Abstract: A positron emission detection scanner includes a first plurality of detecting elements arranged in a first two dimensional geometrical array, the detecting elements defining a first detection surface oriented for receiving radiant energy stimulus incident thereto. The detecting elements each have a second surface for communicating light from a scintillation event occurring in response to receiving a radiant energy stimulus. A light transmitting member is provided for receiving light from the scintillation events from each of the detecting elements. A second plurality of light sensing members is arranged in a second two dimensional geometrical array, different from the first geometrical array, the alignment of the light sensing members is independent of the detecting elements.

Abstract: A method of correcting for deadtime and for emission contamination of a transmission scan in a nuclear camera system is provided. The transmission scan is used to correct positron emission tomography (PET) images for attenuation. The camera system includes two detectors and two corresponding single-photon point sources that are collimated to produce fanbeam illumination profiles. A transmission detection window and an emission contamination detection window is defined on each detector. Radiation from each source is scanned axially across the field of view of the corresponding detector in synchronization with the corresponding transmission detection window to acquire transmission projection data. The emission contamination detection windows are also scanned axially concurrently with, but offset from, the transmission detection windows to acquire emission data.

Abstract: An event detector method and apparatus are described. One embodiment includes a first detector that includes a plurality of zones. Each zone includes a plurality of detector devices, wherein each zone generates a zone trigger signal when an event is detected by a detector device in the zone. The embodiment further includes a first energy source coupled to the first detector, wherein when the first energy source is active, events occur that are detectable by the first detector. A calibration circuit is coupled to the first detector, to perform timing calibration of zone trigger signals of zones of the first detector with respect to timing of a reference zone trigger signal of the predetermined reference zone of the first detector, wherein the zone trigger signals and the reference zone trigger signal are generated when an event is detected.

Abstract: A method and apparatus for selectively integrating PMT channel signals in a gamma camera system are described. A trigger word is decoded to determine which of multiple PMT channels are affected by a given scintillation event. When two scintillation events overlap both spatially and temporally, only those channels which are affected by both events stop integrating in response to the second event. Pre-pulse pile-up is corrected by removing the tail of a preceding pulse from a current pulse using an approximation of the tail of the preceding pulse based upon the instantaneous energy of the current pulse and the current countrate. Extrapolation of the tail of the current pulse may also be performed in essentially the same manner.

Abstract: The imaging system has two detectors which can be rotated in a circular path about an object with the angular displacement between the detectors and their radial position with respect to the axis being adjustable. Preferably, the distance of the detectors from the lateral axis is adjustable to increase resolution of the system. A gantry has supports for drive gear rings for the detectors with radial motion mechanisms connecting one detector to the interior surface of a drive gear ring and the other to the exterior of its drive gear ring via a support arm. A drive gear and idler gear move one detector along the circular path and a radial drive motor moves the detectors radially with respect to the axis.

Abstract: A transmission pre-scan of a patient is used in a nuclear medicine imaging system to determine the duration of a subsequent transmission scan of the patient. The transmission scan is for acquiring an attenuation map of the patient to correct emission data of the patient for non-uniform attenuation. As a result, the patient's exposure to radiation during the transmission scan is not excessive, yet transmission image quality is maintained. A radiation transmission source and a radiation detector are operated to perform the transmission pre-scan of the object, during which the transmission source remains in a fixed position. Downscatter correction is applied to correct the transmission pre-scan data for emission contamination. Count values from the pre-scan data are integrated axially.

Abstract: A technique for correcting for random coincidences in a gamma camera system is provided. The system includes a pair of scintillation detectors coupled to a processing system and is configured to detect radiation coincidences. Each detector generates trigger pulses in response to scintillation events to generate a plurality of event-based trigger pulses. Each detector includes a pulse generator, which generates a plurality of artificial trigger pulses. When an artificial trigger pulse in one detector occurs in coincidence with an event-based trigger pulse in the other detector, data is registered by the corresponding detectors, and the artificial trigger pulse is associated with a predetermined energy level. The data processing system examines the data to identify singles events that were registered as a result of artificial trigger pulses and prevents such singles events from contributing to the coincidence images. Instead, such singles events are used to generate a singles image for each detector.

