Scan sequence in magnetic resonance imaging

Abstract

A control system (126) for a magnetic resonance imaging system (100) is provided. The control system includes a control module (250) configured to control the magnetic resonance imaging system to perform an examination comprising a plurality of scans. The control system further includes a monitor module (252) configured to monitor a sleep state of a patient based on sensor data (310) received from a patient state sensing system (102) of the magnetic resonance imaging system. The control system further includes a sequencing module (254) configured to dynamically determine at least a portion of a sequence in which the control module is to control the magnetic resonance imaging system to perform the scans, the determination being made as a function of the monitored sleep state of the patient and as a function of a sleep suitability score associated with one or more of the scans. A corresponding method is also provided.

Description

TECHNICAL FIELD

[0001] The present invention relates to scan ordering in magnetic resonance imaging, in particular to a control system and a control method for a magnetic resonance imaging system. BACKGROUND

[0002] Patient motion in magnetic resonance imaging (MRI) is the most important source of image artifacts. Patient motion often results in missing of small lesions, blurring of important structures or generally poor image quality, making it necessary to repeat the scan several times. Various methods have been proposed to address patient motion. A first method utilizes data provided by external sensors or the MR data itself to detect motion, thereby selecting not to acquire or discarding parts of the MR data that might otherwise introduce artifacts. This method typically increases the scan time. A second method seeks to minimize patient motion by convenient positioning, immobilization or patient coaching. In some pediatric imaging situations, even sedation is considered the last resort to avoid patient motion, which comes with significant additional effort and side effects. SUMMARY

[0003] There is a need for a technique that effectively avoids or addresses patient motion with minimal staff intervention in an autonomous environment.

[0004] The subject matter of the independent claims meets this need. Optional features are provided by the dependent claims and the following description.

[0005] According to a first aspect, there is provided a control system for a magnetic resonance imaging system. The control system can comprise a control module configured to control the magnetic resonance imaging system to perform an examination comprising a plurality of scans. The control system can further comprise a monitor module configured to monitor a sleep state of a patient based on sensor data received from a patient state sensing system of the magnetic resonance imaging system. The control system can further comprise an ordering module configured to dynamically determine at least part of a sequence in which the control module is to control the magnetic resonance imaging system to perform the scans. The determination can be made as a function of the monitored sleep state of the patient and as a function of a sleep suitability score associated with one or more of the scans.

[0006] In this way, the insight that patient motion problems are effectively and conveniently addressed based on sleep is supported and leveraged to reduce imaging artifacts and save imaging time, thereby providing an improved cost efficiency.

[0007] According to a second aspect, there is provided a computer-implemented method of controlling a magnetic resonance imaging system. The method can comprise controlling the magnetic resonance imaging system to perform an examination comprising a plurality of scans. The method can further comprise monitoring a sleep state of a patient based on sensor data received from a patient state sensing system of the magnetic resonance imaging system. The method can further comprise dynamically determining at least part of a sequence in which the magnetic resonance imaging system is controlled to perform the scans. The determination can be made as a function of the monitored sleep state of the patient and as a function of a sleep suitability score associated with one or more of the scans.

[0008] According to a third aspect, there is provided a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of the second aspect.

[0009] According to a fourth aspect, there is provided a computer readable medium having stored thereon the computer program product of the third aspect and / or computer executable instructions which, when executed by a computer, cause the computer to carry out the method of the second aspect.

[0010] Optional features or sub-aspects described in relation to the first aspect apply suitably to any of the second to fourth aspects.

[0011] A“sleep state” can mean a binary indication of whether a patient is asleep or awake, or a state selected from a set of more than two states including further indications of depth or stage of sleep, e.g. awake, REM sleep, non-REM sleep. A“sleep state” can also be understood as a patient measurement or vector of patient measurements providing sufficient information to determine whether a patient is asleep, such as patient heart rate, respiration rate (e.g. both from vital signs camera) and normal camera vision.

[0012] A“scan” can mean a single scan of a particular type performed for a single purpose as part of a larger“examination” comprising a plurality of such scans. Some examples of scans include gradient echo scans, echo planar scans, spin echo scans, diffusion scans. As used here, a“sequence” thus refers not only to a plurality of such scans, but also to the order in which the scans are performed, and“ordering” can be interpreted accordingly.

