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D T Delpy

Publications and source records attributed to D T Delpy.

At least 19 recordsLinked to original sources
PubMed1995

Performance comparison of several published tissue near-infrared spectroscopy algorithms.

We have collected multiwavelength near-infrared (NIR) attenuation spectra on human forearm muscle, the adult rat head, and newborn piglet head to compare the changes in chromophore concentration derived from these data using published algorithms from four groups. We find differences between the results from the algorithms on each data set, particularly in their estimation of cytochrome oxidase (cyt-aa3) redox changes. We also find some differences when applying the same algorithm to the three data sets, suggesting possible difficulties in transferring algorithms between different physiological systems (e.g., Kurth, C. D., Steven, J. M., Benaron, D., and Chance, B. (1993) J. Clin. Monit. 9, 163-170). We have also compared the algorithms using simulated data generated using measured hemoglobin absorption spectra and a diffusion model for light transport in tissue. We find that while the algorithms from three groups are in broad agreement, that published by Piantadosi (Piantadosi, C. A. (1993) Methods Toxicol. 2, 107-126) produces significantly different results for cyt-aa3 and HbO2. Either the hemoglobin spectra used to produce the simulated data are inaccurate or the modeling is incorrect, or this algorithm is erroneous.

Adult↗
PubMed1995

Optical pathlength measurements on adult head, calf and forearm and the head of the newborn infant using phase resolved optical spectroscopy.

We have used an intensity modulated optical spectrometer, which measures the phase shift across tissue experienced by intensity modulated near-infrared light, to determine the absolute optical pathlength through tissue. The instrument is portable and takes only 5 s to record pathlength at four wavelengths (690 nm, 744 nm, 807 nm and 832 nm). The absolute pathlength divided by the known spacing between the light source and detector on the skin is the differential pathlength factor (DPF) which previous studies have shown is approximately constant for spacings greater than 2.5 cm. DPF results are presented for measurements on 100 adults and 35 newborn infants to determine the statistical variation on the DPF. All measurements were made at a frequency of 200 MHz with source-detector spacings of > 4 cm. Results at 807 nm show a DPF of 4.16(+/- 18.8%) for adult arm, 5.51(+/- 18%) for adult leg, 6.26(+/- 14.1%) for adult head and 4.99(+/- 9%) for the head of a newborn infant. A wavelength dependence was obtained for DPF on all tissues and a difference in DPF between male and female was observed for both the adult arm and leg. The results can be used to improve the quantitation of chromophore concentration changes in adults and newborn infants.

Adult↗
PubMed1995

An improved design for a stable and reproducible phantom material for use in near-infrared spectroscopy and imaging.

In this note, we describe an improved phantom material for use in near-infrared spectroscopy and imaging. The material consists of a clear epoxy resin with absorbing dyes and amorphous silica spheres as scattering particles. It is possible to calculate the scattering coefficient and angular scattering distribution of the material from Mie theory, using the known size and refractive index of the silica spheres together with the measured refractive index of the resin (approximately 1.56). We show a good agreement between prediction and experimental measurements. The scattering properties of the material closely match those of tissue in the near-infrared wavelength region, having an anisotropy factor, g, of approximately 0.93. The absorption coefficient of the epoxy is low (approximately 0.001 mm-1), and addition of the dyes produces an absorption coefficient that covers the same range as that of tissue.

Biophysical Phenomena↗
PubMed1995

Late fetal heart decelerations and changes in cerebral oxygenation during the first stage of labour.

OBJECTIVE: To test the hypothesis that late fetal heart rate decelerations are associated with a decrease in cerebral oxygenation. DESIGN: Changes in fetal cerebral concentrations of oxyhaemoglobin and deoxyhaemoglobin were measured by near infrared spectroscopy, before, during and after contractions with late fetal heart rate decelerations and compared with changes during contractions with no alteration of heart rate. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten women in labour at term. RESULTS: The changes in fetal cerebral oxyhaemoglobin and deoxyhaemoglobin concentrations that occurred during contractions were quantitatively similar, irrespective of the fetal heart rate changes. However, late fetal heart rate decelerations were associated with a significantly greater fall, after the uterine contraction, in the mean concentration of fetal cerebral oxyhaemoglobin of 0.52 mumol/100 g (SD 0.25) (P < 0.001) and a significantly greater rise in the mean concentration of deoxyhaemoglobin of 0.36 mumol/100 g (SD 0.35) (P < 0.01). CONCLUSION: Late fetal heart rate decelerations are associated with a significant decrease in cerebral oxygenation.

Adult↗
PubMed1995

The effect of maternal posture on fetal cerebral oxygenation during labour.

