DE102012205245B4 - Angiographic examination procedure of a patient for 3-D rotational angiography - Google Patents

Abstract

Angiographic examination method for an examination subject of a patient (6) for 3-D rotational angiography using an angiography system, which has an X-ray emitter (3) with a collimator (11), an X-ray image detector (4) attached to the ends of a C-arm (2) have a patient table with a table top (5) for positioning the patient (6), a system control unit (7), an image system (8) and a monitor (9), characterized by the following steps: S1 data acquisition by the angiography system using 3- D-rotation angiography of the examination object to be reconstructed, in which the x-ray system is moved on a scan trajectory (13) and 2-D x-ray images are generated at certain time intervals at certain angles, S2 change due to alternating opening and closing of the opening of the collimator (11 ) by means of a control device (10) during the data acquisition to record a large volume of the examination object kts with a large opening of the collimator (11) and a small volume of the examination object with a small opening of the collimator (11), S3 change in the resolution such that with a large volume the data acquisition takes place in a low resolution and with a small volume in a high resolution, S4 reconstruction a 3-D volume of the examination object from the acquired data and S5 reproduction of the reconstructed 3-D volume.

Description

The invention relates to an angiographic examination method for an examination subject of a patient for 3-D rotary angiography by means of an angiography system, which comprises an X-ray emitter with a collimator, an X-ray image detector which is attached to the ends of a C-arm, a patient table with a table top for positioning the patient , a system control unit, an image system and a monitor.

An X-ray diagnostic device for performing such an angiographic examination method is, for example, from US Pat US 7,500,784 B2 known that based on the 1 is explained below.

The 1 shows a monoplane X-ray system shown as an example with one of a stand 1 C-arm in the form of a six-axis industrial or articulated arm robot 2nd , at the ends of an X-ray source, for example an X-ray source 3rd with x-ray tube and collimator, and an x-ray image detector 4th are attached as an image recording unit.

By means of, for example, from the US 7,500,784 B2 Known arm robot, which preferably has six axes of rotation and thus six degrees of freedom, the C-arm 2nd can be spatially adjusted, for example by moving around a center of rotation between the X-ray tube 3rd and the X-ray image detector 4th is rotated. The angiographic x-ray system according to the invention 1 to 4th is especially about centers of rotation and axes of rotation in the C-arm plane of the X-ray image detector 4th rotatable, preferably around the center of the X-ray image detector 4th and around the center of the x-ray image detector 4th intersecting axes of rotation.

The known articulated arm robot has a base frame, which is fixedly mounted on a floor, for example. A carousel is attached to it so that it can rotate about a first axis of rotation. A robot rocker is attached to the carousel so that it can be pivoted about a second axis of rotation, to which a robot arm is attached so as to be rotatable about a third axis of rotation. A robot hand is attached to the end of the robot arm so that it can rotate about a fourth axis of rotation. The robot hand has a fastening element for the C-arm 2nd which is pivotable about a fifth axis of rotation and rotatable about a sixth axis of rotation running perpendicular thereto.

The implementation of the X-ray diagnostic device is not dependent on the industrial robot. Conventional C-arm devices can also be used.

The X-ray image detector 4th can be a rectangular or square, flat semiconductor detector, which is preferably made of amorphous silicon (a-Si). However, integrating and possibly counting CMOS detectors can also be used.

In the X-ray beam path 3rd is on a table top 5 a patient to be examined 6 as an object of investigation. There is a system control unit on the x-ray diagnostic device 7 with an imaging system 8th connected to the image signals of the X-ray image detector 4th receives and processes (controls are not shown, for example). The x-ray images can then be displayed on a monitor light 9 to be viewed as. In the system control unit 7 is still a control device 10th provided, the function of which is described in more detail.

Instead of the in 1 X-ray system with the stand, for example 1 in the form of the six-axis industrial or articulated arm robot, as in 2nd Simplified, the angiographic X-ray system also includes a normal ceiling or floor-mounted bracket for the C-arm 2nd exhibit.

