WO2014170854A1

WO2014170854A1 - System and method for taking into account actual prepulse delay times in mri pulse sequences with shared prepulses

Info

Publication number: WO2014170854A1
Application number: PCT/IB2014/060786
Authority: WO
Inventors: Tobias Ratko Voigt; Markus Olof Samuel HENNINGSSON
Original assignee: Koninklijke Philips N.V.; Philips Deutschland Gmbh
Priority date: 2013-04-18
Filing date: 2014-04-17
Publication date: 2014-10-23

Abstract

A magnetic resonance imaging system utilizing measured prepulse delay times. A data acquisition module (68) delivers a shared magnetization preparation pulse (102, e.g. an inversion pulse) followed by imaging sequences for generating image profiles (104, 106, 108) of a patient (12). Next, a first plurality of image datasets of the patient (12) is acquired in an ECG-triggered manner. Delay times are measured between the shared pulse (102) delivered and acquisition of each individual image dataset (104a, 104b, 104c) of the image profile (104). The measured delay times are compared to calculate expected delay times for each image dataset. The image datasets are accepted if the delay time is inside a range of the expected delay time, thereby avoiding that arrhythmia of the heartbeat of the patient results in image artifacts. The image datasets are accepted or rejected if a respiratory phase is inside or outside a respiratory window (133). The image profile is accepted if all or the majority of the individual image datasets are accepted.

Description

SYSTEM AND METHOD FOR TAKING INTO ACCOUNT ACTUAL PREPULSE DELAY TIMES IN MRI PULSE SEQUENCES WITH SHARED PREPULSES

The present application relates to the medical arts and finds particular application with magnetic resonance imaging and will be described with particular reference thereto. However, it is to be appreciated that it will also find application in other medical interventions and treatment procedures. When a patient is diagnosed with diffuse and regional cardiomyopathy, it is useful to create an image of the heart. One imaging option is Modified Look Locker Inversion Recovery, i.e. MOLLI, imaging.

Inversion recovery, in general, is a method for creating a signal dependent upon Tl. The longitudinal magnetization is inverted in the opposite direction by a 180 degree pulse. Transverse magnetization remains equal to zero. During the subsequent recovery, the negative longitudinal magnetization decays to zero and then begins to rise. Because transverse magnetization is not possible, no signal is measured. To generate MR signals, the longitudinal magnetization must be converted to transverse magnetization through application of a RF pulse.

Tl mapping has been applied in patients with diffuse and regional cardiomyopathy. A widely used Tl mapping method is two dimensional Modified Look Locker Inversion Recovery (MOLLI) imaging. MOLLI is an ECG-triggered single shot implementation of an inversion recovery (TR) experiment that can address some of the major issues in cardiac MR parameter mapping; including arrhythmias, cardiac and respiratory motion. Cardiac motion can be suppressed through electro cardiogram (ECG) triggering. The single shot implementation can mitigate adverse effects of heart rate variations. Respiratory motion can be suppressed by applying MOLLI in a breath hold.

MOLLI Tl mapping is an ECG-triggered 2D single shot implementation of a Look Locker experiment that addresses major issues in cardiac MR parameter mapping; including arrhythmias, cardiac and respiratory motion.

However, certain disadvantages to MOLLI Tl mapping exist. The single shot implementation negates the impact of heart rate variations, but achieves a limited spatial resolution and signal-to-noise ratio due to a limited acquisition interval in which the heart remains static, e.g. 50-100 milliseconds. Respiratory motion is suppressed by applying MOLLI during a breath hold, which allows a limited number of different inversion delays. The breath hold acquisition restricts MOLLI to one imaging slice (2D) per breath hold. The breath holds are challenging for many patients, particularly elderly patients or patients with low lung capacity. Data artifacts are frequently created by motion.

Three-dimensional (3D) ECG-triggered IR sequences have been attempted without using shared prepulses. A shared prepulse is a prepulse that is applied only once for a number of following readouts in more than one RR-interval.

