Method for operating liquid helium cooling system of magnetic resonance imaging system and magnetic resonance imaging system

Abstract

The invention provides a method for operating a liquid helium cooling system of a magnetic resonance imaging system and the magnetic resonance imaging system. A method for operating a liquid helium cooling system of a magnetic resonance imaging system (11), comprising the steps of: (a) providing a first schedule comprising a scan time and a second schedule comprising a plurality of time slots (8) associated with one of at least two different levels of power availability; (b) determining a shutdown time when the system is not used for scanning based on the first schedule; (c) determining, based on the second schedule, at least one time slot (8, 81) within the shutdown time that is not associated with the level of highest power availability; (d) activating the energy saving mode (4) during the determined at least one time slot (8, 81); (e) activating a standard operating mode (5) of the liquefaction device at the latest at a predefined time before the start of the next scan time.

Description

Technical Field

[0001] The invention relates to a method for operating a liquid helium cooling system for a magnetic resonance imaging system, and a corresponding computer program and a magnetic resonance imaging system. Background Art

[0002] Regardless of the grammatical use of the term, individuals with both male and female identities are included in the term.

[0003] Magnetic resonance imaging (MRI) scanners have high energy consumption. For example, the energy consumption of a typical MRI scanner can be on the order of about 70MWh per year. An important factor is the energy required to cool the MRI scanner, especially the magnets and coils of the scanner. In order to generate the magnetic field required for MRI scanning, the magnetic field is usually in the range of up to 3 Tesla, and in some cases even higher, superconductivity is required, which in turn requires corresponding low temperatures. For this purpose, liquid helium cooling is applied, and the temperature of the liquid helium is at about 4 Kelvin. Due to the absorption of heat, the liquid helium will evaporate into the gas phase over time. When the MRI scanner is actively used, that is, during scanning, due to the heat generated when operating the scanner, this effect of helium evaporation usually occurs to a significantly greater extent. However, even when the scanner is not in use, helium usually evaporates slowly over time. In order to counteract this effect of helium evaporation, MRI scanners usually include a helium liquefaction device, such as a cold head. The liquefaction device recondenses the helium that has evaporated back to the liquid state. Since helium requires a considerably larger amount of space when in the gas phase than when in the liquid phase (approximately 750 times under standard conditions), the system usually has to vent some of the helium if the amount of gaseous helium becomes too large. This is undesirable since resupplying additional helium is quite expensive and may require additional maintenance interruptions of the scanner. Furthermore, if there is too little helium in the liquid phase, the cooling power may no longer be sufficient, for example due to a quench of the magnetic coils, which may result in damage to the MRI system. Therefore, it is usually critical to ensure that the helium remains in the liquid phase.

[0004] On the other hand, the above-mentioned energy consumption of such cooling systems may be a problem, in particular when it comes to applications with renewable energy sources such as photovoltaics and wind energy which are not always available to the same extent. Summary of the invention

[0005] It is therefore an object of the present invention to provide a device which ensures a reliable operation of a magnetic resonance imaging system via its cooling system while at the same time at least temporarily reducing the energy consumption and / or adapting to the problem that renewable energy sources are not always available to the same extent.

[0006] This object is met or exceeded by a method according to the technical solution of the present invention, a computer program according to the technical solution of the present invention and a magnetic resonance imaging system according to the technical solution of the present invention. Additional features and advantages are described by the description and the drawings.

[0007] According to a first aspect of the present invention, there is provided a method for operating a liquid helium cooling system of a magnetic resonance imaging system, the liquid helium cooling system comprising a helium liquefaction device, such as a cold head. The liquefaction device has a standard operating mode, which is suitable for allowing a magnetic resonance scan to be performed without exhausting a large amount of helium. The method comprises the following steps:

[0008] (a) providing a first schedule including a scan time for the system and a second schedule including a plurality of time slots, each time slot being associated with one of at least two different levels of power availability, the at least two different levels of power availability including a highest power availability level;

[0009] (b) determining a shutdown time when the system is not used for scanning based on the first schedule;

[0010] (c) determining, based on the second schedule, at least one time slot within the off-time that is not associated with the level of highest power availability, wherein the at least one time slot is preferably associated with the lowest level of power availability among all time slots within the off-time;

[0011] (d) activating an energy saving mode during the determined at least one time slot, in which the liquefaction plant is supplied with a lower average amount of power than during the standard operation mode;

[0012] (e) activating a standard operating mode of the liquefaction device at the latest at a predefined time before the start of the next scanning time, so that during or before the next scanning time the system is operable during the next scanning time without risk of venting large amounts of helium.

