Abstract:
Disclosed is an injection system ( 1 ) for injecting liquids within a strong magnetic field, an alternating magnetic field, and/or a high-frequency electric field to be used with a technical medical system. Said injection system comprises a space ( 2 ) that is shielded from electromagnetic fields with the aid of a shield, an injection device ( 6 ) by means of which liquid to be injected can be dispensed to a patient ( 23 ), a driving mechanism for the injection device ( 6 ), by means of which at least one conveying element ( 11, 12 ) can be displaced for injection purposes, and a control and monitoring unit ( 8 ) which is located outside said space ( 2 ). The inventive injection system prevents interfering electromagnetic fields from being created exclusively by the fact that a hydraulic driving mechanism ( 10 ) is provided whose at least one hydraulic conduit ( 13, 14, 15, 16 ) is guided out of the space ( 2 ) to a pressure generating unit ( 71, 72, 73, 74 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application filed under 35 U.S.C. 371 of International Application No. PCT/EP2005/006809, filed Jun. 23, 2005, which claims priority to German Application No. 10 2004 030 690.7, filed Jun. 24, 2004. 
     FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to an injection system for injecting liquids within a strong magnetic field, an alternating magnetic field and/or a high-frequency electric field, for use with a medical technical system, comprising a room which is shielded from electromagnetic fields by means of a shield, an injection device, by means of which liquid to be injected can be dispensed to a patient, a drive device of the injection device, by means of which at least one conveying element can be displaced, and a control and monitoring unit which is arranged outside the room. 
     Such injection systems are used in particular in the field of magnetic resonance imaging (MRI), in order by injection of a contrast agent to obtain tomograms of internal organs of a patient that allow diagnosis. It is generally known that MRI systems have to be isolated in the best possible way from external electromagnetic fields, so as to obtain an optimal image quality or tomogram quality using the MRI system. This is achieved by shielding from such (sometimes unpredictable) sources of electromagnetic fields the entire room in which the MRI system is located, by means of a copper shield or by means of conductive mesh material. In order to take full advantage of such a shielded room, attempts are also made to shield from the MRI system the injection system and method for injecting liquids, in particular contrast media and saline solution for use with an MRI system, or to move at least part of said system and method outside, since the injection system and method may themselves be sources of electromagnetic fields and may have an adverse effect on image quality. 
     An injection system of the type described in the introduction is known in general for example from U.S. Pat. No. 5,494,036 A. By extensive design measures, this system prevents the image quality from being too greatly affected by electromagnetic radiation. 
     The injection device disclosed in U.S. Pat. No. 5,494,036 A consists of a drive device in the form of two DC electric motors and two cylinder/piston units in the form of syringes. Via a coupling device, which may optionally also be configured in a hydraulic manner but in particular is formed by two drive spindles (flexible drive shaft), the pistons of the syringes are moved forwards and backwards independently of one another by means of the drive spindles. Here, a rotational movement of a threaded and axially fixed drive element of the respective electric motor is converted into a linear forward and backward movement of the piston in the syringe. As a result of the forward and backward movement of the syringe piston, contrast agent and saline solution can be taken up and subsequently dispensed. The syringes can be connected via a Y-shaped adapter and intermediate hoses to a catheter, through which the contrast agent and the saline solution can be injected into the patient during the imaging process. 
     The electric motors are connected via shielded electric cables to a battery which is located inside the room. The electric motors are in particular controlled by an injection monitoring unit arranged in the room, which is connected to a transmitting and receiving device located in the shielded room. The superior control and monitoring unit is connected to a further transmitting and receiving device located outside the room. Via the two transmitting and receiving devices, the control and monitoring unit controls and monitors the injection monitoring unit. 
     One disadvantage of such a system is that, due to the battery, the transmitting and receiving device and in particular the two electric motors and the injection monitoring unit, possible sources of electromagnetic fields are present which could reduce the quality of the MRI image. In order to avoid these potential sources of interference, therefore, electrically non-conductive materials are used and complicated shielding of all the aforementioned objects and their supply lines and connecting lines is carried out. Moreover, for the reasons mentioned above, a sufficient minimum distance of the objects from the magnet must be maintained at all times during the imaging process, which is associated with a certain risk of imperfect images in the event of the specialist personnel inadvertently not providing this minimum distance. Another disadvantage is the weight of the objects, in particular of the battery, and the space requirement thereof. In view of the high costs of shielding the room, the space required for the known system is very expensive. Finally, another disadvantage is the fact that rapid and unhindered access to the patient and/or magnet in the known system is made difficult due to the presence of tripod or carriage structures on which the known system is partially installed, and due to cables running across the floor. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to minimise or entirely overcome all of the disadvantages described above. 
