TO THE INVENTION
The invention relates to a method and a device for imaging
a moving object and in particular refers to
medical imaging. In particular she deals with X-ray images
of organs or moving parts of organs.
a conventional one
X-ray imaging method
and a conventional one
X-ray imaging device
a device for emitting a radiation, for example a
and a device for detecting the emitted radiation,
For example, a detector with a video camera and an image intensifier. The
The object to be imaged, for example an organ, is placed between the
Source and the detector placed. X-rays emitted by the source
penetrate the organ and are received by the detector.
The rays are amplified by the image intensifier and by the video camera
converted into signals indicating the exposure or irradiation of the detector
medical examinations or some surgical operations
is the acquisition of several consecutive radiographs of the
same anatomical area of a patient required. Around
the appearance of artifacts on images by processing
unprocessed acquired images, or errors
to avoid analyzing these images, it is necessary
that the anatomical area of interest is in the same
Position is when each of the consecutive pictures taken
becomes. Some movements can
However, these are not avoided, and these are in particular movements that
are due to the contraction of the heart.
Requirements of examination or surgical operation
single image per cardiac cycle is sufficient, provides the high-speed acquisition
and the subsequent sorting of images is not an acceptable solution,
because this is an unnecessary
Radiation dose with X-rays
Patients and for
lead the medical staff
includes a synchronization of the acquisition of images with the
Cardiac cycle of the patient. In other words, the source and the
Detector synchronously controlled with a measured heart signal,
that acquires the images with a phase identical to the cardiac cycle
become. Thus, it usually becomes
just a single picture for
receive every heart cycle.
Create digital images with better quality compared to images,
which are generated by devices with a conventional detector,
For example, imaging devices that use digital planar x-ray detectors are used
also known as digital flat panel detectors or flat-panel detectors
be designated. However, solid state x-ray detectors require a perfect
periodic readout, quality pictures
Heart movements are not repeatable, the heart signals are not
periodically. As a result, it is virtually impossible to use an X-ray detector
in solid state construction
to perfectly synchronize with a heart signal. Such a synchronization
that would be
Behavior or the goodness of
Detectors deteriorate, and / or the required correction processing
the acquired images would be
way too complex.
US Pat. No. 6,643,536 describes a method of synchronizing the acquisition of X-ray images with a cardiac signal to produce dual energy images. This method includes measuring the cardiac signal, detecting a diastolic peak, and following a predetermined delay following the systolic peak (the QRS complex), triggering an X-ray emission synchronous with the detector control signal during the diastolic phase. This method of synchronization can be used to generate two images of the lungs with two different X-ray energies during a diastolic period of the heart (a period during which the heart cavities are filled with blood). The diastolic period generally corresponds to a period of the cardiac cycle during which cardiac movement is minimal. The method limits fluctuations in the position of the lungs between the acquired images, even if those images are not acquired at exactly the same phase in the cardiac cycle. First, such a method does not always achieve satisfactory results because existing differences in the cardiac phase between patients are not taken into account. In particular, it has been found that the optimal exposure start time, using the least movement criterion of the viewing organ, does not necessarily correspond to a given delay (or given phase in the cardiac cycle) identified after the systolic start peak. Secondly, such a method is for processing a sequence containing a large number of images, or for an analysis of the heart, whose movements are substantially greater than the movements that are close to it is not suitable.
The invention relates to an imaging method that operates more precisely.
The invention relates to a method for imaging a movable
Object, which includes:
Acquisition of a sequence of reference images of the object; processing
the sequence of reference images of the object, for each image at least one
Movement parameter or a movement date for the image assigned to the image
To determine object; Assignment of a thus determined motion parameter
or movement date to one or more phases of a physiological
The invention further relates to an X-ray device comprising a
Device for emitting a radiation source, a device
for detection and a means for acquisition, the
is able to process images acquired by the detector,
wherein the acquisition means is programmed to implement the one described above
Features and benefits are more readily apparent from the following
Description given for illustrative purposes only
and in no way limiting
is to be understood and read with reference to the attached figures
should, in which:
1 schematically shows an imaging device having a solid state x-ray detector;
2 12 is a diagram schematically illustrating a cardiac signal and the variation of a rate parameter during a heart cycle for a slow heart and for a fast heart;
3 Fig. 16 is a block diagram schematically illustrating a calibration process in an imaging method according to a first embodiment of the invention;
4 Fig. 16 is a block diagram schematically illustrating an image acquisition process in an image forming method according to the first embodiment of the invention;
5 schematically illustrates the various control signals of the imaging device according to the first embodiment of the invention;
6 Fig. 16 is a block diagram schematically showing a calibration process in an image forming method according to a second embodiment of the invention;
7 Fig. 16 is a block diagram schematically showing an image acquiring process in an image forming method according to the second embodiment of the invention;
8th FIG. 12 is a block diagram schematically illustrating determination of a motion parameter in an imaging method according to the first embodiment of the invention; FIG.
