Patent ID: 12196693

DETAILED DESCRIPTION

FIG.1schematically shows a radiation detector100, as an example. The radiation detector100includes an array of pixels150. The array may be a rectangular array (as shown inFIG.1), a honeycomb array, a hexagonal array or any other suitable array. The array of pixels150in the example ofFIG.1has 7 rows and 4 columns; however, in general, the array of pixels150may have any number of rows and any number of columns.

Each pixel150is configured to detect radiation from a radiation source (not shown) incident thereon and may be configured to measure a characteristic (e.g., the energy of the particles, the wavelength, and the frequency) of the radiation. A radiation may include particles such as photons (electromagnetic waves) and subatomic particles. Each pixel150may be configured to count numbers of particles of radiation incident thereon whose energy falls in a plurality of bins of energy, within a period of time. All the pixels150may be configured to count the numbers of particles of radiation incident thereon within a plurality of bins of energy within the same period of time. When the incident particles of radiation have similar energy, the pixels150may be simply configured to count numbers of particles of radiation incident thereon within a period of time, without measuring the energy of the individual particles of radiation.

Each pixel150may have its own analog-to-digital converter (ADC) configured to digitize an analog signal representing the energy of an incident particle of radiation into a digital signal, or to digitize an analog signal representing the total energy of a plurality of incident particles of radiation into a digital signal. The pixels150may be configured to operate in parallel. For example, when one pixel150measures an incident particle of radiation, another pixel150may be waiting for a particle of radiation to arrive. The pixels150may not have to be individually addressable.

The radiation detector100described here may have applications such as in an X-ray telescope, X-ray mammography, industrial X-ray defect detection, X-ray microscopy or microradiography, X-ray casting inspection, X-ray non-destructive testing, X-ray weld inspection, X-ray digital subtraction angiography, etc. It may be suitable to use this radiation detector100in place of a photographic plate, a photographic film, a PSP plate, an X-ray image intensifier, a scintillator, or another semiconductor X-ray detector.

FIG.2Aschematically shows a simplified cross-sectional view of the radiation detector100ofFIG.1along a line2A-2A, according to an embodiment. More specifically, the radiation detector100may include a radiation absorption layer110and an electronics layer120(e.g., an ASIC) for processing or analyzing electrical signals which incident radiation generates in the radiation absorption layer110. The radiation detector100may or may not include a scintillator (not shown). The radiation absorption layer110may include a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor material may have a high mass attenuation coefficient for the radiation of interest.

FIG.2Bschematically shows a detailed cross-sectional view of the radiation detector100ofFIG.1along the line2A-2A, as an example. More specifically, the radiation absorption layer110may include one or more diodes (e.g., p-i-n or p-n) formed by a first doped region111, one or more discrete regions114of a second doped region113. The second doped region113may be separated from the first doped region111by an optional intrinsic region112. The discrete regions114are separated from one another by the first doped region111or the intrinsic region112. The first doped region111and the second doped region113have opposite types of doping (e.g., region111is p-type and region113is n-type, or region111is n-type and region113is p-type). In the example ofFIG.2B, each of the discrete regions114of the second doped region113forms a diode with the first doped region111and the optional intrinsic region112. Namely, in the example inFIG.2B, the radiation absorption layer110has a plurality of diodes (more specifically, 7 diodes corresponding to 7 pixels150of one row in the array ofFIG.1, of which only 2 pixels150are labeled inFIG.2Bfor simplicity). The plurality of diodes have an electrode119A as a shared (common) electrode. The first doped region111may also have discrete portions.

The electronics layer120may include an electronic system121suitable for processing or interpreting signals generated by the radiation incident on the radiation absorption layer110. The electronic system121may include an analog circuitry such as a filter network, amplifiers, integrators, and comparators, or a digital circuitry such as a microprocessor, and memory. The electronic system121may include one or more ADCs. The electronic system121may include components shared by the pixels150or components dedicated to a single pixel150. For example, the electronic system121may include an amplifier dedicated to each pixel150and a microprocessor shared among all the pixels150. The electronic system121may be electrically connected to the pixels150by vias131. Space among the vias may be filled with a filler material130, which may increase the mechanical stability of the connection of the electronics layer120to the radiation absorption layer110. Other bonding techniques are possible to connect the electronic system121to the pixels150without using the vias131.