[0013] Advantageously, when determining at least one time slot in which the energy-saving mode is activated, both the off time and the power availability are considered. Accordingly, the method can be used to adjust the power usage not only according to the first schedule of the scanning time but also according to the availability of power. For this purpose, two schedules can be used, namely the first schedule and the second schedule. In this context, the schedule can be understood as the time during which the MRI system will be used, and the different availability of power is related to the time, such as in the course of a day, or preferably, in the course of more than one day. The time slot of the second schedule can be very small, optionally infinitely small. Very small time slots can be used to represent the basic continuous change of power availability. In this case, the energy-saving mode can be activated during several time slots. On the other hand, at least some of the time slots can represent longer time periods, such as one hour or several hours. When the power availability is constant or almost constant in these longer time periods, for example, when the power price is set differently at different parts of the day or the solar cell generates a relatively constant amount of power during a specific time period, the time slot representing a larger amount of time may be useful, for example. For example, the availability of power may be different in the course of a day, in the course of a week, or in the course of a year. For example, the availability of electricity may be related to the price of electricity, such as the price at certain times at night or in the evening is different from the price at other times of the day. The availability of electricity may also be related to the production of electricity, such as solar cells produce more electricity during the sunshine period, or windmills depend on the strength of the wind. The method can significantly reduce the energy consumption during the time when the energy-saving mode is effective. Therefore, the method can be advantageously used to adapt to the problem that renewable energy sources are not available to the same extent at all times. For example, the energy-saving mode can be effective during the time of the night without sunshine, and the standard operating mode can be activated after sunrise or at sunrise and before performing an examination with the MRI system. Therefore, if the system depends on renewable energy, it may be feasible to reduce the number of batteries or other energy storage devices required for operation during the night due to the method. For example, the operation of the MRI system for inspection can start about two to three hours after sunrise. In addition, since the energy-saving mode requires less energy, the method according to the present invention can be used to reduce the total energy consumption.

[0014] By reactivating the standard operating mode at a predefined time before the start of the next scan time, it can be ensured that no discharge of helium occurs before or when the MRI system is used. Thus, the predefined time is defined such that the system is operable during the next scan time without the risk of discharging a large amount of helium during or before the next MRI scan. The time that the system operates in the standard operating mode can be considered a recovery period in which the magnet of the MRI system is cooled to operating temperature and / or is ready to be operational again.

[0015] According to an embodiment, the activation of the standard operating mode and the activation of the energy saving mode are timed so that the standard operating mode runs during a time slot associated with a higher level of power availability than the time slot in which the energy saving mode is activated, preferably so that the standard operating mode runs during a time slot associated with the level of the highest power availability. Preferably, during step (c) of the method, i.e., when determining at least one time slot within the shutdown time that is not associated with the level of the highest power availability, the level of power availability is taken into account. At least one time slot can be determined so that the activation of the standard operating mode occurs during a time slot of higher power availability, preferably of the highest power availability. Advantageously, the power availability when the standard operating mode is activated at a predefined time can therefore be taken into account. Since this embodiment can ensure that sufficient and / or relatively cheap power is available for the standard operating mode, this can promote a more efficient use of energy.

[0016] Optionally, the predefined time before the start of the scan time can be adjusted according to the next scheduled scan, in particular according to the expected heat generation of the next scheduled scan. For example, if less heat generation is expected, the predefined time can be shortened.

