ct scanners, new areas of use have been established, such as aiding in the diagnosis of gout. biomechanical use ct is used in biomechanics to quickly reveal the geometry, anatomy, density and elastic moduli of biological tissues. other uses industrial use industrial ct scanning (industrial computed tomography) is a process which utilizes x-ray equipment to produce 3d representations of components both externally and internally. industrial ct scanning has been utilized in many areas of industry for internal inspection of components. some of the key uses for ct scanning have been flaw detection, failure analysis, metrology, assembly analysis, image-based finite element methods and reverse engineering applications. ct scanning is also employed in the imaging and conservation of museum artifacts. aviation security ct scanning has also found an application in transport security (predominantly airport security) where it is currently used in a materials analysis context for explosives detection ctx (explosive-detection device) and is also under consideration for automated baggage/parcel security scanning using computer vision based object recognition algorithms that target the detection of specific threat items based on 3d appearance (e.g. guns, knives, liquid containers). its usage in airport security pioneered at shannon airport in march 2022 has ended the ban on liquids over 100 ml there, a move that heathrow airport plans for a full roll-out on 1 december 2022 and the tsa spent $781.2 million on an order for over 1,000 scanners, ready to go live in the summer. geological use x-ray ct is used in geological studies to quickly reveal materials inside a drill core. dense minerals such as pyrite and barite appear brighter and less dense components such as clay appear dull in ct images. cultural heritage use x-ray ct and micro-ct can also be used for the conservation and preservation of objects of cultural heritage. for many fragile objects, direct research and observation can be damaging and can degrade the object over time. using ct scans, conservators and researchers are able to determine the material composition of the objects they are exploring, such as the position of ink along the layers of a scroll, without any additional harm. these scans have been optimal for research focused on the workings of the antikythera mechanism or the text hidden inside the charred outer layers of the en-gedi scroll. however, they are not optimal for every object subject to these kinds of research questions, as there are certain artifacts like the herculaneum papyri in which the material composition has very little variation along the inside of the object. after scanning these objects, computational methods can be employed to examine the insides of these objects, as was the case with the virtual unwrapping of the en-gedi scroll and the herculaneum papyri. micro-ct has also proved useful for analyzing more recent artifacts such as still-sealed historic correspondence that employed the technique of letterlocking (complex folding and cuts) that provided a "tamper-evident locking mechanism". further examples of use cases in archaeology is imaging the contents of sarcophagi or ceramics. micro organism research varied types of fungus can degrade wood to different degrees, one belgium research group has been used x-ray ct 3 dimension with sub-micron resolution unveiled fungi can penetrate micropores of 0.6 μm under certain conditions. interpretation of results presentation types of presentations of ct scans: - average intensity projection- maximum intensity projection- thin slice (median plane)- volume rendering by high and low threshold for radiodensity the result of a ct scan is a volume of voxels, which may be presented to a human observer by various methods, which broadly fit into the following categories: slices (of varying thickness). thin slice is generally regarded as planes representing a thickness of less than 3 mm. thick slice is generally regarded as planes representing a thickness between 3 mm and 5 mm. projection, including maximum intensity projection and average intensity projection volume rendering (vr) technically, all volume renderings become projections when viewed on a 2-dimensional display, making the distinction between projections and volume renderings a bit vague. the epitomes of volume rendering models feature a mix of for example coloring and shading in order to create realistic and observable representations. two-dimensional ct images are conventionally rendered so that the view is as though looking up at it from the patient's feet. hence, the left side of the image is to the patient's right and vice versa, while anterior in the image also is the patient's anterior and vice versa. this left-right interchange corresponds to the view that physicians generally have in reality when positioned in front of patients. grayscale pixels in an image obtained by ct scanning are displayed in terms of relative radiodensity. the pixel itself is displayed according to the mean attenuation of the tissue(s) that it corresponds to on a scale from +3,071 (most attenuating) to −1,024 (least attenuating) on the hounsfield scale. a pixel is a two dimensional unit based on the matrix size and the field of view. when the ct slice thickness is also factored in, the unit is known as a voxel, which is a three-dimensional unit. water has an attenuation of 0 hounsfield units (hu), while air is −1,000 hu, cancellous bone is typically +400 hu, and cranial bone can reach 2,000 hu. the attenuation of metallic implants depends on the atomic number of the element used: titanium usually has an amount of +1000 hu, iron steel can completely extinguish the x-ray and is, therefore, responsible for well-known line-artifacts in computed tomograms. artifacts are caused by abrupt transitions between low- and high-density materials, which results in data values that exceed the dynamic range of the processing electronics. windowing ct data sets have a very high dynamic range which must be reduced for display or printing. this is typically done via a process of "windowing", which maps a range (the "window") of pixel values to a grayscale ramp. for example, ct images of the brain are commonly viewed with a window extending from 0 hu to 80 hu. pixel values of 0 and lower, are displayed as black; values of 80 and higher are displayed as white; values within the window are displayed as a grey intensity proportional to position within the window. the window used for display must be matched to the x-ray density of the object of interest, in order to optimize the visible detail. window