However, further disadvantages remain. The maximum achievable inversion time is limited to less than the duration of one RR-interval, where inversion times are important for accurate Tl mapping. Further, non ECG-synchronized Tl mapping techniques cannot be used for cardiac applications because of the motion of the heart.

The present application provides an improved prepulse technique to overcome the above described deficiencies.

In accordance with one preferred embodiment of the present application, a medical imaging system utilizing measured prepulse delay times, comprising: a data acquisition module (68) to deliver a shared pulse (102) followed by imaging sequences for generating image datasets (104) of a patient (12); a pulse module (74) controlled by a processor (78) configured to: acquire a first plurality of image datasets of the patient (12) using the data acquisition module (68); measure a delay time between the shared pulse (102) delivered by the data acquisition module (68) and acquisition of each individual image dataset of the plurality of image datasets (104); and compare the measured delay time to an expected delay time.

In accordance with one preferred method of the present application, a method for taking into account actual prepulse delay times during image acquisition, the method comprising: delivering a shared pulse (102); acquiring a first plurality of image datasets of the patient (12) using a data acquisition module (68); measuring a delay time between the shared pulse (102) delivered by the data acquisition module (68) and acquisition of each individual image dataset of the plurality of image datasets (104); and comparing the measured delay time to an expected delay time. In accordance with one preferred embodiment of the present application, a shared inversion prepulse analyzer including one or more processors (78) configured to: compute an expected delay time using the average RR-interval of a patient (12) for each image dataset of a plurality of image datasets (104) for an entire inversion interval; instruct a data acquisition module (68) to deliver an inversion pulse (102) to the patient (12); acquire the plurality of image datasets (104) of the patient (12) using the data acquisition module (68); determine a delay time between the inversion pulse (102) delivered by the data acquisition module (68) and acquisition of each individual image dataset of the plurality of image datasets (104); determine a navigator location at the determined delay time; compare the navigator location to a navigator window; and compare the delay time to the expected delay time.

One advantage resides in a Tl mapping technique that is not restricted to single shot implementations.

Another advantage resides in a Tl mapping without the use of breath holds.

Another advantage resides in a technique that covers a whole heart ventricle in clinically acceptable times.

Another advantage resides in Tl mapping without artifacts from varying heart rate of the patient during the MR scan.

A further advantage allows for inversion times longer than one RR-interval for increased Tl mapping accuracy.

Still further advantages of the present invention will be appreciated to those of ordinary skill in the art upon reading and understanding the following detailed description.

The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.

FIGURE 1 illustrates a magnetic resonance (MR) system carrying out an enhanced method for taking into account actual prepulse delay times in sequences with shared prepulses.

FIGURE 2 depicts a three-dimensional MOLLI segmented acquisition using actual shared prepulse delay times. FIGURE 3 depicts a comparison of actual delay times and expected delay times in 3D MOLLI inversion time gating.

FIGURE 4 depicts a comparison of 3D MOLLI acquisition without taking into account actual prepulse delay times vs. 3D MOLLI acquisition taking into account actual prepulse delay times with shared prepulses.

FIGURE 5 depicts a method for a method for taking into account actual delay times.

FIGURE 6 depicts an expanded method to compare measured and expected delay times.

The present application provides functionality to account for actual delay times using shared prepulses. The present application provides functionality to trigger an inversion pulse directed towards a patient. The present application provides functionality to provide shared prepulses to the patient. The present application provides functionality to measure delay times between prepulses and data acquisition. The present application provides functionality to compare the measured delay times and expected delay times. The present application provides functionality to restart or correct the prepulse sequence when the measured delay time is outside a determined range of expected delay time.

Prepulse sequences depend upon the delay time for accurate Tl mapping. FIGURE 1 depicts an embodiment of a prepulse system for utilizing actual delay times in shared prepulse sequences. With reference to FIGURE 1, a magnetic resonance (MR) imaging system 10 utilizes MR to image a region of interest (ROI) of a patient 12. The system 10 includes a scanner 14 defining an imaging volume 16 (indicated in phantom) sized to accommodate the ROI. A patient support can be employed to support the patient 12 in the scanner 14 and facilitates positioning the ROI in the imaging volume 16.

