Radiation imaging apparatus
Provided is a radiographic imaging apparatus including a photon-counting detector that prevents variation in count rate performance by using self-heating of a photon-counting circuit, and improves accuracy in detecting photons. The photon-counting detector is provided with a semiconductor layer configured to generate electrical charge upon receipt of photons of radiation, a photon-counting circuit configured to read current values from pixel electrodes formed on one of the semiconductor surfaces, and a heat amount compensator configured to control an amount of heat of the photon-counting circuit according to a count rate of the photon-counting circuit. The heat amount compensator is activated when the count rate is low so that the amount of heat delivered from the photon-counting circuit when the count is low becomes nearly equal to the amount of heat delivered from the photon-counting circuit when the count rate is high.
1. A radiographic imaging apparatus comprising,
a radiation source and
a photon-counting detector configured to detect radiation emitted from the radiation source and to output electrical signals in association with the number of photons of the radiation, and further comprising,
a photon-counting circuit configured to count the number of the photons, and
a heat amount compensator configured to control an amount of heat of the photon-counting circuit according to detection of the number of photons, so as to provide the amount of heat independent of the number of photons being counted.
2. The radiographic imaging apparatus according to claim 1 , wherein, the heat amount compensator controls the amount of heat, on the basis of a previously-obtained relation between a photon count rate and the amount of heat of the photon-counting circuit.
3. The radiographic imaging apparatus according to claim 1 , wherein,
the heat amount compensator includes a heating element, and
the heat amount compensator controls the heating element according to an output from the photon-counting circuit.
4. The radiographic imaging apparatus according to claim 3 , wherein,
the photon-counting circuit incorporates a plurality of circuit components, and
the heating elements are placed in proximity to the plurality of circuit components.
5. The radiographic imaging apparatus according to claim 3 , wherein,
the heat amount compensator is placed in any of structural components constituting the photon-counting detector.
6. The radiographic imaging apparatus according to claim 3 , wherein,
the photon-counting detector includes the photon-counting circuits more than one, and
the heating elements are placed between the photon-counting circuits being adjacent, among the photon-counting circuits.
7. The radiographic imaging apparatus according to claim 3 , wherein,
the photon-counting detector comprises a semiconductor layer configured to detect radiation photons, and a substrate configured to support the semiconductor layer and to connect the semiconductor layer with the photon-counting circuit, and
the heating elements are placed within the substrate.
8. The radiographic imaging apparatus according to claim 3 , wherein,
the photon-counting detector comprises,
the photon-counting circuits more than one,
a control circuit configured to control the photon-counting circuits, and
a substrate configured to support the control circuit and to connect the photon-counting circuits with the control circuit, and
the heating elements are placed within the substrate.
9. The radiographic imaging apparatus according to claim 1 , wherein,
the heat amount compensator comprises a pseudo pulse generator configured to output a pseudo pulse to the photon-counting circuit, wherein,
the pseudo pulse generator controls at least one of a magnitude of the pseudo pulse and a generation period thereof, by using an output from the photon-counting circuit.
10. The radiographic imaging apparatus according to claim 9 , wherein,
the photon-counting detector comprises the photon-counting circuits more than one, and
the pseudo pulse generator is placed in each of the photon-counting circuits.
11. The radiographic imaging apparatus according to claim 1 , wherein,
the heat amount compensator corresponds to a counter redundant-operation circuit configured to generate (N+M) high-level signals and N low-level signal, with respect to the number of photons M being counted, where M is equal to 1 or 0, and N is an integer equal to or larger than 1.
12. The radiographic imaging apparatus according to claim 11 , wherein,
the photon-counting detector comprises the photon-counting circuits more than one,
the photon-counting circuits are respectively provided with a plurality of counters having different thresholds for the photons being counted, and
at least one of the counters is provided with the counter redundant-operation circuit.
13. The radiographic imaging apparatus according to claim 9 , wherein,
the photon-counting detector comprises the photon-counting circuits more than one, and
the heat amount compensator is placed only in one of the photon-counting circuits adjacent to each other, among the photon-counting circuits.
14. The radiographic imaging apparatus according to claim 13 , wherein,
an output from the photon-counting circuit where the heat amount compensator is placed, among the adjacent photon-counting circuits in the photon-counting detector, is complemented by using an output from the photon-counting circuit where the heat amount compensator is not placed.
15. The radiographic imaging apparatus according claim 1 , wherein,
the radiographic imaging apparatus is an X-ray CT apparatus.
16. The radiographic imaging apparatus according to claim 15 , wherein,
the photon-counting detector is provided in a rotatable manner at a position opposed to the radiation source, placing the center of rotation therebetween, comprising the photon-counting circuits more than one being arranged in the direction of rotation, and
the heat amount compensators are placed in some of the photon-counting circuits, arranged in a region including the center or in proximity to the center of the direction of rotation, among the photon-counting circuits arranged in the direction of rotation.