Chapter 18: Mammography

Detailed Chapter Overview

Chapter 18 is dedicated entirely to mammography, the single most effective imaging modality for the early detection of breast cancer. This chapter provides an exceptionally detailed examination of the science, art, and clinical practice of breast imaging. A profound understanding of the complex breast anatomy—from the lobes and ducts of the glandular tissue to the supportive fibrous network and variable adipose tissue—is presented as the absolute foundation for quality imaging. The chapter's central theme is the uncompromising pursuit of image quality to detect the subtle signs of early malignancy, such as microcalcifications and architectural distortion. It delves deeply into the specialized physics of mammographic equipment, explaining the necessity for low kVp techniques and specific anode-filter combinations (e.g., molybdenum, rhodium) to maximize subject contrast in soft tissue. The critical principle of vigorous and proper breast compression is a major focus, with a thorough explanation of its multifaceted benefits: reduced radiation dose, decreased motion, improved image sharpness, and separation of overlapping tissues. The chapter provides meticulous, step-by-step instructions for the two standard screening projections, the Craniocaudal (CC) and Mediolateral Oblique (MLO), and a host of supplementary diagnostic views used to work up abnormalities. For every projection, exacting evaluation criteria, governed by the Mammography Quality Standards Act (MQSA), are established, training the technologist to become a highly critical evaluator of their own work. The chapter also addresses complex scenarios, such as imaging patients with breast implants, ensuring the technologist is prepared for the full spectrum of clinical situations.

In-Depth Study Guide

Breast Anatomy and Physiology

The breast is a complex, modified sweat gland composed of various tissues. Its composition changes significantly with age and hormonal status.

1. Tissue Composition

• Glandular Tissue: This is the functional tissue of the breast, responsible for milk production. It is organized into 15 to 20 lobes, which are further subdivided into smaller lobules that contain the milk-producing alveoli. Ducts from the lobules converge into a main lactiferous duct for each lobe, which opens at the nipple. Glandular tissue is densest and most prominent in younger, pre-menopausal women, appearing white on a mammogram.
• Fibrous (Stromal) Tissue: This is the supportive, connective tissue framework of the breast. It includes the **Cooper's ligaments**, which are fibrous bands that extend from the chest wall to the skin, providing structural support.
• Adipose (Fatty) Tissue: This tissue surrounds the glandular elements. After menopause, glandular tissue tends to atrophy and is replaced by fatty tissue, which is less dense and appears dark gray or black on a mammogram, making abnormalities easier to detect.

2. Topographical Anatomy

• Quadrants: For localization purposes, the breast is divided into four quadrants (Upper Outer, Upper Inner, Lower Outer, Lower Inner) plus an axillary tail.
• Tail of Spence (Axillary Tail): A band of glandular tissue that extends from the upper outer quadrant into the axilla. It is crucial to include this tissue on mammograms, as a significant percentage of breast cancers occur in this region.
• Lymphatics: The primary lymphatic drainage of the breast is to the axillary lymph nodes. Visualizing these nodes, particularly on the MLO view, is important.

The Principles and Importance of Mammography

Mammography is a low-dose x-ray procedure specifically designed to image the soft tissues of the breast. Its primary goal is the early detection of breast cancer, often before a lump can be felt.

• Screening vs. Diagnostic:
  • Screening Mammogram: Performed on asymptomatic women to detect unsuspected cancer at an early stage. Typically consists of the two standard projections (CC and MLO) for each breast.
  • Diagnostic Mammogram: Performed on patients with a clinical symptom (e.g., a palpable lump, nipple discharge) or to evaluate an abnormality found on a screening exam. It involves specialized views such as spot compression and magnification.
• MQSA (Mammography Quality Standards Act): A federal law enacted in 1992 that requires all mammography facilities in the United States to meet stringent quality standards for personnel, equipment, and image quality to be legally certified.

Specialized Equipment and Technique

• X-ray Tube and Filtration: Mammography units use specialized tubes with molybdenum or rhodium targets. These materials produce a low-energy x-ray spectrum (typically 25-30 kVp) that is optimal for maximizing contrast in soft tissue, allowing for differentiation between fat, glandular tissue, and pathologic masses or calcifications.
• Compression: The Key to Quality Imaging: Vigorous and uniform compression is the most critical component of a high-quality mammogram.
  • Reduces Tissue Thickness: This lowers the required radiation dose and reduces scatter, which improves image contrast.
  • Reduces Motion: The breast is immobilized, preventing motion blur and increasing image sharpness.
  • Separates Overlapping Tissues: Spreading the tissue out reduces the chance that a small cancer could be hidden by superimposed normal glandular tissue.
  • Brings Structures Closer to the IR: This minimizes geometric unsharpness.

Standard and Diagnostic Projections

The Two Routine Screening Views

1. Craniocaudal (CC) Projection

• Purpose: To visualize the medial, central, and subareolar regions of the breast.
• Positioning: The patient faces the machine. The technologist lifts the inframammary fold to its maximum height and places the breast on the image receptor. The patient's head is turned away from the side being imaged. The compression paddle is applied from above.
• Evaluation Criteria: All medial tissue must be included. The nipple should be seen in profile. The pectoral muscle should be visible at the posterior edge of the image in about 30% of cases. The posterior nipple line (PNL) measurement on the CC view should be within 1 cm of the PNL measurement on the MLO view.

2. Mediolateral Oblique (MLO) Projection

• Purpose: This is the single most important projection as it visualizes the most breast tissue, including the axillary tail.
• Positioning: The machine is angled (typically 40-60 degrees, depending on the patient's body habitus) to be parallel with the patient's pectoralis major muscle. The patient is turned slightly, and the corner of the image receptor is placed high in the axilla. The technologist pulls the breast tissue up and out, away from the chest wall, before applying compression.
• Evaluation Criteria: The pectoralis major muscle should be visualized down to the level of the nipple. The inframammary fold should be open. All posterior tissue must be included.

Diagnostic (Supplementary) Views

• Spot Compression: Uses a smaller compression paddle to apply focused compression to a specific area of interest, such as a questionable mass. This spreads the tissue more effectively in that small area to better define the margins of the lesion.
• Magnification Views: Used to obtain a magnified image of a specific area, most commonly to analyze the morphology (shape) and distribution of microcalcifications, which can be an early sign of cancer.
• Exaggerated Craniocaudal (XCCL): A modified CC view to better visualize the lateral tissue and the axillary tail.

Imaging Patients with Breast Implants

• Special Technique Required: Standard compression views can obscure breast tissue and risk implant rupture.
• Eklund Method (Implant-Displaced Views): This is the standard technique. After the standard four views are taken with minimal compression, four additional views are performed. For these views, the implant is manually pushed back against the chest wall, and the compression paddle is applied only to the breast tissue that has been pulled forward. This allows for adequate compression of the natural breast tissue without compressing the implant itself.