Downloaded from www.ajronline.org by 205.217.244.246 on 10/09/15 from IP address 205.217.244.246. Copyright ARRS. For personal use only; all rights reserved
663
Technical
Monitoring Fiber-optic
Heart Rate and Oxygen Pulse Oximeter During
Frank
Stacy
G. Shellock,1’2
M. Myers,1
slice
Department
and Pediatrics,
Cedars-Sinai
March i992 0361-803X/92/i583-0663
Medical
Center,
and Ti
-
(2200/80/2),
thickness,
and a 256 x 256 matrix
were
used for all images.
12-weighted, gra(GRASS), spoiled
GRASS, ultrafast spoiled GRASS, and fast spin-echo
pulse se-
quences. Various combinations of send/receive head and extremity local coils as well as receive-only local coils were used for these studies. The fiber-optic pulse oximeter was observed continuously to dotermine if it operated properly during MR imaging. All images were inspected by experienced radiologists to determine if any pulse oximeter-related artifacts were present. (Because this pulse oximeter
Methods
of Anesthesiology
12-weighted
included Ti -weighted, proton density-weighted, dient-recalled acquisition in the steady state
Initially, we evaluated the fiber-optic pulse oximeter (Nonin Medical Inc., Plymouth, MN) to determine if it produced any artifacts during operation. We used a 1 .5-1/64-MHz MR imager (General Electric Co., Milwaukee, WI) and a fluid-filled Plexiglas phantom. The body coil of the imager was used to send and receive. The pulse oximeter’s
3
to the perimeter of the phantom, [TR/TE/excitations]),
Next, five volunteers (control subjects) had MR imaging of the brain (n = 3) or knees (n = 2) with the pulse oximeter probe attached to either the fingers (n = 3) or the great toes (n = 2). The previously indicated MR imaging parameters were used for this portion of the evaluation. Finally, 24 patients (age range, 12 days to 76 years; 10 males, 14 females) who were either sedated or anesthetized were monitored throughout the MR examination by using the fiber-optic pulse oximeter. The following body parts were imaged: 13 brains, one cervical spine, three abdomens, four chests, four lumbar spines, two thoracic spines, and one orbit. Pulse sequences used for these examinations
,
AJR 158:663-664,
(600/20/2
and proton density-weighted (2200/20/2) images were obtained in the axial, sagittal, and coronal planes. A 24-cm field of view, 5-mm
,
Received June 26, 1991 ; accepted after revision August 29, 1991. I Department of Radiology, Division of MRI, Cedars-Sinai Medical Center, Shellock. 2 Department of Radiological Sciences, University of California, Los Angeles
was attached
probe
weighted
,
and
Saturation with a MR Imaging
and Keith J. Kimble3
Physiologic monitoring during MR imaging is necessary to ensure the safety of patients who are sedated, anesthetized, or unstable [1 2]. Commercially available, modified pulse oximeters have been used, with moderate success, to determine the heart rate and oxygen saturation of sedated and anesthetized patients during MR imaging [1 2]. These pulse oximeters tend to work intermittently during MR imaging because of interference from the gradient and RF electrornagnetic fields. In certain instances, patients have been burned, presumably as a result of excessive current being induced in inappropriately looped conductive cables attached to the probes of the pulse oximeters [3]. Because assessment of heart rate and oxygen saturation is particularly desirable in some patients [1 2, 4, 5], it is imperative that the equipment used to monitor these parameters during MR be safe and reliable. Therefore, we evaluated a newly developed, lightweight, portable pulse oximeter for use on patients during MR imaging. This device specifically incorporates fiber-optic technology designed to eliminate the possibility of any adverse interaction with the MR imager. Materials
Note
contains
ferromagnetic
components,
least 10 ft [3 m] from the opening
it was
securely
positioned
at
of the bore of the 1 .5-T MR
imager.)