Instead of the C-arm shown for example 2nd can the angiographic x-ray system also separate ceiling and / or floor-mounted brackets for the x-ray emitter 3rd and the x-ray image detector 4th have, for example, electronically rigidly coupled.

From the DE 43 28 783 C2 an X-ray diagnostic device for 2-D fluoroscopy is known which enables changing collimation. For this purpose, the X-ray diagnostic device for 2-D fluoroscopy is provided with a variable depth diaphragm, which has a central area and an outer area with different X-ray transparency parities. In a first position, the depth diaphragm only releases the central area without being weakened and it is fully opened for every nth image, so that both the central area and the outside area are not weakened. This takes advantage of the fact that human perception in the visual center has a significantly better spatial resolution than in the rest of the field of vision.

X-rays are applied for examinations with CT and C-arm CT devices. The patient is thus exposed to ionizing radiation, which can be stressful depending on the strength. A reduction in radiation is always positive for the patient and the examiner.

• - zusätzliche Abschirmung des Patienten oder des Untersuchers durch absorbierende Schutzvorrichtungen,
• - alternative Akquisitionsprogramme, die mit adaptiver Belichtung und Software-Nachbearbeitung die Strahlung reduzieren, oder
• - Einschränkung der gescannten Fläche oder des gescannten Volumens nach gegebenenfalls vorherigem notwendigen Scan zur Auswahl des eingeschränkten Volumens

basieren.To date, there are various methods for reducing the patient dose, either based on

• - additional shielding of the patient or the examiner by means of absorbing protective devices,
• - alternative acquisition programs that reduce radiation with adaptive exposure and software post-processing, or
• - Restriction of the scanned area or the scanned volume after a possibly necessary scan to select the restricted volume

based.

In the US 2004/0202283 A1 describes a multi-line computer tomograph in which the volume of interest between two scans can be adjusted by means of a collimator for dose reduction.

The invention is based on the object of designing an angiographic examination method of the type mentioned at the outset in such a way that the applied X-ray radiation to which the patient is exposed can be further reduced.

The object is achieved for an angiographic examination method of the type mentioned by the features specified in claim 1. Advantageous designs are specified in the dependent claims.

• S1 Datenakquisition durch das Angiographiesystem mittels 3-D-Rotationsangiographie des zu rekonstruierenden Untersuchungsobjekts, bei der das Röntgensystem auf einer Scan-Trajektorie (13) bewegt wird und in bestimmten Zeitabständen unter bestimmten Winkeln 2-D-Röntgenbilder erzeugt werden,
• S2 Veränderung durch wechselndes Öffnen und Schließen der Öffnung des Kollimators (11) mittels einer Steuervorrichtung (10) während der Datenakquisition zur Erfassung eines großen Volumens des Untersuchungsobjekts bei großer Öffnung des Kollimators (11) und eines kleinen Volumens des Untersuchungsobjekts bei kleiner Öffnung des Kollimators (11),
• S3 Veränderung der Auflösung derart, dass bei großem Volumen die Datenerfassung in niedriger Auflösung und bei kleinem Volumen in hoher Auflösung erfolgt,
• S4 Rekonstruktion eines 3-D-Volumens des Untersuchungsobjekts aus den erfassten Daten und
• S5 Wiedergabe des rekonstruierten 3-D-Volumens.

According to the invention, the object is achieved by the following method steps:

• S1 data acquisition by the angiography system by means of 3-D rotational angiography of the examination object to be reconstructed, in which the x-ray system is based on a scan trajectory ( 13 ) is moved and 2D X-ray images are generated at certain time intervals at certain angles,
• S2 change by alternately opening and closing the opening of the collimator ( 11 ) by means of a control device ( 10th ) during the data acquisition to record a large volume of the examination object with a large opening of the collimator ( 11 ) and a small volume of the examination object with a small opening of the collimator ( 11 ),
• S3 change the resolution in such a way that data is recorded in low resolution for large volumes and in high resolution for small volumes,
• S4 reconstruction of a 3-D volume of the examination object from the acquired data and
• S5 playback of the reconstructed 3-D volume.

