DE102009034384B4 - Image recording method and tomography device for fast scanning of a patient affected by breathing movement of a patient receiving area - Google Patents

Abstract

Image recording method for fast scanning of a patient by (1) affected recording area (2) using a tomography device (3) with at least two rotatable about a common axis of rotation (4) arranged receiving systems (5, 6, 7, 8), in which At least one recording pulse (10) adapted to the respiratory motion is generated with a respiratory signal (9), with which the tomography device (3) is controlled so that projections (11, 12) are detected by the recording area (2) during the recording pulse (10) wherein projection gaps (13) of the receiving area (2) in captured projections (11) along a first spiral track (14) around the receiving area (2) with the first recording system (5, 6) by projections (12) along a second spiral path (15 ) are filled to the receiving area (2) with the second recording system (7, 8), wherein the recording pulse (10) based on the breath signal (9) from a number of previous breathing cycles (Zi) stati and two consecutive respiratory signal peaks (P-1, P-2) for determining the position and the length of a cycle duration (A-2) are estimated, and the acquisition pulse (10) relative to this cycle duration (A-2 ).

Description

The invention relates to an image recording method and a tomography device for fast scanning of a patient by breathing movement of a patient-influenced recording area.

The lungs of a patient and the body areas in a lungs environment are constantly subject to periodic motion due to the patient's breathing. In functional lung diagnostics, it is a common problem that tomographic images are needed depending on the diagnostic question about a particular respiratory condition or multiple respiratory conditions.

In the simplest case, therefore, the patient is instructed to stop the air in a certain breath for the period of the image acquisition before starting the image recording process. However, this method is very susceptible to interference, since the ingested respiratory state must be maintained over a longer period of time and is difficult to verify and reproducible. In particular, in computer tomography devices, the generation of an image to a respiratory system is problematic according to this procedure, since the images to be generated are calculated by backprojecting a multiplicity of projections acquired from different projection angles. As a rule, backprojection only succeeds without interference if the underlying projections represent an identical phase of respiratory motion.

For this reason, a breathing signal is taken from the patient for the exact selection of the breathing position, for example by means of a breathing signal generator in the form of a breathing belt, which is evaluated and taken into account in the generation of an image.

There are two different approaches to the detection of projections by means of breathing signals, which differ in principle from the approach as follows:
In the first approach, projections are recorded during the entire cycle duration of the respiratory movement and stored together with the respiratory signal. The reconstruction of a tomographic image takes place retrospectively following the data acquisition, wherein projections of defined phases of the respiratory motion are selected by evaluating the respiratory signal. An advantage of this method is that in this way any phases of the respiratory motion can be represented. For the retrospective reconstruction of tomographic images, however, it is necessary for the patient to be exposed to full x-ray dose throughout the scan. In addition, in the case of lung diagnostics, the selected receiving area in the direction of the system axis of the computed tomography device is generally much larger than the coverage of the detector. The scanning is therefore carried out to complete coverage of the recording area with projections by means of a spiral scan. Due to the cycle length of a respiratory cycle compared to the cardiac cycle or the small number of 10 to 15 respiratory cycles per minute, the spiral scan must avoid a projection gap of the acquisition area to a predetermined phase of the respiratory movement with very small pitch values in the range between 0.05 to 0, 1 are performed. Overall, significantly more X-ray dose than required must be applied.

In the second approach to breathing signal-controlled detection of projections, an inspiratory breathing phase respiratory signal peak is used to initiate the scan with a selectable delay after the peak. In general, the delay and thus the start time of the scan after the peak in the breathing signal from an estimated cycle time of the breathing cycles are determined, for. As a percentage of the cycle time. In this approach, the acquisition pulses for recording projections are thus determined prospectively from previous breathing cycles. For complete coverage of the recording area with projections, the computed tomography device is operated in a so-called sequence mode in which successive scanning positions within the recording area in the direction of the system axis of the computed tomography device are approached sequentially, wherein at each of the scanning positions required for the reconstruction of a layer image set of projections completely becomes. One problem with this approach, however, is that even a single error in the prospective estimate of the acquisition pulse can cause step artifacts in the reconstructed image. The sequential scanning for the detection of projections from the recording area also requires such a long period of time that, in the case of a contrast agent examination, image areas at successive scanning positions have different degrees of contrast due to the temporal contrast agent propagation. This also results in image artifacts in the reconstructed image. The advantage of a prospective reconstruction of images is to be seen in particular in that X-ray dose has to be applied by means of a tube current modulation only in the small time intervals of the recording pulses, so that the total X-ray dose applied to the patient is small in comparison to the first-mentioned approach.