9 Fig. 16 is a block diagram schematically illustrating determination of the minimum movement in an imaging method according to the first embodiment of the invention; and
10 FIG. 12 is a block diagram schematically illustrating determination of an optimum acquisition timing in an image forming method according to the first embodiment of the invention. FIG.
DESCRIPTION OF THE INVENTION
In 1 An imaging device has a device for measuring a cardiac signal 1 , an acquisition facility 2 a device for providing a high voltage generator 3 , a device for emitting a radiation, for example an X-ray source 4 a device for detection, for example a solid-state X-ray detector 5 , And a support or support device, such as a table 6 on which a patient 7 can be positioned on. The table 6 is between the source 4 and the detector 5 positioned. The device for measuring a cardiac signal 1 can be used to measure electrical signals delivered by the heart as a function of time. The measuring device 1 sends the signals it has measured to the acquisition facility 2 , The acquisition facility 2 has a processing means programmed to operate the high frequency voltage generator 3 and the solid state x-ray detector 5 to control. The high frequency voltage generator 3 provides energy to the X-ray source 4 , so that the source X-rays 8th can send out. The X-rays 8th by the source 4 out be radiated, pass through the patient 7 through and through the detector 5 receive. The acquisition facility 2 is capable of the detector 5 to periodically read images.
2 shows a graph showing an ECG heart signal as measured by the measuring device 1 is measured, and illustrates a variation or change in a coronary rate parameter during a cardiac cycle for a slow-working heart and for a fast-working heart. The coronary velocity parameter corresponds to the rate of displacement of the coronary arteries due to heartbeats. This parameter is related to the heart movement.
of heart rate parameter during a cardiac cycle
be very different for different people. Especially
can be the minimum movement phase with respect to the diastolic tip
be located very differently. There may even be two relaxation areas
to be available.
3 Figure 12 is a block diagram schematically illustrating a calibration process 10 in an imaging method according to a first embodiment of the invention. The first embodiment may be used to acquire images of the heart of a patient when the heart is in a phase of minimal movement.
The first embodiment has a first calibration process 10 during which the acquisition facility 2 the source 4 and the detector 5 controls to perform the following. The patient 7 is positioned on the table of the imaging device. In step 11 controls the acquisition facility 2 the source 4 and the detector 5 to acquire a sequence of images from an organ or part of an organ. The images are sequentially acquired successively at a rate high enough relative to the heart rate to obtain a good temporal resolution (usually on the order of 30 frames per second). The image sequence is acquired by the acquisition facility 2 recorded as a sequence of reference pictures.
Picture sequence is a sequence of pictures taken during an injection of a
Contrast agent can be acquired in a coronary artery. The pictures
are usually pictures,
which consists of 512 × 512 pixels
or 1024 × 1024
Pixels exist. The pictures are at a rate of the order of magnitude
of 30 frames per second during
acquired a duration of about 5 to 10 seconds.
In step 11 The contrast agent is transported through the blood and spreads in the coronary artery. The contrast agent is then removed through the venous system. The movement of the contrast agent is recorded in the image sequence.
In step 12 reads the device for heart signal measurement 1 the signal generated by the patient's heart over time. The heart signal is transmitted by the acquisition device 2 recorded as a reference heart signal. The image sequence acquisition step 11 and the heart signal measuring step 12 are performed simultaneously by means of a common clock signal. As a result, the acquisition facility contains 2 at the end of the first and second steps 11 and 12 a sequence of reference images, each reference image associated with a phase of the reference heart signal.
In step 13 processes the acquisition facility 2 the reference image sequence and determines a motion parameter associated with each reference image. The determined motion parameter is, for example, a coronary velocity parameter, in other words a parameter which indicates the displacement or displacement speed of the contrast agent in the coronary artery.
