| United States Patent |
5,412,419
|
|
Ziarati
|
May 2, 1995
|
Magnetic resonance imaging compatible audio and video system
Abstract
An audio and video system that is compatible with the strong magnetic
fields generated by Magnetic Resonance Imaging equipment (wherein the MRI
equipment is separated by a penetration panel into a control room and a
magnet room). The system receives an incoming RF signal through a
television or video cassette recorder, and then separates the RF signal
into a video section signal and an audio section signal. The video section
signal passes through appropriate buffering, amplifying, low pass (for the
procession frequency) and RF filtering circuits, and is next conducted
through the penetration panel into the magnet room where it is terminated
and filtered again for spurious noise. A processor and LCD pixel driver
then process the video section signal and send it to an LCD display
screen. A mushroom shaped hook is mounted to the screen and a catch is
mounted to a bore of a main magnet inside the magnet room so that the LCD
screen can be attached to the bore. The audio section signal is separated
into two channels, passed through an amplifier and appropriate RF filters
and chokes, and fed into a pneumatic transducer inside the magnet room. A
headset having an inner set connects the output of the pneumatic
transducer to the patient's ear, while an outer set covers the patient's
ear to block out gradient knocking noises. In an alternate embodiment, a
CCD camera is mounted inside the control room along with a microphone so
that pictures and sounds from the MRI technologist can be broadcast
through the present system to allow the patient to see and hear the
technologist speaking. Fiber optics technology may also be incorporated
into the signal conducted cables provided under this invention.
| Inventors:
|
Ziarati; Mokhtar (Calabasas, CA)
|
| Assignee:
|
Ziarati; Susana (North Hollywood, CA)
|
| Appl. No.:
|
653711 |
| Filed:
|
February 11, 1991 |
| Current U.S. Class: |
348/61; 324/318; 348/77; 600/418 |
| Intern'l Class: |
H04N 007/18 |
| Field of Search: |
358/93,901,102,110,112
|
U.S. Patent Documents
| 4347911 | Sep., 1982 | Bertagna et al. | 181/130.
|
| 4595260 | Jun., 1986 | Kubota | 350/351.
|
| 4824210 | Apr., 1989 | Shimazaki | 350/331.
|
| 4861142 | Aug., 1989 | Tanaka et al. | 350/345.
|
| 4901141 | Feb., 1990 | Costello | 128/653.
|
| 4903703 | Feb., 1990 | Igarashi et al. | 128/653.
|
| 4928123 | May., 1990 | Takafuji | 353/20.
|
| 4933981 | Jun., 1990 | Lederer | 381/90.
|
| 4981137 | Jan., 1991 | Kondo et al. | 128/653.
|
| 4991580 | Feb., 1991 | Moore | 128/653.
|
| 4991587 | Feb., 1991 | Blakeley et al. | 128/653.
|
| 5076275 | Dec., 1991 | Bechor et al. | 128/653.
|
| Foreign Patent Documents |
| 3708518 | Sep., 1988 | DE | 128/653.
|
Other References
AAPM report No. 20, "Site planning for Magnetic Resonance Imaging Systems,"
published in 1986 by the American Association of Physicists in Medicine.
|
Primary Examiner: Kostak; Victor R.
Assistant Examiner: Lee; Michael H.
Attorney, Agent or Firm: Wilson, Sonsini, Goodrich & Rosati
Claims
What is claimed is:
1. An audio and video system compatible with a magnetic resonance imager
disposed in a control room and a magnet room separated by a penetration
panel, wherein the magnet room contains a main magnet having a bore, the
system comprising:
means for receiving an incoming signal and dividing the incoming signal
into a video section signal and an audio section signal, located in the
control room;
means for buffering and amplifying the video section signal, located in the
control room, and connected to the means for receiving;
means for filtering the video section signal for RF and high frequencies,
located in the control room, and connected to the means for buffering and
amplifying;
a first means for conducting the video section signal, connected to the
means for filtering and passing through the penetration panel into the
magnet room;
means for terminating and filtering the video section signal, located in
the main magnet bore, connected to the first means for conducting;
means for processing and converting the video section signal into a display
driving signal, located in the main magnet bore, connected to the means
for terminating;
means for displaying the display driving signal, connected to the means for
processing, and secured to the main magnet bore by an attachment means;
means for amplifying the audio section signal, located in the control room,
connected to the means for receiving;
means for RF filtering and RF choking the audio section signal, located in
the control room, connected to the means for amplifying;
a second means for conducting the audio section signal, connected to the
means for RF filtering and passing through the penetration panel into the
magnet room;
means for converting the audio section signal into audible sound waves,
located in the magnet room, connected to the second means for conducting;
a hollow tube, located in the magnet room, connected to the means for
converting; and
a headset connected to the hollow tube, located in the magnet room,
providing an inner set adapted to engage a human ear to conduct audible
sound waves thereto and disposed inside an outer set, wherein the outer
set is adapted to cover the human ear to block out audible sound.