8700 School
Beverly
Blvd., Los Angeles,
of Medicine,
Los Angeles,
C American Roentgen Ray Society
Los Angeles,
CA 90048.
CA 90048. Address CA 90024.
reprint requests
to F. G.
SHELLOCK
664
Downloaded from www.ajronline.org by 205.217.244.246 on 10/09/15 from IP address 205.217.244.246. Copyright ARRS. For personal use only; all rights reserved
Results Although the fiber-optic pulse oxirneter was not used to record heart rate or oxygen saturation during evaluation of the phantom, it did not appear to be affected by the operation of the MR imager, insofar as no random alterations were seen in the digital display. No imaging artifacts were produced by the presence of the pulse oximeter’s probe or by the operation of the monitor. The pulse oximeter operated properly during each MR examination of control subjects. The measured heart rate was
compared
with
that
mograph, and there minute (SD). Oxygen
recorded
by using
was agreement
during
MR
were
measured
by using
values
plethys-
±1 beats per
were within normal limits for these subjects. No artifacts identified on the MR images. The pulse oximeter apparently recorded appropriate rate and oxygen saturation values for each sedated or thetized patient, although these parameters were not taneously
saturation
a pulse
to within
another
recorded
means
during
heart anessimulthis
portion of the evaluation. No pulse oximeter-related imaging artifacts were seen on any of the MR studies. We saw no evidence that the fiber-optic pulse oximeter produced any unwanted “noise” during any part of any of the evaluations (phantoms, controls, patients). Discussion Currently, mercially
a variety
available
of MR-compatible
for recording
various
ters, including heart rate, blood end-tidal carbon dioxide, oxygen flow, and temperature [1 2]. Each specially designed or specifically ,
imaging. A primary
monitors physiologic
used between
the patient
parame-
pressure, respiratory rate, saturation, cutaneous blood of these devices was either modified for use during MR
source of adverse interactions imager and the monitor (e.g., artifacts, burns)
interface
are corn-
between the has been the
and the monitoring
,
,
AJA:158,
March 1992
Our results indicate that this fiber-optic pulse oximeter functioned satisfactorily during MR imaging when a 1 .5-T/ 64-MHz MR irnager and a variety of conventional as well as more sophisticated pulse sequences were used. The 1 .5-T/ 64-MHz MR imagers are the most widely used MR systems; therefore, this pulse oximeter is compatible with most imagers. However, it remains for this fiber-optic pulse oxirneter to be tested during the operation of lower field strength/ frequency MR imagers to determine its compatibility with these other MR systems. No interruptions occurred during the operation of the fiberoptic pulse oximeter: Heart rate and oxygen saturation were appropriately measured, and the pulse oximeter did not produce any imaging artifacts during simulated or actual MR imaging procedures. More important, the use of fiber optics prevents the risk of pulse oxirneter-related burns in patients undergoing
Although patible,
an MR examination.
this pulse oximeter
because
no adverse
is considered interactions
to be MR corn-
occur
between
the
imager and the monitor (i.e., no imaging artifacts are produced, the monitor operates properly during MR imaging, and so on), the pulse oximeter does contain ferromagnetic cornponents. Therefore, the fiber-optic monitor should not be moved closer than 1 0 ft from the bore of a 1 .5-T MR imager, it should be properly labeled, and it should be firmly anchored in place to prevent it from becoming a potential “missile” [1, 5]. Currently, to our knowledge only one other fiber-optic pulse oximeter is commercially available (In Vivo, Inc., Broken Arrow, OK). However, this is not a stand-alone unit, as the device we evaluated is, and it requires extensive installation before it can be used in the MR suite. For this reason, the fiber-optic pulse oxirneter we tested is more convenient, especially at sites with more than one MR imager, because it is lightweight and portable. In addition, this device is substantially less expensive.
