Standardizing mammographic breast compression: Pressure rather than force?

Transcription

1 Standardizing mammographic breast compression: Pressure rather than force? Poster No.: C-2383 Congress: ECR 2012 Type: Authors: Scientific Paper J. E. de Groot 1, W. Branderhorst 1, M. Broeders 2, G. J. den Heeten 3, C. A. grimbergen 1 ; 1 Amsterdam/NL, 2 Nijmegen/NL, 3 Amsterdam/NL, Nijmegen/NL Keywords: DOI: Breast, Plain radiographic studies, Screening, Physics /ecr2012/C-2383 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 11

2 Purpose Mechanical compression of the breast improves image quality[i] and lowers radiation dose[ii] in digital X-ray mammography[iii]. Compression protocols instruct radiographers to apply a standardized force based on international mammography quality assurance guidelines newtons (U.S.)[iv], newtons (E.C.)[v]. For this purpose, mammography devices display the applied force real time (e.g. figure 1). However, the same force has different effects on different objects. Applying a standardized force on soft or small breasts will cause more deformation than applying the same force on hard or large breasts. What is different is the amount of pressure: force divided by the size of the contact area (figure 2). In this study we investigate the variations in tissue pressure during mammographic breast compression performed with a standardized target force. Due to variations in breast size, we expect large variations between women. Due to different breast geometry in the mediolateral oblique (MLO) compression view and the craniocaudal (CC) view, we also expect differences within women. Images for this section: Page 2 of 11

3 Fig. 1: Mammography device display showing compressed breast thickness (63 mm), View angle (45 deg = MLO), and compression force (17 dan) Fig. 2: Pressure equals force per unit area: force applied to a small breast (left) has a different effect than the same force applied to a large breast (right). Page 3 of 11

4 Methods and Materials In the Academic Medical Center (AMC) Amsterdam we performed an observational study to determine the variation in tissue pressures occurring in mammographic breast compression following a protocol with standardized target force of 180 newtons. The radiographers are instructed to stop at a lower force in case the patient verbally expresses severe pain. 104 patients provided informed consent for synchronous measurements of the contact area between the breast and the compression paddle. This was performed by sideillumination of the breast (figure 3). Throughout the compression, a camera recorded the shady contact area. In both the MLO and CC views, the actual applied force was divided by the contact area to obtain an estimation of the mean tissue pressure. Another camera recorded the applied force and compressed breast thickness (figure 1). We analyzed the means and standard deviations of the applied force, tissue pressure, contact area and compressed breast thickness as a measure for variations between women. Paired t-tests were performed to calculate whether these parameters are different for the MLO and CC view within women. Images for this section: Page 4 of 11

5 Fig. 3: Side-illumination setup (left) and camera view (right) for determining the breastpaddle contact area Fig. 1: Mammography device display showing compressed breast thickness (63 mm), View angle (45 deg = MLO), and compression force (17 dan) Page 5 of 11

6 Results The actual applied forces were 175 ± 23 (13%) newtons (mean ± standard deviation) both for MLO and CC views (figure 4). The paired t-test concludes a non-significant difference of the MLO and CC means of 1.6 ( ) newton (mean; 95% confidence interval) (p=0.2). The corresponding tissue pressures were 14.2 ± 5.3 (37%) kpa for the MLO view and 23.0 ± 16.8 (73%) kpa for the CC view (figure 5). Comparing the MLO and CC compression of each breast shows that the MLO-pressures are significantly 9.0 ( ) kpa lower than the CC-pressures (p<0.001). Contact areas were 137 ± 47 (34%) cm 2 for MLO and 99 ± 49 (49%) cm 2 for CC (figure 6) with a difference of the means of 40 (37-42) cm2 (p<0.001). Compressed breast thicknesses were 63.1 ± 12.3 (20%) mm for MLO and 59.7 ± 10.5 (18%) mm for CC (figure 7) with a difference of the means of 3.5 ( ) mm (p<0.001). Table 1 summarizes our findings. Images for this section: Page 6 of 11

7 Fig. 4: Distribution of applied forces (target force was 18 dan) Page 7 of 11

8 Fig. 5: Distribution of corresponding pressures Page 8 of 11

9 Fig. 6: Distribution of contact areas Page 9 of 11

10 Fig. 7: Distribution of compressed breast thicknesses Table 1: Overview of results s.d. = standard deviation c.i. = confidence interval H_1 = MLO-value is different from CC-value of the same breast Page 10 of 11

11 Conclusion A fixed target compression force is applied consistently in practice without a different force in the MLO and CC views. The corresponding applied pressure (force per unit area) varies significantly between women, standard deviations: 37% (MLO) and 73% (CC), and within women, paired t-test difference of means for MLO and CC: 9.0 kpa (p<0.001). Contact area and compressed breast thickness also show significant variations between and within women. References [i] Saunders RS Jr., Samei E, The effect of breast compression on mass conspicuity in digital mammography, Med Phys, 2008, 35(10), pp [ii] Olsson ML, Tingberg A, Mattsson S, A phantom study showing the importance of compression in conventional diagnostic X-ray examinations, Radiat Prot Dosimetry, 2010, 139(1-3), pp [iii] Romero C, Varela C, Muñoz E, et.al., Impact on breast cancer diagnosis in a multidisciplinary unit after the incorporation of mammography digitalization and computer-aided detection systems, AJR Am J Roentgenol., 2011, 197(6), pp [iv] U.S. FDA, Mammography Quality Standards Act and Program, Regulations (MSQA) on: MammographyQualityStandardsActandProgram/Regulations/default.htm [v] Perry N, Broeders M, de Wolf C, Törnberg S, Holland R, von Karsa L (eds) European Guidelines for quality assurance in breast cancer screening and diagnosis. 4th ed. Office for Official Publications of the European Communities, Luxembourg. Personal Information Page 11 of 11