Artifact in Computed Tomography - Coursework Example

0 Introduction Many sectors in the world have experienced major developments as a result of increased technological advancements. The health sector, through the development of medical imaging is among those sectors that have benefited from increased technological developments in the world today. With the use of Computed tomography (CT) many physicians have been able to come up with important diagnostic information. Although the process has been successful, a number of images production artefacts have been raised to do with high amounts of radiation, high resolution detectors and scattering (Boas and Fleischmann, 78). There four artefacts attributable to this situation include; hardening of beam- based on physics, motion influencers- based on the patient, insensitive detectors- based on the scanner, and spiral interpolation- based on the spiral. Out of the four artefacts the easiest to remedy will be motion-influencers- the one based on the patient since it is easy to see to it that the patient makes no movement during the scanning process (Yazdi and Beaulieu, 108). In this paper a special attention will be given to the four artefacts and propose ways through which the situation can be handled. 2.1 Major Artefacts and Remedies 2.2 Ring Artefact This is a form of artefact evident in the case of a dark circle in the center of rotation mostly as a result of a problem in the detector of a scanner. In this case, the dark circle is known to distort the quality of the image through coronal views or transversal slices (Barrett and Keat, 81). This is a major problem since distortion of the image leads to incorrect readings, mainly from the angular positions. Research has additionally shown that the use of a wide window can remove confusion with the presence of a disease that may be present in the image taken. What has been realized is that an effect on the detector simultaneously affects the quality of the CT image may not be of help in this situation. To deal with the situation, one need to ensure that he/she is using the right scanner that is able to trap clear images without alteration. In addition, one will be required to select the best calibrates that have been tested and proven effective (Barrett and Keat, 84). If these cannot be met, one may have to consider completely replacing the detector. 2.3 Patient Motion Artefact This scenario can be explained under two major points. First is voluntary where an individual has control and second is involuntary that cannot be controlled by the individual. Examples of these scenarios include respiration and bowel movements respectively (Barrett and Keat, 84). When patients are exposed to pain, they also show some kind of movement bringing about this kind of artefact. In form of images, the artefact can be spotted in form of vague images, caused by a change in the patient’s sitting position. In the case of movement, the strikes follows suit but now between the contrast edges and the position of the x-ray tube. Technology has enabled physicians to be able to scan a patient’s heart whilst in the diastole process and also within a single heartbeat. This reduces the artefact caused by the cardiac and also paves way for an analysis of coronary arteries (Leschka et al. 187). The process can also be taken at a higher level through the use of high-speed scanners as they captures the intended image before the patient can move. To reduce this artefact further, a special reconstruction technique may be used as this may eliminate body motions that are rigid mostly in the case of CT scans on the head. To minimize or eliminate movements during this process, the physician can arrange good position areas, sedation of pediatric patients and the use of immobilization aids in a bid to inform the patient of the dangers of movement during the process. It will also be important that the practitioner educates the patient on the various ways through which they can minimize or completely eliminate movements during the scanning process as this would reduce risk (Boas and Fleischmann, 95). The practitioner can also educate patients on the merits and demerits of making movements during the process as this would serve to explain the seriousness of the process to the patients. 2.4 Artefact resulting from Metals Many CT researches have shown metal artefacts to be a common problem, especially in the situation where the patient has visible metallic objects. In such a situation, dark streaks are evident. The image can also show different signs when there is a tilt in the patient’s positions hence the exclusion of interesting axial slices (Hengyong and Ge, 14). This has led to the development of a technique in the name of Metal Deletion Technique (MDT) in a bid to eliminate this artefact. MDT has shown such a great success since it helps in projection of raw data and goes ahead to rely on non-metallic high quality data in the reconstruction of non-metal portions of the image. It is worth noting that the ultimate remedy to this form of artefact would be to ensure that the patient remains in the same intact position during the scanning process. Remedies proposed will therefore heavily relying on ensuring that the patient does not change position during the scanning exercise. This being done, the pixels of the metal can now be removed from the developed image and an immediate replacement with values projected done (Boas and Fleischmann, 98). 