Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/2006—Measuring radiation intensity with scintillation detectors using a combination of a scintillator and photodetector which measures the means radiation intensity

Definitions

• the present invention deals with the diagnostic imaging arts. It finds particular application in conjunction with electronics used in nuclear cameras and will be described with particular reference thereto. However, it is to be appreciated that the present invention has application in other devices that have electronics that require cooling and is not limited to the aforementioned application.
• Nuclear imaging employs a source of radioactivity to image the anatomy of a subject.
• a radiopharmaceutical is injected into the patient.
• This radiopharmaceutical contains atoms that decay at a predictable rate. Each time an atom decays, it releases a ⁇ -ray. These ⁇ - rays are detected, and from information such as their detected position and energy, a representation of the interior of the subject is reconstructed.
• a nuclear camera typically has one, two, or three detector heads. Each head has a large scintillator sheet, such as doped sodium iodide, which converts incident radiation into flashes of light.
• An array of photomultiplier tubes is disposed in back of the scintillator to monitor for light flashes. The output of the photomultiplier tubes and associated circuitry indicates the coordinates of each scintillation on the sodium iodide crystal and its energy.
• Unfortunately there are numerous non-uniformities and inaccuracies when using a large scintillator crystal and an array of photomultiplier tubes.
• each scintillator/photodiode or other detector element is typically on the order of a millimeter square.
• Each of the detector elements needs to be powered and to have its output electrical signals processed.
• the powering and at least a portion of the processing circuitry is mounted in close association with the individual detectors. This leads to a high density of electrical components, many of which generate significant heat. Cooling the electronics becomes a significant problem.
• the present invention provides a new and improved method and apparatus that overcomes the above referenced problems and others .
• a nuclear imaging apparatus is given.
• An array of detectors detects ⁇ -rays, information about the ⁇ -rays are processed by electronics, a cooling system cools the electronics, and a reconstruction processor converts the ⁇ -ray information into an image representation.
• a method of nuclear imaging is given. A subject is injected with a radiopharmaceutical that emits ⁇ -rays. The ⁇ -rays are detected by electronics and reconstructed into an image representation. The electronics are arranged to facilitate their cooling and they are cooled.
• a method of nuclear imaging is given. ⁇ -rays are detected by an array of detector arrays.
• the array is mounted on heat generating circuitry and air is passed along the circuitry to cool it. Signals are processed from the detector array and converted into an image representation.
• One advantage of the present invention is that it keeps electrical components at safe temperature levels.
• Another advantage of the present invention is that it allows for a large number of detectors in a small area.
• Another advantage of the present invention resides in high sensitivity and detailed spatial sampling resolution. Yet another advantage of the present invention is that it avoids the use of liquid coolant or cryogenic cooling.
• the invention may take form in various components and arrangements of components, and in various steps and arrangements of steps.
• the drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.
• FIGURE 1 is a diagrammatic illustration of a nuclear imaging device in accordance with the present invention
• FIGURE 2 is a perspective view of a detector array and associated circuit boards
• FIGURE 3 is a perspective view of one of the circuit boards and detector array
• FIGURE 4 is a flowchart illustrating the activity of an event analyzer, in accordance with the present invention.
• FIGURE 5 is a perspective view of the detector array, circuit boards, and cooling fans.
• a subject 10 defines an imaging region 12.
• a radioactive isotope 14 is injected into the subject, near a region to be imaged.
• the isotope would be injected into the bloodstream upstream from the blockage.
• the radiopharmaceutical is injected into the circulatory system and its absorption by tissue of interest is monitored.
• quantum physics predicts, atomic nuclei of the radioactive isotope decay over time. Energy is released at the time of decay in the form of a photon, more specifically, a ⁇ - ray of characteristic energy.
• the detector array 18 includes a 4x24 array of cadmium zinc telluride (CZT) crystal arrays 20, each having 4x8 individual detectors 22.
• CZT cadmium zinc telluride
• the detector array 18 and collimators 16 are mounted on a mechanized drive 30 that moves the detector array.
• the array moves with lateral rotational components of motion, although various trajectories are contemplated.
• the detector array is stationarily mounted within a movable gantry that is indexed around the region of interest.
• the support is mounted on a rotatable gantry 32 which extends fully around the subject
• a motor control 34 selects a range of motion of the detector array 18, if any, within the rotatable gantry and rotation of the gantry 32 stepwise or continuously around the image region.
