Research in the DOIT Lab

Research activities in our group range from basic theoretical analyses to experimental studies, from instrumentation development to practical applications in vitro and in vivo, from new methods of data collection to new approaches of data analysis, all the way to pilot clinical applications. Click on a research activity listed below to learn more about our work within the domain.

Diffuse Optical Imaging of Tissue Lab logo.

 Frequency-domain near-infrared spectroscopy

Illustration of the time dependence of source emission and fluence rate in tissue for (a) continuous-wave (CW), (b) frequency-domain (FD), and (c) time-domain (TD) techniques.

Diffusion theory: continuous-wave (CW), frequency domain (FD), and time domain (TD)

Light propagation in biological tissue can be described as the diffusion of photons that experience absorption and scattering events.

Diffusion theory (PDF)

Line graph of decreasing energy density of a spherical wave propagating away from the light source.

Photon-density waves

Intensity-modulated light launches strongly damped waves of optical energy into tissue.

Photon-density waves (PDF)

Linear dependence of ln and phase on the source-detector distance r in an infinite medium.

Absolute optical measurements with multi-distance FD-NIRS data

The slopes of the amplitude and phase of photon-density waves yield robust measurements of absorption and scattering properties of tissue.

Absolute optical measurements with multi-distance FD-NIRS data (PDF)

Sensitivity profiles of phase and new FD-NIRS data types in single-distance configurations.

Novel data types in FD-NIRS

Different combinations of DC intensity, AC amplitude, and phase enrich the data space of FD-NIRS.

Novel data types in FD-NIRS (PDF)

A roulette wheel.

Monte Carlo simulations for solving the radiative transfer equation

Stochastic approaches such as Monte Carlo simulations are powerful tools for the solution of the radiative transfer equation.

Monte Carlo simulations for solving the radiative transfer equation (PDF)

 Dual-slope methods

Visual representation of the impact of an additional phase contribution from detector D1 in single slope 1 and single slope 2.

Basic concept of dual slopes

A special combination of two sources and two detectors yields dual-slope data that self-calibrate for instrumental factors.

Normalized absorption sensitivity for FD-NIRS data collected with (a) single distance (banana-shaped), (b) single slope, or (c) dual slope (nut-shaped). S, D are the source and detector locations on the tissue surface.

From going bananas to going nuts

Dual-slope data feature regions of sensitivity that are nut-shaped rather than banana-shaped as typical for single-distance data.

Broadband absorption spectra obtained by combining dual-slope broadband CW-NIRS with multi-distance (or self-calibrated) FD-NIRS.

Dual-slope broadband spectroscopy

The self-calibrated nature of dual-slope data lends itself to broadband absorption spectroscopy.

Cuvette geometry and location of sources and detectors.

Spectrophotometry of turbid media in a cuvette

Dual-ratio methods extend the dual-slope approach to the optical characterization of turbid media in a standard cuvette.

Finger clip housing for two source fibers (1, 2) and two detector fibers (A, B) for dual-ratio pulse oximetry in a transmission geometry.

Finger pulse oximetry

Dual-slope FD NIRS methods are applied to pulsatile hemodynamic measurements for pulse oximetry.

3D rendition of the mold design to accommodate illumination optical fibers (red) and detector optical fibers (black).

Dual-slope imaging

Specially designed source-detector arrays allow for imaging applications based on dual-slope data.

 Functional near-infrared spectroscopy (fNIRS)

Schematic representation of the optical region of sensitivity in noninvasive optical studies of the human brain for one source location and one detector location.

Non-invasive optical sensing of the brain

Cerebral hemodynamics can be measured non-invasively by placing light sources and optical detectors on the scalp.

Study of two-layered media. Ratio of measurement changes in response to an absorption perturbation in the bottom layer and to an absorption perturbation in the top layer for various FD-NIRS data types.

Depth sensitivity of FD-NIRS signals from two-layered media

Theoretical analyses of FD-NIRS data from two-layered media provide indications on their sensitivity to superficial and deep tissue.

Functional activation image of the primary visual cortex obtained with single-distance phase data.

Dual-slope FD-NIRS during visual stimulation

The cerebral hemodynamic response to brain activation is efficiently measured with dual-slope data.

 Coherent hemodynamics spectroscopy (CHS)

Illustration of coherent hemodynamic spectroscopy (CHS) measurement procedure.

The general idea of CHS

Coherent hemodynamics spectroscopy is based on cerebral hemodynamics that are associated with a specific physiological process.

The general idea of CHS (PDF)

Schematic representation of the CHS hemodynamic model, which treats the tissue microvasculature as a linear time-invariant system for which the inputs are blood volume, capillary flow velocity, and oxygen consumption, and the outputs are measured quantities with NIRS or fMRI.

The CHS cerebrovascular model

The CHS model treats the cerebral microvasculature as a linear time-invariant system.

The CHS cerebrovascular model (PDF)

Schematic of CHS measurements of capillary transit time in hemodialysis (HD) patients.

CHS measurements of capillary transit time and cerebral autoregulation

Cerebral blood flow and its autoregulation in response to blood pressure fluctuations can be measured with CHS.

CHS measurements of capillary transit time and cerebral autoregulation (PDF)

CHS measurements of capillary transit time in hemodialysis (HD) patients and healthy controls.

Depth dependence of coherent [Hb] and [HbO2] oscillations

Data interpreted with the CHS model indicate that hemodynamics in the scalp are driven by blood volume and in the brain by blood flow.

Depth dependence of coherent [Hb] and [HbO2] oscillations (PDF)

 Muscle studies with FD-NIRS

[HbT] in the forearm during venous occlusion.

Blood flow and oxygen consumption with vascular occlusions

The rates of blood accumulation and blood desaturation during vascular occlusion yield measures of blood flow and oxygen consumption.

Blood flow and oxygen consumption with vascular occlusions (PDF)

Blood flow measurements in the human forearm with the venous occlusion protocol.

Role of adipose tissue and bone tissue

In addition to adipose tissue, also bone tissue may impact non-invasive optical measurements of skeletal muscle.

Role of adipose tissue and bone tissue (PDF)