WO2004078042A1

WO2004078042A1 - Gating method, gating unit and therapy device

Info

Publication number: WO2004078042A1
Application number: PCT/DE2004/000424
Authority: WO
Inventors: Kathrin Lauckner; Michael Lauk
Original assignee: Seleon Gmbh
Priority date: 2003-03-07
Filing date: 2004-03-04
Publication date: 2004-09-16
Also published as: DE10310127A1; DE112004000860D2

Abstract

The invention relates to a gating method during which the breathing flow of a patient is repeatedly measured. To this end, measured breathing flow values are obtained. A control signal is generated from the measured breathing flow values and serves to control the irradiation of a patient and/or an imaging method. The invention also relates to a gating unit and to a radiotherapy device.

Description

Gating process, gating device and therapy facility

The invention relates to a gating method in which, depending on the breathing and / or cardiac activity, control signals are generated which control the irradiation of a patient and / or the acquisition of images of the patient's interior. The invention further relates to a gating device for performing such a gating method. Finally, the invention relates to an irradiation method and a radiation therapy device.

Computer tomography (CT) is known (Roche Lexicon Medicine, Urban & Fischer, Munich, 4th edition, 1998, ISBN 3-541-17114-6). It is an X-ray diagnostic, imaging procedure in which the human body is irradiated layer by layer. A computer is used to build up the image in order to display the results on the computer screen. The CT enables the display of minimal density differences, e.g. are a result of tissue changes or tumors. The measuring device is a fast rotating X-ray tube with an approximately pencil-strong beam and scintillation counters with a downstream photo multiplier. In this way, a radiation attenuation profile of the layer in question is determined by linear scanning from a slightly changed angle in each case. A local distribution of the attenuation values is calculated from approximately 100,000 measured values and converted into a television picture. The advantage of CT is that there is no overlay by other slices. The CT enables the graded soft tissue display even without contrast medium. A quantitative image evaluation based on the attenuation values given at the edge of the image is possible.

Positron emission tomography (PET) (Roche-Lexikon Medizin op. Cit.) Is also an imaging "computed tomographic" method in which the photons that are generated by positron decay are detected. PET is used, for example, to examine the blood flow and metabolic processes in individual brain sections. The isotopes ⁶⁴ Cu, ⁷⁴ As, ⁷² As, ¹⁹ F, ⁶⁸ Ga serve primarily as positron emitters. These isotopes are injected into the patient, for example, in order to accumulate in malignancies so that they appear bright in a PET image are, for example, manufactured by Siemens Medical Systems and sold under the product names ECAT ART, ECAT EXACT and ECAT HR +.

There is also single-photon emission computed tomography (SPECT) (Roche Lexicon Medicine, op. Cit.). In contrast to PET, gamma emitters are used here.

Nuclear magnetic resonance imaging (MRI) (Roche Lexicon Medicine, loc. Cit.) Is also a non-invasive imaging diagnostic procedure that provides sectional images of the human or animal body. A magnetic field of high field strength and pulsed radio waves in the megahertz band are used for image acquisition. This stimulates protons of the water and fat components in the organism to nuclear magnetic resonance. After switching off the radio frequency, the magnetic resonance signals are transmitted Receiver coils that surround the patient were added. The signal depends on the hydrogen density and the decay times. With computer support, many measurements in different directions are put together to form a tomogram, which provides information about the spatial hydrogen distribution and its interactions with the environment. For example, depending on the recording method, tissues rich in water or fat can appear as light areas, low-hydrogen tissues and fast-flowing blood components as dark areas without being obstructed by bone structures. Thanks to the differences in hydrogen density and relaxation time shown, MRI enables tumors (neoplasia), edema, bleeding (hemorrhage) or necrosis to be clearly distinguished from the healthy environment.

