X-ray physics notes curriculum
Fundamentals of radiation
The X-ray machine
Production of X-rays
Interaction of radiation with matter
X-ray detection and image formation
Image quality
Radiation safety in X-ray imaging
Fluoroscopy
Mammography (current module)
Conventional 2D mammography compresses three-dimensional breast anatomy into a single projection image. Tissue superimposition can obscure lesions or mimic abnormalities, particularly in dense breasts.
Digital breast tomosynthesis (DBT) and other advanced techniques were developed to overcome these limitations, improving lesion visibility while maintaining acceptable dose levels.
Digital Breast Tomosynthesis (DBT)
Principle
Tomosynthesis acquires multiple low-dose projection images of the breast from a limited range of angles during a single compression. By exposing the breast at different angles, overlapping structures can be partially separated in post processing.
These projections are then reconstructed into a series of quasi-3D slices, each representing a thin section through the breast.
Acquisition
- X-ray tube moves through an arc of ±7° to ±25°, typically over 10–25 projection angles.
- Each exposure uses a small fraction of the total dose of a standard mammogram.
- Total dose is approximately equal to or slightly higher than a single 2D view.
Reconstruction
- Raw projection images are processed using filtered back-projection or iterative reconstruction algorithms to form tomographic slices (typically 1 mm thick).
- Reconstruction algorithms correct for geometric blur and limited angular range.
- The resulting volume allows radiologists to scroll through the breast in depth, reducing tissue overlap.
Advantages of Tomosynthesis
| Benefit | Explanation |
|---|---|
| Reduced tissue overlap | Separates superimposed structures, improving lesion conspicuity. |
| Improved cancer detection rate | Particularly beneficial in dense breast tissue. |
| Better margin definition | Clarifies spiculations and lesion boundaries. |
| Lower recall rates | Fewer false positives due to improved lesion localisation. |
Tomosynthesis can be performed as a stand-alone study or combined with standard 2D mammography (synthetic or acquired) for comprehensive screening.
Limitations of Tomosynthesis
| Limitation | Explanation |
|---|---|
| Limited z-axis resolution | Due to restricted angular range; slices are not fully independent. |
| Increased acquisition and reconstruction time | Tube motion and algorithm processing add to workflow. |
| Inability to perform true volumetric quantitative measurements | Slices are quasi-3D, not isotropic voxels. |
| Potential for motion artefacts | Tube movement during exposure requires mechanical precision. |
| Slightly higher dose | Cumulative dose marginally exceeds that of standard 2D mammography. |
Contrast-Enhanced Spectral Mammography (CESM)
Principle
CESM uses an intravenous iodinated contrast agent to enhance vascularised lesions and exploits the K-edge of iodine (33.2 keV) for selective imaging.
Two exposures are taken at different beam energies:
- Low-energy image: similar to standard mammogram (below iodine K-edge).
- High-energy image: above iodine K-edge, highlighting contrast uptake.
Digital subtraction produces an image showing areas of contrast enhancement only.
Advantages
- Improves lesion conspicuity and assessment of tumour vascularity.
- Provides functional information similar to MRI at lower cost.
- Compatible with standard digital mammography systems equipped for dual-energy operation.
Limitations
- Requires iodinated contrast and IV access.
- Slightly higher radiation dose (≈ 20–30% above standard view).
- Limited temporal resolution compared with MRI.
Key Points and Exam Tips:
- Tomosynthesis reconstructs quasi-3D breast slices from multiple low-dose projections.
- Angular range (±7°–25°) determines depth resolution and slice separation.
- Dose is comparable to or slightly higher than standard 2D imaging.
- CESM uses dual-energy imaging around the iodine K-edge (33 keV) to visualise enhancement.
- Common exam question: “Describe the principles of digital breast tomosynthesis and discuss its advantages and limitations compared with conventional mammography.”
Up next
Next, we will move on to Radiation Dose and Protection in Mammography, where we will define and calculate mean glandular dose (MGD), discuss typical values and conversion factors, and review dose-optimisation strategies used in screening and diagnostic mammography.