Basic physics and principles of making a great image: Part 1 (Proceedings)


Basic physics and principles of making a great image: Part 1 (Proceedings)

Aug 01, 2010

Aside from ultrasound, a digital radiography suite is going to be the most expensive upgrade for the private practitioner in the realm of diagnostic imaging. However, this expense will be well worth the investment from a diagnostic imaging standpoint. After more than a century of film and film screen imaging, the backdrop of diagnostic radiology has changed from hanging films on view boxes to LCD monitors.

X-ray Film (analog)

X-ray film has been the mainstay for diagnostic imaging for over 100 years. It provides a wide range of latitude (gray scale presentation), contrast, speed and detail options and is a durable, portable storage medium. However, it degrades over time, is not easily duplicated and requires physical storage. So why go digital? The digital era is upon us and the veterinary market is ultimately going to be dictated by what is happening in the human market. This trend is not going to go away and film screen combinations will be more difficult to get. A major disadvantage of the film era is the developmental process, which can totally destroy great radiographs (even that had the proper exposure factors and anatomic positioning). In the analog film system, the image capture, processing and the storage of the image are all contained on the film. In digital radiography, these processes are separated. Raw data can be re-processed at any time and reviewed in a variety of formats based on the viewing software and stations used.

What are the digital advantages?

Although multiple advantages of digital radiography (DR) and computed radiography (CR) have been sited, each of these advantages may not be directly applicable in the veterinary market and may not make sense for return on the investment for a given practice. Digital radiography is any digital image acquisition technique where the images are captured, reviewed, processed and stored in a digital environment (computer based). The advantages of digital radiography include: rapid acquisition (with review of images in 4 to 6 seconds for digital radiography plate systems), greater case through put; fewer repeat radiographic exposures (in theory) due to incorrect exposure (although positioning and centering errors still must be corrected for by repeating the radiograph). Additionally, there is a greater dynamic range (more latitude than a gray scale film), advanced processing algorithms (edge enhancement techniques) and the ability manipulate the images. Less storage space is needed, no more lost films (hard drive or optical media storage), no image deterioration over time and no more film chemistry is required. Digital images are easy to duplicate and move around in the cyber world and can be used as a suitable medium for easy transfer of images (such as electronic film interpretation).

Image Formats

Image acquisition consists of an acquisition station within the radiology suite. Pre-processing algorithms are used that have been established by the manufacturer such that the initial raw data is "filtered" and the image presented for initial review rapidly. It is silly to think that all of the quality control goes away with the digital era. In fact, if one does not quality control their radiographs currently, the image quality in digital era will be just as bad. The basic image format is called DICOM and has a .dcm tag associated with the file. DICOM stands for digital imaging and communication in medicine. This was an industry agreed upon standard and currently the American College of Radiology is using DICOM 3.0. Within each image, all patient data is saved along with the image data. These images are not secure, encrypted or protected (that is why it is an industry standard). Do not send images in .jpg (photography file format that allows for lossy compression) but in DICOM format for review in teleradiology or if saving images to a CD, etc. There are several freeware software packages for review DICOM images. These include Dicom works (PC) and Osirix (Mac).

Digital radiography systems

There are currently three basic types of digital radiography systems. Digital cameras or digitizing images of films will not be discussed as this is not digital radiography! These systems include: hybrid systems, computed radiography systems, digital radiography systems (direct and indirect).