Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 37 records · Page 2Linked to original sources

PubMed2000

Concurrent MRI and diffuse optical tomography of breast after indocyanine green enhancement.

We present quantitative optical images of human breast in vivo. The images were obtained by using near-infrared diffuse optical tomography (DOT) after the administration of indocyanine green (ICG) for contrast enhancement. The optical examination was performed concurrently with a magnetic resonance imaging (MRI) exam on patients scheduled for excisional biopsy or surgery so that accurate image coregistration and histopathological information of the suspicious lesions was available. The ICG-enhanced optical images coregistered accurately with Gadolinium-enhanced magnetic resonance images validating the ability of DOT to image breast tissue. In contrast to simple transillumination, we found that DOT provides for localization and quantification of exogenous tissue chromophore concentrations. Additionally our use of ICG, an albumin bound absorbing dye in plasma, demonstrates the potential to differentiate disease based on the quantified enhancement of suspicious lesions.

Aged↗

PubMed2000

Near infrared spectrophotometry for the diagnosis of vasculogenic erectile dysfunction.

A specialized near infrared spectrophotometry instrument for noninvasive, continuous monitoring of the hemodynamic events of erection in the human penis has been developed. Its potential application for the diagnostic evaluation of erectile dysfunction was investigated. Thirty-eight patients and 18 volunteer subjects underwent penile near infrared spectrophotometry using an optical sensor probe with wavelength selectivity for hemoglobin absorption spectra. Penile blood volume changes and their time courses were measured following intracavernous pharmacostimulation in patients and visual sexual stimulation in volunteers. Spectrophotometric results were compared with results obtained simultaneously using color duplex ultrasonography, strain gauge penile circumference monitoring, penile tonometry, and clinical assessments. Spectrophotometric recordings of penile erection showed measurable blood volume changes consistent with the hemodynamic events of this biological function. Blood volume per cent (BV%) increase correlated with clinical ratings of erection quality (P < 0.001), penile rigidity measurements (P < 0.005), and penile circumference increases (P < 0.0001), and it correlated with mean peak systolic velocity measurements when BV% increase was restricted to values less than 50% (P < 0.001). The time to reach half the maximum blood volume change (BV T1) correlated directly with the time to reach half the maximum penile circumference size increase (P < 0.001), whereas BV T4 correlated inversely with mean resistive index measurements only when BV T(1/2) was restricted to values greater than 120 s (P < 0.05). Spectrophotometric criteria consisting of BV % less than 35% and BV T(1/2) greater than 120 s affirmed the diagnosis of severe erectile impairment with a similar degree of accuracy as standard ultrasonographic criteria (P < 0.002). Penile near infrared spectrophotometry is a safe, inexpensive and simply used biomedical optics technique that provides quantitative measurements of the vascular physiology of penile erection and appears to offer clinical utility in the diagnosis of vasculogenic erectile dysfunction.

Adult↗

PubMed2000

Near-field diffraction tomography with diffuse photon density waves.

An angular spectrum algorithm is presented for fast, near-field diffraction tomographic imaging with diffuse photon density waves in highly scattering media. A general relation in K space is derived that connects the spatial variations of the optical properties of heterogeneities to the spatial spectra of the measured scattered diffuse photon density waves. The theory is verified experimentally for situations when boundary effects can be neglected. We further describe how to reconstruct absorption and scattering properties simultaneously, and how to incorporate boundary conditions into this angular spectrum algorithm for a turbid medium of finite size (e.g., the slab medium). Limitations and potential improvements of the near-field diffraction tomography are also discussed.

Algorithms↗

PubMed2000

Trans-abdominal monitoring of fetal arterial blood oxygenation using pulse oximetry.