Out DE 10 2005 014 853 A1 For example, a method and a tomography apparatus for fast volume scanning of an examination area with at least two recording systems are known. at In the case of a spiral scan of the examination area, particularly rapid scanning of the volume can be achieved by filling projection gaps of the examination area in the case of acquired projections with the first recording system by means of projections with the second recording system.

Out DE 10 2005 033 471 A1 For example, there are known a method and an x-ray diagnostic device for producing an image of a body region of a living being which makes a movement due to the respiration of the living being. The X-ray diagnostic device comprises an X-ray diagnostic device and a device for recording respiratory signals of the living being. Breathing signals of the living being are detected and X-ray projections are taken by the living being from different projection directions, whereby the intensity of the X-ray radiation emanating from an X-ray source of the X-ray diagnostic device is modulated during the acquisition of the X-ray projections in such a way that the intensity is dependent on the value of the amplitude of the respiratory signal. or the respiratory position of the living being assumes a desired value or a value which is lowered in relation to the desired value.

The object of the present invention is to design an image recording method and a tomography apparatus for scanning a recording region influenced by respiratory movement of a patient in such a way that an X-ray dose applied to the patient is reduced.

This object is achieved by an image recording method according to the features of independent claim 1 and a tomography device according to the features of independent claim 4. Advantageous embodiments of the image recording method or the tomography device according to claim 1 or 4 are the subject matter of the dependent claims 2 and 3 or 5 respectively.

In the image recording method according to the invention for rapid scanning of a recording area influenced by respiratory movement of a patient, a tomography device having at least two recording systems rotatably arranged about a common axis of rotation, for example a computed tomography device, is used. From a detected respiratory signal, at least one recording pulse, which is adapted to the respiratory movement, is generated, with which the tomography device is controlled such that projections of the recording area are acquired during the recording pulse. The scanning is carried out in such a way that projection gaps of the recording area in detected projections along a first spiral path around the recording area with the first recording system are filled by projections along a second spiral path around the recording area with the second recording system.

The detection of projections thus takes place by means of a spiral scan in a so-called helical scan operation of the tomography device, in which a rotation of the two recording systems about the common axis of rotation and an adjustment of the patient and the two recording systems in the direction of the axis of rotation relative to each other are feasible.

With the two recording systems, two projections for each projection direction are recorded at different times during each rotation. As a result of the simultaneous advance of the patient in the direction of the axis of rotation during the spiral scanning, the projections for the same projection direction are recorded at different positions along the axis of rotation. The scanning of the receiving area is thus carried out on two spiral tracks, which have an offset and thus a double helix structure arrangement in dependence of the feed rate of the patient in the direction of the axis of rotation. Projection gaps of the recording area by recorded projections of a recording system can thus be filled or closed at high feed speeds by detected projections of the other recording system.

In the case of spiral scanning with a computed tomography device, the pitch value indicates the ratio between the advancement of the patient or a table top used for the storage of the patient per rotation of the recording systems and the layer thickness of the detector. In a system configuration with 64 detector lines per detector and a 0.6 mm coverage per detector element in the direction of the axis of rotation, spiral scanning with two imaging systems rotated at a 0.285 second rotation speed allows patient advancement rates of up to 450 mm per second be achieved without projection gaps and thus artefacts in the reconstructed image. This corresponds to a spiral scan with a pitch value of about 3.3. A scan of a 300 mm extension area in the direction of the axis of rotation, which is typically set in the lung diagnostics, is therefore possible in less than 700 ms in this case and can therefore already be performed completely within only one respiratory cycle.

In the previously known breath-triggered image recording methods, on the contrary, only pitch values between 0.05 to 0.1 can be achieved, so that the scanning of the recording area with such a large extent in the direction of the System axis is possible only with the inclusion of several breathing cycles. For each scan, a sweep-free scan in the transition region between two scans to different breathing cycles and to set the target power of the X-ray tube, a pre- and post-scan of the scan is required, in which also X-ray dose is applied to the patient.