The scanner 14 includes a main magnet 18 that creates a strong, static Bo magnetic field extending through the imaging volume 16. The main magnet 18 typically employs superconducting coils to create the static Bo magnetic field. However, the main magnet 18 can also employ permanent or resistive magnets. Insofar as superconducting coils are employed, the main magnet 18 includes a cooling system, such as a liquid helium cooled cryostat, for the superconducting coils. The strength of the static Bo magnetic field is commonly one of 0.23 Tesla, 0.5 Tesla, 1.5 Tesla, 3 Tesla, 7 Tesla, and so on in the imaging volume 16, but other strengths are contemplated. A gradient controller 20 of the scanner 14 is controlled to superimpose magnetic field gradients, such as x, y and z gradients, on the static Bo magnetic field in the imaging volume 16 using a plurality of magnetic field gradient coils 22 of the scanner 14. The magnetic field gradients spatially encode magnetic spins within the imaging volume 16. Typically, the plurality of magnetic field gradient coils 22 include three separate magnetic field gradient coils spatially encoding in three orthogonal spatial directions.

Further, one or more transmitters 24, such as a transceiver, are controlled to transmit Bi resonance excitation and manipulation radiofrequency (RF) pulses into the imaging volume 16 with one or more transmit coil arrays, such as a whole body coil 26 and/or a surface coil 28, of the scanner 14. The Bi pulses are typically of short duration and, when taken together with the magnetic field gradients, achieve a selected manipulation of magnetic resonance. For example, the Bi pulses excite the hydrogen dipoles to resonance and the magnetic field gradients encode spatial information in the frequency and phase of the resonance signal. By adjusting the RF frequencies, resonance can be excited in other dipoles, such as phosphorous, which tend to concentrate in known tissues, such as bones.

One or more receivers 30, such as a transceiver, are controlled to receive spatially encoded magnetic resonance signals from the imaging volume 16 and demodulate the received spatially encoded magnetic resonance signals to MR data sets. The MR data sets include, for example, k-space data trajectories. To receive the spatially encoded magnetic resonance signals, the receivers 30 use one or more receive coil arrays, such as the whole body coil 26 and/or the surface coil 28, of the scanner 14. The receivers 30 typically store the MR data sets in a buffer memory 32.

A backend system 58 of the system 10 images the ROI using the scanner 14. The backend system 58 is typically remote from the scanner 14 and includes a plurality of modules 60, discussed hereafter, to perform the imaging of the ROI using the scanner 14. Advantageously, the backend system determines expected prepulse delay times and actual prepulse delay times.

A control module 62 of the backend system 58 controls overall operation of the backend system 58. The control module 62 suitably displays a graphical user interface (GUI) to a user of the backend system 58 using a display device 64 of the backend system 58. The control module unit 65. The control module 62 displays the ECG signal received from the ECG unit 65 on the display device 64.

Further, the control module 62 suitably allows the operator to interact with the GUI using a user input device 66 of the backend system 58. For example, the user can interact with the GUI to instruct the backend system 58 to coordinate the imaging of the ROI.

A data acquisition module 68 of the backend system 58 performs MR scans of the ROI. For each MR scan, the data acquisition module 68 controls the transmitters 24 and/or the gradient controller 20 according to scan parameters, such as number of slices, to implement an imaging sequence within the imaging volume 16. An imaging sequence defines a sequence of Bi pulses and/or magnetic field gradients that produce spatially encoded MR signals from the imaging volume 16. Further, the data acquisition module 68 controls the receivers 30, and the tune/detune control signal of the driver circuit 36, according to scan parameters to acquire spatially encoded MR signals to an MR data set. The MR data set is typically stored in at least one storage memory 70 of the backend system 58.

