Tissue Blood Oxygen Saturation Research Articles

Development of a Three-Wavelength Brain Tissue Oxygen Monitoring System Based on Near Infrared Spectrum

In the past 20 years, near infrared spectrum technology has been widely used in human body monitoring due to its non-invasive and real-time characteristics. Oxygen, as the main metabolic substance of the human body, is consumed the most in brain tissue. In order to prevent complications caused by a decrease in brain tissue oxygen during treatment, the patient's brain tissue blood oxygen saturation needs to be monitored in real time. Currently, most of the clinically used non-invasive cerebral blood oxygen detection equipments use dual wavelengths. Other substances on the detection path will cause errors in the measurement results. Therefore, this article proposes a three-wavelength method based on the basic principle of non-invasive monitoring of cerebral blood oxygen using near-infrared spectrum. The brain tissue oxygen saturation monitoring method of detecting light sources was initially verified through the built system, laying the foundation for subsequent system engineering.

Chassis-based fiber-coupled opticalprobe design for reproducible quantitative diffuse optical spectroscopy measurements.

Advanced optical neuromonitoring of cerebral hemodynamics with hybrid diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS) methods holds promise for non-invasive characterization of brain health in critically ill patients. However, the methods' fiber-coupled patient interfaces (probes) are challenging to apply in emergent clinical scenarios that require rapid and reproducible attachment to the head. To address this challenge, we developed a novel chassis-based optical probe design for DOS/DCS measurements and validated its measurement accuracy and reproducibility against conventional, manually held measurements of cerebral hemodynamics in pediatric swine (n = 20). The chassis-based probe design comprises a detachable fiber housing which snaps into a 3D-printed, circumferential chassis piece that is secured to the skin. To validate its reproducibility, eight measurement repetitions of cerebral tissue blood flow index (BFI), oxygen saturation (StO2), and oxy-, deoxy- and total hemoglobin concentration were acquired at the same demarcated measurement location for each pig. The probe was detached after each measurement. Of the eight measurements, four were acquired by placing the probe into a secured chassis, and four were visually aligned and manually held. We compared the absolute value and intra-subject coefficient of variation (CV) of chassis versus manual measurements. No significant differences were observed in either absolute value or CV between chassis and manual measurements (p > 0.05). However, the CV for BFI (mean ± SD: manual, 19.5% ± 9.6; chassis, 19.0% ± 10.8) was significantly higher than StO2 (manual, 5.8% ± 6.7; chassis, 6.6% ± 7.1) regardless of measurement methodology (p<0.001). The chassis-based DOS/DCS probe design facilitated rapid probe attachment/re-attachment and demonstrated comparable accuracy and reproducibility to conventional, manual alignment. In the future, this design may be adapted for clinical applications to allow for non-invasive monitoring of cerebral health during pediatric critical care.

Classification of emotional stress and physical stress using a multispectral based deep feature extraction model

A classification model (Stress Classification-Net) of emotional stress and physical stress is proposed, which can extract classification features based on multispectral and tissue blood oxygen saturation (StO2) characteristics. Related features are extracted on this basis, and the learning model with frequency domain and signal amplification is proposed for the first time. Given that multispectral imaging signals are time series data, time series StO2 is extracted from spectral signals. The proper region of interest (ROI) is obtained by a composite criterion, and the ROI source is determined by the universality and robustness of the signal. The frequency-domain signals of ROI are further obtained by wavelet transform. To fully utilize the frequency-domain characteristics, the multi-neighbor vector of locally aggregated descriptors (MN-VLAD) model is proposed to extract useful features. The acquired time series features are finally put into the long short-term memory (LSTM) model to learn the classification characteristics. Through SC-NET model, the classification signals of emotional stress and physical stress are successfully obtained. Experiments show that the classification result is encouraging, and the accuracy of the proposed algorithm is over 90%.

