Cerebral and Muscle Tissue Oxygenation During Incremental Cycling in Male Adolescents Measured by Time-Resolved Near-Infrared Spectroscopy.

Near-infrared spectroscopy has long been used to measure tissue-specific O2 dynamics in exercise, but most published data have used continuous wave devices incapable of quantifying absolute Hemoglobin (Hb) concentrations. We used time-resolved near-infrared spectroscopy to study exercising muscle (Vastus Lateralis, VL) and prefrontal cortex (PFC) Hb oxygenation in 11 young males (15.3 ± 2.1 yrs) performing incremental cycling until exhaustion (peak VO2 = 42.7 ± 6.1 ml/min/kg, mean peak power = 181 ± 38 W). Time-resolved near-infrared spectroscopy measurements of reduced scattering (µs´) and absorption (µa) at three wavelengths (759, 796, and 833 nm) were used to calculate concentrations of oxyHb ([HbO2]), deoxy Hb ([HbR]), total Hb ([THb]), and O2 saturation (stO2). In PFC, significant increases were observed in both [HbO2] and [HbR] during intense exercise. PFC stO2% remained stable until 80% of total exercise time, then dropped (-2.95%, p = .0064). In VL, stO2% decreased until peak time (-6.8%, p = .01). Segmented linear regression identified thresholds for PFC [HbO2], [HbR], VL [THb]. There was a strong correlation between timing of second ventilatory threshold and decline in PFC [HbO2] (r = .84). These findings show that time-resolved near-infrared spectroscopy can be used to study physiological threshold phenomena in children during maximal exercise, providing insight into tissue specific hemodynamics and metabolism.

Optical imaging of breast cancer oxyhemoglobin flare correlates with neoadjuvant chemotherapy response one day after starting treatment.

Approximately 8-20% of breast cancer patients receiving neoadjuvant chemotherapy fail to achieve a measurable response and endure toxic side effects without benefit. Most clinical and imaging measures of response are obtained several weeks after the start of therapy. Here, we report that functional hemodynamic and metabolic information acquired using a noninvasive optical imaging method on the first day after neoadjuvant chemotherapy treatment can discriminate nonresponding from responding patients. Diffuse optical spectroscopic imaging was used to measure absolute concentrations of oxyhemoglobin, deoxyhemoglobin, water, and lipid in tumor and normal breast tissue of 24 tumors in 23 patients with untreated primary breast cancer. Measurements were made before chemotherapy, on day 1 after the first infusion, and frequently during the first week of therapy. Various multidrug, multicycle regimens were used to treat patients. Diffuse optical spectroscopic imaging measurements were compared with final postsurgical pathologic response. A statistically significant increase, or flare, in oxyhemoglobin was observed in partial responding (n = 11) and pathologic complete responding tumors (n = 8) on day 1, whereas nonresponders (n = 5) showed no flare and a subsequent decrease in oxyhemoglobin on day 1. Oxyhemoglobin flare on day 1 was adequate to discriminate nonresponding tumors from responding tumors. Very early measures of chemotherapy response are clinically convenient and offer the potential to alter treatment strategies, resulting in improved patient outcomes.

Assessing tumor contrast in radiographically dense breast tissue using Diffuse Optical Spectroscopic Imaging (DOSI).