When radiation from the radiation source (not shown) hits the radiation absorption layer110including diodes, particles of the radiation may be absorbed and generate one or more charge carriers (e.g., electrons, holes) by a number of mechanisms. The charge carriers may drift to the electrodes of one of the diodes under an electric field. The field may be an external electric field. The electrical contact119B may include discrete portions each of which is in electrical contact with the discrete regions114. The term “electrical contact” may be used interchangeably with the word “electrode.” In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete regions114(“not substantially shared” here means less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of these charge carriers flow to a different one of the discrete regions114than the rest of the charge carriers). Charge carriers generated by a particle of the radiation incident around the footprint of one of these discrete regions114are not substantially shared with another of these discrete regions114. A pixel150associated with a discrete region114may be an area around the discrete region114in which substantially all (more than 98%, more than 99.5%, more than 99.9%, or more than 99.99% of) charge carriers generated by a particle of the radiation incident therein flow to the discrete region114. Namely, less than 2%, less than 1%, less than 0.1%, or less than 0.01% of these charge carriers flow beyond the pixel150.

FIG.2Cschematically shows an alternative detailed cross-sectional view of the radiation detector100ofFIG.1along the line2A-2A, according to an embodiment. More specifically, the radiation absorption layer110may include a resistor of a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof, but does not include a diode. The semiconductor material may have a high mass attenuation coefficient for the radiation of interest. In an embodiment, the electronics layer120ofFIG.2Cis similar to the electronics layer120ofFIG.2Bin terms of structure and function.

When the radiation hits the radiation absorption layer110including the resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. A particle of the radiation may generate 10 to 100,000 charge carriers. The charge carriers may drift to the electrical contacts119A and119B under an electric field. The electric field may be an external electric field. The electrical contact119B includes discrete portions. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete portions of the electrical contact119B (“not substantially shared” here means less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of these charge carriers flow to a different one of the discrete portions than the rest of the charge carriers). Charge carriers generated by a particle of the radiation incident around the footprint of one of these discrete portions of the electrical contact119B are not substantially shared with another of these discrete portions of the electrical contact119B. A pixel150associated with a discrete portion of the electrical contact119B may be an area around the discrete portion in which substantially all (more than 98%, more than 99.5%, more than 99.9% or more than 99.99% of) charge carriers generated by a particle of the radiation incident therein flow to the discrete portion of the electrical contact119B. Namely, less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of these charge carriers flow beyond the pixel associated with the one discrete portion of the electrical contact119B.

FIG.3schematically shows a top view of a package200including the radiation detector100and a printed circuit board (PCB)400. The term “PCB” as used herein is not limited to a particular material. For example, a PCB may include a semiconductor. The radiation detector100is mounted to the PCB400. The wiring between the radiation detector100and the PCB400is not shown for the sake of clarity. The PCB400may have one or more radiation detectors100. The PCB400may have an area405not covered by the radiation detector100(e.g., for accommodating bonding wires410). The radiation detector100may have an active area190, which is where the pixels150(FIG.1) are located. The radiation detector100may have a perimeter zone195near the edges of the radiation detector100. The perimeter zone195has no pixels and the radiation detector100does not detect particles of radiation incident on the perimeter zone195.

FIG.4schematically shows a cross-sectional view of an image sensor490, according to an embodiment. The image sensor490may include a plurality of the packages200ofFIG.3mounted to a system PCB450.FIG.4shows only 2 packages200as an example. The electrical connection between the PCBs400and the system PCB450may be made by bonding wires410. In order to accommodate the bonding wires410on the PCB400, the PCB400has the area405not covered by the radiation detector100. In order to accommodate the bonding wires410on the system PCB450, the packages200have gaps in between. The gaps may be approximately 1 mm or more. Particles of radiation incident on the perimeter zones195, on the area405or on the gaps cannot be detected by the packages200on the system PCB450. A dead zone of a radiation detector (e.g., the radiation detector100) is the area of the radiation-receiving surface of the radiation detector, in which incident particles of radiation cannot be detected by the radiation detector. A dead zone of a package (e.g., package200) is the area of the radiation-receiving surface of the package, in which incident particles of radiation cannot be detected by the detector or detectors in the package. In this example shown inFIG.3andFIG.4, the dead zone of the package200includes the perimeter zones195and the area405. A dead zone (e.g.,488) of an image sensor (e.g., image sensor490) with a group of packages (e.g., packages mounted on the same PCB, packages arranged in the same layer) includes the combination of the dead zones of the packages in the group and the gaps among the packages.