Role of Cerebral Oximetry in Extracorporeal Membrane Oxygenation

AbstractCerebral oximetry, which is based on near-infrared spectroscopy (NIRS) technology, is an optical technique that allows for noninvasive and continuous monitoring of brain oxygenation by determining cerebral tissue blood oxygen saturation. Many research and observational studies were performed with neonates using various types of NIRS/cerebral oximetry monitors. However, no food and drug administration (FDA) approved-cerebral oximeter is available for neonates. Successful validation of cerebral oximetry for the FDA has been done in human adult volunteer studies under protocols in which jugular bulb and arterial blood samples were obtained under different levels of fractional inspired oxygen levels.

Color Cherenkov imaging of clinical radiation therapy

Color vision is used throughout medicine to interpret the health and status of tissue. Ionizing radiation used in radiation therapy produces broadband white light inside tissue through the Cherenkov effect, and this light is attenuated by tissue features as it leaves the body. In this study, a novel time-gated three-channel camera was developed for the first time and was used to image color Cherenkov emission coming from patients during treatment. The spectral content was interpreted by comparison with imaging calibrated tissue phantoms. Color shades of Cherenkov emission in radiotherapy can be used to interpret tissue blood volume, oxygen saturation and major vessels within the body.

Human Stress and StO2: Database, Features, and Classification of Emotional and Physical Stress.

Emotional and physical stress can cause various health problems. In this paper, we used tissue blood oxygen saturation (StO2), a newly proposed physiological signal, to classify the human stress. We firstly constructed a public StO2 database including 42 volunteers subjected to two types of stress. During the physical stress experiment, we observed that the facial StO2 right after the stress can be either increased or decreased comparing to the baseline. We investigated the StO2 feature combinations for the classification and found that the average StO2 values from left cheek, chin, and the middle of the eyebrow can provide the highest classification rate of 95.56%. Comparison with other stress classification method shows that StO2 based method can provide best classification performance with lowest feature dimension. These results suggest that facial StO2 can be used as a promising features to identify stress states, including emotional and physical stress.

Temporal Change of Tissue Blood Oxygen Saturation in Rat Skeletal Muscle after Blood Flow Restriction by Manchette

Temporal Change of Tissue Blood Oxygen Saturation in Rat Skeletal Muscle after Blood Flow Restriction by Manchette

Fiber-optic pulseoximeter for local oxygen saturation determination using a Monte Carlo multi-layer model for calibration

Background and objectiveLocal tissue oxygenation determines the relationship between the supply and the demand for oxygen by the tissue and it is an important indicator of the physiological or pathological condition of the tissue. Moreover, some therapeutic methods strongly depend on the oxygen content of the tissue. In photodynamic therapy, when molecular oxygen is present, the irradiation of the photosensitizer with light triggers the generation of reactive oxygen species that kill the target diseased cells within the treated tissue. To ensure the best possible therapy response, the tissue must be well oxygenated; hence, oxygen concentration measurement becomes a decisive factor. In this work, the design, construction and calibration of a module to locally measure the blood oxygen saturation in tissue is presented. MethodsThe system is built using a red (660-nm) and an infrared (940-nm) light emitting diodes as light sources, a photodiode as a detector, and a homemade handheld fiber optic-based reflectance pulse oximetry sensor. In addition, the developed sensor was modeled by means of multilayered Monte Carlo simulations, to study its behavior when used in different thickness and melanin content skin. ResultsFrom the simulation reflectance values, the oxygen saturation calibration curves considering different melanin concentrations and skin thicknesses were obtained for two different skin models, one comprising three skin layers and the second, assuming seven different layers for the skin. A comparison of the performances of the developed pulse oximeter sensor with a commercial one is also presented. ConclusionsA new pulseoximeter for the measurement of local oxygenation in tissue was developed. Its calibration strongly depends on the site of measurement due to the influence of tissue thickness, vascularization, and melanin content. A three-layer skin model is proved to be suitable for the calibration of the pulseoximeter in thin and medium thickness skin.

