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

Abstract

To provide a method for operating a liquid helium cooling system of a magnetic resonance imaging system.SOLUTION: A method for operating a liquid helium cooling system of a magnetic resonance imaging system, comprises the following steps:(a) providing a first timetable including scan times and a second timetable including a plurality of time slots (8) associated with one of at least two different levels of electrical power availability; (b) determining off-times when the system is not used for scanning based on the first timetable; (c) based on the second timetable, determining at least one time slot (8 and 81) within the off-times that is not associated with the level of highest electrical power availability; (d) activating a power-saving mode (4) during the determined at least one time slot (8 and 81); and (e) activating a standard operating mode of liquefying means at the latest at a prescribed time before the beginning of the next scan time.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for operating a liquid helium cooling system of a magnetic resonance imaging system, and to a corresponding computer program and magnetic resonance imaging system. Regardless of grammatical usage of the term, individuals of male, female, or other gender identities are included within the term. [Background technology]

[0002] Magnetic resonance imaging (MRI) scanners are energy intensive. For example, the energy consumption of a typical MRI scanner can be as much as 70 MWh per year. One major factor is the energy required to cool the MRI scanner, specifically the magnets and coils of the scanner. To generate the magnetic fields required for MRI scanning, the magnetic fields are typically in the range of up to 3 Tesla, and sometimes even higher, and require superconductivity, which at the same time requires low temperatures. For this purpose, liquid helium cooling is applied, the temperature of which is approximately 4 Kelvin. Due to the absorption of heat, the liquid helium evaporates over time into the gas phase. This effect of helium evaporation is usually significant when the MRI scanner is actively used, i.e. during scanning, due to the heat generated when the scanner is operated. However, even when the scanner is not in use, the helium usually evaporates little by little over time. To counter this effect of helium evaporation, MR scanners are generally equipped with a helium liquefaction means, such as a cold head, which recondenses the evaporated helium back into a liquid state. Since helium requires a much larger space in the gas phase than in the liquid phase (approximately 750 times larger under standard conditions), if there is too much gaseous helium, the system usually has to vent some of the helium. This is undesirable, as resupplying additional helium is quite expensive and requires unscheduled maintenance interruptions of the scanner. Furthermore, if there is too little helium in the liquid phase, the cooling capacity will not be sufficient and the MRI system may be damaged, for example by quenching the magnet coils. Therefore, it is generally essential to ensure that the helium remains in the liquid phase.

[0003] On the other hand, the above-mentioned energy consumption of such cooling systems can be problematic, especially when it comes to the application of renewable energies such as photovoltaic and wind energy, which are not always available to the same extent. Summary of the Invention

[0004] In view of the above, it is an object of the present invention to provide a means for ensuring reliable operation of a magnetic resonance imaging system using a cooling system, while at the same time reducing energy consumption, at least temporarily, and / or adapting to the challenge that renewable energies are not always available to the same extent.

[0005] This object is met or overcome by a method according to claim 1, a computer program according to claim 14 and a magnetic resonance imaging system according to claim 15. Further features and advantages are disclosed by the dependent claims, the detailed description and the accompanying drawings.

[0006] According to a first aspect of the present invention, there is provided a method of operating a liquid helium cooling system of a magnetic resonance imaging system, the liquid helium cooling system including helium liquefaction means, such as a coldhead, the liquefaction means having a standard mode of operation configured to enable a magnetic resonance scan to be performed without venting a significant amount of helium, the method comprising the steps of: (a) providing a first time table including a system scan time and a second time table including a plurality of time slots, each time slot being associated with one of at least two different power availability levels including a highest power availability level; (b) determining off-times during which the system is not used for scanning based on the first timetable; (c) determining, based on a second timetable, at least one time slot in the off-time that is not associated with a highest level of power availability, the at least one time slot being preferably associated with a lowest level of power availability among all time slots in the off-time; (d) activating a power saving mode during the determined at least one time slot, in which the liquefaction means is powered with a lower average amount of power than during a standard mode of operation; (e) activating the standard operating mode of the liquefaction means at least a predetermined time before the start of the next scan period so that the system is capable of operating at the next scan period without risk of venting significant amounts of helium at or before the next scan period.

