Scanning

(time-base sweep), a method of representing the changes of a physical quantity variable over time by unambiguously converting it into another quantity that varies in space. Scanning is performed by a scanning element, which successively scans space according to specific laws so that certain spatial coordinates of the scanning element correspond to each instant of time and to a certain value of the physical quantity. The reverse transformations usually are also called scanning, obviously on the basis of the similarity of the techniques used in both cases.

Thus, in the picture tube (kinescope) of a television receiver, the electrical voltage at the control electrode, which is variable over time, is converted in a specific manner by means of scanning into a change in brightness over the surface of the screen. In a television camera tube, the reverse process is accomplished by scanning—the brightness of various sections of the image is converted into an electric current that varies accordingly. In both cases, the scanning element is the point on the surface of the screen at which the electron beam is focused. The movement itself of the scanning element is often called scanning.

The scanning element may be (1) a spot of light that moves over the image or screen on deflection of the light beam (optical scanning) or on displacement of the object of the image, (2) a small moving aperture in the screen that covers the image or the pen of an automatic recorder (mechanical scanning), or (3) a luminous point on the screen of a cathode-ray tube (electronic scanning). Since a single scanning system may use a combination of optical, mechanical, and other methods of producing and deflecting the scanning elements, scanning cannot always be classified exactly on the basis of these characteristics.

Scanning may also be classified according to the trajectory of the scanning element. In rectilinear scanning, the trajectory is a straight line, in circular scanning, a circle, and in spiral scanning, a spiral. If the trajectory of the scanning element forms a raster, then the corresponding scans are called raster scans, which are then classified according to the shape of the raster. If the scanning element moves along the image contour as if tracking it, then such a scan is called a tracking scan. The objects scanned may be both continuous and discrete physical quantities.

Scanning is widely used in oscillographs, automatic recording devices, radar displays, and long-distance data transmission equipment. Oscillographs chiefly use rectilinear scanning. The scanning is called multiple scanning if each scanning cycle is immediately and automatically followed by the next cycle. The scanning is called slave sweep if each cycle begins only when a special triggering signal is received.

In radar displays, two-dimensional scans, for example, panorama or radial-circular scans, three-dimensional scans, and other types are used to determine target coordinates on the display screen.

Television and facsimile chiefly use raster scans with a rectangular raster. Systems with tracking scanning are sometimes used in the transmission of contoured and line images in facsimile and in feeding graphic information to an electronic computer.

L. I. FREIDIN

Scanning

the controlled spatial displacement of a ray, such as a light ray, or beam, such as an electron beam, according to some definite pattern. Scanning is frequently used in various areas of science and technology. For instance, scanning by an electron beam is used to produce an image in cathode-ray tubes and in scanning electron microscopes. Scanning by a light ray is used in optical data-processing systems.

Scanning can be achieved by mechanical or nonmechanical methods. Mechanical methods are based on an angular displacement of the radiating system. In nonmechanical scanning the ray is displaced either by electrically controlling individual components of a stationary radiating device or by controlling the properties of the medium through which the ray is propagated. Alternating electric or magnetic fields that act upon a beam of charged particles are used to achieve scanning by such beams.

V. N. PARYGIN

Figure 1. Beam motion in helical scanning. The displacement of the beam is rotational with a constant angular velocity. The relative motion is oscillatory in a plane perpendicular to the plane of rotation and at a significantly lower velocity.

Scanning

in radar, the sequential inspection of a given spatial zone in some prescribed manner by displacing a radar beam or the solid angle of sight of a receiving antenna. The purpose of scanning is the detection and observation of objects located in the scanning zone.

Figure 2. Beam motion in zigzag scanning. Both the displacement and the relative motion of the beam are oscillatory, with varying velocity ratios (a and b).

Scanning can be achieved either with a fan or pencil beam. In a fan beam the beam angle is much smaller in one plane than in the other; a pencil beam is a narrow beam symmetrical with respect to the direction of maximum intensity of radiation. The most common scanning methods with a fan beam are azimuth scan, in which the beam rotates around a stationary axis, and certain methods using sector scanning, in which the beam oscillates periodically through a given sector. Multibeam scanning systems with fan beams are also used. In scanning methods that use a pencil beam the complex motion of the beam can be represented as two simple motions: a displacement motion around a stationary axis and a relative motion around a moving axis.

Figure 3. Beam motion in spiral scanning. The displacement of the beam is rotational, and the relative motion is oscillatory (here, with a lower velocity).

The principal types of scanning with pencil beams are helical scanning (Figure 1), zigzag scanning (Figure 2), spiral scanning (Figure 3), and sequential lobing (Figure 4). Conical scanning (Figure 5) is a special type of sequential lobing.

REFERENCES

See references under RADAR.

B. V. MALANOV

Figure 4. Beam motion in sequential lobing. The displacement of the beam is oscillatory, and the relative motion is rotational (here, at a significantly higher velocity).

Figure 5. Beam motion in conical scanning. The motion of the beam is rotational (circular). The direction of maximum intensity of radiation OA is displaced with respect to the axis of rotation OO’ by some constant angle α, Here, α is less than one-half the beam width in order to ensure a direction of constant signal along the axis of rotation.

