Graduate Student Seminar with Paul Lin on Optical Tomography for Human Neuroimaging

Have you ever gotten a blurry picture when you accidentally shook your hands? Or have you ever gotten annoyed when getting a noisy image? You might be interested in knowing how these annoying effects can end up helping people get valuable information. 

Many techniques have been developed to measure cerebral blood flow (CBF), an important biomarker for many brain diseases. However, current standard techniques, including arterial spin labeling magnetic resonance imaging and positron emission tomography, take only the snapshot of CBF images rather than a continuous change of CBF and are limited by the lack of portability.  High-density speckle contrast optical tomography (HD-SCOT) is an optical imaging technique with cost and signal-to-noise ratio (SNR) advantages compared to traditional diffuse correlation spectroscopy. Free-space HD-SCOT techniques for rodents have been developed and showed fMRI-comparable results. However, this design has difficulty scaling up for measurements in humans due to challenges in focusing the head and obtaining quality signals through hair. Here, we are developing a fiber-based HD-SCOT to address the challenges in measuring CBF in humans by conforming to the complex head shape and combing through the hair with fiber. To investigate the unknown fiber-based HD-SCOT performance, we built a computing pipeline for simulating HD-SCOT measurements and reconstructed images based on an anatomical head model and a 24-sources-by-28-detectors array. Results show that 1) localization error can be reduced by including longer source-detector distances, and  2) although the speckle contrast can reduce with an increased exposure time, the SNR can be improved significantly. In experimental results, we evaluated speckle statics through a cost-efficient and robust multi-mode fiber (MMF) bundle and showed the significant difference between speckle signals and noise, and we demonstrated the feasibility of using MMFs for tracking pulsatile blood in a human subject.