Three-Dimensional Optical-Resolution Photoacoustic Microscopy - Biomedical Optical Imaging Technologies: Design and Applications - page 68

Fig. 2.6 In vivo optical-resolution photoacoustic microscopy of the anterior segment of a living
mouse eye. ( a ) Photograph of the animal positioning. ( b ) Maximum-amplitude projection image
acquired at 570 nm. Scale bar: 200 m

Second, consider the total 2-h laser exposure. For photochemical effects, the MPE
for the total exposure duration is the same as that for each B-scan [Eq. ( 2.11 )].
For thermal effects, the MPE for the total exposure duration is

T max D 1; 093 J=cm 2 : MPE Total .thermal/ D 1:8C E T 0:25 10 3

(2.14)

2

Thus, the MPE/pulse for the total 2-h laser exposure is

D 3:1 10 4 J=cm 2 :

MPE Total .photochemical/
n Total

(2.15)

Rule 3: Repetitive Pulse Limit
The MPE for repetitive pulses is

D 3:3 10 6 J=cm 2 : MPE RP D n 0:25

Total MPE SP

(2.16)

Rule 3 is the most conservative of the three. Therefore, the overall MPE for
each pulse is 3:3 10 6 J=cm 2 . If the pupil diameter is 7 mm [ 25 ], the maximum
permissible single laser pulse energy for OR-PAM ophthalmic imaging is computed
to be 1:3 J. Thus, our experimentally used laser pulse energy ( 40 nJ) is well
within the ANSI limits. Figure 2.6 shows the animal positioning for ophthalmic
OR-PAM imaging and a representative label-free OR-PAM image of the mouse iris
microvasculature [ 11 ].

2.7.2 Laser Safety for Skin Imaging [ 25 ]

For skin imaging, a similar setting of experimental parameters as in the ophthalmic
imaging has been used. Slightly differently, Rule 3 does not apply here. Typi-
cally, OR-PAM focuses 200 m beneath the skin surface with a focal diameter