The image sensor490including the radiation detectors100may have the dead zone488incapable of detecting incident radiation. However, the image sensor490may capture images of all points of an object (not shown), and then these captured images may be stitched to form a full image of the entire object.

FIG.5schematically shows a perspective view of an imaging system500including the image sensor490ofFIG.4and a radiation source system of multiple radiation sources510, according to an embodiment. More specifically, as an example, the image sensor490may include 4 radiation detectors100represented for simplicity by their 4 active areas190A,190B,190C, and190D (or just190A-D for simplicity) which may be arranged in a 2×2 rectangular array. Between the 4 active areas190A-D is the dead zone488which is incapable of detecting incident radiation. In this example, the radiation source system of the imaging system500may include a 3×3 rectangular array of 9 radiation sources510.1-9which may be arranged in a plane512parallel to a top surface492of the image sensor490.

The operation of the imaging system500may be described briefly as follows, according to an embodiment. Firstly, an object520may be placed between the image sensor490and the radiation sources510.1-9. Then secondly, an exposure process may be performed in which the 9 radiation sources510.1-9are sequentially (i.e., one by one) turned on then off resulting in 36 images in the 4 active areas190A-D (each of the 9 radiation sources510.1-9turning on then off creates 4 images in the 4 active areas190A-D, hence 36 resulting images in total). In an embodiment, the arrangement of the active areas190A-D, the radiation sources510.1-9, and the object520is such that each point of the object520is captured in at least one image of the 36 resulting images. In other words, each point of the object520is captured in the 36 resulting images. In yet other words, no point of the object520is not captured in the 36 resulting images. Then thirdly, the 36 resulting images captured by the imaging system500may be stitched to form a full image of the entire object520.

More specifically, the exposure process may begin with a first radiation exposure during which only the radiation source510.1of the 9 radiation sources510.1-9is on and sending out radiation (i.e., the other 8 radiation sources are off). While the radiation source510.1is on, the 4 active areas190A-D capture incident radiation resulting in 4 images in these 4 active areas.

The radiation incident on the 4 active areas190A-D while the radiation source510.1is on may include 3 types of incident particles of radiation: (a) particles of radiation that came directly from the radiation source510.1(i.e., their paths do not intersect the object520), (b) particles of radiation that came from the radiation source510.1and penetrated the object520without changing direction, and (c) particles of radiation that also came from the object520like type (b) but are not of type (b). Examples of type (c) incident particles of radiation include scattered particles of radiation and reflected particles of radiation.

In an embodiment, the radiation from the radiation source510.1is such that incident particles of radiation of type (c) are negligible in comparison to incident particles of radiation of types (a) and (b). As an example of this embodiment, the object520may be an animal, and the radiation from the radiation source510.1may be X-ray. In this example where the object520is an animal, the radiation from the radiation source510.1, in an embodiment, may not be visible lights because that would make incident particles of radiation of type (c) (i.e., reflected photons to be specific) significant whereas incident particles of radiation of type (b) (i.e., photons that penetrated the object520) are negligible.

After the first radiation exposure is complete, the exposure process may continue with (i) reading out the 4 resulting images from the 4 active areas190A-D for later processing, and then (ii) resetting the 4 active areas190A-D.

Next, the exposure process may continue with a second radiation exposure during which only the radiation source510.2of the 9 radiation sources510.1-9is on and sending out radiation. While the radiation source510.2is on, the 4 active areas190A-D capture incident radiation resulting in 4 images in these 4 active areas. In other words, the operation of the imaging system500during the second radiation exposure is similar to during the first radiation exposure. After the second radiation exposure is complete, the exposure process may continue with (i) reading out the 4 resulting images from the active areas190A-D for later processing, and then (ii) resetting the active areas190A-D.

