WO1990002513A1

WO1990002513A1 - Active attenuation system for medical patients

Info

Publication number: WO1990002513A1
Application number: PCT/US1989/004004
Authority: WO
Inventors: Paul Friedlander
Original assignee: Noise Cancellation Technologies, Inc.
Priority date: 1988-09-16
Filing date: 1989-09-18
Publication date: 1990-03-22
Also published as: AU4332889A; KR970006914B1; KR900701216A; CA1319394C

Abstract

An active noise attenuation system (10) for patients undergoing diagnosis in equipment (1) which inherently produces undesirable sounds senses the noise experienced by the patient (P) and supplies a cancelling sound wave pattern to attenuate the noise experienced by the patient (P).

Description

ACTIVE ATTENUATION SYSTEM FOR MEDICAL PATIENTS BACKGROUND AND SUMMARY OF THE INVENTTON

The present invention is related to an active sound attenuation system for patients undergoing diagnosis in equipment which inherently produces undesirable sounds. The preferred embodiments of the invention described herein are related to such an active sound attenuation system for use with magnetic resonance imaging equipment.

Magnetic resonance imaging (MRI) equipment utilizes a large magnet in which the patient lies prone while the magnet is activated to create a magnetic field. A radio signal is used to disorganize the nuclei of hydrogen molecules within the area being scanned. When the radio signal concludes, an MRI computer measures the fraction of a second that elapses before molecules re-orient themselves. Although this procedure is relatively safe and painless, the MRI magnet arrangement inherently generates disturbing undesirable noises.

Prior art arrangements have used music piped in to the patient to "mask" the generated noise. U.S. Patent No. 4,701,952 to Taylor describes such a noise masking arrangement. Also, so-called passive noise attenuating systems such as ear plugs, noise insulation, and the- like have been utilized. However, due to the very confining area that the patient must remain within for a relatively extended period of time, the inherent noises of the magnetic resonance imaging equipment can be quite disturbing, especially to patients with claustrophobic tendencies and/or patients that are ill. An object of the present invention is to provide a sound attenuation or counternoise system that will actively cancel the noises generated during the diagnostic process. Another object of the invention is to construct a counternoise system that will not interfere with the operation of the diagnostic equipment.

The present invention achieves the above-mentioned and other objects by providing an active noise cancellation system which produces counternoise waves to cancel the disturbing, undesirable noise waves in the area of the patients hearing while in the diagnostic equipment. In especially preferred embodiments of the invention, the cancelling sound applied to the area of the patient to cancel the undesirable noise is supplied by non-magnetic lines, preferably pneumatic tubes or the like. Also, to detect the undesirable noise so as to process the same and generate the proper counternoise wave pattern, non-magnetic lines in the form of hollow tubes filled with a sound propagating medium are utilized.

In especially preferred embodiments, headsets are provided which fit over the patients ears and define a small space where the undesirable noise is detected and the counternoise is generated. Prior art arrangements such as disclosed in the above noted Taylor U.S. Patent No. 4,701,952 utilize hollow tubes filled with sound propagating medium for piping in music or the like. According to the invention similar tubes can also be used to communicate the counternoise wave patterns from a counternoise processing unit and counternoise wave generator or speaker disposed remote from the diagnostic equipment. Hollow tubes filled with sound propagating medium are also provided for communicating the undesirable noise to be cancelled to the processing unit. The undesirable noise detection tubes need only be spaced a small distance away from the counternoise speaker tubes so as to provide a reliable signal to the counter noise processing unit.

A microcompressor controller is provided at a remote location for processing the undesirable noise signal supplied through the noise detection tubes and for generating a corresponding counternoise signal and driving a speaker that generates counternoise waves which are then supplied as noise cancelling waves via the counternoise tubes.

In certain preferred embodiments, rather than a headset, the fittings for the noise detection tubes and the counternoise tubes are fixedly arranged in the diagnostic equipment at a position adjacent the position of the patients head and ears.

The noise cancellation system of the present invention can be used in MRI diagnostic equipment and in other environments where the region where the noise is to be cancelled can not tolerate metallic speaker wires or components due to electromagnetic interference problems and the like.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic side sectional view depicting a patient in an MRI diagnostic unit with an active sound attenuation system constructed according to the present invention shown in dashed lines;-

Figure 2 is a schematic sectional view taken along the line II-II of Figure 1;

Figure 3 is a schematic view of a headset having a closed ear coupling means arrangement and active sound attenuation system constructed according to a preferred embodiment of the present invention;

Figure 4 is an enlarged schematic view of a preferred embodiment of a headset having an open ear coupling means arrangement for the sound attenuation system of Figures 1 and 3; and

