iaea human health series publications - SEDIM

8.3. COMPRESSION8.3.1. Compression force and thickness accuracyAdequate compression is essential for high quality mammography. Compression reduces the thickness oftissue that must be penetrated by radiation, thereby reducing scattered radiation and increasing contrast, whilereducing radiation exposure to the breast. Compression improves image sharpness by reducing the breast thickness,thereby minimizing focal spot blurring of structures in the image, and by minimizing patient motion. In addition,compression makes the thickness of the breast more uniform, resulting in more uniform image densities and in animage that may be easier to interpret. The displayed compressed breast thickness is often used to choose thetechnique factors, so it is important that this level of accuracy be achieved.8.3.1.1. Scope— Objective: To check that the mammography system provides adequate compression in manual and automaticmode; to check the accuracy of the compression force indicator, if present on the equipment; to check theaccuracy (or deviation) of the compression thickness indicator.— Frequency: Desirable — semi-annually; essential — annually, or if there is an observed reduction in the breastcompression.8.3.1.2. Instrumentation(1) Bathroom scales (conventional, analogue type, non-digital).(2) Bath towels (cloths) or blocks of rubber foam.(3) Slabs of PMMA used for AEC testing.8.3.1.3. Methodology(a)Power compression mode(1) Place a bath towel on the Bucky and place the platform scale over it. Centre the scale directly under thecompression paddle (Fig. 30).(2) Place one or more towels (or a block of rubber foam) on the scale to protect the compression paddle such thatit does not obscure the reading on the scale.(3) Activate the compression paddle so that it operates and stops at the maximum available powered force. Thismay require a second activation of the compression foot pedal.(4) Read the value of the compression force on both the scale and the machine readout and record this in thecompression–AEC evaluation chart (Chart 2 in Annex II).(5) Release the compression.(b)Manual mode(1) Using the manual compression mode, move the compression paddle until it stops.(2) Read and record the compression force on the data collection sheet.(3) Release the compression.(c)Compression thickness(1) Align the PMMA blocks (20, 45 and 70 mm) with the chest wall edge of the breast support platform. Ideally,18 cm × 24 cm slabs of PMMA should be used, to prevent deformation of the plate and reduce measurementinaccuracies in the indication of thickness due to the tilt angle of the plate.84