OBJECTIVE: To measure the effect of changes in maternal posture on fetal cerebral oxygenation during normal labour. DESIGN: A prospective study comparing changes in the fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume, measured by near infrared spectroscopy, in women with effective epidural analgesia when moved from the left lateral to the supine position during labour. SETTING: A London teaching hospital obstetric unit. SUBJECTS: Fourteen women during uncomplicated labour at term. RESULTS: When compared with the left lateral position, the supine position was associated with a significant decrease in the mean concentration of fetal cerebral oxyhaemoglobin of 1.12 (SD 1.0, 95% CI 0.49 to 1.75) mumol. 100 g-1 (P < 0.01) without any significant change in the mean concentration of deoxyhaemoglobin and cerebral blood volume. These changes were associated with a significant decrease in the mean cerebral oxygen saturation of 8.3 (SD 8.8, 95% CI 1.5 to 15.1)% (P < 0.05, n = 9). CONCLUSION: Changes in maternal posture during labour, in women with effective epidural analgesia, are associated with a significant decrease in fetal cerebral oxygenation.

Adult↗
PubMed1995

The effect of maternal pushing on fetal cerebral oxygenation and blood volume during the second stage of labour.

OBJECTIVE: To measure the effect of maternal pushing during the second stage of labour on fetal cerebral oxygenation and blood volume. DESIGN: A prospective study comparing changes in the fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume, before and during maternal pushing in the second stage of labour. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten term fetuses during labour. RESULTS: Following the onset of maternal pushing, mean cerebral deoxyhaemoglobin concentration increased by a mean of 0.79 (SD 0.59) mumol.100 g-1, (P < 0.01) without any consistent change in the oxyhaemoglobin concentration. These changes were associated with a significant decrease in the calculated mean cerebral oxygen saturation from a mean of 46.8% (SD 8.6) to 38.1% (SD 5.2) (P < 0.01). Pushing was also associated with a significant increase in the mean cerebral blood volume, which rose by a mean of 0.33 ml.100 g-1 (SD 0.37) (P < 0.05). CONCLUSION: Maternal pushing during the second stage of labour leads to a significant decrease in fetal cerebral oxygenation, together with an increase in cerebral blood volume.

Adult↗
PubMed1995

The spatial resolution performance of a time-resolved optical imaging system using temporal extrapolation.

Optical imaging methods are being explored as a potential means of screening for breast cancer. Previous investigations of time-resolved imaging techniques have suggested that due to the lack of photons with sufficiently small pathlengths, the spatial resolution achievable through a human breast would be unlikely to be better than a centimeter. Experimental results presented here indicate, however, that higher resolution may be achieved by extrapolating the measured temporal distribution of transmitted photons. This is performed using a least-squares fit between data and an analytic model of photon transport. The spatial resolution of a time-resolved imaging system was evaluated by measuring the edge response produced by an opaque mask embedded in the center of a 51-mm-thick, very highly scattering medium. The limiting spatial resolution was improved from about 13 mm to about 5 mm.

Breast Neoplasms↗
PubMed1994

Use of the water absorption spectrum to quantify tissue chromophore concentration changes in near-infrared spectroscopy.

We describe a simple method for measuring the 'differential pathlength' of photons in a scattering medium utilizing the spectral absorption features of water. Determination of this differential pathlength is a prerequisite for quantifying chromophore concentration changes measured by near-infrared spectroscopy (NIRS), and the method proposed here achieves this without the need for time- or frequency-resolved measurements. The quantification of tissue chromophore concentration measurements is a major goal in NIRS research, allowing, for example, the non-invasive measurement of blood flow and volume in the brain and other organs. We present the results of validation experiments performed on tissue phantoms comparing the differential path estimates yielded by water absorption and time-resolved measurements, finding that the weak water absorption feature at 820 nm can yield a differential path estimate in addition to the main feature at 975 nm. We also present results from in vivo studies in which we find that whilst the 820 nm feature is measured with lower accuracy for a given light flux than the 975 nm feature, it is intrinsically a more accurate differential path estimator. Studies on the adult forearm showing differences between time-resolved and water absorption differential path estimates suggest that the measurement of both could aid in quantifying NIRS signals in heterogeneous tissues.

Adipose Tissue↗
PubMed1994

Quantification of adult cerebral hemodynamics by near-infrared spectroscopy.