[0017] The liquefaction device is generally suitable for recondensing helium or helium vapor back to a liquid state. In particular, after the MRI magnet has been cooled, some of the helium may be in the gas phase. A typical liquefaction device is a cold head known in the prior art. A cold head may also sometimes be referred to as or classified as a cryocooler. Helium may be contained inside a cryostat. Typically, the superconducting wire material of the MRI coil may be immersed in a pool of liquid helium. Therefore, the energy-saving mode may be a mode in which the liquefaction device is operated with reduced power or the liquefaction device is turned off. Therefore, compared with the standard operating mode, the energy-saving mode may advantageously require a lower average amount of power. The energy-saving mode may be regarded as a controlled temporary disablement of the liquefaction device or as a controlled reduction in the operation of the liquefaction device. During the energy-saving mode, the amount of gaseous helium may increase, particularly due to ambient heat. Therefore, the energy-saving mode may be configured to be insufficient to keep the helium (most of the helium) in the liquid phase for a long time (e.g., a period of more than 5 hours). Therefore, for example, the amount of gaseous helium may increase slowly during the energy-saving mode. If the system is operated at this time, the amount of gaseous helium may potentially become so large that this part of the helium must be discharged. The amount of gaseous helium can be reduced again in the standard operating mode so that when the MRI system is operated, the system is ready to be operated without the need to discharge helium. The standard operating mode is particularly suitable for allowing magnetic resonance scanning to be performed without discharging a large amount of helium. This can be understood as making the cooling capacity of the liquefaction device during the standard operating mode so powerful that enough gaseous helium can be made to enter the liquid phase during the magnetic resonance scanning to prevent the need to discharge some helium. Therefore, the standard operating mode is particularly configured so that: over time, the helium (mostly) is kept in the liquid phase. In this context, "without discharging a large amount of helium" can be understood as: over time, a very small amount of helium may still be lost. In particular, due to the properties of helium, such as helium atoms with very small diameters, the loss of a small amount of helium may be inevitable. According to an embodiment, the amount of electricity per time unit provided to the helium liquefaction device during the energy-saving mode is at least three times lower than during the standard operating mode on average, preferably at least four times lower. For example, lower power consumption may be achieved by temporarily or even permanently switching off the liquefaction plant during the energy saving mode. Alternatively, lower power consumption may be achieved by providing a constantly reduced amount of power.

[0018] Advantageously, at least one time slot is determined to be not associated with the level of the highest power availability, and the energy saving mode is activated during the at least one time slot. Preferably, at least one time slot is selected so as to leave enough time for the standard operating mode to be activated at a predefined time before the start of the next scan time at the latest. Therefore, preferably determining at least one time slot can preferably be performed by considering the time required to activate the standard operating mode in step (e). For this purpose, in some cases, it may be advantageous not to select the time slot with the lowest power availability for the energy saving mode, because in some cases, before the operation of the MRI system is scheduled, there may not be enough time to activate the standard mode at the appropriate time. On the other hand, when possible, it may be particularly advantageous to apply the energy saving mode in the time slot with the lowest power availability among all time slots.

[0019] According to an embodiment, the energy-saving mode is an off mode in which the liquefaction device is turned off or an interleaved mode in which the liquefaction device is alternately turned on and off so that the off time is at least three times longer than the on time. The energy-saving mode as an off mode can advantageously allow a greater amount of energy to be saved during the energy-saving mode. If the energy-saving mode is applied only during a relatively short time slot, this may be particularly beneficial. On the other hand, if a longer time slot is available, the interleaved mode may be particularly advantageous. Therefore, the interleaved mode may allow the energy-saving mode to function for a longer period of time before the discharge of helium occurs or the discharge of helium is required. Additionally and / or alternatively, if the time after activating the standard operating mode and before starting the first scan of the MRI system is quite short, the interleaved mode may also be particularly advantageous. For example, when it is desired that the scan starts early in the day and the higher power availability only starts shortly before that, for example, due to the fact that solar energy is only available after sunrise, this may occur. In this case, the interleaved mode may allow the amount of helium in the gas phase to be reduced when the standard operating mode is activated. Thus, in this particular case, the recovery time can be shorter when using the staggered mode compared to a complete shutdown, at the expense of lower energy savings. Advantageously, both the shutdown mode and the staggered mode can help significantly reduce the energy consumption of the cooling system, and therefore reduce the energy consumption of the magnetic resonance imaging system. It has been found that in the staggered mode, the off time is at least three times longer than the on time, which may be a good ratio for effective energy saving, while having some advantages of the staggered mode. Therefore, having a ratio significantly greater than three may result in the staggered mode being closer to the off mode in nature. The staggered mode may preferably be configured so that: the on time is on the order of one or several minutes, preferably 1 to 20 minutes, more preferably 2 to 8 minutes, and even more preferably 2 to 6 minutes. Accordingly, the off time may be on the order of three times or more of the on time, for example, particularly preferably in the range of 6 to 18 minutes or more. It has been found that these amounts of time may be particularly advantageous for both ensuring an effective amount of energy saving and preventing the discharge of helium for a particularly long time.