In addition, ionized rays are also used for healing purposes. A basic distinction is made between internal radiation therapy, in which radionucleides such as ¹⁹² IR or ¹²⁵ J are introduced into the body, and external radiation therapy, in which the body is irradiated from the outside with X-rays, electrons, neutrons, protons, π-mesons or heavy ions , The particles are accelerated with acceleration voltages in the megavolt range. The radiation is planned so that tumor tissue is damaged as much as possible and healthy tissue as little as possible. The therapy success is supported by the fact that with weak doses the tissue damage increases with the square of the dose. For this reason, it is advantageous to irradiate a tumor from different directions, the tumor forming a kind of focal point. By distributing the radiation exposure over as much healthy tissue as possible, the dose per unit volume of healthy tissue is kept low. Due to the quadratic dependence of the radiation damage on the dose, the radiation damage is reverberated in healthy tissue. Irradiation from different directions can take place successively by moving the radiation source.

Movement of the body, in particular of the thorax due to breathing and heartbeat, is problematic both with imaging methods for diagnostic purposes and with radiation therapy. In imaging diagnostic procedures, moving the inside of the body leads to blurring. Small tumors can be overlooked during diagnosis. With radiation therapy, the treatment field is traditionally enlarged to cover the movement of the tumor during breathing. This can lead to large lung volumes to be irradiated, which require unacceptably high doses. Since the damage to normal tissue determines the maximum dose with which a tumor can be irradiated, some tumors in the thorax cannot be irradiated sufficiently to cure the tumor.

These disadvantages are to be eliminated by gating processes.

Varian medical Systems sells a breathing gating solution that visually resolves the breathing movement with sub-millimeter accuracy. In operation, reflective Markers attached to the patient's chest. A video camera measures the up and down movement. The continuous signal is processed by a computer that turns off the beam in the accelerator when the breathing movement exceeds the parameters determined during the treatment simulation. The software can detect unexpected movements, such as coughing, and interrupt the radiation. The CT images are taken at a specific phase of the breathing cycle that is intended for treatment. This simplifies the treatment planning process because it is ensured that the diagnostic data is recorded at the same time as the treatment (www.varian.com/com/000605.html).

In addition to respiratory gating, cardiac or cardiac gating is also used. This involves taking pictures of a specific phase in a cardiac cycle. The recording is triggered or triggered by an EKG (electrocardiogram) signal. ECG gating is useful whenever data acquisition is too slow to occur in a short part of the cardiac cycle to suppress motion blur. With nuclear medicine imaging methods, 10 to 50 images can be taken during a cardiac cycle. The gating signal starts data acquisition for the first image. Then, after a predetermined time of, for example, 10 to 50 milliseconds, the data acquisition switches to the second image and then to further images until, based on the EKG signal, the next heart phase begins and the data acquisition begins again at the first image. In nuclear medical imaging (e.g. PET), the counting statistics during a heart cycle are insufficient, so that data from 50 to several hundred heartbeats are typically averaged. With MRI, it is possible to record a single image line in k-space within 20 to 50 milliseconds, but only fast MRI devices can record an entire image in this line. In cardiac galing, an image line is therefore recorded during each cardiac cycle

(Www.amershamhealth.com/medcyclopaedia/Volume%20l/cardiac%20gating.asp).

A clean artifact-free ECG signal is required for cardiac gating and also for monitoring the patient's cardiac activity and heartbeat. However, this is difficult to obtain during an MRI examination because the very strong magnetic field gradients and alternating fields within the MRI tube overlay the weaker ECG signal of typically 1 mV or less strong interference signals in the range from 200 to 400 mV. Since the frequency range of the interference signals typically overlaps strongly between 0.5 and 100 Hz with the ECG frequency range from 0.05 to 100 Hz, the acquisition of an ECG signal is difficult. It requires either complex analog filters or digital signal processing (www.reillycomm.com/it_archive/if_to1101_3.htm).

"Real-Time System for Respiratory-Cardiac Gating in Positron Tomography" by GJ Klein et al., 1998, Trans. Nucl. Be., Discloses a gating method both depending on an EGK Signal as well as a breathing signal for an ECAT EXACT HR PET scanner. An EGK monitor delivers an EKG signal that is divided into five cardiac phases. The first and fifth cardiac phases are combined into a cardiac state A, the second and fourth cardiac phase into a cardiac state B and the third cardiac phase results in cardiac state C. Pneumatic bellows were attached around the patient's chest to record breathing activity. The bellows are connected to a pressure sensor that generates an analogue tension corresponding to the expansion of the chest. This arrangement is so sensitive that it even indicates the patient's heartbeat when he is holding his breath. The analog voltage of the pressure sensor is divided into five areas corresponding to five breathing states. A total of 15 states result from the three cardiac states and the five respiratory states, which are arranged in a two-dimensional matrix. One column corresponds to a breathing condition, one row to a heart condition. The PET events that occur during a condition are collected in a histogram over several cardiac and respiratory cycles. A total of 15 histograms are created, which are put together voxel by voxel to form an image. Tomograph data which are recorded in the respiratory signal of the pressure sensor during positive or negative peaks, which occur for example with sighs, are discarded.

