System and method for PET imaging

A system for positron emission tomography-computed tomograph (PET-CT) imaging, comprising:

• a gantry comprising a detection region to accommodate a subject, the detection region including a first portion and a second portion;
• an X ray emission device;
• a first detector assembly surrounding the first portion of the detection region, the first detector assembly being configured to detect at least a portion of an X ray beam emitted by the X ray emission device and traversing the subject located within the first portion of the detection region;
• a second detector assembly surrounding the second portion of the detection region, the second detector assembly being configured to detect radiation rays emitted from the subject located within the second portion of the detection region, the second detector assembly including a plurality of detector rings, each detector ring of the plurality of detector rings including a plurality of scintillators, wherein
• the second detector assembly includes N detector groups arranged along an axial direction of the gantry, each of the N detector groups including at least two of the plurality of detector rings,
• the system further comprises a controller configured to control the N detector groups to detect first cross coincidence events,
• for each of the first cross coincidence events,
• the first cross coincidence event corresponds to a line of response (LOR) that is a straight line connecting a first scintillator and a second scintillator of the scintillators of the Plurality of detector rings, the first scintillator and the second scintillator detecting the first cross coincidence event, the first scintillator belonging to a first detector group of the N detector groups, the second scintillator belonging to a second detector group of the N detector groups different from the first detector group,
• an offset of the LOR refers to a number that equals a count of the detector groups by which the first detector group and the second detector group are separated along the axial direction plus 1, and
• the offset of the LOR corresponding to the first cross coincidence event is no less than 2 and no larger than N, and
• the controller is further configured to set, based on the offset of the LOR corresponding to each of the first cross coincidence events, a time window to detect the first cross coincidence events, the time window being variable with respect to the offset of the LOR corresponding to each of the first cross coincidence events.

A system for imaging, comprising:

• a gantry comprising a detection region to accommodate a subject;
• and
• a detector assembly surrounding the detection region, the detector assembly being configured to detect radiation rays emitted from the subject located within the detection region, the detector assembly including a Plurality of detector rings, each detector ring comprising a Plurality of scintillators and a Plurality of photosensors, the Plurality of detector rings being arranged on the gantry in an axial direction of the gantry, the detector assembly comprising N detector groups each of which comprises one or more of the Plurality of detector rings, the gantry comprising N supporting structures, the N detector groups and the N supporting structures being configured as N positron emission tomography (PET) detectors each of which comprises one of the N supporting structures and one of the N detector groups assembled on the one of the N supporting structures;
• and
• a controller configured to control the N detector groups to detect first cross coincidence events;
• wherein
• for each of the first cross coincidence events,
• the first cross coincidence event corresponds to a line of response (LOR) that is a straight line connecting a first scintillator and a second scintillator of the scintillators of the Plurality of detector rings, the first scintillator and the second scintillator detecting the first cross coincidence event, the first scintillator belonging to a first PET detector of the N PET detector, the second scintillator belonging to a second PET detector of the N PET detectors different from the first PET detector,
• an offset of the LOR refers to a number that equals a count of the PET detectors by which the first PET detector and the second PET detector are separated along the axial direction plus 1, and
• the offset of the LOR corresponding to the first cross coincidence event is no less than 2 and no larger than N, and
• the controller is further configured to set, based on the offset of the LOR corresponding to each of the first cross coincidence events, a time window to detect the first cross coincidence events, the time window being variable with respect to the offset of the LOR corresponding to each of the first cross coincidence events.