Due to the fact that, in the method according to the invention, the scanning of the recording area ideally requires only one respiratory cycle, the total dose of X-ray administered to the patient can be reduced by a factor of up to 20 compared with the previously known respiratory correlated methods. The scanning of the lung is therefore feasible with very low dose values. In addition, image artifacts are completely or at least largely avoided that result from reconstruction of an image based on projections acquired at different breath cycles. Also in the case of a contrast agent examination artefacts in the reconstructed image can be reduced due to the greatly reduced total sampling time required for areas of the lungs, since there are no, or at least few, temporal gaps between projections from adjacent image areas. Therefore, image artifacts due to different contrasting of an image area caused by dynamic propagation of the contrast agent are largely avoided.

These advantages could be achieved with the use of a single recording system only if the detector has a correspondingly large extent in the direction of the axis of rotation and if the X-ray beam generated by an X-ray source has a correspondingly large cone angle.

The construction of detectors with a large extension in the direction of the axis of rotation is complicated and the expansion of the X-ray beam leads to a high thermal load of the X-ray source, which is caused by a strong inclination of the anode plate relative to the electron beam. In addition, the complexity of the algorithms for calculating a reconstructed image is increased by the use of detectors that detect a plurality of detector lines in each projection.

The invention thus provides an efficient alternative to image acquisition techniques employing single-imaging tomography devices designed specifically for fast scanning.

The filling of the projection gaps at high pitch values succeeds well when the two recording systems are offset by a fixed angle, preferably of 90 degrees, in the direction of rotation. Due to the offset of the two recording systems by 90 degrees, the time difference between two successive projections, which are detected for a projection plane, maximum, so that in spiral scan by the advance of the patient in the direction of the axis of rotation and the projection of the second recording system is detected maximum portion that can serve to fill the projection gaps.

In principle, it is not significant for the image recording method according to the invention for rapid scanning how the two recording systems are arranged in the direction of the axis of rotation relative to each other. With regard to the widest possible field of use, however, it is advantageous if the two receiving systems are arranged in a measuring plane, that is to say without an offset in the direction of the axis of rotation. In this case, not only a fast scan can be performed by means of a spiral scan. In addition, it is also possible to realize scans with a high scanning speed, in which the same scanning volume in the direction of the rotation axis must be detected by the two recording systems.

The reconstruction of an image is advantageously carried out on the basis of the obtained projections of both recording systems, wherein the adjustment position in the direction of the axis of rotation and the angular position in the direction of rotation of the recording systems are detected and further processed for the unique geometric assignment of each projection. By including the projection data from both recording systems, a scan with particularly high pitch values is made possible.

The recording pulse is determined statistically on the basis of the respiratory signal from a number of preceding respiratory cycles, so that the position and length of the recording pulse are adjusted in accordance with the currently present respiratory rate of the patient.

Two consecutive respiratory signal peaks are estimated for determining the location and length of a subsequent cycle duration, the acquisition pulse being determined relative to the following cycle duration. In determining the position of the recording window in the progressive temporal direction is thus taken into account the fact that for the acceleration of the patient or the table on which it is stored, a certain amount of time is needed.

With respect to the device, the above-mentioned object is achieved by the features of claim 4. Thereafter, the tomography device for fast scanning of a at least two recording systems rotatably arranged about a common axis of rotation, a signal acquisition unit which generates from a respiratory signal at least one recording pulse tuned to the respiratory motion, and a control unit which activates the tomography device during the generated recording pulse so that projections from the Recording area can be detected, wherein projection gaps of the receiving area in the detected projections along a first spiral path around the receiving area with the first recording system through the projections along a second spiral path around the receiving area with the second recording system can be filled.

The tomography device is, in particular, an X-ray tomograph in a broader sense, in particular a computed tomography device or a rotational angiography device. The control unit is further configured to generate the image data set by numerical backprojection from a plurality of X-ray projection images recorded at different projection angles.

