Jonathan J. Stott

Tomographic optical breast imaging guided by three-dimensional mammography

We introduce a modified Tikhonov regularization method to include three-dimensional x-ray mammography as a prior in the diffuse optical tomography reconstruction. With simulations we show that the optical image reconstruction resolution and contrast are improved by implementing this x-ray-guided spatial constraint. We suggest an approach to find the optimal regularization parameters. The presented preliminary clinical result indicates the utility of the method.

Coregistered tomographic x-ray and optical breast imaging: initial results

We describe what is, to the best of our knowledge, the first pilot study of coregistered tomographic x-ray and optical breast imaging. The purpose of this pilot study is to develop both hardware and data processing algorithms for a multimodality imaging method that provides information that neither x-ray nor diffuse optical tomography (DOT) can provide alone. We present in detail the instrumentation and algorithms developed for this multimodality imaging. We also present results from our initial pilot clinical tests. These results demonstrate that strictly coregistered x-ray and optical images enable a detailed comparison of the two images. This comparison will ultimately lead to a better understanding of the relationship between the functional contrast afforded by optical imaging and the structural contrast provided by x-ray imaging.

Volumetric diffuse optical tomography of brain activity

We present three-dimensional diffuse optical tomography of the hemodynamic response to somatosensory stimulation in a rat. These images show the feasibility of volumetrically imaging the functional response to brain activity with diffuse light. A combination of positional optode calibration and contrast-to-noise ratio weighting was found to improve imaging performance.

Improved sensitivity to cerebral hemodynamics during brain activation with a time-gated optical system: analytical model and experimental validation

Time domain (TD) diffuse optical measurement systems are being applied to neuroimaging, where they can detect hemodynamics changes associated with cerebral activity. We show that TD systems can provide better depth sensitivity than the more traditional continuous wave (CW) systems by gating late photons, which carry information about deep layers of the brain, and rejecting early light, which is sensitive to the superficial physiological signal clutter. We use an analytical model to estimate the contrast due to an activated region of the brain, the instrumental noise of the systems, and the background signal resulting from superficial physiological signal clutter. We study the contrast-to-noise ratio and the contrast-to-background ratio as a function of the activation depth and of the source-detector separation. We then present experimental results obtained with a time-gated instrument on the motor cortex during finger-tapping exercises. Both the model and the experimental results show a similar contrast-to-noise ratio for CW and TD, but that estimation of the contrast is experimentally limited by background fluctuations and that a better contrast-to-background ratio is obtained in the TD case. Finally, we use the time-gated measurements to resolve in depth the brain activation during the motor stimulus.

Optode positional calibration in diffuse optical tomography

Although diffuse optical tomography is a highly promising technique used to noninvasively image blood volume and oxygenation, the reconstructed data are sensitive to systemic difference between the forward model and the actual experimental conditions. In particular, small changes in optode location or in the optode-tissue coupling coefficient significantly degrade the quality of the reconstruction images. Accurate system calibration therefore is an essential part of any experimental protocol. We present a technique for simultaneously calibrating optode positions and reconstructing images that significantly improves image quality, as we demonstrate with simulations and phantom experiments.

Depth of arterial oscillation resolved with NIRS time and frequency domain

We present measurements of the heartbeat obtained on human foreheads, using frequency domain and time domain systems. Preliminary results indicate that we are able to measure signals of the heartbeat originated from intracranial layers (brain).

Improvement of depth sensitivity to cerebral hemodynamics with a time domain system

We use a time-domain system based on a pulsed laser and an intensified CCD camera to detect cerebral hemodynamics. We show experimentally and theoretically an improvement in the depth sensitivity over continuous wave systems.

Linearized optical tomography using the diffusion approximation in regions with curved boundaries

We show that the diffusion approximation with a zero partial-flux boundary condition accurately models photon migration in a highly scattering medium with curved boundaries. In particular, we examine optical mammography in a transmission geometry.

Volumetric diffuse optical tomography of brain activity in rat

We present three-dimensional diffuse optical tomography (DOT) of the hemodynamic response to forepaw stimulation in a rat. DOT results agree with previous fMRI studies and demonstrate feasibility of volumetrically imaging brain activity.

MRI guided fluorescence optical tomography for small animal imaging

We present 3-D reconstructions of ICG fluorescence from time domain optical measurements on a phantom model mouse, imbedded with the near-infrared flurophore, Indocyanine green (ICG) . The complex medium boundary of the mouse phantom was obtained from MRI images, and subsequently incorporated in a linearized, finite-difference diffusion equation based forward model to reconstruct the flurophore properties The procedure illustrated here will subsequently be applied to in-vivo small animal fluorescence measurements, with diffusion and transport based forward models that utilize the detailed MRI images of the mouse tissue structure