2. The audio and video system according to claim 1, wherein the means for
displaying further comprises means for focussing and projecting an image
from the means for displaying onto a projection screen.
3. The audio and video system according to claim 2, wherein the video
section signal includes a chroma signal, a control signal and a power
source signal.
4. The audio and video system according to claim 3, wherein the means for
converting is a pneumatic transducer.
5. The audio and video system according to claim 4, wherein the means for
displaying is a liquid crystal display screen.
6. The audio and video system according to claim 5, wherein the pneumatic
transducer is a piezoelectric driver.
7. The audio and video system according to claim 6, wherein the first means
for conducting is a 25-conductor shielded cable.
8. The audio and video system according to claim 7, wherein the second
means for conducting is a 5-pin shielded cable.
9. The audio and video system according to claim 7, wherein the second
means for conducting is a coaxial cable.
10. The audio and video system according to claim 7, wherein the liquid
crystal display further comprises a fluorescent tube.
11. The audio and video system according to claim 10, wherein the system
further comprises means for remotely controlling the means for receiving
for volume and channel selection.
12. The audio and video system according to claim 11, wherein the hollow
tube is made from a flexible polymer.
13. The audio and video system according to claim 12, wherein the
attachment means further comprises a mushroom shaped hook affixed to the
liquid crystal display screen, and a catch, mounted to the main magnet
bore and adapted to engage the hook.
14. The audio and video system according to claim 13, wherein the means for
receiving is a television.
15. The audio and video system according to claim 13, wherein the means for
receiving is a video cassette recorder.
16. The audio and video system according to claim 1, wherein the system
further comprises a charge coupled device camera and a microphone mounted
inside the control room, wherein a video output of the camera and an audio
output of the microphone are connected to the means for receiving.
17. An audio and video system compatible with a magnetic resonance imager
disposed in a control room and a magnet room separated by a penetration
panel, wherein the magnet room contains a main magnet having a bore, the
system comprising:
means for receiving an incoming signal and dividing the incoming signal
into a video section signal and an audio section signal, located in the
control room;
means for buffering and amplifying the video section signal, located in the
magnet room and contained within a RF shielded enclosure, and connected to
the means for receiving;
means for processing and converting the video section signal into a display
driving signal, located in the main magnet bore, connected to the means
for buffering;
means for displaying the display driving signal, connected to the means for
processing, and secured to the main magnet bore by an attachment means;
means for amplifying the audio section signal, located in the control room,
connected to the means for receiving;
means for RF filtering and RF choking the audio section signal, located in
the control room, connected to the means for amplifying;
a means for conducting the audio section signal, connected to the means for
RF filtering and passing through the penetration panel into the magnet
room;
means for converting the audio section signal into audible sound waves,
located in the magnet room, connected to the means for conducting;
a hollow tube, located in the magnet room, connected to the means for
converting; and
a headset connected to the hollow tube, located in the magnet room,
providing an inner set adapted to engage a human ear to conduct audible
sound waves thereto and disposed inside an outer set, wherein the outer
set is adapted to cover the human ear to block out audible sound.
18. A method of producing audio and video signals compatible with a
magnetic resonance imager disposed in a control room and a magnet room
separated by a penetration panel, wherein the magnet room contains a main
magnet having a bore, the method comprising the steps of:
receiving an incoming signal inside the control room;
separating the incoming signal into a video section signal and an audio
section signal;
buffering and amplifying the video section signal;
filtering the video section signal;
shielding the video section signal;
passing the video section signal through the penetration panel into the
magnet room;
terminating and filtering the video section signal;
processing the video section signal to drive an LCD display screen;
attaching the LCD display screen to the bore;
amplifying the audio section signal;
filtering and choking the audio section signal;
shielding the audio section signal;
passing the audio section signal through the penetration panel into the
magnet room;
transducing the audio section signal into an audible sound wave;
conducting the audible sound wave to a headset; and
blocking out noise external to the headset.
19. An audio and video system compatible with a magnetic resonance imager
disposed in a control room and a magnet room separated by a penetration
panel, wherein the magnet room contains a main magnet having a bore, the
system comprising:
means for receiving an incoming signal and dividing the incoming signal
into a video section signal and an audio section signal, located in the
control room;
means for buffering and amplifying the video section signal, connected to
the means for receiving;
means for filtering out signals above a first high frequency of the video
section signal, connected to the means for buffering;
means for displaying the video section signal, connected to the means for
filtering out signals above a first high frequency, located in the magnet
room;
means for attaching the means for displaying to the bore;
means for amplifying the audio section signal, connected to the means for
receiving, located in the control room;
means for filtering out signals above a second high frequency of the audio
section signal, connected to the means for amplifying;
means for converting the audio section signal into an audible sound wave,
connected to the means for filtering out signals above a second high
frequency, located in the magnet room; and
means for conveying the audible sound wave to a patient in the magnet room
and for blocking out external noise, connected to the means for
converting.
