This is a text written by Jon Berg <jon.berg|a|turtlemeat.com> spring 2005 in the Computer Science course Medical Informatics at Tromsø University, Norway.
Current and future possibilities of Medical Informatics
10. Imaging systems
Creating images of the inside of the human body has been done for a long time. Techniques used to create these images include x-ray, infrared, sound and other energy. Computer technology plays a part in all areas of using images in healthcare. Computer technology is used in acquisitions, storage, transmission, processing, analysis, management and help to integrate images in the various parts of the treatment process.
Acquisition of images
All digital images used are typically stored as bitmaps. Three dimensional images are stored as voxels, a representation of volume and position in the three dimensional space. One example of the change that is taking place for imaging is the use a 100 percent digitized image creation. Not all uses of imaging in health care today are fully digitized, many still uses real film. X-Ray images were traditionally created by sending X-ray beams through the body and on to an X-ray sensitive film. Today there is the possibility to use digital non-film detectors that capture the X-Rays and generate the digital image. There are other methods to create images, their characteristics differ in how expensive they are to use, and what detailed images they can create. Ultrasound is another method that is cheap to use and have no known side effects to use. More advanced and expensive methods of creating images include CT (Computed Tomography), PET (Positron Emission Tomography) and MRI (magnetic resonance imaging).
The management of storage and retrieval of images still suffers from not having sufficient support systems for using digital images. The lack of support systems for images could result in images from CT and MRI scans that are digital, gets transformed into analog film after being optimized for viewing. The films are then view in illuminated boxes. Images are stored in the departments that deal with the patient for about 6 months, and then they are moved to archival facilities where they usually are stored for at least 7 years. Film is often so expensive that it is recycled for the silver content.
This situation described is not likely to continue into the future. Converting to an all digital management of digital media is the right choice. The improvements with digital management of images is that it is more cost effective, it requires less physical space, it requires less manual labor, and storage and retrieval becomes easier. It will be more effective and easy to work with the images. The reasons for the current situation are likely to be a combination of lack of such systems to do these things, and it is also likely to be because of poor integration with current systems. Often one system is dependent of the other or acts as an integrated part of another system. To have full support in all areas would require that all systems got upgraded. This investment may be unjustified for just adding image support. It is likely that image support will be introduced gradually as the systems are updated or replaced.
The use of digital images puts high requirements for the computer hardware that is going to handle the image data. Images will take up a great deal of storage space. Images can be stored in large databases and retrieved quickly. A typical examination can produce 10 Mb of image data, and considering that a clinic may do several hundreds of examinations per day this will create a lot of data per year. It would be feasible to store many hundreds of GB for a department. Old data may be archived to tapes to save space from the hard drives that store the data that may be used in the near future. Transport of this data from servers to client machines requires a fast network. Image compression can help shrink images and ease the requirements on both storage and transmission of data. For health professionals to use the images effectively it is required that good monitors exist. Working with images is often done by comparing various images. Comparing can be done by having multiple images up on the monitor on the same time. This requires that the monitor is fairly large and have a good resolution. It could also be useful when comparing images to have multiple monitors and have different images up on each monitor.
The primary uses of image processing are in image enhancements, screening, quantitation, three-dimensional visualization and display. Image enhancement is the process of improving images by the use of software. The common enhancements are to sharpen an image, or to maximize the visible are of the image by histogram equalization. In screening the software flags images that should be more carefully investigated. In the automated screening process the software is allowed to have some false positives, as long as it has very few misses on potential detection of actual disease. Quantitation uses software to highlight areas of interest, for example highlighting of hart shape or a fetus head. Three-dimensional image visualization is done in CT and MRI scan.
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