After that, the exposure process may continue with a third, fourth, fifth, six, seventh, eighth, and then finally ninth radiation exposures sequentially (i.e., in series). After each of these radiation exposures, the 4 corresponding resulting images are read out for later processing and then the 4 active areas190A-D are reset before the next radiation exposure is performed. The operations of the imaging system500during the third, fourth, fifth, six, seventh, eighth, and ninth radiation exposures are similar to during the first radiation exposure.

In short, during exposure process, a total of 9 radiation exposures are performed, and the 4 active areas190A-D capture a total of 36 images. These 36 images captured by the imaging system500may be stitched to form a full image of the entire object520.

FIG.6Ashows a cross sectional view of the imaging system500ofFIG.5along a plane5A which intersects the object520, the radiation sources510.1,510.2,510.3and the active areas190A,190B. During the first radiation exposure while only the radiation source510.1is on, all points of the portion1A+1A2A of the object520are captured in an image in the active area190A, whereas all points of the portion3A1B+1B+1B2B of the object520are captured in an image in the active area190B.

Later, during the second radiation exposure while only the radiation source510.2is on, all points of the portion1A2A+2A+2A3A of the object520are captured in an image in the active area190A, whereas all points of the portion1B2B+2B+2B3B of the object520are captured in an image in the active area190B. Later, during the third radiation exposure while only the radiation source510.3is on, all points of the portion2A3A+3A+3A1B of the object520are captured in an image in the active area190A, whereas all points of the portion2B3B+3B of the object520are captured in an image in the active area190B.

In short, as a result of the first, second, and third radiation exposures, each point of the portions1A,1A2A,2A,2A3A,3A,3A1B,1B,1B2B,2B,2B3B, and3B is captured in at least one image. In other words, each point of the object520in the plane5A is captured in the images created in the imaging system500as a result of these 3 radiation exposures.

FIG.6Bshows a cross sectional view of the imaging system500ofFIG.5along a plane5BB which intersects the object520, the radiation sources510.2,510.5,510.8and the active areas190B,190C. Similar to the description above with reference toFIG.6A, as a result of the second, fifth, and eighth radiation exposures, each point of the portions2B5B,5B,5B8B,8B,8B2C,2C,2C5C, and5C is captured in at least one image. In other words, each point of the object520in the plane5BB is captured in the images created in the imaging system500as a result of these 3 radiation exposures.

So, in general, as a result of the exposure process, each point of the object520is captured in at least one image in the imaging system500. In other words, each point of the object520is captured in the resulting images created in the imaging system500as a result of the exposure process. Therefore, all the images resulting from the exposure process may be stitched to form a full image of the entire object520.

FIG.7shows a flowchart600listing the steps for operating the imaging system500ofFIG.5. More specifically, in step610, the object520is placed in the imaging system500. Next, in step620, the exposure process is performed during which the 9 radiation exposures are performed sequentially resulting in 36 images. More specifically, each of the 9 radiation exposures includes turning on then off the corresponding radiation source510and capturing 4 images in the 4 active areas190while the corresponding radiation source510is on. Finally, in step630, the 36 resulting images may be stitched to form a full image of the entire object520.

In summary, with reference toFIG.5, as a result of the exposure process, each point of the object520is captured in the 36 resulting images as described above. In other words, no point of the object520is not captured in the 36 resulting images. After the exposure process, the 36 resulting images created by the imaging system500may be stitched to form a full image of the entire object520.

It should be noted with reference toFIG.5that, in a typical imaging system of the prior art, only one radiation source (510.5for instance) is used (instead of 9 as described above) and therefore only one radiation exposure is performed (instead of 9 as described above) resulting in only 4 images (instead of 36 images as described above). As a result, in order for the typical imaging system of the prior art to capture all points of the object520by just one radiation exposure, additional active areas (similar to the active area190A) must be added to completely replace the dead zone488between the active areas190A-D. In other words, the present disclosure uses fewer active areas (hence saving costs) than in the prior art but can still achieve the same goal of capturing each and every point of the object520in the resulting captured images.