[0013] In other words, there is provided a MR scan scheduling system and method in which sleep habits and sleep states are determined, in which the scheduling of examinations and scans within examinations is adjusted according to sleep habits, or in which scan parameters are adjusted according to sleep states, with the overall goal of improving image quality, shortening imaging time and reducing the use of sedation.

[0014] These and other aspects of the application will be apparent from and elucidated with reference to the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0015] In the following, examples are described in more detail with reference to the enclosed drawings, in which:

[0016] Figure 1 Fig. illustrates a magnetic resonance imaging system comprising a control system; and

[0017] Figure 2 a method performed by a control system of Figure 1 .

[0018] LIST OF REFERENCE SIGNS:

[0019] 100 magnetic resonance imaging system

[0020] 102 patient status sensing system

[0021] 104 magnet

[0022] 106 bore

[0023] 108 imaging zone

[0024] 110 magnetic field gradient coil

[0025] 112 magnetic field gradient coil power supply

[0026] 114 radio frequency antenna

[0027] 116 radio frequency transceiver

[0028] 118 subject

[0029] 120 support

[0030] 122 environmental control subsystem

[0031] 126 control system

[0032] 128 hardware interface

[0033] 130 processor

[0034] 132 user interface

[0035] 134 computer storage device

[0036] 136 computer memory

[0037] 201-203 method steps

[0038] 250 control module

[0039] 252 monitor module

[0040] 254 ranking module

[0041] 256 environmental control module

[0042] 310 sensor data

[0043] 312-314 other data DETAILED DESCRIPTION

[0044] Figure 1 An exemplary magnetic resonance imaging system 100 is illustrated. The magnetic resonance imaging system 100 includes a magnet 104, such as a superconducting cylindrical magnet, having a bore 106 therethrough that is large enough to receive a subject 118 on a support 120. Within the bore 106 of the cylindrical magnet 104, there is an imaging zone 108 in which the magnetic field is strong and uniform enough to perform magnetic resonance imaging. Within the bore 106, there is also a set of magnetic field gradient coils 110 for acquiring magnetic resonance data to spatially encode magnetic spins within the imaging zone 108. The magnetic field gradient coils 110 comprise three separate sets of coils for spatial encoding in three orthogonal spatial directions. The magnetic field gradient coils 110 are connected to a magnetic field gradient coil power supply 112 that supplies current to the magnetic field gradient coils 110. Adjacent to the imaging zone 108 is a radio frequency antenna 114 for manipulating the orientation of magnetic spins within the imaging zone 108 and for receiving radio emissions from spins also within the imaging zone 108. The radio frequency antenna 114 can comprise multiple coil elements. The radio frequency antenna 114 is connected to a radio frequency transceiver 116. The radio frequency antenna 114 and radio frequency transceiver 116 can be replaced by separate transmit and receive coils and separate transmitters and receivers. It will be understood that the details of the magnetic resonance imaging system 100 are provided herein for illustrative purposes only, and that the techniques described herein are applicable to any MRI system or any other imaging system susceptible to imaging artifacts caused by patient motion. The magnetic resonance imaging system 100 also includes a patient state sensing system 102, and optionally also an environmental control subsystem 122.

[0045] The magnetic field gradient coil power supply 112, transceiver 116, patient state sensing system 102, and environmental control subsystem 122 are connected to a hardware interface 128 of a control system 126.

[0046] The control system 126 comprises a processor 130 connected to a hardware interface 128 and to a user interface 132, a computer storage device 134 and a computer memory 136. The computer storage device 134 contains, in use, sensor data 310 acquired using the patient state sensing system 102. The computer storage device 134 optionally also contains bore illumination control data 312 and music / video data 314. The computer memory 136 contains a control module 250, a monitor module 252, a sequencing module 254, and optionally also an environmental control module 256. Each of the modules 250-256 contains computer executable instructions.

