A prototype multichannel time-resolved medical optical tomography system is presented, and various instrumental aspects and performance issues are discussed. The instrument has been designed primarily as a continuous bedside monitor for obtaining functional images of premature infants’ brains that are at an increased risk of injury due to dysfunction in cerebral oxygenation or hemodynamics. Separate maps of the internal absorption and scattering properties can be reconstructed from purely temporal measurements of photons transmitted diffusely through the tissue, and without recourse to reference or baseline measurements. The instrument employs 32 source fibers that sequentially deliver near-infrared pulsed laser radiation of picosecond duration. Transit time measurements of very high temporal resolution and stability are made between these sources and 32 detector optodes that are located on the surface. The effectiveness of this instrument is demonstrated by successfully imaging a tissue-equivalent phantom.
Somatosensation as a proximal sense can have a strong impact on our attitude toward physical objects and other human beings. However, relatively little is known about how hedonic valence of touch is processed at the cortical level. Here we investigated the electrophysiological correlates of affective tactile sensation during caressing of the right forearm with pleasant and unpleasant textile fabrics. We show dissociation between more physically driven differential brain responses to the different fabrics in early somatosensory cortex – the well-known mu-suppression (10–20 Hz) – and a beta-band response (25–30 Hz) in presumably higher-order somatosensory areas in the right hemisphere that correlated well with the subjective valence of tactile caressing. Importantly, when using single trial classification techniques, beta-power significantly distinguished between pleasant and unpleasant stimulation on a single trial basis with high accuracy. Our results therefore suggest a dissociation of the sensory and affective aspects of touch in the somatosensory system and may provide features that may be used for single trial decoding of affective mental states from simple electroencephalographic measurements.
We present an overview of time‐resolved optical tomography together with the hardware and software methods that we have developed for a clinical instrument that implements this modality. The hardware is based on a multichannel photon‐counting technique that records the histograms of photons time‐of‐flight through highly scattering and attenuating media. The software is based on a finite element model that is iteratively updated in order to minimize the difference between measured and modeled data. We have presented a first experimental reconstruction of a three‐dimensional (3D) distribution of variable absorption and scattering coefficient, together with an ideal simulation of the same case. © 2000 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 11, 2–11, 2000
We present what is believed to be the first simultaneous reconstruction of the internal scattering and absorbing properties of a highly scattering medium by use of purely temporal data. These results are also the first acquired with the multichannel time-resolved imaging system developed at University College London.
Following several years of development the construction of a multichannel time-resolved imaging device for medical optical tomography has been completed. Images are reconstructed from time-resolved measurements by use of a scheme that employs a finite-element diffusion-based forward model and an iterative reconstruction solver. Prior to testing on clinical subjects the fully automated instrument and the reconstruction software are evaluated with tissue-equivalent phantoms. We describe our first attempt to generate multiple-slice images of a phantom without uniform properties along the axial direction, while still using a computationally fast two-dimensional reconstruction algorithm. The image quality is improved by the employment of an approximate correction method that uses scaling factors derived from the ratios of finite-element forward simulations in two and three spatial dimensions. The 32-channel system was employed to generate maps of the internal scattering and the absorption properties at 14 different transverse planes across the phantom. The images clearly reveal the locations of small inhomogeneous regions embedded within the phantom. These results were obtained by use of purely temporal data and without resource to reference measurements.
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