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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 8 — Apr. 14, 2008
  • pp: 5314–5319
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Photoacoustic tomography imaging using a 4f acoustic lens and peak-hold technology

Yadong Wei, Zhilie Tang, Hanchao Zhang, Yongheng He, and Haifeng Liu  »View Author Affiliations


Optics Express, Vol. 16, Issue 8, pp. 5314-5319 (2008)
http://dx.doi.org/10.1364/OE.16.005314


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Abstract

In this paper we present a new high-contrast photoacoustic tomography (PAT) imaging system using a 4f acoustic lens, a 64-element linear transducer array and peak-hold technology. This PAT imaging system has been developed to obtain three-dimensional (3D) PAT images of experimental samples. By utilizing a 4f acoustic lens, the photoacoustic (PA) signals generated from the sample are directly imaged on the imaging plane and collected by the 64-element linear transducer array, which changes them into the corresponding electronic signals. Then we can get one-dimensional (1D) images from the electronic signals using a peak detection-and-hold circuit. After vertical scanning with a stepping motor on the imaging plane, a 2D PA image of the sample is successfully obtained. Combined with the time-resolved technique, we can then get 3D PAT images. The results show that the reconstructed images agree well with the original samples.

© 2008 Optical Society of America

1. Introduction

Photoacoustic tomography (PAT) imaging is a noninvasive imaging technique for visualizing both structural and functional information about biological tissues. This method has become an active research area in recent years. Compared with the traditional B-Mode ultrasound imaging system, PAT combines a high ultrasonic penetration depth and high optical contrast in tissue imaging [1–4

1. R. J. Siphanto, K. K. Thumma, and R. G. M. Kolkman, “Serial noninvasive photoacoustic imaging of neovascularization in tumor angiogenesis,” Opt. Express 13, 89–95 (2005). [CrossRef] [PubMed]

]. In PAT, when electromagnetic energy (such as optical or radio-frequency waves) is absorbed by a sample of biological tissue, a small temperature rise in the tissue generates a thermoelastic expansion, which leads to a photoacoustic (PA) signal. Because the PA pressure is linearly proportional to the optical energy deposited in the biological tissue, the PA signals carry information about the geometrical structure and optical properties of the tissue. Furthermore, since the tissue attenuates and scatters ultrasound much less than light, we can use a wide-band ultrasonic transducer to detect the PA signals and reconstruct the image of the light-absorption distribution in the biological tissue. Hence, the PAT image can display both the structure and function of the tissue. This technique has been applied to imaging skin cancer, breast cancer, brain tumors, blood concentrations and vascular structure [5–8

5. C. G. A. Hoelen, F. F. M. de Mul, and R. Pongers, “Three-dimensional photoacoustic imaging of blood vessels in tissue,” Opt. Lett. 23, 648–650 (1998). [CrossRef]

].

Many experiments on PAT images have been carried out in recent years [9–14

9. M. H. Xu and L. H. Wang, “Photoacoustic imaging in biomedicine,” Rev. Sci. Instrum. 77, 041101 1–22 (2006). [CrossRef]

]. However, most of these PAT imaging systems were based on time-domain PAT, which needs an algorithm to reconstruct the PA images, making it hard to get real-time images. To obtain these, an acoustic lens, which is able to image the initial PA pressure distribution onto an image space in real time without the need for computational reconstruction, has been developed and applied to PAT imaging [15–17

15. J. J. Niederhauser, M. Jaeger, and M. Frenz, “Real-time three-dimensional optoacoustic imaging using an acoustic lens system,” Appl. Phys. Lett. 85, 846–848 (2004). [CrossRef]

]. Furthermore, to display a three-dimensional (3D) real object, a 4f acoustic lens, which guarantees axial and lateral unit magnification of the images, has also been discussed [18

18. Z. X. Chen, Z. L. tang, and W. Wan, “Photoacoustic tomography imaging based on a 4f acoustic lens imaging system,” Opt. Express 15, 4966–4976 (2007). [CrossRef] [PubMed]

].

