Abstract:
Liquid infusion apparatus includes non-magnetic materials in a pumping structure and drive motor therefor, and in a controller that supplies drive signals to the motor to facilitate convenient operation in intense magnetic fields without distorting the magnetic fields and without radiating objectionable radio-frequency interface.

Description:
FIELD OF THE INVENTION 
   This invention relates to the field of liquid infusion apparatus and more specifically to such apparatus for operation during study within a Magnetic Resonance Imaging (MRI) system in which extraneous radio frequency (RF) signals and magnetic materials within the MRI&#39;s environment cause detrimental interference to the imaging process, upset the function of the infusion device, and present hazards to the patient. 
   BACKGROUND OF THE INVENTION 
   It is desirable to carefully control the intravenous (IV) administration of liquids to a patient. Conventional gravity IV solution delivery via commonly-available IV administration sets is typically not sufficiently accurate for the delivery of many types of fluids and drugs. Various positive displacement pumping devices have been developed for carefully controlling such IV administration. Some types of IV pumps control flow within a standard IV administration set via peristaltic (either linear or rotary) pumping schemes directly on the tubing of a conventional IV infusion set, other types may incorporate a proprietary volumetric cassette, still others utilize a syringe-like device. However, there currently exists no IV controller(s) capable of completely safe operation within a MRI suite wherein a considerable need exists for the controlled delivery of medicinal liquids. Frequently, patients scheduled for MRI examination arrive at the MRI suite with IV solutions being administered and controlled by devices which must be disconnected as the patient is moved into the suite where high magnetic fields are present and no outside RF interference can be tolerated. 
   The basic characteristics of an infusion pump involve the delivery of medicinal or nutritional liquids, over time, into the venous system of a living subject. Certain physical limitations regarding the delivery rate and pressure are elemental in IV liquid-infusion control. IV fluids are pumped at pressures typically in the range of 0.2 to 10 PSI. The infusion device should include detection of over-pressure and operational limits at not more than about 20 PSI. Flow ranges typical of IV pumps are from 0.1 to 2000 ml/hr. Such specifications for conventional IV infusion apparatus are quite different from the specifications for Injector devices which are often used in radiologic settings, including MRI, for purposes of very rapid bolus injection of image enhancing contrast agents. Such devices ‘push’ contrast agents at pressures up to 300 PSI and in very short periods of time in contrast to IV drug delivery. Contrast agents are solely for image enhancement and have no medicinal value in a patient. 
   The high magnetic field surrounding MRI systems can negatively affect the operation of various devices (including conventional IV control devices), especially those devices that are constructed with magnetic materials, and can seriously jeopardize a patient&#39;s safety as a result of devices utilizing magnetic materials that can be attracted at high velocity into the magnetic field of the MRI system where patient or attendant personnel are located. 
   Conventional devices for infusing liquids into a patient are typically small portable units often attached to an IV pole holding both the infusion device and associated liquids to be infused. Some of such devices utilize either stepper-type motors or simple DC motors which include magnetic materials for providing the mechanical power required to drive the pumping unit. Further, some form of electronic control unit receives the user&#39;s prescribed infusion rate settings and controls the pumping unit to deliver the desired quantity of liquid over time, and such control unit may emit spurious radio frequency signals as a result of poor electrical design or insufficient shielding. 
   With the advent of MRI procedures for the imaging of internal body structures, very special requirements must be satisfied in the design of medical devices intended to be used within the MRI environment. MRI systems exploit the physical phenomenon of nuclear magnetic resonance (NMR) by which RF stimulation of atomic nuclei within an associated magnetic field results in the emission of a small RF ‘spin echo’ from the nucleus so stimulated. In the case of patient imaging, hydrogen nuclei bound with water are the usual targets for magnetic resonance at selected frequencies. Other molecules and compounds can also be selected for study, as in Nuclear Magnetic Spectroscopy, by choosing resonance specific magnetic field strengths and associated radio frequencies. For simplicity the typical hydrogen atom-based MRI image-acquisition process is referred to herein, but it should be recognized that the subject invention is equally useful in MRI spectrographic studies at a plurality of field strengths and frequencies. 
