FFDM Performance

Important features of digital mammography are the wide dynamic range, which is about 400 fold compared to that of a film-screen system, and the linear relationship between the radiation dose reaching the detector and the signal intensity produced. Also, the inverse relationship between the radiation dose at the detector and the image contrast is eliminated because both image contrast and brightness can be separately optimised after image acquisition (Obenauer, Hermann, & Grabbe, 2003; Uffmann & Schaefer-Prokop, 2009). Also there are additional benefits of FFDM including easier archiving and easy-to-share image data (Silverstein et al., 2009).

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In FFDM, the overall image quality is determined by spatial resolution, image contrast, signal-to-noise ratio, and dose efficiency (Smith, 2005). Since the image acquisition, display and storage are achieved separately in FFDM, the image optimisation process is different from that in film-screen (Park, Kim, Choi, Oh, & Kim, 2011). Accordingly, the FFDM allows the optimisation of image acquisition, display, and storage processes separately (Pisano & Yaffe, 2005). The optimisation of image acquisition is dependent on digital detector optimisation, selected X-ray spectrum (target/filter combination) and exposure factors (Park et al., 2011). Digital detector characteristics that control the image acquisition process are field and pixel sizes, dynamic range, sensitivity, internal noise and readout (Lança & Silva, 2009b). National and European standards determine the required contrast resolution and the accepted radiation dose (European Commission, 2006; IAEA, 2011). They also proposed 100 µm as the maximum accepted pixel size and 18 ± 1cm X 24 ± 1cm as the minimum detector size to accommodate large breasts (Schulz-Wendtland, Fuchsjager, Wacker, & Hermann, 2009). For soft copy image display, two high resolution monitors (5 megapixels) should be used (IAEA, 2011). This ‗reporting-grade‘ workstation should include software with a wide range of processing tools which enable image manipulation, such as image gray scale invert, window level and width change, zooming, edge enhancement, and measuring tools. Finally, the use of a picture archiving and communication systems (PACS) facilitates better digital archiving and sharing with others (teleradiology) (James, 2004; NHSBSP, 2009).

It has been reported that digital mammography provides better contrast resolution with lower patient dose than film-screen systems (NHSBSP, 2009; Smith, 2005). The superiority of digital mammography has been investigated by many researchers. Work by Gennaro and di Maggio (2006) compared the mean glandular dose (MGD) of 300 film-screen cranio-caudal mammograms with 296 FFDM cranio-caudal mammograms. They found that the use of FFDM reduces MGD by about 15% for thin breast and 30-40% for thick breast. The main limitation of Gennaro and di Maggio‘s (2006) work was that they compared the MGD of images taken by one film-screen system with that of images taken by one FFDM machine; MGD variations of different systems were not considered. More recently, Hendrick et al. (2010) evaluated the technical performance of both film-screen and FFDM systems for 4366

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women who underwent screening mammography by both techniques. They reported a 22% reduction in breast MGD with the use of FFDM.

With regard to FFDM image quality evaluation, most researchers used breast cancer detectability as a means to investigate the performance of FFDM compared to film-screen, see Table (3-1). All of the studies in Table (3-1) concluded that the cancer detectability of FFDM was equal or better than that of film-screen. The mammographic image quality of FFDM was compared with that of film-screen for 200 women wherein one of their breasts was examined by FFDM and the other one by film-screen. The results of this work indicate equal accuracy for both FFDM and film-screen in some studied criteria, while the FFDM was more accurate in other criteria (Fischmann, Siegmann, Wersebe, Claussen, & Muller- Schimpfle, 2005).

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Table (3-1) A summary of the main screening trials which investigated the superiority of FFDM over FSM in breast cancer detection.

Study Author Participants number Study results

Chiarelli et al. (2013) 220520 women by DR, 64210 by CR and 403688 women by FSM

DR and FSM are equivalent, CR showed lower cancer detectability.

Hambly et al. (2009) (INBSP* Study)

35204 women by FFDM and 153619 women by FSM

FFDM has significantly higher cancer detectability and recall rate. Vigeland, Klaasen, Klingen, Hofvind, and Skaane (2008) (Vestfold Study) 18239 women by FFDM and 324763 women by FSM FFDM has statistically significant higher cancer

detection with fewer recalls due to technical issues.

Heddson, Ronnow, Olsson, and Miller (2007)

52172 two-view examinations of 24,875 women. 25901 by FSM, 9841 by photon counting DR, and 16430 by CR.

DR has higher cancer

detectability than FSM but this is statistically non-significant and significant lower recall rate and MGD.

Del Turco et al. (2007)

14385 women by FFDM and 14385 women by FSM

FFDM has greater detection rate but higher recall rate than FSM.

Skaane , Hofvind, and Skjennald (2007) (follow up of Oslo II)

16985 women by FSM and 6944 women by FFDM

FFDM has significantly higher cancer detection rate.

Pisano et al. (2005) (DMIST** trial)

42760 women screened by both FFDM and SFM

Both have equivalent detectability. FFDM more accurate for dense breast and (>50 years) women Skaane and Skjennald (2004) (Oslo II trial) 18054 women by FSM and 7209 women by FFDM

FFDM showed higher but non- significant cancer detection rate.

Skaane, Young, and Skjennald (2003) (Oslo I trial)

3683 women underwent both SFM and FFDM (two view for each breast)

Both FFDM and FSM showed comparable cancer detection rate.

Lewin et al. (2002) 6736 women underwent both FSM and FFDM

No statistical difference between them and fewer recall rate with FFDM.

*Irish National Breast Screening Programme. **Digital Mammographic Imaging Screening Trial.

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