• the collimator 16 limits access to the detector array 18 to radiation following prescribed paths or trajectories, e.g., trajectories perpendicular to the plane of the detector array 18. In this manner, each radiation event defines a trajectory along which a radioisotope decayed. If the movable gantry 32 remains stationary, the detectors define a projection image of the radioisotope distribution in the region of interest. An event analyzer 42 determines the location at which each event strikes the detector array, i.e., which detector receives it and the amount of energy of the radiation event. The radiation events collected at each stationary position of the detector array are stored in an archive 44.
• a reconstruction processor 46 backprojects or otherwise reconstructs the data from the archive memory 44 into a volumetric image representation for storage in a volumetric image memory 48.
• a video processor 50 under operator control selectively withdraws portions of the volumetric image representation and converts them into appropriate form for display on a video or other human-readable monitor 52.
• received ⁇ -rays are detected and their energy measured by electronics attached to the detector array 18.
• Four P-ASIC 60 are mounted on each side of a circuit board or pair of back-to-back circuit boards 62 that support four of the detector arrays. More specifically to the preferred embodiment, each P-ASIC preamplifies half of one of the arrays 20.
• Associated P-ASICs 60 powered by voltage regulator 66 amplify and condition the pulses from the detectors.
• Subsequent electronic components 64 select and multiplex a signal of interest to circuits that digitize and archive the series of outputs to portions of the event analyzer 42 mounted remotely.
• the circuitry 64 or the remote portion of event analyzer 42 is normally idle 70, awaiting an electrical signal.
• the event analyzer 42 When the event analyzer 42 receives an electrical signal, it compares it to a threshold 72. If the signal is less than the threshold, it is ignored as noise, and the analyzer 42 goes back to idle. If the signal is above the threshold, the analyzer classifies it as an event 74, and records 76 the energy of the signal, and the position of the detector 22 that sent the signal. ⁇ The analyzer 42 then communicates 78 this information to the event archive 44 where it is stored for future use. After this communication, the analyzer 42 returns to idle awaiting the next event. In the preferred embodiment, once the analyzer 42 comes out of idle, in the next clock cycle, (preferably within 20 ns) other events are locked out until the analyzer 42 returns to idle.
• the process is completed, and the analyzer is back in idle in less than 2 ⁇ s.
• the analyzer 42 includes a timeout feature that only allows a set amount of time to determine the truth of an event.
• the analyzer waits to see if the threshold is reached, but will return to idle within 2 ⁇ s of detecting the noise.
• the circuit 64 includes plural parallel channels, in the preferred embodiment a channel for each half of an array 20. In the unlikely instance of two or more simultaneous
• both events are discarded as they are difficult to isolate.
• eight low-noise P-ASIC integrated circuits 60 and at least one low noise linear power regulator 66 that preamplify signals from the four detector crystal arrays 20 are supported by each two sided circuit board or circuit board pair. These elements, when in operation, jointly produce a significant amount of heat.
• the P-ASICs typically generate about 300-500 mW each and the voltage regulators about 150-250 mW each. Having all of the components located on a circuit board running parallel to the detector would heat and damage or destroy the components .
• connector patterns are alternated to allow the circuit boards 62 to be placed perpendicular to ,the detector array 18.
• the circuit boards are spaced to define air channels or ducts 80 therebetween to dissipate heat.
• the circuit boards 62 have vertical connector sockets 82. More specifically, each of the detector arrays 20 has two rows of pins extending from its lower side. Each back-to-back circuit board pair or two-sided circuit board 62 includes four sockets 82 mounted facing toward one of the edges. Placing sockets on opposite sides of the circuit board provides a stable mechanical mounting for each array as well as a reliable electrical interconnection.
• a set of fans 84 draw outside air through the channels 80 across the circuit boards 62 cooling the components located thereon. More specifically, the fans are mounted in apertures in one side wall of a housing 84 opposite an air inlet 86.
• a coolant or liquid cryogen, additional fans, or the like are incorporated in the housing to enhance cooling.
• the radioactive source is mounted and fixed on the opposite side of the subject across from the detector array. In this manner, the ⁇ -rays which originate outside the subject either from a point or line source of radioactive material or a low power x-ray tube pass through the subject.

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• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Physics & Mathematics (AREA)
• High Energy & Nuclear Physics (AREA)
• Molecular Biology (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Nuclear Medicine (AREA)
• Measurement Of Radiation (AREA)
• Solid State Image Pick-Up Elements (AREA)
• Cooling Or The Like Of Electrical Apparatus (AREA)

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• 2001
  • 2001-11-21 WO PCT/US2001/043392 patent/WO2003046610A1/en active Application Filing
  • 2001-11-21 EP EP01273249A patent/EP1466191A1/de not_active Withdrawn
  • 2001-11-21 JP JP2003547994A patent/JP4429723B2/ja not_active Expired - Fee Related

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