8th shows a diagram that schematically shows the features of the step 13 for determining a motion parameter. The sequence of reference pictures contains N pictures taken during the step 11 be acquired one after the other. The images in the reference image sequence are indexed with a parameter i that varies from 1 to N depending on the acquisition order of the images. According to the sub-step 131 subtracts the acquisition facility 2 the image i from the image i + 1 for each image i in the reference image sequence. The sub-step 131 gives a sequence of N - 1 subtracted pictures which are obtained. Each subtraction image i in the sequence shows structural movements between two successive successive images i and i + 1 of the sequence of reference images.
In the sub-step 132 filters the acquisition facility 2 each image i in the sequence of subtracted images to eliminate noise consisting of high spatial frequencies.
In the sub-step 133 The acquisition device converts each image i of the filtered image sequence into a binary image. To achieve this, the acquisition facility applies 2 a threshold function on each pixel in the filtered image i as follows: if the pixel intensity is less than a predetermined threshold, the threshold function assigns 0 to the pixel; if the pixel intensity is greater than or equal to the vorbe If the threshold is true, the threshold function assigns 1 to the pixel. As a result of the substep 133 a sequence of binary images is obtained in which the pixels are equal to 0 or 1. In each binary image, the number of pixels whose value is 1 quantitatively determines the motion of structures between two consecutive images i and i + 1 in the sequence of reference images.
In the sub-step 134 calculates the acquisition facility 2 for each image i in the sequence of binary images, a motion parameter associated with image i as the sum of the values of pixels making up the binary image i. In other words, the motion parameter associated with image i corresponds to the number of pixels in the binary image whose value is equal to one. Other image analysis algorithms may also be used to obtain characteristic motion characteristics from some structures from a sequence of images, cf. For example, U.S. Patent 5,054,045.
In step 14 determines the acquisition facility 2 the moments in which the organ shown has minimal movement, in other words, the times in which the movement parameter, as in the step 13 has been determined is minimal.
9 are illustrated a graph in which changes in the value of the motion parameter p i as a function of the index i of the image in the sequence shown by reference images.
In step 15 manages the acquisition facility 2 a phase of the cardiac signal for which the movement parameter is minimal. The phase of the cardiac signal is formed by a percentage or percentage of the cardiac cycle. Specifically, the acquisition facility determines 2 an optimal acquisition delay δ that starts with the diastolic peak and for which the motion parameter is minimal.
10 illustrates a schematic representation showing the fluctuations of the motion parameter p i, of each pixel i is assigned in the reference image sequence, and the cardiac signal (ECG) illustrates over time. The thus determined optimal delay δ is specific to the patient being examined. This optimal delay is used to trigger image acquisition during a subsequent acquisition process. In 10 δ corresponds to one phase of the cardiac cycle in the range between 43 and 49%.
4 shows a block diagram, which schematically shows an acquisition process 20 illustrated according to the first embodiment of the invention. The acquisition process, as in 4 is shown after the in 3 illustrated calibration process.
In step 21 measures the device for heart signal measurement 1 a heart signal and transmits the measured signal to the acquisition device 2 , In step 22 captures the acquisition facility 2 a diastolic peak in the measured heart signal and starts a stopwatch. In step 23 controls the acquisition facility 2 the high voltage generator after a period of time δ equal to the optimal acquisition delay during the calibration process 10 has been determined to trigger the x-ray source. The high voltage generator drives the source which emits X-rays. The detector then reads out an exposed image.
5 illustrates the following signals over time: A: the cardiac signal (ECG) measured by the cardiac output measuring device; B: the power supply control signal generated by the acquisition unit; C: the detector read control signal; D: the x-ray source control signal; and E: X-rays emitted by the source and detected by the detector.
The detector read control signal is a periodic signal, usually having a frequency of about 30 Hz. As long as the X-ray source is not activated, the detector generates dark or black images. When the X-ray source is activated, the detector reads out an exposed image. After a period of time δ equal to the optimal acquisition delay during the calibration process 10 has been determined controls the acquisition device 2 the high voltage generator 3 to the X-ray source 4 to trigger. The high voltage generator 3 supplies the source 4 with energy, being the source 4 the x-rays emitted. The detector 5 reads an exposed image during the detection cycle immediately following the X-ray emission made by the source.
