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Radiography 18 (2012) 55–56
Contents lists available
Radiography
journal homepage: www.elsevier .com/locate/radi
Letter to the Editor
Blurred digital mammography images
Figure 1. Blurred mammography image.
Dear Sir,
We should like to outline a problem that exists on digitalmammography machines and point out some observations wehave made in relation to the problem. We feel our observationsmay partly explain the problem and consequently this correspon-dence may be of value to your readers.
We recently completed a multicentre analysis of compressionpaddle bend and distortion using a phantom breast mountedonto a rigid torso.1 During the study we noticed that once compres-sion was applied to the phantom a significant period of time had toelapse, because of motion, before we mapped the paddle surface.Around the same time conversations with clinical staff revealedblurring was present on some digital mammography images. Weacknowledged that blurring on mammographic images was nota new phenomenon but the introduction of full field digitalmammography has exacerbated the problem – blurring is moreapparent than previously seen on film. We therefore assumed theincreased frequency was due to improved image resolution ondigital images as blur had always been present on film but it wasnot as easily detectable.
An audit conducted within the Countess of Chester Hospitaldemonstrated that the whole image can show blurring butfrequently a segment of the image only appears affected, withcranio-caudal (CC) and mediolateral-oblique (MLO) projectionsbeing equally involved (no obvious trends have been identifiedfrom the audit). In June & July 2011 blurred images accounted for45% and 67% of technical repeats respectively. Additionally, blurringaffects many more images than those which are repeated – someimages are therefore suboptimal but still considered of diagnosticquality. Up to about 20% images in any screening set can exhibitelements of blurring.
It was noted that blurring has the potential to obscure smallcancers and microcalcifications and as a result significant abnor-malities may be undetected until they become much larger. Fig. 1(right medio-lateral projection) illustrates an example of blurring.Here blurring has occurred over the majority of the breast. Inparticular, there is a focus of microcalcification in the posterioraspect of the lower breast which cannot be clearly identified andwould therefore go undetected. In this instance the image wasrepeated and the sharp repeated image demonstrated it clearly -this proved to be a cancer.
Having observed motion in the bend and distortion study wehypothesised that it may be linked to the blurred images (motionartefact), however until very recently we could not establish howmuch motion was occurring and whether it may be clinicallyimportant. Recently, on analysing data from a different research
1078-8174/$ – see front matter � 2011 The College of Radiographers. Published by Elsedoi:10.1016/j.radi.2011.11.008
project (human female mammography compression data (131compression sets for CC; 128 from MLO) to generate compositecompression graphs) from the Countess of Chester Hospital wenoticed unusual appearances (CC – Fig. 2; MLO – Fig. 3). The datafor these figures was generated from the practitioner applying1 dN of pressure and then recording the breast thickness readout,then applying a further 1 dN of pressure, and so on. The X axisrepresents the applied pressure (dN); the Y axis represents thechange in breast thickness (mm) from the thickness at the initialpoint of applied pressure, (5 dN). On reviewing the CC and MLOgraphs it seems that the paddle is not holding its position, this isclearly demonstrated at 6 dN. At this pressure level the paddleappears to relax and when 7 dN is applied the breast thicknessactually increases. This phenomenon is demonstrated clearly atseveral points on both graphs. We speculate that this could bedue to the paddle relaxing, or the breast relaxing, or both relaxing.This theory fits well with the regional or global blurring that isnoticed in the breast: for the former an aspect of the breast mightrelax to incur local blur; for the latter the paddle and breast bothrelax to incur global blur.
vier Ltd. All rights reserved.
Figure 2. CC – change in breast thickness versus compression pressure.
Figure 3. MLO – change in breast thickness versus compression pressure.
Letter to the Editor / Radiography 18 (2012) 55–5656
With these observations in mind we have already commencedan engineering project to measure paddle motion to determinewhether the motion has clinical importance (i.e. degradation ofperceptual image quality due to motion artefact). This study maytake several months to complete and in the meantime we felt ourobservations would beworthy of a broader readership. In particularwe are keen to know if others have experienced image blurring indigital mammography and also whether any alternative explana-tions to the blurring exist.
Please note that ethical and/or audit approval has been grantedfor all our research work which involves humans.
Yours sincerely
Reference
1. Hauge I, Hogg P, McGill G, Mercer C, Szczepura K, Connolly P. The readout thick-ness versus the measured thickness for a range of screen film mammography(SFM) and full-field digital mammography (FFDM) units.Medical Physics, in press.
Peter Hogg*, Katy SzczepuraUniversity of Salford, Manchester, UK
Judith KellyCountess of Chester Hospital, Cheshire, UK
Melanie TaylorNorth Manchester General Hospital, Manchester, UK
* Corresponding author. Directorate of Radiography,University of Salford, Allerton Building, Frederick Road,Salford, Greater Manchester M6 6PU, United Kingdom.
Tel.: þ44 161 295 3182.E-mail address: [email protected] (P. Hogg)
Available online 9 December 2011