[0020] According to an embodiment, the liquefaction device is shut down for no more than a predefined amount of time, wherein the predefined amount of time is defined so as to avoid a large amount of helium discharge. The predefined amount of time may depend on the MRI system and / or its discharge configuration. For example, the liquefaction device may preferably be shut down for up to 4 hours, preferably up to 3 hours. During testing with a real MRI system, it has been found that, depending on the specific discharge conditions of a particular system, the time until exhaust occurs is within a time range between 4 hours 3 minutes and 5 hours 21 minutes. The test has been performed by keeping the MRI magnet in a stable configuration and then shutting off the cold head. Then, the time until the magnet is discharged is measured. This time is defined as when the safety valve opens and the magnet begins to lose helium to the recovery line. Therefore, based on the test, a maximum amount of time of 4 hours may be feasible. A maximum amount of up to 3 hours may be more beneficial to provide a safety margin, so for example, potential technical problems are allowed to occur without necessarily directly causing the discharge of helium. It has been found that for commercially available MRI systems, approximately 12kWh can be saved during a 3-hour energy-saving mode. This is equivalent to 4kW per hour saved by switching the cold head and the helium compressor. The amount of savings is likely to vary between different systems.

[0021] According to an embodiment, the level of power availability is based on the expected price of electricity during the corresponding time slot and / or based on the expected amount of electricity produced during the corresponding time slot, and the level of the lowest power availability is associated with a high expected price and / or a low expected amount of electricity production. The expected amount of electricity production may, for example, depend on the productivity of renewable energy equipment (such as solar cells or wind turbines). For example, the energy-saving mode can be activated near the end of the night (for example, 2 to 3 hours before sunrise), and the standard operating mode can be activated after sunrise and before the planned start of scanning with the MRI system is sufficient time (for example, 2 hours). The expected price can, for example, vary based on the user's electricity contract. For example, the user may have a contract that the energy during the night is cheaper than during the day. For example, the energy-saving mode can be activated at the end of a few hours close to the high cost, and the standard operating mode can be activated during a few hours at a low cost.

[0022] According to an embodiment, the second schedule is dynamically updated based on the received power availability data. The power availability data may include information about the availability of renewable energy sources and / or about energy prices, in particular forecasts and / or estimates. For example, the received power availability data may include a weather forecast or data derived from a weather forecast. Additionally and / or alternatively, the power availability data may include hours of sunshine. The weather forecast may include information about the appearance of clouds in the sky above the solar panels. The weather forecast may include a prediction of the wind speed at the location of a wind turbine for providing energy for the MRI system. Advantageously, the dynamic updating of the schedule may allow the timing of the energy saving mode to be adjusted to actual current conditions and / or conditions estimated in the near future.

[0023] According to an embodiment, the first schedule is dynamically updated based on the scheduling of the magnetic resonance scan, in particular the user input schedule. Thus, advantageously, the timing of the energy saving mode and the standard operating mode can be dynamically adjusted, in particular by taking into account changes even on short notice. For example, the first schedule can be updated in the evening or at night based on the schedule for the next day, and the energy saving mode and the standard operating mode for that night can be set according to the updated first schedule. For example, in the case of starting to use the MRI system particularly early the next day, the energy saving mode can be shortened compared to other nights. In this case, since the energy saving mode is activated for a shorter time and therefore the amount of gaseous helium is smaller, the time during which the standard operating mode must be activated before the scan can start can also be shorter.

[0024] According to an embodiment, the predefined time before the start of the next scan time is between 0.5 hours and 5 hours, preferably between 1 hour and 4 hours, more preferably between 1.5 hours and 3 hours. A predefined time in the range of 0.5 hours to 5 hours may be sufficient to make the system operational again. The required time generally depends on the specific system, in particular the cooling system and the generation of heat during the scan. Therefore, the predefined time may vary depending on the system. A predefined time in the range between 1 hour and 4 hours may be suitable for many typical systems. It has been found that, at least for some commercially available systems, in particular 1.5 Tesla systems, a predefined time between 1.5 hours and 3 hours may be particularly advantageous.