The robust detection of breaths is known from WO 02 / 083221A2. This is explained with reference to FIG. 3. FIG. 3 shows the upper flow values 31 of a patient recorded over 50 s. A high breath flow indicates inspiration (above) and a low flow (below) indicates expiration. During the transition from inspiration to expiration, a distinctive flank can be seen in the respiratory flow, which is used to detect individual breaths.

To detect the flanks, the first and second derivatives of the respiratory flow curve are estimated over time. The estimated first derivative multiplied by (-1) is shown in Fig. 3 below. Due to noise in the respiratory flow curve, the respiratory flow curve is not only derived, but also low-pass filtered. The derivation and low-pass filtering is carried out in one filter step by suitable selection of the coefficients of a digital filter.

The local minima 34 of the first derivative correspond to the maximum slope of the respiratory flow during the transition from inspiration to expiration. From the end of inspiration, the beginning of inspiration is sought by looking for the first local minimum 35 in the estimated derivative.

The middle curve in FIG. 3 shows the automatically detected transitions between inspiration and expiration, which are marked by vertical lines.

Oxygen glasses for oxygen treatment are also known from the prior art. With the oxygen goggles, air with an increased oxygen partial pressure (> 210 mbar) or pure oxygen is applied to the patient's nose. Oxygen treatment takes place at, for example acute or chronic hypoxemia as a result of respiratory or cardiovascular disorders (myocardial infarction, shock) or certain poisonings, e.g. through carbon monoxide, carbon dioxide, luminous gas or smoke.

It is the object of this invention to provide a gating method which improves the localization of parts of the human body. According to an aspect of this task related to imaging techniques, motion blur is reduced. According to a second part of the task, which relates to radiation therapy, the radiation is directed more precisely at the tumor, so that the radiation exposure to healthy tissue surrounding the tumor is reduced.

This task is solved by the teaching of the independent claims.

Preferred embodiments of the invention are the subject of the dependent claims.

The advantage of generating a gating signal based on a respiratory flow curve is that even in the case of particularly obese patients the detection of the respiratory condition, in particular the reversal points "completely inhaled" and "completely exhaled", can take place reliably. In the case of particularly obese patients, the method no longer works to determine the general condition and thus the tumor movements via the position of reflective markings on the patient's chest, because the movement of the markings is no longer directly related to the tumor movements.

An advantage of measuring the respiratory flow using a face or nose mask and a flow sensor is that this measurement method provides an exact value for the respiratory flow.

An advantage of the indirect measurement of the air flow through air glasses is that air glasses are more comfortable for the patient than a face or nose mask and the pressure sensor can be attached away from the patient and thus away from interference fields of the image recording device or the radiation device. In addition, unlike a face or nasal mask, air glasses are a cheap item that can be discarded after a single use and therefore do not need to be disinfected before reuse.

The determination of maxima and / or minima in the measured respiratory flow values and / or their estimated first derivation enables the division of a respiratory cycle into respiratory phases, even if the measured respiratory flow values are not linearly related to the actual respiratory flow.

The additional storage of a breathing phase value when recording PET events enables the subsequent evaluation of the raw PET data and the subsequent grouping of raw PET data in breathing phases in order to optimally suppress motion blur. In particular, the movement of the anterior, lateral and lower parts of the lungs have a good correlation to the lung volume and thus to the tidal volume obtained by integration from the measured respiratory flow values. The respiratory volume is therefore a suitable scatter or trigger parameter for the irradiation of tumors in these lung areas.

The definition of a respiratory phase value based on several prominent points in a respiratory cycle, such as extremes in the measured respiratory flow values and / or extremes in the estimated derivation of the measured respiratory flow values, leads to a better correlation between body movement and respiratory phase.