     The object of the invention is achieved by a hydraulic drive device, the at least one hydraulic line of which is guided to a pressure generating unit. 
     Due to the use of hydraulic components in the invention, assemblies used to date such as the battery, electric motors, power cable, injection monitoring unit and the two transmitting and receiving devices inside the room are no longer required. In particular, due to the use of the injection system according to the invention, no undesirable electromagnetic fields are produced since no power and no conductive material has to be used inside the room for the injection system. It is also advantageous that the injection device, in comparison to known injection devices, can be placed directly next to the patient and can even be moved into the MRI tube without adversely affecting the imaging results. As a result, the length of the hose via which the contrast agent is supplied from the injection device to the injection needle can be reduced to an easy-to-handle minimum. Since short hoses can be used, it is possible in particular to make a saving in terms of contrast agent, which must be present without bubbles in the hoses prior to injection. As a result, a considerable reduction in costs can be achieved, and above all patient safety can be further increased due to the fact that it is easier to check the shorter hose connections to ensure they are free of bubbles. 
     Therefore, while according to the invention it is possible in principle to arrange the pressure generating unit either inside or outside the room, placing it outside the room offers particularly good possibilities for avoiding electromagnetic interference effects. If the pressure generating unit is arranged inside the room, it should preferably be located at the greatest possible distance away from the imaging system, for example in a corner of the room at a distance of approx. 3 to 5 m away from the imaging system (e.g. MRI tube). 
     According to the invention, the hydraulic lines guided out of the room to a pressure generating unit and the hydraulic fluid guided in said lines simultaneously serve as a direct or indirect drive means for a conveying element and as an information carrier, in that hydraulic parameters such as pressure, change in pressure, throughflow and other parameters, such as displacement of the hydraulic fluid within the lines and the units connected thereto, can be transmitted from the hydraulic fluid itself to the pressure generating unit and at the latter can be measured outside the room either directly or indirectly, in a manner known per se. The passing of the hydraulic lines through the shielding of the room is important, since outside thereof no particular requirements can be placed on the magnetic properties of any further components of the drive device, in particular the pressure generating unit. Of course, the positive properties of the hydraulic system can in principle also be transferred to a pneumatic system, in which pneumatic instead of hydraulic operating means are used. 
     Since, when using hydraulic lines, the position and potential of electromagnetic fields need not be taken into account, it is also advantageous to use hydraulic lines in other similarly sensitive medical technical systems. By way of example, in the case of a nuclear spin tomography device, the hydraulic line can easily be integrated in a shaft of the MRI device. 
     In a further development of the invention, it is proposed that the pressure generating unit is integrated in the control and monitoring unit, in order to reduce the space requirement and save on double assemblies, such as those used to generate the operating voltage. It is also readily possible to use an electric motor as the drive for the pressure generating unit arranged outside the room, without having to provide special shielding of this electric motor. 
     It is further proposed that the injection system inside the room consists of essentially electrically non-conductive material, in order not to generate any sources of electromagnetic interference inside the room. Another advantage is achieved by deliberately omitting active components of the injection system in the vicinity of the imaging field, along with the associated elimination of risks such as artificial magnetic or electric interference fields which could adversely affect the imaging result. Direct risks from elements of the system that are accelerated by magnetic attraction are completely avoided if these elements are placed outside the room, since no element of the injection system inside the room has to be magnetised. 
     Another advantageous further development of the invention consists in that at least part of the hydraulic lines run in a concealed manner inside the room, in and/or on the floor, the wall and/or the ceiling, in order thus to allow the specialist personnel to enter the shielded room in a safe and flexible manner when working with the medical technical system, in particular with the MRI system. 