Figure 5 is an enlarged sectional view taken along line V-V of Figure 4.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to Figures 1 and 2, there is schematically depicted a magnetic resonance scanning unit 1 with a human patient P in position on a table 2 for a diagnostic scanning procedure. The MRI unit 1 includes a large permanent magnet 3 which surrounds the table 2 for the patient P. Arranged concentrically within the permanent magnet 3, and also surrounding the table 2, are a magnetic coil 4 and a radio frequency RF coil 5. The entire structure with magnet 3, magnetic coil 4, RF coil 5 and patient accommodating table 2 are disposed within a shielded chamber 6 which includes shielding to prevent electromagnetic interference with the operation of the MRI control unit 8. The magnetic coil 4 is connected by circuit 7 (shown only schematically), with a MRI control unit 8. The RF coil 5 is connected by a circuit 9

(also shown only schematically) also to the MRI control unit 8.

The details of the operating circuits and parts of the MRI unit 1 are not included herein so as not to obscure the disclosure of the present invention. An MRI unit that could be used with the present invention is marketed and serviced by the company TME of Houston, Texas.

In Figure 1, there is only a schematic depiction in dash line form of a sound attenuating system 10 for cancelling undesirable noises otherwise experienced by the patient during normal operation of the MRI unit 1. In Figure 3, the shielded chamber walls 6 are shown only schematically in dashed outline form and further details of the sound. attenuating system 10 are schematically illustrated.

Referring to Figure 3, the sound attenuating system 10 includes a headset 11 with a right ear coupling means 12R and a left ear coupling means 12L for coupling the counternoise to the auditory system of the patient. The ear coupling means 12R, 12L comprise, for example, earpieces which have an open or closed back and transmit the counternoise to the auditory system of the patient's body. In a closed ear coupling means arrangement, the ear of the patient is surrounded by the ear coupling means so as to isolate the patient's ear from ambient air and form a chamber which enclosed the ear. The closed ear coupling means arrangement comprises, for example, a cup-like configuration which surrounds the ear to form a chamber as shown in Figure

3. In an open ear coupling arrangement, the ear coupling means is placed within an effective range of the patient's ear, but is not isolated from the ambient air surrounding the patient, as best shown, for example, in Figure 4.

A flexible hollow tube 13R extends from an opening at the ear coupling means opening 14R at the ear coupling means 12R to a speaker 15R. In a similar manner, hollow tube 13L extends from an opening 14L at ear coupling means 12L to an opening facing a speaker 15L. A hollow tube 16R extends between an opening 17R into ear coupling means 12R to a microphone 18R. In a like manner, hollow tube 16L extends from an opening 17L in ear coupling means 12L to an opening facing a microphone 18L.

The speakers 15R, 15L and the microphones 18R, 18L form part of a noise detection and -cancellation control unit 19 which includes a multi-channel microprocessor unit 20. A commercially available controller 20 that could be used with the present invention is the NCT 2000 controller marketed by Noise Cancellation Technologies, Inc., and therefore further details of that controller are dispensed with herein. The noise attenuation system of Figure 3 operates as follows. The undesirable noise that is generated in the area of the patients head during magnetic resonance scanning operations is communicated via the respective openings 17R, 17L and hollow tubes 16R, 16L to the respective microphones 18R and

18L. The signal from these microphones 18R and 18L is supplied to different channels of the controller 20, where they are processed, and a cancelling sound wave pattern is supplied by the controller 20 to drive the speakers 15R and 15L as a function of the sound wave pattern reaching the microphones.

The antinoise sound waves are transmitted from the respective speakers 15R, 15L via the hollow tubes 13R, 13L to the openings

14R, 14L and their respective ear coupling means, to thereby apply a cancelling noise wave pattern into the ear coupling means and substantially attenuate the noise experienced by the patient P.

In preferred practical embodiments of the invention, the tubes 13R, 13L, 16R, 16L are constructed as hollow vinyl tubes with an outside diameter of, for example, 1/2-inch and an inside diameter of, for example, 3/8-inch. The diameter of the tubes are sufficiently smaller than the length of the tube to negate any destructive interference, the wave velocity impedance for any given diameter and length being the main consideration in selecting these dimensions. Such hollow tubes are sufficiently flexible to accommodate positioning thereof with respect to the headset and the MRI equipment so as to minimize disruption of the conventionally available MRI equipment. Since the hollow tubes 13R, 13L, 16R, 16L are made cf non-magnetic, non-metallic materials and since they protrude from the outside into the chamber 6, the sound attenuation system 10 does not interfere with the magnetic resonance scanning operation. The headset ear coupling means 12R, 12L are likewise preferably constructed of non-magnetic, non-metallic material, such as plastic, so as not to interfere with the magnetic fields being generated.