width and window level parameters are used to control the windowing of a scan. multiplanar reconstruction and projections typical screen layout for diagnostic software, showing one volume rendering (vr) and multiplanar view of three thin slices in the axial (upper right), sagittal (lower left), and coronal planes (lower right) special planes are sometimes useful, such as this oblique longitudinal plane in order to visualize the neuroforamina of the vertebral column, showing narrowing at two levels, causing radiculopathy. the smaller images are axial plane slices. multiplanar reconstruction (mpr) is the process of converting data from one anatomical plane (usually transverse) to other planes. it can be used for thin slices as well as projections. multiplanar reconstruction is possible as present ct scanners provide almost isotropic resolution. mpr is used almost in every scan. the spine is frequently examined with it. an image of the spine in axial plane can only show one vertebral bone at a time and cannot show its relation with other vertebral bones. by reformatting the data in other planes, visualization of the relative position can be achieved in sagittal and coronal plane. new software allows the reconstruction of data in non-orthogonal (oblique) planes, which help in the visualization of organs which are not in orthogonal planes. it is better suited for visualization of the anatomical structure of the bronchi as they do not lie orthogonal to the direction of the scan. curved-plane reconstruction is performed mainly for the evaluation of vessels. this type of reconstruction helps to straighten the bends in a vessel, thereby helping to visualize a whole vessel in a single image or in multiple images. after a vessel has been "straightened", measurements such as cross-sectional area and length can be made. this is helpful in preoperative assessment of a surgical procedure. for 2d projections used in radiation therapy for quality assurance and planning of external beam radiotherapy, including digitally reconstructed radiographs, see beam's eye view. examples of different algorithms of thickening multiplanar reconstructions type of projection schematic illustration examples (10 mm slabs) description uses average intensity projection (aip) the average attenuation of each voxel is displayed. the image will get smoother as slice thickness increases. it will look more and more similar to conventional projectional radiography as slice thickness increases. useful for identifying the internal structures of a solid organ or the walls of hollow structures, such as intestines. maximum intensity projection (mip) the voxel with the highest attenuation is displayed. therefore, high-attenuating structures such as blood vessels filled with contrast media are enhanced. useful for angiographic studies and identification of pulmonary nodules. minimum intensity projection (minip) the voxel with the lowest attenuation is displayed. therefore, low-attenuating structures such as air spaces are enhanced. useful for assessing the lung parenchyma. volume rendering main article: volume rendering 3d human skull from computed tomography data a threshold value of radiodensity is set by the operator (e.g., a level that corresponds to bone). with the help of edge detection image processing algorithms a 3d model can be constructed from the initial data and displayed on screen. various thresholds can be used to get multiple models, each anatomical component such as muscle, bone and cartilage can be differentiated on the basis of different colours given to them. however, this mode of operation cannot show interior structures. surface rendering is limited technique as it displays only the surfaces that meet a particular threshold density, and which are towards the viewer. however, in volume rendering, transparency, colours and shading are used which makes it easy to present a volume in a single image. for example, pelvic bones could be displayed as semi-transparent, so that, even viewing at an oblique angle one part of the image does not hide another. dose versus image quality an important issue within radiology today is how to reduce the radiation dose during ct examinations without compromising the image quality. in general, higher radiation doses result in higher-resolution images, while lower doses lead to increased image noise and unsharp images. however, increased dosage raises the adverse side effects, including the risk of radiation-induced cancer – a four-phase abdominal ct gives the same radiation dose as 300 chest x-rays. several methods that can reduce the exposure to ionizing radiation during a ct scan exist. new software technology can significantly reduce the required radiation dose. new iterative tomographic reconstruction algorithms (e.g., iterative sparse asymptotic minimum variance) could offer super-resolution without requiring higher radiation dose. individualize the examination and adjust the radiation dose to the body type and body organ examined. different body types and organs require different amounts of radiation. higher resolution is not always suitable, such as detection of small pulmonary masses. artifacts although images produced by ct are generally faithful representations of the scanned volume, the technique is susceptible to a number of artifacts, such as the following:chapters 3 and 5 streak artifactstreaks are often seen around materials that block most x-rays, such as metal or bone. numerous factors contribute to these streaks: under sampling, photon starvation, motion, beam hardening, and compton scatter. this type of artifact commonly occurs in the posterior fossa of the brain, or if there are metal implants. the streaks can be reduced using newer reconstruction techniques. approaches such as metal artifact reduction (mar) can also reduce this artifact. mar techniques include spectral imaging, where ct images are taken with photons of different energy levels, and then synthesized into monochromatic images with special software such as gsi (gemstone spectral imaging). partial volume effectthis appears as "blurring" of edges. it is due to the scanner being unable to differentiate between a small amount of high-density material (e.g., bone) and a larger amount of lower density (e.g., cartilage). the reconstruction assumes that the x-ray attenuation within each voxel is homogeneous; this may not be the case at sharp edges. this is most commonly seen in the z-direction (craniocaudal direction), due to the conventional use of highly anisotropic voxels, which have a much lower out-of-plane resolution, than in-plane resolution. this can be