Diagnostic Radiography Image Evaluation - Essay Example

Introduction 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 based on the chosen plate of intravenous urography, the factors related to the contrast agent. The factors which might be involved here will be analysed through the description to justify whether this image will be rejected. The description of ideal conditions would also guide what is needed to be done in order to get a better radiographic image in this patient when a repeat investigation will be done, so a clear diagnosis can be arrived at. This would also provide a scope to define the conditions for repeating the image and ways to improve collimation of the image while repeating the investigation. Report There are multiple gas shadows in the parietal areas of the abdomen which tend to obscure the renal field. The spinal shadow appears very prominent and the intensity of the bone density appears more than that of the contrast shadow. There has been pelviureteric delineation up to L3-4 levels on both the sides; however, beyond that point, it is not possible to visualize the ureters. It is very difficult to comment on this lack of visualization due to superimposition of gas and colonic shadows. Thus given only this film, it is also impossible and unreasonable to comment whether the absence of contrast in the ureters is due to some obstruction at any point below the pelviureteric junction (Carter, 2006). The control film has not been provided, but as expected, this would also demonstrate similar gas shadows. It is also apparent that there would be a series of films that would follow this film, which are not provided here. One point is very clear. The patient has a large size, and there is no comment whether any augmentation through abdominal compression was done for this patient. One of the commonest causes of such obstruction is presence of an obstructing stone, which classically appear as a filling defect in the IVU series. A possible presence of such stones cannot be ruled out confidently due to superimposition of the gas shadows. It may also be the fact that there are obstructive lesions at the cystoureteric junctions, which have not been captured in the current film. Briefly, all these factors combined together, namely, poor patient preparation, inadequate exposure, inappropriate machine settings, inaccurate field of exposure provide sufficient reasons for a repeat examination, more so due to the fact that this imaging may overlook a potentially treatable lesion. Given the large size of the patient there must be an appropriate machine setting which can bring about the best possible image quality. Moreover, applying abdominal compression may also improve the quality of image in subsequent views due to retention of the contrast over a more prolonged period of time in the ureteropelvic region (Jansson et al., 2007). Synthesis Resolution The resolution of an image is determined by the imaging process (Jansson et al., 2006). The more is the blurring, the less is the resolution. Factors that contribute to lower resolution are dependent on the characteristics of the imaging system, focal spot, and the extent of detector blur. The scene characteristics are also important determinants of sharpness of the image. By scene characteristics, it is meant the physical properties, size and shape of the object imaged, and the use of contrast agents. These would include the shape of the object, its position, and any motion This means if the subject has a larger size, a big abdomen, or is moving during the examination, all will affect the quality of the image. As evident in this case, the patient has a larger abdomen with the need for a wide area of focus and deeper penetration. The movement was not mentioned in the scenario, but it is quite possible that the patient had been moving during the examination leading to blurring of the image. Use of contrast is routine in intravenous urography, and contrast would improve the resolution, hence quality of image of the focus area. It is also contributed to by the viewing conditions. Classically optical transfer function which indicates the frequency of light in the image has been utilised to define resolution (Persliden et al., 2004). Some disorders produce faint shadows in radiologic plates. These faint shadows are due to small amplitude lights. For an effective diagnosis, it is important to recognise these faint shadows in the radiographic image. These are indicated from the number of line pairs per millimeter of the image and are indicated by lp/mm at specified small amplitude (Denby and Heaton, 1999). This is determined by some instrument, but this is a subjective measure of quality of the image, although it has been criticised to be of limited value as the measure of quality. Contrast Contrast is defined by the difference of intensity of adjacent regions of the image (Andrews et al., 2002). The contrast has appeared in the renal pelvicalyceal system on both the sides. A radio-contrast agent has been used to intensify the anatomy of the focus area. Contrast is the difference in intensities of adjacent regions of the image. More accurately, it is the amplitude of the Fourier transform of the image as a function of spatial frequency. Likewise, the imaging processes will influence the contrast. These would include the source intensity, the absorption efficiency, or the sensitivity of the capturing device. The scene properties such as the physical properties, size and shape of the object, and the use of contrast agents all determine the contrast. The viewing conditions also play important parts in quality of the image reading, and these would include room illumination and display equipment. The OTF or optical transfer function, drops off for large frequencies. This expresses relative amplitude of an object as indicated by the frequency of light in the image. This indicates the contrast of very small objects will be influenced by the resolution. A small stone at any constriction point of the ureter including the pelviureteric junction thus may go undetected (Farr and Allisy-Roberts, 1999). The aim of image enhancement is to allow all relevant details to be detected. It is impossible for the human eye to read all the gray shades at once in a single image. This may lead to missing details in the radiographic plate. To allow better diagnosis, meaningful details must have a sufficiently high contrast. As in this plate, the number of gray values is higher, better diagnosis would need higher contrast. Therefore, image enhancement will be necessary. Optimal abdominal compression will distend the pelvicalyceal system. In a bulky patient, application of compression is difficult where it is most necessary. A 10 minute plate would thus be indicated following application of the compression, which would improve ureteral visualization. Sometimes axial tomography should be combined with timed excretory urography performed by conventional radiography. When a filling defect in the pelvicalyceal system is suspected from the initial findings, due to facts that contrast is poor and possibility of a renal tumor cannot be excluded through intravenous Urography, a