 Hello everyone. My name is Dr. Ashwati Srinil. I am doing my third year residency in Usmani Medical College, Hyderabad, and my topic is Artifacts. In computer tomography, the term artifact is applied to any systematic discrepancy between the city numbers and the reconstruction and the true evolution coefficient of the object. We can seriously degrade the quality of images sometimes to the point of meeting them diagnostically unused. To optimize image quality, it is necessary to understand why artifacts occur and how they can be prevented or affected. Types of artifacts can be divided into physics-based, patient-based, and scanner-based artifacts. Under physics-based artifacts, we see beam hardening, volume averaging, photon starvation, and understanding. First is beam hardening artifact. Because when the beam passes through a dense object, lower-energy photons get absorbed by higher-energy photons are transmitted. The mean energy of the transmitted beam increases and the rays become hardened, resulting in misregistration of them. Two types of artifacts can result from this effect, cupping artifact, and stripping dogma. Such as cupping artifact, where we see the extra passing through the middle portion of a uniform cylindrical factor are hardened, more than those passing through the edges, because they are passing through more material. The mean energy increases, and hence, the center is assigned a lower-hounds weight limit. This can be corrected. Streaks in dark bands, in very heterogeneous cross-sections, dark bands of streaks can appear between two dense objects in an image. This is a beam hardening artifact in test, where we see bright and dark streaks come the SBC due to contrast within, which may sometimes give the appearance of higher-density motion. This can be resolved by use of saline flash. This is a beam hardening artifact in the Portia de Porta, where we see alternate dark and bright streaks in a narrow band extending across the Portia de Porta. Because beam hardening streaks from the dense cul-base follow the acquisition state, when using a non-tilted gantry, these beams can pass through the Portia de Porta. When the reconstructed images are tilted, the streaks appear in multiple layers. Correction uses metal filters to pre-harden the beam, so as to filter out the low-energy photons, periodic calibration correction, use of beam hardening correction software, and tilting the gantry or changing the position of the patient, such that the dense object does not come in the acquisition state. Next artifact is volume averaging of partial volume artifact. It occurs because of the presence of different densities in a waffle and thus the final density is influenced by high-end low-intimation value. It can be caused in a number of ways. One way of partial volume artifact occurs when a dense object lines off-center to towards part 2 into the width of the excavation. Here, when the tube is pointing from left to right, the object is within the beam and hence seen by the detector. While when the tube is pointing from right to left, the object is outside the beam and hence not seen by the detector. Another way is if a dense object can be partially protruded into a detector stream, the attenuation is averaged with a set of things and it will be assigned a lower-hounds period. Here we see a dense object lying in a less dense background and there are 3 detector streams, 1, 2 and 3. In detector stream 2, the object is filling the stream which results in high attenuation. In stream 3, none of the dense object is damaged and hence the attenuation is low. In stream 1, the image is only partially imaged so the attenuation is an average between the dense object and the less dense background. Example, here we see the right upper-low segmental arterial branch appears to have a low attenuating filling defect. Now this is a 16-inch obtained with 5 mm slice thickness. This is a 16-inch obtained with 0.625 mm slice thickness where we see a resolution of the artifact. So correction can be done by the use of thin-acquisition section bits and thus reduces the voxel size. Next artifact is photon-starvation artifact cause when the X-ray beam is travelling horizontally, the attenuation is greatest and insufficient photons raise the detector. This results in very noisy predictions. The reconstruction process has the effect of greatly magnifying the noise resulting in horizontal streaks in the lens. This is seen in a site of obese patients and around their shoulders. This is a statistical CT method cervical spine where we see significant noise and decreased contrast discrimination. Correction, this can be corrected by increasing the tube current but if we increase the tube current the patient will receive an unnecessary dose when the beam is passing through less active parts. How can we overcome this? By the use of automatic tube current modulation and adaptive filtration. In automatic tube current modulation more current is applied when the gantry rotation is horizontal and lower current is applied when the gantry rotation is vertical. This is known as milliamperage modulation. This allows sufficient photons to pass through the widest part of the patient without unnecessary dose to the narrow part. Adaptive filtration, the software correction smoothens the attenuation profile in areas of high attenuation before the image is reconstructed. Next artifact is looming artifact. Small, highly dense structures such as calcification and dense appear larger than they truly are. Here we see coronary artery calcification appear larger in this image but after changing the window width and window length it appears smaller. Cores, very high CT numbers of the structure cause pixel saturation when using typical look-up table windows causing the structure to appear larger than it is. Also, using a smoothing filter kernel makes smaller bright objects appear larger. Correction, use a look-up window table that is wide enough so that the displayed pixels are not saturated. Use a standard or sharper filter kernel with an iterative noise reduction algorithm. Reduce the display phobia to improve the spatial resolution and use a small section. Next is undersampling. If the interval between projections is too large, misregistration of information relating to sharp edges and small objects occur. It may not have too serious an effect on the diagnostic quality of an image since the evenly spaced lines do not normally mimic any lines. Appearances, there are two appearances ray aliasing and view aliasing. Ray aliasing is stripes appearing closer to the object by view aliasing is stripes appearing away from the object at a distance. Correction, acquiring more number of projections for rotation and flow of rotation speed use of higher resolution thickness such as quarter-detectorship or flying