iaea human health series publications - SEDIM

2.3.8.1. Soft copy displayFlat panel liquid crystal displays (LCDs) are more compact and produce far less heat than do conventionalcathode ray tubes (CRTs); however, they have a more limited viewing angle than do CRTs. The display must havea suitable number of high quality monitors (normally two 5 megapixel (MP) monitors are recommended) [31] toallow viewing of as much of the mammogram as possible at the required resolution level. A 5 MP monitor iscapable of displaying only a single mammogram with 100 μm dels at full resolution. If multiple images or imageswith smaller dels are displayed simultaneously, as is normally the case in mammography, they will have to beviewed at a reduced resolution and the images panned and zoomed to inspect structures of interest at full resolution.The monitor on the acquisition workstation is often overlooked. Generally, a single 3 MP monitor isrecommended. The quality must be high enough to allow the radiographer to assess the adequacy of the acquiredimage without having to walk to the radiologist workstation, which may be located a considerable distance away. Ifneedle localizations are to be performed on the system, the image quality of the acquisition monitor and associatedimage manipulation operations must be adequate to provide the required image quality.Display software varies greatly between system types and is a major factor determining user satisfaction withthe digital mammography system, where there is a natural tension between the intellectual property interests ofmanufacturers and the need for seamless integration between different systems. Some important questions whenconsidering monitor software include:— How convenient are basic image manipulation operations, especially those that will be used with everyimage?— What is the flexibility of image hanging protocols?— Can the system handle images acquired on another vendor’s system and display them at an acceptable level ofquality?These issues, particularly the last, have taken on greater significance as digital mammography has becomemore widely accepted, with facilities increasingly purchasing multiple acquisition units. To address these issues, theIHE [19] is developing guidelines and standards in the form of an integration profile for image display andintersystem compatibility for mammography. Future purchases should comply with this profile. Ongoing activity inthis rapidly developing area can be seen at the IHE web site (http://www.ihe.net). In a screening situation, automaticfetching and display of prior images is highly desirable and increases efficiency. Image annotation (patient name,etc.) must be displayed such that it does not obscure the breast image.2.3.8.2. Hard copy displayHard copy display systems produce a printout of the digital image on radiographic transparent film. Theradiographer usually adjusts the image brightness and contrast before printing out the image, making use of thecontrols provided at the acquisition workstation. Hard copy image displays have the disadvantage of not allowingthe radiologist to control image processing operations during viewing. Therefore, it is strongly recommended thatimages be displayed for interpretation on a high quality soft copy device. Nevertheless, some facilities will chooseto perform hard copy interpretation. In other cases, it may still be necessary to provide hard copy printed images toreferring physicians. In this respect, several studies that compared the interpretation of digital mammograms usingboth hard and soft copy formats did not find significant differences in diagnostic accuracy [32, 33].Both wet and dry laser imagers are available and produce breast images of similar quality. However, wet laserprinters require chemical development, which is expensive, contributes to environmental pollution and requirescareful QC to maintain consistent image quality. In addition, dry laser printers are preferred due to their stability.Most manufacturers have discontinued the production of wet laser printers.The spatial sampling (resolution) of laser imagers should at least match the del size, thus the printing deviceshould not be the limiting factor [19]. Using too low a resolution for printing results in pixelation; that is, printedfilm with large, coarse looking pixels and an image that is magnified to an unrealistic size. Using too high aresolution (pixels smaller than the mammography system can produce) increases the file size and slows printing ofthe image. Most of the commercially available printers for digital mammography have two pixel sizes, 100 µm and50 µm or smaller (around 600 dots per inch) with a pixel bit depth of 12 or 14 bits.15