Evaluation of radiological images is the key to an accurate medical diagnosis and hence bears significant importance in radiography. When a radiographer is required to image a particular organ, there must be certain procedures followed which would ensure the quality of the image. Otherwise, the quality of the image may be compromised in such a fashion that diagnosis from the image plate becomes either erroneous or impossible (Barten, 1999). Since evaluation of the radiographic image depends on visual appreciation of the apparent image on the radiographic plate, a good quality image would need to fulfill certain physical criteria for an accurate diagnostic yield, although some parts of it are contributed to by technical soundness of the process of imaging and some are contributed to by the factors essentially related to the patient. Whatever may be the reason, a poor image quality compromises the diagnostic yield, and in some cases, a reading or a diagnosis is not possible, where the radiographic plate needs to be rejected, and re-examination is mandated (Beutel et al., 2000). In this assignment, an evaluatory report of a radiographic image will be presented with a critical discussion about the reasons for it being discarded and a re-examination being recommended.
Criteria for Image Evaluation
While evaluating an image, it must be borne in mind that evaluation of image is dependent on human vision as related to the examiner. Since radiographic images are essentially black and white, it is to be considered that ideal white light has flat spectrum in which all wavelengths of lights are present. In practice white light sources approximates this property. The light which has no colour or is achromatic such as in radiographic plates has only one descriptor, which is its brightness or grey value. This light has a saturation of 0% and it contains only white light. However, when the saturation varies, it becomes difficult to differentiate between two adjacent differing shades of gray which are considered to be mixtures of varying blacks and whites. Therefore, it is also to be noted that equal distances in physical intensity are not perceived as equal distances in brightness. This occurs due to the fact that intensity levels are dynamic and hence must be measured and indicated logarithmically. Intensity levels must be spaced logarithmically rather than linearly to accomplish equal steps in perceived brightness (Dougeni et al., 2007). The most important parameter of an image is its resolution. The perceived resolution is also determined by the imaging process. This means the more the blurring, the less the resolution. Resolution also means sharpness of the image. When it is a small image, a bright point on the dark background will appear as a dot, but normally it would not appear as sharp as it actually is. It will appear smooth, whereas the intended resolution of the image would need it to appear sharp.
While reading an image, the sharpness of the organ delineated becomes very important, and with increased blurring, there would be lower resolution. The imaging system may determine the sharpness or resolution of the image. The characteristics of the imaging system that determine resolution are the focal spots and the amount of the detector blur. There are certain specific criteria of the patient, the clinical condition for which the imaging is being done, his position on the radiology table all contribute to resolution of the radiologic image. The geometry of the area or body part to be examined and other factors such as the shape of the subject, motion, and positioning; and the viewing conditions, (Bushberg et al., 2002) all determine a good resolution of the image. In evaluating the image in this assignment, therefore, certain criteria will be utilised which would justify as evaluative parameters for the diagnosis.
These are contrast, density, resolution, image geometry, image artifacts, equipment variables, patient variables and their impacts on image quality and diagnosis, and specifically