Embodiments of the invention and further advantageous embodiments of the invention according to the subclaims are shown in the following schematic drawings. Show it:

1 a tomography device according to the invention for the rapid scanning of a receiving area influenced by respiratory movement of a patient,

2 Plotted a breathing curve with recorded recording pulse and scanning positions of the two recording systems in yz plane shown against time, and

3 Projections of the two recording systems in a yz-section plane for seamless scanning of the recording area.

Corresponding parts and sizes are always provided with the same reference numerals in all figures.

In 1 is a tomography device according to the invention 3 , here a computed tomography device, shown in perspective view.

Inside the computed tomography device 3 There are two on a gantry 18 around a common axis of rotation 4 rotatably arranged recording systems 5 . 6 . 7 . 8th for recording in 3 shown projections 11 . 12 one in 2 shown receiving area 2 , For example, a portion of the lung of a patient 1 , from a variety of different projection directions. The second recording system 7 . 8th points opposite to the first recording system 5 . 6 in the direction of rotation φ shown on an angular offset of 90 degrees. Both recording systems 5 . 6 . 7 . 8th are essentially in the same measuring level. For capturing projections 11 . 12 show the two recording systems 5 . 6 . 7 . 8th in each case a radiator in the form of an x-ray tube 5 . 7 and a detector disposed opposite thereto 6 . 8th on.

The respective X-ray tube 5 . 7 can by means of a generator 19 for generating X-radiation according to one of a control unit 17 generated control pulses are applied to a tube current. The tube current is modulable so that only during a sample time interval for detecting the projections 11 . 12 the patient 1 the full X-ray dose is applied.

The respective detector 6 . 8th is from detector elements 20 constructed, which are lined up in this embodiment to 64 lines, each detector element 20 in the direction of the axis of rotation 4 has an extension of 0.6 mm. For reasons of clarity, only one detector element is provided with a reference numeral. Every detector 6 . 8th therefore has a so-called z-coverage of 384 mm. The attenuation values generated for each projection during the scan are sent to the control unit 17 forwarded and charged to an image, which on a display unit 21 is representable.

The computed tomography device 3 is still a not completely shown storage device with a movable table top 22 assigned to the patient 1 is storable. The tabletop 22 is in the direction of the axis of rotation 4 adjustable, so that one with the patient 1 connected recording area 2 through an opening 23 in the housing of the computed tomography device 3 into the measuring ranges of the two recording systems 5 . 6 . 7 . 8th can be moved. But it would also be possible other adjustments. It is essential that only the recording area 2 and the two recording systems 5 . 6 . 7 . 8th in the direction of the axis of rotation 4 are arranged relative to each other adjustable.

To detect the respiratory movement and to detect a specific phase of the respiratory movement, the computed tomography device 3 in the case of the present embodiment, further, a breathing belt 24 which is a stretchable belt around the patient's chest 1 is laid. In a non-explicitly illustrated pocket of the breathing belt 24 there is a pressure sensor 25 , By appropriate arrangement of the pressure sensor 25 in the bag and Bias of the breathing belt 24 gives the pressure sensor 25 when breathing the patient 1 in which the chest of the patient 1 continuously raises and lowers signals, hereinafter referred to as respiratory signals 9 be designated.

In addition to the breathing belt mentioned in this embodiment 24 Of course, other devices for detecting the respiratory signals can be used. For example, the use of a so-called real-time position management (RPM) would be conceivable in which a reflective in the infrared spectral marker is mounted on the chest and tracked by means of an infrared camera. As a result of the tracking you get breath signals 9 , which also reflect the state of motion of the lungs. In addition, it would also be conceivable, for example, respiratory signals 9 directly from the breath of a patient through a mouthpiece 1 to generate by means of a device provided for this purpose.

The respiratory signals 9 become a signal acquisition unit 16 fed. The signal processing unit 16 generated by evaluation of the respiratory signals 9 the respiratory motion, in 2 shown recording pulse 10 , for example a square pulse, at a certain stage of the respiratory movement. The control unit 17 receives the recording pulse 10 and generates on the basis of control signals with which the adjustment units 26 . 27 for driving the tabletop 22 and the gantry 18 be controlled so that projections 11 . 12 from the receiving area 2 be recorded.