Due to the variable collimation for the acquisition of a 3-D scan and the possibility to simultaneously scan a large volume in low spatial resolution and a small volume in high spatial resolution, completely different acquisition paradigms result. Corresponding changes during the scan affect the type of the reconstructed image. Depending on the requirements of the reconstruction, different images can be generated using different acquisition scenarios.

For example, an area with high resolution and an area with continuously reduced spatial resolution can be achieved by alternately opening and closing the diaphragm. If the collimator diaphragm moves quickly, a reconstruction can be achieved by switching from image to image, which has two different resolutions.

According to the invention, the change in the opening of the collimator according to step S2 between two x-rays.

It has proven to be advantageous if the change in the opening of the collimator according to step S2 continuously or alternatively, by leaps and bounds between a large and a small exposure area.

According to the invention, the collimation according to step S2 done asymmetrically.

A braking of the x-ray system, which may interfere with the data acquisition, is not necessary if its movement on the scan trajectory in accordance with step S1 done continuously.

The reconstruction can advantageously be carried out according to step S4 be carried out using an analytical, iterative or mixed method.

• 1 ein bekanntes C-Bogen-Angiographiesystem mit einem Industrieroboter als Tragvorrichtung,
• 2 eine Aufnahmegeometrie des Röntgensystems gemäß 1,
• 3 eine schematische Darstellung einer dynamischen Kollimation,
• 4 bis 9 verschiedene Akquisitionsprotokolle zur dynamischen Kollimation gemäß 3 und
• 10 eine schematische Darstellung einer asymmetrischen dynamischen Kollimation.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. Show it:

• 1 a known C-arm angiography system with an industrial robot as a carrying device,
• 2nd a recording geometry of the x-ray system according to 1 ,
• 3rd a schematic representation of a dynamic collimation,
• 4th to 9 various acquisition protocols for dynamic collimation according to 3rd and
• 10th a schematic representation of an asymmetrical dynamic collimation.

In the 2nd is the recording geometry of the X-ray system according to 1 shown in its starting position for a full scan. The X-ray tube attached to the ends of the C-arm 3rd with x-ray tube and collimator 11 generates an x-ray beam 12th that is on the table top 5 patient lying on the patient table 6 penetrates and onto the X-ray image detector 4th falls. The X-ray system is based on a scan trajectory for a rotational image 13 moved continuously, taking a full scan trajectory 13 extends over 180 degrees plus fan angle φ. The fan angle φ is that through the collimator 11 certain opening angles of the X-ray beam 12th of the X-ray tube 3rd .

In the 3rd the basic idea of the dynamic collimation according to the invention is illustrated during a complete scan for the reconstruction of a 3-D x-ray image. The collimator is used to carry out the dynamic collimation 11 by means of the control device 10th toggled between a large and a small area.

Through the collimator 11 so becomes the X-ray beam 12th limited, so that on the X-ray image detector 4th an irradiation or exposure area 15 and an unexposed outdoor area 14 surrender. By the control device 10th will now be the size of the opening of the collimator 11 and thus the size of the x-ray beam 12th and the irradiated area of the exposure area 15 changed.

At the beginning of the acquisition, for example, a first x-ray image can be taken 18th be created in which the exposure range 15 is only very small. With progressive rotation of the x-ray system on the scan trajectory 13 becomes the opening of the collimator 11 further enlarged and a second X-ray image is created 19th with a larger, medium exposure area 16 . At a later time the collimator is opened again 11 a third x-ray 20 that captures the entire area 17th of the X-ray image detector 4th can cover.

Now the collimator can be opened 11 closed again slowly, so that next an x-ray 21 is recorded. After minimal opening of the collimator 11 with x-ray 22 becomes the collimator 11 opened again, so that x-rays 23 and 24th surrender.