In the embodiments described above, with reference toFIG.5, the 9 radiation sources510.1-9are sequentially turned on then off in the order of510.1,510.2,510.3,510.4,510.5,510.6,510.7,510.8, and then510.9. In general, the 9 radiation sources510.1-9may be sequentially turned on then off in any order. For example, the 9 radiation sources510.1-9may be sequentially turned on then off in the order of510.9,510.8,510.7,510.6,510.5,510.4,510.3,510.2, and then510.1.

In the embodiments described above, with reference toFIG.5, the imaging system500include 4 active areas190A-D arranged in a 2×2 rectangular array and 9 radiation sources510.1-9arranged in a 3×3 rectangular array. In general, the imaging system500may include M active areas (M being an integer greater than 0) and N radiation sources (N being an integer greater than 1), and these M active areas and N radiation sources may be arranged in any way as long as each point of the object520is captured in the resulting images created as a result of the exposure process.

As an example, with reference toFIG.5andFIG.6A, the imaging system500may include only one active area190A and only two radiation sources520.1and520.2(i.e., M=1 and N=2). As a result, the exposure process would include 2 consecutive radiation exposures thereby creating only 2 resulting images. In this example, the object520is too big to have each and every point of it captured by the imaging system500. For instance, portion3B of the object520(FIG.6A) would not be captured in the 2 resulting images. However, a smaller object (such as portion1A+1A2A+2A of the object520inFIG.6A) would have each and every point of it captured by the imaging system500. More specifically, as seen inFIG.6A, each point of the smaller object1A+1A2A+2A is captured in the 2 resulting images.

In the embodiments described above, with reference toFIG.5, the imaging system500includes 9 radiation sources510.1-9which are sequentially turned on then off during the exposure process. In an alternative embodiment, the imaging system500may include only a single radiation source which (a) is similar to the radiation sources510.1-9described above and (b) moves through the 9 radiation positions of the 9 radiation sources510.1-9(hereafter referred to as radiation positions510.1-9for simplicity) in series during the exposure process so as to play the roles of the 9 radiation sources510.1-9.

More specifically, during the first radiation exposure, the single radiation source may be in the radiation position510.1inFIG.5and plays the role of the radiation source510.1. Later, during the second radiation exposure, the single radiation source may be in the radiation position510.2inFIG.5and plays the role of the radiation source510.2, and so on until the exposure process is complete. After that, the resulting 36 images may be stitched to form a full image of the entire object520.

As can be inferred from the descriptions above, in general, the method of the present disclosure will work as long as (a) during the first radiation exposure, there is radiation only from the radiation position510.1toward the 4 active areas190A-D, and (b) during the second radiation exposure, there is radiation only from the radiation position510.2toward the 4 active areas190A-D, and so on for the third, fourth, fifth, sixth, seventh, eighth, and ninth radiation exposures. The 9 radiations from the 9 radiation positions510.1-9(a) may come from9different radiation sources510.1-9as described in some embodiments above, or (b) may come from only one single radiation source moving through the 9 radiation positions510.1-9as described in some other embodiments above, or (c) may come from any number of radiation sources which may be used to play the roles of the 9 radiation sources510.1-9during the exposure process.

FIG.8Aschematically shows an embodiment of the radiation source system ofFIG.5. Specifically, the radiation source system ofFIG.8Amay include an electron gun810and an electron bombardment target820.

In an embodiment, the electron gun810may be configured to shoot electrons to the 9 radiation positions510.1-9in sequence. In an embodiment, the electron gun810may be a typical electron gun of a typical CRT (cathode ray tube) television set. As a result, the electron gun810may be configured to generate an electron beam and then deflect or steer the generated electron beam to the 9 radiation positions510.1-9in sequence.

In an embodiment, the electron bombardment target820may be a plate comprising a material of high atomic weight such as tungsten (W). In an embodiment, the 9 radiation positions510.1-9may be on a target surface822(i.e., the bottom surface) of the plate820. In an embodiment, the electron gun810and the plate820may be arranged such that the target surface822of the plate820faces the image sensor490and the electron gun810.

