RADIOGRAPHIC SYSTEM AND METHOD FOR REDUCING MOTION BLUR AND SCATTER RADIATION

Abstract

A radiographic system including a radiation source emitting a radiation beam, a radiation sensor for detecting incident radiation from the radiation beam on a sensor area, at least one collimator arranged between the radiation source and the radiation sensor for masking the radiation beam to irradiate a radiation area on the sensor which is smaller than the sensor area and means for moving the collimator across the radiation beam, whereby the radiation area is moved across the sensor area.

Claims

1-20. (canceled)

21. A radiographic system comprising: a radiation source emitting a radiation beam; a radiation sensor for detecting incident radiation from the radiation beam, on a sensor area; at least one collimator arranged between the radiation source and the radiation sensor for masking the radiation beam to irradiate a radiation area on the sensor which is smaller than the sensor area; means for moving the collimator across the radiation beam, whereby the radiation area is moved across the sensor area. wherein: the sensor is a rolling shutter type sensor; the radiographic system is a computational tomography (CT) scanner; and compensation of motion skew from the movement of the radiation source and the radiation sensor in the CT scanner is based on the time at which the collimator moves across the radiation beam,

22. A radiographic system according to claim 21, further comprising a computer controlled device connected to the radiation sensor, the computer controlled device comprising software for reading the sensor output of the radiation area as the collimator is moved across the radiation beam.

23. A radiographic system according to claim 21, wherein the sensor area comprises an active area where incident radiation is detected and an Inactive area where incident radiation not detected.

24. A radiographic system according to claim 23, wherein the active area is larger than the radiation area.

25. A radiographic system according to claim 23, wherein the active area overlaps the radiation area.

26. A radiographic system according to claim 23, wherein the active area follows the radiation area as it is moved across the sensor area.

27. A radiographic system according to claim 21, wherein the rolling shutter type sensor comprises an integration period defining the size of the active area of the sensor.

28. A radiographic system according to claim 21, wherein the size of the active area is determined by the number of active sensor rows active during the integration period.

29. A radiographic system according to clam 21, wherein the rolling shutter type sensor comprises wherein at least two rows of the sensor is read out sequentially.

30. A radiographic system according to claim 21, wherein the collimator masks the radiation beam in cycles, such that the radiation area moves across the sensor area in at least two subsequent cycles during operation of the radiographic system.

31. A radiographic system according to claim 30, wherein the movement direction and movement speed of the radiation area across the sensor area is the same in the at least two cycles.

32. A radiographic system according to claim 21, wherein the at least one collimator comprises a disc formed of a radiopaque material with at least one radially extending opening or area formed of a radiolucent or radio-transparent material.

33. A radiographic system according to claim 32, wherein the disc plane and sensor plane are arranged parallel and a drive is coupled to the disc for rotating it around its center.

34. A radiographic system according to claim 21, wherein the at least one collimator comprises a wheel with a center axis arranged centered with the radiation source and wherein the rim of the wheel is formed of a radiopaque material and comprises at least one opening or area formed of a radiolucent or radio-transparent material.

35. A radiographic system according to claim 34, wherein a drive is couple to the wheel for rotating the wheel around its center.

36. A radiographic system according to claim 34, wherein the least one opening or area formed of a radiolucent or radio-transparent material extends parallel with the sensor area during rotation of the wheel.

37. A radiographic system according to claim 21, wherein the system comprises at least two collimators, wherein: a first collimator is arranged between the radiation source and the radiation sensor for masking the radiation beam to irradiate a radiation area on the sensor which is smaller than the sensor area; and a second collimator arranged between the radiation source and the first collimator.

38. A radiographic system according to claim 37, wherein the second collimator comprises a second opening or second area formed of a radiolucent or radio-transparent material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The above and/or additional objects, features and advantages of the present invention, will be further described by the following illustrative and non-limiting detailed description of embodiments of the present invention, with reference to the appended drawings, wherein:

[0051] FIG. 1 shows a first embodiment of a radiographic system as disclosed herein,

[0052] FIG. 2a shows the first embodiment of FIG. 1 along section II-II,

[0053] FIG. 2b shows an enlarged area of the first embodiment of FIG. 2a, and

[0054] FIG. 3 illustrates in general the principles of the function of a radiographic system as disclosed herein.

DETAILED DESCRIPTION

[0055] A first embodiment of a radiographic system 1 is illustrated in FIGS. 1, 2a and 2b. The radiographic systems is formed of a radiation source 2 and a standard collimator 3 formed of a radiopaque material 4 having an opening 5. The radiopaque material absorbs the radiation from the radiation source, thus, the collimator only allows radiation to pass through the opening 5, thereby generating a radiation beam 6.