[0007] Preferably, both off-time and power availability are taken into account when determining at least one time slot for activating the power saving mode. That is, the method is used to adapt the power usage according to the first time table of scan times but also according to the availability of power. For this purpose, two time tables are used, namely a first time table and a second time table. In this context, the time table can be understood as relating to the time when the MRI system should be used and the availability of different powers, for example during a day or preferably over a day. The time slots of the second time table are very small, optionally infinitely small. Very small time slots can be used to represent an essentially continuous change in power availability. In this case, the power saving mode is activated in some time slots. On the other hand, at least some of the time slots may represent a longer period, such as one or several hours. Time slots representing a larger amount of time are useful when the power availability is constant or nearly constant over this long period, for example when the power price is set to vary during the hours of the day or when a solar cell provides a relatively constant amount of power during certain hours. The availability of electricity can vary, for example, during a day, a week, or a year. For example, the availability of electricity can be linked to the price of electricity, such as a different price at certain times during the night or in the evening compared to other times of the day. The availability of electricity can also be linked to power generation methods, such as solar cells that generate more electricity on sunny days, or windmills depending on the wind strength. The method allows to significantly reduce the energy consumption during the time when the power saving mode is activated. Thus, the method can be used to advantage to adapt to the problem of renewable energy not being available to the same extent all the time. For example, the power saving mode may be activated during the nighttime hours when there is no sunlight, and the standard operating mode may be activated after or with sunrise and before an examination is performed with the MRI system. In this way, when the system relies on renewable energy, the method allows to reduce the number of batteries or other energy storage devices required for operation at night.For example, the operation of the MRI system for the examination can be started about 2 to 3 hours after sunrise. Furthermore, in the method according to the present invention, the overall energy consumption can be reduced by a power saving mode that requires less energy.

[0008] By reactivating the standard operating mode at a predetermined time before the start of the next scan time, it can be ensured that no venting of helium occurs before or when using the MRI system. To this end, the predetermined time is defined such that the system can be operational at the next scan time without risking venting significant amounts of helium during or before the next MRI scan. This time that the system operates in the standard operating mode can be considered a recovery period during which the magnet of the MRI system cools down to operating temperature and / or is ready to be operational again.

[0009] According to one aspect, the activation of the standard operation mode and the activation of the power saving mode are timed such that the standard operation mode is performed in a time slot associated with a higher level of power availability than the time slot in which the power saving mode is activated, preferably in a time slot associated with the highest level of power availability. Preferably, the level of power availability is taken into account in step (c) of the method, i.e. when determining at least one time slot in the off-time that is not associated with the highest level of power availability. This at least one time slot may be determined such that the activation of the standard operation mode occurs in a time slot of higher power availability, preferably the highest power availability. Thus, preferably, the power availability when the standard operation mode is activated at a given time can be taken into account. This aspect ensures that sufficient and / or relatively cheap power is available for the standard operation mode, thereby enabling a more efficient use of energy.

[0010] Optionally, the predetermined time before the start of the scan time is adjusted depending on the next scheduled scan, and in particular depending on the expected heating of the next scheduled scan, for example, the predetermined time may be shortened if less heating is expected.