2. Imaging system setup and peak-hold technology

The experimental setup is shown schematically in Fig. 1. A Q-switched Nd:YAG (yttrium aluminum garnet) laser operates at 1064 nm with a pulse duration of 7 ns. The laser beam is expanded to illuminate the object to be imaged. Then the optical absorption of the object generates a proportional distribution of the PA signals. This acoustic pressure distribution is imaged onto the image plane by a 4f acoustic lens in10% milk liquor. A linear array transducer then detects the acoustic pressure distribution on the image plane. This transducer consists of 64 piezoelectric probes with a center frequency of 1 MHz. The radius of each probe is about 0.22 mm, and the central distance between two neighboring probes is 1.5 mm. The linear array transducer is fixed on a computer-controlled scanning stage. The scanning stage drives the linear transducer vertically to detect the planar PA signals. These signals are chosen and amplified in turn (triggered by the Q-switched laser) by the electronic switching of the 64 lines and are input to the peak-hold module, which can hold the peak values of the PA signals. Then the peak-value signal is delivered to a computer via an acquisition card (ADC, model Advantech PCL-818HG) and transformed into 256 corresponding gray levels to display the image. An oscillograph (model: TDS1002) monitors the PA signals and the output peak values from the peak-hold module.

In our former system [17–18

17. W. Wan, R. S. Liang, and Z. L. Tang, “The imaging property of photoacoustic Fourier imaging and tomography using an acoustic lens imaging system,” J. Appl. Phys. 101, 063103 1–7 (2007). [CrossRef]

], we used a Boxcar for keeping the peak values. Owing to the mechanical scanning of the detector, the distance between the object plane and the detecting plane would not be always the same during the scanning, which would bring the delay-time excursion of the PA signals. As a result, the boxcar could not always catch the peak of photoacoustic signals from one object plane, because the delay time and the width of sampling gate of the boxcar were fixed. Thus the boxcar could acquire the phtoacoustic signals from the near object planes, which could blur the image. In the new system, the peak-hold module had ability to catch the peak value of the PA signals automatically within the gate width when there was delay-time excursion of the PA signals. So it could improve the photoacoustic image obviously.

Fig. 1. Experimental setup for PAT imaging based on a 4f acoustic lens and peak-hold technology.

3. Experimental results and discussion

3.1. Output of the peak-hold module

The peak-hold module can detect the peak values of the PA signals automatically within the gate width, and its output is a direct-current voltage that is equal to the maximum value of a PA signal. Figure 2 shows a PA signal and its peak-value signal held by the peak-hold module, both of which were observed by an oscilloscope.

Fig. 2. A PA signal (a) and its peak-value signal (b) observed by an oscilloscope.

We can conclude from Fig. 2 that the peak-hold module can acquire the peak value of the PA signal efficiently. Thus this peak value can be used to reconstruct a 2D PA image and the corresponding image of the sample can be acquired by scanning on the image plane.

3.2. 2D PA imaging

To demonstrate the feasibility of the PAT imaging system, we carried out a series of experiments. First, we tried to use the system for 2D PA imaging. Figure 3(a) shows a sample consisting of two black adhesive tape points stuck to a piece of polymethylmethacrylate and submerged in 10% milk liquor. The sample was heated by the YAG pulsed laser, and PA signals from the sample were imaged on the imaging plane by the 4f acoustic lens. The PA signals were detected by the linear array transducer to reconstruct the corresponding 2D PA image on the imaging plane (see Fig. 3(b)).

Fig. 3. Sample consisting of two black adhesive tape points stuck to a piece of polymethylmethacrylate submerged in milk (a) and the corresponding PA image using the new system (b).
Fig. 4. Sample consisting of two black adhesive tape points stuck to a piece of polymethylmethacrylate submerged in milk (a) and the corresponding PA image using our former system (b).

It is obvious that the acoustic image is in perfect agreement with the sample, and that this system possesses 2D imaging ability. Comparing this image with that shown in Fig. 4 from our former system [17–18

17. W. Wan, R. S. Liang, and Z. L. Tang, “The imaging property of photoacoustic Fourier imaging and tomography using an acoustic lens imaging system,” J. Appl. Phys. 101, 063103 1–7 (2007). [CrossRef]

], it is clear that the image has a sharper edge than before.