[0047] The control module 250 contains computer executable code which enables the processor 130 to control the operation and functionality of the magnetic resonance imaging system 100 in the manner described herein. In particular, the control module 250 is configured to control the magnetic resonance imaging system 100 to perform an examination comprising a plurality of scans. The control module 250 can be configured to adjust scan parameters during said scans performed by the magnetic resonance imaging system 100 in dependence on the monitored sleep state.

[0048] The monitor module 252 is configured to monitor the sleep state of the patient based on the sensor data 310 received from the patient state sensing system 102. In this example, the monitor module 252 is configured to detect whether the patient is asleep (in a sleep state) or awake (in a non-sleep state) based on the sensor data 310. Sleep can be detected by methods such as camera-based measurements of heart rate and respiration rate, and closed-eye detection. The sensor data 310 received from the patient state sensing system 102 can therefore comprise one or more of (i) motion sensor data; (ii) patient heart rate data; (iii) patient respiration rate data; (iv) data indicative of detection of the patient’s closed eyes.

[0049] The sequencing module 254 is dynamically configured to determine at least part of a sequence in which the control module is to control the magnetic resonance imaging system to perform scans. The determination is made in dependence on the monitored sleep state of the patient and in dependence on sleep suitability scores associated with one or more of the scans. The sequencing module 254 can be configured to respond to the monitored sleep state of the patient indicating that the patient has entered a sleep state by prioritising a first one of the scans having a first sleep suitability score over a second one of the scans having a second sleep suitability score as the next scan in the sequence, the first sleep suitability score being higher than the second sleep suitability score. Advantageously, the more sleep suitable scan is therefore prioritised to occur when the patient is asleep, and other less sleep suitable scans which have a lower priority in terms of scheduling can occur at any other time during the examination.

[0050] The ranking module 254 can be configured to associate one or more scans with a respective sleep suitability score using a rule-based scoring algorithm that takes as input one or more of the following parameters: (i) scan duration, (ii) scan noise level, (iii) scan type (related to sensitivity to patient motion); (iv) patient interaction level during the scan. The sleep suitability score S can be defined as the sum of terms, each term comprising a weighting factor w i and a function f i (p) depending on the parameter p. The factors w i may be adjusted empirically to set the relative weight of the parameters. The function can be any analytical function of the parameter p as a polynomial, exponential or other function. In the case of scan duration, the function can simply be the identity function f(p) = p. In the case of scan noise level, the function can be defined as f(p) = -p 2 , since higher noise levels are increasingly less suitable for sleep. The parameter scan type is introduced into the score to account for the different sensitivity of various scan types to patient motion. More motion sensitive scan types should deliver a high score since they are more suitable to be performed during sleep, and vice versa. Accordingly, the respective function can be a table of values attributed equally to one of the scan types. For example, the table value for diffusion scans can be set to 5, the table value for all non-diffusion cartesian scans to 3, and the table value for non-diffusion radial and spiral scans to 1. The function for the parameter representing the level of patient interaction can also be implemented as a table. For example, scans that require patient response to a request as a breath hold command can be assigned a value of -1, all other scans are assigned a value of 0.

[0051] The ranking module 254 can be configured to prioritize the ranking of scans associated with a noise level lower than the noise level associated with at least one other of said scans to occur at or near the beginning of the sequence, thereby helping the patient to fall asleep. The scans can comprise at least one interactive scan involving a degree of patient interaction. The interactive scan can be associated with a requirement for one or more of patient repositioning and patient breath holding. In this case, the ranking module 254 can also be configured to prioritize the ranking of the interactive scan to occur at a point in the sequence where the sleep state of the patient is determined to be awake. This can occur at or near the end of the scan, advantageously preventing the interactive scan from hindering the patient from falling asleep. The ranking module 254 can be configured to omit the motion tracking portion of one or more subsequent scans from the sequence in response to the monitored sleep state of the patient indicating that the patient has entered a sleep state. Motion tracking can form part of many motion sensitive scans, and typically makes them longer. Therefore, omitting the motion tracking within these scans when the patient is detected to be asleep advantageously shortens the scans.

