基于柱弥散光源体内辐照的前列腺扫描光声成像仿体实验

摘要

Photoacoustic imaging has recently emerged as a promising imaging modality for prostate cancer. As a usual light illumination model in the previous studies, the external light illumination is diffcult to obtain an accurate reconstructed photoacoustic image. It suffers a great deal of light absorption attenuation by the surrounding scattering tissue and cannot colletct suffcient ultrasound signals for image reconstruction. Some particular methods are required to be considered in the photoacoustic imaging technique for examining prostate, such as a light delivery to prostate with suffcient penetrating depth and minimal invasiveness. According to the structural characteristic of prostate tissue, a photoacoustic imaging system is built by using a novel technique for prostate in this paper. In our photoacoustic imaging system, a cylindrical diffusing source with a 2-cm-long diffuser tip is used for an internal light irradiation through a urethra, and a focused transducer with a 3.5 MHz central frequency and 30.3 mm extended focal zone is located in the rectum for scanning the photoacoustic signal. Phantom experimental imaging is carried out. In the experiment, a transverse resolution of 2.21 mm and an axial resolution of 0.39 mm are obtained. The results demonstrate that the system could achieve the accurate imaging position of the absorber in the tissue sample. Because of the symmetrical emitting of the cylindrical diffusing light source and a relatively better lateral uniformity of light absorption around the light source through the internal irradiation model via urethra, light absorption of the upper side of the light source is almost the same as that of the lower side. Therefore the lengthways and lateral imaging ranges can be improved. In addition, the laser energy is allowed to be increased appropriately to obtain a further imaging result without worrying about heat damages to normal tissues, for the light absorption is less around the cylindrical diffusing light source. In conclusion, the preliminary studies show that the new technique, where the internal light irradiation is implemented by using a cylindrical diffusing source and a focused transducer with extended focal zone, has a potential application in the early noninvasive diagnosis of prostate cancer.