DISTRIBUTED ARCHITECTURE FOR APPARATUS USED IN A HIGH MAGNETIC FIELD AND/OR RF ENVIRONMENT

Abstract: A distributed architecture for adapting apparatus for use in a high magnetic field and/or intense RF environment. In one embodiment, an advanced ventilator is adapted to be MRI-compatible by creating a mechanical and electrical separation between the functional elements of the ventilator with only a minimum ensemble of electronics remaining near the MRI coil. Local components of the ventilator that must be close to the MRI are positioned accordingly. These items will typically include the ventilator control panel, the status display, and the breathing bellows. Remote components that are sensitive to magnetic and/or RF fields or may adversely impact the MRI image are placed away from the immediate influence of the MRI. These devices will typically include the control processor, monitoring sensors, and proportional gas control solenoids.

Description: DISTRIBUTED ARCHITECTURE FOR APPARATUS USED IN A HIGH MAGNETIC FIELD AND/OR RF ENVIRONMENT CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of prior filed copending U.S. provisional application serial No. 60/154,064, filed September 16, 1999, which is incorporated herein by reference in its entirety. BACKGROUND OF THE INVENTION The invention relates to apparatus for use in a high magnetic field and/or intense radio frequency (RF) environment, e.g., apparatus for use with magnetic resonance imaging (MRI) machines. In one embodiment the invention is a distributed architecture that enables ventilators and other apparatus to be MRI-compatible, i.e., to be usable with an MRI machine. Ventilators are used to provide respiratory function in cases where natural respiration has failed and/or for the delivery in inhalational anesthetics. Basic ventilators are designed to control the tidal volume and the respiration rate. These ventilators have little or no sensor capability and they work in an open loop control mode. The control technology tends to be pneumatic rather than electronic. Today, the use of advanced technology ventilators is more common in medical practice. Advanced ventilators provide the ability to respond to instantaneous and long-term physiological conditions by the use of monitors and closed loop control; major portions of the advanced ventilator involve active electronic components and circuits. A functional block diagram of a representative "integrated" advanced ventilator is shown in Fig. 1. MRI is a diagnostic tool that affords noninvasive imaging capability to the physician. MRI utilizes large static and dynamic magnetic fields and large dynamic RF fields to create images. The magnetic fields can cause magnetic materials to become lethal projectiles. Magnetic materials in the vicinity of the MRI will adversely affect the quality of the resultant images, and the existence of magnetic and RF fields may cause non-MRI hardened electronic equipment to malfunction. New minimally-invasive surgical techniques involve the integration of the MRI machine and the surgical suite. Life support during MRI procedures and delivery of general anesthetic during MRI-assisted surgery mandates that a ventilator be used in close proximity to the MRI machine. It is, therefore, necessary to use a basic ventilator because advanced ventilators are not MRI-compatible. What is needed is a new architecture that will allow apparatus to function in a high magnetic field and/or RF environment and lead to a redesigned advanced ventilator that can function with an MRI machine. SUMMARY OF THE INVENTION The invention solves the above-recited problem by implementing a "distributed" architecture to the maximum extent possible. In the case of the advanced ventilator, the distributed architecture of the invention creates a mechanical and electrical separation between the functional elements of the ventilator with only a minimum ensemble of electronics remaining near the MRI coil. Those components of the ventilator that must be close to the MRI ("local") are positioned accordingly. These items will typically include the ventilator control panel, the status display, and the breathing bellows. Those components that are sensitive to magnetic and/or RF fields or may adversely impact the MRI image are placed away from the immediate influence of the MRI ("remote"). These devices will typically include the control processor, monitoring sensors, and proportional gas control solenoids. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a functional block diagram of an advanced ventilator that is currently used in a general clinical environment. Fig. 2 is a functional block diagram of an advanced ventilator that implements the distributed architecture of the invention. DETAILED DESCRIPTION As shown in Fig. 2, the invention implements a "distributed" architecture to the maximum extent possible resulting in a redesigned advanced ventilator 10. The distributed architecture creates a mechanical and electrical separation between the functional elements of the ventilator with only a minimum ensemble of electronics remaining near the MRI coil. "Local" components 12 of the ventilator are those that must be close to the MRI machine and are positioned accordingly. These items will typically include the ventilator control panel 14, the status display 16, and the breathing bellows 18. "Remote" components 20 are those that are sensitive to magnetic and/or RF fields or may adversely impact the MRI image and, hence, are placed away from the immediate influence of the MRI. These devices will typically include the control processor 22, monitoring sensors 24, and proportional gas control solenoids 26. An interface is provided between the local and remote components in order to preserve ventilator functionality and comprises both non-electronic and electronic links 27,28, respectively. The non-electronic link to the bellows 27 is typically pneumatic, e.g., tubing. The electronic link 28 between the control/display and the processor can be fiber/optic (F/O), but may also be in any other form (i.e., infrared) that has no interaction with MRI's magnetic and/or RF fields. To facilitate the electronic interface, a "distribution interface" device 30a, 30b may be incorporated to provide translation and formatting functions. Prudent selection of the display, controls, and distribution interface components is necessary in order to assure system function. Pressure and flow at the patient can be measured at the remote location. In a pneumatic circuit, as in an electric circuit, flow is the same anywhere in the circuit and can thus be measured anywhere (in this case at the remote location away from the MRI). However, in a pneumatic circuit, this is only true if reinforced non-distensible tubing is used. Otherwise the remotely measured air would be partially going into distending the tubing and not into the patient. Secondly, pressure at the patient can be fairly well estimated by measuring the pressure at the remote end and estimating the pressure drop (from flow resistance) at the other end. Since the flow is measured and the resistance is known from the diameter and length of the tubing, the pressure drop can be calculated. A calibration port could be added to take some measurements of flow and pressure on the ventilator before plugging it into the patient. This would compensate for different lengths and diameters of tubing being used. The distributed architecture of the invention preserves full ventilator functionality with minimal system redesign and in a manner that is fully transparent to the user. The concept of distributing system components as described above for the ventilator can also be applied to other sensors, devices and/or systems, such as patient monitors, that may be required in the MRI environment. The invention can also be implemented in high magnetic field and/or RF environments other than those created by MRI machines.