It is clear to the person skilled in the art that between the described X-ray images 18th to 24th in each case there are a large number of further x-ray images required for a reconstruction of a volume, in which, however, only little changes from the previous x-ray image.

The following results for the reconstructed image: Is the exposure area 15 small, you get an associated small volume, whereby the data is recorded with maximum resolution. With a large exposure area, the total area 17th , depending on the frequency of switching between large and small with lower spatial resolution. The more X-ray images are taken in the large collimator position, the higher the resolution in the large exposure area 17th .

Because the unexposed outdoor areas 14 Not missing in all projections and ideally evenly subsampled, depending on the type of undersampling, a better or worse image quality results in the edge area.

For example, on the basis of clinical studies, the extent to which this reduction in image quality is related to the reduction in radiation must be weighed. This applies, for example, to a simultaneous scan of detailed anatomy or implants, e.g. a stent that is high-contrast and small, and at the same time excludes bleeding from the top of the skull that is large and low-contrast.

In the following 4th to 9 different acquisition protocols are shown as exemplary embodiments. In the curves, the irradiated areas F are plotted over time t as area profiles. Successive exemplary embodiments in pairs result in opposing configurations.

At the in the 4th Acquisition log shown is an area course 25th , the size of the irradiated area F of the exposure area 15 indicates in the course of the investigation, triangular. That means opening the X-ray beam 12th limiting collimator 11 the exposure area 15 continuously from minimum to maximum size, the total area 17th , will be changed. The process is then reversed, this process being carried out until the end of the acquisition of the rotary recording.

In the 5 is a surface course 26 Another acquisition protocol is shown, with the acquisition protocol according to the course of the area 24th only the frequency was increased.

That in the 6 Acquisition log shown with an area course 27 resembles that of the previous figure, in which case a pause is made between the opening and closing processes, so that, for example, every second process is omitted or suppressed.

According to the acquisition protocol 7 is a surface course 28 shown, which is about an inversion of the surface course 27 is. So here is the opening of the collimator 11 held at the maximum value for a long time, so the total area 17th is irradiated.

The acquisition protocol according to 8th shows as a further embodiment a rectangular surface course 29 , where between the small exposure range 15 and the whole area 17th is switched.

With one in the acquisition protocol according to 9 shown surface course 30th it is again an inversion of the surface course 29 , so that the exposure pauses are made smaller.

• Je nach Geschwindigkeit der Veränderung der Öffnung des Kollimators 11 wird der Belichtungsbereich dazwischen mit einer abgestuften Ortsauflösung zwischen der maximalen und der minimalen Auflösung aufgenommen. Bei niedriger Frequenz gemäß 4 ist der Unterschied in der Ortsauflösung zwischen dem kleinen Belichtungsbereich 15 und dem großen Gesamtbereich 17 höher.

When acquiring data, the following applies to the acquisition logs:

• Depending on the speed of change of the opening of the collimator 11 the exposure area in between is recorded with a graduated spatial resolution between the maximum and the minimum resolution. At low frequency according to 4th is the difference in spatial resolution between the small exposure area 15 and the large total area 17th higher.

This can be changed even further by giving one of the two exposure areas a preference and taking this setting longer, as is the case with the 6 and 7 is illustrated.

Changes the opening of the collimator 11 so fast that two neighboring projections completely occupy the small and the large exposure area and therefore no intermediate steps as in 3rd necessary, there is a constant resolution for both exposure areas. Here, too, a preference can be given for one of the exposure areas (cf. 8th and 9 ).

In the 10th An alternative of the dynamic collimation according to the invention is illustrated during a complete scan for the reconstruction of a 3-D X-ray image, in which the collimator is used for the dynamic collimation 11 such from the control device 10th in the size and position of the opening of the collimator 11 is switched between a large and a small area that the exposure area 15 asymmetrical, shifted off center. In the example shown, this is the top left corner.