Abstract: A universal nuclear medicine imager (UNMI) enables planar, SPECT and PET studies. The UNMI is a “position sensitive” type of detector which has a relatively thick (e.g., {fraction (6/8)} in.) NaI(TI) crystal optically divided by a thin non-scintillating material into two half-thicknesses of ⅜ in. each. The UNMI detector uses a light collimator system to enable a depth of interaction (DOI) determination in addition to a two-dimensional location of gamma photons in the half-thicknesses of the crystal. The system includes a combination of a scintillating, optically more dense material with a non-scintillating, optically less dense material and uses the light refraction reflection law with PM tubes and coincidence circuits. For obtaining the optimal spatial resolution in planar and SPECT studies, a known DOI enables the use of only the lower ⅜ in.

Abstract: The imaging system has two detectors which can be rotated in a circular path about an object with the angular displacement between the detectors and their radial position with respect to the axis being adjustable. Preferably, the distance of the detectors from the lateral axis is adjustable to increase resolution of the system. A gantry has supports for drive gear rings for the detectors with radial motion mechanisms connecting one detector to the interior surface of a drive gear ring and the other to the exterior of its drive gear ring via a support arm. A drive gear and idler gear move one detector along the circular path and a radial drive motor moves the detectors radially with respect to the axis.

Abstract: A method and apparatus are provided for detecting scintillation events in a gamma camera detector using virtual photomultiplier tubes (PMTs). The gamma camera detector includes multiple real PMTs within the actual field of view of the detector as well as multiple virtual PMTs defined outside the actual field of view. In response to a scintillation event occurring near the edge of the field of view, one of the real PMTs responding to the event is identified. The event is then mapped to one or more virtual PMTs based on the identified real PMT. Data representing a response of the virtual PMT is then generated based on a response of a corresponding one of the real PMTs. Data representing responses of both the affected real PMTs and selected ones of the virtual PMTs are used in a centroid computation for the event, to increase the effective field of view of the detector.

Abstract: A method and apparatus for selectively integrating PMT channel signals in a gamma camera system are described. A trigger word is decoded to determine which of multiple PMT channels are affected by a given scintillation event. When two scintillation events overlap both spatially and temporally, only those channels which are affected by both events stop integrating in response to the second event. Pre-pulse pile-up is corrected by removing the tail of a preceding pulse from a current pulse using an approximation of the tail of the preceding pulse based upon the instantaneous energy of the current pulse and the current countrate. Extrapolation of the tail of the current pulse may also be performed in essentially the same manner.

Abstract: A nuclear medicine imaging system provides three-axis linear and rotary detector motion. The imaging system includes an overhead gantry, which includes a carriage supported above the object and movable in translation along a first horizontal axis. Support arms are suspended downward from the carriage and are movable along a second horizontal axis perpendicular to the first horizontal axis. A detector is coupled to a lower end of each support arm. Each support arm is retractably extendible along a substantially vertical axis, and each detector is pivotable about a horizontal axis parallel to the first horizontal axis. Each support arm cooperates with the carriage to enable the corresponding detector to be positioned at multiple angular positions about a longitudinal axis corresponding to multiple projection angles by using combinations of independent linear movements of the detectors along any of three perpendicular axes.

Abstract: A method and apparatus for calibrating a programmable delay in a timing circuit of a gamma camera detector are provided. The programmable delay has an error, the value of which is to be determined. An input signal that is applied as input to the programmable delay is simultaneously applied as input to a precision fixed delay. The fixed delay has a delay value within the programmable range of the programmable delay, but has an error that is substantially smaller than that of the programmable delay. The output of the programmable delay is applied to one input of a decision circuit, and the output of the fixed delay is applied to another input of the decision circuit. The delay of the programmable delay is initially programmed to a value that is substantially greater than the delay of the fixed delay, and input pulses are then applied to both delays.