INTRODUCTION: Radiographic density adversely affects the performance of X-ray mammography and can be particularly problematic in younger and high-risk women. Because of this limitation, there is significant ongoing effort to develop alternative cancer screening and detection strategies for this population. This pilot study evaluates the potential of Diffuse Optical Spectroscopic Imaging (DOSI) to image known tumors in dense breast tissue. METHODS: We performed a retrospective analysis on 24 radiographically dense breast cancer subjects measured with DOSI over a four-year period (Breast Imaging Reporting and Data System - BI-RADS, category 3 and 4, average age = 39 ± 7.6, average maximum size 31 ± 1 7 mm). Two previously-described DOSI contrast functions, the tissue optical index (TOI) and the specific tumor component (STC), which are based upon the concentrations and spectral signatures of hemoglobin, water and lipids, respectively, were used to form 2D optical images of breast tumors. RESULTS: Using TOI and STC, 21 out of 24 breast tumors were found to be statistically different from the surrounding highly vascularized dense tissue and to be distinguishable from the areolar region. For these patients, the tumor to normal contrast was 2.6 ± 1.2 (range 1.3 to 5.5) and 10.0 ± 7.5 (range 3.3 to 26.4) for TOI and STC, respectively. STC images were particularly useful in eliminating metabolic background from the retroareolar region which led to identification of two out of four retroareolar tumors. CONCLUSIONS: Using both the abundance and the disposition of the tissue chromophores recovered from the DOSI measurements, we were able to observe tumor contrast relative to dense breast tissue. These preliminary results suggest that DOSI spectral characterization strategies may provide new information content that could help imaging breast tumors in radiographically dense tissue and in particular in the areolar complex.

Optical imaging correlates with magnetic resonance imaging breast density and reveals composition changes during neoadjuvant chemotherapy.

INTRODUCTION: In addition to being a risk factor for breast cancer, breast density has been hypothesized to be a surrogate biomarker for predicting response to endocrine-based chemotherapies. The purpose of this study was to evaluate whether a noninvasive bedside scanner based on diffuse optical spectroscopic imaging (DOSI) provides quantitative metrics to measure and track changes in breast tissue composition and density. To access a broad range of densities in a limited patient population, we performed optical measurements on the contralateral normal breast of patients before and during neoadjuvant chemotherapy (NAC). In this work, DOSI parameters, including tissue hemoglobin, water, and lipid concentrations, were obtained and correlated with magnetic resonance imaging (MRI)-measured fibroglandular tissue density. We evaluated how DOSI could be used to assess breast density while gaining new insight into the impact of chemotherapy on breast tissue. METHODS: This was a retrospective study of 28 volunteers undergoing NAC treatment for breast cancer. Both 3.0-T MRI and broadband DOSI (650 to 1,000 nm) were obtained from the contralateral normal breast before and during NAC. Longitudinal DOSI measurements were used to calculate breast tissue concentrations of oxygenated and deoxygenated hemoglobin, water, and lipid. These values were compared with MRI-measured fibroglandular density before and during therapy. RESULTS: Water (r = 0.843; P < 0.001), deoxyhemoglobin (r = 0.785; P = 0.003), and lipid (r = -0.707; P = 0.010) concentration measured with DOSI correlated strongly with MRI-measured density before therapy. Mean DOSI parameters differed significantly between pre- and postmenopausal subjects at baseline (water, P < 0.001; deoxyhemoglobin, P = 0.024; lipid, P = 0.006). During NAC treatment measured at about 90 days, significant reductions were observed in oxyhemoglobin for pre- (-20.0%; 95% confidence interval (CI), -32.7 to -7.4) and postmenopausal subjects (-20.1%; 95% CI, -31.4 to -8.8), and water concentration for premenopausal subjects (-11.9%; 95% CI, -17.1 to -6.7) compared with baseline. Lipid increased slightly in premenopausal subjects (3.8%; 95% CI, 1.1 to 6.5), and water increased slightly in postmenopausal subjects (4.4%; 95% CI, 0.1 to 8.6). Percentage change in water at the end of therapy compared with baseline correlated strongly with percentage change in MRI-measured density (r = 0.864; P = 0.012). CONCLUSIONS: DOSI functional measurements correlate with MRI fibroglandular density, both before therapy and during NAC. Although from a limited patient dataset, these results suggest that DOSI may provide new functional indices of density based on hemoglobin and water that could be used at the bedside to assess response to therapy and evaluate disease risk.

Head-up tilt and hyperventilation produce similar changes in cerebral oxygenation and blood volume: an observational comparison study using frequency-domain near-infrared spectroscopy.