     Another further development of the invention may consist in that the hydraulic lines are filled with medically compatible, i.e. biocompatible hydraulic fluid, in order to completely rule out the risk of skin irritation or other possible damage in the event of leakage from the lines and any contact of the hydraulic fluid with the patient. 
     The invention can also advantageously be further developed in that the hydraulic fluid is present in the hydraulic lines under a resting pressure of 0.5 to 2 bar. By continually monitoring the pressure inside or outside the pressure generating unit, it can be ensured that a pressure drop caused by a leakage can be detected immediately. This could be used for example to immediately switch off the entire infusion system for safety reasons. 
     Another embodiment of the invention provides that a pressure transducer can be supplied by two pressure generating units, each of which is connected to a drive. Here, the control and simultaneous measurement of the respective drive parameters of one drive can be used to monitor the respective other drive, since the pressure converted by the pressure transducer directly determines the state of a drive of the other drive, and vice versa. For example, if the drive is configured as an electric motor, the state of the other motor can be determined via a current measurement of the motor, which is almost linearly proportional to the force required to apply the hydraulic pressure, with simultaneous direct measurement of the pressure in the hydraulic line, if the current is also measured and evaluated in the latter. Here the drives may even work in opposition, wherein then of course a certain power difference between the two drives would be necessary for injection purposes. 
     Another advantage is the fact that the pressure transducer comprises a piston/cylinder unit with two working chambers which are separated from one another by a piston coupled to the driven element. The hydraulic principle of the double-acting piston, which is known in principle, can thus also be used in an energy-efficient, cost-effective and easily controllable manner in the medical technical sector. 
     Unlike known injection devices which are placed on tripods or the like and require a considerable amount of space, the very light drive device according to the invention can be fixed directly to the MRI tube, which can usually hold only a little weight, in particular by means of a simple Velcro strip. 
     One advantage of a drive device according to the invention is the fact that it can easily be locked mechanically, for example by means of latching rods, threaded rods or other mechanical embodiments known in principle. For safety reasons, the injection system can in this simple manner be stopped very quickly. 
     The method for injecting liquid into a patient during MRI imaging by an MRI system is also advantageous due to the use of hydraulic parameters such as pressure, change in pressure per unit time, throughflow, volume of liquid, etc. as monitoring and control parameters, since the hydraulic transmission of information to outside means that there is no longer any need for complex electronic monitoring inside the room. 
     It is also advantageous that the pressure generating unit can be controlled by a control signal of a remote control which is located in the room, wherein the remote control transmits control signals in a unidirectional manner and a receiving unit inside the room receives the control signals and feeds them via a supply line into the electrical network, since such devices can be produced in a relatively cost-effective manner. In this case, it is preferably provided that the control signals are infrared signals and transmission takes place through a window of the room or by modulation of the control signals to a network frequency by the receiving unit, which can be inserted into a socket. 
     According to another embodiment of the injection system, it is provided according to the invention that the pressure generating unit is a hydraulic pump or the pressure generating device contains a hydraulic pump. In this way, a single pressure generating unit can be used for a plurality of pressure transducers, wherein the pressurised hydraulic fluid is allocated to the individual pressure transducers as necessary. 
     The allocation of the respectively required volume flow of hydraulic fluid to the individual pressure transducers takes place in a particularly advantageous manner via a respective proportional valve which establishes a connection between the pressure side of the hydraulic pump and the respective pressure transducer. It is particularly advantageous if the proportional valve is connected to both working chambers of the associated pressure transducer. In this way, forward and backward movements of the piston of the respective pressure transducer can be controlled by means of the same proportional valve. 
     In the hydraulic system which is used, there should also be a pressure accumulator arranged on the pressure side of the hydraulic pump and also a pressure sensor, by means of which the pressure on the pressure side of the hydraulic pump can be measured and the hydraulic pump can be switched off in the event of exceeding an upper limit and switched on in the event of falling below a lower limit. In this way, there is always a certain pressure reserve in the hydraulic system, so that even when the pump is idle the adjusting movement of the piston of the pressure transducer can start immediately. As soon as a sufficiently large pressure drop occurs in the hydraulic system, the pump starts to convey fluid, until the upper limit is again reached. 
