Consequences of digital imaging in radiography

Chapter 36 Consequences of digital imaging in radiography



Chapter contents



36.1 Aim 265


36.2 Image processing 265


36.2.1 Data clipping 265

36.2.2 Plate sensitivity 266

36.2.3 Edge enhancement 266

36.2.4 Magnification 266

36.2.5 Image annotation 266

36.2.6 Image stitching 266

36.3 Image storage and retrieval 266


36.3.1 Patient demographics 266

36.3.2 Sign on and password 266

36.3.3 Bedside image retrieval 266

36.3.4 Case conferences and teleconferences 267

36.3.5 Teleradiology 267

36.4 Picture archiving and communications systems (PACS) 267


36.5 Digital imaging and communication in medicine (DICOM) 268


Further reading 268



36.1 Aim


The aim of this chapter is to introduce the reader to the principal consequences of digital imaging in radiography.



36.2 Image processing


The analogue image produced on a film is not capable of further processing. The digital image, however, is capable of undergoing a number of processes which aid image interpretation. These will now be discussed.



36.2.1 Data clipping


The X-ray pattern which hits the imaging plate covers a wide range of exposures. Processing all this data into an image would produce an image of very low contrast which would make image interpretation difficult. For this reason, an algorithm is applied to the image depending on the area of the body selected by the radiographer when inputting the patient data. This algorithm discards data which are not of clinical interest to the examination and so increases the contrast of the image produced. The effect of this ‘data clipping’ is shown in Figure 36.1.


image

Figure 36.1 Graph to show the effect of ‘data clipping’ on the contrast. The contrast is represented by the gradient of the coloured line. The black line shows the image as it would be displayed without data clipping. The blue line shows the data as displayed if only pixels with a value between 50 and 150 are used to produce the image. Note the increase in gradient compared to the blue line.



36.2.2 Plate sensitivity


Once the system has clipped the data to data of clinical interest, it then has to correct the image for overall exposure. This is possible because of the linear response of the imaging plates to exposure. This is done by applying a formula which defines the average exposure within the clinically useful range. This is given a different name by different manufacturers – S number (Fuji), Exposure index (Kodak), LogM (Agfa), etc. Thus, if the plate has been overexposed, an image can be produced which has the correct density range displayed on the monitor. The principles behind this are illustrated in Figure 36.2.

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Mar 6, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Consequences of digital imaging in radiography

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