PURPOSE: During anesthesia, maneuvers which cause the least disturbance of cerebral oxygenation with the greatest decrease in intracranial pressure would be most beneficial to patients with intracranial hypertension. Both head-up tilt (HUT) and hyperventilation are used to decrease brain bulk, and both may be associated with decreases in cerebral oxygenation. In this observational study, our null hypothesis was that the impact of HUT and hyperventilation on cerebral tissue oxygen saturation (SctO2) and cerebral blood volume (CBV) are comparable. METHODS: Surgical patients without neurological disease were anesthetized with propofol-remifentanil. Before the start of surgery, frequency-domain near-infrared spectroscopy was used to measure SctO2 and CBV at the supine position, at the 30° head-up and head-down positions, as well as during hypoventilation and hyperventilation. RESULTS: Thirty-three patients were studied. Both HUT and hyperventilation induced small decreases in SctO2 [3.5 (2.6)%; P < 0.001 and 3.0 (1.8)%; P < 0.001, respectively] and in CBV [0.05 (0.07) mL x 100 g(-1); P < 0.001 and 0.06 (0.05) mL x 100 g(-1); P < 0.001, respectively]. There were no differences between HUT to 30° and hyperventilation to an end-tidal carbon dioxide (ETCO2) of 25 mmHg (from 45 mmHg) in both SctO2 (P = 0.3) and CBV (P = 0.4). DISCUSSION: The small but statistically significant decreases in both SctO2 and CBV caused by HUT and hyperventilation are comparable. There was no correlation between the decreases in SctO2 and CBV and the decreases in blood pressure and cardiac output during head-up and head-down tilts. However, the decreases in both SctO2 and CBV correlate with the decreases in ETCO2 during ventilation adjustment.

Characterization of metabolic differences between benign and malignant tumors: high-spectral-resolution diffuse optical spectroscopy.

PURPOSE: To develop a near-infrared spectroscopic method to identify breast cancer biomarkers and to retrospectively determine if benign and malignant breast lesions could be distinguished by using this method. MATERIALS AND METHODS: The study was HIPAA compliant and was approved by the university institutional review board. Written informed consent was obtained. By using self-referencing differential spectroscopy (SRDS) analysis, the existence of specific spectroscopic signatures of breast lesions on images acquired by using diffuse optical spectroscopy imaging in the wavelength range (650-1000 nm) was established. The SRDS method was tested in 60 subjects (mean age, 38 years; age range, 22-74 years). There were 17 patients with benign breast tumors and 22 patients with malignant breast tumors. There were 21 control subjects. RESULTS: Discrimination analysis helped separate malignant from benign tumors. A total of 40 lesions (22 malignant and 18 benign) were analyzed. Twenty were true-positive lesions, 17 were true-negative lesions, one was a false-positive lesion, and two were false-negative lesions (sensitivity, 91% [20 of 22]; specificity, 94% [17 of 18]; positive predictive value, 95% [20 of 21]; and negative predictive value, 89% [17 of 19]). CONCLUSION: The SRDS method revealed localized tumor biomarkers specific to pathologic state.

Parametric Diffuse Optical Imaging in Reflectance Geometry.

Diffuse optical imaging (DOI) is a model-based technique used for noninvasive characterization of subsurface tissue function and structure. Compared to more common transmission geometries, reflectance DOI has the advantage of being portable and easily implemented in a clinical setting. However, reflectance measurements are generally not compatible with conventional DOI image reconstruction methods because they typically provide a limited number of unique tissue views. In this paper, we describe a fast and reliable DOI image reconstruction method based on parameterization of tissue and tumor optical contrast, using physiological a priori knowledge. The reconstruction method is formulated within the general Bayesian inversion framework and is capable of handling both model and measurement errors. Simulations are carried out to illustrate the application of this approach, using a limited number of source-detector combinations. It is also shown that parametric reflectance DOI is robust to model misspecifications and measurement noise.

Diffuse optical spectroscopy measurements of healing in breast tissue after core biopsy: case study.

