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US 4,066,902 AGranted
Radiography with detector compensating means
AssigneeEMI Limited
InventorChristopher Archibald Gordon LeMay
Life of this patent
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AssigneeEMI Limited
InventorChristopher Archibald Gordon LeMay
Estimating the term…
Radiographic apparatus utilizing a plurality of radiation-sensitive detectors to quantify the radiation emerging from a body along respective paths is provided with means for compensating for differences between the sensitivities of the various detectors. The compensating means includes an arrangement for displacing the source of the radiation relative to the detectors and for utilizing output signals obtained from one detector when the source is in its undisplaced and displaced positions respectively to predict what the output of a second detector, closely adjacent the first, should be if the sensitivities of the two detectors were equal. By comparing the prediction with the actual output signal provided by the second detector, differences in sensitivity are evaluated and allowed for. A technique for convolving difference signals rather than net signals is also disclosed.
A method of producing a representation of the distribution of absorption coefficients, with respect to penetrating radiation, over a planar section of a body comprising the steps of passing said radiation from a source thereof through said body along a plurality of paths, some of which intersect, detecting the radiation emergent from the body along each of said paths using a plurality of detector devices, displacing the source relative to the detectors to provide information enabling the amount of radiation emergent along a first of said paths to be predicted from the measured amounts of radiation emergent along second and third paths, closely adjacent said first path, as monitored by a first detector device whilst the source and detectors occupy respective dispositions in relation to each other, comparing the predicted amount with the amount emergent from said body along said first path as measured by a second detector, and utilising a difference signal derived from said comparison to correct readings obtained from said second detector thereby to compensate for differences in sensitivity between said first and second detectors.
A method of producing a representation of the distribution of absorption coefficients, with respect to penetrating radiation, over a planar section of a body comprising the steps of passing said radiation from a source thereof through said body along a plurality of paths, some of which intersect, detecting the radiation emergent from the body along each of said paths using detector means, deriving output signals indicative of the amount of radiation transmitted through the body along each of said paths as detected by said detector means, forming the difference between each of said output signals and a datum signal and performing a convoluting operation upon the difference signals so formed to evaluate said coefficients.
A medical radiology device comprising:
An apparatus for examining a slice of a body by means of penetrating radiation such as X- or .gamma. - radiation including a source of a substantially planar fan of radiation intersecting the said slice and originating substantially from a point, a plurality of detectors for detecting the radiation after passage through the body along a plurality of beams at different angles within the fan, means for angularly displacing at least the source through a substantial angle about an axis which intersects the slice, and means for subjecting the said point of origin to a periodic displacement, of period short compared with the time of said angular displacement, relative to the detectors and in the plane of said fan.
Dependencies are inferred from the claim text.
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No related US applications are recorded in the indexed filing history.
Computed tomography [CT]: transmission computed tomography [CT]
Involving movement of the focal spot: resulting in acquisition of views from substantially different positions, e.g. EBCT
Constructional features of apparatus for radiation diagnosis: means for cooling
X-ray or gamma ray systems or devices: computer tomography program or processor
Term ended 3 Jan 1995 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
This invention relates to a method of and apparatus for examining a body by means of radiation such as X or .gamma.- radiation.
The method and apparatus according to the invention can be used to assist in the production of radiographs in any convenient form, such as a picture on a cathode ray tube or other image forming device, a photograph of such a picture, or a map of absorption co-efficients such as may be produced by digital computer and on which contours may be subsequently drawn.
In the method of, and apparatus for, examining the body described in U.S. Pat. No. 3,778,614 radiation is directed through part of the body, from an external source, in the form of a pencil beam. A scanning movement is imposed on the beam so that it takes up in turn a large number of differing dispositions, and a detector is used to provide a measure of the absorption of the beam in each such disposition after the beam has passed through the body. So that the beam takes up these various dispositions the source and the detector are reciprocated in a plane and are orbited about an axis normal to the plane. The various dispositions thus lie in a plane through the body over which the distribution of the absorption co-efficient for the radiation used is derived by processing the beam absorption data provided by the detector. The processing is such that the finally displayed distribution of absorption is the result of successive approximations.
In order that the invention may be clearly understood and readily carried into effect, some embodiments thereof will now be described by way of example only with reference to the accompanying drawings of which:
FIG. 1a shows, in side elevation and partly in cross section, apparatus incorporating the invention,
FIG. 1b is a view taken on arrows bb of FIG. 1 a,
Referring now to FIGS. 1a and 1b, a body 1 to be examined is supported supine on a suitable couch 2. The couch 2 is supported at either end by respective support members 3 and 4 which are secured to a plinth 5. The support member 4 supports its end of the couch 2 indirectly via a drum 6 and an axle 7, the latter being rotatably mounted in an L-shaped member 8 which supports the couch 2.
An X-ray tube 9 and a bank of detectors 10 are mounted by respective supports 11 and 12 to the outside of a cylindrical drum 13 which surrounds part of the body 1 and is arranged to be rotated around the body by means of an electric motor 14 which drives a gear wheel 15 having teeth which engage with those of a gear ring 16 formed on the outside of the drum 13. The closed end of drum 13 carries, in its centre, a bearing 17 free to rotate on the axle 7; axle 7 being aligned with the longitudinal axis of the drum 13 and constituting the rotational axis of the system as a whole. The open end of drum 13 is supported on bearings 18, of which only one is visible in FIG. 1a, the bearings 18 being supported by the support member 3. Electrical power supplies for the X-ray tube 9 and electrical signals from the detectors are carried respectively by cables 19 and 20, and these cables are passed along the outside of drum 13 and through suitable cable guides 21, 22 respectively to the drum 6 which carries sufficient turns of the cables to allow for rotation of the drum 13 through a complete revolution thereof. It will be appreciated that because of this the drum 13 has to be returned to its initial position after the completion of each scan.
The patient is placed so that the part of his body which is to be examined is disposed in the path of the X-rays from the tube 9 to the detector 10; the tube 9 including collimator means for ensuring that the radiation is emitted in the form of a planar, fan shaped swath 23 (see especially FIG. 1b) the wide dimension of the fan being perpendicular to the plane of the paper in FIG. 1a and parallel to the plane of the paper in FIG. 1b. The region of interest of the body being investigated is surrounded by a locating ring 24 which contains packing material 25 of similar absorption characteristics to the body 1, the material 25 being tightly compressed between the ring 24 and the body 1 for the purpose of excluding, as far as possible, air from the immediate vicinity of the body.