Near-infrared spectroscopy was used to measure global cerebral blood flow and volume in 10 healthy adult volunteers. High- and low-cerebral blood flow compartments were detected with mean flows for all 10 subjects of 59 +/- 21 (SD) and 11 +/- 4 ml.100 g-1.min-1, respectively. The mean cerebral blood volume of the group was 2.85 +/- 0.97 ml/100 g. Analysis of spontaneous changes in the cerebral concentrations of oxyhemoglobin and deoxyhemoglobin demonstrated strong correlations between respiratory rate and the oscillation frequency of cerebral oxyhemoglobin concentration (r = 0.99) and arterial oxygen saturation (SaO2) (r = 0.99). An estimate of the mean cerebral oxygen saturation for all subjects averaged 59.4 +/- 12.4% when their mean SaO2 was 91.8 +/- 2.4% (equivalent to 67.6 +/- 13.8% at a normoxic SaO2 of 98%). These results demonstrate that near-infrared spectroscopy can be used as a noninvasive bedside technique for both qualitative and quantitative evaluation of cerebral hemodynamics and oxygenation in adults.

Adult↗
PubMed1993

Effects of N-omega-nitro-L-arginine methyl ester on the cerebral circulation of newborn piglets quantified in vivo by near-infrared spectroscopy.

The effects of N-omega-nitro-L-arginine methyl ester (L-NAME) on basal cerebral vascular tone, the vasodilatory effects of acetylcholine (ACh), and the cerebrovascular response to alterations in arterial carbon dioxide tension (CBVR) were investigated using near-infrared spectroscopy. Seven newborn piglets were anesthetized and mechanically ventilated; mean arterial blood pressure (MAP) was monitored and near-infrared spectroscopy used to measure changes in total cerebral Hb concentration. At the beginning of the experiment, CBVR was measured and then 10, 20, 30, and 100 mg.kg-1 L-NAME were administered sequentially; ACh (1, 2, 3, and 5 micrograms) was given before and after each injection of L-NAME. At the end of this sequence, CBVR was measured again and finally sodium nitroprusside (1.5 mg.kg-1) was administered. Ten and 20 mg.kg-1 L-NAME caused a significant decrease in total cerebral Hb concentration of -0.59 (-3.21 to -0.02) and -1.46 (-6.50 to -0.15) mumol.L-1 (median and range), respectively (Wilcoxon p < 0.05), but subsequent injections did not. Ten, 20, and 100 mg.kg-1 L-NAME caused an increase in MAP (Wilcoxon p < 0.05). ACh caused an increase in total cerebral Hb concentration and a decrease in MAP that was impaired but not abolished by L-NAME (ANOVA p < 0.05). CBVR was not affected by L-NAME. Sodium nitroprusside caused a reduction in mean (SD) MAP of 4.7 (1.6) kPa, and a slower rise in [tHb] of 13.44 (2.03) mumol.L-1. Postmortem examination of three animals revealed NADPH-diaphorase staining in neurons, cerebral blood vessels, carotid artery, and jugular vein.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1992

Changes in human fetal cerebral hemoglobin concentration and oxygenation during labor measured by near-infrared spectroscopy.

OBJECTIVE: The purpose of this study was to measure by near-infrared spectroscopy changes in human fetal cerebral oxyhemoglobin, deoxyhemoglobin, and cerebral blood volume during labor and to calculate mean cerebral hemoglobin oxygen saturation. STUDY DESIGN: The effects of uterine contractions with and without fetal heart rate decelerations were compared in eight singleton term fetuses. Results were analyzed by analysis of variance. RESULTS: In six of eight fetuses normal uterine contractions were associated with proportional decreases in both oxyhemoglobin and deoxyhemoglobin and a fall in cerebral blood volume without desaturation of cerebral hemoglobin. Contractions with fetal heart rate decelerations produced different results in that oxyhemoglobin fell but deoxyhemoglobin rose, indicating cerebral desaturation. In two of the eight fetuses normal contractions were associated with increases in oxyhemoglobin, deoxyhemoglobin, and cerebral blood volume; no decelerations were seen in either fetus. Mean cerebral hemoglobin oxygen saturation calculated during normal contractions was 43% +/- 10% (SD). CONCLUSION: Uterine contractions were associated with detectable changes from baseline in cerebral oxyhemoglobin, deoxyhemoglobin, and cerebral blood volume.

Blood Volume↗
PubMed1992

The theoretical basis for the determination of optical pathlengths in tissue: temporal and frequency analysis.

A concise theoretical treatment is developed for the calculation of mean time, differential pathlength, phase shift, modulation depth and integrated intensity of measurements of light intensity as a function of time on the surface of tissue, resulting from either the input of picosecond light pulses, or radio frequency-modulated light. The treatment uses the Green's function of the diffusion approximation to the radiative transfer equation, and develops this and its Fourier transform in a variety of geometries. Detailed comparisons are made of several of these parameters in several geometries, and their relation to experimentally measured clinical data. The limitations of the use of phase measurements is discussed.

Diagnostic Imaging↗