Considering that the detector 5 is not synchronized with the heart signal of the patient, the delay in the detection of the image compared to the source trigger signal varies between 0 and the period T of the detector read control signal C. Thus, for a read control signal C of the detector having a frequency of 30 Hz, the resulting detection delay is between 0 and 33 milliseconds. For an average adult patient, this delay corresponds to a phase error that is between 0 and 4% of the duration of the cardiac cycle. Considering that the image is acquired during a phase of the cycle in which the movement of the organ is minimal, the phase error has little effect on the position of the organ on the acquired images.
can the first embodiment of
Produce a sequence of images in which the organ as
appears stationary or immovable.
In a modification of this first embodiment, the X-ray source 4 be triggered after a delay time of δ - 1 / 2T. In this modification, the phase error is in a range between -1 / 2T and 1 / 2T. Thus, the phase error is never greater than half the period of the detector read signal.
In another modification of this first embodiment, the X-ray source 4 are triggered after a delay of δ - τ, where τ represents the reaction time of the x-ray source control system. This modification is used to correct the systematic detection delay.
In a further variant of this first embodiment, the X-ray source 4 are triggered after a delay of δ + θ, where θ represents a correction parameter that depends on the current heart rate. The correction parameter θ takes into account fluctuations in the heart rate.
According to a still further modification of this first embodiment, the X-ray source 4 after a delay equal to δ - 1 / 2pw, where pw represents the X-ray emission time. This variant makes it possible to arrange the center of the exposure (the "middle" point of the image acquired over time) at the optimal time in the cardiac cycle.
Four modification modes described above may be used together
combined to fine-tune the optimal acquisition time
6 Fig. 12 is a block diagram schematically illustrating a calibration process 30 an imaging device in a method according to a second embodiment of the present invention. The second embodiment has a first calibration process 30 on, in which the acquisition facility 2 , the source 4 and the detector 5 controls to perform the following. The patient 7 is on the table 6 the imaging device positioned. In step 31 controls the acquisition facility 2 the source 4 and the detector 5 to acquire a sequence of images of an organ or part of an organ. The images are acquired over time in a sequence. The sequence of images is by the acquisition facility 2 recorded as a sequence of reference pictures. In step 32 who at the same time as the step 31 is performed, the device measures the cardiac signal generated by the patient's heart over time. The acquisition facility 2 records the heart signal as a reference heart signal. At the end of the steps 31 and 32 contains the acquisition facility 2 a sequence of reference images, each reference image associated with a phase of the reference heart signal. In step 33 processes the acquisition facility 2 the reference image sequence and determines the motion data associated with each reference image. In step 34 determines the acquisition facility 2 a motion function that assigns motion data to each phase of a cardiac cycle.
7 Fig. 12 is a block diagram schematically showing an image acquisition process 40 in a method according to the second embodiment of the invention. The in 7 The acquisition process is carried out according to the in 6 illustrated calibration process. During this acquisition process, the acquisition facility controls 2 the source 4 and the detector 5 to perform the following steps. In step 41 controls the acquisition facility 2 the source 4 and the detector 5 to acquire a sequence of images of an organ or part of an organ. In step 42 The device measures the heart signal generated by the patient's heart over time.
The image sequence acquisition step 41 and the heart signal measuring step 42 are simultaneously executed using a common clock signal. As a result, the acquisition facility contains 2 at the end of the steps 41 and 42 a sequence of images, each image associated with a phase of the cardiac cycle. In step 43 The acquisition device corrects each acquired image by applying the correction function to the image that depends on the cardiac phase that is associated with the image based on the motion function determined during the calibration process. The second embodiment of the method corrects each image in the sequence of images to bring the organ into an identical position in each acquired image. This second embodiment produces a sequence of corrected images in which the imaged organ is in nearly the same position from one image to the next image.
