Critical Evaluation of the Impact of Digital Imaging - Essay Example

?CRITICAL EVALUATION OF THE IMPACT OF DIGITAL IMAGING Radiography has been traditionally used in the field of medicine to produce images of human body parts. It is commonly used for both diagnosis and treatment of patients’ conditions using x-rays (Davidson 2007). Through the years of medical innovations, the generation of medical images has evolved from using plain radiography to more advanced nuclear medicine applications. This paper is intended to present the basic types of medical radiography. The comparison of the types of medical radiography will only be limited upon the use of x-rays for film, digital and computed imaging. Nature of Medical Radiography The use of radiography in the field of medicine is often termed as x-ray technology. It usually involves sophisticated instruments to take photographs of the human body parts (Gateway Community College, 2012). Furthermore, medical radiography is also defined by the US Food and Drug Administration (2010) as a “a technique for generating and recording an x-ray pattern for the purpose of providing the user with a static image(s) after termination of the exposure”. Moreover, radiography may also be used during the planning of radiation therapy treatment since low energy x-rays have been observed to produce good effects on skin therapy and other health conditions. However, the long term exposures can possibly induce cancer, fetal and hereditary effects but the long term risk to an individual is low. This field is often distinguished from mammography, fluoroscopy, and computed tomography which are also types of x-ray imaging. The discovery of x-rays has given birth to medical imaging that we take advantage in the present age. Linton (1995) explained that the principle behind this technology is solely based upon the recognition that body parts absorb a beam of X-rays according to their density. In effect, an image is produced which allows the identification of body structures and is very useful in the recognition of abnormalities that can be an indication of an injury or a disease. The earliest medical x-ray images has successfully aid mostly the surgeons to locate bone fractures and displacements, gallstones, kidney stones, and bullets or metallic objects. However, the inside images of the organs have never been achieved which became a challenge to most of radiation scientists. This dilemma has lead to the discovery and development of more advanced modes of diagnostic imaging using x-rays. Medical imaging using general radiography The most basic type of imaging for diagnosis is famously known as general/projection radiography. Generally, x-ray intensities that exit the body are recorded for viewing and storage. The image generated may be recorded using different media. The recording media used usually defines the type of general radiography (Davidson 2007). Film/Screen (F/S) radiography: This type of radiography utilize films in combination with intensifying screens developed by Thomas Edison (Haus and Cullinan 1989). The purpose of the intensifying screen is to convert the x-ray energy to light. The increased efficiency of exposure of the film over exposure directly by the x-ray beam helps lower the risk of x-ray absorption of patient during exposure (Davidson 2007). The screens are usually made of scintillating material like phosphor which can reduce radiation dose to patient by a factor of 50. (Kanal 2010). X-ray films are designed to be sensitive to the specific spectral emission of a given intensifying screen. Consequently, films and screens are matched for optimized efficiency of conversion of x-ray photons to optical densities on the film (Davidson 2007). The factors that are usually considered in F/S radiography are the optical density (OD), conversion efficiency, F/S latitude, and contrast. Fauber (2007, as cited in Davidson 2007, p. 12) showed that optical density (OD) can range from 0.20 to 4 (maximum wherein the light intensity is high). Another characteristic of F/S combinations is F/S latitude. The dynamic range of an x-ray film is equivalent to the film’s latitude. Digital radiography: This type of radiography is sub-divided into three various types of detectors: the computed radiography (CR), direct digital radiography (DR) and indirect radiography. In contrast with F/S radiography, x-rays are absorbed by the digital detector and transformed into electrical charges. The latter are digitized and quantified into a gray scale which is sent to post-processing software to produce a clinically meaningful image. The images are then sent to archives to update the patient’s demographic information (Kanal 2010) while S/F images are reviewed and processed manually. Computed radiography (CR) is a cost-effective solution to move from analogue to digital imaging. With CR, X-ray cassettes (which use X-ray film) are replaced with CR cassettes (which use imaging plates). The processing of image is done thru a reader that can immediately display the image and erase the imaging plate for reuse (Siemens Medical Solution, 2006). Direct radiography (DR) is a cassetteless technology wherein x-rays are converted into electrical charges by means of a direct readout process. It uses an x-ray photoconductor, such