It should be noted that when a bombarding electron from the electron gun810hits the target surface822of the plate820at a bombardment position, there may be 3 possibilities. The first possibility is that the bombarding electron interacts with the nucleus of an atom of the plate820at the bombardment position and loses energy via the emission of an X-ray photon from the bombardment position. This process is usually referred to as the Bremsstrahlung process.

The second possibility is that the bombarding electron knocks an orbital electron out of an inner shell of an atom of the plate820at the bombardment position. In response, another electron from an outer shell of the atom fills the resulting vacancy in the inner shell and thereby releases energy via the emission of an X-ray photon from the bombardment position. This process is usually referred to as the X-ray fluorescence process (or the characteristic X-ray emission process). The third possibility is that the bombarding electron causes the plate820at the bombardment position to heat up without causing any X-ray emission.

In an embodiment, the electron gun810may be configured to generate electrons with high energy so that when these generated electrons bombard the target surface822of the plate820at a bombardment position, these bombarding electrons have enough energy to cause the emission of X-ray photons from the bombardment position according to either the first or second possibility mentioned above or both.

It should be noted that an X-ray photon emitted according to either the first or second possibility as described above may propagate in any direction from the bombardment position. On one hand, if the emitted X-ray photon propagates deeper into the plate820(i.e., upward inFIG.8A), then the emitted X-ray photon is likely absorbed by the plate820. On the other hand, if the emitted X-ray photon propagates in an opposite direction (i.e., downward and away from the plate820), then the emitted X-ray photon likely escapes the plate820and propagates toward the image sensor490.

In short, when the electron gun810shoots electrons of sufficiently high energy to a bombardment position on the target surface822of the plate820, these bombarding electrons cause the emission of X-ray photons from the bombardment position toward the object520and the image sensor490.

In an embodiment, the operation of the radiation source system810+820ofFIG.8Aduring the exposure process may be as follows. During the first radiation exposure of the exposure process, the electron gun810may be configured to shoot electrons to the first radiation position510.1along a path812.1. The bombardment of electrons on the target surface822of the plate820at the first radiation position510.1causes the emission of X-ray photons from the first radiation position510.1toward the object520and the image sensor490. As a result, during the first radiation exposure, the electron gun810and the electron bombardment target820play the role of the first radiation source510.1as described in the embodiments above with reference toFIG.5.

Similarly, during the second radiation exposure of the exposure process, the electron gun810may be configured to shoot electrons to the second radiation position510.2along a path812.2. The bombardment of electrons on the target surface822of the plate820at the second radiation position510.2causes the emission of X-ray photons from the second radiation position510.2toward the object520and the image sensor490. As a result, during the second radiation exposure, the electron gun810and the plate820play the role of the second radiation source510.2as described in the embodiments above with reference toFIG.5.

Similarly, during the third, fourth, fifth, sixth, seventh, eighth, and ninth radiation exposures of the exposure process, the electron gun810may be configured to shoot electrons to the radiation positions510.3-9respectively in sequence. As a result, during the third, fourth, fifth, sixth, seventh, eighth, and ninth radiation exposures of the exposure process, the electron gun810and the plate820play the role of the third, fourth, fifth, sixth, seventh, eighth, and ninth radiation sources510.3-9respectively as described in the embodiments above with reference toFIG.5.

In summary, as a result of the exposure process performed using the radiation source system810+820as described above, a total of 9 radiation exposures are performed, and the 4 active areas190A-D capture a total of 36 images which contain each and every point of the object520. These 36 images captured by the imaging system500may be stitched to form a full image of the entire object520.

In some embodiments described above with reference toFIG.8A, the electron bombardment target820has the shape of a plate. In general, the electron bombardment target820may have any shape and size provided that the 9 radiation positions510.1-9are on target surfaces of the electron bombardment target820so as to receive electron bombardments.

