SYNCHRONIZING AN MR IMAGING PROCESS WITH ATTAINMENT OF THE BREATH-HOLD STATE

Abstract

A method for synchronizing an MR imaging process with a breathing rest state of a patient during an examination using held breath is provided. In the method, an instruction is output to the patient to hold his breath. In addition, the respiratory behavior of the patient is identified in real time. An MR imaging process is started according to the identified respiratory behavior. A breathing synchronization device and a magnetic resonance imaging system are also provided.

Claims

1. A method for synchronizing an MR imaging process with a breathing rest state of a patient during an examination using held breath, the method comprising: outputting an instruction to the patient to hold breath; identifying a respiratory behavior of the patient in real time; and starting the MR imaging process according to the identified respiratory behavior.

2. The method of claim 1, wherein identifying the respiratory behavior comprises: recording a respiratory curve at least after the output of the instruction to the patient; identifying a start time of a breathing rest state of the patient based on the recorded respiratory curve.

3. The method of claim 2, wherein the MR imaging process is started based on the identified start time (T.sub.AAH), preferably immediately after the identified time (T.sub.AAH).

4. The method of claim 3, wherein the MR imaging process is started immediately after the identified start time.

5. The method of claim 2, wherein when a start time (T.sub.AAH) for a breath-hold state of the patient has not been identified within a preset time interval: the MR imaging process is started automatically; or the MR imaging process is interrupted, and the operating personnel are automatically given notification of the interruption; or the method is repeated, and a reminder is automatically communicated to the patient to follow carefully the instruction to the patient.

6. The method of claim 1, wherein identifying the respiratory behavior of the patient in real time comprises monitoring the respiratory cycle of the patient using an external apparatus.

7. The method of claim 6, wherein the external apparatus comprises a breathing belt or a sensor, preferably based on an electromagnetic reflection or a radar technology.

8. The method of claim 7, wherein the sensor is based on an electromagnetic reflection or a radar technology.

9. The method of claim 2, wherein identifying the respiratory behavior of the patient in real time comprises monitoring the respiratory cycle of the patient using an internal mechanism.

10. The method of claim 9, wherein monitoring the respiratory cycle of the patient using the internal mechanism comprises outputting an MR navigator sequence, the MR navigator sequence comprising a series of gradient echo sub-sequences without phase encoding.

11. The method of claim 9, wherein recording the respiratory curve comprises acquiring MR signals at a k-space center at a plurality of time instants and extracting a phase component of the acquired MR signals.

12. The method of claim 11, wherein recording the respiratory curve further comprises capturing MR signals using a body coil, applying a Fourier transform and calculating a signal-weighted sum of signal phases for each readout time interval, or a combination thereof.

13. The method of claim 12, wherein identifying the start time of a breathing rest state of the patient comprises: comparing time-dependent standard deviation values of the phase values of the acquired MR signals, which have been obtained using a sliding time window; comparing time-derivative values of the phase values of the acquired MR signals with derivative values from earlier in time; comparing time-derivative values of the phase values of the acquired MR signals with a threshold value; comparing absolute values of the phase values of the acquired MR signals with a reference value; or any combination thereof.

14. A breathing synchronization device comprising: an instruction output unit configured to output an instruction to a patient to hold breath; a respiratory-movement identification unit configured to identify a respiratory behavior of the patient in real time; and a start synchronization unit configured to start an MR imaging process according to the identified respiratory behavior.

15. A magnetic resonance imaging system comprising: an RF transmit system; a gradient system; and a controller configured to: control the RF transmit system and the gradient system to perform a desired measurement based on a specified pulse sequence; and a breathing synchronization device comprising: an instruction output unit configured to output an instruction to a patient to hold breath; a respiratory-movement identification unit configured to identify a respiratory behavior of the patient in real time; and a start synchronization unit configured to start an MR imaging process according to the identified respiratory behavior.

16. A computer program product comprising a non-transitory computer-readable storage medium that stores instructions executable by a controller, a magnetic resonance imaging system, or the controller and the magnetic resonance imaging system to synchronize an MR imaging process with a breathing rest state of a patient during an examination using held breath, the instructions comprising: outputting an instruction to the patient to hold breath; identifying a respiratory behavior of the patient in real time; and starting the MR imaging process according to the identified respiratory behavior.