20. The audio and video system according to claim 19, wherein the first
high frequency is above 4.5 MHz.
21. The audio and video system according to claim 20, wherein the second
high frequency is above 20 kHz.
22. The audio and video system according to claim 21, wherein the system
further comprises:
a fiber optics generator, connected to the means for filtering out signals
above a first high frequency, located in the control room;
a fiber optics cable connected to the fiber optics generator to conduct the
video section signal;
a fiber optics receiver connected to the fiber optics cable, located in the
magnet room; and wherein
the means for displaying the video section signal is connected to the fiber
optics receiver.
23. A video display system for a patient disposed within a magnetic
resonance imaging device having a magnetic field, said magnetic resonance
imaging device comprising a control room and a magnet room separated by a
penetration panel, said magnet room comprising a main magnet having a
bore, said video display system comprising:
a magnetically inert display comprising a liquid crystal display (LCD)
screen;
said magnetically inert display positioned within the magnetic field of
said magnetic resonance imaging device; and
a filter preventing electrical signals generated by said magnetically inert
display from interfering with said magnetic resonance imaging device.
24. The system of claim 23, further comprising means for preventing
electrical signals generated by said magnetic resonance imaging device
from interfering with said magnetically inert display.
25. The system of claim 23 or 24, wherein said filter comprises a low pass
filter.
26. The system of claim 25, further comprising means for attaching said
magnetically inert display to the main magnet bore, said means comprising
a mushroom-shaped hook affixed to the LCD screen, and a catch mounted to
the main magnet bore and adapted to engage the hook.
27. A video display system for a patient disposed within a magnetic
resonance imaging device having a magnetic field, said magnetic resonance
imaging device comprising a control room and a magnet room separated by a
penetration panel, said magnet room comprising a main magnet having a
bore, said video display system comprising:
a magnetically inert display comprising a liquid crystal display (LCD)
screen;
said magnetically inert display positioned within the magnetic field of
said magnetic resonance imaging device; and
means for preventing electrical signals generated by said magnetically
inert display from interfering with said magnetic resonance imaging
device.
28. The system of claim 27, further comprising means for preventing
electrical signals generated by said magnetic resonance imaging device
from interfering with said magnetically inert display.
29. The system of claim 27 or 28, wherein at least one of said means for
preventing comprises a low pass filter.
30. The system of claim 29, further comprising means for attaching said
magnetically inert display to the main magnet bore, said means comprising
a mushroom-shaped hook affixed to the LCD screen, and a catch mounted to
the main magnet bore and adapted to engage the hook.
31. A video display system for a patient disposed within a magnetic
resonance imaging device having a magnetic field, said magnetic resonance
imaging device comprising a control room and a magnet room separated by a
penetration panel, said magnet room comprising a main magnet having a
bore, said video display system comprising:
a video signal;
a magnetically inert display comprising a liquid crystal display (LCD)
screen;
said magnetically inert display positioned within the magnetic field of
said magnetic resonance imaging device; and
means for preventing electrical signals generated by said video signal from
interfering with said magnetic resonance imaging device.
32. The system of claim 31, further comprising means for preventing
electrical signals generated by said magnetic resonance imaging device
from interfering with said video signal.
33. The system of claim 32, wherein at least one of said means for
preventing comprises a low pass filter.
34. The system of claim 31, 32 or 33, wherein said video signal is supplied
to said magnetically inert display through a shielded cable.
35. The system of claim 31, 32 or 33, wherein said video signal is supplied
to said magnetically inert display through a fiber optic cable.
36. The system of claim 33, further comprising an amplifier located in the
control room, for amplifying the video signal before the video signal is
filtered by said filter.
37. The system of claim 36, further comprising means for attaching said
magnetically inert display to the main magnet bore, said means comprising
a mushroom-shaped hook affixed to the LCD screen, and a catch mounted to
the main magnet bore and adapted to engage the hook.
38. The system of claim 32, further comprising a charge coupled device
camera and a microphone mounted inside the control room, wherein a video
output of the camera supplies said video signal.