Abstract: A dual-purpose transmission source for use in a nuclear medicine imaging system is described. A Cs-137 point source is used to transmit radiation having a 662 keV photopeak to a corresponding detector during a transmission scan of an object. The Cs-137 source can be used in transmission scans for correcting either coincidence or single-photon emission data for non-uniform attenuation. When performing a transmission scan to correct single-photon emission data, a collimator may remain mounted to the detector, since a substantial portion of the transmitted radiation completely penetrates the radiation-absorbing material of the collimator to reach the detector.

Abstract: A method of correcting for deadtime and for emission contamination of a transmission scan in a nuclear camera system is provided. The transmission scan is used to correct positron emission tomography (PET) images for attenuation. The camera system includes two detectors and two corresponding single-photon point sources that are collimated to produce fanbeam illumination profiles. A transmission detection window and an emission contamination detection window is defined on each detector. Radiation from each source is scanned axially across the field of view of the corresponding detector in synchronization with the corresponding transmission detection window to acquire transmission projection data. The emission contamination detection windows are also scanned axially concurrently with, but offset from, the transmission detection windows to acquire emission data.

Abstract: A method of correcting for deadtime in an attenuation map generated by a nuclear medicine imaging system is provided. The imaging system includes a gamma ray detector that is rotatable about an object to be imaged. A region is defined on the imaging surface of the detector, such as the edge of the field of view of the detector, such that during a transmission scan of the object, the radiation shadow of the object is substantially less likely to fall upon the defined region than upon other regions of the imaging surface. A blank transmission scan is then performed, including recording the radiation intensity level detected in the region as a reference intensity level. A transmission scan of the object is then performed to acquire an attenuation map of the object, including recording a radiation intensity level detected in the first region during the transmission scan.

Abstract: A method and apparatus for correcting for random coincidences in a gamma camera imaging system are provided, based on the distribution of the object to be imaged as well as the measured singles and coincidence rates. Gamma radiation emitted from the object is detected for multiple projection angles, including detection of a plurality of coincidence events, to generate an object profile. The singles rate and the coincidence rate are also measured for each of the projection angles. A randoms distribution representing random coincidences in the detected coincidence events is then determined, including computing a randoms profile as the convolution of the object profile and a Gaussian function.

Abstract: A method of acquiring transmission self-contamination data for correcting transmission scan data in a nuclear camera system including two transmission radiation sources and two scintillation detectors. A first source is for transmitting radiation to only a first detector and a second source is for transmitting radiation to only a second detector during a transmission scan of an object to be imaged. To acquire the calibration data, radiation is transmitted from the second source to the second detector while the first source is maintained in a non-transmitting state. While the second source is transmitting, the first detector is used to detect the radiation transmitted from the second source. A set of self-contamination data is then generated based on the radiation from the second source detected with the first detector. The calibration data is used to correct a subsequent transmission scan of the object by subtracting the self-contamination data from the transmission scan data.

Abstract: A method of correcting for attenuation during emission imaging in a gamma camera medical imaging system. Attenuation values are determined empirically and are stored in a look-up table in a memory that is readable by the imaging system, with each attenuation value corresponding to a given thickness value. The attenuation values are computed before imaging is performed by first measuring the number of photons which pass from a transmission source through various known depths of water or another suitable model attenuator, using the same radiation source as will be used for emission imaging. For each depth, the measurement is then used to compute the actual attenuation for a thickness of the model attenuator. The attenuation is then stored as a value in the look-up table with corresponding values of attenuator thickness and is later used to correct emission data for the effects of attenuation.

Abstract: An improved image acquisition system allows the angular displacement between two detectors to be adjusted between 90° and 180° to reduce the imaging time for both 360° and 180° scans. A patient table is displaced vertically and horizontally from a lateral axis to allow the body of a patient to be positioned next to the detectors and to improve resolution.