Wenming Xie

Determination of optical absorption coefficient with focusing photoacoustic imaging

Absorption coefficient of biological tissue is an important factor for photothermal therapy and photoacoustic imaging. However, its determination remains a challenge. In this paper, we propose a method using focusing photoacoustic imaging technique to quantify the target optical absorption coefficient. It utilizes the ratio of the amplitude of the peak signal from the top boundary of the target to that from the bottom boundary based on wavelet transform. This method is self-calibrating. Factors, such as absolute optical fluence, ultrasound parameters, and Grüneisen parameter, can be canceled by dividing the amplitudes of the two peaks. To demonstrate this method, we quantified the optical absorption coefficient of a target with various concentrations of an absorbing dye. This method is particularly useful to provide accurate absorption coefficient for predicting the outcomes of photothermal interaction for cancer treatment with absorption enhancement.

Photoacoustic imaging of prostate cancer using cylinder diffuse radiation

Prostate cancer is one of diseases with high mortality in man. Many clinical imaging modalities are utilized for the detection, grading and staging of prostate cancer, such as ultrasound, CT, MRI, etc. But they lacked adequate sensitivity and specificity for finding cancer in transition or central zone of prostate. To overcome these problems, we propose a photoacoustic imaging modality based on cylinder diffuse radiation through urethra for prostate cancer detection. We measure the related parameters about this system like lateral resolution (~2mm) and axial resolution(~333μm). Finally, simulated sample was imaged by our system. The results demonstrate the feasibility for detecting prostate cancer by our system.

New optical method for noninvasive blood glucose measurement by optical ultrasonic modulation

A new optical technique for continuous, noninvasive monitoring of blood glucose levels based on ultrasonic modulation of scattering light is proposed. The ultrasound-modulated scattered light has an accurate separation of scattering and absorption changes in tissue. And the optical scattering and absorbing coefficient of tissue depend on the concentration of glucose in the extracellular fluid. As the glucose induced to scattering and absorption changes, the ultrasoundmodulated light also changes. In this paper, a correlation is observed between ultrasound-modulated light intensity as well as its modulation depth and blood glucose concentration in phantom experiments. In addition, some researches about ultrasound-modulated signal affected by the temperature of glucose aqueous solution are done. Preliminary experiments find that this method is a promising noninvasive blood glucose measurement.

Characterization of photoacoustic signal using wavelet analysis

In this paper, we present the continuous wavelet analysis for extract the information of photoacoutical signal sampled with a focoused transducer. The results demonstrate that wavelet transform of photoacoustic signals with 1 time averaging could reconstruct the localization and the size of absorbers, and it greatly reduced the data acquisition time. In addition, the results indicate that the localization and the size of absorbers could be recovered as the value of signal-to-noise ratio (SNR) is in the range from 0.3 to1.

Simulation of a pulsed light propagation in the prostate phantom

In recent years, more and more Americans are diagnosed with prostate cancer, and the current detection methods still have some disadvantages. Photoacoustic imaging, as a new non-invasive imaging technique, has the capable of imaging complex tissue and owns the ability of early tumor imaging. And the photoacoustic signal of the tumor is bound up with its light energy distribution. In this paper, Monte Carlo method was used to simulate the light propagation in the prostate phantom. The pictures of light energy distribution by the irradiation of a pulsed laser were obtained. With the pulsed laser, according to the absorption coefficient of tumor, the local energy temporal changes in prostate can be illustrated. As we known, the local photoacoustic signal has a relationship with the change of light energy. Then we can see the influence of photoacoustic signal under the changes of the absorption coefficient of tumor.

Measurements of light energy distribution in pathological lesions using focused photoacoustic imaging

Generally, measuring the location and optical properties of pathological lesions in biological tissue is pretty helpful for accurate diagnosis and effective treatment of diseases. In order to have a further diagnosis, it is necessary to implement a further study on the distribution of light energy inside the pathological lesions. In this paper, we focused on the localization of lesions and measurements of light energy distribution inside the lesions using photoacoustic (PA) imaging. Ink blocks were used to mimic the lesions in the sample. Some graphite rods were utilized as probes to help mapping the light distribution in lesions. As a result, our experiments are able to locate specific lesions in the sample. Furthermore, this method can be used to uncover the light energy distribution inside the lesions and to analyze qualitatively the influences of optical properties of the lesions and the ambient medium on the light energy distribution. It is promising for our method in diagnosing tumors in the early stage and identifying benign and malignant lesions in clinical applications.

Morphological Granulometric Feature of Speckled Speckles for Characterizing the Scattering Coefficient of Tissue Phantoms

We demonstrated that the combination of speckled light and the granulometric density distribution is used as means of distinguishing the different scattering coefficient of highly scattering tissue phantom. The average size of granulometric density distribution is dependent on the scattering coefficient of strongly scattering samples. Finally, we use the space correlation theory to explain the phenomenon, and demonstrate that the average size is approximately inverse proportional to scattering coefficient of highly scattering tissue phantoms.

New photoacoustic imaging modality for imaging internal organs based on single focus ultrasonic transducer

Photoacoustic imaging is a promising technique in practical medicine to image biological tissues function and diagnose internal organs. In this paper, a new photoacoustic imaging modality for imaging internal organs was presented. A laser which wavelength is tunable was coupled into a multimode optical fiber. And the fiber was inserted into the inner tract of the samples to deliver light for exciting photoacoustic signals. The outgoing PA signal was detected by a focal ultrasound transducer with long focal length which was placed on the surface of the samples. By transducer scanning, we obtained a 2D cross-section photoacoustic image. Finally, we evaluate this systems performance and demonstrate its capabilities by imaging phantoms with complex structure.

Speckle imaging by combination of mathematical morphology and contrast ratio

This paper reports a combined speckle and polarization-difference approach for imaging absorbing inhomogeneities embedded in optical scattering medium. Mathematical morphological operation has been used to suppress the speckle coarse grains and reconstruct the position of the absorbing inhomogeneities embedded in turbid medium. Moreover, we quantify the scattering coefficient of the background medium using the average granulometric size. Then the local speckle contrast ratio is applied to enhance the edges of absorbing objects.