39. A video and audio display system for a patient disposed within a
magnetic resonance imaging device having a magnetic field, said magnetic
resonance imaging device comprising a control room and a magnet room
separated by a penetration panel, said magnet room comprising a main
magnet having a bore, said video and audio display system comprising:
an incoming signal comprising a video signal portion and an audio signal
portion;
a video and audio receiver, wherein said receiver divides said incoming
signal into a video signal portion and an audio signal portion;
a magnetically inert display comprising a liquid crystal display (LCD)
screen;
said magnetically inert display positioned within the magnetic field of
said magnetic resonance imaging device; and
means for preventing electrical signals generated by said video signal
portion from interfering with said magnetic resonance imaging device.
40. The system of claim 39, further comprising means for preventing
electrical signals generated by said magnetic resonance imaging device
from interfering with said video signal portion.
41. The system of claim 39, further comprising a filter preventing said
audio signal portion from interfering with the magnetic resonance imaging
device.
42. The system of claim 41, wherein said filter comprises a low pass
filter.
43. The system of claim 39, 40 or 41, wherein said video signal portion is
supplied to said magnetically inert display through a shielded cable.
44. The system of claim 39, 40 or 41, wherein said video signal portion is
supplied to said magnetically inert display through a fiber optic cable.
45. The system of claim 39, 40 or 41, further comprising a piezoelectric
transducer for converting said audio signal portion into audio sound
waves.
46. The system of claim 45, further comprising a hollow tube connected to
said piezoelectric transducer, and a headset connected to said hollow
tube, said headset comprising an inner set portion adapted to engage a
human ear to conduct audible sound waves thereto and disposed inside an
outer set portion, wherein the outer set portion is adapted to cover the
human ear to block out audible sound.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of magnetic resonance imaging
equipment. More precisely, the present invention relates to an audio and
video system including a liquid crystal display that is not disrupted by
strong magnetic fields created by Magnetic Resonance Imaging devices.
2. Description of the Prior Art and Related Information
Magnetic Resonance Imaging (i.e., "MRI") is a relatively new scanning
procedure being used in the medical community extensively. MRI is a valued
technique for assisting doctors diagnose numerous medical ailments. The
scanning procedure requires that a patient lie still inside a tunnel
shaped enclosure called the bore. The MRI device uses a strong magnetic
field that is generated around the patient's body. Disturbances in the
field due to the presence of the body can be detected and translated into
images displayed on a viewing screen.
MRI technology involves very sophisticated hardware. The most prominent
piece of hardware is a large magnet that induces a strong, uniform, and
static magnetic field. Generally, the magnetic field ranges from 0.5 Tesla
to 2.0 Tesla inside the bore. Gradient coils disposed around the bore
induce spatially variant magnetic fields (i.e., gradients) that modify the
existing uniform magnetic field. To induce nuclear resonance, a
transmitter emits radio waves through a coil, which coil couples the radio
wave energy with the resonating nuclei inside the magnetic field. A
receiver, also connected to the coil, receives the disrupted
electromagnetic waves. The waves are filtered, amplified, and processed
into visual data for viewing by an MRI technologist attending to the
procedure. More detailed information regarding MRI equipment is available
in a book entitled Nuclear Magnetic Resonance, pp. 53-66 (1st ed. 1981),
the contents of which are incorporated by reference.
As useful as an MRI scanning procedure is, it exacts a toll on the patient.
For example, on many occasions patients cannot complete the exam due to
claustrophobia caused by having to lie prone inside the bore for a long
time while the procedure takes place. To be sure, the procedure is rather
long in duration, lasting about half an hour up to two hours. Or, the
patient simply gets bored or restless from being in a tight area.
Another discomforting factor is that during the MRI exam there is a harsh
and loud knocking noise generated by the MRI gradient amplifier. This
noise is commonly called gradient pulse, which naturally is very annoying
to the patient who must endure the drone for a long period of time.
Accordingly, there is a great demand for some method of comforting the
patient to keep his mind off the MRI scanning procedure. He should be
entertained in some way without having the entertainment aspect detracting
from the quality of the images that are being taken by the MRI
technologist. Indeed, the patient should be relaxed somehow since the MRI
device is formidable-looking and the patient is most likely already
nervous from having to undergo such an examination.
A quick and simple solution to the entertainment problem is to provide the
patient with a television to view, or a radio to listen to. But by virtue
of the operating principles behind MRI technology, the exam room where the
main magnet is located is permeated with very strong magnetic fields. So
it is nearly impossible for a typical television, video cassette recorder
(VCR), stereo, cassette player, or any electronic device to function
properly in those conditions. In short, the effect of the strong magnetic
field and the sensitivity of the MRI hardware to high frequency RF leakage
(mainly from 10 MHz to 70 MHz) do not allow an ordinary television or
audio system to function inside the magnet room (i.e., exam room).