As in the example according to 3rd X-rays will be used in the course of the acquisition 30th to 36 created where the exposure range 15 between a small area and the total area 17th fluctuate with the exposure areas 15 and 16 no longer in the middle, but asymmetrically in one of the corners.

Scanning a large volume in low resolution and a small volume in high resolution at the same time is achieved if a CT or C-arm CT scan is performed with dynamic collimation. The 2nd shows a typical CT acquisition geometry. The X-ray tube 3rd and the x-ray image detector 4th revolve around the patient 6 . X-rays are taken, which are used for CT reconstruction.

• In dem kleinen Belichtungsbereich 15 und somit dem dazugehörigen kleinen Volumen werden gesteuert von der Steuervorrichtung 10 mit maximaler Auflösung Daten aufgenommen. In dem großen Gesamtbereich 17 werden je nach Frequenz der Umschaltung zwischen groß und klein aufgrund der Steuervorrichtung 10 mit geringerer Auflösung Daten akquiriert. Je mehr Röntgenbilder in der großen Kollimatorstellung aufgenommen werden, desto höher ist die Auflösung in dem großen Gesamtbereich 17. Die Bilder 18 bis 24 gemäß 3 stellen jeweils die volle Detektorfläche als großen Bereich dar; diese kann jedoch auch nur ein Teil des gesamten Röntgenbilddetektors 4 sein. D.h., dass die Steuervorrichtung 10 den Kollimator 11 nicht zwischen voller und kleiner Öffnung umschaltet, sondern die volle Öffnung kann kleiner als die maximale Öffnung sein.

In the 3rd the idea of dynamic collimation is given as an example. The collimation is between a large exposure area, the total area 17th , and a small exposure range 15 by means of the control device 10th switched. The following properties result for the reconstructed image:

• In the small exposure area 15 and thus the associated small volume are controlled by the control device 10th Data recorded with maximum resolution. In the large area 17th are depending on the frequency of switching between large and small due to the control device 10th Data acquired with lower resolution. The more X-ray images are recorded in the large collimator position, the higher the resolution in the large overall area 17th . The pictures 18th to 24th according to 3rd each represent the full detector area as a large area; however, this can only be a part of the entire X-ray image detector 4th be. Ie that the control device 10th the collimator 11 does not switch between full and small opening, but the full opening can be smaller than the maximum opening.

The 4th to 9 show examples of different acquisition protocols where the speed of change of the opening of the collimator 11 be included in the intermediate area with graded spatial resolutions between the maximum and the minimum resolution, the spatial resolution between the small and the large area having a greater difference at low frequencies.

The small exposure area 15 can also be outside the isocenter of the rotation. This is achieved through asymmetric collimation, as is shown in the 10th was shown. Again, the various acquisition protocols can be used in accordance with the 4th to 9 be used.

Such collimation has so far only been used statically in the acquisition. Neither real-time control of the collimator 11 during the scan, still asymmetrical collimation was possible. This further development opens up new opportunities for the acquisition of X-ray images.

• - Iterative Rekonstruktion:
  • Prinzipiell können alle Daten mit einem iterativen Verfahren rekonstruiert werden, da diese besonders robust auf wechselnde Eingangsdaten sind. Besonders sogenannte „Compressed Sensing“ Verfahren, also regularisierte Rekonstruktionsverfahren, sind hier geeignet.
• - Analytische Rekonstruktion:
  • Weiterhin ist es möglich, die Daten mit einem analytischen Verfahren zu rekonstruieren. Allerdings müssen hier gängige Verfahren, die auf einer gefilterten Rückprojektion basieren, verändert werden, da die Redundanzgewichtung nicht mehr stimmt. Die entsprechende Gewichtungsfunktion muss dem Akquisitionsprotokoll angepasst werden. Dies kann sowohl im Projektionsraum als auch im Objektraum geschehen.
  • Dies lässt sich numerisch bestimmen; aber auch eine analytische Herleitung ist möglich. Dieses Rekonstruktionsverfahren kann aber zu Streifenartefakten führen, die in einem weiteren Schritt dann beispielsweise durch nicht lineare Filterung oder Regularisierung reduziert werden sollten.
• - Gemischte Verfahren:
  • Das Rekonstruktionsproblem wird in mehrere unterabgetastete Probleme zerlegt:
    • Diese graduieren sich zwischen einem Problem mit wenigen Projektionen mit vollem (großen) Messfeld und einem Problem mit vielen Projektionen mit stark trunkiertem Messfeld, die initial unabhängig gelöst werden können.