FIG.8Bschematically shows an electron bombardment target850as an alternative embodiment of the electron bombardment target820ofFIG.8A. Specifically, the electron bombardment target850ofFIG.8Bmay be a disk as viewed from the image sensor490(FIG.8A), with the 9 radiation positions510.1-9being on a target surface852of the disk850facing the image sensor490(FIG.8A). In an embodiment, the disk850may comprise a material of high atomic number such as tungsten (W).

In an embodiment, during the 9 radiation exposures of the exposure process, the disk850may rotate around an axis pole854(which is perpendicular to the page) such that the 9 radiation positions510.1-9, which may be stationary with respect to the image sensor490(FIG.8A), remain on the target surface852of the disk850during the rotation. In an embodiment, the axis pole854may comprise a metal such as copper (Cu). In an embodiment, the axis pole854may be perpendicular to the top surface492(FIG.8A) of the image sensor490. In an alternative embodiment, the axis pole854may make an angle of less than 90° with the top surface492(FIG.8A) of the image sensor490. In this alternative embodiment, the disk850should look like an oval (instead of a circle) when viewed from the image sensor490(FIG.8A).

As a result of the 9 radiation positions510.1-9remaining on the target surface852of the disk850during the rotation, the operation of the radiation source system810+850as described above with reference toFIG.8Ais not affected. In addition, the heat generated in the disk850at the 9 radiation positions510.1-9due to the bombardment of electrons on the target surface852of the disk850at the 9 radiation positions510.1-9may be quickly spread out in the disk850due to the rotation and then dissipated away through the axis pole854.

FIG.9Aschematically shows another embodiment of the radiation source system ofFIG.5. Specifically, the radiation source system ofFIG.9Amay include an electron gun910and an electron bombardment target920. In an embodiment, the electron gun910may be similar to the electron gun810ofFIG.8A. As a result, the electron gun910may be configured to shoot electrons to the 9 radiation positions510.1-9in sequence. In an embodiment, the electron bombardment target920may be a target block comprising a material of high atomic weight such as tungsten (W).

In an embodiment, a first method of operating the radiation source system910+920ofFIG.9Aduring the exposure process may be as follows. During the first radiation exposure of the exposure process, the electron gun910may be configured to shoot electrons to the first radiation position510.1along a path912.1while the target block920may be arranged such that the first radiation position510.1is on a target surface922of the target block920facing the image sensor490and the electron gun910.

The bombardment of electrons on the target surface922of the target block920at the first radiation position510.1causes the emission of X-ray photons from the first radiation position510.1toward the object520and the image sensor490. As a result, during the first radiation exposure, the electron gun910and the target block920play the role of the first radiation source510.1as described in the embodiments above with reference toFIG.5.

Similarly, during the second radiation exposure of the exposure process, the electron gun910may be configured to shoot electrons to the second radiation position510.2along a path912.2while the target block920may be arranged such that the second radiation position510.2is on the target surface922of the target block920facing the image sensor490and the electron gun910. This means that, in an embodiment, after the first radiation exposure ends but before the second radiation exposure starts, the target block920may be moved from the first radiation position510.1to the second radiation position510.2. In an embodiment, the target block920may be configured to move from one radiation position510to another radiation position510(e.g., from the radiation position510.1to the radiation position510.2) by translating (i.e., all points of the target block920move in the same direction by the same distance), tilting (i.e., rotating for less than a full circle), or both translating and tilting.

The bombardment of electrons on the target surface922of the target block920at the second radiation position510.2causes the emission of X-ray photons from the second radiation position510.2toward the object520and the image sensor490. As a result, during the second radiation exposure, the electron gun910and the target block920play the role of the second radiation source510.2as described in the embodiments above with reference toFIG.5.

Similarly, during the third, fourth, fifth, sixth, seventh, eighth, and ninth radiation exposures of the exposure process, the electron gun910and the target block920play the role of the third, fourth, fifth, sixth, seventh, eighth, and ninth radiation sources510.3-9, respectively, as described in the embodiments above with reference toFIG.5.