Therefore, a need presently exists for an electronic device that can
operate in the environment of an MRI magnet room to entertain a nervous
patient while he or she undergoes the scanning procedure. The electronic
device should also not interfere with the MRI process.
SUMMARY OF THE INVENTION
The present invention relates to an electronic entertainment device
suitable for operation within strong magnetic fields. In a preferred
embodiment, the present invention provides an audio and video system with
properly filtered and shielded circuitry so that the system can be
operated in a strong magnetic field created by MRI equipment. For the
patient's benefit, the system also provides a liquid crystal display (LCD)
screen for watching and a headset for listening.
The audio and video system provided by the present invention is divided
between two rooms occupied by the MRI equipment. Although not part of the
present invention, description of the rooms is given as background
information. One room is called the control room and is where the MRI
technologist controls the MRI process. The other room is the magnet or
exam room, which is separated from the control room by a penetration
panel, and contains the main magnet of the MRI device.
According to the present invention, the system receives an incoming RF
signal through a television receiver or video cassette recorder, which
then separates the RF signal into a video section signal and an audio
section signal. The video section signal passes through appropriate
buffering, amplifying, low pass and RF filtering circuits. The low pass
filter is necessary to block out high frequency noise around the
procession frequency of a hydrogen proton, which resonates during the MRI
process. Next, the video section signal is conducted through the
penetration panel into the magnet room where it is terminated and filtered
again for noise.
Inside the magnet room, a processing circuit and LCD pixel driver then
process the video section signal and send it to an LCD display screen. An
optional magnifying lens system may be adapted to the LCD display screen
to project the pictures on to a large reflective screen (as in a big
screen TV). A patient lying prone inside the magnet bore can then watch
the television pictures on the reflective screen through a pair of prism
glasses worn by him.
But without the lens system, the patient views the LCD display screen
directly. To facilitate viewing, a mushroom shaped hook is mounted to the
LCD screen and a catch is mounted to the bore so that the LCD screen can
be attached to the bore.
The audio section signal is separated into two channels, passed through an
amplifier and appropriate RF filters and chokes, and fed through the
penetration panel and into a pneumatic transducer inside the magnet room.
The pneumatic transducer converts the electrical impulses of the audio
section signal into audible sound waves.
Also provided by the present invention is a headset designed to fit the
skull of the patient undergoing the MRI procedure. The headset comprises
an inner set and an outer set. The inner set connects the output of the
pneumatic transducer to the patient's ear, thereby bringing sounds of the
television or VCR to the patient. By contrast, the outer set is
circumaurel in construction so that each ear cup covers the patient's ears
to block out gradient knocking noises.
Another feature of the preferred embodiment system is for the patient to be
able to see and hear the MRI technologist speaking to him from the control
room via the LCD display screen and headset. This is achieved by mounting
a CCD (charge coupled device) camera with a microphone in the control room
and using a television signal interrupt switch to turn the CCD camera and
microphone on, and then patching into the television receiver. The
receiver then functions as before to direct the pictures and sounds to the
patient. Hence, this feature allows the patient to see and hear the
technologist.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a preferred embodiment of the present
invention illustrating the entire audio and video system separated between
a control room and a magnet room.
FIG. 2 illustrates a headset provided by the present invention and a
supplemental side view of an ear cup of the headset.
FIG. 3 provides a magnified view of an ear tip component of the inner set.
FIG. 4 is a view of a preferred embodiment LCD video display screen.
FIG. 5 is an enlarged view of the hook mounted to the LCD display screen.
FIGS. 6A and 6B provide side and bottom views, respectively, of the catch
mechanism designed to engage the hook shown in FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
The following detailed description outlines an MRI compatible audio and
video system having an LCD display screen. In the following description,
numerous details such as specific materials and configurations are set
forth in order to provide a more complete understanding of the present
invention. But it is understood by those skilled in the art that the
present invention can be practiced without these specific details. In
other instances, well known elements are not described in detail so as not
to obscure the present invention. In any event, the scope of the invention
is best determined by reference to the appended claims.
GENERAL ARRANGEMENT
In a preferred embodiment, the present invention provides an MRI compatible
audio and video system. FIG. 1 gives a general overview of how the present
invention system is set up in relation to the MRI equipment, which is
disposed partly in a magnet room and partly in a control room.
One portion of the present invention system is located inside the MRI
control room 1. That portion of the system includes a receiver and
associated electronic filters and circuitry. Dashed lines in FIG. 1
circumscribe the borders of that room. Everything outside the dashed lines
represents the examination or magnet room 2. The other portion of the
system that includes an LCD screen and its circuitry are located within
the magnet room 2. As the name implies, the magnet room 2 contains a main
magnet of the MRI device (not shown) that generates a strong magnetic
field.