[0052] As described above, the control module 250 can be configured to adjust scan parameters during the scans performed by the magnetic resonance imaging system 100 in dependence of the monitored sleep state. Most MR scan types trade off image quality or resolution between shorter imaging times and resulting lower sensitivity to motion artifacts. If the patient is detected to be awake, the scan parameters can be adjusted by adjusting this trade-off in the direction of shorter and thus less sensitive scans, whereas a longer scan time with lower noise level can be chosen for the currently sleeping patient. The rule-based scoring algorithm as disclosed herein can be used to adjust the scan using e.g. an optimization algorithm to achieve this trade-off. If the patient is currently sleeping, the scan parameters can be iteratively adjusted to increase the sleep suitability score of the corresponding scan. If the patient is currently awake, the scan parameters can be iteratively adjusted to decrease the sleep suitability score. The optimization can be performed using any known optimization algorithm such as the method of steepest gradient descent. The optimization can be performed in a user-defined parameter space. For example, the parameter space of the scan duration can be given by a maximum and a minimum scan duration that the optimization algorithm should not exceed or fall below, respectively.

[0053] The environmental control module 256 can be configured to instruct the environmental control subsystem 122 to control the in-bore illumination conditions to assume a sleep support state, e.g. based on the in-bore illumination control data 312. The environmental control module 256 can be configured to instruct the environmental control subsystem 122 to play back music and / or videos that are identified as personal sleep triggers of the individual patient, e.g. that have been pre-stored as music / video data 314.

[0054] Figure 2 A method for controlling a magnetic resonance imaging system 100 performed by the control system 126 is illustrated. The method comprises controlling (by the control module 250) the magnetic resonance imaging system 100 to perform an examination comprising a plurality of scans at step 201. The method further comprises monitoring (by the monitor module 252) a sleep state of a patient based on sensor data 310 received from a patient state sensing system 102 of the magnetic resonance imaging system 100 at step 202. The method further comprises dynamically determining (by the sequencing module 254) at least part of a sequence in which the magnetic resonance imaging system 100 is controlled to perform scans at step 203. The determination can be made in dependence of the monitored sleep state of the patient and in dependence of a sleep suitability score associated with one or more of the scans.

[0055] One use case of the technology described herein comprises one or more of the following methods:

[0056] 1. Identifying potential sleepers and deriving personal sleep habits and sleep triggers;

[0057] 2. Guiding the patient to sleep during the examination;

[0058] 3. Patient scheduling according to sleep habits (time of day, scanner type);

[0059] 4. Application of individual sleep triggers at the beginning of the examination;

[0060] 5. Rescheduling of scans within the examination to support sleep;

[0061] 6. Adjustment of scans according to sleep state;

[0062] 7. Adjustment of imaging environment to support sleep (adaptive lighting).

[0063] With reference to method 1 (“Identify sleepers and derive individual sleep habits and sleep triggers”), potential sleepers can be identified based on an app-based questionnaire, which includes questions such as:

[0064] o “Do you fall asleep during driving or flying?”

[0065] o “How would you rate the noise that would disturb your sleep on a scale of 1-5?”

[0066] o “How long do you usually need to fall asleep?”

[0067] o “Which is your best sleep posture?” (If not supine, the sleeper is not eligible)

[0068] o “Do you remain calm and confident in new situations? Rate on a scale of 1-5”

[0069] o The app can also be used to produce some low-level MR noise, helping to ask questions such as “You will hear similar sounds during your upcoming MR examination. Do you think you will be able to sleep during that examination (which would benefit you and the image quality)?”

[0070] Each of these questions can be rated with a weight, and a professional sleep answer adds a corresponding weight to the total score. If the total score exceeds a limit, the patient is identified as a sleeper.

[0071] The criteria (weights, total limit) for deciding sleepers / non-sleepers can be set heuristically at product launch, and can be continuously improved during product usage. Thus, the pre-examination decision can be compared to data about the sleep state obtained during the actual examination of each patient. The criteria can then be updated so that the number of correct decisions for all patients is maximized. Correct here means that the patient falls asleep after a decision is made that he is a sleeper.