[0011] The liquefaction means is usually configured to recondense the helium gas or helium vapor back into a liquid state. In particular, part of the helium is in gas phase after cooling the MRI magnet. A common liquefaction means is a coldhead as known in the state of the art. A coldhead may also be called or classified as a cryocooler. The helium is contained in a cryostat. Typically, the superconducting wire material of the MRI coil is immersed in a bath of liquid helium. The power saving mode can therefore be a mode in which the liquefaction means operates at low power or in which the liquefaction means is switched off. That is to say, the power saving mode is beneficial in that a lower average amount of power is required than in the standard operating mode. The power saving mode may be considered as a controlled suspension of the liquefaction means or a controlled reduction in operation of the liquefaction means. In the power saving mode, the amount of gaseous helium may increase, especially due to ambient heat. The power saving mode is therefore not configured to be sufficient to maintain (most of) the helium in liquid phase for long periods of time, such as for periods of more than 5 hours. Thus, for example, the amount of gaseous helium may gradually increase during the power saving mode. If the system is operated at this point, the amount of gaseous helium may be very high and some of the helium may have to be vented. The amount of gaseous helium is reduced from this again in the standard operating mode, so that the operation of the system can start without the need to vent helium when the MRI system is operated. The standard operating mode is particularly adapted to be able to carry out a magnetic resonance scan without venting a significant amount of helium. This is understood to mean that the cooling capacity of the liquefaction means in the standard operating mode is so strong that it is possible to return sufficient gaseous helium to the liquid phase during a magnetic resonance scan, making it unnecessary to vent some of the helium. The standard operating mode is therefore particularly configured to keep (most of) the helium in the liquid phase over time. In this context, "without venting a significant amount of helium" is understood to mean that only a very small amount of helium may be lost over time. A small loss of helium is unavoidable due to the properties of helium, in particular the very small diameter of the helium atoms.According to one embodiment, the amount of power per unit time supplied to the helium liquefaction means during the power saving mode is on average at least three times lower, preferably at least four times lower, than during the standard operating mode. Low power consumption can be achieved, for example, by switching off the liquefaction means temporarily or continuously during the power saving mode. Alternatively, low power consumption can be achieved by providing a continuously low amount of power.

[0012] In an advantageous manner, at least one time slot is determined that is not associated with the highest level of power availability, during which the power saving mode is activated. Preferably, the at least one time slot is selected such that there remains sufficient time for the standard operation mode to be activated at the latest at a predefined time before the start of the next scan period. Thus, the suitable determination of the at least one time slot is preferably performed as early as by taking into account the time required to activate the standard operation mode in step (e). To this end, in some circumstances it may be advantageous not to select the time slot with the lowest power availability for the power saving mode, since in some circumstances there may not be sufficient time thereafter to activate the standard mode in a timely manner before the operation of the MRI system is scheduled. On the other hand, if possible, applying the power saving mode is particularly advantageous in the time slot with the lowest power availability among all the time slots.

[0013] According to one embodiment, the power saving mode is a switch-off mode in which the liquefaction means is switched off or an interleaved mode in which the liquefaction means is alternately switched on and off such that the switch-off time is at least three times longer than the switch-on time. The power saving mode as a switch-off mode is advantageous because it allows to save a larger amount of energy during the power saving mode. This is particularly beneficial when the power saving mode is only applicable in a relatively short time slot. On the other hand, the interleaved mode is particularly advantageous when a longer time slot is available. That is to say, the interleaved mode allows to keep the power saving mode activated for a longer time before venting of helium occurs or is required. Additionally and / or alternatively, the interleaved mode is also particularly useful when the time before starting the first scan of the MRI system after activating the standard operation mode is rather short. This is the case, for example, when the scan is supposed to start early in the day and high power availability starts only a little before that, for example because solar power energy is only available after sunrise. In this case, the interleaved mode allows to reduce the amount of helium in the gas phase when the standard operation mode is activated. Thus, in this particular case, when using the interleaved mode, which comes at the expense of lower energy savings, the recovery time is shorter compared to a complete switch-off. Both the switch-off and interleaved modes are beneficial as they help to significantly reduce the energy consumption of the cooling system and thus of the magnetic resonance imaging system. It has been found that in the interleaved mode, the switch-off time is at least three times longer than the switch-on time, which is a good ratio for efficient energy saving while maintaining some of the advantages of the interleaved mode. As a result, a ratio significantly greater than three would essentially make the interleaved mode closer to the switch-off mode. The interleaved mode is preferably configured such that the switch-on time is of the order of one minute or several minutes, preferably between 1 and 20 minutes, more preferably between 2 and 8 minutes, even more preferably between 2 and 6 minutes.Correspondingly, the switch-off time is particularly preferably in the order of three times the switch-on time or more, for example in the range of 6 to 18 minutes or more. These time periods have been found to be particularly advantageous both in terms of ensuring efficient energy savings and in particular in terms of preventing long helium vents.