Pulse oximetry (oxygen saturation monitoring) has markedly improved medical care in many fields, including anesthesiology, intensive care, and newborn intensive care. In obstetrics, fetal heart rate monitoring remains the standard for intrapartum assessment of fetal well being. Fetal oxygen saturation monitoring is a new technique currently under development. It is potentially superior to electronic fetal heart rate monitoring (cardiotocography) because it allows direct assessment of both the fetal oxygen status and fetal tissue perfusion. Here we present the analysis for determining the most optimal wavelength selection for pulse oximetry. The wavelengths we chose as the most optimal are the first in the range of 670-720 nm and the second in the range of 825-925 nm. Further, we discuss the possible systematic errors during our measurements and their contribution to the obtained saturation results. We present feasibility studies for fetal pulse oximetry, monitored noninvasively through the maternal abdomen. Our preliminary experiments show that the fetal pulse can be discriminated from the maternal pulse and thus, in principle, the fetal arterial oxygen saturation can be obtained. We present the methodology for obtaining these data, and discuss the dependence of our measurements on the fetal position with respect to the optode assembly.

Abdomen↗

PubMed2000

Quantification of ischemic muscle deoxygenation by near infrared time-resolved spectroscopy.

The purpose of this study was to quantify muscle deoxygenation in human skeletal muscles using near infrared time-resolved spectroscopy (NIRTRS) and compare NIRTRS indicators and blood saturation. The forearm muscles of five healthy males (aged 27-32 yrs.) were monitored for changes in hemoglobin saturation (SO2) during 12 min of arterial occlusion and recovery. SO2 was determined by measuring the temporal profile of photon diffusion at 780 and 830 nm using NIRTRS, and was defined as SO2-TRS. Venous blood samples were also obtained for measurements of SvO2, and PvO2. Interstitial PO2(PintO2) was monitored by placing an O2 electrode directly into the muscle tissue. Upon the initiation of occlusion, all parameters fell progressively until reaching a plateau in the latter half of occlusion. It was observed at the end of occlusion that SO2-TRS (24.1 +/- 5.6%) agreed with SvO2 (26.2 +/- 6.4) and that PintO2 (14.7 +/- 1.0 Torr) agreed with PvO2 (17.3 +/- 2.2 Torr). The resting O2 store (oxygenated hemoglobin) and O2 consumption rate were 290 microM and 0.82 microM s-1, respectively, values which reasonably agree with the reported results. These results indicate that there was no O2 gradient between vessels and interstisium at the end of occlusion.

Adult↗

PubMed2000

Photon migration through fetal head in utero using continuous wave, near-infrared spectroscopy: development and evaluation of experimental and numerical models.

In this work experimental tissue phantoms and numerical models were developed to estimate photon migration through the fetal head in utero. The tissue phantoms incorporate a fetal head within an amniotic fluid sac surrounded by a maternal tissue layer. A continuous wave, dual-wavelength (lambda = 760 and 850 nm) spectrometer was employed to make near-infrared measurements on the tissue phantoms for various source-detector separations, fetal-head positions, and fetal-head optical properties. In addition, numerical simulations of photon propagation were performed with finite-difference algorithms that provide solutions to the equation of radiative transfer as well as the diffusion equation. The simulations were compared with measurements on tissue phantoms to determine the best numerical model to describe photon migration through the fetal head in utero. Evaluation of the results indicates that tissue phantoms in which the contact between fetal head and uterine wall is uniform best simulates the fetal head in utero for near-term pregnancies. Furthermore, we found that maximum sensitivity to the head can be achieved if the source of the probe is positioned directly above the fetal head. By optimizing the source-detector separation, the signal originating from photons that have traveled through the fetal head can drastically be increased.

Cerebrovascular Circulation↗

PubMed2000

Photon migration through fetal head in utero using continuous wave, near infrared spectroscopy: clinical and experimental model studies.

Near infrared (NIR) measurements were made from the maternal abdomen (clinical studies) and laboratory tissue phantoms (experimental studies) to gain insight into photon migration through the fetal head in utero. Specifically, a continuous wave spectrometer was modified and employed to make NIR measurements at 760 and 850 nm, at a large (10 cm) and small (2.5/4 cm) source-detector separation, simultaneously, on the maternal abdomen, directly above the fetal head. A total of 19 patients were evaluated, whose average gestational age and fetal head depth, were 37 weeks +/- 3 and 2.25 cm +/- 0.7, respectively. At the large source-detector separation, the photons are expected to migrate through both the underlying maternal and fetal tissues before being detected at the surface, while at the short source-detector separation, the photons are expected to migrate primarily through the superficial maternal tissues before being detected. Second, similar NIR measurements were made on laboratory tissue phantoms, with variable optical properties and physical geometries. The variable optical properties were obtained using different concentrations of India ink and Intralipid in water, while the variable physical geometries were realized by employing glass containers of different shapes and sizes. Third, the NIR measurements, which were made on the laboratory tissue phantoms, were compared to the NIR measurements made on the maternal abdomen to determine which tissue phantom best simulates the photon migration path through the fetal head in utero. The results of the comparison were used to provide insight into the optical properties and physical geometry of the maternal and fetal tissues in the photon migration path.