Short radiation pulses emitted to a constant phase during repetitive processes freeze a movement like a stroboscope. As a result, motion blur is taken from images on the one hand and tissue is repeatedly irradiated in the same position on the other hand. This applies to both breathing and heart cycles.

The speed of movement of tissue becomes zero in the fully inhaled and fully exhaled state. Since the patient is not moving at these times, image acquisition and radiation are associated with particularly little movement blur or movement errors. These points are located at zero crossings in the respiratory flow curve or at extrema in its first derivative.

The first derivative is insensitive to zero point drift and non-linearities in flow measurement.

The tidal volume has a high correlation to tissue movements in the anterior lateral lower lung area.

The generation of a control signal at a certain alem phase, when the respiratory volume is in a predetermined range at this time, ensures that atypical breaths, such as sighing or coughing, are not used for imaging or radiation.

Uniform breathing cycles are also selected if it is required that the correlation between the measured respiratory flow values before the determined breathing phase and the reference respiratory flow values lies above a threshold value.

Generating the control signal at the same phase in successive heartbeats also freezes the heart's movement.

The additional storage of a cardiac phase value for each PET event enables the subsequent evaluation of the PET events and the adaptation of cardiac phase limits in order to avoid motion blur as far as possible. Combining raw PET data into an image with at least two phases in a cardiac cycle reduces the motion blur in each image.

The stroboscopic switching on of a radiation source at a certain phase in the cardiac cycle also freezes the cardiac movement.

If the radiation source is switched on both at a specific phase in the cardiac cycle and at a specific phase in the breathing cycle, both cardiac and respiratory movements are frozen.

It is particularly advantageous to select the same breathing and / or cardiac phase for both diagnosis and therapy, because this avoids simulation inaccuracies in treatment planning.

A preferred embodiment of the invention is explained in more detail below with reference to the accompanying drawing. Show:

1 shows a tomography and / or radiation therapy device which is gated depending on the patient's respiratory flow, the respiratory flow being detected via air glasses,

FIG. 2 shows a tomography and / or radiation therapy device like FIG. 1, but the respiratory flow is recorded via a face mask, and

3 shows a respiratory flow curve at the top, its time derivative multiplied by (-1) at the bottom and detected maxima and minima in the middle.

This invention is essentially based on the fact that Galing signals are generated as a function of the patient's respiratory flow.

1 shows a tomography and / or radiation device which is gated depending on the respiratory flow of the patient 1. The respiratory flow is recorded via air glasses 3, which include sensor nipples 2, and a hose loop 3, which protrude into the patient's nose. Since the patient is usually lying on his back during diagnosis and therapy, the tubes of the tube loop 3, as shown in FIG. 1, are passed behind the ears to the patient's chin. Here is a cuff 4, through which the length of the loop of the air goggles can be adapted to the size of the patient's head. For example, conventional oxygen glasses, as described above, can be used as air glasses. However, since it is not used to supply oxygen, the term “air glasses” is preferred below. Both ends of the hose loop are connected to one another and a further hose section 16 by a Y-switch 5. There is also the possibility of leading the hose loop 3 backwards over the ears, the cuff 4 connects the tube loop behind the back of the patient's head and adjusts it to the size of the head, as shown in broken lines in FIG. 1. The hose section 16 connects the Y-switch 5 to a pressure sensor 6. This feeds its electrical output signal to a microprocessor 7. The microprocessor 7 digitizes the analog pressure signal and outputs control signals to an irradiation device and an image generation device.

An X-ray tube 9 is shown as an example of the radiation device, the cathode of which is heated via voltage supply 10 and supplied with high voltage via amplifier 8. The aperture 11 allows a more or less wide x-ray beam to pass through in the direction of the patient. For the explanation of the gating method, it is irrelevant whether the X-ray tube is used to treat a tumor or is part of a CT device, that is to say is used for diagnostic purposes. The only important thing is that the radiation can be switched on and off within milliseconds, i.e. briefly compared to breathing or cardiac cycles. This option is also available for other radiation sources, such as electron, proton or heavy ion accelerators, which are also used for tumor therapy. The irradiated radio waves can also be switched off quickly in the case of MRI, so that the gating method according to the invention is also suitable for MRI. The gating method according to the invention can, however, be used for all radiation sources which can be switched on and off within a short line compared to cardiac or Alem cycles. Switch-on and switch-off times of milliseconds are short enough for this in any case.