Scanning

in radiology, the study of the distribution of radioactive preparations introduced into the body of a person or animal for purposes of diagnosis, treatment, or research. Scanning utilizes radioisotopes or their compounds, which, upon decaying, emit gamma quanta. A scanner is used to make the distribution of the radioactive preparations visible; it consists of a movable gamma-radiation detector (scintillation counters) and of systems for translating an electrical signal into a light signal. The resulting image is then recorded graphically or by means of black-and-white or color photography.

In clinical practice, scanning is used to obtain images of almost all internal organs and systems. It makes it possible to determine the position, shape, size, nature, and functional state of an organ’s internal structure and to detect the presence of sizable lesions. The method is safe, simple, and causes no discomfort.

V. Z. AGRANAT and F. M. LIASS

scanning

In radar, the motion of the radar antenna assembly when searching for targets. Scanning usually follows a systematic pattern involving one or more of the following:
i. In horizontal scanning (or search lighting), the antenna is continuously rotated in an azimuth around the horizon or in a sector (sector scanning). This is used to find the azimuth of the targets and generate plan-position-indicator-scope displays.
ii. Vertical scanning is accomplished by holding the azimuth constant but varying the elevation angle of the antenna. It is used in height-finding radars to generate the relative-height-indicator-scope display.
iii. For conical scanning, a somewhat off-center radiating element is rotated while its parabolic reflectors remain fixed in position, so that the radiated beam generates a conically shaped volume with the antenna at the apex. It is used to determine an accurate bearing and the elevation angle of targets and is employed in automatic-tracking radars.
iv. In helical scanning (or spiral scanning), the azimuth and the elevation angle of the antenna are constantly varied, so that at a given distance from the radar the radiated beam generates the surface of a hemisphere. It is used for radio direction finding, in certain types of search radars, and in tracking radars to search areas for targets. See sector scan, conical scanning, helical scan, and height-finder radar.

scanning

[skan´ing] 1. close visual examination of a small area or of different isolated areas.2. any of several diagnostic radiologic techniques, including tomography" >computed tomography, magnetic resonance imaging, and tomography" >positron emission tomography.3. a manner of utterance characterized by somewhat regularly recurring pauses.brain scanning see brain scanning.MUGA scanning (multiple gated acquisition scanning) equilibrium radionuclide angiocardiography.radioisotope scanning production of a two-dimensional record or image of the gamma rays emitted by a radioactive isotope concentrated in a specific organ or tissue of the body, as brain, kidney, or thyroid gland.scintillation scanning the process resulting in a scintiscan.thallium scanning production of a scintillation scan involving the use of thallium 201; see also thallium scan.total body scanning use of tomography" >computed tomography to examine a cross section of the entire body. The scanner produces an image of tissue density in a complete cross section of the part of the body being scanned. Total body scanning does not require the injection of a radiopaque substance, nor is there a need for use of a radioactive material to produce a record of the findings. The total body scanner is particularly useful in visualizing organs in the retroperitoneal space, for example, the pancreas, liver, spleen, and ovaries, and the abdominal section of the aorta.

scan·ning

(skan'ing), The act of imaging by traversing with an active or passive sensing device, often identified by the technology or device employed.

scan·ning

(skan'ing) The act of imaging by traversing with an active or passive sensing device, often identified by the technology or device employed.

scan·ning

(skan'ing) Act of imaging by traversing with an active or passive sensing device, often identified by technology or device employed.

Patient discussion about scanning

Q. Anybody to tell me more about MRI scan? had an MRIscan and this has snown adenocarcinoma of endometrium early stage There is no lymphatic involvement but is it possible an MRIscan to miss some tumor?A. MRI is a very effective machine but it has it's limits. it has a great resolution but will not see very small tumors. therefore- it can miss metastasis sometime. but if your adenocarcinoma is in early stage- it might not sent metastasis. they did a biopsy? that can give you some idea what to expect.

Q. I am 15 weeks pregnant. I had my NT scan and blood draw today. Iam using my Hubby user name here.I am 15 weeks pregnant. I had my NT scan and blood draw today. I doubt whether I am in a risky state because I read in medical journal that women with certain amount of risk go for second trimester screening and not healthy pregnant women. Is it so? Please clarify?A. There's something called an integrated sequential screening. You have the NT scan and blood draw in your first trimester, and then go back for an additional blood draw in your second trimester. They then calculate a unified result and present the results in the second trimester. Several other sources mentioned that often a high risk based on the NT scan and the first blood draw will prompt a diagnostic test. Yes, women with low or acceptable risk go on for the second trimester screening.

Q. I'm worried if she has ADHD. Is there any MRI or brain scan test to diagnoses the problem? My daughter Elba is 15. She regularly goes to school but often forgets to do daily activities. I'm worried if she has ADHD. Is there any MRI or brain scan test to diagnoses the problem?A. Although in general practice MRI is not carried out to diagnose ADHD, the studies have shown that the ADHD brain has considerably less activity than does a normal brain when MRI's are compared. Stimulant drugs increases the chemical activity level, which decreases the symptoms. I shall suggest you to consult a physician specialized in this area.

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Words related to scanning

noun the process of translating photographs into a digital form that can be recognized by a computer

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noun the act of systematically moving a finely focused beam of light or electrons over a surface in order to produce an image of it for analysis or transmission

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