In preparing for MR acquisition, the ROI is positioned within the imaging volume 16.

For example, the patient 12 is positioned on the patient support. The surface coil 28 is then positioned on the patient 12 and the patient support moves the ROI into the imaging volume 16.

A reconstruction module 72 of the backend system 58 reconstructs the MR data sets of the MR diagnostic scans into MR images or maps of the ROI. This includes, for each MR signal captured by the MR data sets, spatially decoding the spatial encoding by the magnetic field gradients to ascertain a property of the MR signal from each spatial region, such as a pixel or voxel. The intensity or magnitude of the MR signal is commonly ascertained, but other properties related to phase, relaxation time, magnetization transfer, and the like can also be ascertained. The MR images or maps are typically stored in the storage memory 70.

A pulse module 74 of the backend system 58 controls shared pulses to the patient 12. A shared prepulse is a prepulse that is applied only once for a number of following readouts. The pulse module 74 delivers shared pulses, such as inversion pulses, and shared prepulse profiles to the patient 12.

With reference to FIGURE 2, a shared prepulse 102, in this particular embodiment an inversion pulse, is shared by a profile 104. The profile 104 is a set of imaging readouts 104a, 104b, 104b of the patient 12. A readout includes image data for reconstruction into slice image or other image or image segment of the ROI of the patient 12. Each readout 104a, 104b, 104c corresponds to acquisition of a part of the data for different inversion time imaging slice. Subsequent profiles 106, 108 having sets of further readouts 106a, 106b, 106b, 108a, 108b, 108c sharing prepulses 102, 107 respectively. An expanded view 110 of a shared pulse 107 and two following readouts 108a, 108b depicts a detailed signal and readout diagram for acquiring imaging readouts sharing a prepulse. After a delivered inversion 107, a restore pulse (RNAV) signal 112 is delivered to undo the inverted magnetization locally. A Regional Saturation Technique (REST) signal 114 is delivered as a method for fat suppression. It is appreciated that other fat suppression techniques may be used in other embodiments. A navigator signal 132 is used for a reading motion state of the ROI within the patient 12.

The pulse module 74 includes a gating mechanism to read and compare actual delay times TI for each readout. The delay time refers to the time from the inversion pulse 102 and an individual readout 104a, 104b, 104c. FIGURE 3 depicts measured delay times 140 TIi and TI₂ corresponding to consecutive readouts sharing an inversion pulse 102. Expected delay times 142 are computed by the pulse module 74 during a preparation phase prior to the imaging sequence. The expected delay times 142 are compared to the actual delay times 140 directly to determine accuracy of the actual delay times 140. Actual delay times can be different from expected delay times if using patient physiology dependent acquisition time points. Artifacts of unusable data are created when the actual delay time strays from the expected delay time too much, such as in cases of an arrhythmia. These artifacts are undesirable and lead to inaccurate and distorted outputs and artifacted images. The gating mechanism of the pulse module 74 compares the actual measured delay times 140 to expected delay times 142. A visual depiction of the comparison is shown in FIGURE 3 by a dotted line 144. In this case, the actual TI₂ differs from the expected TI₂ and potentially creates an artifact.

The pulse module 74 accepts an individual readout when the actual delay time is within a critical limit, i.e. an acceptable range, of the expected delay time. The pulse module 74 rejects a readout when the actual delay time exceeds the critical limit of the expected delay time. The pulse module 74 evaluates effective inversion times at the end of each inversion interval. In one embodiment, A fixed inversion time gating window, such as within 15% of expected delay time, is used. Acquired readouts, i.e. k-space lines, inside this interval will be accepted, while lines acquired outside the window will be rejected. In one embodiment, a critical limit, such as within 30% of the expected delay time, is used used to reject a whole inversion interval independent of the inversion times of the other profiles.