In therapy devices, the diaphragm 11 can be changeable in order to adapt the radiation cross section to the size and shape of the tumor. In the case of therapy devices, the radiation device can generally be moved relative to the patient in order to select a short path through healthy tissue to the tumor and to irradiate the tumor from different directions. Even with imaging methods that work with thin bundles of rays, such as CT, the radiation source can usually be moved with respect to the patient.

Diagnostic devices contain, in addition to or instead of the radiation device, an image generation device, which is exemplified by detector 12, computer 13 and display 14. In the case of PET and SPECT, the patient is injected with a contrast agent so that it emits radiation itself and a radiation source is not required. In most nuclear medicine imaging methods, the detector 12 consists of a plurality of semiconductor detectors which, on the one hand, provide a large amount of location information and, on the other hand, energy information about the detected particles, as a rule gamma quanta. In PET, two detectors opposite the patient are provided in order to detect the two gamma quanta emitted in opposite directions in a predetermined time window. In PET scanners too, both detectors consist of a large number of individual detectors in order to obtain location information. The gating signal generated by the microprocessor 7 can only consist of a trigger signal for a brief stroboscopic switching on of the radiation device, which occurs synchronously with the breathing and / or cardiac activity of the patient and is applied to the signal line 14. The patient's pulsed radiation can increase the radiation density during the pulses so that the mean radiation density corresponds to the radiation density in continuous operation. Under these circumstances, the counting statistics in the detector 12 are not deteriorated by the pulse operation. An increase in the radiation density is not possible in the case of PET, since the contrast medium in the patient decays continuously and not in a pulsed manner and the maximum dose of the contrast medium is limited. For this reason, the number of PET events is limited. In order not to unnecessarily worsen their counting statistics, the detected events in PET are not only faded out, but first processed into several partial images, which are then superimposed voxel by voxel in order to remove motion blur from the images. Therefore, preferably in the case of PET, the gating signal can also consist of a number for the partial image, to which current events are assigned and output on signal line 15.

A typical breathing signal is shown in Figure 3 above. The sign of the river was chosen positive for inspiration and negative for expiration. Since the absolute height of the flow is unimportant, and with cheap pressure gauges 6 and flow gauges 23 an offset has to be expected anyway, the respiratory flow curve was shifted towards positive flow values. The steep flanks at the transition between inspiration and expiration can be seen well in the respiratory flow curve. These can be used as distinctive marks for determining a breathing phase. The inverted estimated time derivative 33 of the respiratory flow values 31 in FIG. 3 above is shown in FIG. 3 below. Here Maxima 35 and Minima 34 clearly indicate the steep flanks in the respiratory flow curve.

A breathing phase can now be defined as the quotient of the time since the last minimum 34 in the derivation of the respiratory flow curve divided by the time interval between the last two minima in the respiratory flow curve. In the online evaluation, the time of the next maximum of the respiratory flow curve is not yet known. However, if the measurement data are first recorded and only evaluated later, as can happen, for example, in the case of PET, a breathing phase can also be a quotient between the time difference of an event and the last maximum divided by the time difference between the preceding and the maximum following the event.

When defining a breathing phase, other striking points, such as minima in the derivation of the breathing phase or minima and maxima in the respiratory flow values themselves, can also be used. Breath phase values between 0 and 0.5 can be assigned to expiration and between 0.5 and 1 to inspiration. For the expiration the Breathing phase is thus the time since the last minimum in the derivation of the respiratory flow curve divided by twice the expiration time of the previous breathing cycle and the inspiratory breathing phase 0.5 plus time since the last maximum of the derivation of the respiratory flow curve divided by the duration of the last inspiration phase.

Similarly, maxima or minima can be used in the respiratory flow curve additionally or instead. The extrema in the respiratory flow curve are preferably determined by adapting parabolas to an inspiratory or expiratory phase. The vertex of the adjusted parabola is regarded as the maximum or minimum.

Gating signals for triggering the radiation device can therefore always be generated at a specific breathing phase in successive breathing pulses.