Adult↗

PubMed2000

Preliminary evaluation of dual wavelength phased array imaging on neonatal brain function.

Imaging of human tissue using noninvasive techniques has been of great interest in biomedical fields. Optical imaging has attracted a lot of attention because of its portability and economy. The possibility that a highly portable, fast, safe, and affordable imaging system which could obtain interpretable images of brain function for pre- and full-term neonates in a few seconds, has been explored in this article. We have used a sensitive optical topography system, termed phased array, in which a pair of equal-amplitude and antiphase light sources are applied to generate a sharp amplitude null and phase transition plane. This two-wavelength (750 and 830 nm), frequency encoded (50 and 52 MHz) phased array imaging system can indicate the blood concentration and oxygenation changes in blood model studies and during parietal brain activation in neonates. Significant functional responses, particularly to parietal stimulation in normal and pathological states of neonatal brain, have been revealed in our study. The preliminary clinical results are presented in this article.

Blood Flow Velocity↗

PubMed2000

Study of near infrared technology for intracranial hematoma detection.

Although intracranial hematoma detection only requires the continuous wave technique of near infrared spectroscopy (NIRS), previous studies have shown that there are still some problems in obtaining very accurate, reliable hematoma detection. Several of the most important limitations of NIR technology for hematoma detection such as the dynamic range of detection, hair absorption, optical contact, layered structure of the head, and depth of detection are reported in this article. A pulsed light source of variable intensity was designed and studied in order to overcome hair absorption and to increase the dynamic range and depth of detection. An adaptive elastic optical probe was made to improve the optical contact and decrease contact noise. A new microcontroller operated portable hematoma detector was developed. Due to the layered structure of the human head, simulation on a layered medium was analyzed experimentally. Model inhomogeneity tests and animal hematoma tests showed the effectiveness of the improved hematoma detector for intracranial hematoma detection.

Absorption↗

PubMed2000

Optical imaging as an adjunct to sonograph in differentiating benign from malignant breast lesions.

The role of near infrared (NIR) diffusive light imaging as an adjunct to ultrasound in differentiating benign from malignant lesions was evaluated in 27 mammography patients with infiltrating ductal carcinomas, apocrine metaplasia, fibroadenomas, radial scar and ductal hyperplasia, cysts, and normal tissues. Conventional ultrasound/mammography images were graded based on BI-RADS assessment categories. The spatial NIR measurements were made at wavelengths of 750 and 830 nm. Functional images, such as relative changes of deoxyhemoglobin (deoxyHb) and total blood concentration, were estimated from the dual wavelength measurements. Maximum relative deoxyHb and blood concentration changes were measured, and spatial correlation of masses in relative deoxyHb and blood concentration images for each breast were calculated. For the five biopsy proven benign lesions, ultrasound/mammography diagnoses were suspicious for malignancy (four cases) and highly suspicious for malignancy (one case). Four lesions showed less than 1.0 V maximum deoxyHb and less than 1.5 V maximum blood concentration levels on average and spatial image correlation showed no correlated masses in both deoxyHb and blood concentration images. For the four biopsy proven malignant lesions, ultrasound/mammography diagnoses were highly suspicious for malignancy. Maximum deoxyHb and blood concentration changes were greater than 2.9 V on average except one lesion which showed smaller deoxyHb signal (maximum 0.85 V) but the deoxyHb mass and blood concentration mass were highly correlated.

Adult↗

PubMed2000

Three-dimensional diffuse optical mammography with ultrasound localization in a human subject.