2.5 Beam Hardening Artefact If we take the case of objects with high attenuation, we find out that there can be the creation of dark streaks resulting from scattered radiations. In addition, there may also be the production of white and dark streaks mostly in adjacent positions to each other in the same high attenuation object. The hardening of the beam is a common practice where the x-ray passes through the body. The chemistry behind this phenomenon is that x-ray photons with low energy get attenuated with ease as compared to those with high energy. Elements such as metals have high atomic numbers and high energy and hence are not easily attenuated (Jiang, 18). In CT imaging, scattering is seen to result from a change in the direction and energy of x-ray photons and this leads to the dispersion and detection of photons from different sources. As a result, there is the exaggeration of the total number of photons counted and hence poor results. Practitioners have tried to address this problem by developing modern scanners with the capability to state the level of beam hardening on average. Correcting the case of metals with a high number of atoms becomes a challenge since the results show a higher level of hardening than usual. To address the situation, iterative reconstructions may be put in place, such as the use of bowtie filter that brings consistency and uniformity in the detector thereby reducing the effects of the artefacts in form of hardened beams. Additionally, the effects can be remedied through the use of correction software that seeks to reduce the effects of beam hardening and consequently improving the proximity of densities in the soft body tissues (Goldman, 52). In this case, the amount of scattering can be examined and have the effects subtracted from results obtained from the detector. The other remedy that has been offered to this specific artefact is that of iterative reconstruction of the image (Joseph, 26). In this case, an image from previous iteration is used to estimate the mode of scatter correction hence the attainment of good clear images. 2.6 Noise Artefact In CT imaging process, noise is seen to be as a result of striking of the detectors by the released photons. This is experienced in the situation where the patient assumes a bad position during the scan. The artefact could also result from unintended speed scan speed or techniques that give improper exposures to the patient in consideration. Theoretically this scenario can be explained to result from the reduction in the number of photons that initiates increased noise leading to what has been referred to as the streak artefact. To remedy the situation, the attendant should ensure that the patient assumes a good position and also overlook on the issue of exposure techniques. The attendant may also overlook on the speed of the scan through the use of adaptive filtering algorithms that act to reduce noise from the detectors. 2.7 Artefacts away from the field This is a form of an artefact resulting from the reconstruction of suboptimal algorithms. The artefact has been on the rise given that many modern scanners are known to generate pixels at the field of view’s edge in the situation where there is an extension-away from the field of view of the object in consideration. To fix the situation there should be the introduction of advanced reconstruction algorithms and the use of relatively smaller fields than the object may be used to obtain clear and precise images (Boas and Fleischmann, 101). Theoretically, the use of smaller fields of view than the object is known to reduce the dose of the radiation hence better images. Practitioners have also thought of reducing the size of the object in consideration but this did not produce good results since most of the objects got retarded or damaged when they were reduced. 2.8 Artefacts related to Partial Volumes When calculating the number of CTs it is important to consider the coefficient of linear attenuation, especially the one related to voxel of the tissue. In this case, there will be a simple calculation if only one type of tissue is witnessed in the voxel. In the situation where the voxel is dense bone, the number of the CT will be computed at 1000. On the other hand, a situation of three or more tissue types requires the use of partial volume averages. This can be seen in the case where the numbers of a CT are close together, like in the case of blood where the white matter has 46, the grey matter has 43 and the overall CT number is 40 (Nukaga, Kitazawa, and Kamimura, 43). If we were to compute the CT number of voxel with the numbers above, we find that the result will be the average of the three numbers amounting to 43 (40 + 43 + 46 / 3). Here, we realize that the quality of the image can be degraded as a result of partial volume averaging leading to partial volume artefacts. The resultant effect is a poor image quality as the image comes out in form of rings and streaks. Various methods have been provided as remedies to the partial volume artefact. First is through the use of thin slice scans. Using tin scans ensures that the image is not impaired as light goes through the tissues and also increases the speed through which light has to go through. Second is through the use of computer algorithms. Manual algorithms are seen to be faced with many challenges related to obtaining and interpretation of data. With the use of computer algorithms, practitioners will be assured of getting correct and precise interpretations that will help in explaining the true nature of the image obtained (Nukaga, Kitazawa, and Kamimura, 46). The use of adaptive filtration has also been proposed as one of the best methods that can be used to remedy the effects of partial volume artefacts. This method has shown effectiveness since it can be used to resample the information obtained to a lattice with a greater emphasis on the density of the sample used. The resultant effect is the smoothening of the attenuation profile, especially on those areas with high attenuation before the image can actually be reconstructed. Works Cited Barrett, JF, and N Keat. "Artifacts in Ct: Recognition and Avoidance." Radiographics : a Review Publication of the Radiological Society of North America, Inc. 24.6 (2004). Print. Boas, F.E, and D Fleischmann. "Ct Artifacts: Causes and Reduction Techniques." Imaging in Medicine. 4.2 (2012): 229-240. Print. Cone-beam Composite-Circling Scan and Exact Image Reconstruction for a Quasi-Short Object. International Journal of Biomedical Imaging, 2007. Internet resource. Read More