Patient physiology dependent acquisition time points are acquired using respiratory triggering. In one embodiment, respiratory phase is tracked using the navigator pulses. To obtain suitable navigator signals in an inversion recovery sequence, the inversion is undone locally using the slice selective adiabatic restore pulse 112. A respiratory navigator 132 is evaluated at the end of each inversion interval TI. A respiratory gating window 133 is implemented such that when the respiratory navigator 132 is outside of the respiratory gating range 133 by more than a critical limit, e.g., when the patient is not in a selected respiratory phase, the entire profile is rejected independent of the navigators of the other profiles.

With reference again to FIGURE 2, the pulse module 74 determines acceptances and rejections 136 for each readout. For example, the first acquired readout 104a of the first profile 104 is rejected because the respiratory phase as measured by the navigator pulse is outside the selected respiratory window 133. The second readout 104b is rejected because the actual delay time is outside of the inversion time gating window due to an arrhythmia. The third readout 104c is accepted as the actual delay time is within the inversion time gating window TI of the expected delay time and the navigator gating window 133. The pulse module 74 records the acceptances and rejections 136 for each readout to determine whether to accept or reject the entire profile after the inversion. The pulse module 74 rejects an entire profile if one or the majority of the readouts are rejected, and accepts an entire profile if all or the majority of readouts are accepted. In this example, two of the three readouts were rejected 104a, 104b while only the third 104c was accepted. Therefore, the pulse module 74 rejects the first profile 104. When a profile is rejected, the profile is immediately reacquired using the same delay time TI. In this example, the inversion 102 is repeated after the first profile 104 is rejected. The repeated profile 106 is a set of readouts 106a, 106b, 106c. at the same delay times after the inversion pulse as the rejected profile. The pulse module 74 determines acceptances and rejections based upon the same criteria. In this example, the first readout 106a is rejected because the respiratory phase is outside the navigator gating window 133. The second and third readouts 106b, 106c are accepted as the actual delay times are within the inversion time gating window of the expected delay times and the respiratory gating window 133. The pulse module 74 determines acceptance sharing the inversion pulse, were accepted. After a profile is accepted, a subsequent shared pulse 107 is delivered to acquire a next profile 108 with a different delay time TI₂ with a set of readouts 108a, 108b, 108c in an imaging sequence.

With reference to FIGURE 4, a plot of measured relaxation time Tl versus expected relaxation time Tl is shown. A reference line depicts an ideal sequence where both times are equal. The square plot points depict a profile acquisition without using inversion time gating. The diamond points depict a profile acquisition using inversion gating concepts as described herein. Plot points 150 that divert greatly from the reference ideal profile cause artifacts in the resultant image. The creation of artifacts is greatly reduced using the inversion time gating concepts described herein as the inversion time gating readouts track the reference more closely than accepting all profiles without taking into account the actual delay times.

In one embodiment the shared prepulse 102 is an inversion pulse and the mechanism is a gating mechanism that rejects profiles if delay times are outside a pre-defined gating window. ECG triggering yields patient physiology dependent acquisition time points. In another embodiment the mechanism corrects acquired profiles for delay times TI that are outside a predefined target window. For example, the pulse module 74 uses iterative reconstruction methods in Tl mapping. In other embodiments, the prepulse is a black blood pulse, a T2 prep pulse, a Tl prep pulse, a fat suppression pulse, or a saturation pulse.

The same slice or segment of a three-dimensional image is acquired with different delay times TI and reconstructed into a series of images of the same slice or region, but with different delay times. The contrast evolution of each corresponding voxel of the series of slices or regions is evaluated to generate a value for the corresponding voxel of the final image.

Each of the plurality of modules 60 can be embodied by processor executable instructions, circuitry (i.e., processor independent), or a combination of the two. The processor executable instructions are stored on at least one program memory 76 of the backend system 58 and executed by at least one processor 78 of the backend system 58. As illustrated, the plurality of modules 60 is embodied by processor executable instructions. However, as is to be appreciated, variations are contemplated. For example, the data acquisition module 68 can be circuitry.

