Abstract:
An ear protection comprises a monitoring device, which is designed in order to be able to continuously monitor the effectiveness of the ear protection during use. The invention provides that, in a method for operating a noise-emitting device,during which at least one individual is wearing an ear protection and located in the area in which the noise-emitting device is generating noise, the noise-emitting device, in the event of a monitoring result of the ear protection indicating a risk of damage to the individual&#39;s hearing, is controlled whereby appropriately reducing the noise emission thereof.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is directed to a hearing protection as well as to a method for operating a noise-emitting device having a region in which noise produced by the device is present wherein at least one person with the hearing protection is situated.  
           [0003]    2. Description of the Prior Art  
           [0004]    A magnetic resonance apparatus in the scanning (data acquisition) mode, for example, represents a noise-emitting device with at least some of the noise having extremely high acoustic pressure levels. In a magnetic resonance apparatus, rapidly switched gradient fields that are generated by a gradient coil system are superimposed on a static basic magnetic field that is generated by a basic field magnet. The magnetic resonance apparatus also has a radiofrequency system that emits radiofrequency signals into the examination subject for triggering magnetic resonance signals and that picks up the magnetic resonance signals that have been triggered on the basis of which magnetic resonance images are produced.  
           [0005]    For generating gradient fields, appropriate currents must be set in gradient coils of the gradient coil system. The amplitudes of the required currents amount to several 100 A. The current rise and decay rates amount to several 100 kA/s. Given a basic magnetic field on the order of magnitude of 1 Tesla, Lorentz forces that lead to oscillations of the gradient coil system act on these time-variable currents in the gradient coils. These oscillations are transmitted to the surface of the device via various propagation paths. These mechanical oscillations are converted thereat into acoustic oscillations that ultimately lead to undesirable noise emission.  
           [0006]    The problem of noise emission has intensified as a consequence of the greatly enhanced performance capability of the gradient coil systems in recent years, particularly in combination with intensities of the basic magnetic field that have likewise increased. In modern high-performance magnetic resonance devices, the noise emissions reach peak values of approximately 140 dB. It is therefore recommended that a patient wear a double hearing protection composed of hearing protection plugs and a headphone-like hearing protection during an examination in the magnetic resonance apparatus.  
           [0007]    The hearing protection plug is manually elastically tapered before introduction into the outer auditory canal and is thus pushed into the auditory canal. Therein, the hearing protection plug elastically expands, so that approximately 30 dB of externally occurring acoustic pressure levels are typically attenuated by the hearing protection plug.  
           [0008]    At the beginning of an examination, a patient having normal reactions is given a pushbutton to hold, to allow the patient to signal the occurrence of a problem during the examination to an operator of the magnetic resonance apparatus by actuation of the pushbutton. When, for whatever reasons, the patient senses that the noises acting on him/her during, for example, the examination lie above a hearing-damaging level, then the patient can actuate the pushbutton. Damage to the hearing of the patient may already have occurred by the time the pushbutton is actuated. The risk of hearing damage is further intensified in case of sedated patients, who are not capable of actuating the pushbutton.  
         SUMMARY OF THE INVENTION  
         [0009]    An object of the invention is to provide an improved hearing protection and an improved method for the operation of a noise-emitting device with which—among other things—hearing damage can be reliably suppressed.  
           [0010]    This object is achieved in a hearing protection having a monitoring device that is fashioned such that, given application of the hearing protection, the effectiveness of the hearing protection is continuously monitored. An acoustic pressure level that acts on a person protected by the hearing protection is directly or indirectly known at all times, so that, for example given an upward transgression of a prescribable limit value, corresponding counter-measures can be initiated, preferably automatically, so that damage to the person&#39;s hearing can be reliably precluded. The continuous monitoring need not be uninterrupted in time. The continuous monitoring can be implemented with digital or partially digital embodiment of the monitoring device that, as known, are based on a sampling of a temporally continuous signal and/or can be implemented with a method based on acquiring changes.  
           [0011]    In an embodiment, the monitoring device has an output unit that emits a control signal. Given acoustic pressure levels that are too high, the control signal can deactivate the source causing the acoustic pressure levels or throttle it with respect to its noise emissions. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a coronal section through a human head in the region of the outer auditory canal.  
