Evaluation of image receptor angulation during mediolateral oblique positioning for optimised pressure and area distribution in mammography

Osmanu, M

Abstract

Background
Mammography is the gold standard diagnostic tool for the screening and diagnosis of breast cancer; however, it is associated with pain and discomfort. The pain and discomfort are mostly due to positioning and the compression applied during the procedure. Currently there are variations in the way clients are positioned for mammography and the amount of compression applied during the procedure. In addition, there are sparse guidelines and published literature on mammographic positioning and the application of compression. It is suggested that for the medio lateral oblique (MLO) position, for an effective compression force balance and increased breast footprint, the sternal angle and the image receptor (IR) be parallel to each other. This aim of this research is to evaluate the angle of IR during MLO positioning for optimised pressure and area distribution; this in turn may help reduce pain and discomfort associated with the procedure.

Method
The experimental work described in this report is in two phases.

Phase one was an anthropomorphic phantom study to establish a structured and reproducible method of using the angle of the sternum to measure the correct angle of the IR for MLO projection. An inclinometer was used to measure the sternal angle of phantom model used. Six sets of compressions were made on the breast phantom with the IR at different angles ranging from 400 to 700 at 50 angle increments. Contact pressure and contact area footprint readings between breast phantom/paddle interface and breast phantom/IR interface were recorded using Xsensor pressure mapping system. Pressure uniformity (PU) and area uniformity (AU) between phantom breast/paddle interface and phantom breast phantom/IR interface were then calculated.

Phase two was a human study with participants to investigate contact pressure and area balance on MLO compressions using two angles. A digital inclinometer was used to measure the angle at which the sternum for each participant. This angle was referred to as the ‘experimental angle’. The other angle was a ‘reference angle’ of 450. Compression at the ‘experimental angle’ may result into a better distribution of pressure through the breast and juxtathoracic structures, this may reduce the pain associated with the procedure. In addition to this, compression at this angle may increase breast surface area.
The hypotheses set out to ascertain if there is no significant difference between contact pressure distribution when the IR is positioned parallel to the sternal angle (experimental angle) and it is positioned at a reference angle.
An Xsensor pressure mapping system was used to record and analyse pressure distribution and surface area for compressions at the ‘experimental angle’ and the ‘reference angle’ (450). Pressure and area balance between the IR and compression paddle on both of these angles were compared and T-test conducted to accept or reject the hypotheses set out.
In addition, participants were asked to score their pain experience after each compression, that is, compression at the ‘reference angle’ and the ‘experimental angle’.

Results
The results from phase one indicated there was greater balance of pressure between breast/IR interface and breast/paddle interface at IR angle 600 compared the rest of IR angles investigated. PU of zero indicated equal distribution of pressure from the IR and the paddle. IR angled at 600 recorded a PU value of 0.21 which was the closest to zero from the PU recorded for the various angles. AU of zero indicates equal distribution of area footprint from the IR and the paddle. IR at 600 (Sternal angle for phantom model) produced the greatest area footprint balance compared to the other angles with AU of 0.05. An IR angled at 600, being parallel to the sternal angle of the phantom model which was recorded at 600 on the inclinometer, was the angle which produced the greatest balance of pressure and area footprint.
The results from human study indicated there was no significant difference between contact pressure and area distribution when the IR is positioned parallel to the experimental angle or positioned at a reference angle.

Conclusion
For the phantom study it has been shown that positioning the IR parallel to the angle of the sternum produces a more balanced contact pressure distribution and improved breast surface area footprint.
The human study demonstrated no statistically significant difference between pressure and area balance on the reference angle and the experimental angle.
For pain experienced score, although there was a 95% chance that the actual pain score for the compression on the reference angle fell within 3.81 and 5.76. and that of the experimental angle fell within 3.02 and 4.79, there was no statistically significant difference between pain experienced from compression on both angles.

Citation

Osmanu, M. Evaluation of image receptor angulation during mediolateral oblique positioning for optimised pressure and area distribution in mammography. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Feb 2, 2023
• Publicly Available Date: Feb 2, 2023
• Award Date: Jan 20, 2022