摘要:
光声成像技术是一种非常有前景的前列腺早期检测与成像的新技术。在现有前列腺光声成像技术中，通常采用的腺体外光源辐照方式由于受外围组织的影响，容易减弱深部前列腺组织的光能量吸收，导致辐照范围减小，引起光声成像深度不足，难以实现无损前列腺癌的检测。本文基于前列腺组织的结构特征，依据一种以柱状弥散光纤在尿道对前列腺实施光辐照、并利用外置于直肠内的长焦区聚焦式超声换能器检测光声信号的前列腺光声扫描成像技术，构建了光声成像实验系统，开展了仿体实验。测试结果表明，系统能够实现样品中吸收体的定位和成像，结合柱弥散光源体内辐照可使成像深度提高，同时侧向成像范围也较大。初步结果表明，借助柱弥散光源进行体内光辐照的光声信号新激发方式结合长焦区超声探头在前列腺癌早期无创诊断上具有潜在的应用前景。
Abstract:
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.
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