Cardiovagal regulation and transcutaneous pO2 in breast cancer patients - a pilot study.

Vagal activity in patients with metastatic or recurrent breast cancer can predict their survival and it can be altered by behavioral, pharmacological and surgical interventions. Tumor oxygenation is important in defining the cellular metabolic microenvironment of human malignancies, O2-depleted areas coincide with nutrient and energy deprivation and with a hostile metabolic microenvironment. In our work, we simultaneously measured two oxygen-sensitive parameters in breast cancer patients; blood oxygen saturation (SpO2) and trans-cutaneous O2 partial pressure (tcpO2) in breast tissue. Concurrently, 5-minute beat-to-beat heart rate recording was carried out in order to get heart rate variability (HRV) data from time-domain analyses, frequency-domain analyses and entropy and symbolic dynamic non-linear methods. We compared these parameters in patients newly diagnosed with breast cancer, in patients after therapy and in healthy controls. We found lower tcpO2 in patients with presence of malignant tumor compared to those post-treatment and/or without presence of malignancy. We also detected lower 2UV% (two unlike variations) and entropy in non-linear HRV analysis in all breast cancer patients and these parameters associated with parasympathetic activity did not return to the values comparable with healthy individuals after anti-cancer therapy, contrary to tcpO2. Our findings show that breast tissue tcpO2 can recover after the anti-cancer treatment, but complex heart rate control and cardio-vagal regulation remain impaired. This supports the idea that cancer patients and survivors might benefit from non-pharmacological interventions aimed at enhancing vagal activity, such as HRV biofeedback or Yoga.

WST11 Vascular Targeted Photodynamic Therapy Effect Monitoring by Multispectral Optoacoustic Tomography (MSOT) in Mice.

Objective: Monitoring emerging vascular-targeted photodynamic therapy (VTP) and understanding the time-dynamics of treatment effects remains challenging. We interrogated whether handheld multispectral optoacoustic tomography (MSOT) could noninvasively monitor the effect of VTP using WST11, a vascular-acting photosensitizer, on tumor tissues over time using a renal cell cancer mouse model. We also investigated whether MSOT illumination can induce VTP, to implement a single-modality theranostic approach.Materials and Methods: Eight BalB/c mice were subcutaneously implanted with murine renal adenocarcinoma cells (RENCA) on the flank. Three weeks later VTP was performed (10 min continuous illumination at 753 nm following intravenous infusion using WST11 or saline as control. Handheld MSOT images were collected prior to VTP administration and subsequently thereafter over the course of the first hour, at 24 and 48 h. Data collected were unmixed for blood oxygen saturation in tissue (SO2) based on the spectral signatures of deoxy- and oxygenated hemoglobin. Changes in oxygen saturation over time, relative to baseline, were examined by paired t-test for statistical significance (p < 0.05). In-vivo findings were corroborated by histological analyses of the tumor tissue.Results: MSOT is shown to prominently resolve changes in oxygen saturation in tumors within the first 20 min post WST11-VTP treatment. Within the first hour post-treatment, SO2 decreased by more than 60% over baseline (p < 0.05), whereas it remained unchanged (p > 0.1) in the sham-treated group. Moreover, unlike in the control group, SO2 in treated tumors further decreased over the course of 24 to 48 h post-treatment, concomitant with the propagation of profound central tumor necrosis present in histological analysis. We further show that pulsed MSOT illumination can activate WST11 as efficiently as the continuous wave irradiation employed for treatment.Conclusion: Handheld MSOT non-invasively monitored WST11-VTP effects based on the SO2 signal and detected blood saturation changes within the first 20 min post-treatment. MSOT may potentially serve as a means for both VTP induction and real-time VTP monitoring in a theranostic approach.

Identifying individual sleep apnea/hypoapnea epochs using smartphone-based pulse oximetry.