In the acquisition protocols according to the invention, the 2-D projections are converted into a correct 3-D volume with the correct, adapted reconstruction algorithm. Various reconstruction methods can be used:

• - Iterative reconstruction:
  • In principle, all data can be reconstructed using an iterative process, since they are particularly robust to changing input data. So-called “Compressed Sensing” methods, ie regularized reconstruction methods, are particularly suitable here.
• - Analytical reconstruction:
  • It is also possible to reconstruct the data using an analytical method. However, current methods based on a filtered back projection have to be changed here because the redundancy weighting is no longer correct. The corresponding weighting function must be adapted to the acquisition protocol. This can be done both in the projection space and in the object space.
  • This can be determined numerically; but an analytical derivation is also possible. However, this reconstruction method can lead to streak artifacts, which should then be reduced in a further step, for example by non-linear filtering or regularization.
• - Mixed procedures:
  • The reconstruction problem is broken down into several subsampled problems:
    • These graduate between a problem with a few projections with a full (large) measuring field and a problem with many projections with a heavily truncated measuring field, which can initially be solved independently.

Thereafter, entangled problems can be formed, which use information from the other problem to reduce artifacts. For example, you can use the subsampled reconstruction with a full measurement field to solve the truncation problem in the projections with a reduced measurement field.

Finally, the different reconstructions can be merged into a single reconstruction. When merging, you have to make sure that there are no artifacts because of the different resolutions. This can be achieved by appropriate regularization with common criteria, such as smoothness or minimal TV norm.

Claims (7)

Angiographic examination method for an examination subject of a patient (6) for 3-D rotational angiography using an angiography system, which has an X-ray emitter (3) with a collimator (11), an X-ray image detector (4) attached to the ends of a C-arm (2) have a patient table with a table top (5) for positioning the patient (6), a system control unit (7), an image system (8) and a monitor (9), characterized by the following steps: S1 data acquisition by the angiography system using 3- D-rotation angiography of the examination object to be reconstructed, in which the X-ray system is moved on a scan trajectory (13) and 2-D X-ray images are generated at certain time intervals at certain angles, S2 change due to alternating opening and closing of the opening of the collimator (11 ) by means of a control device (10) during the data acquisition to record a large volume of the examination object project with a large opening of the collimator (11) and a small volume of the examination object with a small opening of the collimator (11), S3 change in the resolution such that with a large volume data acquisition takes place in a low resolution and with a small volume in a high resolution, S4 reconstruction a 3-D volume of the examination object from the acquired data and S5 reproduction of the reconstructed 3-D volume. Angiographic examination procedure after Claim 1 , characterized in that the change in the opening of the collimator (11) takes place according to step S2 between two x-ray images. Angiographic examination procedure after Claim 1 , characterized in that the change in the opening of the collimator (11) takes place continuously according to step S2. Angiographic examination method according to one of the Claims 1 to 3rd , characterized in that the change in the opening of the collimator (11) according to step S2 takes place suddenly between a large and a small exposure area (17, 15). Angiographic examination method according to one of the Claims 1 to 4th , characterized in that the collimation takes place asymmetrically according to step S2. Angiographic examination method according to one of the Claims 1 to 5 , characterized in that the movement of the x-ray system on the scan trajectory (13) takes place continuously according to step S1. Angiographic examination method according to one of the Claims 1 to 6 , characterized in that the reconstruction according to step S4 is carried out according to an analytical, iterative or mixed method.

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