         [0013]    [0013]FIG. 2 is a sectional view of a first embodiment of a hearing protection plug in accordance with the invention, with a hydrostatic pressure sensor.  
         [0014]    [0014]FIG. 3 is a sectional view of a second embodiment of a hearing protection plug in accordance with the invention, with a pressure sensor.  
         [0015]    [0015]FIG. 4 is a sectional view of a third embodiment of a hearing protection plug in accordance with the invention, with a microphone.  
         [0016]    [0016]FIG. 5 illustrates a first embodiment of a hearing protection module in accordance with the invention, with an arrangement for arranging an under-pressure.  
         [0017]    [0017]FIG. 6 illustrates a second embodiment of a hearing protection module in accordance with the invention, with a transmission unit.  
         [0018]    [0018]FIG. 7 is a schematic illustration of the basic components of a magnetic resonance apparatus operating in accordance with the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    [0019]FIG. 1 shows an excerpt of a coronal section through a human head  11  in the region of the outer auditory canal  13 . At one side, the outer auditory canal  13  is limited by the tympanic membrane  14 . Further, a hearing protection plug  12  has been introduced into the outer auditory canal  13 .  
         [0020]    [0020]FIG. 2 shows a hearing protection plug  12 A with a hydrostatic pressure sensor as a first exemplary embodiment of the invention. The hearing protection plug  12 A has an elastically deformable inner part  31 , an outer part  30  and an oblong cavity  33  that extends through the inner part  31  and the outer part  32 . At a side facing toward the inner part  31 , the cavity  33  is filled with, preferably, a dark-colored fluid  34 , and the cavity  33  forms a reservoir for a preferably transparent gas  35  at a side facing toward the outer part  32 . In one embodiment, the gas  35  is separated from the fluid  34  by a flexible membrane. A light transmission unit  38  as well as a light reception unit  39  are arranged in the region of the outer part  32  immediately adjacent to the cavity  33 . The light transmission unit  38  and the light reception unit  39  are connected to respective light waveguides  36  and  37  for supplying a light signal and for conducting a light signal conducting.  
         [0021]    Upon introduction of the hearing plug  12 A into the outer auditory canal  13 , the inner part  31  and, thus, the cavity  33  in the region of the inner part  31  are deformed, resulting in the boundary line between the fluid  34  and the gas  35  shifting dependent on the degree of deformation. A large shift of the boundary line in the direction of the outer part  32  results from a high pressure on the inner part  31 , which indicates a high pressing force of the hearing protection plug  12 A inside the outer auditory canal  31  and indicates a good noise-damping effect of the hearing protection plug  12 A. The aforementioned information is output via the light signal of the light waveguide  37  connected to the light reception unit  39  and, for example, can be employed for controlling a device that emits the noises to be damped by the hearing protection plug  12 A.  
         [0022]    In one embodiment, the light signal is emitted at only two signal levels—for example, light on and light off—for indicating whether the pressure lies above or below a prescribable limit value. In another embodiment, the light signal is output with a changing intensity that continuously represents a measure of the pressure. Dependent on the position of the boundary line, more or less light from the light transmission unit  38  is transmitted to the light reception unit  39 , a low intensity thus corresponding to a high pressure onto the inner part  31 . An evaluation device (not shown) connected to the light waveguide  37  continuously converts the intensity of the light signal into an indication of the effectiveness of the hearing protection plug  30  to attenuate the acoustic pressure level.  
         [0023]    As a result of its hydrostatic pressure conversion and the purely optical pressure detection based thereon, the hearing protection plug  12 A of FIG. 2 can be fashioned free of metallic, particularly ferro-magnetic, component parts in a simple way, so the hearing protection plug  12 A can be unproblematically utilized within a magnetic resonance apparatus  20  (see FIG. 7) with an optimally high electromagnetic compatibility.  