Sleep apnea, characterized by frequent pauses in breathing during sleep, poses a serious threat to the healthy growth and development of children. Polysomnography (PSG), the gold standard for sleep apnea diagnosis, is resource intensive and confined to sleep laboratories, thus reducing its accessibility. Pulse oximetry alone, providing blood oxygen saturation (SpO2) and blood volume changes in tissue (PPG), has the potential to identify children with sleep apnea. Thus, we aim to develop a tool for at-home sleep apnea screening that provides a detailed and automated 30 sec epoch-by-epoch sleep apnea analysis. We propose to extract features characterizing pulse oximetry (SpO2 and pulse rate variability [PRV], a surrogate measure of heart rate variability) to create a multivariate logistic regression model that identifies epochs containing apnea/hypoapnea events. Overnight pulse oximetry was collected using a smartphone-based pulse oximeter, simultaneously with standard PSG from 160 children at the British Columbia Children's hospital. The sleep technician manually scored all apnea/hypoapnea events during the PSG study. Based on these scores we labeled each epoch as containing or not containing apnea/hypoapnea. We randomly divided the subjects into training data (40%), used to develop the model applying the LASSO method, and testing data (60%), used to validate the model. The developed model was assessed epoch-by-epoch for each subject. The test dataset had a median area under the receiver operating characteristic (ROC) curve of 81%; the model provided a median accuracy of 74% sensitivity of 75%, and specificity of 73% when using a risk threshold similar to the percentage of apnea/hypopnea epochs. Thus, providing a detailed epoch-by-epoch analysis with at-home pulse oximetry alone is feasible with accuracy, sensitivity and specificity values above 73% However, the performance might decrease when analyzing subjects with a low number of apnea/hypoapnea events.

Near-Infrared Spectra in Buccal Tissue as a Marker for Detection of Hypoxia.

Hypoxia caused by high altitude exposure can impair cerebral and mental functions. Blood flow and oxygenation of the buccal tissue can be reliable markers to detect hypoxia. In this study, near infrared spectroscopy was used in combination with a novel optical probe to evaluate the applicability of the novel probe in measuring hypoxia markers in buccal tissue under a hypoxic condition. Six healthy participants were tested at altitudes from 2000 to 16,000 ft inside a hypobaric chamber. The buccal reference measurements of blood flow and oxygen saturation were synchronized with the spectral measurements of the novel near infrared probe and the relationship between the reference measurements and spectral data were evaluated by multivariate partial least square method. In addition, finger oxygen saturation was measured during the experiment and the recordings were compared with buccal oxygen saturation. The spectral analysis illustrated that the spectral data from the near infrared probe correlated strongly with the absorption features of both buccal flow and oxygenation measured by the reflectance sensors (average R(2) = 0.89). The results showed probably overestimated values for buccal oxygen saturation recorded by the reference pulse oximeter in comparison with finger oxygen saturation, with the mean difference increasing from 1.8% at 2000 ft to 11.4% at 16,000 ft. The novel near infrared probe showed promising results for simultaneous measurement of blood flow and oxygen saturation in the buccal tissue. The suggested method can be used as a new technique for early indication of hypoxia in future clinical applications.

Bedside monitoring of patients with shock using a portable spatially-resolved near-infrared spectroscopy

Clinical monitoring of shock mainly depends on blood-oxygen-indices obtained from invasive blood sample tests. The central internal jugular central vein oxygenation level (ScvO2) has been considered as a gold standard indicator for shock prediction. We developed a noninvasive spatially-resolved near-infrared spectroscopy (SR-NIRS) to measure tissue blood oxygen saturation (StO2) surrounding the region of taking blood sample for the ScvO2 test in 25 patients with shock. StO2 values were found to be highly correlated (r = 0.84, p < 0.001) with ScvO2 levels and the concordance coefficient of 0.80 is high. The results suggest the potential of noninvasive SR-NIRS for bedside shock monitoring.