With reference to FIGURE 5, a method 160 for taking into account actual delay times is shown. At a step 162, expected delay times are calculated for each readout. The expected delay times can be calculated using the average RR-interval length of the patient 12. At a step 164, an inversion pulse is delivered to the patient 12. At a step 166, readouts are acquired of the patient for form a profile comprising a plurality of readouts. At a step 168, the delay times are measured from the inversion pulse to each readout. At a step 169, a navigator signal 132 is acquired to determine the respiratory phase which is compared to the respiratory phase gating window 133. At a step 170, the measured delay times are compared to the expected delay times by the pulse module 74.

With reference to FIGURE 6, the comparison steps 169 and 170 are expanded. At a step 173, the pulse module 74 determines from the navigator signal 132 if the respiratory state is within the gating window 133. If NO, then the pulse module 74, at a step 173, rejects the readout as an unsuccessful readout of the patient 12. If YES, then at a step 174, the pulse module 74 determines if the measured delay time is within range of the expected delay time for the single readout. If YES, then the pulse module 74, at a step 176, accepts the readout as a successful readout of the patient 12. If NO, then the pulse module 74, at step 173, rejects the readout as an unsuccessful readout of the patient 12.

Next, at a step 177, the pulse module 74 determines if there are subsequent readouts in the profile. If YES, the pulse module 74 reverts back to step 172 for the subsequent readout. If NO, at a step 178, the pulse module 74 determines if the majority of readouts in the profile are accepted. If YES, then the pulse module 74, at a step 180, proceeds to acquire subsequent profiles using method 160 until there are not any more profiles to acquire in the inversion. If NO, then the pulse module 74, at a step 182, repeats acquisition of the rejected profile using method 160

While this invention has been described with respect to novel and inventive system and method for taking into account actual prepulse delay times in sequences with shared prepulses, for example, one having ordinary skill in the art shall appreciate in view of the teachings provided herein that exemplary embodiments of the present invention can be implemented in and/or used with a wide range of medical systems, devices and methods, including but not limited to Magnetic Resonance Imaging (MRI) and other imaging modalities. One having ordinary skill in the art should also appreciate in view of the teachings provided herein that a free-breathing three-dimensional Tl map acquisition available to users of, e.g., MRI scanners, may be described in detail by the supplier. Further, one having ordinary skill in the art shall appreciate in view of the teachings provided herein that a particular application of exemplary embodiment of a system and method in accordance with the present disclosure for free breathing three dimensional Tl mapping can be in heart failure patients. For example, Tl mapping can be used for diffuse fibrosis detection or in grey zone quantification. Moreover, one having ordinary skill in the art shall appreciate in view of the teachings provided herein that there are many other applications for which exemplary embodiments of the present invention can be implemented, configured and used. For example, an oncologic application could be liver imaging where cardiac and respiratory motion plays an important role.

Although the system and method of the present disclosure have been described with reference to exemplary embodiments thereof, the present disclosure is not limited to such exemplary embodiments. Rather, the system and method disclosed herein are susceptible to a variety of modifications, enhancements and/or variations, without departing from the spirit or scope hereof. Accordingly, the present disclosure embodies and encompasses such modifications, enhancements and/or variations within the scope of the claims appended hereto.

Claims

CLAIMS:

1. A medical imaging system utilizing measured prepulse delay times (TI), comprising:

a data acquisition module (68) which delivers a shared pulse (102) followed by an imaging profile (102, 104, 108) for generating image datasets (104a, 104b, 104c, 106a, 106b, 106c, 108a, 108b, 108c) of a patient (12);

a pulse module (74) controlled by a processor (78) configured to:

acquire a first plurality of image datasets (104a, 104b, 104c) of the patient (12) using the data acquisition module (68);

measure a delay time (Ή) between the shared pulse (102) delivered by the data acquisition module (68) and acquisition of each individual image dataset (104a, 104b, 104c) of the image profile (104); and

compare the measured delay time to an expected delay time.