     The position of the piston of the pressure transducer should preferably be able to be detected by means of a distance sensor assigned thereto, preferably a potentiometer. This distance detection is important for controlling and monitoring the respective injection parameters. 
     In order to prevent the piston of a pressure transducer when stationary from being inadvertently moved by means of external forces, the piston of this pressure transducer should be able to be acted upon by pressure from both sides at the same time in such a way that the piston remains at rest. With such a pressure control system, the precise desired rest position is always ensured regardless of any external forces acting on the piston. 
     In medical technical systems comprising hydraulic components, the aspect of ventilating the hydraulic system in particular represents a not inconsiderable problem. In order to solve this, it is proposed according to the invention that the surfaces of the piston assigned to the working chambers of each piston/cylinder unit are of different size, and there is a bypass cross section, preferably within the piston, through which a small leakage flow always flows in the event of a pressure difference between the working chambers. According to the invention, a small leakage flow is thus deliberately provided through the piston/cylinder units in order to achieve a continuous circulation of the hydraulic fluid. It will be understood that the bypass cross section need only be made large enough that a sufficient build-up of pressure is still possible over the piston to generate the necessary displacement forces. The leakage flow is therefore at most a few percent of the volume flow which is provided when the piston is displaced at maximum speed. 
     Due to the continuous circulation of hydraulic fluid, i.e. circulation in a loop, the fluid also reaches the hydraulic tank. According to the invention, it is further proposed that a surface of the hydraulic fluid in the hydraulic container is acted upon by a negative pressure, preferably a vacuum, which is generated and/or continuously maintained by means of a negative pressure pump. The air bubbles and gas bubbles reaching the hydraulic container are in this way absorbed by the negative pressure and conveyed out of the system by the negative pressure pump. 
     In addition to this continuous ventilation function, it is sometimes also desirable to achieve rapid removal of any gas bubbles by means of a large volume flow guided in a loop. For this purpose, it is provided that, in a ventilation position of the piston of the piston/cylinder unit, which is preferably a dead centre position, there is a ventilation bypass cross section which is larger than the bypass cross section, wherein the ventilation bypass cross section is preferably formed by a widening of the cross section of the cylinder of the piston/cylinder unit. As long as the piston is in the ventilation position, therefore, a large volume flow is set up in the loop and in this way leads to rapid removal of the gas bubbles from the system and transportation into the hydraulic container. For operation of the piston/cylinder unit, the large ventilation bypass cross section is not critical since, during the ventilation, no forces have to be applied via the driven element. However, the ventilation bypass cross section must be limited such that, with freedom of the driven element to external forces, at least the ventilation position can be left again in order automatically to re-close the ventilation bypass cross section, so that correspondingly large forces can again be generated via sufficient pressure differences over the piston. 
     According to one embodiment of the invention, it is proposed that the widening of the cross section of the cylinder in the ventilation position is designed in the form of a recess and/or channel which is located in the inner cylindrical surface of the cylinder and bridges over the axial length of the piston. 
     According to the invention, a method for injecting liquid into a patient during MRI imaging by an MRI system, wherein liquid is injected into a patient by displacing a conveying element by means of a drive device, is characterised by a hydraulic drive device which is acted upon by pressure via hydraulic lines from inside or outside the room. 
     In order to prevent inadvertent displacement of the piston of a pressure transducer when the latter is idle, it is provided that during these times the piston is set to the respective stationary position in order thus to make it insensitive to displacements by external forces. Here, the control parameter used is preferably the piston travel, which is detected via a distance sensor. The adjusting parameters used are advantageously the pressures acting in the two working chambers, wherein these two pressures are always kept above a certain minimum pressure. 
     Moreover, the pressures in all the hydraulic lines of the system according to the invention are always kept above a certain minimum pressure, even at times when the respective piston is stationary, in order to be able to quickly determine any leaks. 
     According to the invention, a hydraulic line can also be used as a control line for actuating specific functions of the injection process. This can advantageously be provided for a start function for dispensing the liquid to the patient, a stop function for stopping the injection system, a filling function for the uptake of liquid by the conveying element and/or a ventilation function for ventilating the conveying element, in that signals are generated for example by mechanical signal transmitters in order to be converted outside the room in a manner depending on the function. 