[0014] According to one embodiment, the liquefaction means is not switched off for longer than a predetermined time, the predetermined time being defined such that a substantial venting of helium is avoided. The predetermined time depends on the MRI system and / or its venting settings. For example, the liquefaction means is preferably switched off for a maximum of 4 hours, preferably for a maximum of 3 hours. In tests with real MRI systems, it has been found that the time until venting begins ranges from 4 hours 3 minutes to 5 hours 21 minutes, depending on the specific venting conditions of a particular system. The tests were carried out by keeping the MRI magnet in a stable position and switching off the cold head. This measures the time until the magnet vents. This time is defined as the time when the relief valve opens and the magnet starts to release helium gas into the collection line. Based on these tests, a time of up to 4 hours is feasible. A maximum of up to 3 hours is more useful to provide a safety margin, which allows for consideration of technical problems that may occur without necessarily directly resulting in a venting of helium, for example. It has been shown that a single 3-hour power save mode can save approximately 12 kWh on commercially available MRI systems, which translates into a savings of 4 kW per hour by switching the cold head and helium compressor. Savings may vary from system to system.

[0015] According to one aspect, the level of power availability is based on the expected price of power during the corresponding time slot and / or the expected amount of power generation during the corresponding time slot, with the lowest level of power availability being associated with a higher expected price and / or a lower expected amount of power generation. The expected amount of power generation depends on the productivity of the renewable energy devices, e.g., solar cells and wind turbines. For example, the power saving mode can be activated towards the end of the night, e.g., 2-3 hours before sunrise, and the standard operation mode can be activated after sunrise and well before the planned start of the scan by the MRI system, e.g., 2 hours. The expected price can vary, e.g., based on the user's power contract. For example, the user may have a contract for cheaper energy during the night than during the day. For example, the power saving mode is initiated towards the end of the high cost hours, and the standard operation mode is activated during the low cost hours.

[0016] According to one embodiment, the second timetable is dynamically updated based on the received power availability data. The power availability data includes information, in particular forecasts and / or estimates, on the availability of renewable energies and / or on energy prices. For example, the received power availability data includes weather forecasts or data derived from weather forecasts. Additionally and / or alternatively, the power availability data includes sunshine hours. The weather forecast may include information on the occurrence of clouds in the sky above the solar panels. The weather forecast may include a forecast of wind speeds at the location of the wind turbines used to power the MRI system. Advantageously, the dynamic update of the timetable allows the timing of the power saving modes to be adjusted to actual current conditions and / or upcoming estimated conditions.

[0017] According to one embodiment, the first timetable is dynamically updated based on the schedule of the magnetic resonance scan, in particular the schedule input by the user. This has the advantage that the timing of the power saving mode and the standard operation mode are dynamically adjusted, in particular taking into account sudden changes. For example, the first timetable is updated in the evening or night based on the schedule of the next day, and the power saving mode and the standard operation mode for this night are set according to the updated first timetable. For example, in the case of a particularly early start of use of the MRI system on the next day, the power saving mode can be shortened compared to other nights. In this case, the time that the standard operation mode has to be activated before the scan can start can also be shortened because the power saving mode has been activated for a shorter time and the amount of gaseous helium is smaller.

[0018] According to one embodiment, the predetermined time before starting the next scan period is 0.5 to 5 hours, preferably 1 to 4 hours, more preferably 1.5 to 3 hours. A predetermined time in the range of 0.5 to 5 hours is sufficient to make the system operational again. The time required usually depends on the details of the system, in particular the cooling system and the heat generation during the scan. Thus, the predetermined time may vary from system to system. A predetermined time in the range of 1 to 4 hours is applicable to many common systems. A predetermined time of 1.5 to 3 hours has been found to be particularly advantageous for at least some commercially available systems, particularly 1.5 Tesla systems.