Events between the minimum of the derivative and the minimum of the respiratory flow curve have respiratory phase values between 0 and 0.25. Time points between a maximum in the respiratory flow curve and the subsequent minimum in its derivation are assigned respiratory phase values between 0.25 and 0.5. Points in time between a maximum in the derivation and the subsequent maximum in the respiratory flow curve are assigned breath phase values between 0.5 and 0.75 and points in time between the maximum in the respiratory flow curve and the subsequent minimum in its derivation breath phase values between 0.75 and 1.

It is advantageous to trigger the radiation device when the patient has inhaled completely and exhaled completely because then the lung movement has a speed of 0. These points in time are marked by maxima and minima in the derivation of the respiratory flow curve.

In the case of PET, the breathing cycles can be in four phases, for example a first breathing phase from 7/8 to 1 and 0 to 1/8, a second breathing phase from 1/8 to 3/8, a third breathing phase from 3/8 to 5 / 8 and a fourth breathing phase from 5/8 to 7/8. A first telephoto is generated from the first breathing phase, a second partial image from the second and fourth breathing phases, and a third partial image from the third breathing phase. These sub-images can be suitably distorted and then superimposed voxel by voxel to reduce motion blur.

If the raw PET data is also recorded and a respiratory phase value is saved with each PET event, the boundaries between the respiratory phases can be shifted afterwards and in this way optimal limits for the respiratory phases can be selected in order to keep the motion blur as low as possible.

Instead of the breathing phase, a breathing volume can also be used as a trigger criterion for the radiation device or to determine breathing phases in the case of PET. The respiratory volume is the integral of the respiratory flow values from a given point in time in a respiratory cycle. A minimum in the derivation of the respiratory flow curve can be used as the specified point in time. The integration of new things begins after every minimum. A breath volume defined in this way drops to a minimum value during expiration and then rises again to approximately zero during inspiration. The radiation device can thus be triggered twice per breathing cycle if the breathing volume defined in this way has a predetermined value. In another embodiment, the radiation device can also be triggered only when the predetermined breathing volume is reached for the first time, that is to say during the expiration. If triggering is to take place during inspiration, it makes sense to set the starting point for the integration to the maximum in the derivation of the respiratory flow curve.

In the case of PET, all PET events are combined into a first partial image, the respiratory volume of which is greater than a first value. The events in which the respiratory volume lies between a first and a second value are combined into a second partial image and the remaining events into a third partial image.

In another embodiment, in which the radiation device is triggered or, in the case of PET, phases are subdivided as a function of the breathing phase, it is additionally required that the tidal volume lies in a predetermined range. If this is not the case, the acceleration device is not triggered or the PET events are not taken into account in order to rule out atypical breaths.

For the same purpose, a correlation r between respiratory flow values before a trigger line point and reference respiratory flow values can be calculated according to the following formula:

In equation (1), Vj stands for the i-th respiratory flow value, V for the arithmetic average of

N respiratory flow _values , V _Rj for the i-th reference respiratory flow value, VR for the middle one

Reference respiratory flow value. The correlation is calculated for N respiratory flow values. The N respiratory flow values preferably belong to one breath. So N can go from breath to breath change because the breath flow is usually sampled at a constant rate. Will a change

permitted by N, the numbers of the reference _{breath flow values} V _Rj must also be adapted to the measured breath, for example by interpolation and temporal extension and compression of the reference breath.

If the correlation r is less than a required threshold value, the irradiation device is not triggered or a PET event is rejected or at least does not flow into image generation.

In another embodiment, the trigger time can also be determined via the tidal volume and the correlation r can be used to suppress atypical breathing pulses, such as coughing or sighing.

In a further embodiment, double gating, that is to say both as a function of the breathing phase and of a heart phase, can be used. The cardiac phase can be provided by a conventional EKG device or, as explained below, can be obtained from the respiratory flow signal. In the preferred embodiment, the cardiac phase has a value between 0 and 1, which increases linearly during a cardiac cycle. With such double gating, the radiation device is triggered when both the desired heart phase and the desired breathing phase assume the respectively desired value in a predetermined time window. In the case of PET, combined respiratory and cardiac cycle states are formed that can be arranged in a two-dimensional field, as described above.