         [0024]    In a second exemplary embodiment of the invention, FIG. 3 shows a lead-free hearing protection plug  12 B with a pressure sensor  46 . The pressure sensor  46  is thereby arranged such in the inner part of the hearing protection plug  12 B so that it normally comes to lie just barely inside the outer auditory canal  13  after introduction of the hearing protection plug  12 B. For example, the pressure sensor  46  can be fashioned such that it continuously converts the pressure acting on it into a corresponding signal. The pressure sensor  46  is connected to a central unit  43  arranged in the outer part  42  of the hearing protection plug  40  among other things, for forwarding the signal. Further, the central unit  43  is connected to a transmission unit  48  for non-hardwired transmission of information that is likewise arranged in the outer part  43 . The transmission unit  48  is fashioned, for example, as an infrared or microwave transmission unit. For the energy supply of the central unit  43 , of the pressure sensor  46  as well as of the transmission unit  48 , the central unit  43  contains an energy supply unit  44  having a double-film capacitor  45  with high capacitance and high power density. German 199 35 915 A1—which is incorporated herein by reference —provides a more detailed description of the energy supply unit  44  and of the transmission unit  48 .  
         [0025]    In one embodiment, a continuous evaluation of the signal of the pressure sensor  46  ensues in the central unit  43  in order to determine whether the pressure lies above or below a prescribable limit value, so that the transmission unit  48 , for sending a signal, in conformity with the evaluation, need only have two signal states that are distinguishable from one another. In another embodiment, the values of the pressure acquired by the pressure sensor  46  are continuously sent with an appropriately encoded signal to an evaluation device (not shown) that is arranged remote from the hearing protection plug  40 . The signal of the pressure sensor  46  is correspondingly edited in the central unit  43  for transmission by the transmission unit  48 .  
         [0026]    Given the fashioning of the transmission unit  48  as microwave transmission unit and employment of the hearing protection capsule  40  in or at a magnetic resonance apparatus  20 , care must be exercised to see that a transmission frequency of the microwave transmission unit lies above a nuclear magnetic resonance frequency of the magnetic resonance apparatus  20 , particularly above 100 MHz. Harmonics of the transmitted signal can thus also not cause interferences with the nuclear magnetic resonance frequency. The nuclear magnetic resonance frequency, which is proportional to a basic magnetic field strength, amounts to approximately 84 MHz given a basic magnetic field strength of, for example, 2 Tesla. Care must also be exercised in the selection of the transmission frequency that this is respectively approved by the appertaining authorities. In Germany, for example, the transmission frequency of 433.92 MHz is approved.  
         [0027]    As a third exemplary embodiment of the invention, FIG. 4 shows a hearing protection plug  12 C with a microphone  56 . For the continuous detection of an acoustic pressure level acting on the tympanic membrane  14 , the microphone  56  is arranged directly at that side of an inner part  51  of the hearing protection plug  12 C that faces toward the tympanic membrane  14 . For, among other things, forwarding the acoustic pressure level acquired by the microphone  56 , the microphone  56  is connected to a central unit  53  arranged in an outer part  52  of the hearing protection plug  12 C. Further, the central unit  53  is connected to a transmission unit  58  and reception unit  59  likewise arranged in the outer part  52  for the non-hardwired transmission and reception of information. For the energy supply of the central unit  53 , of the microphone  56  as well as of the transmission and reception unit  58  and  59 , the central unit  53  contains an energy supply unit  54  with a double-film capacitor  55  having high capacitance and high power density. The description pertaining to the embodiment of FIG. 3 applies to the further design and operation of the microphone  56 , of the central unit  53  (including its power supply unit  54 ), and the transmission unit  58 . Via the reception unit  59 , further, it is possible to control operation of the hearing protection plug  12 C, particularly operation of the central unit  53 . In one embodiment wherein a speaker (not shown) is arranged in addition to the microphone  56 , an externally controllable output of tones, voice message and/or prospective anti-sound can be realized.  
         [0028]    As a fourth exemplary embodiment of the invention, FIG. 5 shows one half of a coronary section through a human head  11  with a hearing protection module  61 . For forming a hearing protection  60  similar to headphones, the hearing protection module  61  is connected to a further hearing protection module (not shown) by a connector  62 . The hearing protection module  61  is connected to a first and a second lead conduits  68  and  69  with which the space formed by the head  11  and the hearing protection module  61  is connected to a control device  63  at a distance from the hearing protection.  