Diffuse optical spectroscopy (DOS) has been used to monitor and predict the effects of neoadjuvant (i.e., presurgical) chemotherapy in breast cancer patients in several pilot studies. Because patients with suspected breast cancers undergo biopsy prior to treatment, it is important to understand how biopsy trauma influences DOS measurements in the breast. The goal of this study was to measure the effects of a standard core breast biopsy on DOS measurements of tissue deoxyhemoglobin, hemoglobin, water, and bulk lipid concentrations. We serially monitored postbiopsy effects in the breast tissue in a single subject (31-year-old premenopausal female) with a 37x18x20 mm fibroadenoma. A baseline measurement and eight weekly postbiopsy measurements were taken with a handheld DOS imaging instrument. Our instrument used frequency domain photon migration combined with broadband steady-state spectroscopy to characterize tissues via quantitative measurements of tissue absorption and reduced scattering coefficients from 650 to 1000 nm. The concentrations of significant near-infrared (NIR) absorbers were mapped within a 50 cm(2) area over the biopsied region. A 2-D image of a contrast function called the tissue optical index (TOI=deoxyhemoglobinxwaterbulk lipid) was generated and revealed that a minimum of 14 days postbiopsy was required to return TOI levels in the biopsied area to their prebiopsy levels. Changes in the TOI images of the fibroadenoma also reflected the progression of the patient's menstrual cycle. DOS could therefore be useful in evaluating both wound-healing response and the effects of hormone and hormonal therapies in vivo.

Effect of contact force on breast tissue optical property measurements using a broadband diffuse optical spectroscopy handheld probe.

We investigated the effects of operator-applied force on diffuse optical spectroscopy (DOS) by integrating a force transducer into the handheld probe. Over the typical range of contact forces measured in the breasts of eight patients, absorption and reduced scattering coefficients (650 to 1000 nm) variance was 3.1 +/- 1.0% and 1.0 +/- 0.4%. For trained operators, we observed <5% variation in hemoglobin and <2% variation in water and lipids. Contact force is not a significant source of variation, most likely because of a relatively wide probe surface area and the stability of the DOS method for calculating tissue optical properties.

Intrinsic near-infrared spectroscopic markers of breast tumors.

We have discovered quantitative optical biomarkers unique to cancer by developing a double-differential spectroscopic analysis method for near-infrared (NIR, 650-1000 nm) spectra acquired non-invasively from breast tumors. These biomarkers are characterized by specific NIR absorption bands. The double-differential method removes patient specific variations in molecular composition which are not related to cancer, and reveals these specific cancer biomarkers. Based on the spectral regions of absorption, we identify these biomarkers with lipids that are present in tumors either in different abundance than in the normal breast or new lipid components that are generated by tumor metabolism. Furthermore, the O-H overtone regions (980-1000 nm) show distinct variations in the tumor as compared to the normal breast. To quantify spectral variation in the absorption bands, we constructed the Specific Tumor Component (STC) index. In a pilot study of 12 cancer patients we found 100% sensitivity and 100% specificity for lesion identification. The STC index, combined with other previously described tissue optical indices, further improves the diagnostic power of NIR for breast cancer detection.

Design and testing of a miniature broadband frequency domain photon migration instrument.

A board-level broadband frequency domain photon migration (mini-FDPM) instrument has been constructed to replace a conventional network-analyzer-based FDPM instrument. The mini-FDPM instrument with four wavelengths (681, 783, 823, and 850 nm), matches conventional FDPM instrument in performance (-88 dBm noise level, 100 dB dynamic range) and bandwidth (1 GHz), and recovers the same optical properties within about 6% in absorption and 4% in reduced scattering for liquid phantoms covering a wide range of relevant optical properties. Compared to the conventional FDPM instrument, the mini-FDPM instrument is more than 5x faster (approximately 200 ms per 401 modulation frequencies) and several orders of magnitude less in size and cost. Standard fiber-optic-based probes can be used with the mini-FDPM instrument, which increases applications in a number of clinically relevant measurement scenarios. By drastically reducing size and cost, FDPM miniaturization lowers barriers to access and will help promote FDPM in clinical research problems. The mini-FDPM instrument forms the core of a modular broadband diffuse optical spectroscopy instrument that can be used for a variety of clinical problems in imaging and functional monitoring (i.e., breast/skin cancer, brain activation, and exercise physiology).