17. In a non-transitory computer-readable storage medium that stores instructions executable by a processor of a controller of a magnetic resonance imaging system to synchronize an MR imaging process with a breathing rest state of a patient during an examination using held breath, the instructions comprising: outputting an instruction to the patient to hold breath; identifying a respiratory behavior of the patient in real time; and starting the MR imaging process according to the identified respiratory behavior.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 shows an exemplary graph illustrating a respiratory curve as a function of a sampling time;

[0030] FIG. 2 is a flow diagram illustrating one embodiment of a method for synchronizing an MR imaging process with a breathing rest state of a patient during an examination using held breath;

[0031] FIG. 3 contains two graphs that show exemplary respiratory curves recorded and analyzed as part of the method;

[0032] FIG. 4 is a block diagram illustrating one embodiment of a breathing synchronization device; and

[0033] FIG. 5 shows one embodiment of a magnetic resonance imaging system.

DETAILED DESCRIPTION

[0034] FIG. 1 shows an example of a respiratory curve AK acquired using a magnetic resonance (MR) navigator sequence containing a gradient echo without phase encoding and having a repetition time TR=5 ms and a flip angle of 4°, with 3200 repetitions performed in 16 seconds. In FIG. 1, the phase values PHW of acquired MR resonance signals from the MR navigator sequence are plotted as a function of the current repetition ZRP. The curve was acquired by simple extraction of the phase component of the MR signal, obtained from a body coil, from the k-space center for each individual point in time. A smoother curve may be obtained, for example, by using surface coils and/or using a Fourier transform and by the signal-weighted summation of the image phases for each echo. The respiratory graph presented in FIG. 1 shows even, flat respiration of a patient without held breath.

[0035] FIG. 2 shows a flow diagram 200 illustrating one embodiment of a method for synchronizing an MR imaging process with a breathing rest state of a patient during an examination using held breath. In act 2.I, first an acoustic instruction AAH is issued automatically to the patient to hold his respiratory movement. In act 2.II (see act 2.IIb), a respiratory curve AK is acquired immediately after the output of the breath-hold instruction AAH. Optionally, in act 2.IIa, the respiratory curve may be recorded for a learning phase LPH. The recording of the respiratory curve AK may be based, for example, on the acquisition of MR signals using an MR navigator sequence. The phase values PHW reconstructed from the MR signals are in this case used as the amplitude values of the respiratory curve AK, which may be associated with the particular phase of the respiratory movement. For example, phase values PHW at which the breathing rest state starts are identified. Alternatively, derivatives of the respiratory curve AK or other values that are correlated with the start of the breath-hold state may also be calculated. Reference values RW are thereby formed, which are used for comparison with the recorded respiratory curve AK during the subsequent real-time curve recording and analysis for identifying a start time of a breath-hold state. In act 2.IIb, the respiratory curve AK is recorded after the end of the learning phase LPH, again on a breath-hold instruction AAH, as given in act 2.I. Alternatively or additionally, in act 2.II, the respiratory curve AK may also be acquired using external units such as a breathing belt, for example, or using sensors (e.g., based on an electromagnetic reflection or a radar technology).

[0036] In act 2.III, the recorded respiratory curve AK is analyzed by comparing the recorded phase values PHW of the respiratory curve AK with the reference values RW recorded during the learning phase. Based on the analysis of the recorded respiratory curve AK, the current stage of the respiratory process of the patient may be identified. For example, it is identified in act 2.III whether the patient is starting to hold his breath. This process may be associated with a plateauing of the recorded respiratory curve AK, for example. For the case in which the start time T.sub.AAH of the breath-hold state has not yet been reached, which is labeled “n” in FIG. 2, then in act 2.IV, a check is performed as to whether a preset maximum wait time T.sub.W, for example 1.5 s, has been reached yet. For the case in which the preset maximum wait time T.sub.W has not been reached yet, which is labeled “n” in FIG. 2, then a return is made to act 2.II or 2.IIb, and recording of the respiratory curve AK continues. If, however, in act 2.IV, the preset wait time T.sub.W has already been reached, which is labeled “y” in FIG. 2, then a move is made to act 2.V, in which the actual MR image acquisition of a field of view FOV of the patient is started. As an alternative to automatically starting the MR image acquisition after the wait time T.sub.W, it is also possible to return to act 2.I, which is indicated in FIG. 2 by a dashed arrow, and a new breath-hold instruction AAH may be output. Then a respiratory curve AK is recorded again in act 2.II or 2.IIb etc. If it was identified in act 2.III that the start time T.sub.AAH of the breath-hold state has been reached, which is labeled “y” in FIG. 2, then a move is likewise made to act 2.V, and the actual MR image acquisition of a field of view FOV of the patient is started.

