Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/10—Safety means specially adapted therefor
  • A61B6/107—Protection against radiation, e.g. shielding
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
  • A61B6/03—Computed tomography [CT]
  • A61B6/037—Emission tomography
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
  • G01T1/2914—Measurement of spatial distribution of radiation
  • G01T1/2985—In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis)

Definitions

• the present invention relates to the diagnostic imaging systems and methods. It finds particular application in conjunction with the Positron Emission
• PET is a valuable patient imaging scanner employing positron emitting compounds. PET provides specific metabolic information about tissues that conventional scanners such as CT and MRI can not provide. Typically, PET scanners include a circular bore that is surrounded by a circular array of detectors which detect concurrent energy events. Prior to the scan, the patient is injected with a positron emitting radioisotope which is taken up by cells. When a positron emits from a radioisotope, it combines with an electron to produce an annihilation reaction, in which the pair's mass is converted into energy.
• positron emitting radioisotope Prior to the scan, the patient is injected with a positron emitting radioisotope which is taken up by cells. When a positron emits from a radioisotope, it combines with an electron to produce an annihilation reaction, in which the pair's mass is converted into energy.
• the energy is dispersed in the form of two 511 kev gamma rays or photons, traveling 180 degrees apart.
• the detectors register a coincidence along the line between the detector points - a line of response (LOR).
• LOR line of response
• the PET system draws lines of responses between each detection pair, registering coincidence events during the scan.
• the system uses this information to reconstruct a three dimensional image of radioisotope concentration in the body.
• the scanner accepts photons from anywhere from the field of view, and, in addition, accepts photons originating outside of field of view that into travel into the field of view.
• the photons originating outside of the field of view do not contain useful information that is used in image reconstruction. Note that one of the 180° opposite photons for a point outside the field of view normally cannot strike the detector.
• the PET systems are designed to only accept coincidence events within a narrow window. Problems arise when trying to run the scanner in a high flux photon situation where the total activity seen by the system is high. The higher the number of photons detected per unit time, the higher the probability that not-paired photons will be detected within the coincidence time window. The systems performance degrades with high activity levels in patient bodies.
• the shield is a lead flange at the entrance and exit of the PET scanner bore.
• the flange extends from the outer periphery of the bore toward the central axis of the bore and leaves a circular patient aperture of about 50-60cm in diameter.
• a radiographic imaging system In accordance with one aspect of the present invention, a radiographic imaging system is disclosed.
• a means detects emission radiation emitted by a radioisotope injected into a subject, the detecting means arranged around a circular bore, which has an entrance and an exit.
• a means shields the detecting means from the emission radiation originating outside of the bore.
• the shielding means includes at least one rigid radiation opaque shield rigidly mounted to one of the entrance and the exit of the bore. The shield extends from an outer periphery of the bore toward and surrounding a central axis of the bore and defining a fixed non-circular subject receiving aperture.
• a method of radiographic imaging is disclosed.
• Emission radiation which is emitted by a radioisotope injected into a subject, is detected along a detecting means defined around a circularly cylindrical bore.
• the detecting means is shielded from the emission radiation originating outside of the bore with at least one shield rigidly mounted to one of an entrance and an exit of the bore and extending from an outer periphery of the bore toward and surrounding a central axis of the bore.
• the at least one shield defines a fixed non-circular subject receiving aperture.
• One advantage of the present invention resides in reducing out-of-the- field- of-view events reaching the detectors.
• Another advantage of the present invention resides in fitting radiation shielding to the patient, yet providing an easy to maintain and inexpensive shielding.
• Another advantage of the present invention resides in its mechanical simplicity and lack of moving parts. Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.
• FIGURE 1 is a diagrammatic illustration of a PET imaging system in accordance with present invention
• FIGURE 2 is a diagrammatic illustration of a non-circular subject receiving aperture in a shape of an ellipse
• FIGURE 3 is a diagrammatic illustration of a non-circular subject receiving aperture tailored to the couch.
• an imaging system 10 includes a subject support means 12, such as a table or couch, which supports a subject 14 being imaged.
• the subject 14 is injected with one or more radioisotopes to induce the emission of the positron.
• An annular array of detectors 16 is arranged around a circular bore 18. Because the detectors may have planar faces the detector array 16 may be an octagon or other regular polygon that approximates a circle.
• the subject support 12 is advanced and retracted to achieve the desired positioning of the subject 14 within the bore 18, e.g. with the region of interest centered in the field of view of the detectors. Radiation events detected by detectors 16 are collected by a line of response (LOR) calculating circuit 20.
• LOR line of response
• the LOR calculator 20 includes a coincidence detector 22 that determines when two events are within a preselected temporal window of being simultaneous. From the position of the detectors 16 and the position within each detector, at which the coincident radiation was received, a ray between the radiation detection points is calculated by line extrapolator 24.
• the acquired LOR data are preferably stored in a data memory or buffer 26.
• a data reconstruction processor 28 reconstructs an electronic image representation fiom the LOR data stored in data memory 26 and stores the resultant image representation in an image memory 30. Portions of the stored image representation are retrieved by an image processor 32 and converted to an appropriate format for display on a monitor 34, such, as a video, CCD, active matrix, or other monitor.
• a non-circular receiving area or aperture 36 of the PET scanner is defined by radiation shields 38 mounted at the entrance and exit of the circular bore 18 and extending from an outer periphery of the bore 18.
• the shields 38 are manufactured from a LEAD or other high density shielding material and is up to 25mm thick.
• the aperture 36 has a larger dimension Dl along the axis substantially parallel to the horizontal, transverse axis drawn through the shorter dimension of the couch 12.
• the aperture 36 is an ellipse, with the larger dimension or major axis Dl equal to 70cm.
• the aperture 36 has a smaller dimension or minor axis D2 along the vertical axis perpendicular to the axis drawn through the shorter dimension of the couch 12.
• the smaller dimension D2 of oval aperture 36 is 50cm.
• aperture is sized such that a nominally sized subject centered in the aperture is generally equidistant from the shield in all directions.
• the PET scanner has a radiation shield 38 mounted at the entrance 40 and exit 42 of the circular bore 18, which defines a non-circular aperture 36.
• a bottom boundary 50 of aperture 36 is disposed underneath the couch 12 and follows closely the shape of a bottom surface 52 of tfcie couch 12.
• a top boundary 54 of aperture 36 fo ⁇ ned by shield 38 is positioned above the subject 14. Preferably, it is curved to allow the subject 14 of maximum girth to be received in the subject receiving aperture 36 with the couch 12 in the lower most position.
• Side boundaries or sides 56 are formed between the top and bottom boundaries of aperture 36.
• the sides 56 of the aperture 36 are linear vertical segments, which are closely adjacent the sides 58 of couch. 12 and extend a vertical distance commensurate with the permitted vertical travel of the couch 12.
• the sides 56 transition into the top boundary 54 with curved surfaces that conform to an upper side contour of the subject 14.

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• Health & Medical Sciences (AREA)
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• Radiology & Medical Imaging (AREA)
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• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
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Citations (3)

• 2004
  • 2004-09-01 EP EP04769914A patent/EP1663003A1/en not_active Withdrawn
  • 2004-09-01 WO PCT/IB2004/051658 patent/WO2005023113A1/en active Application Filing
  • 2004-09-01 JP JP2006525252A patent/JP2007505290A/ja active Pending
  • 2004-09-01 CN CNB2004800256883A patent/CN100542484C/zh not_active Expired - Fee Related

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