The image recording process takes place in an in 2 shown way. The run index i identifies the time reference of quantities or events, with the current index 0 being assigned to the run index. Time points with negative running index are in the future, whereby the negative value increases according to the distance at the current time increasingly. Times with a positive running index are in the past, but are in the 2 not shown. In the lower part of the 2 is a breathing curve 28 the respiratory signals 9 shown, which includes three inspiratory breathing phases that are in the breathing curve 28 each represent by a breath signal peak P _i . The occurrence of a breathing signal peak P _i is characterized in the illustration by the times t _i . The cycle duration A _{i of} a breathing cycle Z _i corresponds to the time interval between two respiratory signal peaks P _i . The time t ₀ triggers a trigger pulse T ₀ for controlling the image recording method, from which the recording pulse 10 is generated delayed. A detection of the time t ₀ is, for example, by means of a threshold criterion on the respiratory signal 9 detectable. The recording pulse 10 is generated in this embodiment for an exhaled breath for the next breath following Z _-2 cycle, so that sufficient lead time to accelerate the table top 22 and the gantry 18 is available. The times t _-1 and t _{-2 of} the cycle duration to the next following breathing cycle Z _-2 are calculated on the basis of a number of preceding breathing cycles A _i with i> 0. In the calculation, for example, the mean or median value of the cycle duration A _{i of} past breathing cycles Z _i with i> 0 is taken into account. The recording impulse 10 is then determined relative to the estimate of this cycle duration Z _-2 . The times t _a and t _e for the beginning and end of the recording pulse 10 for example, calculate as follows: t _a = t _-1 + 0.3 · Z _-2 t _e = t _-1 + 0.7 · Z _-2

In 2 are beyond the scanning positions of the two recording systems 5 . 6 . 7 . 8th for scanning a recording area 2 the lung in yz plane shown in relation to the respiratory curve 28 shown. By rotation of the gantry 18 with simultaneous continuous feed of the table top 22 become, as shown, of each recording system 5 . 6 . 7 . 8th projections 11 . 12 along a spiral path 14 . 15 around the reception area 2 detected. Due to the 90 degree offset of the recording systems 5 . 6 . 7 . 8th in the direction of rotation φ are the two spiral paths 14 . 15 arranged with an offset to each other in a double-helical structure. The pitch value is adjusted so that in 3 shown projection gaps 13 of the recording area 2 at recorded projections 11 along the first spiral path 14 with the first recording system 5 . 6 through projections 12 along the second spiral path 15 around the reception area 2 with the second recording system 7 . 8th be filled.

The projection gaps 13 are still at a z-coverage of the detectors 6 . 8th of 384 mm and a rotation time of the recording systems 5 . 6 . 7 . 8th 0.285 seconds at table speeds of up to 40-45 cm. Therefore, pitch values between 3 and 3.4 can be achieved. A reception area 2 with an extension of 30 cm in the direction of the axis of rotation 4 can be sampled in a time interval of about 700 to 800 ms, so that a complete set of projections needed for the reconstruction 11 . 12 within a respiratory cycle Z _-2 can be gained.

Thus, it is possible to record two different respiratory conditions in a contrast agent examination by first taking the first respiratory position in the craniocaudal direction and then immediately after the second respiratory position in the caudocranial direction with a delay of a total of 3 to 4 seconds.

The 3 shows projections 11 . 12 the two recording systems 5 . 6 . 7 . 8th in a yz cutting plane for seamless scanning of the recording area 2 , where the projections 11 . 12 the two recording systems 5 . 6 . 7 . 8th come from two offset by 180 degrees to each other projection directions during a spiral scan.

Each direction of projection will be at each revolution of the two recording systems 5 . 6 . 7 . 8th recorded two projections. By the offset of the two recording systems 5 . 6 . 7 . 8th in the direction of rotation φ go through the two recording systems 5 . 6 . 7 . 8th the same projection direction not at the same time, but at different times. The projections 11 . 12 For this reason, they are not in the same position, but depending on the feed of the recording area 2 at different positions in the direction of the axis of rotation 4 added. projection gaps 13 that when scanning with only the first recording system 5 . 6 at the pitch value set high, are projected by the projection 12 of the second recording system 7 . 8th filled up with each circulation.