[0056] A radiation sensor 7 is arranged opposite the radiation source. The radiation sensor is a rolling shutter type sensor. The distance to the radiation sensor and the size of the opening 5 in the standard collimator is dimensioned so that the expected incident radiation from the radiation beam 6 covers the surface of the radiation sensor.

[0057] A collimator disc 8 is placed between the standard collimator 3 and the radiation sensor 7. The collimator disc 8 is formed of a radiopaque material 9 and slits 10, the slits being separated by teeth 16. The collimator disc 8 provides a masked radiation beam 11, which irradiates a radiation area 12 on the radiation sensor that is smaller than the sensor area of the radiation sensor.

[0058] The slits 10 are provided as radial openings along the periphery of the disc. Each slit is identical in size and shape. A drive (not shown) is provided in order to rotate the disc 8 around its center axis 13 in an anti-clockwise direction as indicated by the arrow 14. As the collimator disc 8 is rotated the slits are moved across the radiation beam 6, thereby generating the masked radiation beam 11 which as a consequence of the motion generates the radiation area 12 which is moved across the sensor area of the radiation sensor 7. As can be understood each time a slit is moved across the radiation beam a cycle passes, and with the current setup it is possible to provide a masked radiation beam and thus also a radiation area that is identical in movement direction, movement speed, size and shape for each cycle.

[0059] During operation a subject such as the head of a patient (not shown) is placed in the scan volume 15 between the collimator disc and the radiation sensor. When the radiographic system is activated the radiographic system rotates around a rotation axis A-A extending through the scan volume while the radiation area repeatedly is moved across the sensor area.

[0060] To have an approximate constant flux of radiation the total width of the tooth and slit, w.sub.total=w.sub.slit+w.sub.tooth, should approximate be equal to the height of the opening 5 in the standard collimator 3. The ratio between the slit width and the total width, w.sub.slit/w.sub.tooth, controls the effect of the wheel. A smaller ratio, w.sub.slit/w.sub.tooth=>0, decreases the scattering and motion blur but at the cost of increased load on the radiation source.

[0061] It is important to have a perfect synchronization with the radiation sensor to avoid unwanted radiation. For a rolling shutter type of sensor the number of integrating rows is calculated such that the active area of the radiation sensor always can encapsulate the radiation, i.e. the radiation area 12. For this a photo detector 17 is provided on the collimator disc which registers when slits and teeth pass. The synchronization can be achieved by first starting the radiation sensor and then adjusting the wheel speed such that photo detector signal is phase locked to the radiation sensors new frame signal. A constant phase delay has to be added to the photo detector signal for correcting for the relative position between the photo detector and the collimator.

[0062] The principle of the radiographic system and the method is schematically described in FIG. 3 which shows a sequence of radiographic sensor 7 registration 3a-3g, illustrating a full cycle.

[0063] FIG. 3 illustrates a radiation sensor 107 of a rolling shutter type similar to that described above with respect to FIGS. 1 and 2. The sensor has nine rows 111-119, where each row comprises capacitors for detecting radiation. The current embodiment of nine rows is for illustration purposes and it should be understood that in actual sensor the number of rows are typically much higher, such as 100 or 1000.

[0064] A row can either be active, wherein incident radiation is detected and an electric charge representative of the amount of radiation received while active is accumulated, or a row can be inactive wherein no radiation is detected.

[0065] In FIG. 3a the fifth row 115 activated at integration start, I.sub.start and the first row 111 is read and then deactivated (made inactive) at integration read. The time period between integration start and integration read is called the integration period I.sub.T and defines the active area 120, which in the FIG. 3a covers the first, second, third, fourth and fifth row 111, 112, 113, 114, 115.

[0066] However, in FIG. 3a direct radiation from the masked radiation beam is only received in the radiation area 122 which is in the second, third and fourth row. Scatter radiation may be received in the first and fifth row, which is unwanted. However, no radiation is received in rows six to nine 115, 116, 117, 118 and 119 as these are inactive. This is an advantage since any radiation incident on the inactive rows would be scatter radiation, which we want to avoid.

[0067] The active area 120 is slightly larger than the radiation area 122. This is in order to ensure that all the direct radiation incidents on the radiation are is received.

[0068] As described above the radiation sensor is synchronized with the motion of the collimator and thus the motion of the radiation area across the sensor. Accordingly, after a first time period t.sub.1 the radiation area 122 now covers the third, fourth and fifth row and the sixth row is activated and the second row is read and subsequently deactivated. This sequence is followed at second t.sub.2, third t.sub.3 and fourth t.sub.4 time periods until the integration start activates the ninth row 119, where the radiation area covers the sixth, seventh and eight row.

[0069] After the fifth time period t.sub.5 the first row is activated in FIG. 3d in order to activate the upper row for a new pass of the radiation area. For example with the embodiment disclosed in FIG. 1-2 this is ensured by correct dimensioning of the width of the slits and the width of teeth of the collimator disc such that when the radiation area created by a slit passes the bottom of the radiation sensor, i.e. the ninth row 119, the radiation area created by a subsequent slit passes the top of the radiation sensor, i.e. the first row 111.