Continuing with the general overview, FIG. 1 shows that the system
contained in the magnet room 2 is again divided such that certain parts of
the system are mounted inside the bore of the main magnet (so labeled in
FIG. 1) and other parts remain outside the bore. The parts inside the bore
include a terminator, filter circuits, an LCD pixel driver, and an LCD
screen. Of course the patient (not shown) undergoing the scanning process
is positioned inside the bore, too. Outside the bore but still within the
magnet room 2 is a pneumatic transducer 21 for generating sound, which is
connected to a headset 23 worn by the patient.
Aside from being physically divided into two portions, the system in a
preferred embodiment is separated in terms of electronics into two major
sections; namely, a video section and an audio section. Each section is
explained in detail below.
THE VIDEO SECTION (CONTROL ROOM)
The video section is located partially in the control room 1 and partially
in the magnet room 2, as illustrated in FIG. 1. In the control room 1, a
television receiver 3 picks up an incoming RF signal through an antenna or
from a video source like a video cassette recorder (VCR) player. The
receiver 3 processes the incoming RF signal and separates out the sound or
audio section signal 17 from the picture or video section signal 4. Since
a television receiver and VCR are devices well known in the art, no
detailed discussion is required here.
In the video section, the video section signal 4 is processed from the
incoming RF signal in the television receiver 3 to obtain red, green, and
blue chroma video signals (labeled R, G, and B in FIG. 1), and a control
signal. The red, green and blue chroma signals along with the control
signal, collectively labeled the video section signal 4, are sent to a
buffer board 5. A power supply, well known in the art, delivers as part of
the video section signal 4 a power signal (labeled PWS in FIG. 1) to the
buffer circuit board 5.
At this point all the signals necessary to drive the LCD display screen 6
are present, but since the LCD screen 6 is located a distance away from
the television receiver 3 (in a preferred embodiment, about 100 feet away
from the television unit) the video section signal 4 needs to be amplified
and buffered. Hence the need for a buffer and amplifier board 5. For some
types of signals, only a unity-gain, current driver amplifier is
sufficient. In this preferred embodiment, a high gain bandwidth
operational amplifier is used as a buffer to drive the video section
signal 4 through the approximately 100 feet. In some signals,
amplification along with a driver are necessary.
A typical MRI signal is very sensitive to the electrical noise around the
procession frequency of a hydrogen proton, wherein this frequency varies
from 12 MHz to 80 MHz depending on the field strength of the magnet. This
relationship is generally expressed as:
f=(42.5).times.(B)
wherein B is the field strength in Tesla and f is the frequency in
Megahertz.
Mindful of the foregoing relationship, a filter board 7 is included to
block out all other frequencies above the video frequency range, typically
above 4.5 MHz. To do that, a LP filter and an RF filter are required for
the filter board 7. All of the signals from the buffer board 5 have to
pass through the filter board 7 before entering the magnet room 2.
As alluded to above, after leaving the filter board 7, the video section
signal 4 can travel up about 100 feet before interfacing with the LCD
screen 6. Thus, a 25-conductor shielded cable 8 is used to carry the video
section signal 4 for that distance.
In an alternate embodiment (not shown), a fiber optic cable may be used in
place of the shielded cable 8. Further, a fiber optic generator is added
to the filter board 7 to convert the electrical video section signal 4 to
optical impulses to be carried by the fiber optic cable. In this
embodiment, the terminator board 9 is not required. In its place is a
fiber optic receiver to decode and convert the optical impulses into
electrical signals.
THE VIDEO SECTION (MAGNET ROOM)
The 25-conductor shielded cable 8 is fed into the magnet room 2 where the
other part of the video section is located. But first, the cable 8 must
pass through a penetration panel (not shown) separating the magnet room 2
from the control room 1. In the magnet room 2, the incoming video section
signal 4 from the 25-conductor shielded cable 8 is terminated with the
proper load resistor 9 known in the art. Appropriate filters are also
provided on that same circuit board 9 to eliminate the effects of RF
signals and gradient noise from the MRI equipment upon the video section
signal 4, and vice versa.
The video section signal 4 next proceeds to circuit board 10. Here, the
incoming analog and digitized signal 4 from the terminator and filter
board 9 is processed and fed into an LCD pixel driver circuit 10. The
output of the processor circuit and pixel driver 10 is sent to the LCD
display screen 6. As seen in FIG. 1, located just behind the LCD screen 6
is a light source 10 such as a fluorescent tube to supply backlighting for
the picture on the LCD screen 6. Naturally, other means of backlighting
known in the art are possible. FIG. 4 provides a more detailed view of the
LCD display screen 6.