equip-
ment, because this usually requires a conductive cable or other device [1 2]. Special shielding is often used for the cables and leads of monitors within the MR environment, with acceptable results [1 5]. However, the presence of a conductive material in the immediate area of the MR imager remains a safety concern because of the potential for monitorrelated burns [3]. It has been shown that fiber-optic technology used to obtain and transmit physiologic signals from patients having an MR examination does not produce any MR-related electrornagnetic interference [1 2, 6-8]. Therefore, a fiber-optic pulse oximeter was designed with the intent that it be unperturbed by electromagnetic fields and that it effectively eliminate the possibility of monitor-related burns during MR imaging (i.e., no metallic, conductive materials are used for the patientmonitor interface). It is physically impossible for a patient to be burned by this fiber-optic pulse oxirneter during MR imaging because no conductive pathways are formed by any metallic materials. ,
ET AL.
REFERENCES 1 . Shellock
FG. Monitoring during MAI: an evaluation of the effect of highfield MRI on various patient monitors. Med Electronics September 1986:93-97
2. Holshouser physiological
BA,
Hinshaw
DB,
Shellock
FG.
Sedation,
anesthesia,
and
monitoring during MRI. In: ARRS Syllabus. Aeston, VA: American Roentgen Ray Society, 1991:9-15 3. Shellock FG, Slimp G. Severe bum of the finger caused by using a pulse oximeter during MA imaging (letter). AiR 1989:153:1105 4. Standards for basic intraoperative monitoring. In: Directory of members, 55th ad. Park Ridge, IL: American Society of Anesthesiologists, 1990: 640-641 5. Cohen MD. Pediatric sedation. Radiology i990;175:61 1-612 6. Shellock FG, 5chaefer DJ, Crues JV. Alterations in body and skin temperatures caused by MA imaging: is the recommended exposure for radiofrequency radiation too conservative? Br J Radiol 1989;62:904-909 7. Aces CF. Carrol FE. Fiber-optic pressure transducer for use near MA magnetic fields. Radiology i985;156:548 8. Legendre JP, Misner A, Forester GV, Geoffrion Y. A simple fiber-optic monitor of cardiac and respiratory activity for biomedical magnetic resonance applications. Magn Reson Med i986;3:953-957
663
Technical
Monitoring Fiber-optic
Heart Rate and Oxygen Pulse Oximeter During
Frank
Stacy
G. Shellock,1’2
M. Myers,1
slice
Department
and Pediatrics,
Cedars-Sinai
March i992 0361-803X/92/i583-0663
Medical
Center,
and Ti
-
(2200/80/2),
thickness,
and a 256 x 256 matrix
were
used for all images.
12-weighted, gra(GRASS), spoiled
GRASS, ultrafast spoiled GRASS, and fast spin-echo
pulse se-
quences. Various combinations of send/receive head and extremity local coils as well as receive-only local coils were used for these studies. The fiber-optic pulse oximeter was observed continuously to dotermine if it operated properly during MR imaging. All images were inspected by experienced radiologists to determine if any pulse oximeter-related artifacts were present. (Because this pulse oximeter
Methods
of Anesthesiology
12-weighted
included Ti -weighted, proton density-weighted, dient-recalled acquisition in the steady state
Initially, we evaluated the fiber-optic pulse oximeter (Nonin Medical Inc., Plymouth, MN) to determine if it produced any artifacts during operation. We used a 1 .5-1/64-MHz MR imager (General Electric Co., Milwaukee, WI) and a fluid-filled Plexiglas phantom. The body coil of the imager was used to send and receive. The pulse oximeter’s
3
to the perimeter of the phantom, [TR/TE/excitations]),
Next, five volunteers (control subjects) had MR imaging of the brain (n = 3) or knees (n = 2) with the pulse oximeter probe attached to either the fingers (n = 3) or the great toes (n = 2). The previously indicated MR imaging parameters were used for this portion of the evaluation. Finally, 24 patients (age range, 12 days to 76 years; 10 males, 14 females) who were either sedated or anesthetized were monitored throughout the MR examination by using the fiber-optic pulse oximeter. The following body parts were imaged: 13 brains, one cervical spine, three abdomens, four chests, four lumbar spines, two thoracic spines, and one orbit. Pulse sequences used for these examinations
,
AJR 158:663-664,
(600/20/2
and proton density-weighted (2200/20/2) images were obtained in the axial, sagittal, and coronal planes. A 24-cm field of view, 5-mm
,
Received June 26, 1991 ; accepted after revision August 29, 1991. I Department of Radiology, Division of MRI, Cedars-Sinai Medical Center, Shellock. 2 Department of Radiological Sciences, University of California, Los Angeles
