Broad-band light reflectance spectroscopy (LRS) of tissue with sub-millimeter fiber optic probes in the visible and nearinfrared
range has shown its utility in differentiation of tissue types, identification of cancer, and measurement of
stimulus-induced physiological responses. So far, single point measurement set-up has been widely employed to
determine local optical properties of tissue. However, it may often be of interest to obtain a 2D map of a surface area of a
tissue under investigation, rather than a single point reading, as in case of cancer margin detection or intraoperative
perfusion measurement. It is thus imperative to expand the LRS technique to multipoint measurement covering a larger
surface area. Here we describe the two methods that we use to quantify the hemoglobin derivatives and scattering of
tissue under investigation, and then utilize two bifurcated fiber optic probes with different fiber diameters and different
source-detector separations, to demonstrate the 2D imaging capability of LRS technique. In this study, we constructed a
tissue phantom, simulating tissue and blood vessel, and used 2D scanning to determine the spatial resolution and depth
resolution using two different probe geometries. Our results suggest that the depth sensitivity of these probes was limited
to sub-millimeter for hemoglobin derivatives, whereas scattering changes could be observed up to 2mm deep. It was
also found that the lateral resolution was affected, and the scattering signal became more diffuse, as a function of depth.
KEYWORDS: Hemodynamics, Functional magnetic resonance imaging, Magnetic resonance imaging, Data modeling, Near infrared spectroscopy, Blood, Sensors, Scanners, Visualization, Brain
Blood oxygenation level dependent (BOLD) response, which is measured by functional magnetic resonance imaging
(fMRI), is known to be a combination of various vascular parameters, among which deoxy-hemoglobin is argued to be a
major contributor. Functional near infrared spectroscopy (fNIRS), though being limited in its spatial resolution, provides
a promising tool to study cortical activations, due to its specificity of independent measurement of blood parameters
(Oxy, De-oxy and Total Hemoglobin), high temporal resolution and ease of use. To study the close relationship between
these imaging modalities, a finger tapping task with stimulus durations (2, 4, 8 & 16 sec) with variable inter-stimulation
intervals was chosen to compare spatio-temporal properties and non-linearity of BOLD signal with HbO, HbR and HBT
signal. This helped determine what parameter (HbO, HbR and HbT) BOLD signals correlate to most and how factors like neural adaptation that cause non-linearity can affect the hemodynamic behavior. It investigates the non-linearity in
HbO, HbR and HbT concentrations as compared to BOLD signal obtained using simultaneous fNIRS and fMRI measurement. Investigating non-linearity in hemodynamic response could provide a better understanding of neuronal function by modeling neural adaptation. The paper also discusses a method to model the neural adaptation and hemodynamic response.
Radio surgical interventions such as Gamma Knife and Cyberknife have become attractive as therapeutic interventions.
However, one of the drawbacks of cyberknife is radionecrosis, which is caused by excessive radiation to surrounding
normal tissues. Radionecrosis occurs in about 10-15% of cases and could have adverse effects leading to death.
Currently available imaging techniques have failed to reliably distinguish radionecrosis from tumor growth.
Development of imaging techniques that could provide distinction between tumor growth and radionecrosis would give
us ability to monitor effects of radiation therapy non-invasively. This paper investigates the use of near infrared
spectroscopy (NIRS) as a new technique to monitor the growth of brain tumors. Brain tumors (9L glioma cell line) were
implanted in right caudate nucleus of rats (250-300 gms, Male Fisher C) through a guide screw. A new algorithm was
developed, which used broadband steady-state reflectance measurements made using a single source-detector pair, to
quantify absolute concentrations of hemoglobin derivatives and reduced scattering coefficients. Preliminary results from
the brain tumors indicated decreases in oxygen saturation, oxygenated hemoglobin concentrations and increases in
deoxygenated hemoglobin concentrations with tumor growth. The study demonstrates that NIRS technology could
provide an efficient, noninvasive means of monitoring vascular oxygenation dynamics of brain tumors and further
facilitate investigations of efficacy of tumor treatments.
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