printer artifacts can be seen as horizontal or vertical lines or streaks, as a crisscrossed background, or as too light or too dark images. Image display monitor artifacts can occur as areas of nonuniformities, lines, streaks, black and white dots, or non-matching images. These artifacts are easily prevented by regular service and quality control of equipment.

A significant artifact in MRI is due to motion and is often seen while imaging elderly patients. Even with an optimal prescribed protocol, any amount of motion can degrade image quality, or even render a study completely nondiagnostic. Artifacts from blood flow as well as cardiac, respiratory (Fig. 19.18), and patient motion all propagate in the phase-encoding direction, regardless of the direction of the motion. Motion results in blurring of moving tissues but also causes a structured noise pattern, resulting in “ghosting” of brighter moving tissues in the phase-encoding direction (Pusey et al. 1986; Rausch and Hendrick 2006). Motion artifacts can be due to physiologic motion and non-physiologic motion.

Physiologic motion can be due to various causes. Pulsation of blood vessels may affect only a few image slices (Fig. 19.19). Periodic motion from vessel pulsation is specifically referred to as ghosting (Fig. 19.20). Generally, the pseudo-image appears as a hyperintense signal-replicated image of a normal structure in the phase-encoding direction. As motion always propagates in the phase-encoding direction, regardless of the direction of the motion, even minimal motion will cause misregistration on subtraction images that may limit their usefulness. The correct choice of the phase-encoding direction for breast MRI is left to right for axial images and superior to inferior for sagittal images. To eliminate pulsation artifacts, a saturation band can be placed over the moving structure using a standard sequence. The smearing from respiratory or cardiac motion occurs across the lateral chest rather than the breasts. If the phase-encoding direction is incorrectly chosen to be anterior to posterior with either axial or sagittal sequences, smearing from cardiac or respiratory motion can obscure large amounts of breast tissue. Periodic motion, such as vascular pulsation, results in ghosting occurring at regular intervals in the phase-encoding direction. Ghosting is a form of phase-encoding artifact (Morris 2002; Harvey et al. 2007). Reducing the repetition time may help reduce ghosting so that it is not propagated throughout the entire image, but doing so is often impractical in breast MRI.

Non-physiological motion is due to patient movement during the scan and can lead to unsatisfactory images affecting the entire series (Coulthard and Potterton 2000). Claustrophobia and patient anxiety remain the major contributors of this artifact, which are more commonly encountered in the geriatric age group due to different grades of senility. Patient motion can be reduced by assuring optimum patient comfort. This can be obtained by explaining the study to the patient, reassuring the patient before the examination, appropriate positioning with comfortable arm and head rests, optimizing examination time, providing sedatives, using physical restraints (straps), providing earplugs and blankets, and communication with the patient throughout the study as and when required (Rausch and Hendrick 2006).

Misregistration artifact is a type of motion artifact specific to subtraction imaging used in interpretation of breast MR images. This artifact is encountered when there is movement between the pre- and post-contrast image data sets to be subtracted (i.e., contrast-enhanced T1-weighted and non-enhanced T1-weighted image subtraction image). Edge artifact is a term used to describe the color mapping artifact caused by subtle misregistration that occurs in computer-aided detection. This artifact is identified as a mass appearance in a single section of one plane, but reformatted multiplanar images demonstrate no mass. The edge of the fat–parenchyma interface is color mapped in a planar fashion.

Ferromagnetic metals (such as iron, nickel, cobalt) cause severe inhomogeneity in the magnetic field. Metallic objects, including biopsy clips, jewelry, snaps on clothing, or imaging equipment on or near the patient, can interfere with the main magnetic field, resulting in metallic artifacts. The metallic object is devoid of mobile protons and hence does not emit a MR signal. However, the induced fixed heterogeneities of the magnetic field cause additional artifacts around the metallic object, resulting in a local signal intensity void in the vicinity of the metal (Haydee Ojeda-Fournier et al. 2007), often with a surrounding area of high signal intensity and image distortion. Similar but less prominent effects are seen due to the varying magnetic susceptibility of different tissues, such as bone and soft tissue. The size of the susceptibility artifact is dependent on the size and composition of the metallic object.

Surgical clips (Fig. 19.21a–d) and percutaneous biopsy clips may cause considerable distortion. If extensive, the artifact could preclude diagnosis of local recurrence at the lumpectomy site. On the other hand, signal intensity void from percutaneous biopsy clips may help confirm the biopsy location (Genson et al. 2007). MRI is sensitive for detection of metallic susceptibility artifacts, even when no metal is perceptible at mammography, due to the deposition of tiny metal fragments from the core needle biopsy or from devices used during surgery (Finder et al. 1998; Haigh et al. 2000a; Genson et al. 2007).