Biomedical Engineering Reference
In-Depth Information
photon pathlength is long; this happens when the distance between emitting and receiv-
ing fibres is higher. The multiple scattering leads to an underestimation of the perfusion
level. The multiple scattering underestimation effect could be avoided by using the cor-
rection factor presented by Nilsson
et al.
[2] but
in vitro
tests with blood are required to
implement that.
In the simulation, results demonstrate that M1 increases with the emitting-receiving
fibre distance. The same happens in the perfusion measurements, as it increases with
the fibre distance. However, when wavelengths are compared, M1 firstly decreases from
635 to 785 nm and then increases for 830 nm. This may be due to the Doppler photons
percentage that exceeds the reticular dermis. In the perfusion measurements, when dif-
ferent wavelengths are compared there was a trend to the decrease of the perfusion
for the highest fibre distances and for the highest wavelengths, probably due too the
multiple scattering.
3.3
Rat Brain
Rat Brain Simulations.
In the simulation made for the rat brain model, it can be
seen that the photons Doppler shifted travelled a mean depth of 0.15 mm (cf. table 8).
This value is in accordance with Frediksson
et al.
[10] which obtained 0.16 mm of
measurement depth. Each photon suffers, in average, 2.23 scattering events. In a total
of 5,000,000 photons detected 11.9% had suffered Doppler shift and M1 was predicted
to be
3
.
51
10
17
Hz. These results will help in the rat brain probe positioning as it shall
be 0.15 mm above the mean measurement depth.
×
Ta b l e 8 .
The percentage of Doppler events detected, the mean of Doppler scattering, the mean
depth of the Doppler events for each photon and M1 for the rat model
Mean depth Doppler (mm) Detected Doppler (%) Mean Doppler scattering
M1 (Hz)
3
.
51
×
10
17
0.15
11.9
2.23
Rat Brain Measurements.
The signals collected in the rat brain were processed and
compared with those obtained with the Perimed probe. Signals were collected in one
animal with the 785 nm micro-probe located in the rigth brain hemisphere and the
Perimed probe located in the left rat brain hemisphere. The Periflux 5000, CM, AM,
M0 and M1 results are presented in Fig. 3.
An initial baseline can be seen during the first 5 minutes in Perifllux 5000, CM,
AM, M0 and M1 results. After the nitrite injection the mean amplitude decreases in
Periflux 5000. This could be due to a probe displacement during the nitrite injection.
Despite that, the perfusion increases in the next 19 minutes followed by an amplitude
oscillation and finally the amplitude decreases after 27 minutes of acquisition during the
cardiac arrest in Perimed, CM, AM, M0 and M1 results. A peak registered in Perimed
at 28 min, caused by cardiac arrhythmias, can also be seen in the results obtained in our
prototype.
In vivo
results with the new probes show good agreement when compared with the
signals obtained with the Perimed device. Blood perfusion variations promoted by ni-
trite intraperitoneal injection are clearly visible on the signals obtained with the tested
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