[0037] FIG. 3 shows two respiratory curves AK of a patient. For the respiratory curve AK in the left-hand graph, the patient was given a breath-hold instruction AAH immediately before recording of the respiratory curve AK was started. The reaction time T.sub.AAH of the patient may be identified from the plateauing of the curve at about 600 repetition cycles, which for a repetition time TR=5 ms gives a reaction time of about 3 s. With regard to the respiratory curve AK in the right-hand graph of FIG. 3, the patient was given a breath-hold instruction AAH approximately after 1000 repetition cycles. As is evident from the right-hand graph, the respiratory curve AK plateaus at around 1500 repetition cycles, and therefore a reaction time T.sub.AAH of about 2.5 s may be identified from the graph given a repetition time TR=5 ms. The start time of the actual MR image acquisition may thus be set very precisely using the recorded respiratory curve AK. The time at which the patient holds his breath may be identified in various ways. For example, a standard deviation of phase values PHW that have been recorded in a sliding time window may be calculated. If a value of the standard deviation drops below a preset threshold value, for example, because the respiratory curve AK plateaus as a result of the start of the breath-hold state of the patient, then this is used as the trigger signal for starting the MR imaging process. Alternatively, a time derivative of the recorded phase values PHW may be calculated. If the value for the derivative of the recorded phase values PHW drops below a preset threshold value, then it may be assumed therefrom that the patient is holding his breath and the MR imaging process may be started. Alternatively, instead of using a threshold value, the comparisons mentioned may also be performed with values that were recorded at earlier points in time during the real-time recording of the respiratory curve. If in a learning phase LPH, phase values PHW were associated with specific breathing states, then the phase values PHW may be compared directly with a reference value RW or reference-value interval obtained in the learning phase, and the start time T.sub.AAH of the MR imaging process may be set based on the comparison result.

[0038] FIG. 4 shows schematically an exemplary breathing synchronization device 40. The breathing synchronization device 40 may be part of a controller (e.g., a processor) of a magnetic resonance imaging system, for example (see FIG. 5). The breathing synchronization device 40 includes a raw-data acquisition unit 41, which receives raw data (e.g., navigator k-space data NKRD) recorded during a navigator image acquisition. The raw data NKRD is transmitted to a phase-value calculation unit 42, which extracts phase values PHW from the raw data NKRD. The phase values PHW are then passed to a respiratory-movement identification unit 43. The respiratory-movement identification unit 43 includes a respiratory-curve recording unit 43a, which is configured to use the received phase values PHW as the basis for recording in real time a respiratory curve AK of a patient under examination. The respiratory-movement identification unit 43 also includes an analysis unit 43b that identifies, based on the recorded respiratory curve AK, the time T.sub.AAH at which the patient starts actually to hold his breath. Based on this time information T.sub.AAH, a trigger signal SB, for example, may be transmitted via a start synchronization unit 44 to a sequence control unit (not shown), which starts the output of an MR pulse sequence for an image recording of a region of interest of a patient in response to the trigger command. The breathing synchronization device 40 also includes an instruction output unit 45 for the automatic output of an instruction AAH to the patient O to hold his breath. The instruction output unit 45 is connected to the respiratory-movement identification unit 43 in order to trigger the respiratory-movement identification unit 43 to start operating (e.g., by transmitting a trigger signal AS2) after a breath-hold instruction AAH has been issued. The breathing synchronization device 40 also includes a navigator sequence generator 46, which is used to generate a navigator pulse sequence NPS in order to acquire navigator k-space data NKRD from the respiratory movement of the patient. The navigator sequence generator 46 transmits to the instruction output unit 45 a trigger signal AS1 in order to cause the instruction output unit 45 to output automatically a breath-hold instruction AAH (e.g., after the output of the navigator pulse sequence NPS). Other points in time for the output of the breath-hold instruction AAH are also possible. For example, the breath-hold instruction may also be output earlier in time than the output of the navigator pulse sequence NPS. In the event that a preset time has elapsed without the patient holding his breath, the opposite case, in which a trigger signal AS3 is transmitted from the respiratory-movement identification unit 43 to the instruction output unit 45, is also possible in order to output a breath-hold instruction AAH again to the patient.

[0039] FIG. 5 shows one embodiment of an MR machine 1. The MR machine 1 includes the actual magnetic resonance scanner 2 containing an examination space 3 or patient tunnel, into which an object under examination O may be moved on a couch 8 (e.g., a patient or subject under examination in whose body the object under examination such as a specific organ is located).

