**6. Image display**

Image display of digital images can be performed with a laser printer onto hard copy "filmlike" medium or viewed on high-resolution computer monitors. Regardless of display type, it is important to know how the image is being seen relative to its full spatial resolution. Commercial laser printers for digital mammography can support spatial resolutions, grey scale and optical density similar to mammographic film. If the images are printed with a laser printer, it may be done with 8, 10, or 12 bits per pixel displayed. If a digital mammography system uses larger bits than the printer, there will be loss of the dynamic range of digital image and the contrast scale will be compressed (Pisano et al., 2004). Consequently, not all the shades of grey can be displayed. If more than one version of the image is needed to display a finding, another image may need to be printed and this is a disadvantage. However, an advantage of laser-printed film is that it allows radiologists to use the same reading and workflow protocols as SFM.

Softcopy display is performed with high-resolution mammography monitors that allow the flexibility of image display and contrast. An early study by Pisano et al. compared the speed and accuracy of the interpretation of Fischer digital mammograms on softcopy versus those on laser-printed film (Pisano et al., 2002). In the study, 8 radiologists interpreted 63 digital mammograms both on a prototype softcopy display system and on laser-printed film per the manufacturer's recommendation. All studies had comparisons for review. All

maximum contrast adjustments by clipping and renormalizing the histogram (Pisano, 2000;

Unsharp Masking (UM) is a post-processing technique that is created by subtracting a lowpass filtered version of the original image from the original image (Chan et al., 1987). This process enhances high frequencies in the image such as calcifications and mass edges. A disadvantage of UM is that it also adds noise to the images. Also, it may falsely enhance a margin of a mass (i.e. an indistinct mass may appear more circumscribed and lead to inappropriate classification and follow-up of a mass instead of the need for a biopsy)

Peripheral Equalization or Peripheral Enhancement (PE) is a post-processing technique developed to improve the visualization of the less compressed (and over penetrated) outer edges of the breast. A filter is used to obtain a blurred version of the mammogram representing tissue thickness. This blurred image "mask" is scaled from 0 to 1, and the mammogram is divided by means of the mask values on a pixel-by-pixel bases (Byng et al., 1997). The applied algorithm acts on the pixels in the breast and where there is a thickness change. The result is that the pixels near the periphery are changed so the image becomes

Image processing is a vital component of digital mammography. We may find that it may take more than one algorithm and not necessarily "film-like display" to evaluate for masses, distortion and calcifications. Image processing algorithms are currently not assessed as part of QA protocols. However, they should be to ensure the image chain is working optimally. Automated systems may be of great importance for efficient use of technologist and physicist time in QA and QC. There is a great need to continue to develop and evaluate this

Image display of digital images can be performed with a laser printer onto hard copy "filmlike" medium or viewed on high-resolution computer monitors. Regardless of display type, it is important to know how the image is being seen relative to its full spatial resolution. Commercial laser printers for digital mammography can support spatial resolutions, grey scale and optical density similar to mammographic film. If the images are printed with a laser printer, it may be done with 8, 10, or 12 bits per pixel displayed. If a digital mammography system uses larger bits than the printer, there will be loss of the dynamic range of digital image and the contrast scale will be compressed (Pisano et al., 2004). Consequently, not all the shades of grey can be displayed. If more than one version of the image is needed to display a finding, another image may need to be printed and this is a disadvantage. However, an advantage of laser-printed film is that it allows radiologists to

Softcopy display is performed with high-resolution mammography monitors that allow the flexibility of image display and contrast. An early study by Pisano et al. compared the speed and accuracy of the interpretation of Fischer digital mammograms on softcopy versus those on laser-printed film (Pisano et al., 2002). In the study, 8 radiologists interpreted 63 digital mammograms both on a prototype softcopy display system and on laser-printed film per the manufacturer's recommendation. All studies had comparisons for review. All

"flatter" across the mammogram and the periphery appears less black.

Karssemeijer, 2010).

(Pisano et al., 2000).

area of digital mammography.

use the same reading and workflow protocols as SFM.

**6. Image display** 

radiologists read both conditions with at least one month between reads. Six cancers, 13 biopsy-proven benign lesions, 23 probably benign findings and 20 normal cases were included. The results demonstrated that softcopy display interpretations tended to be faster than film: mean time 34 seconds versus 40.5 seconds. In contrast, the ROC curve and sensitivity favored film (0.67:0.71 for film and 0.65:0.69 for softcopy). Specificity was slightly higher with softcopy (0.563 versus 0. 528), but not significant (Pisano et al., 2002).

With specificity of softcopy as a concern, a retrospective study comparing the specificity for calcifications in digital mammograms using softcopy versus film was performed by Kim et al. in 2006 (Kim et al., 2006). Eight radiologists reviewed 130 biopsy-proven cases of calcifications on softcopy and screen film. For each condition, the radiologists were asked to rate the probability of malignancy on a 5-point scale. For film, the radiologists could use a magnifying glass for further evaluation of the images, and for softcopy they could "roam and zoom" to manually window for contrast. The study concluded that there was no statistically significant difference in specificity achievable using softcopy digital versus screen-film mammography.

For radiologists using softcopy display for interpretations, appropriate room ergonomics and viewing conditions are absolutely necessary to minimize radiologist distractions and fatigue. Vendors need to continue developing hanging protocols and other tools that allow the radiologists to view all digital images with little manipulation of buttons or clicks of the mouse.