Monitoring tissue blood oxygen saturation in the internal jugular venous area using near infrared spectroscopy.

Central venous blood oxygen saturation (ScvO2) is an important monitoring index of fluid resuscitation. However, monitoring of ScvO2 is not continuous and invasive. Near infrared spectroscopy (NIRS) is an optical technology for the noninvasive detection of hemodynamic changes, with advantages of being real-time, continuous, low-cost, and portable. The present study aimed to determine whether a correlation exists between the tissue blood oxygen saturation in the internal jugular venous area (StO2) data obtained with NIRS and the ScvO2 and whether these two quantities are equivalent. Data were collected from 13 patients. We used ultrasound to locate the placement site for the NIRS light source outside the internal jugular vein. Meanwhile, a sample for blood gas analysis was obtained through the central venous catheter. A correlation analysis between the StO2 and ScvO2 of 13 samples was performed (Pearson correlation coefficient), suggesting a high correlation between them (r = 0.906, StO2 =1.0018 ScvO2 +2.8524). Bland-Altman analysis was also performed between the StO2 and ScvO2. Results were as follows: 100% of monitored points fell within the range of the mean ± 1.96 SD of the difference between the StO2 and ScvO2; range of the mean ± 1.96 SD of the difference between the StO2 and ScvO2 was 3 ± 10.2; confidence interval of the difference between the StO2 and ScvO2 was -7.2 to 13.2%. The StO2 monitored with NIRS correlated highly with the ScvO2 measured in the internal jugular vein. Therefore, the StO2 can be used for directing clinical treatment with further research.

Maternal tissue blood flow and oxygen saturation in pre-eclampsia and intrauterine growth restriction

ObjectiveTo investigate the hypothesis that impaired maternal tissue perfusion occurs in pre-eclampsia and intrauterine growth restriction (IUGR) and this correlates with maternal tissue oxygenation. Study designStrain gauge plethysmography was used to compare maternal calf blood flow during the third trimester in 16 women with pre-eclampsia, 6 women with IUGR and 16 normal pregnant controls. A Mediaid iPOX pulse oximeter was used to measure maternal tissue oxygenation in the three groups and these were compared with tissue blood flow. ResultsMaternal tissue blood flow was significantly reduced in pre-eclampsia compared to the two other groups (p=0.003). Blood flow was significantly reduced in pre-eclampsia compared to IUGR (p=0.03). However there was no difference in blood flow between normal pregnancy and IUGR groups (p=0.76). No significant difference was noted in maternal tissue oxygenation between the normal pregnancy, pre-eclampsia and IUGR groups (mean±S.E.M. [97.13±0.4, 96.69±0.33, 97.83±0.47 respectively], p=0.26). No correlation was noted between blood flow and tissue oxygenation in the three groups of women. ConclusionWe have demonstrated that reduced maternal resting tissue blood flow present in women with pre-eclampsia is not seen in women with IUGR and the reduction in blood flow in pre-eclampsia is not associated with changes in maternal tissue oxygenation.

Multimodal ultrasound-photoacoustic imaging of tissue engineering scaffolds and blood oxygen saturation in and around the scaffolds.

