IMPROVEMENT OF DEPTH SENSITIVITY TO CEREBRAL HEMODYNAMICS W/ TIME GATED SYSTEM

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 通过记录光子飞行时间的分布，时间域(TD)系统本质上提供了比连续波(CW)系统更多的信息。特别是，它们能够在单源-探测器(SD)分离时实现深度辨别。这对脑功能成像特别有意义，因为皮层的激活通常被表面的全身反应所掩盖。 我们的TD装置是基于钛宝石脉冲激光器和增强型CCD相机(ICCD)。我们开发了一种结合了深度敏感和2D成像的探头。它由两半组成，每半半球一个，每个半球有4？4个源和3？3个探测器，呈正方形(SD=2.5厘米)。每个探测器由7根不同长度的光纤组成，以7个延迟进行并行检测。所有126根光纤在ICCD阵列上并行成像。32个信号源按顺序照明，在同一个CCD帧期间打开4组8个信号源，而不会产生明显的串扰。这种源时分复用和并行检测允许整个头部的成像频率几乎为2赫兹。 在成功演示了该系统改善了幻影和人体的深度渗透后，我们现在正在开发线性3D图像重建，同时使用所有延迟门和所有SD对的信息，以更好地实现这项新技术的全部潜力。正向灵敏度矩阵A(体素的大小[SD对的数目]延迟门的数目]将吸收系数的变化与归一化Born近似中的归一化强度i/I0的变化相关联：i/I0=A。利用正则化中的协方差矩阵对灵敏度矩阵求逆，得到重建图像。这种重建既能实现深度分辨率，又能实现比CW数据更好的横向一致性。关于这些重建结果的手稿正在准备中。在接下来的几年里，我们将把重建应用于更多的人类数据。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. By recording the distribution of times of flight of photons, Time Domain (TD) systems intrinsically provide more information that continuous wave (CW) ones. In particular, they enable depth discrimination at a single source-detector (SD) separation. This is of particular interest for functional brain imaging, where cortical activation is often hidden by superficial systemic response. Our TD device is based on a Ti:Sapphire pulsed laser and an intensified CCD camera (ICCD). We have developed a probe combining depth sensitivity and 2D imaging. It consists in 2 halves  one per hemisphere  each with 4¿4 sources and 3¿3 detectors in a square geometry (SD = 2.5 cm). Each detector consists of 7 fibers of different lengths, for parallel detection at 7 delays. All 126 fibers are imaged in parallel on the ICCD array. The 32 sources are illuminated sequentially, with 4 sets of 8 sources that are turned on during the same CCD frame without causing significant cross-talk. This source time-multiplexing and the parallel detection allow for an imaging frequency of almost 2 Hz for the whole head. After successful demonstration of the systems improved depth penetration in phantoms and humans, we are now developing a linear 3D image reconstruction, using the information at all delay gates and all SD pairs simultaneously to better realize the full potential of this new technology. The forward sensitivity matrix A (size number of voxels ¿ [number of SD pairs ¿ number of delay gates]) relates the changes in the absorption coefficient ¿¿a to the changes in normalized intensity ¿I/I0 in the normalized Born approximation: ¿I/I0 = A . ¿¿a. The reconstructed image is obtained by inversion of the sensitivity matrix, using the covariance matrix in the regularization. This reconstruction enables both depth resolution and better lateral uniformity than CW data. A manuscript on these reconstruction results is being prepared. We will be applying the reconstructions to more human data over the next years.