We describe an approach that combines clinical ultrasound and photon migration techniques to enhance the sensitivity and information content of diffuse optical tomography. Measurements were performed on a postmenopausal woman with a single 1.8 x 0.9 cm malignant ductal carcinoma in situ approximately 7.4 mm beneath the skin surface (UCI IRB protocol 95-563). The ultrasound-derived information about tumor geometry enabled us to segment the breast tissue into tumor and background regions. Optical data was obtained with a multifrequency, multiwavelength hand-held frequency-domain photon migration backscattering probe. The optical properties of the tumor and background were then computed using the ultrasound-derived geometrical constraints. An iterative perturbative approach, using parallel processing, provided quantitative information about scattering and absorption simultaneously with the ability to incorporate and resolve complex boundary conditions and geometries. A three to four fold increase in the tumor absorption coefficient and nearly 50% reduction in scattering coefficient relative to background was observed (lambda = 674, 782, 803, and 849 nm). Calculations of the mean physiological parameters reveal fourfold greater tumor total hemoglobin concentration [Hbtot] than normal breast (67 microM vs 16 microM) and tumor hemoglobin oxygen saturation (SOx) values of 63% (vs 73% and 68% in the region surrounding the tumor and the opposite normal tissue, respectively). Comparison of semi-infinite to heterogeneous models shows superior tumor/background contrast for the latter in both absorption and scattering. Sensitivity studies assessing the impact of tumor size and refractive index assumptions, as well as scan direction, demonstrate modest effects on recovered properties.

Absorption↗

PubMed2000

Modeling photon transport in transabdominal fetal oximetry.

The possibility of optical oximetry of the blood in the fetal brain measured across the maternal abdomen just prior to birth is under investigation. Such measurements could detect fetal distress prior to birth and aid in the clinical decision regarding Cesarean section. This paper uses a perturbation method to model photon transport through an 8-cm-diam fetal brain located at a constant 2.5 cm below a curved maternal abdominal surface with an air/tissue boundary. In the simulation, a near-infrared light source delivers light to the abdomen and a detector is positioned up to 10 cm from the source along the arc of the abdominal surface. The light transport [W/cm2 fluence rate per W incident power] collected at the 10 cm position is Tm = 2.2 x 10(-6) cm(-2) if the fetal brain has the same optical properties as the mother and Tf = 1.0 x 10(-6) cm(-2) for an optically perturbing fetal brain with typical brain optical properties. The perturbation P=(Tf - Tm)/Tm is -53% due to the fetal brain. The model illustrates the challenge and feasibility of transabdominal oximetry of the fetal brain.

Abdomen↗

PubMed2000

Oximetry based on diffuse photon density wave differentials.

The quantification of tissue optical properties for calculating blood saturation and hemoglobin concentration using measurements of diffuse photon density waves at some distance away from an intensity-modulated light source, generally requires the determination of the amplitude and phase of this light source. This determination may become a severe impediment for measurements performed in the clinical environment. In this work we extend a self-calibrating methodology developed for constant wave and modulation depth-phase measurements, to include amplitude and phase measurements of diffuse photon density waves. The method uses amplitude and phase changes of intensity modulated light, under the assumption of known index of refraction and invariant reduced scattering coefficient mu's, to quantify the absorption coefficient mu(a) without requiring initial amplitude and phase knowledge. Quantification of the mu(a) at selected time points during a measurement can then be employed to calibrate numerical solutions of the diffusion equation and compute the mu(a) for the remaining time points of the experiment. It is shown that the method is quite insensitive to the knowledge of the exact mu's value so that an assumption on the average mu's value for the tissue measured may be employed. The sensitivity of calculating blood saturation and hemoglobin concentration, as a function of the deviation of the mu's used in the calculation versus the real mu's value is investigated using simulated data. It is also demonstrated that the saturation calculation is especially insensitive to the mu's guess. The performance of the method to quantify blood oxygen saturation and the concentrations of oxy- and deoxy-hemoglobin is examined with experimental measurements at two wavelengths on specially constructed blood model phantoms. To validate the method the measurements are monitored by a time-resolved spectrometer. The method is shown to be accurate to within +/-5% in calculating blood saturation and to within +/-10% in calculating hemoglobin concentration compared to the results obtained with the time-resolved spectrometer and the expected theoretical values.