In summary, during the exposure process performed using the radiation source system910+920as described above, the electron beam generated by the electron gun910is steered to the 9 radiation positions510.1-9in sequence as the target block920moves through the 9 radiation positions510.1-9respectively in sequence so as to receive the electron beam. As a result of the exposure process, a total of 9 radiation exposures are performed, and the 4 active areas190A-D capture a total of 36 images which contain each and every point of the object520. These 36 images captured by the imaging system500may be stitched to form a full image of the entire object520.

FIG.9Bschematically illustrates a second method of operating the radiation source system910+920ofFIG.9Aduring the exposure process. In an embodiment, the second method of operating the radiation source system910+920may be similar to the first method of operating the radiation source system910+920except that in the second method, the electron gun910and the 3 radiation positions510.1,510.2, and510.3are arranged such that the electron gun910may be configured to shoot an electron beam along a path912.123through all 3 radiation positions510.1,510.2, and510.3.

As a result, in the second method, during the first, second, and third radiation exposures of the exposure process, the electron beam generated by the electron gun910may remain stationary with respect to the image sensor490(i.e., remain on the path912.123) as the target block920moves through the 3 radiation positions510.1,510.2, and510.3in sequence.

In contrast, in the first method as described above with reference toFIG.9A, during the first, second, and third radiation exposures of the exposure process, the electron beam generated by the electron gun910has to be steered to the 3 radiation positions510.1,510.2, and510.3in sequence as the target block920moves through the 3 radiation positions510.1,510.2, and510.3respectively in sequence so as to receive the electron beam.

In an embodiment, the second method may be similar to the first method regarding the fourth, fifth, sixth, seventh, eighth, and ninth radiation exposures of the exposure process. Specifically, in both the first and second methods, the electron beam generated by the electron gun910is steered to the 6 radiation positions510.4-9in sequence as the target block920moves through the 6 radiation positions510.4-9respectively in sequence so as to receive the electron beam. In an embodiment, the path912.123may be a straight line.

In an embodiment, with reference toFIGS.8A,9A, and9B, each of the radiation source system810+820and the radiation source system910+920may further include a glass vacuum tube (not shown) in which the electron gun810/910and the electron bombardment target820/920reside and/or move. As a result, the electrons generated by the electron gun810/910may travel freely through vacuum to the radiation positions510.1-9on the electron bombardment target820/920without any interaction with air molecules which might otherwise scatter and/or decelerate the generated electrons.

In an embodiment, with reference toFIGS.8A,9A, and9B, each of the radiation source system810+820and the radiation source system910+920may further include a DC (direct current) voltage source (not shown) whose cathode is electrically connected to the electron gun810/910and whose anode is electrically connected to the electron bombardment target820/920. As a result, an electric field is created between the electron gun810/910and the electron bombardment target820/920. This electric field helps further accelerate the bombarding electrons generated by the electron gun810/910.

In some embodiments described above with reference toFIGS.8A,8B,9A, and9B, there are 9 radiation positions arranged in an array of 3×3 and in the plane512(FIG.5). In general, there may be any number of radiation positions arranged in any way in space (i.e., arranged not necessarily in the form of an array and not necessarily in a plane).

In some embodiments described above with reference toFIG.9A, the radiation source system has one target block920that moves through the 9 radiation positions510.1-9in sequence during the exposure process. In an alternative embodiment, the radiation source system may have 9 target blocks similar to the target block920. These 9 target blocks may be arranged at the 9 radiation positions510.1-9. As a result, during the exposure process, there is no need to move any one of the 9 target blocks.

In some embodiments described above with reference toFIG.9B, in the second method of operating the radiation source system910+920, the electron gun910and the 3 radiation positions510.1,510.2, and510.3are arranged such that the electron gun910may be configured to shoot an electron beam along the path912.123through all 3 radiation positions510.1,510.2, and510.3. In general, the electron gun910and P radiation positions (of the 9 radiation positions) may be arranged such that the electron gun910may be configured to shoot an electron beam through all the P radiation positions (P is an integer greater than 1 but not exceeding 9).

As a result, in the second method of operating the radiation source system910+920, during the P radiation exposures of the exposure process corresponding to the P radiation positions, the electron beam generated by the electron gun910may remain stationary with respect to the image sensor490as the target block920moves through the P radiation positions in sequence.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.