[0019] According to one embodiment, a partial power saving mode is operated during off-times when neither the power saving mode nor the standard operation mode is operating, in which the liquefying means is supplied with a lower average amount of power than during the standard operation mode and a higher average amount of power than during the power saving mode. Advantageously, the power saving mode saves energy. In particular, the partial power saving mode may be used whenever a scan is not scheduled and is not a time slot in which the power saving mode or the standard operation mode following the power saving mode until the cooling system is restored is activated. The partial power saving mode is useful as an addition to the power saving mode, for example, when there is no suitable time slot for the standard operation mode to restore the cooling system before the next scan. The partial power saving mode is preferably configured not to vent helium unless the scanner is operating. The partial power saving mode includes a switch-off time and a switch-on time. For example, the partial power saving mode is configured corresponding to the interleaved mode described herein with respect to the power saving mode. For example, in the partial power saving mode, the liquefying means is alternately switched on and off such that the switch-off time is less than three times the switch-on time. According to one embodiment, during the partial power saving mode the liquefaction means is alternately switched on and off such that the switch-off time is at least as long as the switch-on time and at most 2.5 times the switch-on time. It has been found that a partial power saving mode with such relative times can, on the one hand, provide an effective way to save power and, on the other hand, ensures that no significant amount of helium is expelled under normal conditions. For example, the switch-off time is in the range of 5 to 12 minutes, preferably 6 to 10 minutes. Preferably, the partial power saving mode comprises a switch-off time that is at least 1.5 times as long as the switch-on time and at most 2.5 times the switch-on time. For example, the switch-off time can be twice as long as the switch-on time, such as a switch-off time of 8 minutes and a switch-on time of 4 minutes. Alternatively, the partial power saving mode comprises, for example, operating the liquefaction means with an essentially constant low power consumption.

[0020] According to another 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 carry out the steps of the method described herein. All features and advantages of the method apply to the computer program and vice versa.

[0021] According to another aspect of the invention, there is provided a magnetic resonance imaging system including a helium liquefaction means, such as a cold head, configured to have a standard operation mode and a power saving mode, in which in the standard operation mode the liquefaction means is provided with an amount of power such that a magnetic resonance scan can be performed without venting a significant amount of helium, and in the power saving mode the liquefaction means is provided with a lower average amount of power than during the standard operation mode. The system is configured to activate the power saving mode in time slots where there are no scheduled scans and where power availability is reduced, and to activate the standard operation mode at the latest a predefined time before the start of the next scheduled scan, so that the system can operate at the next scan without risk of venting a significant amount of helium at or before the next scan time. The system may in particular be configured to carry out the method described herein. All the features and advantages of the method and computer program apply to the magnetic resonance imaging system and vice versa. The system may comprise a control unit configured to control the liquefaction means and to activate the multiple modes of the liquefaction means.

[0022] The aspects described herein can be combined with each other unless otherwise stated. [Brief description of the drawings]

[0023] The accompanying drawings illustrate various embodiments and methods of various aspects of the present invention. [Figure 1] 2 illustrates a flow diagram of a method for operating a liquid helium cooling system of a magnetic resonance imaging system according to an embodiment of the present invention. [Diagram 2] 3 shows a diagram of the power supplied to the liquefaction means of a helium cooling system of a magnetic resonance imaging system during the application of a method according to an embodiment of the invention. [Diagram 3] 4 shows a diagram of the power supplied to the liquefaction means of a helium cooling system of a magnetic resonance imaging system during the application of a method according to another embodiment of the invention; [Figure 4] 1 illustrates a magnetic resonance imaging system according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] FIG. 1 shows a flow diagram 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. In a first step 101, a first timetable and a second timetable are provided. The first timetable includes a scanning time of the magnetic resonance imaging system 11. The second timetable includes a plurality of time slots 8, each time slot 8 being associated with one of at least two different levels of power availability. The level of power availability is based on a forecast price of power during the corresponding time slot 8. Additionally or alternatively, the level of power availability is based on a forecast amount of power generation during the corresponding time slot 8. The second timetable is dynamically updated based on the received power availability data. That is, a current weather forecast is used to update the second timetable taking into account the weather forecast to determine, for example, the forecast amount of power generation generated by wind turbines, solar panels, etc. Dynamically updating the second timetable can provide a second timetable that more accurately predicts the actual power availability of power generation.