2. The system according to claim 1, wherein the individual image data sets (104a, 104b, 104c) are acquired at a characteristic point in the cardiac cycle and the pulse module (74) calculates the expected delay time base on an average RR-interval length of the patient (12) during a preparation phase.

3. The system according to any one of claims 1 or 2, wherein the shared pulse includes an inversion prepulse.

4. The system according to any one of claims 1-3, wherein the pulse module (74) accepts or rejects an individual image dataset of the plurality of image datasets if the delay time is inside or outside a predetermined range of the expected delay time.

5. The system according to any one of claims 1-4, wherein the pulse module (74) compares a respiratory phase at the measured delay time of the image dataset to a respiratory gating window (133).

6. The system according to claim 5, wherein the pulse module (74) accepts or rejects the image dataset based on whether the respiratory phase is inside or outside the respiratory gating window (133).

7. The system according to any one of claims 1-6, wherein the pulse module (74) accepts or rejects the whole image profile (104) based on whether the majority of image data sets are accepted or rejected.

8. The system according to claim 5, wherein the pulse module (74) repeats acquiring the first image profile (106) before acquiring a second image profile (108) in response to the first plurality of image profile (104) being rejected.

9. A method for taking into account actual prepulse delay times during image acquisition, the method comprising:

delivering a shared pulse (102);

acquiring a first image profile (102) including a plurality of image datasets (104a, 104b, 104c) of the patient (12) using a data acquisition module (68);

measuring a delay time between the shared pulse (102) and acquisition of each individual image dataset (104a, 104b, 104c) of the image profile; and

comparing the measured delay time to an expected delay time.

10. The method according to claim 9; including:

triggering the acquiring of the individual image data sets based on cardiac phase; calculating the expected delay time based on an average RR-interval length of the patient (12) during a preparation phase.

11. The method according to any one of claims 9 or 10; wherein the shared pulse is an inversion prepulse.

12. The method according to any one of claims 9-11 ; including:

accepting or rejecting an individual image dataset of the plurality of image datasets based on whether the delay time is inside or outside a predetermined range of the expected delay time.

13. The method according to any one of claims 9-12; including:

comparing a respiratory phase at the measured delay time of the image dataset to a respiratory gating window (133).

14. The method according to any one of claims 9-14, including:

accepting or rejecting each image dataset in response to the respiratory phase being inside or outside the respiratory gating window (133).

15. The method according to any one of claims 9-15, including:

accepting or rejecting the whole image profile when the majority of image data sets is accepted or rejected.

16. The method according to claim 15, including

repeating acquiring the first plurality of image datasets (104) before acquiring a second plurality of image datasets (108) in response to the majority of the first image datasets (104a, 104b, 104c) being rejected.

17. A non-transitory computer readable medium carrying software for controlling one or more processors (78) to perform the method according to any of claims 9-16.

18. A shared inversion prepulse analyzer including one or more processors (78) configured to: compute an expected delay time using the average RR- interval of a patient (12) for each image dataset (104a, 104b, 104c) of an image profile (104) for an entire inversion interval;

instruct a data acquisition module (68) to deliver an inversion pulse (102) to the patient (12);

acquire the plurality of image datasets (104a, 104b, 104c) of the patient (12) based on cardiac phase;

determine a delay time (TI) between the inversion pulse (102) delivered by the data acquisition module (68) and acquisition of each individual image datasets (104a, 104b, 104c);

determine a respiratory phase at the determined delay time from a navigator echo; compare the respiratory phase to a respiratory window; and

compare the delay time to the expected delay time.

19. The inversion pulse analyzer according to claim 18, wherein the inversion pulse analyzer

accepts an image dataset collected during the inversion interval when the delay time is inside a range of the expected delay time and accepts an image dataset if the respiratory phase is inside the respiratory window; and

accepts the image profile if the majority of the individual image datasets are accepted.

20. A magnetic resonance imaging system including the inversion pulse analyzer according to claim 18.