Preclinical, noninvasive imaging of tissue engineering polymeric scaffold structure and/or the physiological processes such as blood oxygenation remains a challenge. In vitro or ex vivo, the widely used scaffold characterization modalities such as porosimetry, electron or optical microscopy, and X-ray microcomputed tomography have limitations or disadvantages-some are invasive or destructive, others have limited tissue penetration (few hundred micrometers) and/or show poor contrast under physiological conditions. Postmortem histological analysis, the most robust technique for the evaluation of neovascularization is obviously not appropriate for acquiring physiological or longitudinal data. In this study, we have explored the potential of ultrasound (US)-coregistered photoacoustic (PA) imaging as a noninvasive multimodal imaging modality to overcome some of the above challenges and/or provide complementary information. US-PA imaging was employed to characterize poly(lactic-co-glycolic acid) (PLGA) polymer scaffolds or single-walled carbon nanotube (SWCNT)-incorporated PLGA (SWCNT-PLGA) polymer scaffolds as well as blood oxygen saturation within and around the scaffolds. Ex vivo, PLGA and SWCNT-PLGA scaffolds were placed at 0.5, 2, and 6 mm depths in chicken breast tissues. PLGA scaffolds could be localized with US imaging, but generate no PA signal (excitation wavelengths 680 and 780 nm). SWCNT-PLGA scaffolds generated strong PA signals at both wavelengths due to the presence of the SWCNTs and could be localized with both US and PA imaging depths between 0.5-6 mm (lateral resolution = 90 μm, axial resolution = 40 μm). In vivo, PLGA and SWCNT-PLGA scaffolds were implanted in subcutaneous pockets at 2 mm depth in rats, and imaged at 7 and 14 days postsurgery. The anatomical position of both the scaffolds could be determined from the US images. Only SWCNT-PLGA scaffolds could be easily detected in the US-PA images. SWCNT-PLGA scaffolds had significant four times higher PA signal intensity compared with the surrounding tissue and PLGA scaffolds. In vivo blood oxygen saturation maps around and within the PLGA scaffolds could be obtained by PA imaging. There was no significant difference in oxygen saturation for the PLGA scaffolds at the two time points. The blood oxygen saturation maps complemented the histological analysis of neovascularization of the PLGA scaffolds.

Abstract 4338: Monitoring radiation response in tumor vasculature using intravital photoacoustic imaging in a murine window chamber model in vivo

Abstract VisualSonics has recently developed a preclinical photoacoustic (PA) imaging system called the VevoLAZR that combines the sensitivity of optical imaging and the high resolution of micro-ultrasound. The system incorporates a 40 MHz (centre frequency) ultrasound transducer linear array probe (LZ550) and a tuneable 680-970 nm nanosecond pulsed-laser. We used this system to study in vivo changes in tumor oxygen saturation and haemoglobin density caused by exposure to radiation therapy (RT). For this, DsRed-Me180 human cervical tumors were grown in a nude mouse dorsal skinfold window chamber model until they reached 2.5 mm in diameter. Specifically, we investigated the system's sensitivity and dynamic range to measure relative changes in oxygen saturation in tumor and surrounding healthy tissues 10 days after treatment. Tumors (∼2.5 mm diameter) were focally irradiated with a single dose of 30 Gy using a small animal microirradiator (XRAD225, Precision XRay Inc., North Branford, CT). To measure the dynamic range and stability of our setup for measuring oxygen saturation in vivo, we altered the anesthetised animal's inhaled oxygen from 100% to 7% for 1 min during PA imaging. This test showed that blood oxygen saturation in the healthy dorsal skinfold tissue decreased from 82% to 8% and confirmed the linearity of the measurement technique. Furthermore, we compared vascular morphology obtained by photoacoustic imaging and intravital fluorescent microscopy using FITC-Dextran (2 MDa, injected 20 mins prior). This comparison showed good correlation and confirms that PA imaging can provide important structural information of vascularity. Photoacoustic imaging was performed before and 10 days after irradiation to assess changes in tumour volume, relative blood oxygen saturation, relative tissue oxygen saturation, and relative hemoglobin density. Ten days after irradiation, PA imaging showed that the tumour volume increased from 5.7 to 14.2 mm3, relative blood oxygen saturation decreased from 75.3 to 48.2%, relative tissue oxygen saturation decreased from 40.7 to 0.1%, and hemoglobin density decreased from 18457 to 3253 a.u. These data illustrate the capability of PA imaging to simultaneously measure multiple radiobiological response metrics from a single imaging scan. Pilot results demonstrate: i) the compatibility of the VisualSonics small animal VevoLAZR photoacoustic imaging system with intravital murine tumor models, ii) the sensitivity of the system to detect RT-induced changes in tumor vascular oxygen saturation non-invasively, in real time and in vivo, and iii) a new preclinical application of PA imaging for longitudinal monitoring of tumor response to RT in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4338. doi:1538-7445.AM2012-4338