   The typical MRI system includes several components, as shown in  FIG. 1 . For example, the operator&#39;s console  25 ,  27  and various processing  37 , display  29 ,  31  and radio frequency and magnetic gradient amplifying equipment  33 ,  35  are all located outside of the environment of the MRI scanning suite which must be configured to eliminate image-degrading radio frequency interference and field effects of metallic structures that can introduce field distortions and become safety hazards. The MRI scanning unit produces large magnetic and RF fields, and must be capable of receiving the extremely small RF nuclear ‘echoes’, and is therefore typically located within a shielded room  11 . Such rooms greatly attenuate outside RF noise and may also some provide containment of the scanner&#39;s magnetic field. 
   However, certain devices are required to be placed in the scan room either to assist with care of the patient being imaged or for the use of attending staff. Of particular interest are those devices which must be placed in the scan room during the time of image acquisition when the patient is present and the magnetic fields are ‘up’ and RF reception of the tiny. nuclear ‘echoes’ must be cleanly acquired. Electrically passive metallic items such as oxygen bottles or ‘crash carts’ present safety hazards to the patient due to their potential to be strongly attracted by the scanner&#39;s magnetic field. Such items can be ‘pulled’ into the imaging volume where the patient is located, creating potential for serious injury or death. Additionally, great effort is made during the manufacture and installation of the scanner/magnet to assure that the lines of flux within the imaging volume are highly homogenous to assure that acquired images have minimal spatial distortion. Thus, devices formed of magnetic material that are positioned within the scanner&#39;s magnetic field can introduce distortions into this homogeneous field and the resultant images. The level of hazard and the degree of field/image distortion due to magnetic materials depends upon the composition and location with respect to the imaging volume. 
   The hazards due to ‘flying’ objects can be controlled to some degree by the use of non-ferrous devices such the aluminum oxygen bottle. Additionally, the gravitational weight of some devices or their rigid fixation in the scanning room maybe sufficient to overcome the force of magnetic attraction on the ferrous mass of such devices toward the imaging volume. However, such devices with some ferrous mass, though inhibited from being pulled into the magnetic field, may nevertheless introduce in homogeneity in the magnetic field. Distortions in the homogeneity of the magnetic field within the imaging volume must be kept at such a level as to be of minimal consequence to the operator reading the resultant image or data. And, the possibility of field distortion is proportionally increased as devices with metallic materials are positioned closer to the imaging volume, with the most critical position being near the center of the imaging volume, essentially where the patient is positioned. Additionally, because of the extremely low levels of RF signals produced by the target image nuclei, great care must be taken to assure that devices with active electronic circuits do not emit spurious RF signals as forms of electronic noise. Such noise can so degrade the signal-to-noise ratio of signals received by the MRI sensor coils and receivers that image resolution is reduced or rendered completely unreadable. Active circuits must be carefully shielded to assure that their RF emissions are extremely low at the specific frequencies of the imaging process. Conversely, it is possible through careful design, to place a source of RF energy for signal transmission, therapy, or the like, within the MRI environment, but such signals must be chosen to avoid the discreet Lamar frequencies unique to the particular magnetic field strength of a given MRI scanner, and must be of such high spectral purity as to coexist with the MRI without causing any deleterious effects. The intense magnetic fields produced by the MRI scanner can cause detrimental effects on the performance of common DC and stepper motors in devices needed within the MRI scanning room, to the point of making their control difficult or causing their complete failure. 
   For example, injectors of image-enhancing contrast agents are commonly required to inject such contrast agent during actual imaging acquisition, and such devices include motors that contain magnetic material and that must therefore be located at a sufficient distance to reduce interactive effects with the magnet of the MRI scanner for proper operation and safety. Controllers and consoles of electronics and displays that generate spurious RF signals are therefore located outside the MRI scan room to avoid interference with the sensitive RF receivers of the RF scanner. 
   Accordingly, it is desirable to provide a self-contained, MRI-compatible infusion pump for the relatively long term control and delivery of the various infusion solutions and drugs routinely delivered to a patient within the MRI environment during image acquisition. Such devices must not emit any significant RF emissions that might adversely affect image acquisition operation from within the MRI scan room and must not interact with the magnetic fields therein either to cause distortion of the field or to be influenced by these fields sufficiently to jeopardize reliable operation of such devices. 
