Focal spot motion in digital breast tomosynthesis and its effect on spatial resolution

Area of Science:

• Medical Imaging Physics
• Radiological Technology
• Diagnostic Imaging

Background:

• Digital breast tomosynthesis (DBT) is standard, but vendor acquisition methods differ.
• Key DBT techniques include continuous motion, step-and-shoot, and continuous motion with flying focal spot.
• These techniques involve trade-offs between scan time and focal spot blur.

Purpose of the Study:

• To quantify the effective focal spot size increase in DBT versus 2D mammography.
• To evaluate how this size increase affects spatial resolution using modulation transfer function (MTF).

Main Methods:

• Focal spot size was measured using a 10 µm slit phantom for 2D and DBT (0° projection).
• Acquisitions simulated 2, 4, and 8 cm thick breasts (50/50 adipose/fat).
• MTF curves were assessed using a copper edge phantom at two positions relative to the breast support.

Main Results:

• Effective focal spot size increase in DBT correlated with breast thickness across all systems.
• Continuous motion systems exhibited the largest focal spot size increases (101%-462%).
• Flying focal spot systems showed minimal increases (3%-25%), while step-and-shoot and flying focal spot systems maintained MTF, unlike continuous motion systems.

Conclusions:

• Step-and-shoot and flying focal spot DBT systems effectively minimize effective focal spot size increases.
• These methods preserve spatial resolution better than continuous tube motion systems.