tomography will increase the rate of diagnosis (Kawashima et al., 2004) Noise The third quality factor of an image is noise. The emission and detection of light and any other process involving electromagnetic waves are associated with noise. Noise is considered to be a random component of the image. If the noise level is high compared to the image intensity of the object, very meaningful information may be lost in the noise. The signal-to-noise ratio and the contrast-to-noise ratio are important determinants of the quality of image. It is to be remembered that both contrast and noise are dependent on frequency (Hendee and Ritenour, 2002). For example in this radiograph, the noise created by the colonic gas shadows and the colonic wall soft tissue structures will limit perception of low-contrast details in the plate. This noise may normally be produced by the fact that radiographic images are projection images where multiple structures are superimposed. Artifacts Artifacts are artificial image features. These may appear as streaks or image distortions that may compromise the quality of the image and hence interpretation of the anatomical area. Artifacts are known to hamper diagnostic accuracy and may yield incorrect measurements (Kyriakou et al., 2009). Therefore it is important to repeat the investigation for avoiding them and to understand their origin. It has been recognized from imaging principles that it is physically impossible to distinguish all gray values in a single image and hence diagnostic information may not be total in a single film. Taking the example of, this intravenous urogram is therefore not suitable to extract all information necessary. There is no apparent artifact in this image plate, but the reading of gray scale shadows has been rendered virtually impossible with the coincident gas shadows with a different superimposing gray scale shadow over the possible pertinent findings. This all the more indicates a repeat investigation of this patient (Spendiff and Rockall, 2008) Equipment Variable It is known that to produce an x-ray image from an attenuated x-ray beam, there is a necessity to capture the x-ray beam. This capture is then converted to image. Consequently, apart from the machine, the photographic films are very efficient in capturing x-rays. Apparently, while considering these variables, only 2% of the incoming x-ray photons create the image output. This percentage of the photons would correspond to the probability of the quantum to be absorbed by the detector, which is known as absorption efficiency. Also, another point to consider is that a low-sensitivity film for the x-rays would lead to large patient dosage that may become prohibitive or associated with complications. In this regard, phosphorescence of the film must be prohibited in order to avoid undesirable effects, may be through the use of filters in order to avoid film fogging and ghost images. Although these specifications are not mentioned, there is a high probability of such problem in this film, which indicates the need for further imaging (Guy and Ffytche, 2005). There are several equipment variables for a quality image. The size of the focal spot is the first important parameter. The anode tip should make large angles with the electron beam in order to produce a reasonably focused beam of X-ray. The light scattering properties of the fluorescent screen is the second important parameter. The grain size of the film also determines resolution. The resolving power of clinical screen-film combination would normally vary from 5 to 15 lp/mm, which would yield a 10% contrast. The image is sufficient to read, however the size of the image would determine that. Contrast in the image can be defined as the intensity difference in the adjacent regions of the image, which obviously is lacking in this study. The image intensity is also a byproduct of the attenuation coefficient and thickness of different layers of tissue that is encountered along the line of projection. It can thus be reasoned that since the attenuation coefficient is dependent on the energy of the incident X-ray beam, the spectrum of the incident beam has important bearing on the contrast, and a soft radiation would yield a higher contrast than a harder radiation contributed to by higher absorption efficiency. It seems none of these parameters were fulfilled in this imaging and hence there is a reason to repeat the study (Kim and Horii, 2000). Patient Variables The patient is an important consideration. The size and preparation of the patient and their importance in such investigation are important, and these have been highlighted earlier. Although there is no information regarding the size of the patient, thicker patients cause more x-ray scattering, which would deteriorate the resolution of the image. In such patients, the scatter would have been reduced by use of a collimation grid in front of the screen so the grid will allow only the photons with low incidence angles to reach the screen (Sonka and Fitzpatrick, 2000). Bigger size, continuous patient movements, and even low nonperiodic motion such as peristalsis would cause blurring of image. Abdominal compression and patient counseling about the need for momentary standstill may lead to improved quality of images in such situations. Factors Related to Contrast Agent Urography is a set of dynamic radiographs, and it should ideally be done with an image intensifier that can be viewed on a monitor and exposures taken, although other way of doing it is a sequence of static radiographic images. When x-ray images are taken, the differences in attenuation of various nonbody matters are usually too small to distinctively recognize. A contrast agent is a substance with high attenuation coefficient, and these are classically used in intravenous urogram. Despite use of a contrast agent, the quality of image is poor due to accompanying radiodensities of the surrounding organs (El-Diasty et al., 2003). Other added views such as lateral views and addition of tomography will also improve the diagnostic yield. Conclusion In conclusion, this study could be repeated with a use of a larger x-ray plate to accommodate the size of the patient. During the investigation, it is also imperative that the patient does not move. 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Appendix History of the Patient The patient is a 45-year-old male with history of haematuria referred for investigation and radiologic imaging studies of the kidney to indicate any possible renal cause or any other pathology involving urinary tract. Description of Investigation The patient was cooperative during the examination. The investigation suggested was a standard intravenous urogram (IVU) series. In the beginning and following positioning, the patient was subjected to a controlled image. Then the contrast was injected, and a 5-minute film was taken with the following instrumental parameters. Imaging Factors A standard CR cassette was used with the bucky with 80 kV energy, the AEC with a broad focal spot from a 100 cm distance (SID) and with a standard 70% tube loading. The resultant image has been given below. Read More