3.3. PAT imaging

PAT imaging is realized by combining the long focal depth of the acoustic lens and the time-resolved technique. We previously obtained some experimental results using a Boxcar [17–18

17. W. Wan, R. S. Liang, and Z. L. Tang, “The imaging property of photoacoustic Fourier imaging and tomography using an acoustic lens imaging system,” J. Appl. Phys. 101, 063103 1–7 (2007). [CrossRef]

]. More careful experiments have now been carried out to test the new system.

Figure 5 shows an example of two different patterns, consisting of three black adhesive tape points stuck to the front and two black adhesive tape points stuck to the back of a piece of polymethylmethacrylate. The polymethylmethacrylate is about 15 mm thick, so the distance between the two patterns is also about 15 mm. The PA signals of the different layers and their peak-value signals, as observed by oscilloscope, are shown in Fig. 6.

Fig. 5. Front (a) and side (b) elevations of a sample which consists of two different patterns: three black adhesive tape points stuck to the front and two black adhesive tape points stuck to the back of a piece of polymethylmethacrylate.
Fig. 6 (a). PA signal and its peak-value signal of the front layer. (b) PA signal and its peak-value signal of the back layer.

The results shown in Fig. 6 indicate that the peak-hold module is able to catch and hold the peak values of the different layers by adjusting its delay time. According to the axial unit magnification of the 4f acoustic lens, the distance between the two image planes must be equal to the distance between the two object planes, namely 15 mm. This distance can be expressed as D=ν·Δt, where ν≈2.640mm/µs is the acoustic velocity, and Δt≈5.7µs is the time difference of the two PA signals reaching the detector. So D=ν·Δt≈2.640×5.7≈15.048mm, it is just equal to the distance between the two object planes.

Figure 7 shows the computer-reconstructed image of the two different layers.

Fig. 7. PAT images of the two sides of the sample: (a) the front, consisting of three points, and (b) the back, consisting of two points.

4. Conclusion

We have presented a novel photoacoustic tomography (PAT) imaging system based on a 4f acoustic lens and peak-hold technology. The experimental results indicate that the system can obtain the PAT images of samples inside strongly scattering media, and the reconstructed images agree well with the samples. In this PAT system, the focusing ability of the 4f acoustic lens greatly enhances the signal–noise ratio, and improves the imaging contrast. As the peak-hold technology can catch and hold the peak values of the PA signals automatically, this new PAT system can has better imaging quality. It still has the potential advantages of forming real-time images and acquiring them more rapidly without any complex algorithms. This method may provide a more convenient method for future in vivo noninvasive imaging of tissues and clinical diagnosis.

Acknowledgments

This work is supported by the National Natural Science Foundation of China (grant No.60377009), National 863 Program Project of China (grant No. 2006AA02Z4B4) and the Natural Science Foundation of Guangdong Province, China (Grant No.05005926).

References and links

1.

R. J. Siphanto, K. K. Thumma, and R. G. M. Kolkman, “Serial noninvasive photoacoustic imaging of neovascularization in tumor angiogenesis,” Opt. Express 13, 89–95 (2005). [CrossRef] [PubMed]

2.

R. G. M. Kolkman, J. H. G. M. Klaessens, and E. Hondebrink, “Photoacoustic determination of blood vessel diameter,” Phys. Med. Biol. 49, 47454756 (2004). [CrossRef]

3.

X. D. Wang, Y. J. Pang, and G. Ku, “Non-invasive laser-induced photoacoustic tomography for structural and functional in vivo imaging of the brain” Nat. Biotechnol. 21, 803–806 (2003). [CrossRef] [PubMed]

4.

A. A. Oraesky, A. A. Karabutov, and V. S. Solomatin, “Laser optoacoustic imaging of breast cancer in vivo,” Proc. SPIE 4256, 12–22 (2001).

5.

C. G. A. Hoelen, F. F. M. de Mul, and R. Pongers, “Three-dimensional photoacoustic imaging of blood vessels in tissue,” Opt. Lett. 23, 648–650 (1998). [CrossRef]

6.