MOUNTING THE LCD DISPLAY SCREEN
According to the present invention, placement of the LCD display screen 6
is important. There are basically two different ways of positioning a
patient inside the main magnet bore for an MRI exam; he can be positioned
inside the bore either with his head in first or with his feet in first.
Needless to say, this complicates the way the LCD display screen 6 can be
oriented. For instance, the LCD display screen 6 cannot be mounted in a
horizontal plane if the patient goes into the bore feet first because the
picture on the LCD display screen 6 would appear upside down to him. Of
course the screen 6 would then have to be rotated 180.degree. along a
vertical axis of rotation to obtain an upright image.
Fortunately, most of the MRI devices on the market already have a built-in
reflection mirror inside the magnet bore. With this mirror, the patient
can see outside of the bore along a horizontal axis as he lies on his back
on a patient carriage oriented head first in the magnet bore. To take
advantage of the orientation of the patient, the present invention
provides that the LCD display screen 6 be mounted vertically a quarter of
the distance inside the magnet bore. When the patient is placed inside the
magnet head first, he can see the LCD display screen 6 through its
reflection in the mirror. If the patient enters the magnet bore feet
first, he has a direct view of the LCD display screen 6 if the screen 6 is
pivoted around a vertical axis.
FIGS. 4, 5, 6A and 6B illustrate the means by which the LCD display screen
6 is held in position inside the magnet bore. In this preferred
embodiment, a mushroom shaped hook 12 extends from the top of the LCD
display screen 6 as depicted in FIG. 4. The display screen 6 in FIG. 4 is
tilted slightly to reveal the placement of the hook 12. FIG. 5 shows an
enlarged view of the mushroom-shape hook 12. As the name implies, the hook
12 has a round shaft 13 capped at one end by a circular dome 14. A catch
15, shown in FIGS. 6A and 6B, mounted to the bore is designed to receive
the hook 12 of the LCD screen 6, holding the screen 6 up in the bore. It
can be seen that the large dome 14 of the hook 12 slides into the dovetail
opening 16 of the catch 15. Moreover, the hook 12 is designed to rotate,
slide or disengage if the LCD display screen 6 is accidentally knocked
along a horizontal direction, thus avoiding any damage to the LCD screen
6. Alternatively, the LCD screen 6 can be mounted to the bore with
something as simple as a hook and pile fastener (i.e., Velcro).
THE AUDIO SECTION
The next part of the system as provided in the preferred embodiment of the
present invention is an audio section that enables the patient to hear the
signal from the television receiver 3. Going back to FIG. 1, the
television receiver 3 separates out the audio section signal 17 from the
received RF signal in a manner known in the art. Next, the audio output
from the receiver 3 is separated into two channels for left and right
stereo imaging (labeled L and R in FIG. 1), then amplified through a
dedicated audio amplifier 18 with a volume control.
The output of the audio section signal 17 from the audio amplifier 18 needs
to be filtered to block out electromagnetic interference having a
frequency above 20 kHz. Therefore, the present invention provides an
appropriate RF filter and RF choke 19 to block out the unwanted electrical
noise, obtaining approximately -50 dbA attenuation for all frequencies
above 5 MHz. The outputted audio section signal 17 is then conducted into
the magnet room 2 through an audio cable 20 that passes through the
penetration panel. In a preferred embodiment, the audio cable 20 can be
about 100 feet in length of either a five-pin shielded conductor, or two
separate coaxial cables. Optical fiber technology may also be incorporated
herein to conduct the audio section signal 17 too.
The magnet room 2 where the patients undergo the MRI procedure is
completely shielded for RF signals. As mentioned above, the magnet room 2
features a penetration panel that helps shield out unwanted RF signals.
Any cable that goes into the magnet room 2 must pass through the
penetration panel. As a result, all of the audio and video signals have to
be RF shielded and passed through a low pass filter before going through
the penetration panel and into the magnet room 2.
Inside the magnet room 2, the audio cable 20 is connected to a box
containing a pneumatic transducer 21 to convert electrical impulses of the
audio section signal 17 into audible sound waves (i.e., pneumatic
impulses). The pneumatic transducer 21 can be made in several different
ways. In the preferred embodiment, piezoelectric speakers known in the art
are ideal since they utilize the piezoelectric effect and are
non-magnetic. Thus, the function of the speaker is not affected by the
main magnet.
The sound waves generated by the transducer 21 are conveyed through a
hollow tube 22 connected at one end to a headset 23 worn by the patient.
In the preferred embodiment, the tubing 22 is made from a flexible polymer
material, has a 1/8th inch inside diameter, and extends about 36 inches
long. Clearly, there are many other possible methods known in the art of
conducting audible sound from the transducer to the headset, of which
plastic tubing is only one.