     In order to permit simple and reliable ventilation of the hydraulic system which is used, it is proposed according to the invention that a certain small volume flow is continuously maintained by a bypass cross section through the piston/cylinder unit, which volume flow is returned to the hydraulic container in which a surface of the hydraulic fluid is acted upon by a negative pressure, preferably by means of a negative pressure pump. In order to allow particularly rapid ventilation, it is provided that the volume flow in a particular position of the piston of the piston/cylinder unit is increased, so that faster circulation of the hydraulic fluid and faster removal of any gas bubbles temporarily takes place. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below with reference to an example of embodiment, in which: 
         FIG. 1  shows a schematic view of a first embodiment of an injection system in conjunction with an MRI system, and 
         FIG. 2  shows a schematic view of a second embodiment of an injection system in conjunction with an MRI system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An injection system  1  shown in  FIG. 1  is arranged inside and outside a room  2  which is shielded from electromagnetic fields. Also located in the room  2  is the MRI device  3  in the form of a tube, in which a patient bed  4  is mounted such that it can be moved in and out. The injection system  1  comprises a remote control  5  located inside the room  2 , from which control signals can be transmitted for controlling an injection device  6 . The injection device  6  also comprises four pressure generating units  71 ,  72 ,  73 ,  74  which are arranged outside the room  2  and are combined to form a pressure generating device  7 , and a control and monitoring unit  8 , wherein these units are combined and connected to one another within a housing  9 . Inside the room  2 , the injection device  6  comprises a drive device  10  and two conveying elements  11 ,  12  connected thereto in the form of cylinder/piston units, in particular syringes. The injection device also includes the hydraulic lines  13 ,  14 ,  15 ,  16  which connect the drive device  10  and the pressure generating units  71 ,  72 ,  73 ,  74  through the shielding of the room  2 . The drive device  10 , the pressure generating unit  7 , the control and monitoring unit  8  and the hydraulic lines  13 ,  14 ,  15 ,  16  form the injection device  6 . 
     The two conveying elements  11 ,  12  are connected to a Y-shaped element  20  via hoses  18 ,  19 . By means of a further hose connection  21 , the Y-shaped element  20  can be connected to an injection needle  22  which is placed in a patient  23  for administering contrast agent  23 ′ during an MRI examination. 
     The aforementioned devices and elements will be explained below in more detail. 
     The pressure generating units  71 ,  72 ,  73 ,  74  convey hydraulic fluid  28  into and out of the drive device  10  located in the room  2 . Here, in each case two pressure generating units are connected by a respective hydraulic line  13 ,  14 ,  15 ,  16  to two pressure transducers  29 ,  30  of the drive device  10 . The pressure generating units  71 ,  72 ,  73 ,  74  of the pressure generating device  7  in each case consist of a drive  31 ,  32 ,  33 ,  34  in the form of an electric motor, which drives a spindle  35 ,  36 ,  37 ,  38 , and a cylinder/piston unit  39 ,  40 ,  41 ,  42 , to the end of which a respective hydraulic line  13 ,  14 ,  15 ,  16  is connected. The cylinder/piston unit  39 ,  40 ,  41 ,  42  consists of the cylinder and a piston which can be displaced in a linear manner therein and which is connected to a threaded piston rod  43 ,  44 ,  45 ,  46 . The piston rod  43 ,  44 ,  45 ,  46 —and thus the piston—is furthermore protected against rotation in that a spring (not shown here) of the cylinder engages in a groove (likewise not shown) of the piston rod  43 ,  44 ,  45 ,  46 . The drive  31 ,  32 ,  33 ,  34  and the cylinder/piston unit  39 ,  40 ,  41 ,  42  are connected in that the spindle  35 ,  36 ,  37 ,  38  is screwed by its internal thread onto the piston rod  43 ,  44 ,  45 ,  46 . By means of an outer toothing on the spindle  35 ,  36 ,  37 ,  38 , the electric motor can engage in the spindle  35 ,  36 ,  37 ,  38  by means of a toothed wheel  47 ,  48 ,  49 ,  50  connected to its shaft, and can rotate said spindle. As a result of the rotation of the spindle  35 ,  36 ,  37 ,  38 , the piston rod  43 ,  44 ,  45 ,  46  and thus the piston undergo a lateral movement in the cylinder. Due to a retaining element  51 ,  52 ,  53 ,  54 , the spindle  35 ,  36 ,  37 ,  38  furthermore cannot move in the lateral direction. The axes of rotation of the spindle  35 ,  36 ,  37 ,  38 , of the toothed wheel  47 ,  48 ,  49 ,  50  and of the shaft moreover point in the same lateral direction as the direction of displacement of the piston rod  43 ,  44 ,  45 ,  46 . 
     The drive device  10  consists of two pressure transducers  29 ,  30 . A pressure transducer  29 ,  30  consists of a cylinder/piston element  55 ,  56  with a laterally movable piston  57 ,  58  and a driven element  59 ,  60  in the form of a piston rod which is connected thereto and is guided outwards. Between the piston  57 ,  58  and the end sides of the cylinder/piston element  55 ,  56 , there are two working chambers A, B which are separated by the piston and are connected by hydraulic connections to the hydraulic lines  13 ,  14 ,  15 ,  16 . Hydraulic fluid  28  which is under a pressure of approximately 0.5 to 2 bar is located in each case in the two chambers A, B, in the hydraulic lines  13 ,  14 ,  15 ,  16  and in the cylinder chambers of the pressure generating units  71 ,  72 ,  73 ,  74 . 
