1. Photo acoustic tomography

2. Index: Basics and history Major fields of Pat
Creation of photoacoustic wave
Different setups for PAT
1. photo acoustic computed tomography in linear-view
2. Photo acoustic probe that uses a Q-switched, frequency- doubled by ND-YAG
3. a multispectral opto-acoustic tomography
4. Experimental setup for PAT with Mach-Zehnder interferometer as a acoustic line detector
* *Image reconstruction algorithms for PAT
5. OR-PAM
6. PAT based on an acoustic lens system
7. Photo acoustic flowmetry
Resolution
pressure

3. Bsics:

4. Two major modes: 1. focused scanning tomography
• Dark-field confocal photoacoustic microscopy (PAM)
• Macroscopic photoacoustic
2. Computed tomography
Pic: PA macroscopy imaging
speed of sound to be 1.54 mm μs−1,

5. Creation of PAW and its relation with pressure

6. ΔT(x,y,z)= 𝜇 𝑎 ∅/ 𝑐 𝑝 𝜏 𝑠 = 𝑑 𝑐 𝜏 𝑝≤ 𝜏 𝑠

7. Diferente setups : 1. optical excitation(imaging)
2. Ultrasonic waves imaging.
3. macroscopic and microscopic photoacoustic
4. track various nanoparticles
5. Reporter gene imaging
6. Conventional reporter gene imaging
7. A sensitive chromogenic assay with X-gal
8. Remote optical method
9. Technical implementation of US-Modulated Optical Tomography

9. *. In linear-view photoacoustic computed tomography, ultrasonic detection follows a line. Linear ultrasound arrays in medical ultrasound imaging systems can be adapted for PAT

10. Photo acoustic probe that uses a Q-switched, frequency-doubled Nd:YAG (neodymium, yttrium, aluminum, garnet) laser
operating at 532 nm to generate acoustic pulses in skin in vivo piezoelectric. few nanosecond pulses produced by Q-switched lasers are appropriate.
When probing soft tissues at depths limited to 1 or 2 cm, propagation delays of ultrasonic waves are below 20 μs since the propagation velocity is about 1.5 mm∕μs.

11. A multispectral opto-acoustic tomography technique
capable of high-resolution visualization of fluorescent proteins deep within highly light-scattering living organisms. The method uses multiwavelength illumination over multiple projections combined with selective-plane opto-acoustic detection for artifact-free data collection. Accurate image reconstruction is enabled by making use of wavelength-dependent light propagation models in tissue.

12. Experimental setup for PAT with Mach-Zehnder interferometer as a acoustic line detector:
A line detector can be an optical fiber-based Fabry–Perot interferometer or a Mach–Zehnder interferometer.

13. Image reconstruction algorithms for PAT
Imaging speed and image quality of pat rely on the reconstruction algorithms.
Invers Radon transformation
Exact reconstruction require either enclosed detection surfaces such as sphere or unbounded open surface such as infinite plane or cylinder.

14. OR-PAM:
Within the ballistic regime, light focusing is feasible. Instead of using higher frequency transducers, OR-PAM uses optical focusing to provide the lateral resolution, while the axial resolution is still derived from the time-resolved PA signals.

15. PAT based on an acoustic lens system:

16. Biological cell detection:
Figure demonstrates the mechanism of PAFC (PA flow cytometry) ,where the pulsed laser beam is focused on the circulation system, with a width of approximately 6 μm.

17. Photo acoustic flowmetry:
If the absorber moves during the PA process, the PA signal changes in the signl, the speed and orientation of the moving absorber can be detected.
PA Doppler (PAD)
M-mode method

18. Resolution
Depending on the method used to determine the lateral resolution, there are two types of PAM: acoustic-resolution PAM (AR-PAM) and optical-resolution PAM (OR-PAM).
High-resolution optical imaging technologies
1. confocal microscopy
2. two-photon microscopy
We have lateral and axial resolution:
Axial resolution=C/∆f where c is speed of sound and ∆f is band width of transducer

21. Pressure:
β is the thermal expansivity [strain/degree C], (for water: 2.29x10-4 strain/degree C).
Cp is the specific heat [J/(kg degreeC)], (for water: 4180 J/(kg degreeC)).
cs is the speed of sound
W= µ 𝒂 Ø,
Ø is the optical radiation fluency( the heat deposition density)
µ𝑎 is the absorption cofficient

22. An example:
For soft tissue:
λ= 800nm
Ø=20 mj/ 𝑐𝑚 2
µ 𝑎 =4.3 𝑐𝑚 −1
W=9* j 𝑚 −3
P=2.2* pa ( 200 mbar)
These information are given from: Phy. Med. Bio.54(2009)R59-R97

23. We tried to reach dr :
V= 4 3 π 𝑟 3
dV= 4π 𝑟 2 dr
dr= 𝑑𝑉 4π 𝑟 2
K= -V 𝑑𝑝 𝑑𝑟
So we have:
K= 𝑝𝑟 3𝑑𝑟
But after changing the size of target (radius of target) we got dr:
𝑑 0 = 10µ r=1cm p=20 pa dr= nm
With 𝑑 0 = 100 µ we got dr= 0.3 nm

25. thank you