[0025] According to an embodiment, the partial energy-saving mode is active during the off time when the scanner is not operated in the energy-saving mode or the standard operation mode, wherein in the partial energy-saving mode, the liquefaction device is supplied with a lower average amount of power than during the standard operation mode, and is supplied with a higher average amount of power than during the energy-saving mode. Advantageously, the energy-saving mode can allow further energy saving. In particular, when there is no scheduled scan, the partial energy-saving mode can always be used, and outside the time slot, the energy-saving mode or the standard operation mode after the energy-saving mode is activated until the cooling system is restored. For example, in the case when there is no suitable time slot for the standard operation mode to restore the cooling system before the next scan, the partial energy-saving mode can be a useful supplement to the energy-saving mode. The partial energy-saving mode is preferably configured so that: as long as the scanner is not operated, helium is not discharged. The partial energy-saving mode may include an off time and an on time. For example, the energy-saving mode may be configured to correspond to the staggered mode described herein with respect to the energy-saving mode. For example, in the partial energy-saving mode, the liquefaction device can be alternately turned on and off so that the off time is less than three times longer than the on time. According to an embodiment, during the partial energy-saving mode, the liquefaction device is alternately switched on and off so that the off time is at least as long as the on time and is at most 2.5 times longer than the on time. It has been found that the partial energy-saving mode with these relative times can provide an effective way to save electricity on the one hand, and ensure that a large amount of helium is not discharged under normal circumstances on the other hand. For example, the off time can be in the range of 5 minutes to 12 minutes, preferably in the range of 6 minutes to 10 minutes. Preferably, the partial energy-saving mode includes an off time that is at least 1.5 times and at most 2.5 times the on time. For example, the off time can be twice the on time, for example the off time is 8 minutes and the on time is 4 minutes. Alternatively, the partial energy-saving mode can, for example, include operating the liquefaction device with a substantially constant reduced power consumption.

[0026] According to a further aspect of the invention, there is provided a computer program comprising instructions which, when executed by a control unit of a magnetic resonance imaging system or a control unit of a liquid helium cooling system of a magnetic resonance imaging system, cause the control unit to perform the steps of the method as described herein. All features and advantages of the method may apply to the computer program, and the computer program may apply to all features and advantages of the method.

[0027] According to another aspect of the present invention, there is provided a magnetic resonance imaging system comprising a helium liquefaction device, such as a cold head. The liquefaction device is configured to have a standard operating mode and an energy-saving mode, in which the liquefaction device is supplied with an amount of power that allows the magnetic resonance scan to be performed without discharging a large amount of helium, and in the energy-saving mode, the liquefaction device is supplied with an average amount of power lower than during the standard operating mode. The system is configured to activate the energy-saving mode during a time slot when there is no scheduled scan and the availability of power is reduced, and to activate the standard operating mode at a predefined time before the start of the next scheduled scan at the latest, so that during or before the next scan time, without the risk of discharging a large amount of helium, the system is operable during the next scan. The system can be particularly configured to perform the method as described herein. All features and advantages of the method and computer program can be applied to the magnetic resonance imaging system, and the magnetic resonance imaging system can be applied to all features and advantages of the method and computer program. The system can include a control unit configured to control the liquefaction device and activate different modes of the liquefaction device.

[0028] Unless otherwise indicated, the embodiments described herein may be combined with each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings illustrate various exemplary embodiments and methods of various aspects of the invention.

[0030] Figure 1 A flow chart showing a method for operating a liquid helium cooling system for a magnetic resonance imaging system according to an embodiment of the present invention;

[0031] Figure 2 A diagram showing the power fed to a liquefaction device of a helium cooling system of a magnetic resonance imaging system over time when applying a method according to an embodiment of the invention;

[0032] Figure 3 a diagram showing the power fed to a liquefaction device of a helium cooling system of a magnetic resonance imaging system over time when applying a method according to another embodiment of the invention; and

[0033] Figure 4 A magnetic resonance imaging system according to an embodiment of the invention is shown. DETAILED DESCRIPTION

[0034] Figure 1A flow chart of a method for operating a liquid helium cooling system of a magnetic resonance imaging system 11 according to an embodiment of the present invention is shown. In a first step 101, a first schedule and a second schedule are provided. The first schedule includes a scanning time of the magnetic resonance imaging system 11. The second schedule includes a plurality of time slots 8, and each time slot 8 is associated with one of at least two different levels of power availability. The level of power availability can be based on the expected price of power during the corresponding time slot 8. Additionally or alternatively, the level of power availability can be based on the expected amount of power production during the corresponding time slot 8. The second schedule can be dynamically updated based on received power availability data. Thus, for example, the current weather forecast can be used to update the second schedule by taking into account the weather forecast to determine the expected amount of power production, such as produced by a wind turbine or solar panels. Dynamically updating the second schedule can provide a second schedule that more accurately predicts the actual power availability for power production.