[0025] In the next step 102, an off-time is determined based on the first timetable, during which the system is not used for scanning.

[0026] In a next step 103, based on the second timetable, at least one time slot 8, 81 is determined within the off-time, which time slot is not associated with the highest power availability level. If possible, at least one time slot 81 is preferably associated with the lowest power availability level among all time slots 8 within the off-time. The lowest power availability level is in particular associated with a high expected price and / or a low expected generation amount. Preferably, the at least one time slot 8, 81 is further determined later in step 105 such that the standard operation mode 5 is activated in the time slot 8 associated with a higher power availability level compared to the time slot 8, 81 in which the power saving mode 4 is activated in step 104.

[0027] In step 104, a power saving mode 4 is activated during at least one determined time slot 8, 81. In the power saving mode 4, the liquefaction means of the liquid cooling system, such as a cold head, are powered with a lower average amount of power compared to the standard operating mode 5. The standard operating mode 5 is configured to allow magnetic resonance scanning to be performed without venting significant amounts of helium. Preferably, the amount of power per unit time supplied to the helium liquefaction means in the power saving mode 4 is on average at least three times lower than in the standard operating mode 5. The power saving mode 4 is a mode in which the liquefaction means only operates in intervals or is completely switched off. The power saving mode 4 is configured such that it is not sufficient to keep the helium of the cooling system in liquid phase for a long period of time. In particular, the amount of gaseous helium may be gradually increased during the power saving mode 4.

[0028] In a next step 105, the standard operating mode 5 of the liquefaction means is activated before the start of a scan by the magnetic resonance imaging system 11. This occurs at the latest a predefined time before the start of the next scan time. This predefined time is defined such that the system is operable at the next scan time without the risk of venting significant amounts of helium at or before the next MRI scan. The standard operating time is therefore started early enough to allow recovery of the cooling system and / or recovery of the temperature of the magnet cooled by the cooling system. For example, the predefined time before the start of the next scan time is 1.5 to 3 hours, for example 2 hours, before the next scan time. Preferably, the standard operating mode 5 is started such that it is activated in a timeslot 8 associated with the highest level of power availability. To achieve this, in the previous step 103, at least one timeslot 8, 81 is preferably determined accordingly to ensure that the power saving mode 4 is correctly terminated when the timeslot 8 with the highest level of power availability begins.

[0029] FIG. 2 shows a diagram of the power supplied to the liquefaction means of a helium cooling system of a magnetic resonance imaging system 11 during the period during which a method according to an embodiment of the invention is applied. In this embodiment, the power is either on (for example at maximum power setting) or off. Initially, the liquefaction means is operated in a partial power saving mode 6. This is for example during the early hours of the evening. In the partial power saving mode 6, the power of the liquefaction means is alternately switched on and off. In this example, the switch-off time is about 1.5 times the length of the switch-on time. However, optionally, another ratio may be applied. Optionally, the liquefaction may instead be operated at least temporarily in a standard operating mode 5. During or before this time, a first step 201-203 of the method according to the invention is performed: in a first step 201, a first timetable is provided which includes the scanning times of the magnetic resonance imaging system 11 and a second timetable which includes a number of time slots 8. Each time slot 8 is associated with one of at least two different levels of power availability. Although the time slots 8 are depicted in this example at approximately equal intervals, they may be differently spaced depending on the time evolution of the power availability. A next step 202 involves determining, based on a first time table, an off-time during which the system is not used for scanning. A next step 203 involves determining, based on a second time table, at least one time slot 81 in the off-time that is not associated with a highest level of power availability. This may be, for example, late at night. In this example, the at least one time slot 81 comprises three time slots 81. When the first of the determined time slots 81 begins, in step 204, a power saving mode 4 is activated by switching off the power of the liquefaction means. That is to say, the power saving mode 4 is a switch-off mode 41 in which the cooling system is not operational. The liquefaction means is not switched off for longer than a defined time period (time window) such that a vent of a significant amount of helium is avoided. For example, the liquefaction means is switched off for a maximum of three hours. In this example this corresponds to three selected time slots 81.For example, in partial power saving mode 6, the cooling system may consume about 4 kW on average. Thus, in this example, 12 kWh can be saved during power saving mode 4. After power saving mode 4 ends at the end of the last corresponding timeslot 81, standard operation mode 5 is activated in step 205. The activation of standard operation mode 5 and the activation of power saving mode 4 are timed such that standard operation mode 5 is activated in a timeslot 8 associated with a higher level of power availability than the timeslot 81 in which power saving mode 4 is activated. During this recovery step 205, the helium cooling system recovers until the scanner of the magnetic resonance imaging system 11 can be immediately operated in step 206 without venting helium. During the scan, standard operation mode 5 is also activated.

