PET DETECTOR SHIELDING METHOD AND SYSTEM
Publication Date: 2005-Apr-08
The IP.com Prior Art Database
In an embodiment, the system comprises a thin layer of isolation maintained between a mu metal shield 18 for a PMT 15 circuitry and an outer shield 20. This thin layer of isolation creates a capacitance between the mu metal shield 18 and the outer shield 20, and hence serves as a low impedance path for high frequency EMI noise directly to chassis, thereby shunting any noise energy away from the sensitive circuitry.
FIELD OF THE INVENTION
 This invention relates generally to shielding methods, and more particularly to, a method and system for shielding a Positron Emission Tomography (PET) detector.
BACKGROUND OF THE INVENTION
 Typically, in a PET scanner, a ring of detectors is configured to detect emitted gamma ray photons given off during the decay/annihilation process of a radioactive isotope material. The first stage of the detection process occurs in the detector where the gamma photons are converted into an electronic signal.
 The detectors accomplish this in two steps: (i) the first part of the detector consist of a scintillator crystal material that absorbs the photon energy and converts to visible light. (ii) The second part of the detector consist of a Photo Multiplier Tube (PMT) and a preamp circuit which converts the emitted light into a small electric current. The preamp circuitry has a high impedance input and a high gain and high slew rate output. This facilitates accurate detection and timing of the emitted signal.
 Additional circuitry is then used to determine if the current pulse shape and amplitude is representative of a ‘real’ emitted photon and whether a coincident photon was detected on an opposing detector within the same plane of the ring. The detector’s high impedance and high gain/slew rate circuitry designed to facilitate accurate detection and timing of photons also creates sensitivity problems to other noise sources such as radiated electromagnetic fields. The effect of this susceptibility is likely to result in loss of performance and sensitivity of the overall system. The ability to demonstrate immunity to outside noise sources improves the performance requirement in relation to international compliance tests.
 Thus, there exists a need for a method and system for shielding PET scanner, wherein the method and system provides a scanner with improved sensitivity, high noise immunity and improved overall performance.
SUMMARY OF THE INVENTION
 In one embodiment, a method of shielding a PET scanner comprises connecting an outer shield of a detector module to a chassis ground.
 In another embodiment, a method of shielding a PET scanner comprises providing a mu metal shielding at the inner side of an outer shield and grounding the mu metal shield directly to the outer shield using a gasket tape.
 In yet another embodiment, a method of shielding a PET scanner comprises providing an outer layer of conductive tape over a substantially thin layer of high dielectric insulating tape, to isolate an inner mu metal shield from an outer shield.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 shows an example of shielding a PET detector according to one embodiment of this invention.
 FIG. 2 shows an arrangement for shielding a PET detector according to another embodiment of the present invention.
 FIG. 3 s...