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: A method of performing image reconstruction in a gamma camera system comprises the steps of performing a transmission scan of an object about a number of rotation angles to collect transmission projection data and performing an emission scan of the object about numerous rotation angles to collect emission projection data. The outer boundary of the object is then located based on the transmission projection data. Information identifying the boundary is then either stored in a separate body contour map or embedded in an attenuation map. The information identifying the boundary can be in the form of flags indicating whether individual pixels are inside or outside the boundary of the object. The emission projection data is then reconstructed, using the attenuation map if desired, to generate transverse slice images.

Abstract: A method of calibrating an attenuation map for use in emission imaging in a gamma camera system. The attenuation map is generated using a transmission scan of the object of interest. The map includes a number of attenuation coefficients for the object. A computer program for generating the attenuation map includes an instruction for scaling the attenuation coefficients in the map from the transmission energy level to the emission energy level using a scaling factor. The scaling factor includes an effective attenuation coefficient for water, which is determined empirically. To determine the effective attenuation coefficient, the number of photons which pass from a transmission source through known depths of water using the emission energy level is counted. The effective attenuation coefficient is computed based on a standard equation describing the attenuation of photons by an absorber. The scaling factor used by the computer program is then set based on the effective attenuation coefficient.

Abstract: A method of coregistering medical image data of different modalities is provided. In the method, an emission scan of an object is performed using a nuclear medicine imaging system to acquire single-photon emission computed tomography (SPECT) image data. A transmission scan of the object is performed simultaneously with the emission scan using the same nuclear medicine imaging system in order to acquire nuclear medicine transmission image data. The emission scan is performed using a roving zoom window, while the transmission scan is performed using the full field of view of the detectors. By knowing the position of the zoom windows for each detection angle, the nuclear medicine transmission image data can be coregistered with the SPECT emission image data as a result of the simultaneous scans.

Abstract: A scan speed procedure and method wherein a minimum radiation exposure period is determined on an object by object basis for a transmission study. Two transmission scans are performed including a prescan followed by a second transmission scan phase. The first transmission prescan is performed using a radiation source over the object. This prescan is of a rapid and predetermined duration (Tp). A resultant count density associated with the object is then generated and examined. The portion having the smallest count density (Cm) is determined and a value (Co) representing the minimum required number of counts for transmission study is given. From the above, a transmission period (Ts) is determined by the system and the second transmission scan phase is performed for the duration Ts using a multi-pass scan phase.

Abstract: A method and apparatus for collecting transmission information utilizing a large field of view of a detector and for collecting emission data using a small field of view window of the same detector. The system employs the large field of view of a scintillation detector in order to collect transmission data for the entire body being scanned. Such a technique improves the quantitative capability of emission data by acquiring non-truncated attenuation factors. The emission data of a small field of view window is collected so that high resolution image pixels are used for processing the emission data (e.g., of a particular body organ). Since a large field of view is used for collecting the transmission data, the imaging pixels for transmission data are of lower resolution than the emission data. The emission data can be collected using a roving zoom technique during an ECT scan.

Abstract: A mechanism and method for performing transmission and emission scanning sessions with two line sources and two detectors wherein two sliding transmission detection windows are employed to differentiate between transmission and emission photons. Transmission and emission data can be collected simultaneously. This system provides that the dual transmission detection windows are each associated with a particular line source and move in synchronization with the associated line source. Further, the two line sources and the two detector windows all move in synchronization in the direction of the long axis of the object being scanned and at any given position all are within a given spatial plane that is transverse to the long axis of the object. In this configuration, the system can effectively reduce the amount of cross-talk detected by a detector (e.g., cross-talk being scattered photon radiation detected by a given detector but not originating from the detector's associated line source).

Abstract: A variable filter arrangement wherein differently sized and shaped filters are automatically selected and installed from a collection of filters housed within a configuration for use with a radiation source. The line source is typically used for transmission scanning to collect attenuation correction factors. A line source is utilized in the preferred embodiment and a series of filters (e.g., differently sized "bow-tie" filters) are rotatably attached to a central junction so that a particular filter can be rotated into an installed position. When installed, the filter acts to attenuate the radiation emitted from the line source to reduce radiation emitted on an otherwise unobstructed area of a scintillation detector. Differently sized filters are advantageously used to accommodate differently sized patents and also to accommodate different unobstructed parts of a detector for different angles of rotation during an ECT transmission scan.