From these data the CT images are reconstructed including the use of mathematical procedures like convolution filtering and back projection.Ī computerized tomography (CT) or computerized axial tomography (CAT) scan combines data from several X-rays to produce a detailed image of structures inside the body. Raw data are the values of all measured detector signals during a scan.
Each tissue/object only partially fills the voxel and is therefore a partial volume. Partial volume effect: When different tissues/objects are represented by the same voxel. The matrix determines the number of rows and columns. Matrix: Two dimensional grid of pixels, used to compose images on a display monitor. SFOV: Scan field of view–the parameter that determines how much anatomy is scanned.Ī voxel is the smallest 3D element of the volume,2 and is typically represented as a cube or a box, with height, width and depth. A basic requirement for adequate multiplanar reconstruction is that the resolution is isotropic eg, the resolution is approximately equal in all directions. Spatial resolution is ultimately limited by sampling, but both image noise and resolution are strongly affected by the reconstruction filter.Īn increase in mA will increase the quantity of exposure decreased mA will reduce the quantity of exposure.Ĭurrent CT scanners have a spatial resolution of 0.5–0.625 mm in the z-axis, and approximately 0.5 mm in the x- to y-axes. What is image quality in CT?ĬT image quality, as in most imaging, is described in terms of contrast, spatial resolution, image noise, and artifacts. In general, the larger the number of photons transmitted, the greater the SNR. It is calculated by comparing the level of the desired signal to the background deviation from normal pixel values. The higher the ratio, the less noise is present in the image. Often noise is defined loosely as the grainy appearance on cross-sectional imaging more often than not, this is quantum mottle. Noise in computed tomography is an unwanted change in pixel values in an otherwise homogenous image. In conventional analytic filtered backprojection (FBP)–based reconstruction, a smooth filter is typically applied to control noise. Noise reduction can occur at various stages of the CT imaging process. This causes the x-ray beams to become cone-shaped as opposed to fan-shaped 2. Modern CT scanners use more detector arrays to increase the number of sections acquired per rotation. The common understanding regarding photon starvation streaks is that they are a manifestation of irregularities caused by noise in the raw data profile.Ĭone beam effect artifacts are seen in multidetector row CT (cone beam CT) acquisitions 1. This photon starvation artifact phenomenon occurs frequently when a pelvis or shoulder is scanned with thin slices. Because of high attenuation, insufficient photons reach the detector. It is seen in high attenuation areas, particularly behind metal implants. Photon starvation is one source of streak artifact which may occur in CT. Radiographic errors may be due to technical errors or processing errors What is photon starvation? CT beam hardening artifact has two distinct manifestations, streaking (dark bands) and cupping artifacts.ĭefinition : An artifact is a structure or an appearance that is not normally present on the radiograph and is produced by artificial means. What does artifact mean on CT scan?īeam hardening is the phenomenon that occurs when an x-ray beam comprised of polychromatic energies passes through an object, resulting in selective attenuation of lower energy photons. Physicians typically learn to recognize some of these artifacts to avoid mistaking them for actual pathology.ġa : a usually simple object (such as a tool or ornament) showing human workmanship or modification as distinguished from a natural object especially : an object remaining from a particular period caves containing prehistoric artifacts. In medical imaging, artifacts are misrepresentations of tissue structures produced by imaging techniques such as ultrasound, X-ray, CT scan, and magnetic resonance imaging (MRI). What are motion artifacts TV?ĭisplay motion blur, also called HDTV blur and LCD motion blur, refers to several visual artifacts (anomalies or unintended effects affecting still or moving images) that are frequently found on modern consumer high-definition television sets and flat panel displays for computers. Motion artifacts are due to shaking with rhythmic movement.
As a result of artifacts, the components of the electrocardiogram (ECG) such as the baseline and waves can be distorted. a.Įlectrocardiographic artifacts are defined as electrocardiographic alterations, not related to cardiac electrical activity.
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