[0040] The magnetic resonance scanner 2 is equipped in the usual manner with a main magnetic field system 4, a gradient system 6, and an RF transmit antenna system 5 and an RF receive antenna system 7. In the exemplary embodiment shown, the RF transmit antenna system 5 is a whole-body coil that is fixed in the magnetic resonance scanner 2, whereas the RF receive antenna system 7 consists of local coils (represented in FIG. 5 by a single local coil) arranged on the patient or subject under examination. The whole-body coil may also be used as the RF receive antenna system, and the local coils may be used as the RF transmit antenna system, provided these coils may each be switched into different operating modes.

[0041] The MR machine 1 also includes a central controller 13 (e.g., a processor) that is used to control the MR machine 1. This central controller 13 includes a sequence control unit 14 (e.g., a sequence controller) for controlling the pulse sequence. This is used to control the sequence of radio frequency (RF) pulses and gradient pulses according to a selected imaging sequence. Such an imaging sequence may be specified, for example, in a measurement or control protocol. Different control protocols for different measurements are typically stored in a memory 19 and may be selected by an operator (and possibly modified if required), and then used to perform the measurement.

[0042] For the output of the individual RF pulses, the central controller 13 includes an RF transmit unit 15, which generates and amplifies the RF pulses and feeds the RF pulses into the RF transmit antenna system 5 via a suitable interface (not shown in detail). The controller 13 includes a gradient system interface 16 for controlling the gradient coils of the gradient system 6. The sequence controller 14 communicates in a suitable manner (e.g., by sending out sequence control data SD) with the RF transmit unit 15 and the gradient system interface 16 for the emission of the pulse sequences. The controller 13 also includes an RF receive unit 17 (likewise communicating with the sequence controller 14 in a suitable manner) for the purpose of coordinated acquisition of magnetic resonance signals received by the RF transmit antenna system 7 (e.g., of raw data). A reconstruction unit 18 receives the acquired image data and reconstructs the MR image data therefrom. This image data may then be stored, for example, in a memory 19 and/or, for the case of navigator image data, processed in a breathing synchronization device 40 according to one or more of the present embodiments in order to start an MR imaging process in the phase of a breathing rest state of the patient O. The breathing synchronization device 40 gives a control command SB, for example, to the sequence controller 14 in order to start sequence control data SD relating to a navigator pulse sequence NPS or an MR image acquisition pulse sequence BPS. In addition, the breathing synchronization device 40 also has a connection to an audio communications unit 11 on the magnetic resonance scanner 2, in order to communicate breath-hold instructions AAH to the patient O.

[0043] The central controller 13 may be operated by a terminal having an input unit 10 and a display unit 9, via which an operator may hence also operate the entire MR machine 1. MR images may also be displayed on the display unit 9. The input unit 10, if applicable in combination with the display unit 9, may be used to plan and start measurements, and, for example, to select and, if applicable, modify suitable control protocols containing suitable measurement sequences, as described above.

[0044] The MR machine 1 according to one or more of the present embodiments and, in particular, the controller 13 may also include a plurality of further components that are not shown here in detail but are typically present in such machines (e.g., components such as a network interface to connect the entire machine to a network and to be able to transfer raw data, image data, parameter maps, other data such as patient-related data or control protocols, or any combination thereof).

[0045] The principles of how suitable raw data may be acquired by applying RF pulses and generating gradient fields, and how MR images may be reconstructed from the raw data, are known to a person skilled in the art and are not explained further here. Likewise, a large variety of measurement sequences such as, for example, EPI measurement sequences or measurement sequences for generating diffusion-weighted images are known in principle to a person skilled in the art.

[0046] The method and devices described above are merely exemplary embodiments, and the invention may be modified by a person skilled in the art without departing from the scope of the invention insofar as this is defined by the claims. For instance, the method for synchronizing an MR imaging process with a breathing rest state of a patient during an examination using held breath and the breathing synchronization device 40 have primarily been described with reference to acquisition of a respiratory curve AK using a navigator pulse sequence. The invention is not limited to this use, however; a respiratory curve may also be acquired using external detection such as, for example, breathing belts or sensors. The use of the indefinite article “a” or “an” does not rule out the possibility of there also being more than one of the features concerned. Likewise, the term “unit” does not exclude the possibility that the unit consists of a plurality of components, which may also be spatially distributed if applicable.

[0047] The elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent. Such new combinations are to be understood as forming a part of the present specification.

[0048] While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.