Assessing the spatial extent of breast tumor intrinsic optical contrast using ultrasound and diffuse optical spectroscopy.

Little is known about the relationship between anatomic and functional contrast derived from intrinsic optical signals. In order to address this relationship, finite-element (FEM) forward simulations were compared to diffuse optical spectroscopy (DOS) reflectance measurements obtained from 10 breast tumor patients. Clinical ultrasound images were used to estimate anatomical tumor size and depth for the FEM simulations. Actual DOS-measured tumor absorption could not be matched by forward model simulations when tumor size was constrained to match ultrasound dimensions. However, agreement was achieved when the lesion was viewed as a distribution of optical properties (i.e., an extended target). This result suggests that the spatial extent of optical contrast in breast tumors may be significantly greater than anatomical dimensions reported by standard imaging modalities. Analysis indicates that invasive breast tumors with anatomical dimensions of 1 cm may still be detectable at depths of 30 mm or more (the center of the lesion to the surface of tissue) using DOS in a reflectance geometry.

Assessing the future of diffuse optical imaging technologies for breast cancer management.

Diffuse optical imaging (DOI) is a noninvasive optical technique that employs near-infrared (NIR) light to quantitatively characterize the optical properties of thick tissues. Although NIR methods were first applied to breast transillumination (also called diaphanography) nearly 80 years ago, quantitative DOI methods employing time- or frequency-domain photon migration technologies have only recently been used for breast imaging (i.e., since the mid-1990s). In this review, the state of the art in DOI for breast cancer is outlined and a multi-institutional Network for Translational Research in Optical Imaging (NTROI) is described, which has been formed by the National Cancer Institute to advance diffuse optical spectroscopy and imaging (DOSI) for the purpose of improving breast cancer detection and clinical management. DOSI employs broadband technology both in near-infrared spectral and temporal signal domains in order to separate absorption from scattering and quantify uptake of multiple molecular probes based on absorption or fluorescence contrast. Additional dimensionality in the data is provided by integrating and co-registering the functional information of DOSI with x-ray mammography and magnetic resonance imaging (MRI), which provide structural information or vascular flow information, respectively. Factors affecting DOSI performance, such as intrinsic and extrinsic contrast mechanisms, quantitation of biochemical components, image formation/visualization, and multimodality co-registration are under investigation in the ongoing research NTROI sites. One of the goals is to develop standardized DOSI platforms that can be used as stand-alone devices or in conjunction with MRI, mammography, or ultrasound. This broad-based, multidisciplinary effort is expected to provide new insight regarding the origins of breast disease and practical approaches for addressing several key challenges in breast cancer, including: Detecting disease in mammographically dense tissue, distinguishing between malignant and benign lesions, and understanding the impact of neoadjuvant chemotherapies.

Tissue oxygen saturation predicts response to breast cancer neoadjuvant chemotherapy within 10 days of treatment.

Ideally, neoadjuvant chemotherapy (NAC) assessment should predict pathologic complete response (pCR), a surrogate clinical endpoint for 5-year survival, as early as possible during typical 3- to 6-month breast cancer treatments. We introduce and demonstrate an approach for predicting pCR within 10 days of initiating NAC. The method uses a bedside diffuse optical spectroscopic imaging (DOSI) technology and logistic regression modeling. Tumor and normal tissue physiological properties were measured longitudinally throughout the course of NAC in 33 patients enrolled in the American College of Radiology Imaging Network multicenter breast cancer DOSI trial (ACRIN-6691). An image analysis scheme, employing z-score normalization to healthy tissue, produced models with robust predictions. Notably, logistic regression based on z-score normalization using only tissue oxygen saturation (StO2) measured within 10 days of the initial therapy dose was found to be a significant predictor of pCR (AUC = 0.92; 95% CI: 0.82 to 1). This observation suggests that patients who show rapid convergence of tumor tissue StO2 to surrounding tissue StO2 are more likely to achieve pCR. This early predictor of pCR occurs prior to reductions in tumor size and could enable dynamic feedback for optimization of chemotherapy strategies in breast cancer.