The second embodiment can be executed in real time; in other words, for each acquired image, its position in the cardiac cycle is immediately examined and the corrections or processing associated with the correspondingly predetermined movement function (for example, space-time filtering after a spatial correction made). In addition, the determination of the motion function performed during the calibration process may be used to apply processing to each acquired image that is dependent on the motion data associated with the image. For example, the processing employed may include a space-time filter to enhance some of the objects of interest in the image or to reduce noise. The processing parameters are adjusted or adjusted as a function of the phase of the cardiac signal assigned to the image. In other words, the step combines 43 an image correction with a space-time filtering, wherein the applied correction and filtering are dependent on the measured heart signal.
of the method is based on a prior acquisition of a sequence
of reference pictures. A processing of this reference picture sequence
an analysis of the movement of an organ in a particular patient,
then causing this movement to be physiological
Signal corresponds. In a first embodiment, this method becomes
used: at least one phase of the physiological reference signal
to determine, for
the associated motion parameters
is minimal; for an optimal delay for triggering or
Driving a source of an X-ray imaging device
derive. The thus determined reference phase is for everyone
Patient specific. If the reference signal is a heart signal,
the reference phase represents the phase of the cardiac cycle in which the
Heart movement is minimal.
of the method allows
thus triggering the radiation source of the imaging device
in a suitable manner depending
from each patient to a minimal fluctuation or change
to get the position of the organ. More precisely, the procedure can
according to the first
comprising: measuring a physiological signal; detection
the beginning of a cycle of the physiological signal; after the
optimal delay time
is control of the radiation source in an X-ray imaging apparatus
in such a way that the source receives one or more x-ray pulses
sending out. As the source during
a phase of the cycle is triggered in which the movement is minimal
is, indicates the lack of strict synchronization between the
Detector working with its own clock and physiological
Signal little influence on the acquired image.
a second embodiment
Method a determination of a correction function, the movement data
assigns each phase of the physiological reference signal.
According to the invention, the method can be used to image any image
in the image sequence to correct, for example, a sequence
corrected images in which the imaged organ
in each successive pair of pictures approximately in the
same position. More specifically, the method according to the second
comprising: acquiring a sequence of images; Measurement
a physiological signal simultaneously with the acquisition; correction
each image based on the correction function performed during a
previous step, and at the phase of the measured
physiological signal. The second embodiment is particular
helpful to monitor
how the organ changes on the corrected image sequence, where
approximate the organ from one image to the next image
immovable. In particular, the method can be used
become, the change
a bloodstream or
the position of an artery during
a cardiac cycle or the position of a surgical operation tool,
for example, a management tool,
a catheter or stent.
The method may further include filtering each image based on
the correction function and the phase of the physiological signal
have, for example, by using a time filter
whose characteristic properties are measured by the
Movement function to be adjusted.
While one embodiment of the present invention has been described in terms of exemplary embodiments, it will be understood by those skilled in the art that various changes in function and / or method (s) and / or result may be made, and elements can be replaced by equivalent means without thereby affecting the scope and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential core thereof. Therefore, it is intended that the invention not be limited to any particular embodiment disclosed herein for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, using the terms first (r, s), second (r, s), etc., or steps does not denote any order or any importance, rather the terms are first (r, s), second (r, s), etc. or steps used to an item or distinguishing feature from another. Further, by the use of terms a, a, etc., no quantity limitation, but the presence of at least one of the referenced element or feature shall be referred to.
is a method and apparatus for radiographic imaging
of a moving organ in which a sequence of
Reference images of the institution is acquired (11). The sequence of pictures
is processed (13) for
each image has at least one motion parameter or movement date
Organ to be assigned to the image. It becomes a movement parameter or
Movement date determines the one or more phases of a physiological
Reference signal is assigned (14).
- 1 Heart signal sensing device
- 2 acquisition unit
- 3 High voltage generator
- 4 X-ray source
- 5 Solid-state X-ray detector
- 6 table
- 7 patient
- 8th X-rays
- Speed (mm / s)
- slow heart
- fast heart
- Acquisition of a sequence of reference images
- Determination of a motion parameter
- Determination of a minimum movement
- Determination of an optimal acquisition delay δ
- Recording a reference heart signal
- Measurement of a heart signal
- Detection of a diastolic tip
- Delay δ
- Triggering the X-ray source
- Acquisition of a sequence of reference images
- Determination of a motion parameter
- Determination of a movement function
- Recording a reference heart signal
- Acquisition of a picture sequence
- Correction of the image sequence
- Recording a heart signal
i = 1 to N
- Subtraction pictures i + 1 - picture
- pixel sum
- Movement parameter p i
- Pictures 1 to N
- subtracted pictures 1 to N - 1
Pictures 1 to N - 1