[0072] If the patient qualifies as a "sleeper" based on current criteria, sleep habits and sleep triggers can be derived from patient characteristics, personal device usage and extended questionnaires. An example of a characteristic is that sleep time usually varies with age and depends on the age of the specific patient, which allows for the most likely sleep time. The time of personal device usage can also be evaluated to derive the personal sleep time.

[0073] Referring to method 2 ("Encourage and guide patients to sleep during examination"), the patient can again be provided with information via the app on the personal device that sleep helps both good image quality and patient experience. The app can be used to play MR noise so that the patient can acclimate themselves to the sound. The sound can be played at a low volume shortly after the patient falls asleep at home.

[0074] Referring to method 3 ("Schedule patients according to sleep habits and apply sleep triggers"), personal sleep habits can be used to schedule the patient. "Night owls" are scheduled in the morning, "early birds" are scheduled in the afternoon or evening. Non-sleepers are preferably scheduled on high-field systems (e.g. 3T), where scans are usually shorter than on medium or low-field systems and thus less sensitive to motion artifacts. Personal sleep triggers (personal music or video clips, some personal items, usual evening drinks, e.g. night tea and food) can be applied at the beginning of the MR examination.

[0075] Referring to method 4 ("Reschedule scans within the examination to induce or maintain sleep"), loud scans can be avoided at the beginning of the MR examination to allow the patient to fall asleep or not to wake the patient during actual sleep. Loud scans can be rescheduled to the end of the examination to wake the patient again. Similarly, any scans that require active patient interaction (breathhold scans, repositioning, etc.) can be avoided at the beginning of the MR examination or during sleep.

[0076] Referring to method 5 ("Reschedule motion sensitive scans within the examination according to sleep state"), this is based on the insight that MR scans have very different motion sensitivity. Longer scans, diffusion scans and functional scans are examples with very high motion sensitivity. Such scans can be rescheduled to the detected sleep phase.

[0077] Referring to method 6 ("Adjust scanning according to sleep habits and sleep state"), most MR scan types allow a trade-off between shorter imaging time with associated lower sensitivity to motion artifacts and image quality or resolution. For non-sleepers the scan can be shortened, while for sleep patients a longer scan time can be chosen. Many scan types acquire additional MR data to track motion and discard the affected MR image data (such as PROPELLER, RADIAL acquisition, MR navigator). The additional acquisition requires additional imaging time. The scan can be adjusted to avoid this additional acquisition during the patient's sleep stage, thus saving imaging time.

[0078] Referring to method 7 ("Adjust imaging environment to support sleep"), the room and bore illumination conditions can be adjusted to support sleep. If the patient is asleep, patient communication can be avoided.

[0079] Aspects of the application can take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects that can all generally be referred to herein as a "module," or "system." Furthermore, aspects of the application can take the form of a computer program product on one or more computer-readable medium(s) having computer executable code embodied thereon. Any combination of one or more computer-readable medium(s) can be utilized. The computer- readable medium can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium used herein excludes transitory computer-readable signals. A "computer-readable storage medium" is any tangible storage medium that can store instructions which can be executed by a processor of a computing device. A computer-readable storage medium can be referred to as a non-transitory computer-readable storage medium. A "computer memory" or "memory" is an example of a computer-readable storage medium. A computer memory is any memory accessible by a processor. A "computer storage device" or "storage device" is another example of a computer-readable storage medium. A computer storage device is any non-volatile computer-readable storage medium. In some embodiments, a computer storage device can also be a computer memory, or vice versa. A "processor" as used herein encompasses an electronic component which is able to execute a program or machine executable instruction or computer executable code. A reference to a computing device comprising "a processor" should be interpreted as possibly containing more than one processor or processing core.

[0080] While the application has been illustrated and described in detail in the drawings and the foregoing description, the same is to be considered as illustrative or exemplary only, and not restrictive. The application is not limited to the disclosed embodiments. Numerous modifications and variations are possible in light of the above teachings without departing from the scope of the application. It is therefore to be understood that within the scope of the claims and their equivalents, the application can be practiced otherwise than as specifically described.