Algorithms↗

PubMed2000

Hydrophilic cyanine dyes as contrast agents for near-infrared tumor imaging: synthesis, photophysical properties and spectroscopic in vivo characterization.

We have synthesized a group of glucamine and gluosamine-substituted cyanine dyes structurally related to indocyanine green (ICG) and have characterized these compounds with regard to their potential as contrast agents for biomedical optical imaging. The compounds reported herein exhibit increased hydrophilicity and less plasma protein binding (< 50%), and are thus expected to have different pharmacokinetic properties compared with ICG. Furthermore, we measured enhanced fluorescence quantum yields (7-15%) in a physiological environment with respect to ICG. For the derivative with the highest hydrophilicity (5a) the efflux from tumor and normal tissue was monitored by intensity-modulated diffuse optical spectroscopy after intravenous injection into tumor-bearing rats. In comparison with ICG, 5a exhibited a considerably enhanced tissue-efflux half-life (73 min versus less than 10 min for ICG in tumor tissue), a two-fold higher initial tissue absorption coefficient compared to ICG, and finally, it generated an elevated tumor-to-tissue concentration gradient up to 1 h after injection. In conclusion, compounds such as 5a are promising contrast agents for optical imaging, and could facilitate highly sensitive and specific detection of breast cancer or other malignancies by utilizing mechanisms similar to contrast-enhanced magnetic resonance imaging or computerized tomography.

Animals↗

PubMed1999

In vivo determination of altered hemoglobin saturation in dogs with M-type phosphofructokinase deficiency.

Muscle-type phosphofructokinase (M-PFK) deficiency causes an exertional myopathy and chronic hemolysis in affected humans and dogs, the only animal model available. Deficient individuals have impaired glycolytic metabolism, impaired oxidative metabolism, and increased hemoglobin-oxygen (HbO2) affinity as a result of low 2,3-diphosphoglycerate (2,3-DPG) levels. The purpose of this study was to determine if PFK-deficient muscle has abnormal oxygen saturation during exercise. Oxygen saturation of hemoglobin/myoglobin was measured noninvasively in skeletal muscle during progressive muscle activation using near-infrared spectroscopy (NIRS). Muscle metabolites were also measured using magnetic resonance spectroscopy (MRS). PFK-deficient and normal dogs were anesthetized and the cranial tibial muscles stimulated for 6 min at each of four different rates (1, 2, 4, and 8 Hz). With increasing stimulation, muscles from normal dogs showed progressive decrease in hemoglobin saturation. In contrast, PFK-deficient dogs exhibited either an increase in hemoglobin saturation or an initial decrease with no further change. PFK-deficient muscles accumulated 11.1 +/- 3.5 mmol/L of sugar phosphate which was not seen in normal muscle and had higher calculated [ADP] levels at each stimulation level, indicating impaired oxidative metabolism. These findings are consistent with the hypothesis that these animals have impaired oxidative metabolism and impaired muscle O2 extraction from hemoglobin due to increased HbO2 affinity. NIRS appears to be a useful noninvasive method of monitoring tissue oxygen saturation in normal or disease conditions.

Adenosine Diphosphate↗

PubMed1999

Three-dimensional redox image of the normal gerbil brain.

Regional differences in the redox ratio were studied in the gerbil brain. Brains were frozen using an in situ funnel-freezing method, and sliced coronally for scanning of mitochondrial redox imaging. The relative local redox ratio of nicotinamide-adenosine dinucleotide to its reduced form was calculated from fluorescence signals of intrinsic fluorochromes, i.e. reduced nicotinamide-adenosine dinucleotide and flavoproteins, using a high resolution fluorometer developed in our laboratory. Twelve consecutive coronal images were obtained from each of 10 gerbils. The mean value of the regional redox ratio in both the cerebral and cerebellar gray matter were found to be significantly lower than that in the cerebral and cerebellar white matter (P < 0.01, Mann-Whitney test). Local differences in the redox ratio were also found among subregions of gray matter. The redox ratio in the globus pallidus was significantly higher than values in other subregions of gray matter (P < 0.01, Mann-Whitney test) We postulate that a high concentration of the reduced form of pyridine nucleotide is maintained to provide redox energy for rapid turnover of ATP in the areas of high energy consumption.