[0030] FIG. 3 shows a diagram of the power supplied to the liquefaction means of a helium cooling system of a magnetic resonance imaging system 11 during the application of a method according to another embodiment of the invention. In this example, the power is either on (for example at maximum power setting) or off. Initially, the liquefaction means operates in a partial power saving mode 6. In the partial power saving mode 6, the power of the liquefaction means is alternately switched on and off. In this example, the switch-off time is approximately twice as long as the switch-on time. However, optionally, another ratio may be applied. 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 can be performed, for example, in the same way as described with respect to the embodiment shown in FIG. 2. In this example, one time slot 81 is determined for a power saving mode 4. When the determined time slot 81 starts, the power saving mode 4 is activated in step 304. The power saving mode 4 is an interleaved mode 42 which alternately switches the liquefaction means on and off. In this example, the switch-off time is about 4.5 times longer than the switch-on time. The power saving mode 4 is not longer than a predefined time period defined such that venting of significant amounts of helium is avoided. The power availability may be relatively constant in this timeslot 81. For example, the timeslot 81 is associated with the lowest power availability, such as at night when power is obtained from solar panels. After the power saving mode 4 is ended, in this example at the end of the corresponding timeslot 81, the standard operation mode 5 is activated in step 305. The activation of the standard operation mode 5 and the activation of the power saving 4 mode are timed such that the standard operation mode 5 is activated in the timeslot 8 associated with a higher level of power availability than the timeslot 81 in which the power saving mode 4 is activated. During this recovery step 305, the helium cooling system recovers until the scanner of the magnetic resonance imaging system 11 can be immediately operated in step 306 without venting helium. During the scan, the standard operation mode 5 is also activated.

[0031] 4 shows a magnetic resonance imaging system 11 according to an embodiment of the invention. The magnetic resonance imaging system 11 comprises a liquefaction means (not shown) at least partially inside the gantry 12. The liquefaction means is configured to have a standard operation mode 5 in which the liquefaction means is powered with an amount of power that allows the liquefaction means to perform a magnetic resonance scan without venting a significant amount of helium, and a power saving mode 4 in which the liquefaction means is powered with a lower average amount of power than in the standard operation mode 5. The magnetic resonance imaging system 11 comprises a control unit 13 and is configured to activate the power saving mode 4 in time slots 8, 81 in which there are no scheduled scans and power availability is reduced, and to activate the standard operation mode 5 at the latest a predefined time before the start of the next scheduled scan, such that the system can operate for the next scan without the risk of venting a significant amount of helium at or before the next scan time.