Intrinsic tumor biomarkers revealed by novel double-differential spectroscopic analysis of near-infrared spectra.

We develop a double-differential spectroscopic analysis method for broadband near-infrared (NIR, 650 to 1000 nm) absorption spectra. Application of this method to spectra of tumor-containing breast tissue reveals specific cancer biomarkers. In this method, patient-specific variations in molecular composition are removed by using the normal tissue as an internal control. The effects of concentration differences of the four major tissue absorbers (oxyhemoglobin, deoxyhemoglobin, water, and bulk lipid) between the tumor and normal tissue are accounted for to reveal small spectral components unique to cancer. From a pilot study of 15 cancer patients, we find these spectral components to be characterized by specific NIR absorption bands. Based on the spectral regions of absorption at about 760, 930, and 980 nm, we identify these biomarkers with changes in state or addition of lipid and/or water. To quantify spectral variation in the absorption bands, we construct the specific tumor component (STC) index. The STC index identifies regions of the breast with tumors.

Hemoglobin measurement patterns during noninvasive diffuse optical spectroscopy monitoring of hypovolemic shock and fluid replacement.

The purpose of this study is to demonstrate the feasibility of broadband diffuse optical spectroscopy (DOS) for noninvasive optical monitoring of differentiating patterns of total tissue hemoglobin (THC), oxy- (OxyHb), and deoxyhemoglobin (DeOxyHb) concentrations during hypovolemic shock and subsequent fluid replacement with saline and whole blood. The goal of this DOS application is to determine the efficacy of resuscitation efforts at the tissue level rather than currently available indirect and invasive measurements of hemodynamic parameters. 16 New Zealand white rabbits are hemorrhaged 20% of their total blood volume. In resuscitated animals, shed blood volume is replaced with equal volume of crystalloid or whole blood (five animals each). Physiological variables (cardiac output, mean arterial pressure, systemic vascular resistance, hematocrit) are measured invasively, while (OxyHb) and (DeOxyHb) are measured during the interventions using broadband DOS. During the pure hypovolemic hemorrhages, the decrease in THC is mainly due to the decrease in (OxyHb), since the decrease in THC due to blood loss results in decreased tissue perfusion, with a resultant increased tissue extraction of oxygen. The hemorrhage with the whole blood resuscitation model shows significant changes in (OxyHb) during resuscitation phases due to the higher oxygen carrying capacity of whole blood, as opposed to the limited volume replacement effects and the decreased tissue oxygen content from the euvolemic anemia of the saline resuscitation. Broadband DOS noninvasive optical monitoring reveals distinct patterns of total tissue hemoglobin, oxy-, and deoxyhemoglobin during hemorrhage. Further studies are needed to confirm potential clinical utility and accuracy under more complex clinical conditions in animal models and patients.

Diffuse optical monitoring of blood flow and oxygenation in human breast cancer during early stages of neoadjuvant chemotherapy.

We combine diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS) to noninvasively monitor early hemodynamic response to neoadjuvant chemotherapy in a breast cancer patient. The potential for early treatment monitoring is demonstrated. Within the first week of treatment (day 7) DOS revealed significant changes in tumor/normal contrast compared to pretreatment (day 0) tissue concentrations of deoxyhemoglobin (rctHHbT/N=69+/-21%), oxyhemoglobin (rctO2HbT/N=73+/-25%), total hemoglobin (rctTHbT/N=72+/-17%), and lipid concentration (rctLipidT/N=116+/-13%). Similarly, DCS found significant changes in tumor/normal blood flow contrast (rBFT/N=75+/-7% on day 7 with respect to day 0). Our observations suggest the combination of DCS and DOS enhances treatment monitoring compared to either technique alone. The hybrid approach also enables construction of indices reflecting tissue metabolic rate of oxygen, which may provide new insights about therapy mechanisms.

Vertical-cavity surface-emitting laser sources for gigahertz-bandwidth, multiwavelength frequency-domain photon migration.