Animals↗

PubMed1999

Application of near-infrared time-resolved spectroscopy to rat liver--a preliminary report for surgical application.

The applicability of near-infrared time-resolved spectroscopy to rat liver surgery was investigated. First, the technical reliability in determining the absorption coefficient (mu(a)) and reduced scattering coefficient (mu'(s)) of the liver was checked. Next, boundary effects in determining mu(a) and mu'(s) of the rat liver were examined. Finally, changes in mu(a) and mu'(s) of rat liver with ischaemia were directly measured by TRS. Our TRS system showed that the mu(a) value held a linear correlation with the ink concentration in a lipid emulsion until mu(a) reached 1.2 cm(-1), while the mu'(s) was fairly independent. The mu(a) values of blood-free rat liver and blood-containing rat liver at 780 nm were observed to be 0.43 cm(-1) and 0.67 cm(-1) by using the matching method, indicating that TRS is reliable in determining mu(a) and mu'(s) of the liver. Possible errors in mu(a) and mu'(s) determination due to the boundary effects of the rat liver were as small as 7%, when the mu(a) value was as high as observed for the liver. The oxygen saturation of haemoglobin (SO2) was changed from 64.9% to 8.0%, and the haemoglobin content (THB) from 189.1 microM to 131.6 microM by ischaemia. Mu'(s) dynamically changed in the range 7.06 cm(-1) to 11.36 cm(-1). We conclude that time-resolved measurement is applicable in the high-mu(a) region observed in the liver, and can give quantitative estimations of SO2 and THB in the liver.

Animals↗

PubMed1999

The kinetics of the enzyme-substrate compound of peroxidase. 1943.

Under the narrow range of experimental conditions, and at a temperature of approximately 25 degrees, the following data were obtained. 1. The equilibrium constant of peroxidase and hydrogen peroxide has a minimum value of 2 x 10(-8). 2. The velocity constant for the formation of peroxidase-H2O2 Complex I is 1.2 x 10(7) liter mole-1 sec.-1, +/- 0.4 x 10(7). 3. The velocity constant for the reversible breakdown of peroxidase-H2O2 Complex I is a negligible factor in the enzyme-substrate kinetics and is calculated to be less than 0.2 sec.-1. 4. The velocity constant, k3, for the enzymatic breakdown of peroxidase-H2O2 Complex I varies from nearly zero to higher than 5 sec.-1, depending upon the acceptor and its concentration. The quotient of k3 and the leucomalachite green concentration is 3.0 x 10(4) liter mole-1 sec.-1. For ascorbic acid this has a value of 1.8 x 10(5) liter mole-1 sec.-1. 5. For a particular acceptor concentration, k3 is determined solely from the enzyme-substrate kinetics and is found to be 4.2 sec.-1. 6. For the same conditions, k3 is determined from a simple relationship derived from mathematical solutions of the Michaelis theory and is found to be 5.2 sec.-1. 7. For the same conditions, k3 is determined from the over-all enzyme action and is found to be 5.1 sec.-1. 8. The Michaelis constant determined from kinetic data alone is found to be 0.44 x 10(-6). 9. The Michaelis constant determined from steady state measurements is found to be 0.41 x 10(-6). 10. The Michaelis constant determined from measurement of the overall enzyme reaction is found to be 0.50 x 10(-6). 11. The kinetics of the enzyme-substrate compound closely agree with mathematical solutions of an extension of the Michaelis theory obtained for experimental values of concentrations and reaction velocity constants. 12. The adequacy of the criteria by which experiment and theory were correlated has been examined critically and the mathematical solutions have been found to be sensitive to variations in the experimental conditions. 13. The critical features of the enzyme-substrate kinetics are Pmax, and curve shape, rather than t1/2. t1/2 serves as a simple measure of dx/dt. 14. A second order combination of enzyme and substrate to form the enzyme-substrate compound, followed by a first order breakdown of the compound, describes the activity of peroxidase for a particular acceptor concentration. 15. The kinetic data indicate a bimolecular combination of acceptor and enzyme-substrate compound.

History, 20th Century↗