Claims

1. A method of operating a liquid helium cooling system of a magnetic resonance imaging system (11), comprising the steps of: the liquid helium cooling system including means for liquefying helium, such as a coldhead, the liquefying means having a standard mode of operation (5) configured to enable magnetic resonance scanning to be performed without venting significant amounts of helium; Each of the following steps: (a) providing a first timetable including a scan time of the magnetic resonance imaging system (11) and a second timetable including a plurality of time slots (8), each of the time slots (8) being associated with one of at least two different power availability levels including a highest power availability level; (b) determining off-times during which the magnetic resonance imaging system (11) is not used for scanning based on the first timetable; (c) determining, based on the second timetable, at least one time slot (8, 81) within the off-time that is not associated with the highest level of power availability, the at least one time slot (8, 81) being preferably associated with a lowest level of power availability among all time slots (8) within the off-time; (d) activating a power saving mode (4) during said determined at least one time slot (8, 81), in which said liquefaction means is powered with a lower average amount of power than in said standard operating mode (5); (e) activating the standard operating mode (5) of the liquefaction means at least a predetermined time before the start of a next scan period so that the magnetic resonance imaging system (11) can operate at the next scan period without risk of venting significant amounts of helium at or before the next scan period.

2. 2. The method according to claim 1, wherein the amount of power per unit time supplied to the liquefaction means during the power 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. 3. The method according to claim 1 or 2, wherein the activation of the standard operation mode (5) and the activation of the power saving mode (4) are timed such that the standard operation mode (5) is executed in a time slot (8) associated with a higher level of power availability than the time slot (8, 81) in which the power saving mode (4) is activated, preferably such that the standard operation mode (5) is executed in the time slot (8) associated with the highest level of power availability.

4. The power saving mode (4) is a switch-off mode (41) in which the liquefaction means is switched off, or A method according to any one of claims 1 to 3, in an interleaved mode (42) in which the liquefaction means are alternately switched on and off such that the switch-off time is at least three times longer than the switch-on time.

5. 5. A method according to claim 4, wherein the liquefaction means is not switched off for longer than a predetermined time, the predetermined time being defined such that substantial venting of helium is avoided.

6. 6. The method according to claim 4 or 5, wherein the liquefaction means is switched off for a maximum of 4 hours, preferably for a maximum of 3 hours.

7. 7. The method of claim 1, wherein each level of power availability is based on a forecasted price of electricity during a corresponding time slot and / or a forecasted amount of electricity generation during the corresponding time slot, and wherein the lowest level of power availability is associated with a high forecast price and / or a low forecast amount of electricity generation.

8. The method of any one of claims 1 to 7, wherein the second timetable is dynamically updated based on received power availability data.

9. The method of claim 8 , wherein the received power availability data comprises a weather forecast or data derived from a weather forecast.

10. The method according to any one of claims 1 to 9, wherein the first timetable is dynamically updated based on a schedule of magnetic resonance scans, in particular a schedule input by a user.

11. The method according to any one of claims 1 to 10, wherein the predetermined time before starting the next scan period is between 0.5 and 5 hours, preferably between 1 and 4 hours, more preferably between 1.5 and 3 hours.

12. a partial power saving mode (6) is operated during off-time when neither the power saving mode (4) nor the standard operating mode (5) is operating; 12. The method according to any one of claims 1 to 11, wherein in the partial power saving mode (6) the liquefaction means is supplied with a lower average amount of power than in the standard operating mode (5) and a higher average amount of power than in the power saving mode (4).

13. 13. The method according to claim 12, wherein during the partial power saving mode (6) the liquefaction means are alternately switched on and off such that the switch-off time is at least as long as the switch-on time and at most 2.5 times the switch-on time.

14. A computer program including instructions, A computer program comprising instructions, when said program is 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), causing said control unit to perform the steps of the method according to any one of claims 1 to 13.

15. 1. A magnetic resonance imaging system including a means for liquefying helium, such as a coldhead, comprising: the liquefaction means is configured to have a standard mode of operation (5) and a power saving mode (4), in which the liquefaction means is supplied with an amount of power such that a magnetic resonance scan can be performed without venting significant amounts of helium, and in which the liquefaction means is supplied with a lower average amount of power than during the standard mode of operation (5); The system is activating said power saving mode (4) during time slots (8, 81) that are not scheduled for scanning and have reduced power availability; configured to activate said standard operating mode (5) at the latest a predetermined time before the start of a next scheduled scan, such that the system can operate at said next scan without risk of venting significant amounts of helium at or before the next scan time; The system is in particular a magnetic resonance imaging system adapted to carry out the method according to any one of claims 1 to 13.

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