Martin E. Fry

A 32-channel time-resolved instrument for medical optical tomography

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.

Simultaneous reconstruction of absorption and scattering images by multichannel measurement of purely temporal data

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.

A method for three‐dimensional time‐resolved optical tomography

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.

The brain's response to pleasant touch: an EEG investigation of tactile caressing.

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.

Combined MR imaging towards subject-specific knee contact analysis

A combined magnetic resonance (MR) imaging method has been proposed to investigate individual’s knee functionality quantitatively under weight-bearing condition. High resolution MR data were acquired first to reconstruct the subject-specific anatomical model. A dynamic MR acquisition was obtained afterwards to record the motion of knee joint. A tri-rigid registration was applied to retrieve the knee joint motion, leading to a 12 degree-of-freedom (DoF) knee functional model. Using this model, the tibiofemoral contact mechanism was studied and analysed in both 2D and 3D. A mathematical definition of contact points of cartilage surfaces is given by modelling these surfaces as manifolds. It is believed that such subject-specific motion of contact points on cartilage surfaces of femur and two tibia plateaus can provide valuable insights for clinical applications such as knee replacement surgery.

An in vivo subject-specific 3D functional knee joint model using combined MR imaging

PurposeWe aim to quantitatively characterise the knee joint function in vivo under body-weight-bearing conditions via subject-specific models extracted from magnetic resonance (MR) data, in order to better understand the knee joint kinematic function in 3D.MethodsSix healthy volunteers without any record of knee abnormality were scanned using a combined MR imaging strategy to record quasi-squatting motion and 3D knee anatomy. After a semi-automatic segmentation to delineate tibio-femoral articulation components, motion data were mapped to the anatomical data using a bi-rigid registration in order to achieve six degrees of freedom. The individual knee joint function was characterised by analysing the tibio-femoral articulation contact mechanism based on the reconstructed models in 3D and MR images in 2D. Contact points were extracted and their trajectory was plotted on the tibia plateau.ResultsThe 3D models clearly show the relative rotation and gliding between tibia and femur during global flexion. Within the measured flexion arc, the contact points move less between 30

A method for 3D time-resolved optical tomography

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T2 anisotropy in articular cartilage - a model based approach.

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