In summary, the following can be said:
The invention relates to an image recording method for rapid scanning of a respiratory movement of a patient 1 affected recording area 2 using a tomography device 3 with at least two about a common axis of rotation 4 rotatably arranged recording systems 5 . 6 . 7 . 8th in which a breath signal 9 at least one recording pulse adapted to the breathing movement 10 is generated, with which the tomography device 3 is controlled. During the recording pulse 10 become projections 11 . 12 from the receiving area 2 captured, with projection gaps 13 of the recording area 2 at recorded projections 11 along a first spiral path 14 around the reception area 2 with the first recording system 5 . 6 through projections 12 along a second spiral path 15 around the reception area 2 with the second recording system 7 . 8th be filled. It becomes the recording pulse 10 based on the respiratory signal 9 is statistically determined from a number of previous breathing cycles Z _i , wherein two following respiratory signal peaks P _-1 , P _-2 are estimated for determining the position and length of a cycle duration A _-2 and the acquisition pulse 10 relative to this cycle duration A _{-2 is} set. With this procedure, shooting ranges 2 ideally be detected from the lungs with only one respiratory cycle Z _i , allowing the patient 1 total applied X-ray dose is greatly reduced. In addition, level artifacts in the reconstructed image are avoided. The invention also relates to a tomography device 3 , which is set up to carry out such a method.

Claims (5)

Image recording method for fast scanning of a respiratory movement of a patient ( 1 ) ( 2 ) using a tomography device ( 3 ) with at least two about a common axis of rotation ( 4 ) rotatably arranged recording systems ( 5 . 6 . 7 . 8th ), in which a breath signal ( 9 ) at least one recording pulse ( 10 ) is generated, with which the tomography device ( 3 ) is controlled so that during the recording pulse ( 10 ) Projections ( 11 . 12 ) from the receiving area ( 2 ), whereby projection gaps ( 13 ) of the recording area ( 2 ) in recorded projections ( 11 ) along a first spiral path ( 14 ) around the recording area ( 2 ) with the first recording system ( 5 . 6 ) through projections ( 12 ) along a second spiral path ( 15 ) around the recording area ( 2 ) with the second recording system ( 7 . 8th ), the recording pulse ( 10 ) based on the respiratory signal ( 9 ) is statistically determined from a number of preceding respiratory cycles (Z _i ) and wherein two following respiratory signal peaks (P _-1 , P _-2 ) are estimated for determining the position and the length of a cycle duration (A _-2 ) and the acquisition pulse ( 10 ) relative to this cycle duration (A _-2 ). Image recording method according to claim 1, wherein the two recording systems ( 5 . 6 . 7 . 8th ) offset in the direction of rotation (φ) by 90 degrees in a plane perpendicular to the axis of rotation ( 4 ) are arranged to each other. Image recording method according to claim 1 or 2, wherein a reconstruction of a tomographic image from the projections ( 11 . 12 ) of both recording systems ( 5 . 6 . 7 . 8th ) is carried out. Tomography device for rapid scanning of a patient by breathing movement ( 1 ) ( 2 ) with at least two about a common axis of rotation ( 4 ) rotatably arranged recording systems ( 5 . 6 . 7 . 8th ), comprising - a signal detection unit ( 16 ), which consist of a respiratory signal ( 9 ) at least one on the respiratory motion matched recording pulse ( 10 ), the recording pulse ( 10 ) based on the respiratory signal ( 9 ) is statistically determinable from a number of preceding respiratory cycles (Z _i ), and wherein two following respiratory signal peaks (P _-1 , P _-2 ) for determining the position and the length of a cycle duration (A _-2 ) can be estimated and the acquisition pulse ( 10 ) relative to the duration of this cycle (A _-2 ), - a control unit ( 17 ), which the tomography device ( 3 ) during the generated recording pulse ( 10 ) so that projections ( 11 . 12 ) of the Recording area ( 2 ), whereby projection gaps ( 13 ) of the recording area ( 2 ) in the recorded projections ( 11 ) along a first spiral path ( 14 ) around the recording area ( 2 ) with the first recording system ( 5 . 6 ) through the projections ( 12 ) along a second spiral path ( 15 ) around the recording area ( 2 ) with the second recording system ( 7 . 8th ) are refillable. Tomography apparatus according to claim 4, wherein the two recording systems ( 5 . 6 . 7 . 8th ) offset in the direction of rotation by 90 degrees in a plane perpendicular to the axis of rotation ( 4 ) are arranged to each other.

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