was attached
probe
weighted
,
and
Saturation with a MR Imaging
and Keith J. Kimble3
Physiologic monitoring during MR imaging is necessary to ensure the safety of patients who are sedated, anesthetized, or unstable [1 2]. Commercially available, modified pulse oximeters have been used, with moderate success, to determine the heart rate and oxygen saturation of sedated and anesthetized patients during MR imaging [1 2]. These pulse oximeters tend to work intermittently during MR imaging because of interference from the gradient and RF electrornagnetic fields. In certain instances, patients have been burned, presumably as a result of excessive current being induced in inappropriately looped conductive cables attached to the probes of the pulse oximeters [3]. Because assessment of heart rate and oxygen saturation is particularly desirable in some patients [1 2, 4, 5], it is imperative that the equipment used to monitor these parameters during MR be safe and reliable. Therefore, we evaluated a newly developed, lightweight, portable pulse oximeter for use on patients during MR imaging. This device specifically incorporates fiber-optic technology designed to eliminate the possibility of any adverse interaction with the MR imager. Materials
Note
contains
ferromagnetic
components,
least 10 ft [3 m] from the opening
it was
securely
positioned
at
of the bore of the 1 .5-T MR
imager.)
8700 School
Beverly
Blvd., Los Angeles,
of Medicine,
Los Angeles,
C American Roentgen Ray Society
Los Angeles,
CA 90048.
CA 90048. Address CA 90024.
reprint requests
to F. G.
SHELLOCK
664
Downloaded from www.ajronline.org by 205.217.244.246 on 10/09/15 from IP address 205.217.244.246. Copyright ARRS. For personal use only; all rights reserved
Results Although the fiber-optic pulse oxirneter was not used to record heart rate or oxygen saturation during evaluation of the phantom, it did not appear to be affected by the operation of the MR imager, insofar as no random alterations were seen in the digital display. No imaging artifacts were produced by the presence of the pulse oximeter’s probe or by the operation of the monitor. The pulse oximeter operated properly during each MR examination of control subjects. The measured heart rate was
compared
with
that
mograph, and there minute (SD). Oxygen
recorded
by using
was agreement
during
MR
were
measured
by using
values
plethys-
±1 beats per
were within normal limits for these subjects. No artifacts identified on the MR images. The pulse oximeter apparently recorded appropriate rate and oxygen saturation values for each sedated or thetized patient, although these parameters were not taneously
saturation
a pulse
to within
another
recorded
means
during
heart anessimulthis
portion of the evaluation. No pulse oximeter-related imaging artifacts were seen on any of the MR studies. We saw no evidence that the fiber-optic pulse oximeter produced any unwanted “noise” during any part of any of the evaluations (phantoms, controls, patients). Discussion Currently, mercially
a variety
available
of MR-compatible
for recording
various
ters, including heart rate, blood end-tidal carbon dioxide, oxygen flow, and temperature [1 2]. Each specially designed or specifically ,
imaging. A primary
monitors physiologic
used between
the patient
parame-
pressure, respiratory rate, saturation, cutaneous blood of these devices was either modified for use during MR
source of adverse interactions imager and the monitor (e.g., artifacts, burns)
interface
are corn-
between the has been the
and the monitoring
,
,
AJA:158,
March 1992
Our results indicate that this fiber-optic pulse oximeter functioned satisfactorily during MR imaging when a 1 .5-T/ 64-MHz MR irnager and a variety of conventional as well as more sophisticated pulse sequences were used. The 1 .5-T/ 64-MHz MR imagers are the most widely used MR systems; therefore, this pulse oximeter is compatible with most imagers. However, it remains for this fiber-optic pulse oxirneter to be tested during the operation of lower field strength/ frequency MR imagers to determine its compatibility with these other MR systems. No interruptions occurred during the operation of the fiberoptic pulse oximeter: Heart rate and oxygen saturation were appropriately measured, and the pulse oximeter did not produce any imaging artifacts during simulated or actual MR imaging procedures. More important, the use of fiber optics prevents the risk of pulse oxirneter-related burns in patients undergoing
Although patible,
an MR examination.