     A latching element  61 ,  62  engages at the free end of the piston rod. The latching element is connected to a piston rod  63 ,  64  of the conveying unit  11 ,  12  in the form of a cylinder/piston unit, in particular a syringe. Connected to the piston rod  63 ,  64  is a piston  65 ,  66  which can be displaced within the syringe. One syringe is used to take up and dispense saline solution  67 , while the other syringe takes up and dispenses the contrast agent  23 ′. 
     The electric motors of the pressure generating unit  7  are supplied with power from the control and monitoring unit  8  via connection lines  75 ,  76 ,  77 ,  78 . Sensor data from sensors (not shown here) are also supplied to the control and monitoring unit  8 . The sensors measure the pressure in all the hydraulic lines  13 ,  14 ,  15 ,  16 , the position of the piston rods  43 ,  44 ,  45 ,  46  of the cylinder/piston units  39 ,  40 ,  41 ,  42 , the temperature of the motors, the temperature of the hydraulic fluid  28  and/or the expansion of sections of the hydraulic lines  13 ,  14 ,  15 ,  16 . The sensors are thus primarily assigned to the pressure generating unit  7  and are installed within the latter. It is not necessary to install the sensors inside the room  2 , since all the aforementioned parameters can also be determined outside the room. 
     Using suitable evaluation software of the control and monitoring unit  8 , the injection system  1  is kept ready for operation, that is to say essentially the motor currents of the electric motors are kept within the required ranges. An intervention on the control and monitoring procedure of the injection system  1  is therefore possible at any time by an operator outside the room  2  by means of suitable input means, such as a PC keyboard (not shown here). It is also possible that a further operator located inside the room  2  controls the injection system  1  via the control and monitoring unit  8  by means of the remote control  5 . The infrared signal which is transmitted by the remote control  5  can be received by means of a receiving unit  79  in the form of an infrared receiver which is arranged inside the room, and can be modulated to the local network voltage. The receiving unit  79  is inserted into a socket inside the room  2 . The network voltage, which is necessary in any case to operate the control and monitoring unit  8  and which is supplied to the latter via a supply line  90 , can be decoded by the control and monitoring unit  8  so that the signals of the remote control  5  can ultimately be further processed by the software of the control and monitoring unit  8 . 
     The second operator also has inside the room the possibility of mechanically intervening directly in the injection process, by actuating a mechanical lock  80 ,  81  in the form of a latching element which is provided on the pressure transducer  29 ,  30 . When actuated, the latching element engages in particular in the respective driven element  59 ,  60  in the form of the piston rod, which for this purpose is provided with a toothing in some sections and prevents the further dispensing of contrast agent  23 ′ or saline solution  67  by the injection device  6 . 
     The dispensing or uptake of liquid by the conveying elements  11 ,  12  is determined exclusively by the pressure ratio between the two working chambers A, B of the pressure generating units  29 ,  30 . 
       FIG. 2  shows an alternative injection system  100  in which, instead of piston/cylinder units for generating pressure for the entire system, a single hydraulic pump  102  is provided which is driven by a motor  103 . The drive device  110 , which again consists of two cylinder/piston units  155 ,  156 , is in principle unchanged compared to the system shown in  FIG. 1 . The two conveying elements in the form of syringes for injecting a contrast agent on the one hand and a saline solution on the other hand are not shown in  FIG. 2  but are also present in this variant of the injection system  100 . The patient bed and the patient himself, located for example within the tubular magnet of the MRI system, are also not shown. 
     Via a suction line  104 , the hydraulic pump  102  sucks hydraulic fluid through a hydraulic filter  105  from a hydraulic container  106  in which the hydraulic fluid is under a positive pressure compared to atmospheric pressure. A filling level sensor  107  detects the level of the hydraulic fluid in the hydraulic container  106 . 
     On the pressure side of the hydraulic pump  102 , there is on the one hand a pressure accumulator  108  which ensures that always a certain volume of pressurised hydraulic fluid can be removed on the pressure side, even when the hydraulic pump  102  is idle. A pressure sensor  108 ′ continuously detects the pressure and ensures that the control and monitoring unit (not shown) receives a switch-on signal in the event of falling below a lower limit and a switch-off signal in the event of exceeding an upper limit. On the other hand, branching off from the pressure line  109  is also a line  111  which leads back to the hydraulic container  106  and in which an adjustable positive pressure valve  112  is located. 
     The pressure line  109  splits into two lines  113  and  114  which each lead to a proportional valve  115 ,  116 , by means of which the hydraulic fluid is allocated to the two working chambers A, B of the two piston/cylinder units  155  and  156 . 