Another acceptable pneumatic transducer is a small, full-range speaker
packaged in a manner such that its cone driver faces and abuts the plastic
tubing to transfer the sound to the headset. Yet another type of pneumatic
transducer is a 4" mid-range driver, model LM1824, manufactured by Electro
Voice. This type of driver is configured into a horn where the sound is
emitted out of a one-inch diameter opening. The opening can be adapted to
a one-half inch diameter plastic tubing which conducts the sound waves to
the patient. With this specific horn speaker design, however, the speaker
has to be mounted outside of the magnet room because this particular horn
driver has a large magnet that might be disrupted by the main magnet of
the MRI imager.
THE HEADSET
The audible sound waves from the pneumatic transducer 21 propagate through
the hollow tube 22 and into a headset 23. As mentioned above, during the
MRI procedure, data is usually collected by a high current RF signal
called a gradient pulse. Gradient pulse causes an audible and loud
knocking noise that tends to be very annoying to the patient. To overcome
this problem, the present invention provides a specially designed headset
23 to block the gradient noise by 21 decibels or approximately 92%
attenuation from its original level.
According to the present invention, the diagram in FIG. 2 shows a preferred
embodiment headset 23. The two major parts of the headset 23 are an outer
set 24 and an inner set 25. The outer set 24 is similar to the ear muff
type headsets used at gun ranges. That particular design is intended to
muffle the loud crack or sound impulse generated by a discharging gun. The
outer set 24 as provided by this preferred embodiment has ear cups 26
(shown in a supplemental side view in FIG. 2) that are circumaural,
meaning that the ear cups 26 completely enclose each ear. The ear cups 26
are all plastic and have very soft and comfortable cushions that conform
to the side of the patient's head while sealing out external sounds. Also,
the headpiece is adjustable and the ear cups 26 are hinged to ensure a
proper fit around the patient's skull. In sum, the outer set 24 by virtue
of its circumaural design blocks out the gradient knocking noise.
Disposed inside the outer set 24 is the inner set 25, to which the tubing
22 conducting the sound waves is connected. As shown in FIG. 3, the inner
set 25 is configured somewhat like the headsets rented out to passengers
by airlines on long distance flights. The basic inner set 25 has an L
shape so that its eartip 27 easily hooks into the patient's ear canal
while its base connects with the tubing 22. Operating together, the outer
set 24 blocks out any gradient knocking noise while the inner set 25
supplies to the patient soothing sounds broadcast from the receiver 3.
In an alternate embodiment, the present invention is modified with an array
of magnifying lenses (not shown) disposed adjacent to the LCD display
screen. A reflective screen is set up a distance away from the lenses but
aligned therewith. In this manner, the pictures on the LCD display screen
are projected through the lenses onto the larger reflective screen. In
effect, a big screen TV effect can be obtained for easier viewing by the
patient.
Many other modifications are possible. For example, a volume control, VCR
controls, along with a television channel control could be accessed
remotely from the patient's end through a means known in the art. In the
same vein, even a panic switch for the patient could be adapted to the
system. This way, if the patient has an emergency, he can immediately
signal the MRI technologist through a remote controller. One such
controller is a handheld infra-red remote controller well known in the art
that could be easily adapted by one having ordinary skill in the art to
incorporate all of the above-mentioned functions.
In another alternate embodiment, the system may be modified for the patient
to be able to see and hear the MRI technologist in the control room via
the LCD display screen and headset as the technologist talks to him. This
is achieved by mounting a CCD (charge coupled device) camera and a
microphone in the control room and using an RF signal interrupt switch in
the television, known in the art, to turn the CCD camera and microphone
on. The pictures and sounds are then supplied to the patient's LCD display
screen and headset in the same manner as described for the preferred
embodiment audio and video section signals.
In yet another alternate embodiment, the present invention provides that
one cable from the television receiver or VCR located outside the magnet
room be passed through the penetration panel. Along with video signal, the
cable could carry the power source signal for the television
processor/pixel driver circuit and the buffer circuit board. The buffer
board and the television processor circuit are both kept in the magnet
room inside an RF shielded enclosure, which connects with the incoming
cable. An outgoing cable from the shielded enclosure then conducts the
signals to the LCD display screen.
An advantage of the foregoing alternate embodiment is that only one filter
is required for the video section signal and one filter for the power
supply. By contrast, the preferred embodiment requires about twenty
filters. Also, it is much easier to install since this embodiment can be
adapted to use the RG 58 coaxial cable typically already connected to the
penetration panel. No opening has to be cut into the panel to provide
access for other cables.
Unfortunately, the buffer board and associated filters for this alternate
embodiment might create spurious RF signals that adversely affect the
ongoing MRI imaging scan. Indeed, the quality of the patient scan image
may be adversely affected by such RF signal leaks.
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