![]() ![]() The CT image is a digital image and consists of a square matrix of elements ( pixel), each of which represents a voxel (volume element) of the tissue of the patient. Using the computer, it presents the elementary surfaces of the reconstructed image from a projection of the data matrix reconstruction, the tone depending on the attenuation coefficients. It gathers together all the data coming from the elementary volumes of material through the detectors. The image of the section of the object irradiated by the x-ray is reconstructed from a large number of measurements of attenuation coefficient. Sir Godfrey Hounsfield, the co-developer of CT, chose a scale that reflects the four basic x-ray densities in the human body, with the following values: I(x) is smaller where the body is more radiopaque. The outgoing intensity I(x) of the beam of photons measured will depend on the location. If the x-ray at the exit of the tube is made monochromatic or quasimonochromatic with the proper filter, one can calculate the attenuation coefficient corresponding to the volume of irradiated tissue by the application of the general formula of absorption of the x-rays in the field (see Figure 1). To obtain tomographic images of the patient from the "preprocessed" CT dataset, the computer uses complex mathematical algorithms for image reconstruction. The image of that section is taken from different angles, and this allows to retrieve the information on the depth (in the third dimension). They measure the transmission of a thin beam (1-10 mm) of x-rays through a full CT of the body. Unlike x-ray radiography, the detectors of the CT scanner do not produce an image. In the particular case of CT, the emitter of x-rays rotates around the patient and the detector, placed on diametrically opposite sides, picks up the image of a body section (beam and detector move in synchrony). ![]() This phenomenon is represented by a single coefficient, mju. There are two processes of absorption: the photoelectric effect and the Compton effect. Attenuation values of the x-ray beam are recorded and the data is used to build a 3D representation of the scanned object/tissue. A detector placed at the exit of the sample, measures N + ΔN photons, ΔN smaller than 0. The emitted x-rays form a beam that passes through the layer of biological material of thickness Δx. The CT x -ray tube (typically with energy levels between 20 and 150 keV), emits N photons (monochromatic) per unit of time. Using this principle, CT allows the reconstruction of the density of the body, by a two-dimensional section perpendicular to the axis of the acquisition system. Cross-sections are reconstructed from measurements of attenuation coefficients of x-ray beams passing through the volume of the object studied.ĬT is based on the fundamental principle that the density of the tissue passed by the x-ray beam can be measured from the calculation of the attenuation coefficient. Note 8) Non condensing.Computed tomography (CT), also known as, especially in the older literature and textbooks, computerized axial tomography (CAT), is an imaging modality that uses x -rays to build cross-sectional images ("slices") of the body. External power supply for 100-240 AC is provided if requested. Note 7) Operational voltage is supplied to detector. deviation from ideal response line defined by zero offset and signal at 80% of dynamic range. Note 5) Digital interface has 16-bit as data format, but user can select actual data to be 14, 12, 10 or 8-bits. Note 4) Dynamic range is defined as saturation signal/RMS noise, normal detector sensitivity. integration time) for “fast” version is specified for active length up to 2048 pixels. +358 | Fax +358 | | Note 1) When the USB 2.0 interface is used, the active area length will be 102-614 mm Note 2) When the USB 2.0 interface is used, the number of pixels will be 512-3072 Note 3) Max. Integration Time Fast Version 0.5 ms 0.3 ms 0.5 ms 0.24 ms 0.24 ms 0.24 ms See Note 3) Max Integration Time 128 ms A/D Resolution 14-bits Dynamic Range > 2000 See Note 4) Data Digital Interface 16-bits See Note 5) Linearity (Non-Linearity) < 1% See Note 6) Operational Voltage +12 V DC See Note 7) Power Consumption 60 W max Ambient Temperature 0 - 40✬ Relative Humidity 30 - 80% See Note 8) Storage Temperature -10 - 50✬ Detection Technology, Inc. ![]()
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