Nuclear medicine diagnostic apparatus

1 . A nuclear medicine diagnostic apparatus comprising:

a plurality of detector units configured to detect gamma rays, each of the detector units including

detection circuitry configured to detect an analog signal based on a result of detecting the gamma rays,

generation circuitry configured to generate a clock signal, and

first production circuitry configured to produce time information by measuring a time over which an intensity of the analog signal detected by the detection circuitry exceeds a predetermined threshold and converting the time into a digital signal on the basis of the clock signal generated by the generation circuitry, wherein

the plurality of detector units includes a first detector unit and a second detector unit different from the first detector unit, the first detector unit including a first generation circuitry configured to generate a first clock signal, the second detector unit including a second generation circuitry configured to generate a second clock signal, and the generation circuitry comprising the first and second generation circuitry, and

the nuclear medicine diagnostic apparatus further includes:

first acquisition circuitry configured to acquire, on the basis of a synchronization signal generated by synchronization signal generation circuitry, first time information produced by the first production circuitry of the first detector unit, on the basis of the first clock signal;

second acquisition circuitry configured to acquire, on the basis of the synchronization signal, second time information produced by the first production circuitry of the second detector unit on the basis of the second clock signal; and

processing circuitry configured to correct an offset of the time information between the first detector unit and the second detector unit on the basis of the first time information and the second time information.

2 . The nuclear medicine diagnostic apparatus according to claim 1 , wherein

the processing circuitry is further configured to store difference information between the first time information and the second time information in a memory, and correct the offset of the time information between the first detector unit and the second detector unit by using the difference information.

3 . The nuclear medicine diagnostic apparatus according to claim 2 , wherein

each of the detector units further comprises:

second production circuitry configured to produce counting information including a detection time of the gamma rays on the basis of the analog signal and the time information, and

the processing circuitry is further configured to use the difference information and correct a detection time included in the counting information produced by the second production circuitry of the second detector unit so as to match the detection time with a detection time included in the counting information produced by the second production circuitry of the first detector unit.

4 . The nuclear medicine diagnostic apparatus according to claim 2 , wherein

the processing circuitry is further configured to use the difference information and correct time information produced by the first production circuitry of the second detector unit so as to match the time information with time information produced by the first production circuitry of the first detector unit.

5 . The nuclear medicine diagnostic apparatus according to claim 2 , wherein

the first acquisition circuitry and the second acquisition circuitry are further configured to re-acquire the first time information and the second time information after the difference information is stored in the memory, and

the processing circuitry is further configured to verify whether correction of the offset of the time information using the difference information is correctly performed, on the basis of the re-acquired first time information and second time information.

6 . The nuclear medicine diagnostic apparatus according to claim 1 , wherein

the first acquisition circuitry and the second acquisition circuitry are further configured to, after a rise in power of all the detector units, acquire the first time information and the second time information on the basis of the synchronization signal.

7 . The nuclear medicine diagnostic apparatus according to claim 1 , wherein

the processing circuitry is further configured to use a linear equation representing a relationship between the time information and an elapsed time defined for each frequency of the clock signal, and correct the offset of the time information caused by a frequency offset of the clock signal between the first detector unit and the second detector unit.

8 . The nuclear medicine diagnostic apparatus according to claim 1 , wherein

the synchronization signal generation circuitry is a scintillator included in the detection circuitry, the synchronization signal being a gamma ray generated by spontaneous decay of the scintillator, and

the first acquisition circuitry and the second acquisition circuitry are further configured to acquire the first time information and the second time information when the gamma ray due to the spontaneous decay is generated.

9 . The nuclear medicine diagnostic apparatus according to claim 1 , further comprising:

processing circuitry configured to

reconstruct a PET image on the basis of data on the gamma rays detected by the detector units, and

reconstruct the PET image by using data collected after a detector unit for a last scan to be started starts the scan.

10 . The nuclear medicine diagnostic apparatus according to claim 1 , wherein

the generation circuitry is an oscillator, and

the first production circuitry is a time to digital converter.