focus point. Next, we are coming into patient-based artifacts which include metallic artifacts, motion artifacts and incomplete projection. The presence of metal objects in this canopy can lead to severe streaking artifacts cause they occur because the density of the metal is beyond the normal range that can be handled by the computer resulting in incomplete attribution. Additional artifacts due to beam hardening, partial volume and aliasing are likely to come out. Here we see dark and bright streets radiating from and between the high-density objects like metallic earrings and acid research. Correction, take off removable metal objects like jewelry before scanning for non-removable items like dental beams, prosthetic devices and surgical eclips use of gantry angulation to exclude the metal inserts from the scans of the abinatomy, increase the voltage to better penetrate dense objects use a dual energy acquisition technique use metal artifact reduction software which uses interpolation techniques to substitute the overrange values in attenuation profiles. However, the usefulness of the software is sometimes limited because although the streaking distance of the metal implant is removed there still remains a loss of detail around the metal tissue interface which is often the main area of diagnostic development. The use of skill sections to reduce partial volume averaging and use of beam hardening production software. Next is motion artifact. Patient motion can cause misregistration artifacts which usually appear as shading or streaking in the reconstituted image. Appearance, here we see double contouring of most of the base of skull with streaking. This is respiratory motion artifact where we see double contouring along the media chain on the left side with a two-door bronchic cases appearing in the left epilogue. Correction, avoidance of motion artifact by the operator prevent voluntary movement with proper patient preparation and breath hold, breath hold coaching prior to the examination initiation. Use of straps and sedation pediatric patients and use of short scanner. There are some built-in features to minimize motion artifact. First is over scan and under scan mode. The maximum discrepancy in detector reading occur between view subtains towards the kidney and end of a 360 degree scan. Over scan mode can be used for actual body scan whereby an extra 10% of so is added to the standard 360 degree rotation. Software correction, application of reduced spacing to begin and end views to reduce the contribution to the final image. Encarding gating, where execution of images in dice shape. Incomplete projection, there's a 3D image of the body obtained with the arms of the patient to the side of the body. But outside the scanner will be showing streaking artifact. Calls, if any portion of the patient lies outside the scan field of view the computer will have incomplete information relating to this portion and streaking or shading artifact are likely to be generated. Corrections, proper patient position so that no parts lie outside the scan field. Now coming to scanner based artifacts which include ring artifact helical and multi-section artifact cone beam effect, multi-planar three-dimensional reformation artifact which we put there's this and zebra artifact. First is ring artifact. If one of the detectors is out of calibration the detector will consistently give an error in its rating at each angular position resulting in a circular artifact. Appearance, here we see concentric circular structures expanding from the scan data center which may be seen in multi communication. Now it may not be always this obvious things we see like this where we see a vague hypotensity in the fault which may mix up the topology. Resolution, recalibrate the faulty detector and perform routine preventative maintenance on the detector. Next is helical artifact. In spiral scanning as the generator rotates it is also moving in the zebra axis. This means that our old detectors is moving in a spiral path. Any object that changes in position of size along the zebra axis may be distorted in different positions for different positions. This is worsened by increasing the pitch and increased contrast between objects and the surroundings. Now there's a serial CT images of a conical phantom where we see a change in shape of the objects in the pigment section. Next is cone beam effect. As the number of sections acquired for rotation increases a wider column is required and the X-ray beam becomes cone shaped rather than fan shaped. The X-ray beam is used by each detector as it rotates around the patient as a volume instead of a flat beam. The resulting artifact is similar to partial volume artifact for off-center objects. Now this is the usual phantom where the collimator is narrow which produces the fan. As number of sections to be missed increases we have to widen the collimator which results in a cone beam. The artifacts are more pronounced for outer detector rows than for the inner one where the data collected correspond Here the beam towards the outer detector looks like a cone while the beam towards the center detector looks more or less like a plane. Cone beam effects get worse for increasing numbers of detector rows. Thus a 60 slice scanner should potentially be more badly affected than a partial scan. Appearance, this is a CT image of a Teflon road. This is an image from the outer detector row and this is an image from the inner detector row and this is an image from the outer detector row. Correction, Cone Beam Reconstruction Algorithm and Modern Scanners Limitly. There is an artifact because it arises when axial images with a large image interval which has thick non-ovelat images are used to create corona or sagittal reformatted images or by the use of anisotropic voxel. Here we see irregular margins along the borders of right actor and subclavian vessels constructed coronal image obtained with 5mm section axial expression. Now this is a corrected image wherein coronal image is reconstructed using a 0.625mm section thickness axial expression. So the resolution is by the use of inflection data. Coming to the last artifact, Radar Artifact. Appearance, we see same horizontal stripes apparent in reformatted epimism of the abdomen cause helical interpolation process if striped through a degree of noise in homogeneity along the right actor. Constitution, artifacts originate from a range of sources and can degrade the quality of a CTMH to varying dates. Design features incorporated into the modern feature scanner minimize some types of artifacts and some can be potentially partially corrected by the scanner. However in many instances, careful patient counselling, positioning and optimum selection of scanning parameters are the most important factors in avoiding CTR. Thank you.