[0070] The current specific embodiment describes how it is possible to provide cycles of sensor registrations where the radiation area is identical for each cycle, both in movement, speed, size and shape. This has the advantage that rolling type sensors can be used in such a manner that the scanning speed is increased, while the radiation scatter and motion blur is reduced. The latter in particular when used in setups with rotating gantries, such as CT and CBCT scanners.

[0071] As understood and discussed previously a small radiation area 122 reduces motion blur since the radiographic system moves shorter (e.g. in the embodiment in FIGS. 1-2 the rotation around axis A-A is shorter) during the time a row is active than if the whole surface of the sensor was used to detect the radiation at once, i.e. the rows would be active for a longer time.

[0072] Moreover, interference from scatter radiation is reduced since rows which are not directly radiated are deactivated.

EMBODIMENTS

[0073] 1. A radiographic system comprising [0074] a radiation source emitting a radiation beam, [0075] a radiation sensor for detecting incident radiation from the radiation beam on a sensor area, [0076] at least one collimator arranged between the radiation source and the radiation sensor for masking the radiation beam to irradiate a radiation area on the sensor which is smaller than the sensor area, and [0077] means for moving the collimator across the radiation beam, whereby the radiation area is moved across the sensor area.

[0078] 2. A radiographic system according to embodiment 1, further comprising a computer controlled device connected to the radiation sensor, the computer controlled device comprising software for reading the sensor output of the radiation area as the collimator is moved across the radiation beam.

[0079] 3. A radiographic system according to embodiment 1 or 2, wherein the sensor area comprises an active area where incident radiation is detected and an inactive area where incident radiation is not detected.

[0080] 4. A radiographic system according to embodiment 3, wherein the active area is larger than the radiation area.

[0081] 5. A radiographic system according to embodiment 3 or 4, wherein the active area overlaps the radiation area.

[0082] 6. A radiographic system according to embodiment 3, 4 or 5, wherein the active area follow the radiation area as it is moved across the sensor area.

[0083] 7. A radiographic system according to embodiment 2, 3, 4, 5 or 6, wherein the sensor is a rolling shutter type sensor.

[0084] 8. A radiographic system according to embodiment 7, wherein the rolling shutter type sensor comprises an integration period defining the size of the active area of the sensor.

[0085] 9. A radiographic system according to embodiment 8, wherein the size of the active area is determined by the number of active sensor rows active during the integration period.

[0086] 10. A radiographic system according to embodiment 7, 8 or 9, wherein the rolling shutter type sensor comprises wherein at least two rows of the sensor is read out sequentially.

[0087] 11. A radiographic system according to any one of the embodiments 1-10, wherein the radiographic system is a computational tomography (CT) scanner.

[0088] 12. A radiographic system according to embodiment 11, wherein compensation of motion skew from the movement of the radiation source and the radiation sensor in the CT scanner is based on the time at which the collimator moves across the radiation beam.

[0089] 13. A radiographic system according to any one of the embodiment 1-12, wherein the collimator masks the radiation beam in cycles, such that the radiation area moves across the sensor area in at least two subsequent cycles during operation of the radiographic system.

[0090] 14. A radiographic system according to embodiment 13, wherein the movement direction and movement speed of the radiation area across the sensor area is the same in the at least two cycles.

[0091] 15. A radiographic system according to any one of the embodiments 1-14, wherein the at least one collimator comprises a disc formed of a radiopaque material with at least one radially extending opening or area formed of a radiolucent or radio-transparent material.

[0092] 16. A radiographic system according to embodiment 15, wherein the disc plane and sensor plane are arranged parallel and a drive is coupled to the disc for rotating it around its center.

[0093] 17. A radiographic system according to any one of the embodiments 1-16, wherein the at least one collimator comprises a wheel with a center axis arranged centered with the radiation source and wherein the rim of the wheel is formed of a radiopaque material and comprises at least one opening or area formed of a radiolucent or radio-transparent material.

[0094] 18. A radiographic system according to embodiment 17, wherein a drive is coupled to the wheel for rotating the wheel around its center.

[0095] 19. A radiographic system according to embodiment 17 or 18, wherein the least one opening or area formed of a radiolucent or radio-transparent material extends parallel with the sensor area during rotation of the wheel.

[0096] 20. A radiographic system according to any one of the embodiments 1-19, wherein the system comprises at least two collimators, wherein a first collimator is arranged according to the at least one collimator of any one of the claims 1-19 and a second collimator arranged between the radiation source and the first collimator.

[0097] 21. A radiographic system according to embodiment 20, wherein the second collimator comprises a second opening or second area formed of a radiolucent or radio-transparent material.