   SUMMARY OF THE INVENTION 
   In accordance with the illustrated embodiment of the present invention a safe and effective infusion device for use within the MRI scan room achieves reduction of magnetic material and accurate pumping control as well as reduction of RF emissions. In one embodiment, the infusion device includes an ultrasonic motor that eliminates magnetic materials and that does not produce any detrimental magnetic fields and that is not affected by external magnetic fields. The ultrasonic motor drives a peristaltic or other suitable fluid pumping mechanism, and is driven by a multiphasic electronic signal specifically designed to produce very little RF harmonic noise in the spectral range of about 6 Mhz to 130 Mhz in which MRI receivers are most sensitive. 
   Control electronics receive commands through an input keypad for setting prescribed fluid dose to be delivered and such inputs are translated into signals to control the motor and pumping mechanism. Various safety devices feed back operational information to the control electronics, including detection of motor speed and motion of pump elements, air bubbles in the fluid path, drip rate, high pressure, low fluid, low/no flow, overtime, and the like. The present infusion device includes battery power for portability, and is housed in one RF shielded housing for convenient location anywhere within the MRI scan room without introducing image degrading RF interference or producing distortions of the homogeneous magnetic field, and without being affected by the strong magnetic fields or high-level RF energy produced by the MRI system. Such unrestricted placement of the device is of great importance to the safety and convenience of the attending MRI staff and imaging patient. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a pictorial plan view of a conventional MRI system showing typical placement of operational components; 
       FIG. 2  is a partial perspective view of an infusion device in accordance with one embodiment of the present invention; and 
       FIG. 3  is a block schematic diagram of the infusion device of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the plan view in  FIG. 1  of an MRI system, the scanning room  9  is disposed within shielding boundary walls  11 , with a control room  13  for operators or attendant personnel positioned outside the boundaries of the scanning room  9 . The scanning room  9  includes the image acquisition equipment including a source  15  of intense magnetic field  16  that emanates from the source in substantially homogenous array throughout the adjacent space and around a patient  17 . Various components of the system for performing the image acquisition operations, including gradient  19  and sensor  21  and RF coils  23  are disposed about the patient  17  for stimulating the nuclei ‘echos’ to map the positions thereof within the spatially-homogenous magnetic field  16  as the patient&#39;s body is scanned in conventional manner along multiple orthogonal axes. The shielding boundary walls  11  (and ceiling and floor) provide shielding against radio-frequency interference and, as fabricated with ferrous materials, may also establish outer limits of the magnetic field distribution around magnetic  15 . 
   The control room  13  is disposed outside the shielding boundary walls  11  and is equipped with computer input keyboard  25 , computer display  27 , monitor  29  of patient&#39;s vital life signs, controls  31  for liquid infusion apparatus, and the like. Such representative equipment is housed outside the shielding boundary walls  11  to inhibit intrusion of spurious magnetic and electrostatic and RF signals into the image acquisition operations within the scanning room  9 . Similarly, the gradient amplifiers  33  for amplifying signals from conventional gradient coils  1921 , along X, Y, and Z coordinates and RF amplifiers  35  and the image-processing computer  37  are also located outside the shielding boundary walls  11  for the same reason. The thru-wall interconnections  39  between the components within the scanning room  9  and the electronic equipment  25 ,  27 ,  29 ,  31 ,  33 ,  35 ,  37  disposed outside the room  9  typically also includes RF shielding to diminish the sources and the portals by which and through which RFI signals may enter the scanning room  9 . 
   A liquid-infusion device  41  commonly resides within the scanning room  9  to administer IV injection into the patient  17  of liquid compositions, for example, that enhance image acquisition (e.g., contrast medium) or that otherwise provide diagnostic or therapeutic benefits to the patient  17  being scanned. Such conventional infusion device  41  should desirably be positioned close to the patient  17  to facilitate IV liquid infusion, but must be positioned remotely to avoid disrupting the homogeneous magnetic field  16 , and to minimize RFI and operational failures of the infusion device  41  resulting from operating in the intense magnetic field adjacent the patient  17 . Control of such infusion device  41  may be via remote controller  31  disposed within control room  13 . 