A cardiac phase signal can also be obtained from the breathing signal. Breathing cycles typically last from 3 to 5 seconds, cardiac cycles of approx. 1 second at rest. The frequency difference of a factor of 3 to 4 is retained even with moderate exertion. The respiratory phase signal can thus be obtained from the cardiac phase signal from the measured respiratory flow values by high-pass filtering. A Fourier analysis of the respiratory flow signal can be carried out to determine the cutoff frequency of the high-pass filtering, a large peak for the respiratory flow signal being found at approx. 0.3 Hz and a smaller peak for the cardiac phase signal around 1 Hz at a frequency three to four times higher becomes. The cut-off frequency is set, for example, to the geometric mean between the two peaks.

Regarding the cardiac phase signal, similar evaluations and gating signals can be obtained as with the respiratory phase signal. After the cardiac phase signal has been obtained, double gating after the breathing phase and cardiac phase is also possible. FIG. 2 shows a device similar to FIG. 1. The only difference from FIG. 1 is the measurement of the respiratory flow signal. A nose or face mask 21 is placed on the patient, to which a flow sensor 23 is connected via a short tube 22. The electrical signal supplied by the flow sensor is fed to the microprocessor 7, as in FIGS. 1, 5. The microprocessor can then carry out similar evaluations which have been explained in connection with the arrangement shown in FIG. 1.

In another embodiment, the tube piece 22 between the flow sensor and mask can be omitted, so that the flow sensor 23 can also be integrated into the mask 21.

The invention was previously explained in more detail with the aid of preferred embodiments. However, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. Therefore, the scope of protection is determined by the following claims and their equivalents.

LIST OF REFERENCE NUMBERS

15 1 patient 14 display

2 sensor nipples 30 14.15 signal lines

3 hose loop 21 face or nose mask

4 cuff 22 hose

5 Y-switch 23 flow sensor

20 16 hose section 31 measured respiratory flow values

6 Pressure sensor 35 32 marking for extremes

7 microprocessor 33 estimated derivative

8 high voltage amplifiers 34 minimum

9 X-ray tube 35 maximum

25 10 Power supply 36 maximum

11 aperture 40 37 minimum

12 detector

13 computers

Claims

claims

1. Gating process with:

Repeatedly measuring a patient's respiratory flow to get measured respiratory flow values

To get (31); and

Generating a first control signal (14, 15) as a function of the measured respiratory flow values for controlling the radiation (8, 9, 10, 11) of the patient and / or an imaging method (12, 13).

2. The method according to claim 1, characterized in that the measurement of the respiratory flow takes place via a face or nose mask (21) which the patient wears and which is connected to a flow sensor (23).

3. The method according to claim 1, characterized in that the measurement of the respiratory flow takes place via air goggles (2, 3, 5, 16) which is connected to a pressure sensor (6) which outputs a pressure signal associated with the patient's respiratory flow is in a monotonous context.

4. The method as claimed in one of the above claims, characterized by estimating the first time derivative (33) of the measured respiratory flow values over time, positive respiratory flow values representing inspiration and negative respiratory flow values representing expiration.

5. The method according to claim 4, characterized by determining minima (34) in the estimated first time derivative (33).

6. The method of claim 4, wherein generating the first control signal comprises:

Determining maxima and minima (34, 35, 36, 37) in the measured respiratory flow values and their first derivation;

Subdivide the breathing cycles in the measured respiratory flow values (31) into four phases, the first phase being the maximum (36) of the respiratory flow curve, the second phase being the minimum (34) of the first derivative, the third phase being the minimum (37) the

Respiratory flow curve and the fourth phase extends around the maximum (35) of the first derivative; Processing of raw PET data, which were recorded during the repeated measurement of the respiratory flow values, into three partial images, wherein the raw PET data, which were recorded during a first or third phase, are processed into a first telephoto image, the raw PET data, which were recorded during a second Phase were recorded to a second field and processed during the fourth phase to be processed into a third field.

7. The method according to any one of claims 1 to 4, wherein generating the first

Control signal (14, 15) comprises determining a respiratory phase value and the method further comprises:

Recording of raw PET data, whereby a time stamp, the crystal addresses and a respiratory phase value are saved for each PET event.