H. F. Zhang, K. Maslov, and M. L. Li, “In vivo volumetric imaging of subcutaneous microvasculature by photoacoustic microscopy,” Opt. Express 14, 9317–9323 (2006). [CrossRef] [PubMed]

7.

K. H. Song, G. Stoica, and L. H. V. Wang, “In vivo three-dimensional photoacoustic tomography of a whole mouse head,” Opt. Lett. 31, 2453–2455 (2006). [CrossRef] [PubMed]

8.

X. D. Wang, X. Y. Xie, and G. Ku, “Noninvasive imaging of hemoglobin concentration and oxygenation in the rat brain using high-resolution photoacoustic tomography,” J. Biomed. Opt. 11, 024015 1–9 (2006). [CrossRef] [PubMed]

9.

M. H. Xu and L. H. Wang, “Photoacoustic imaging in biomedicine,” Rev. Sci. Instrum. 77, 041101 1–22 (2006). [CrossRef]

10.

M. H. Xu and L. H. Wang, “Time-Domain Reconstruction for Thermoacoustic Tomography in a Spherical Geometry,” IEEE Trans. Med. Imag. 21, 814–822 (2002). [CrossRef]

11.

K. P. Köstli and P. C. Beard, “Two-dimensional photoacoustic imaging by use of Fourier-transform image reconstruction and a detector with an anisotropic response,” Appl. Opt. 42, 1899–1908 (2003). [CrossRef] [PubMed]

12.

Y. Wang, D. Xing, and Y. G. Zeng, “Photoacoustic imaging with deconvolution algorithm,” Phys. Med. Biol. 49, 3117–3124 (2004). [CrossRef] [PubMed]

13.

B. Z. Yin, D. Xing, and Y. Wang, “Fast photoacoustic imaging system based on 320-element linear transducer array,” Phys. Med. Biol. 49, 1339–1346 (2004). [CrossRef] [PubMed]

14.

D. W. Yang, D. Xing, and H. M. Gu “Fast multielement phase-controlled photoacoustic imaging based on limited-field-filtered back-projection algorithm,” Appl. Phys. Lett. 87, 194101 1–3 (2005). [CrossRef]

15.

J. J. Niederhauser, M. Jaeger, and M. Frenz, “Real-time three-dimensional optoacoustic imaging using an acoustic lens system,” Appl. Phys. Lett. 85, 846–848 (2004). [CrossRef]

16.

Z. X. Chen, Z. L. tang, and W. Wan “Photoacoustic tomography imaging based on an acoustic lens imaging system,” Acta. Phys. Sin. 55, 4365–4370 (2006).

17.

W. Wan, R. S. Liang, and Z. L. Tang, “The imaging property of photoacoustic Fourier imaging and tomography using an acoustic lens imaging system,” J. Appl. Phys. 101, 063103 1–7 (2007). [CrossRef]

18.

Z. X. Chen, Z. L. tang, and W. Wan, “Photoacoustic tomography imaging based on a 4f acoustic lens imaging system,” Opt. Express 15, 4966–4976 (2007). [CrossRef] [PubMed]

OCIS Codes
(170.0110) Medical optics and biotechnology : Imaging systems
(170.3010) Medical optics and biotechnology : Image reconstruction techniques
(170.5120) Medical optics and biotechnology : Photoacoustic imaging
(170.6920) Medical optics and biotechnology : Time-resolved imaging

ToC Category:
Medical Optics and Biotechnology

History
Original Manuscript: February 11, 2008
Revised Manuscript: March 22, 2008
Manuscript Accepted: March 28, 2008
Published: April 2, 2008

Virtual Issues
Vol. 3, Iss. 5 Virtual Journal for Biomedical Optics

Citation
Yadong Wei, Zhilie Tang, Hanchao Zhang, Yongheng He, and Haifeng Liu, "Photoacoustic tomography imaging using a 4f acoustic lens and peak-hold technology," Opt. Express 16, 5314-5319 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-8-5314