[0035] In a further step 102 , a switch-off time is determined based on the first schedule, during which switch-off time the system is not used for scanning.

[0036] In a further step 103, based on the second schedule, at least one time slot 8, 81 within the off time is determined which is not associated with the level of the highest power availability. If possible, the at least one time slot 81 is preferably associated with the level of the lowest power availability of all time slots 8 within the off time. The level of the lowest power availability can in particular be associated with a high expected price and / or a low expected power production. Preferably, the at least one time slot 8, 81 is also determined such that later in step 105 the standard operating mode 5 runs during a time slot 8 which is associated with a higher level of power availability than the time slot 8, 81 during which the energy saving mode 4 was activated in step 104.

[0037] In step 104, energy saving mode 4 is activated during at least one of the determined time slots 8, 81. In energy saving mode 4, a liquefaction device of the liquid cooling system, such as a cold head, is supplied with a lower average amount of power than during standard operation mode 5. Standard operation mode 5 is suitable for allowing magnetic resonance scanning to be performed without discharging a large amount of helium. Preferably, the amount of power per time unit supplied to the helium liquefaction device during energy saving mode 4 is at least three times lower than during standard operation mode 5 on average. Energy saving mode 4 can be a mode in which the liquefaction device is operated only in intervals or the liquefaction device is completely shut down. Energy saving mode 4 can be configured to be insufficient to keep the helium of the cooling system in the liquid phase for a long time. In particular, the amount of gaseous helium can be slowly increased during energy saving mode 4.

[0038] In a further step 105, before starting a scan with the magnetic resonance imaging system 11, the standard operating mode 5 of the liquefaction device is activated. This occurs at the latest at a predefined time before the start of the next scan time. The predefined time is defined so that: the system is operable during the next scan time without the risk of discharging a large amount of helium during or before the next MRI scan. Therefore, the standard operating time starts early enough to enable the temperature of the cooling system and / or the magnet to be cooled by the cooling system to be restored. For example, the predefined time before the start of the next scan time is between 1.5 hours and 3 hours, such as 2 hours, before the next scan time. Preferably, the standard operating mode 5 is started so that the standard operating mode 5 runs during the time slot 8 associated with the level of the highest power availability. To achieve this, in the previous step 103, at least one time slot 8, 81 is preferably determined accordingly to ensure that when the time slot 8 with the level of the highest power availability starts, the energy saving mode 4 ends just in time.

[0039] Figure 2A diagram showing the power of a liquefaction device of a helium cooling system of a magnetic resonance imaging system 11 fed over time when a method according to an embodiment of the invention is applied is shown. In this embodiment, the power is turned on, for example, to a maximum power setting, or the power is turned off. First, the liquefaction device is operated in a partial energy-saving mode 6. This may be, for example, during the early hours of the night. In the partial energy-saving mode 6, the power of the liquefaction device is alternately turned on and off. In this example, the off time is about 1.5 times the on time. However, alternatively, another ratio may be applied. Optionally, alternatively, the liquefaction may be operated at least temporarily in a standard operating mode 5. During or before this time, the first steps 201 to 203 of the method according to the invention are performed. That is, in the first step 201, a first schedule including the scanning time of the magnetic resonance imaging system 11 and a second schedule including a plurality of time slots 8 are provided. Each time slot 8 is associated with one of at least two different levels of power availability. Although in this example, the time slots 8 are drawn at approximately equal intervals, the time slots 8 may also be different intervals according to the time development of power availability. A further step 202 comprises: determining a shutdown time when the system is not used for scanning based on a first schedule. A further step 203 comprises: determining at least one time slot 81 within the shutdown time that is not associated with the level of the highest power availability based on a second schedule. This may be, for example, later in the night. In this example, the at least one time slot 81 comprises three time slots 81. In step 204, when the first time slot in the determined time slots 81 begins, energy saving mode 4 is activated by shutting down the power of the liquefaction device. Therefore, energy saving mode 4 is a shutdown mode 41 in which the cooling system does not function. The liquefaction device is shut down for no more than a predefined amount of time, which is defined so that a large amount of helium is avoided. For example, the liquefaction device can be shut down for up to 3 hours. In this example, this corresponds to three selected time slots 81. For example, in the partial energy saving mode 6, the cooling system may consume an average of about 4kW. Therefore, in this example, 12kWh can be saved during energy saving mode 4. In step 205, after energy saving mode 4 ends at the end of the last corresponding time slot 81, standard operation mode 5 is activated. The activation of the standard operating mode 5 and the activation of the energy saving mode 4 are timed such that the standard operating mode 5 runs during the time slot 8 associated with a higher level of power availability than the time slot 81 during which the energy saving mode 4 is activated. During this recovery step 205, the helium cooling system is recovered without venting helium until the scanner of the magnetic resonance imaging system 11 is ready for operation in step 206. During scanning, the standard operating mode 5 is also active.