     The two proportional valves  115 ,  116  in each case have a piston rod  117 ,  118 , on which there are in each case two pistons  117  I,  117  II and  118  I,  118  II at a distance from one another. Each of the proportional valves  115 ,  116  is provided with a central connection  119 ,  120  for the pressurised hydraulic fluid, and two connections  121 ,  122  arranged close to the end sides which are in each case connected via lines to the hydraulic container  106 . 
     In each case two lines  123  I,  123  II and  124  I,  124  II lead from the opposite side of the proportional valves  115 ,  116 , which lines lead to the working chambers A and B, respectively, of the piston/cylinder units  155 ,  156 . In each of these lines  123  I,  123  II and  124  I,  124  II there is a respective pressure sensor  125 , and there is a volume flow meter  126  in the lines  123  II and  124  I. 
     Depending on the position of the piston rods  117 ,  118  and of the pistons  117  I,  117  II and  118  I,  118  II connected thereto, a greater or lesser volume flow in the direction of a working chamber A or B of the cylinder/piston units  155 ,  156  is enabled, along with a corresponding return flow from the respective other working chamber B or A to the proportional valve  115 ,  116 . 
     The respective position of the piston  157 ,  158  of the piston/cylinder units  155 ,  156  and of the piston rods connected thereto in the form of the driven elements  159 ,  160  (which lead to the conveying elements (not shown) in the form of syringes) can be detected by means of the distance sensors  127 ,  128 . Using a control algorithm, which is integrated in the control and monitoring device (not shown in detail in the drawing), the position of the pistons  157 ,  158  at times when the latter are to assume a rest position is kept unchanged in that, in the event of external forces being applied via the driven elements  159 ,  160 , the pressures in the working chambers A and B are adjusted such that no change in position of the pistons  157 ,  158  occurs. The proportional valves  115 ,  116  are accordingly actuated by the control and monitoring device. 
     A first error prevention measure of the injection system  100  consists in that, by means of the volume flow meter  126  and the pressure sensors  125 , it is possible to check whether, for a measured displacement of the pistons  157 ,  158 , expected pressure and volume flow conditions are actually obtained in the respective lines  123  I,  123  II and  124  I,  124  II. 
     In the injection system  100  shown in  FIG. 2 , the pressure generating device  170  may be arranged either inside or outside the room in which the device having a high field strength, i.e. in the case of MRI systems in particular the magnet, is located. If the pressure generating unit  170  is located inside the room, it is preferably positioned as far away as possible from the magnet itself so that the only lines that now run in the region of greatest field strength are the hydraulic lines  123  I,  123  II and  124  I,  124  II, and in particular not the electrical lines which were previously needed to operate electrical components such as, for example, actuating motors for the mechanical actuation of the conveying elements. 
     In order to achieve simple and reliable ventilation of the hydraulic system, the surfaces  161 A,  161 B,  162 A,  162 B of the pistons  157 ,  158  of the piston/cylinder units  155 ,  156  are of different size. This is achieved by means of a different cross-sectional area of the piston rod  159  in the region of the two working chambers A, B. While the piston rod  159  has a larger cross section on the driven side, i.e. in the region of the working chamber B, it is designed with a smaller diameter in the region of the working chamber A, since here only the operation of reading the distance sensor  127 ,  128  has to take place. 
     Due to the different surfaces  161 A compared to  161 B and  162 A compared to  162 B, there must always be a certain pressure difference between the two working chambers A and B, even in the rest state of the piston  157 ,  158 . There is now a bypass cross section B in the form of a small bore in each of the pistons  157 ,  158 . A small volume flow always takes place through the bypass cross section B, which brings about looped circulation of the hydraulic fluid. Any gas bubbles present in the system are thus guided through the corresponding hydraulic lines to the hydraulic container  106 . 
     The surface  165  of the hydraulic fluid is acted upon by a negative pressure by means of a negative pressure pump  166 , so that gas bubbles leave the hydraulic fluid and are removed from the system by means of the negative pressure pump  166 . 
     In order to allow rapid ventilation when necessary, in a ventilation position E of the piston  155 ,  156  a ventilation bypass cross section EB is provided in the inner cylindrical surface of the cylinder  163 ,  164 . In the ventilation position E, which corresponds to the left dead centre position of the piston  157 ,  158 , this ventilation bypass cross section brings about ventilation via a much larger volume flow compared to the bypass cross section B in the piston  157 ,  158 . Also in the case of this “rapid ventilation”, removal of any gas bubbles takes place via the negative pressure pump  166  which is connected to the hydraulic container  106 . 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCES 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 injection system 
               
