Biomedical Engineering Reference
In-Depth Information
(a)
(b)
500
250
0
-250
-
+
50fT/step
-500
Latency = 300 [msec]
0
100
200
300
400
500
Latency [msec]
+
-
50fT/step
Latency = 300 [msec]
Fig. 3.64. a
The comparison between the waveforms of the responses to the fre-
quent tone (
black lines
) and the infrequent tone (
gray lines
). Both are the averaged
data of 30 epochs. The MEG signals from all 150 sensors are overlapped.
b
The
isofield contour maps at 300 ms of the latency. The left and right maps correspond
to the responses to the frequent and infrequent tones, respectively
3.4.2
Other Biomagnetic Measurements
In this section, we consider the biomagnetometer system for the measurement
of spinal cord evoked fields.
As shown in the preceding section, one of the most successful applications
of SQUIDs is the magnetoencephalography (MEG) system [74,75]. On the
other hand, there is a strong demand for the measurement of the magnetic
field from the spinal cord and peripheral nerves, that enables orthopaedic
surgeons to observe the neuronal activity noninvasively. The biomagnetic
recording of signal propagation in the peripheral nerves and spinal cord is
expected to be a highly effective tool in diagnostic study of the conduction
blocks, such as carpal tunnel syndrome [76], and in the analysis of spinal cord
function, due to the fact that magnetic recording can provide information on
the propagation of neuronal signals with a much higher spatial resolution than
the conventional electrical potential measurement with electrodes attached
to the skin.
Several measurements of the biomagnetic fields from peripheral nerves
have already been reported [77,78]. We have developed a biomagnetometer
system especially designed to measure the spinal cord evoked magnetic field
(SCEF), taking clinical applications into consideration.