[0040] Figure 3A diagram is shown of the power fed to the liquefaction device of the helium cooling system of the magnetic resonance imaging system 11 over time when a method according to another embodiment of the invention is applied. In this embodiment, the power is turned on, for example to the maximum power setting, or the power is turned off. First, the liquefaction device is operated in the partial energy-saving mode 6. In the partial energy-saving mode 6, the power of the liquefaction device is alternately turned on and off. In this example, the off time is approximately twice the on time. However, another ratio may be applied alternatively. During or before this time, the first steps 301 to 303 of the method according to the invention are performed. These steps 301 to 303 may, for example, be similar to the steps described with regard to Figure 2 304, when the determined time slot 81 starts, the energy-saving mode 4 is activated. The energy-saving mode 4 is a staggered mode 42 that alternately turns on and off the liquefaction device. In this example, the off time is about 4.5 times longer than the on time. The energy-saving mode 4 lasts for no more than a predefined amount of time, which is defined so as to avoid a large amount of helium emissions. The power availability can be relatively constant in this time slot 81. For example, the time slot 81 can be associated with the lowest power availability during the night when power is obtained from solar panels, for example. In step 305, after the energy-saving mode 4 ends, here at the end of the corresponding time slot 81, the standard operation mode 5 is activated. The activation of the standard operation mode 5 and the activation of the energy-saving mode 4 are timed so that the standard operation mode 5 runs during the time slot 8 associated with a higher level of power availability than the time slot 81 in which the energy-saving mode 4 is activated. During this recovery step 305, the helium cooling system is recovered without venting the helium until the scanner of the magnetic resonance imaging system 11 is ready for operation in step 306. During the scan, the standard operating mode 5 is also active.

[0041] Figure 4A magnetic resonance imaging system 11 according to an embodiment of the invention is shown. The magnetic resonance imaging system 11 comprises a liquefaction device (not shown) which is at least partially inside a gantry 12. The liquefaction device is configured to have a standard operation mode 5 in which the liquefaction device is supplied with an amount of power that allows a magnetic resonance scan to be performed without discharging a large amount of helium, and an energy saving mode 4 in which the liquefaction device is supplied with a lower average amount of power than during the standard operation mode 5. The magnetic resonance imaging system 11 comprises a control unit 13, and the magnetic resonance imaging system 11 is configured to activate the energy saving mode 4 via the control unit 13 during time slots 8, 81 in which there is no scheduled scan and the availability of power is reduced, and to activate the standard operation mode 5 at the latest at a predefined time before the start of the next scheduled scan, so that during or before the next scan time, the system is operable during the next scan without the risk of discharging a large amount of helium.