According to the invention, the openings 14R, 17R in the ear coupling means 12R are located sufficiently close to one another so that the detected unwanted sound wave pattern via opening 17R, tube 16R and microphone 18R is an accurate real time representation of the sound that should be generated by the speaker 15R and transmitted via tube 13R, 14R to the ear coupling means 12R, thereby resulting in an optimum noise cancellation sound wave as experienced by the patient P. The left side ear coupling means and tubes, speakers and microphones likewise are configured for optimum noise cancellation.

According to certain preferred embodiments, the tubes 13R, 13L can also be used to transmit pleasant sounds to the patient P such as music or the like, which music pattern will not disrupt the noise cancellation waves. In such embodiments, not only is the undesirable noise level substantially reduced, the pleasant music sound can be provided with optimum fidelity. Figure 4 schematically depicts a preferred form of construction for the headset having an open ear coupling means. Referring to Figure 4, the headset 11A includes a right ear coupling means 12AR and a left ear coupling means 12AL.

The ear coupling means 12AR and.12AL are held together by a resilient yoke 21 and each include a foam padding 22 at the side facing the patients ears. As shown in Figure 5, the hollow tubes 13AL and 16AL for the left ear coupling means 12AL may be joined together to facilitate handling, for example, in a rigid plastic mounting 23L which merges into the ear coupling means 12AL. The hollow tubes 13AL and 16AL open into the space for the ear at predetermined spaced locations, within this space. Since the efficiency of the perceived noise cancellation is determined by the quality of the coupling of the counternoise to the ear, in an open system as depicted b

Figure 4, close proximity of the ear coupling means to the patient's ear is preferred. The tubes for the right ear coupling means 12AR are constructed similarly.

Although the preferred illustrated embodiments include headsets with ear coupling means that cup over the patients ears, embodiments are also contemplated wherein the magnetic resonance unit is outfitted with permanently fixed supports for the hollow tubes for detecting the unwanted sound to be cancelled and transmitting the counternoise cancelling sound waves. These tubes can be held in a predetermined position adjacent the table 2, with adjustment provisions being provided to position the same for differently shaped patients heads. Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.

Claims

WHAT IS CLAIMED;

1. Patient diagnosing apparatus comprising: patient accomodating means for holding a patient in a predetermined position, diagnosing means including means for generation of undesirable noise adjacent a patient during diagnostic operation, and active noise cancellation means for cancelling said undesirable noise at least in the area of the patient accomodating means at or near the patient's head during diagnosing operations.

2. Apparatus according to Claim 1, wherein said active noise cancellation means includes: undesirable noise detection means for detecting undesirable noise waves in the area of a patient's head, and counternoise speaker means for generating counternoise waves to cancel the noise wave detected by the noise detection means.

3. Apparatus according to Claim 2, wherein said noise detection means includes non-magnetic, non-metallic sound propagating noise line means leading from said patient accomodating means to a remote location such that detection of said noise does not interfere with operation of diagnosing means.

4. Apparatus according to Claim 3, wherein said counternoise speaker means includes non-magnetic, non-metallic sound propagating counternoise line means leading to said patient accomodating means from a remote location such that operation of said counternoise speaker means does not interfere with operation of the diagnosing means.

5. Apparatus according to Claim 2 , wherein said counternoise speaker means includes non-magnetic, non-metallic sound-propagating counternoise line means leading to said patient accomodating means from a remote location such that operation of said counternoise speaker means does not interfere with operation of the diagnosing means.

6. Apparatus according to Claim 3, wherein said noise line means includes hollow noise tube means filled with a sound wave propagating medium.

7. Apparatus according to Claim 5, wherein the counternoise line means includes hollow counternoise tube means filled with a sound wave propagating medium.

8. Apparatus according to Claim 4, wherein both the noise line means of and the counternoise line means include hollow tube means filled with a sound wave propagating medium.

9. Apparatus according to Claim 1, wherein a headset with a pair of ear coupling means for coupling counternoise to the auditory system of the patient are provided for the patient, and wherein the detection means and the counternoise speaker means include respective sound propagating line means which extend between the respective ear coupling means and a respective channel of a controller for controlling generation of counternoise in each of the respective ear coupling means as a function of the detected noise at each of said respective ear coupling means.

10. Apparatus according to Claim 9, wherein said sound propagating line means are hollow tube means filled with a sound wave propagating medium.

11. Apparatus according to Claim 10, wherein said sound wave propagating medium is air.

12. Apparatus according to Claim 1, wherein said diagnosing means includes magnetic resonance scanning means.