as amorphous selenium, that directly converts x-ray photons into an electric charge (Bushong 2001). The cassette is replaced with an electronic detector that captures the radiographic image and sends it directly to a display screen for review (Relner et. al. 2005). Indirect radiography has a two-step process for x-ray detection. The process starts upon striking of x-rays into the scintillator - the primary material for x-ray interaction – to produce energy and convert it into visible light. The light emitted is then converted into an electric charge by means of photodetectors such as amorphous silicon photodiode arrays or CCDs. The electric charge pattern that remains after x-ray exposure is then processed and displayed same as with the DR (Chotas et. al. 1999). Comparison of image quality The display of image for F/S usually has the lowest quality compared to digital imaging. However, according to Ewert et al. (2007) this has been improved over the years upon optimization of medical film systems for low patient dose and medium. Special film systems yield also high image quality (e.g. mammography films). In F/S, radiographers may produce a radiographic image with high contrast or a radiographic image with low contrast. Radiographers cannot produce high and low radiographic contrast of a single image at the same time. Two films must be used which can be advantageous during preparation and image processing (Davidson 2007). In recent years, digital imaging has challenged the traditional film imaging for projection radiography in terms of technical and economic feasibility, not to mention its higher image quality output. The high luminance and high-resolution display monitors are one of the factors that significantly increase the quality of image produced (Kodak 2000). Furthermore, Kodak (2000) indicated that the optimal digital systems are better than those of best film-screen and CR systems because of its high spatial and contrast resolution as well as its dose efficiency. For computed radiography, an advantage of CR over F/S is the increased dynamic range of CR images. The CR’s greater dynamic range through manipulation of the displayed brightness and contrast of the image can be taken advantage during reviews. For anatomical regions viewed within the field of x-ray, attenuations can be better visualized using one exposure of ionizing radiation to the patient (Davidson 2007). In the field of mammography and teeth radiology, new high definition CR-systems (HD CR) was developed. These HD CR-systems with spatial resolutions better than 25 ?m have the potential to substitute the film radiography also in the low X-ray and low wall thickness region. CR uses the image plate systems which has high linearity, dynamic range, and sensitivity. Furthermore, it can be reused for 1000 exposure cycles (Ewert 2007). The displayed brightness and contrast during anatomical region viewing can be adjusted within the image. Direct converting systems are characterized by a higher inherent spatial resolution than the systems which use fluorescence screens. Flat panel systems substitute film radiography and radioscopy systems and open new possibilities for the application of computed tomography (CT). These techniques are not applicable for CR and film based techniques. Therefore, this system permits low noise imaging in radiography and pave the way for new applications which require extra high contrast, sensitivity and wall thickness dynamics in the images (Ewert 2007). Moreover, DR has two to three times lesser radiation dose compared to CR (Davidson 2007). The Dental Evaluation and Consultation Services (DECS) of the United States Air Force (2008) presented some of the considerations for digital imaging. Firstly, the spatial resolution in radiography is generally stated in line pairs per mm (lp/mm). The naked eye can usually perceive between 8-10lp/mm which makes digital imaging suitable for viewing with a perceived range of 8-15 lp/mm. Secondly, shades of gray in images can be represented by a pixel. The number of grays available constitutes the dynamic range or commonly known as contrast resolution. This may be stated as the actual number of grays or it may be stated as bit depth that progresses in powers of 2. Digital radiography enables you to perform windowing which may provide some advantages. It has been found out that 8 bit data provides very satisfactory images and diminishing returns are obtained from bit depths. Conclusion Digital imaging has clearly overtaken the use of film/screen for the generation of diagnostic images in the medical field. The quality of the image generated using digital radiography has better spatial and contrast resolution compared to the traditional F/S radiography. High quality digital image projections are produced for viewing internal organs and detection of abnormalities in the human body. With the becoming economically competitive cost of digital devices and continuously evolving technical advantages of digital imaging, the acceptance of this technology has increased significantly especially for the medical world. Bibliography Bushong, S.C. (2001) Radiological science for technologists: physics, biology, and protection. 7th ed. Mosby, St. Louis. 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