Claims

1. A method for operating a liquid helium cooling system of a magnetic resonance imaging system (11), the liquid helium cooling system comprising a helium liquefaction device, such as a cold head, the liquefaction device having a standard operating mode (5), the standard operating mode (5) being adapted to allow a magnetic resonance scan to be performed without exhausting a large amount of helium, the method comprising the following steps: (a) providing a first schedule including scanning times of the magnetic resonance imaging system (11) and a second schedule including a plurality of time slots (8), each time slot (8) being associated with one of at least two different levels of power availability, the at least two different levels of power availability including a level of highest power availability; (b) determining a shutdown time when the system is not used for scanning based on the first schedule; (c) determining, based on the second schedule, at least one time slot (8, 81) within the off-time that is not associated with the level of the highest power availability, wherein the at least one time slot (8, 81) is preferably associated with the lowest level of power availability among all time slots (8) within the off-time; (d) activating an energy-saving mode (4) during the determined at least one time slot (8, 81), in which energy-saving mode the liquefaction plant is supplied with a lower average amount of electricity than during the standard operating mode (5); (e) activating the standard operating mode (5) of the liquefaction device at the latest at a predefined time before the start of a next scanning time, so that the system can be operated during or before the next scanning time without the risk of discharging large amounts of helium.

2. The method according to claim 1, in, The amount of electrical power per time unit supplied to the helium liquefaction plant during the energy-saving mode (4) is on average at least three times lower, preferably at least four times lower, than during the standard operating mode (5).

3. A method according to any one of the preceding claims, wherein: Activation of the standard operating mode (5) and activation of the energy saving mode (4) are timed so that: the standard operating mode (5) operates during time slots (8) associated with a higher level of power availability than time slots (8, 81) when the energy saving mode (4) is activated, preferably so that the standard operating mode (5) operates during time slots (8) associated with the highest level of power availability.

4. The method according to any one of the preceding claims, in, The energy saving mode (4) is: - a shut-down mode (41), in which the liquefaction device is shut down, or - a staggered mode (42), in which the liquefaction device is switched on and off alternately, so that the off time is at least three times longer than the on time.

5. The method according to claim 4, in, The liquefaction plant is shut down for no more than a predefined amount of time, wherein the predefined amount of time is defined such that a large discharge of helium is avoided.

6. The method according to claim 4 or 5, in, The liquefaction plant is shut down for at most 4 hours, preferably at most 3 hours.

7. The method according to any one of the preceding claims, in, The levels of power availability are based on an expected price of power during a corresponding time slot (8) and / or an expected amount of power production during the corresponding time slot (8), the lowest level of power availability being associated with a high expected price and / or a low expected amount of power production.

8. The method according to any one of the preceding claims, in, The second schedule is dynamically updated based on the received power availability data.

9. The method according to claim 8, in, The received power availability data may include a weather forecast or data derived from a weather forecast.

10. The method according to any one of the preceding claims, in, The first timetable is dynamically updated based on a schedule of magnetic resonance scans, in particular a user input schedule.

11. The method according to any one of the preceding claims, in, The predefined time before the start of the next scanning time is between 0.5 hours and 5 hours, preferably between 1 hour and 4 hours, more preferably between 1.5 hours and 3 hours.

12. The method according to any one of the preceding claims, in, During the off time when the system is neither operating in the energy saving mode (4) nor in the standard operating mode (5), the partial energy saving mode (6) is active, Wherein, in the partial energy-saving mode (6), the liquefaction device is supplied with a lower average amount of electricity than during the standard operation mode (5), and is supplied with a higher average amount of electricity than during the energy-saving mode (4).

13. The method according to claim 12, in, During the partial energy-saving mode (6), the liquefaction device is alternately switched on and off, so that the off time is at least as long as the on time and at most 2.5 times longer than the on time.

14. A computer program comprising instructions which, when executed by a control unit of a magnetic resonance imaging system (11) or a control unit of a liquid helium cooling system of a magnetic resonance imaging system (11), cause the control unit to perform the steps of the method according to any one of claims 1 to 13.

15. A magnetic resonance imaging system (11) comprising a helium liquefaction device, such as a cold head, in, The liquefaction device is configured to have a standard operation mode (5) and an energy-saving mode (4), in which the standard operation mode (5) is supplied with an amount of power that allows magnetic resonance scanning to be performed without discharging a large amount of helium, and in which the energy-saving mode (4) is supplied with an average amount of power lower than during the standard operation mode (5), Wherein, the system is configured as follows: activating the energy saving mode (4) during time slots (8, 81) when there is no scheduled scan and the availability of power is reduced, and activating the standard operating mode (5) at the latest at a predefined time before the start of the next scheduled scan, so that during or before the next scan time, the system is operable during the next scan without the risk of venting large amounts of helium, Therein, the system is particularly configured to perform the method according to any one of claims 1 to 13.

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