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References

  1. R. J. Siphanto, K. K. Thumma, and R. G. M. Kolkman, "Serial noninvasive photoacoustic imaging of neovascularization in tumor angiogenesis," Opt. Express 13, 89-95 (2005). [CrossRef] [PubMed]
  2. R. G. M. Kolkman, J. H. G. M. Klaessens, and E. Hondebrink, "Photoacoustic determination of blood vessel diameter," Phys. Med. Biol. 49, 47454756 (2004). [CrossRef]
  3. X. D. Wang, Y. J. Pang, and G. Ku, "Non-invasive laser-induced photoacoustic tomography for structural and functional in vivo imaging of the brain" Nat. Biotechnol. 21, 803-806 (2003). [CrossRef] [PubMed]
  4. A. A. Oraesky, A. A. Karabutov, and V. S. Solomatin, "Laser optoacoustic imaging of breast cancer in vivo," Proc. SPIE 4256, 12-22 (2001).
  5. C. G. A. Hoelen, F. F. M. de Mul, and R. Pongers, "Three-dimensional photoacoustic imaging of blood vessels in tissue," Opt. Lett. 23, 648-650 (1998). [CrossRef]
  6. H. F. Zhang, K. Maslov, and M. L. Li, "In vivo volumetric imaging of subcutaneous microvasculature by photoacoustic microscopy," Opt. Express 14, 9317-9323 (2006). [CrossRef] [PubMed]
  7. K. H. Song, G. Stoica, and L. H. V. Wang, "In vivo three-dimensional photoacoustic tomography of a whole mouse head," Opt. Lett. 31, 2453-2455 (2006). [CrossRef] [PubMed]
  8. X. D. Wang, X. Y. Xie, and G. Ku, "Noninvasive imaging of hemoglobin concentration and oxygenation in the rat brain using high-resolution photoacoustic tomography," J. Biomed. Opt. 11, 024015 1-9 (2006). [CrossRef] [PubMed]
  9. M. H. Xu and L. H. Wang, "Photoacoustic imaging in biomedicine," Rev. Sci. Instrum. 77, 041101 1-22 (2006). [CrossRef]
  10. M. H. Xu and L. H. Wang, "Time-Domain Reconstruction for Thermoacoustic Tomography in a Spherical Geometry," IEEE Trans. Med. Imag. 21, 814-822 (2002). [CrossRef]
  11. K. P. Köstli and P. C. Beard, "Two-dimensional photoacoustic imaging by use of Fourier-transform image reconstruction and a detector with an anisotropic response," Appl. Opt. 42, 1899-1908 (2003). [CrossRef] [PubMed]
  12. Y. Wang, D. Xing, and Y. G. Zeng, "Photoacoustic imaging with deconvolution algorithm," Phys. Med. Biol. 49, 3117-3124 (2004). [CrossRef] [PubMed]
  13. B. Z. Yin, D. Xing, and Y. Wang, "Fast photoacoustic imaging system based on 320-element linear transducer array," Phys. Med. Biol. 49, 1339-1346 (2004). [CrossRef] [PubMed]
  14. D. W. Yang, D. Xing, and H. M. Gu "Fast multielement phase-controlled photoacoustic imaging based on limited-field-filtered back-projection algorithm," Appl. Phys. Lett. 87, 194101 1-3 (2005). [CrossRef]
  15. J. J. Niederhauser, M. Jaeger, and M. Frenz, "Real-time three-dimensional optoacoustic imaging using an acoustic lens system," Appl. Phys. Lett. 85, 846-848 (2004). [CrossRef]
  16. Z. X. Chen, Z. L. tang, and W. Wan "Photoacoustic tomography imaging based on an acoustic lens imaging system," Acta. Phys. Sin. 55, 4365-4370 (2006).
  17. W. Wan, R. S. Liang, and Z. L. Tang, "The imaging property of photoacoustic Fourier imaging and tomography using an acoustic lens imaging system," J. Appl. Phys. 101, 063103 1-7 (2007). [CrossRef]
  18. Z. X. Chen, Z. L. tang, and W. Wan, "Photoacoustic tomography imaging based on a 4f acoustic lens imaging system," Opt. Express 15, 4966-4976 (2007). [CrossRef] [PubMed]

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