   In accordance with the embodiment of the invention illustrated in  FIG. 2 , an improved liquid infusion device  43  is operable within intense magnetic fields and with negligible RFI to provide positive displacement of a liquid  45  such as saline or contrast medium, or sedative, or the like, in controlled volumes per unit time. The device does not include any ferrous or magnetic materials, and is substantially shielded against irradiating any RFI during operation. Specifically, the device  43  includes a pump in the lower chamber  47 , as later described herein. The pump chamber  47  receives therein the flexible, resilient tubing  49  that is pre-packaged and sterilized as a component of a conventional IV liquid infusion set that also includes a conventional drip chamber  51  as part of the infusion set. Controls for the pump in chamber  47  include an operator&#39;s input keypad  48  for setting infusion parameters, and a drip detector  85  that can be disposed about the drip chamber  51  to detect flow of liquid from the supply  45 . A display  53  is positioned in the upper portion of the housing  55  which may be formed of non-magnetic, RF-shielding material such as conductively-coated plastic or aluminum, or the like. The housing  55  attaches with one or more clamps  57  to a rigid support  59  formed of non-magnetic material such as fiberglass or aluminum, or the like. Various visual and audible annunciators  61  may be provided to signal operational conditions either within acceptable limits, or within error or failure conditions. 
   Referring now to the pictorial block schematic diagram of  FIG. 3 , there is shown a peristaltic-type positive-displacement pump  60  disposed within the pump chamber  47  of the housing  55  to operate with the length of tubing  49  that passes therethrough between the drip chamber  51  and the patient. The peristaltic pump  60  (linear or rotational) is driven by an ultrasonic motor  64  via appropriate mechanical linkage  65  to actuate a squeeze roller against the tubing  49  in known peristaltic pumping manner, or to actuate a series of elements  67  through a linear tubing-squeezing sequence to produce peristaltic pumping action in known manner. 
   A conventional ultrasonic driving motor  64  is powered in known manner by multiphasic signals applied thereto from the motor drive circuit  69 . A controller  71  for the device includes a central processing unit  73  with associated peripheral components including Random Access Memory  75 , Read-Only Memory  77 , Digital-to-Analog converter  79 , and an Input/Output channel  81 . This controller  71  receives input control information from the operator&#39;s keypad  48 , and receives feedback information about motion of pump elements from sensor  84 , about pump speed from sensor  83  and about liquid flow from drip detector  85  disposed about the drip chamber  51 . In response to the inputs supplied thereto, the controller  71  operates on stored programs to actuate a display  53  of operating parameters (or other data), and to actuate the motor drive circuit  69  for energizing the ultrasonic motor  64  for rotation at a controlled speed. A power supply  63  is connected to the controller  71  and drive circuit  69  to supply electrical power thereto, and is connected to a battery  87  to receive electrical power therefrom during stand-alone operation, or to receive line voltage via plug  63 , as required. 
   In accordance with this embodiment of the present invention, no magnetic material is used in any of the components of the infusion device  43  including the ultrasonic motor  64 , pump  60 , power supply  63 , controller  71  and associated components. Additionally, none of such components is adversely affected during operation by a strong magnetic field. And, any RF energy that may be generated by electronic signals within the ultrasonic motor  64 , drive circuit  69 , controller  71 , power supply  63  or associated components is specifically shielded by conductive structures  91 ,  93  disposed around such components to inhibit radiation of RFI. Additionally, radio-frequency interference filters  95  are disposed about all throughshield conductors to inhibit radiation of RFI through such portals. 
   Therefore, the liquid infusion device of the present invention is configured without magnetic materials for operation within intense magnetic fields to administer I.V. fusion of liquids to a patient in an MRI environment. The infusion device may be positioned close to a patient during image acquisition without significantly distorting the homogeneous magnetic field around an MRI scanner, and without emitting harmful RFI in the vicinity around a patient from whom extremely low-level RF ‘echos’ are being detected during image acquisition.