Dedicated breast computed tomography system

1. A computed tomography system, comprising:

a table with a hole therein, wherein the table is configured to support a person lying face down thereon, with at least one of the person's breasts projecting through the hole;

an X-ray source;

an X-ray detector comprising a plurality of pixels;

wherein the X-ray source is configured to rotate around the at least one of the person's breasts;

wherein the X-ray detector comprises:

an X-ray absorption layer comprising an electric contact;

a first voltage comparator configured to compare a voltage of the electric contact to a first threshold;

a second voltage comparator configured to compare the voltage to a second threshold;

a controller;

a plurality of counters each associated with a bin and configured to register a number of X-ray photons absorbed by one of the pixels wherein the energy of the X-ray photons falls in the bin;

wherein the controller is configured to start a time delay from a time at which the first voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the first threshold;

wherein the controller is configured to determine whether an energy of an X-ray photon falls into the bin;

wherein the controller is configured to cause the number registered by the counter associated with the bin to increase by one;

wherein a rate of change of the voltage is substantially zero at expiration of the time delay.

2. The computed tomography system of claim 1 , wherein the X-ray detector further comprises a capacitor module electrically connected to the electric contact, wherein the capacitor module is configured to collect charge carriers from the electric contact.

3. The computed tomography system of claim 1 , wherein the controller is configured to activate the second voltage comparator at a beginning or expiration of the time delay.

4. The computed tomography system of claim 1 , wherein the controller is configured to connect the electric contact to an electrical ground.

5. The computed tomography system of claim 1 , wherein the X-ray absorption layer comprises a diode.

6. The computed tomography system of claim 1 , wherein the X-ray absorption layer comprises silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof.

7. The computed tomography system of claim 1 , wherein each pixel of the X-ray detector is configured to count numbers of X-ray photons incident thereon whose energy falls in a plurality of bins, within a period of time; and wherein the X-ray detector is configured to add the numbers of X-ray photons for the bins of the same energy range counted by all the pixels.

8. The computed tomography system of claim 7 , wherein the X-ray detector is configured to compile the added numbers as a spectrum of the X-ray photons incident on the X-ray detector.

9. The computed tomography system of claim 1 , wherein the X-ray detector does not comprise a scintillator.

10. The computed tomography system of claim 1 , wherein the plurality of pixels are arranged in an array.

11. The computed tomography system of claim 1 , wherein the pixels are configured to count the numbers of X-ray photons within a same period of time.

12. The computed tomography system of claim 1 , wherein each of the pixels comprises an analog-to-digital converter (ADC) configured to digitize an analog signal representing the energy of an incident X-ray photon into a digital signal.

13. The computed tomography system of claim 1 , wherein the pixels are configured to operate in parallel.

14. The computed tomography system of claim 1 , wherein each of the pixels is configured to measure its dark current.

15. The computed tomography system of claim 1 , wherein the X-ray detector is configured to capture images for X-ray at different wavelengths.