               
                   
                  2 
                 room 
               
               
                   
                  3 
                 MRI device 
               
               
                   
                  4 
                 patient bed 
               
               
                   
                  5 
                 remote control 
               
               
                   
                  6 
                 injection device 
               
               
                   
                  7 
                 pressure generating device 
               
               
                   
                  8 
                 control and monitoring unit 
               
               
                   
                  9 
                 housing 
               
               
                   
                  10 
                 drive device 
               
               
                   
                  11, 12 
                 conveying element 
               
               
                   
                  13, 14, 15, 16 
                 hydraulic line 
               
               
                   
                  18, 19 
                 hose 
               
               
                   
                  20 
                 Y-shaped element 
               
               
                   
                  21 
                 hose connection 
               
               
                   
                  22 
                 injection needle 
               
               
                   
                  23 
                 patient 
               
               
                   
                  23′ 
                 contrast agent 
               
               
                   
                  28 
                 hydraulic fluid 
               
               
                   
                  29, 30 
                 pressure transducer 
               
               
                   
                  31, 32, 33, 34 
                 drive 
               
               
                   
                  35, 36, 37, 38 
                 spindle 
               
               
                   
                  39, 40, 41, 42 
                 cylinder/piston unit 
               
               
                   
                  43, 44, 45, 46 
                 piston rod 
               
               
                   
                  47, 48, 49, 50 
                 toothed wheel 
               
               
                   
                  51, 52, 53, 54 
                 retaining element 
               
               
                   
                  55, 56 
                 cylinder/piston element 
               
               
                   
                  57, 58 
                 piston 
               
               
                   
                  59, 60 
                 driven element 
               
               
                   
                  61, 62 
                 latching element 
               
               
                   
                  63, 64 
                 piston rod 
               
               
                   
                  65, 66 
                 piston 
               
               
                   
                  67 
                 saline solution 
               
               
                   
                  71, 72, 73, 74 
                 pressure generating unit 
               
               
                   
                  75, 76, 77, 78 
                 connection lines 
               
               
                   
                  79 
                 receiving unit 
               
               
                   
                  80, 81 
                 lock 
               
               
                   
                  90 
                 supply line 
               
               
                   
                 100 
                 injection system 
               
               
                   
                 102 
                 hydraulic pump 
               
               
                   
                 103 
                 motor 
               
               
                   
                 104 
                 suction line 
               
               
                   
                 105 
                 filter 
               
               
                   
                 106 
                 hydraulic container 
               
               
                   
                 107 
                 filling level sensor 
               
               
                   
                 108 
                 pressure accumulator 
               
               
                   
                 108′ 
                 pressure sensor 
               
               
                   
                 109 
                 pressure line 
               
               
                   
                 110 
                 drive device 
               
               
                   
                 111 
                 line 
               
               
                   
                 112 
                 positive pressure valve 
               
               
                   
                 113, 114 
                 line 
               
               
                   
                 115, 116 
                 proportional valve 
               
               
                   
                 117, 118 
                 piston rod 
               
               
                   
                 117I/II, 118I/II 
                 piston 
               
               
                   
                 119, 120 
                 connection 
               
               
                   
                 121, 122 
                 connection 
               
               
                   
                 123I/II, 124I/II 
                 line 
               
               
                   
                 125 
                 pressure sensor 
               
               
                   
                 126 
                 volume flow meter 
               
               
                   
                 127, 128 
                 distance sensors 
               
               
                   
                 129, 130 
                 pressure transducer 
               
               
                   
                 155, 156 
                 piston/cylinder unit 
               
               
                   
                 157, 158 
                 piston 
               
               
                   
                 159, 160 
                 drive element 
               
               
                   
                 161A/B, 162A/B 
                 surfaces 
               
               
                   
                 163, 164 
                 cylinder 
               
               
                   
                 165 
                 surface 
               
               
                   
                 166 
                 negative pressure pump 
               
               
                   
                 B 
                 bypass cross section 
               
               
                   
                 E 
                 ventilation position 
               
               
                   
                 EB 
                 ventilation bypass cross section 
               
               
                   
                 170 
                 pressure generating device