Frequency-domain photon migration (FDPM) uses modulated laser light to measure the bulk optical properties of turbid media and is increasingly applied for noninvasive functional medical imaging in the near-infrared. Although semiconductor edge-emitting laser diodes have been traditionally used as miniature light sources for this application, we show that vertical-cavity surface-emitting lasers (VCSELs) exhibit output power and modulation performance characteristics suitable for FDPM measurements of tissue optical properties at modulation frequencies exceeding 1 GHz. We also show that an array of multiple VCSEL devices can be coherently modulated at frequencies suitable for FDPM and can improve optical power. In addition, their small size and simple packaging make them an attractive choice as components in wearable sensors and clinical FDPM-based optical spectroscopy systems. We demonstrate the benefits of VCSEL technology by fabricating and testing a unique, compact VCSEL-based optical probe with an integrated avalanche photodiode. We demonstrate sensitivity of the VCSEL-based probe to subcutaneous tissue hemodynamics that was induced during an arterial cuff occlusion of the upper arm in a human subject.

Performance assessment of diffuse optical spectroscopic imaging instruments in a 2-year multicenter breast cancer trial

We present a framework for characterizing the performance of an experimental imaging technology, diffuse optical spectroscopic imaging (DOSI), in a 2-year multicenter American College of Radiology Imaging Network (ACRIN) breast cancer study (ACRIN-6691). DOSI instruments combine broadband frequency-domain photon migration with time-independent near-infrared (650 to 1000 nm) spectroscopy to measure tissue absorption and reduced scattering spectra and tissue hemoglobin, water, and lipid composition. The goal of ACRIN-6691 was to test the effectiveness of optically derived imaging endpoints in predicting the final pathologic response of neoadjuvant chemotherapy (NAC). Sixty patients were enrolled over a 2-year period at participating sites and received multiple DOSI scans prior to and during 3- to 6-month NAC. The impact of three sources of error on accuracy and precision, including different operators, instruments, and calibration standards, was evaluated using a broadband reflectance standard and two different solid tissue-simulating optical phantoms. Instruments showed <0.0010 mm−1 (10.3%) and 0.06 mm−1 (4.7%) deviation in broadband absorption and reduced scattering, respectively, over the 2-year duration of ACRIN-6691. These variations establish a useful performance criterion for assessing instrument stability. The proposed procedures and tests are not limited to DOSI; rather, they are intended to provide methods to characterize performance of any instrument used in translational optical imaging.

Noninvasive in vivo monitoring of methemoglobin formation and reduction with broadband diffuse optical spectroscopy.

We present noninvasive, quantitative in vivo measurements of methemoglobin formation and reduction in a rabbit model using broadband diffuse optical spectroscopy (DOS). Broadband DOS combines multifrequency frequency-domain photon migration (FDPM) with time-independent near infrared (NIR) spectroscopy to quantitatively measure bulk tissue absorption and scattering spectra between 600 nm and 1,000 nm. Tissue concentrations (denoted by brackets) of methemoglobin ([MetHb]), deoxyhemoglobin ([Hb-R]), and oxyhemoglobin ([HbO2]) were determined from absorption spectra acquired in "real time" during nitrite infusions in nine pathogen-free New Zealand White rabbits. As little as 30 nM [MetHb] changes were detected for levels of [MetHb] that ranged from 0.80 to 5.72 microM, representing 2.2 to 14.9% of the total hemoglobin content (%MetHb). These values agreed well with on-site ex vivo cooximetry data (r2= 0.902, P < 0.0001, n = 4). The reduction of MetHb to functional hemoglobins was also carried out with intravenous injections of methylene blue (MB). As little as 10 nM changes in [MB] were detectable at levels of up to 150 nM in tissue. Our results demonstrate, for the first time, the ability of broadband DOS to noninvasively quantify real-time changes in [MetHb] and four additional chromophore concentrations ([Hb-R], [HbO2], [H2O], and [MB]) despite significant overlapping spectral features. These techniques are expected to be useful in evaluating dynamics of drug delivery and therapeutic efficacy in blood chemistry, human, and preclinical animal models.