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Hanli Liu

Publications and source records attributed to Hanli Liu.

13 recordsLinked to original sources
PubMed2006

Determination of hemoglobin oxygen saturation in rat sciatic nerve by in vivo near infrared spectroscopy.

The purpose of this study is to investigate the values of hemoglobin oxygen saturation in the sciatic nerve of the rat following spinal nerve ligation. An optical spectroscopic technique along with a fiber optic probe was used to test the hypothesis that demyelination and degeneration after nerve injury lead to a significant decrease in the percentage of hemoglobin oxygen saturation. A modified spinal nerve ligation method was used to induce the degeneration, and three types of ligation on left spinal nerve (L4, L4 and L5, L5) were performed in rats. The optical reflectance measurements were taken from the left and right sciatic nerves on postoperative days 1, 4, 7, and 14. No significant difference was found among the three types of ligation, nor was between left and right sciatic nerve at postoperative day 1. Significant decreases in oxygen saturation percentages were found between left and right sciatic nerves at postoperative days 4, 7, and 14. This study continues to show the effectiveness of optical methods in determining/differentiating tissue properties, providing an excellent and robust in vivo technique that can have a potential clinical application in detecting demyelination and degeneration of the nervous system.

Algorithms↗
PubMed2006

Reconstruction method with data from a multiple-site continuous-wave source for three-dimensional optical tomography.

A method is presented for reconstruction of the optical absorption coefficient from transmission near-infrared data with a cw source. As it is distinct from other available schemes such as optimization or Newton's iterative method, this method resolves the inverse problem by solving a boundary value problem for a Volterra-type integral-differential equation. It is demonstrated in numerical studies that this technique has a better than average stability with respect to the discrepancy between the initial guess and the actual unknown absorption coefficient. The method is particularly useful for reconstruction from a large data set obtained from a CCD camera. Several numerical reconstruction examples are presented.

Algorithms↗
PubMed2005

Tumour oxygen dynamics measured simultaneously by near-infrared spectroscopy and 19F magnetic resonance imaging in rats.

Simultaneous near-infrared spectroscopy (NIRS) and magnetic resonance imaging (MRI) were used to investigate the correlation between tumour vascular oxygenation and tissue oxygen tension dynamics in rat breast 13762NF tumours with respect to hyperoxic gas breathing. NIRS directly detected global variations in the oxygenated haemoglobin concentration (Delta[HbO(2)]) within tumours and oxygen tension (pO(2)) maps were achieved using (19)F MRI of the reporter molecule hexafluorobenzene. Multiple correlations were examined between rates and magnitudes of vascular (Delta[HbO(2)]) and tissue (pO(2)) responses. Significant correlations were found between response to oxygen and carbogen breathing using either modality. Comparison of results for the two methods showed a correlation between the vascular perfusion rate ratio and the mean pO(2) values (R(2) > 0.7). The initial rates of increase of Delta[HbO(2)] and the slope of dynamic pO(2) response, d(pO(2))/dt, of well-oxygenated voxels in response to hyperoxic challenge were also correlated. These results demonstrate the feasibility of simultaneous measurements using NIRS and MRI. As expected, the rate of pO(2) response to oxygen is primarily dependent upon the well perfused rather than poorly perfused vasculature.

Animals↗
PubMed2005

Detection of degeneration in rat sciatic nerve by in vivo near infrared spectroscopy.

We have recently developed an optical spectroscopy technique to monitor light scattering changes of the nervous system in vivo. Near infrared (NIR) spectroscopy emphasizes the detection of light scattering properties, which are prominent within the wavelength range of 700 to 850 nm wavelength. The purpose of this study is to test the hypothesis that demyelination and degeneration of the sciatic nerves after nerve injury will lead to a change in light scattering properties and be detected by the NIR technique. Left spinal nerve ligations (L4, L4 and L5, L5) were performed in rats. The scattering properties of the left (ligated) and right (control) sciatic nerve were measured by the NIR reflectance using a bifurcated needle probe at postoperative days 1, 4, 7, and 14. The results show that there was no significant difference among three types of ligation, and neither did the readings between left and right sciatic nerve at postoperative day 1. Significant decreases in light scattering indexes were found between left and right sciatic nerves at postoperative days 4, 7, and 14. It is concluded that our initial hypothesis is proven, suggesting that the NIR technique may have a potential for clinical application in detecting demyelination and degeneration of the nervous system.

Animals↗
PubMed2003

Dynamic response of breast tumor oxygenation to hyperoxic respiratory challenge monitored with three oxygen-sensitive parameters.