this pulse oximeter
because
no adverse
is considered interactions
to be MR corn-
occur
between
the
imager and the monitor (i.e., no imaging artifacts are produced, the monitor operates properly during MR imaging, and so on), the pulse oximeter does contain ferromagnetic cornponents. Therefore, the fiber-optic monitor should not be moved closer than 1 0 ft from the bore of a 1 .5-T MR imager, it should be properly labeled, and it should be firmly anchored in place to prevent it from becoming a potential “missile” [1, 5]. Currently, to our knowledge only one other fiber-optic pulse oximeter is commercially available (In Vivo, Inc., Broken Arrow, OK). However, this is not a stand-alone unit, as the device we evaluated is, and it requires extensive installation before it can be used in the MR suite. For this reason, the fiber-optic pulse oxirneter we tested is more convenient, especially at sites with more than one MR imager, because it is lightweight and portable. In addition, this device is substantially less expensive.
equip-
ment, because this usually requires a conductive cable or other device [1 2]. Special shielding is often used for the cables and leads of monitors within the MR environment, with acceptable results [1 5]. However, the presence of a conductive material in the immediate area of the MR imager remains a safety concern because of the potential for monitorrelated burns [3]. It has been shown that fiber-optic technology used to obtain and transmit physiologic signals from patients having an MR examination does not produce any MR-related electrornagnetic interference [1 2, 6-8]. Therefore, a fiber-optic pulse oximeter was designed with the intent that it be unperturbed by electromagnetic fields and that it effectively eliminate the possibility of monitor-related burns during MR imaging (i.e., no metallic, conductive materials are used for the patientmonitor interface). It is physically impossible for a patient to be burned by this fiber-optic pulse oxirneter during MR imaging because no conductive pathways are formed by any metallic materials. ,
ET AL.
REFERENCES 1 . Shellock
FG. Monitoring during MAI: an evaluation of the effect of highfield MRI on various patient monitors. Med Electronics September 1986:93-97
2. Holshouser physiological
BA,
Hinshaw
DB,
Shellock
FG.
Sedation,
anesthesia,
and
monitoring during MRI. In: ARRS Syllabus. Aeston, VA: American Roentgen Ray Society, 1991:9-15 3. Shellock FG, Slimp G. Severe bum of the finger caused by using a pulse oximeter during MA imaging (letter). AiR 1989:153:1105 4. Standards for basic intraoperative monitoring. In: Directory of members, 55th ad. Park Ridge, IL: American Society of Anesthesiologists, 1990: 640-641 5. Cohen MD. Pediatric sedation. Radiology i990;175:61 1-612 6. Shellock FG, 5chaefer DJ, Crues JV. Alterations in body and skin temperatures caused by MA imaging: is the recommended exposure for radiofrequency radiation too conservative? Br J Radiol 1989;62:904-909 7. Aces CF. Carrol FE. Fiber-optic pressure transducer for use near MA magnetic fields. Radiology i985;156:548 8. Legendre JP, Misner A, Forester GV, Geoffrion Y. A simple fiber-optic monitor of cardiac and respiratory activity for biomedical magnetic resonance applications. Magn Reson Med i986;3:953-957