Claims: We claim: 1. A distributed architecture for an apparatus used in a high magnetic field and/or radio frequency (RF) environment comprising: local components of the apparatus for use in or near the high magnetic field and/or RF environment; remote components of the apparatus for use outside of the influence of the high magnetic field and/or RF environment; and an interface for linking the local and remote components. 2. The distributed architecture as recited in claim 1, the interface comprising an electronic link between the local and remote components. 3. The distributed architecture as recited in claim 2, the electronic link comprising fiber optic cable. 4. The distributed architecture as recited in claim 2, the electronic link comprising infrared. 5. The distributed architecture as recited in claim 2, the electronic link further comprising means for translating and formatting. 6. The distributed architecture as recited in claim 1, wherein the high magnetic field and/or RF environment comprises a magnetic resonance imaging (MRI) machine. 7. The distributed architecture as recited in claim 6, wherein the apparatus comprises a ventilator. 8. The distributed architecture as recited in claim 7, the interface comprising an electronic link and a non-electronic link. 9. The distributed architecture as recited in claim 8, the local components comprising a control panel, status display and bellows. 10. The distributed architecture as recited in claims 8 or 9, the remote components comprising a processor, a sensor and a gas control solenoid. 11. The distributed architecture as recited in claim 10, wherein the non-electronic link is pneumatic. 12. The distributed architecture as recited in claim 11 , wherein the electronic link comprises fiber optic cable. 13. The distributed architecture as recited in claim 6, wherein the apparatus comprises a monitor. 14. A method for making an apparatus for use in a high magnetic field and/or radio frequency (RF) environment, the method comprising the steps of: separating local components of the apparatus that must be located in or near the high magnetic field and/or RF environment from the remote components of the apparatus that must be outside of the influence of the high magnetic field and/or RF environment; and interfacing the local and remote components. 15. The method as recited in claim 14, the interfacing step comprising the step of linking the local and remote components. 16. The method as recited in claim 15, the interfacing step further comprising the step of translating and formatting signals between the local and remote components. 17. The method as recited in claim 14, wherein the high magnetic field and/or RF environment comprises a magnetic resonance imaging (MRI) machine. 18. The method as recited in claim 17, wherein the apparatus comprises a ventilator. 19. The method as recited in claim 18, wherein the local components comprise a control panel, a status display and a bellows. 20. The method as recited in claims 18 or 19, wherein the remote components comprise a processor, a sensor and a gas control solenoid. 21. The method as recited in claim 20, the interfacing step comprising the step of electronically linking the local and remote components. 22. The method as recited in claim 21, the interfacing step further comprising the step of non-electronically linking the local and remote components.

Inventors: CUTCHIS PROTAGORAS N, FRIEDMAN GERALD E, MURPHY JOHN C, STERNBERGER WAYNE I, CUTCHIS, PROTAGORAS, N., FRIEDMAN, GERALD, E., MURPHY, JOHN, C., STERNBERGER, WAYNE, I.
Applicants: UNIV JOHNS HOPKINS, THE JOHNS HOPKINS UNIVERSITY
Application year: 2000
Main classification: A61M
IPC codes: A61B5, A61M16, G01R33