8. The method according to any one of claims 1 to 4, characterized by integration of the measured respiratory flow values (31) from an extremum (36, 37) in the measured respiratory flow values or an extremum (34, 35) in their estimated derivation in order to calculate a respiratory volume ; and

Recording of raw PET data, one time stamp per PET event

Crystal addresses and tidal volume at the time of the PET event are saved.

9. The method according to claim 6, wherein the breathing phase value corresponds to a fraction of an entire breathing cycle and for calculating the Alemphasewert minima and / or

Maxima of the measured respiratory flow values and / or the estimated derivation can be used.

10. The method according to any one of the above claims, characterized by switching on a radiation source (9) by the control signal in order to emit a radiation pulse to the patient, the radiation pulse being short compared to the duration of a breathing cycle.

11. The method according to claim 10, characterized by generating the first control signal close to the extrema (34, 35) of the estimated first time derivative (33) of the measured respiratory flow values (31).

12. The method according to claim 8 or 9, characterized by generating the first

Control signal to a predetermined breathing phase value in the successive breathing cycles.

13. The method according to claim 10 or 11, characterized by:

Integration of the measured respiratory flow values (31) from an extremum (36, 37) in the measured respiratory flow values or an extremum (34, 35) in their estimated derivation in order to calculate a respiratory volume; and

Generating the first control signal (14, 15) when the respiratory volume reaches a threshold value.

14. The method according to claim 12, characterized by:

Generating the first control signal (14, 15) only for the specific breathing phase if the alem volume is in a predetermined range at this point in time.

15. The method according to claim 12, characterized by:

Calculating a correlation between the measured respiratory flow values (31) before the determined respiratory phase value and reference respiratory flow values; and

Generating the first control signal (1, 15) only for the determined respiratory phase value if the correlation lies above a threshold value.

16. The method according to any one of claims 1 to 4, characterized by:

Determining a heartbeat signal from the measured respiratory flow values (31); and

Generating the first control signal (14, 15) at the same heart phase value in the successive heartbeats.

17. The method according to any one of claims 1 to 15, characterized by: Determining a heartbeat signal from the measured respiratory flow values; and

Generating a second control signal (14, 15) depending on the heartbeat signal.

5 18. The method according to claim 17, characterized by:

Determining a heart phase value from the heartbeat signal;

Recording of raw PET data, a time stamp, the 10 crystal addresses and the heart phase value at the time of the PET event being recorded for each PET event.

19. The method according to claim 17, characterized by:

15 dividing the cardiac cycle in the heartbeat signal into at least two phases;

Processing of raw PET data, which was recorded during the repeated measurement of the respiratory flow values, into a partial image per phase.

20. The method according to claim 17, characterized by:

Generating a second control signal (14, 15) depending on the heartbeat signal.

21. The method according to claim 20, characterized by:

25

Switching on a radiation source (9) by the second control signal (14, 15) in order to deliver a radiation pulse to the patient, the radiation pulse being short compared to the duration of a cardiac cycle.

22. The method of claim 20 insofar as it relates to claims 12 to 14, wherein the radiation source (9) is only switched on when the first and second control signals are generated in a time window of a certain duration.

23. The method according to any one of the above claims, with:

35

Generating an image of the interior of an animal or human body for diagnostic purposes at a specific breath and / or cardiac phase value; and Irradiation of the human or animal body for therapeutic purposes at the determined respiratory and / or cardiac phase value.

24. Gating device with:

5 a respiratory flow sensor (2, 3, 4, 5, 6, 16, 21, 22, 23) for repeated measurement of the respiratory flow;

a processor (7) for performing one of the methods according to one of the above 10 claims;

a control output for outputting a control signal (14, 15) to an irradiation and / or imaging device.

15 25. Radiotherapy facility with:

a respiratory flow sensor (2, 3, 4, 5, 6, 16; 21, 22, 23) for the repeated measurement of the patient's flow (1);

20 an evaluation device (7) which evaluates the measured respiratory flow values and thus one

Breath and / or heart phase determined;

an imaging device (12, 13, 14) which generates an image of the interior of an animal or human body at a specific respiratory and / or cardiac phase value; 25 and

an irradiation device (9, 10, 11) which irradiates the animal or human body at the same respiratory and / or cardiac phase value.