The simultaneous measurement of three oxygen-sensitive parameters [arterial hemoglobin oxygen saturation (SaO2), tumor vascular-oxygenated hemoglobin concentration ([HbO2]), and tumor oxygen tension (pO2)] in response to hyperoxic respiratory challenge is demonstrated in rat breast tumors. The effects of two hyperoxic gases [oxygen and carbogen (5% CO2 and 95% O2)] were compared, by use of two groups of Fisher rats with subcutaneous 13762NF breast tumors implanted in pedicles on the foreback. Two different gas-inhalation sequences were compared, i.e., air-carbogen-air-oxygen-air and air-oxygen-air-carbogen-air. The results demonstrate that both of the inhaled, hyperoxic gases significantly improved the tumor oxygen status. All three parameters displayed similar dynamic response to hyperoxic gas interventions, but with different response times: the fastest for arterial SaO2, followed by biphasic changes in tumor vascular [HbO2], and then delayed responses for pO2. Both of the gases induced similar changes in vascular oxygenation and regional tissue pO2 in the rat tumors, and changes in [HbO2] and mean pO2 showed a linear correlation with large standard deviations, which presumably results from global versus local measurements. Indeed, the pO2 data revealed hetergeneous regional response to hyperoxic interventions. Although preliminary near-infrared measurements had been demonstrated previously in this model, the addition of the pO2 optical fiber probes provides a link between the noninvasive relative measurements of vascular phenomena based on endogenous reporter molecules, with the quantitative, albeit, invasive pO2 determinations.

Adenocarcinoma↗
PubMed2003

Limited possibility for quantifying mean particle size by logarithmic light-scattering spectroscopy.

Recent studies have shown that the slope of logarithmic scattering spectroscopy of a turbid medium is related to the sizes of the scattering particles within the turbid medium. Mie theory can be used to generate a logarithmic plot of the reduced-scattering coefficient versus wavelength. According to Nilsson et al. [Appl. Opt. 37, 1256 (1998)], the slope value of a linear fit of the logarithmic scattering spectroscopy between 600 and 1050 nm can be used for direct determination of particle size. We performed similar calculations using the Rayleigh-Gans approximation and obtained an analogous overall shape with additional sinusoidal features. Our calculations indicate a possible relationship between the slope and the particle size when the size is used to calculate the slope, namely, in the forward calculation. However, because of the sinusoidal pattern, the inverse calculation to obtain the particle size from the slope may be applied only for particles with a radius of <0.13 microm in combination with 650-1050-nm light. Caution should be exercised when inverse calculation is performed to determine the scattering particle sizes in the range of radii >0.13 microm, with the slope of logarithmic scattering spectroscopy within 650-1050 nm.

Models, Theoretical↗
PubMed2003

Tumor oxygen dynamics: comparison of 19F MR EPI and frequency domain NIR spectroscopy.

Oxygen plays a key role in tumor therapy and may be related to tumor development: e.g., angiogenesis and metastasis. Using noninvasive techniques to accurately measure tumor oxygenation could assist in developing novel therapies. Here, we have used the FREDOM (Fluorocarbon Relaxometry using Echo planar imaging for Dynamic Oxygen Mapping) approach based on hexafluorobenzene (HFB) to monitor tissue oxygen tension (pO2) of rat breast and prostate tumors and compared the results with changes in tumor vascular hemoglobin saturation (sO2) and concentration observed using a new dual wavelength homodyne near-infrared (NIR) system. The dynamic changes in pO2 and sO2 were assessed while rats were breathing various gases. NIR showed significant changes in vascular oxygenation accompanying respiratory interventions. 19F MR-EPI also showed significant changes in tissue pO2 and revealed considerable regional heterogeneity in both absolute values and rate of change accompanying interventions. Generally, changes in vascular sO2 preceded tissue pO2, particularly for smaller tumors.

Animals↗
PubMed2003

Interplay of tumor vascular oxygenation and tumor pO2 observed using near-infrared spectroscopy, an oxygen needle electrode, and 19F MR pO2 mapping.