Quantitative MR estimates of blood oxygenation based on T2*: A numerical study of the impact of model assumptions

Several MR methods have been proposed over the last decade to obtain quantitative estimates of the tissue blood oxygen saturation (StO2) using a quantification of the blood oxygen level dependent effect. These approaches are all based on mathematical models describing the time evolution of the MR signal in biological tissues in the presence of magnetic field inhomogeneities. Although the experimental results are very encouraging, possible biases induced by the model assumptions have not been extensively studied. In this study, a numerical approach was used to examine the influence on T(2)*, blood volume fraction, and StO2 estimates of possible confounding factors such as water diffusion, intravascular signal, and presence of arterial blood in the voxel. To evaluate the impact of the vessel geometry, straight cylinders and realistic data from two-photon microscopy for microvascular geometry were compared. Our results indicate that the models are sufficiently realistic, based on a good correlation between ground truth and MR estimates of StO2.

Oxygen saturation and perfusion changes during dermatological methylaminolaevulinate photodynamic therapy

Methylaminolaevulinate (MAL)-photodynamic therapy (PDT) is a successful topical treatment for a number of (pre)cancerous dermatological conditions. In combination, light of the appropriate wavelength, the photosensitizer protoporphyrin IX (PpIX) and tissue oxygen result in the production of singlet oxygen and reactive oxygen species inducing cell death. This study investigates real-time changes in localized tissue blood oxygen saturation and perfusion in conjunction with PpIX fluorescence monitoring for the first time during dermatological MAL-PDT. Oxygen saturation, perfusion and PpIX fluorescence were monitored noninvasively utilizing optical reflectance spectroscopy, laser Doppler perfusion imaging and a fluorescence imaging system, respectively. Patients attending for standard dermatological MAL-PDT were recruited to this ethically approved study and monitored prior to, during and after light irradiation. Significant reductions in mean blood oxygen saturation (P < 0·005) and PpIX fluorescence (P < 0·001) were observed within the first minute of irradiation (4·75 J cm(-2) ) while, in contrast, perfusion was observed to increase significantly (P < 0·01) during treatment. The changes in oxygen saturation and PpIX fluorescence were positively correlated during the initial phase of treatment (r(2) = 0·766). Rapid reductions in the localized blood oxygen saturation have been observed for the first time to occur clinically within the initial minutes of light irradiation and positively correlate with the concurrent PpIX photobleaching. Furthermore, perfusion increases, suggesting that the microvasculature compensates for the PDT-induced oxygen depletion.

Noninvasive spectral imaging of skin chromophores based on multiple regression analysis aided by Monte Carlo simulation

In order to visualize melanin and blood concentrations and oxygen saturation in human skin tissue, a simple imaging technique based on multispectral diffuse reflectance images acquired at six wavelengths (500, 520, 540, 560, 580 and 600 nm) was developed. The technique utilizes multiple regression analysis aided by Monte Carlo simulation for diffuse reflectance spectra. Using the absorbance spectrum as a response variable and the extinction coefficients of melanin, oxygenated hemoglobin, and deoxygenated hemoglobin as predictor variables, multiple regression analysis provides regression coefficients. Concentrations of melanin and total blood are then determined from the regression coefficients using conversion vectors that are deduced numerically in advance, while oxygen saturation is obtained directly from the regression coefficients. Experiments with a tissue-like agar gel phantom validated the method. In vivo experiments with human skin of the human hand during upper limb occlusion and of the inner forearm exposed to UV irradiation demonstrated the ability of the method to evaluate physiological reactions of human skin tissue.