[0081] In the claims, the term "comprising" does not exclude other elements or steps, and the wording "a" or "an" does not exclude a plurality. A single processor or other unit can fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program can be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state storage medium supplied together with or as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A control system (126) for a magnetic resonance imaging system (100), the control system comprising: a control module (250) configured to control the magnetic resonance imaging system to perform an examination comprising a plurality of scans; a monitor module (252) configured to monitor a sleep state of a patient based on sensor data (310) received from a patient state sensing system (102) of the magnetic resonance imaging system; and a sequencing module (254) configured to dynamically determine at least part of a sequence in which the control module is to control the magnetic resonance imaging system to perform the scans, the determination being made in dependence on the monitored sleep state of the patient and in dependence on sleep suitability scores associated with one or more of the scans. The sequencing module (254) is configured to, in response to the monitored sleep state of the patient indicating that the patient has entered the sleep state, prioritize a first one of the scans having a first sleep suitability score over a second one of the scans having a second sleep suitability score as a next scan in the sequence, the first sleep suitability score being higher than the second sleep suitability score.

2. The control system of claim 1, wherein, The sequencing module (254) is configured to associate the one or more scans with respective sleep suitability scores using a rule-based scoring algorithm that takes as input one or more of the following parameters: (i) scan duration, (ii) scan noise level, (iii) scan type in relation to sensitivity to patient motion; (iv) patient interaction level during the scan.

3. The control system of claim 1 or 2, wherein, The function of the item of the input parameter p being the scan duration is defined as f(p) = p.

4. The control system of claim 3, wherein, The rule-based scoring algorithm determines the sleep suitability score S for the respective scan based on a sum of terms, each term comprising a weighting factor w i and a function f depending on an input parameter p i (p).

5. The control system of claim 4, wherein, The function of the item of the input parameter p being the scan type or patient interaction level is defined as a table of values, each value being attributed to one of the scan type or the patient interaction level, respectively.

6. The control system of claim 4 or 5, wherein, The function of the term with the scanning noise level as the input parameter p is defined as f(p) = -p 2 .

7. The control system of claim 4 or 5, wherein, The control module (250) is configured to adjust a scan parameter in dependence on the monitored sleep state during the scans performed by the magnetic resonance imaging system (100).

8. The control system of claim 1 or 2, wherein, The control module (250) is configured to adjust the scan parameter by reducing a scan duration when detecting that the patient is awake and / or by increasing a scan duration when detecting that the patient is asleep.

9. The control system of claim 8, wherein, The sequencing module (254) is configured to, in response to the monitored sleep state of the patient indicating that the patient has entered the sleep state, omit one or more subsequent scans of a motion tracking portion from the sequence.

10. The control system of claim 1 or 2, wherein, The sensor data received from the patient state sensing system of the magnetic resonance imaging system comprises one or more of: (i) motion sensor data; 11. The control system of claim 1 or 2, wherein, (ii) patient heart rate data; (iii) patient respiration rate data; (iv) data indicative of detecting that the patient has closed their eyes. ​ 12. The control system of claim 1 or 2, further comprising an environment control module (256) configured to instruct an environment control subsystem (122) of the magnetic resonance imaging system (100) to control bore illumination conditions to assume a sleep support state.

13. The control system of claim 1 or 2, further comprising an environment control module (256) configured to instruct an environment control subsystem (122) of the magnetic resonance imaging system (100) to play back music and / or video identified as a personal sleep trigger of the individual patient.

14. A computer-implemented method of controlling a magnetic resonance imaging system (100), the method comprising: controlling (201) the magnetic resonance imaging system to perform an examination comprising a plurality of scans; monitoring (202) a sleep state of a patient based on sensor data received from a patient state sensing system (102) of the magnetic resonance imaging system; and dynamically determining (203) at least part of a sequence in which the magnetic resonance imaging system is controlled to perform the scans, the determination being made in dependence on the monitored sleep state of the patient and in dependence on a sleep suitability score associated with one or more of the scans.

15. A computer readable medium having stored thereon computer executable instructions which, when executed by a computer, enable the computer to perform the method of claim 14.

16. A magnetic resonance imaging system comprising a control system according to any one of claims 1 to 13.

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