This study investigates the correlation of tumor blood oxygenation and tumor pO(2) with respect to carbogen inhalation. After having refined and validated the algorithms for calculating hemoglobin concentrations, we used near-infrared spectroscopy (NIRS) to measure changes of oxygenated hemoglobin concentration (delta[HbO(2)]) and used an oxygen needle electrode and (19)F MRI for pO(2) measurements in tumors. The measurements were taken from Dunning prostate R3327 tumors implanted in rats, while the anesthetized rats breathed air or carbogen. The NIRS results from tumor measurements showed significant changes in tumor vascular oxygenation in response to carbogen inhalation, while the pO(2) electrode results showed an apparent heterogeneity for tumor pO(2) response to carbogen inhalation, which was also confirmed by (19)F MR pO(2) mapping. Furthermore, we developed algorithms to estimate hemoglobin oxygen saturation, sO(2), during gas intervention based on the measured values of delta[HbO(2)] and pO(2). The algorithms have been validated through a tissue-simulating phantom and used to estimate the values of sO(2) in the animal tumor measurement based on the NIRS and global mean pO(2) values. This study demonstrates that the NIRS technology can provide an efficient, real-time, noninvasive approach to monitoring tumor physiology and is complementary to other techniques, while it also demonstrates the need for an NIR imaging technique to study spatial heterogeneity of tumor vasculature under therapeutic interventions.

Algorithms↗
PubMed2003

Validation of a near-infrared probe for detection of thin intracranial white matter structures.

OBJECT: The authors have developed an intracranial near-infrared (NIR) probe that analyzes the scattering of light emitted from its tip to measure the optical properties of cerebral tissue. Despite its success in distinguishing graymatter from white matter in humans during stereotactic surgery, the limits of this instrument's resolution remain unclear. In this study, the authors determined the spatial resolution of this new probe by using a rodent model supplemented with phantom measurements and computer simulation. METHODS: A phantom consisting of Intralipid and gelatin was constructed to resemble a layer of white matter overlying a layer of gray matter. Near-infrared measurements were obtained as the probe was inserted through the gray-white matter transition. A computer simulation of NIR measurements through a gray-white matter transition was also performed using Monte Carlo techniques. The NIR probe was then used to study 19 tracks from the cortical surface through the corpus callosum in an in vivo rodent preparation. The animals were killed and histological sections through the tracks were obtained. Data from the phantom models and computer simulations showed that the NIR probe samples a volume of tissue extending 1 to 1.5 mm in front of the probe tip (this distance is termed the "lookthrough" distance). Measurements obtained from an NIR probe passing through a thin layer of white matter consisted of an initial segment of increasing values, a maximum (peak) value, and a trailing segment of decreasing values. The length of the initial segment is the lookthrough distance, the position of the peak indicates the location of the superficial white matter boundary, and the length of the trailing segment is the thickness of the layer. These considerations were confirmed in experiments with rodents. All tracks passed through the corpus callosum, which was demonstrated as a broad peak on each NIR graph. The position of the dorsal boundary of the corpus callosum and its width (based on histological measurements) correlated well with the peak of the NIR curve and its trailing segment, respectively. The initial segments correlated well with estimates of the lookthrough distance. Five of the tracks transected the smaller anterior commissure (diameter 0.2 mm), producing a narrow NIR peak at the correct depth. CONCLUSIONS: Data in this study confirm that the NIR probe can reliably detect and measure the thickness of layers of white matter as thin as 0.2 mm. Such resolution should be adequate to detect larger structures of interest encountered during stereotactic surgery in humans.

Animals↗
PubMedDate not supplied

Light scattering from rat nervous system measured intraoperatively by near-infrared reflectance spectroscopy.

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 mu(s)' 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 mu(s)' 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.

Animals↗
PubMedDate not supplied

Effect of photothermal therapy on breast tumor vascular contents: noninvasive monitoring by near-infrared spectroscopy.

The goal of this study was to investigate the effect of photothermal laser irradiation on rat breast tumor (DMBA-4) vascular contents. An 805-nm diode laser was used in our experiment with a power density ranging from 0.32 to 1.27 W/cm2. The dynamic changes of oxygenated hemoglobin and total hemoglobin concentrations, delta[HbO2] and delta[Hb]total, in rat tumors during photothermal irradiation were noninvasively monitored by a near-infrared spectroscopy system. A multichannel thermal detection system was also used simultaneously to record temperatures at different locations within the tumors. Our experimental results showed that: (1) photoirradiation did have the ability to induce hyperthermic effects inside the rat breast tumors in a single exponential trend; (2) the significant changes (P < 0.005) of delta[HbO2] and delta[Hb]total in response to a low dosage of laser irradiation (0.32 W/cm2) have a single exponential increasing trend, similar to that seen in the tumor interior temperature; and (3) the increase in magnitude of delta[HbO2] is nearly two times greater than that of delta[Hb]total, suggesting that photoirradiation may enhance tumor vascular oxygenation. The last observation may be important to reveal the hidden mechanism of photoirradiation on tumors, leading to improvement of tumor treatment efficiency.

Animals↗