28.1 Mammography: Equipment, CC and MLO Positioning, Compression & Breast Pathology

28.1 Mammography: Equipment, CC and MLO Positioning, Compression & Breast Pathology

The Enhanced TOS lists Mammography as its own sub-topic worth 4 items, with three competencies: show the skills in preparation and proper positioning technique, illustrate positioning principles, indications and contraindications and patient preparation, and distinguish the aspects on the differential diagnosis of breast diseases. Mammography is the most technically demanding plain-film examination in radiography because it must resolve microcalcifications under 100 micrometres and differentiate soft tissues whose subject contrast is inherently tiny.

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1. Why Mammography Needs Dedicated Equipment

The breast is composed of fibroglandular tissue, fat and skin — all with effective atomic numbers within about one unit of each other. General-radiography physics simply cannot separate them. The dedicated unit solves this with low-energy, high-contrast physics.

The physics in one sentence: the molybdenum K-characteristic lines at about 17.5 and 19.6 keV, isolated by a matched molybdenum filter, produce a beam whose energy sits exactly where the small attenuation difference between fibroglandular tissue and fat is largest.

Anode heel effect is exploited deliberately. The cathode side is placed at the chest wall, where the breast is thickest, and the anode side toward the nipple, where it is thinnest — because beam intensity is greater on the cathode side.

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2. Compression: Six Reasons, Not One

Compression is the single most important technical act in mammography and the one patients most resist, so you must be able to explain it.

1. Reduces thickness, so dose falls — a thinner part needs less exposure.
2. Reduces scatter, so contrast improves.
3. Brings structures closer to the receptor, reducing geometric unsharpness (magnification and penumbra).
4. Separates overlapping tissues, so a lesion is not hidden by superimposed glandular tissue.
5. Equalises thickness across the breast, so a single exposure covers both the dense posterior tissue and the thin anterior tissue.
6. Immobilises the breast, eliminating motion unsharpness.

Applied firmly but gradually, with clear explanation and with the patient told she may ask the technologist to stop, compression is tolerable. It is applied until the tissue is taut, not until the patient is in severe pain.

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3. The Two Standard Projections

Craniocaudal (CC)

• The image receptor is placed beneath the breast; the central ray passes from superior to inferior.
• The inframammary fold is elevated to its maximum natural height before the breast is placed on the receptor — this is the manoeuvre that determines how much posterior tissue is included.
• The patient's head is turned away from the side being examined; the shoulder is relaxed and the arm on the imaged side hangs relaxed or rests on the handgrip.
• Evaluation criteria: the nipple is in profile; the breast is centred with medial tissue included; pectoralis major is visualised in about 20-30% of cases as a small tongue at the posterior edge; there is no skin fold; and the posterior nipple line (PNL) is measured from the nipple straight back to the edge of the image or to the pectoralis.

Mediolateral Oblique (MLO)

• The single most important projection in mammography, because it demonstrates more breast tissue — including the axillary tail of Spence — than any other.
• The tube and receptor are angled together, typically 30 to 60 degrees, chosen so the receptor is parallel to the patient's own pectoralis major. Tall thin patients need a steeper angle (about 60 degrees); short broad patients a shallower one (about 30-40 degrees).
• The receptor edge is placed behind the posterior axillary fold, the arm rests over the corner of the receptor, and the breast and pectoral muscle are pulled up and out away from the chest wall before compression.
• Evaluation criteria: the pectoralis major is seen down to or below the level of the posterior nipple line, and is convex rather than concave; the inframammary fold is open and demonstrated; the nipple is in profile; the breast is not drooping; and there are no skin folds.

The posterior nipple line rule

Measure the PNL on the MLO from the nipple perpendicular to the pectoralis; measure it on the CC from the nipple straight to the posterior edge. The CC measurement should be within 1 cm of the MLO measurement. If the CC PNL is much shorter, posterior tissue has been left out and the CC must be repeated.

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4. Supplementary Projections

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5. Patient Preparation, Indications and Contraindications

Preparation

• Schedule 7 to 14 days after the onset of menstruation in premenopausal women, when the breast is least tender and least dense.
• No deodorant, antiperspirant, talcum powder, lotion or perfume on the breasts or axillae on the day — aluminium-containing antiperspirant mimics microcalcification.
• Take a full history: previous breast surgery, biopsy, implants, hormone therapy, family history, current symptoms and their duration, and the exact location of any lump or nipple discharge.
• Document scars, moles, nipple piercings and skin lesions on a body diagram and mark them with radiopaque markers so they are not mistaken for lesions.
• Always ask about pregnancy and lactation.

Indications

• Screening in an asymptomatic woman at the interval set by national policy.
• Diagnostic evaluation of a palpable lump, focal pain, skin or nipple change, or nipple discharge.
• Follow-up of a known abnormality, post-operative or post-radiotherapy surveillance.
• Evaluation of a man with gynaecomastia or a suspicious breast mass.

Contraindications and cautions

• Pregnancy is a relative contraindication — ultrasound is first-line in a pregnant or lactating woman with a breast lump.
• Screening is not the correct test for an acutely inflamed, abscessed breast; ultrasound leads.
• Age. In a woman under about 30, dense fibroglandular tissue makes mammography insensitive, and ultrasound is the first-line modality.

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6. Differential Diagnosis: Benign versus Malignant Signs

Common entities:

• Fibroadenoma — the commonest benign solid mass in young women; circumscribed and oval, with coarse "popcorn" calcification when it involutes.
• Simple cyst — circumscribed and round; ultrasound confirms an anechoic lesion with posterior acoustic enhancement.
• Fat necrosis — post-traumatic or post-surgical; classic oil cyst with rim calcification.
• Invasive ductal carcinoma — the commonest malignancy; a spiculated, high-density irregular mass, often with pleomorphic microcalcifications.
• Ductal carcinoma in situ — frequently presents as calcifications only, with no mass.
• Inflammatory carcinoma — diffuse skin thickening and trabecular coarsening rather than a discrete mass; clinically mimics mastitis.

Findings are communicated using a standardised assessment lexicon in which each category carries a management recommendation, running from a negative or benign result through probably benign short-interval follow-up, suspicious findings requiring biopsy, and biopsy-proven malignancy. The radiologic technologist does not assign the category, but must recognise when an image demands additional projections before the patient leaves the department.

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7. Quality Control the Technologist Performs

The phantom image must demonstrate the specified minimum number of fibres, speck groups and masses; a drop below that minimum stops clinical imaging until corrected.