Chance B, Kang K, He L, Weng J, Sevick E
Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104-6089.
Proc Natl Acad Sci U S A. 1993 Apr 15;90(8):3423-7. doi: 10.1073/pnas.90.8.3423.
Based upon previous observations of low-frequency photon diffusion waves within highly scattering tissue, this paper explores the "near-field" phenomena of such waves of approximately 10-cm wavelength with 200-MHz phase modulation equipment. Multiple-element source arrays consist of laser diode sources modulated at 180 degrees out of phase with respect to the other sources. The diffusing waves originating from the out-of-phase sources give, in the midplane, an amplitude null and a sharp phase transition. These may be observed in a highly scattering intralipid medium simulating the breast or brain (0.5% intralipid), 3-5 cm from the transmitting laser diodes. In the plane containing the array, there is a high sensitivity for a small volume of a hidden absorber (indocyanine green) deep within a highly scattering medium; 20 pmol in a volume of 70 microliters can be detected. Two-dimensional arrays consisting of four or more elements in two orthogonal planes give sensitivity on both axes similar to the one-dimensional array. Measurements show that in the presence of a light-absorbing object, the amplitude null and the interference plane becomes a curved surface which is deflected toward the heterogeneity. The degree of deflection is related to the volume and the absorption characteristics of the heterogeneity and provides detection of the heterogeneity, and thereby may provide localization information for the detection of small tumors within the human breast, or stroke volumes, aneurysms, and tumors in the human brain.
基于先前对高散射组织内低频光子扩散波的观察，本文使用200兆赫相位调制设备探索波长约为10厘米的此类波的“近场”现象。多元件源阵列由激光二极管源组成，这些源相对于其他源以180度异相调制。来自异相源的扩散波在中平面产生幅度零值和尖锐的相位转变。这些现象可以在模拟乳房或大脑的高散射脂质介质（0.5%脂质）中观察到，距离发射激光二极管3 - 5厘米。在包含阵列的平面中，对于高散射介质深处少量隐藏吸收体（吲哚菁绿）具有高灵敏度；70微升体积中的20皮摩尔可以被检测到。由两个正交平面中的四个或更多元件组成的二维阵列在两个轴上的灵敏度与一维阵列相似。测量表明，在存在光吸收物体的情况下，幅度零值和干涉平面变成一个朝向异质性弯曲的曲面。弯曲程度与异质性的体积和吸收特性相关，可用于检测异质性，从而可为检测人乳腺内的小肿瘤或人脑内的中风体积、动脉瘤和肿瘤提供定位信息。