         [0029]    The first lead conduit  68  is connected to a pump  64  in the control device  63  for producing an under-pressure within the space. Further, the space is connected via the first lead conduit  68  to a gas pressure sensor  65  and a microphone  66 . A measurement of the under-pressure within the space and, dependent on a corresponding drive of the pump  64  can be implemented via the gas pressure sensor  65 . An under-pressure of, for example, 200 mbar that a person still finds to be pleasant is thereby set. The under-pressure effects a good seating of the hearing protection conduit  61  at the head  11 . A frequent actuation of the pump  64  for maintaining the under-pressure thereby indicates a poor fit of the hearing protection capsule  61  at the head  11 . An acoustic pressure level within the space can be continuously monitored with the microphone  66 .  
         [0030]    The second lead conduit  69  is connected to a pressure chamber speaker  67  in the control device  63 . With an appropriate drive, the pressure chamber speaker  67  can be used, for example, for producing prospective anti-noise within the space. Given employment of the hearing protection  60  in or at a magnetic resonance apparatus  20 , a characteristic pattern with reduced amplitude values that repeats within the examination sequence is implemented once for the sequence to be implemented. The noises resulting therefrom are recorded and correspondingly employed for the control of the prospective anti-noise per repetition of the characteristic pattern upon implementation of the sequence.  
         [0031]    As a fifth exemplary embodiment of the invention, FIG. 6 shows a hearing protection module  71  of a hearing protection  70  for a human head  11  fashioned like a headset. For the continuous monitoring of an acoustic pressure level within the space formed between the head  11  and the inside of the hearing protection module  71 , the hearing protection module  71  has a microphone  76 , a central unit  73  (including an energy supply unit  74 ), and a transmission unit  78 . The description pertaining to the embodiment of FIG. 4 applies for the units  73  through  78  as well as their functioning.  
         [0032]    It should be noted that the relative damping effect of the hearing protection plugs  12 A and  12 B on the acoustic pressure level is only indirectly monitored via their pressing force in the outer auditory canal  13 , and the absolute acoustic pressure level occurring at the tympanic membrane  14  is not monitored. In the hearing protections  50 ,  60  and  70 , in contrast, the absolute acoustic pressure level occurring at the tympanic membrane  14  can be monitored.  
         [0033]    [0033]FIG. 7 is a schematic illustration of a magnetic resonance apparatus  20 . The magnetic resonance apparatus  20  thereby has a basic field magnet system  21  for generating a basic magnetic field and a gradient coil system  22  for generating gradient fields. The magnetic resonance apparatus  20  has an antenna system  23  for emitting radiofrequency signals in as well as for acquiring the magnetic resonance signals generated as a result thereof. The gradient coil system  22  is connected to a central control system  24  for controlling currents in the gradient coil system  22  on the basis of a selected sequence. The antenna system  23  is likewise connected to the central control system  24  for controlling the radiofrequency signals to be emitted according to the selected sequence as well as for the further-processing and storing of the magnetic resonance signals acquired by the antenna system  23 . For, among other things, positioning a region of a patient  10  under examination to be imaged in the magnetic resonance apparatus  20 , the magnetic resonance apparatus  20  has a movable support mechanism  26  on which the patient  10  is placed. The central control system  24  is connected to a display and operating device  25  via which inputs of an operator, for example the desired sequence type and sequence parameters, are supplied to the central control system  24 . Among other things, further, the generated magnetic resonance images are displayed at the display and operating device  25 .  
         [0034]    The patient  10  on the support mechanism  26  wears, for example, the hearing protection  70  according to FIG. 6. The central control system  24  of the magnetic resonance apparatus  20  is fashioned such that it receives information about the acoustic pressure level at the tympanic membranes  14  of the patient  10  continuously transmitted from the hearing protection  70 , and can automatically control or abort an ongoing sequence such that an acoustic pressure level at the tympanic membranes  14  of the patient  10  does not exceed a prescribable limit value of, for example, 80 dBA. Damage to the hearing of the patient  10  is thus reliably precluded. This also applies to sedated patients.  
         [0035]    Although modifications and changes may be suggested by those skilled in the art, it is the invention of the inventor to embody within the patent warranted heron all changes and modifications as reasonably and properly come within the scope of his contribution to the art.