In this study, we report the development of a near infrared broadband, steady-state, multi-channel imaging system to
quantify hemodynamic parameters, which is to be used for measuring the rat brain tumors in vivo. The imager was
calibrated with laboratory phantoms to eliminate spectral effects of the CCD spectrometers, optical fibers, and
multiplexer channels. The calibration procedures also help determine the source strength in order to obtain accurate
image reconstructions. A multi-channel, multi-wavelength, spectrally constrained reconstruction algorithm is under
development to obtain tomographic maps of concentrations of hemoglobin derivatives and reduced scattering
coefficients. The developed imaging system and reconstruction algorithm were validated with dynamic multi-tube
phantoms.
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.
Our goal is to quantify scattering properties of near-IR light in the rat spinal cord region and to differentiate healthy and demyelinated peripheral nerves intraoperatively based on differential light scattering. For the rat spinal cord, optical reflectance is measured from the spinal cord surface at spatial intervals of 1 mm using a needle probe. Data are acquired from left and right lumbar regions of the animals as well as on the central blood vessels. The reduced scattering coefficient µs[prime] is found to be higher (34.2±2.1 cm–1) in the lumbar regions of the spinal cord than on the central blood vessel (19.9±1.0 cm–1). This methodology is extended to detect differences in the rat sciatic nerves following left L4 spinal nerve ligation. The reflectance is taken at the same five regions at postoperative days 1, 4, 7, and 14. Significant differences are seen in both the spectral slope and µs[prime] values on postoperative days 4, 7, and 14, indicating that either of the two quantities could be used as a marker for demyelination. We prove the usefulness of the technique, which may have a possible clinical application for minimally invasive, intraoperative diagnosis and monitoring of demyelination diseases, such as multiple sclerosis in the central nervous system or degeneration of the peripheral nervous system.
The ability to retrieve particle size information from back scattering reflectance with a small source-detector separation would significantly enhance the potential for development of non-invasive and minimally invasive diagnostic techniques. We present a technique for inverse determination of particle size distribution and volume fractions and validate it with polystyrene microspheres. Two of monotonic, third-degree polynomial equations were fitted from Mie theory to relate wavelength exponent 'n' and particle radii. These two equations allow us to inversely estimate the particle size from the measured 'n' value. A genetic algorithm was applied to optimize the particle size distribution and volume fraction. The experimental setup consisted of a tungsten light, CCD spectrometer with a bifurcated optical fiber for light delivery and detection. The measurement system was calibrated with a reflectance standard; different sizes and volume fractions of the suspensions were chosen for measurements. The wavelength dependence of reduced scattering coefficient was derived from the measured reflectance. Polystyrene microsphere suspensions with diameters 0.43 - 2.00 μm were characterized using the developed algorithm. The results show a good agreement between the particle size retrieved by our algorithm and manufacturer’s data, demonstrating a robust method for particle size determination using near infrared reflectance and small source-detector separation.
Determination of blood flow changes will be helpful for evaluation of tumor prognosis and therapy. Our study is to develop an in vitro hemodynamic phantom model, which allows us to show the feasibility of using near infrared spectroscopy (NIRS) to determine flow changes as a dynamic imaging modality to monitor tumor responses to therapy. In the hemodynamic phantom model, both single and multiple, transparent, plastic tubes were used to pass through a cylindral glass chamber. The chamber was filled with either an Intralipid solution or a soft gelatin phantom, while the tube or tubes were pumped with either an Intralipid-ink mixture or animal whole blood to simulate the tumor vasculature. The Intralipid solutions that were filled in the chamber and tubes had optical scattering and absorption properties similar to those of tumor tissues and tumor vasculature. A single-channel, broadband, NIRS system with a tungsten light source and a CCD-array spectrometer was used to quantify the changes in optical density (OD) of the intralipid-ink mixture with variations in flow rate and concentration. A single-exponential curve fit has been used to determine the time constant (τ) from the change in OD to estimate the flow rate. The obtained preliminary results show a strong correlation between changing rates of concentration and flow; a multivariable dynamic mathematical model may be also established to relate changes of Hb, HbO and blood volume with blood flow.
This study was done to use near infrared (NIR) spectroscopy to bring out differences in the anatomical substructures in the rat spinal cord and further to differentiate scattering between demyelinated and normal sciatic nerves in rat models, thereby exploring a new methodology to localize MS (multiple Sclerosis) lesions in vivo for animal studies. The experimental setup consisted of a tungsten light source, CCD array spectrometer, and bifurcated optical fibers for light delivery and detection of back scattered light from tissue. The measurement system was calibrated with reflectance standard. The spinal cord of 14 rats was exposed by laminectomy, and the measurements were taken on 8 points at intervals of 1 mm on the right and left lumbar-sacral regions and the central blood vessel. For measurements on the sciatic nerve, the spinal nerves of 84 rats were ligated according to the Chung Model. Measurements were taken on five points on both the ligated and the control nerve side after 1, 4, 7 and 14 days. The reduced scattering coefficient, μs', was found to be higher in the lumbar-sacral regions (34.17 ± 2.05 cm-1) than that near the central blood vessel (19.9 ± 3.8 cm-1). Statistically, there was significant difference in scattering between the control side and the ligated side on postoperative days 4, 7, and 14. This study shows a promising diagnostic value in the future for monitoring of demyelinated CNS (central nervous system) diseases, like Multiple Sclerosis.
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