Biomedical Engineering Reference
In-Depth Information
95.5
112.7
123.8
131.5
133.0
126.2
116.6
5
115.2
130.3
156.6
171.6
178.7
176.2
137.3
4
3
100.5
87.0
109.7
141.9
203.9
196.8
162.3
FIGURE 16.13
Uniformity of the PER for the gray-scale
imaging array. Densities of the gray patches
correspond to the response amplitudes shown
in millivolts. Densities of the smaller patches
represent the response variances relative to
the amplitudes.
2
96.6
138.7
166.9
185.2
186.9
182.5
148.4
1
98.8
135.0
142.1
145.9
151.2
145.2
121.9
1
2
3
4
5
6
7
1.2
1
0.8
0.6
FIGURE 16.14
Pulsing frequency dependence of the PER
for an element in the gray-scale imaging
array when pulsing at low intensity of
light. The vertical lines represent the
range of at least 20 responses for each
frequency.
0.4
0.2
0
10
0
10
1
10
2
Light pulse frequency [Hz]
photovoltage, it is clear that the arrays were not able to handle higher pulsing
frequencies at high intensities for a long time. When the level of optical power was
increased close to or above the saturation limit, the PER dropped to zero (see Figure
16.15). If the array was used in an application requiring high frame rates, the popula-
tions at each intermediate state could be estimated by models developed for analyzing
the photocycle (37). If necessary, photostimulation could be used to return the BR mol-
ecules to the ground state. Frequency sensitivity of the other two types of BR was not
measured but it would give interesting information where the different photocycles are
concerned.
16.5.5
Results
The spatial resolution of the imaging arrays is limited but it is possible to downscale the
element size with suitable design. The PERs generated by the gray-scale imaging array
