Abstract P4-01-12: Optical imaging of breast density correlates with magnetic resonance imaging in patients undergoing neoadjuvant chemotherapy

Background: In addition to being a strong risk factor for breast cancer, data from recent studies suggests that breast density changes correlate with response to preventative or adjuvant tamoxifen treatment for breast cancer. Breast density may be a surrogate biomarker for survival and indication of the need for additional treatments such as radiotherapy. However, quantitative methods to assess breast density in the clinic are limited. In this study, we assess how Diffuse Optical Spectroscopic Imaging (DOSI) may be used to evaluate and understand changes in breast density in patients undergoing neoadjuvant chemotherapy.

Methods: DOSI was used to measure hemodynamic and metabolic information from the contralateral normal breast of 28 breast cancer patients undergoing neoadjuvant chemotherapy. DOSI uses near-infrared light to determine absolute tissue molar concentrations of oxyhemoglobin (ctO2Hb), deoxyhemoglobin (ctHHb), water, and lipid content without requirement of an exogenous contrast agent. DOSI measurements were compared to 3.0T MRI measured fibroglandular density before and during therapy.

Results: Water (r = 0.843; P<0.001), ctHHb (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. During neoadjuvant treatment measured at ∼90 days after treatment commenced, significant reductions were observed in ctO2Hb 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 (- 1.9%; 95% CI, -17.1 to -6.7) compared to baseline. Lipid content 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).

Discussion: For this patient cohort, non-invasive optical measurement may provide an assessment of breast density and yield additional information that complements MRI and mammography techniques. We demonstrate a strong baseline correlation between water and ctHHb with breast density, reflecting the increased water content and rate of metabolism in fibroglandular breast tissue. Significant changes in optical markers for vascular density and supply (ctO2Hb and water) are observed during treatment. A significant decrease in ctO2Hb is observed in both menopausal groups. The steady reduction of ctO2Hb without a corresponding decrease in ctHHb suggests that chemotherapy agents act directly on the normal breast tissue, perhaps by causing a reduction of perfusion. The greater reduction in breast-tissue water in premenopausal subjects suggests that chemo-reduced ovarian hormone levels may exert a role in reducing breast-tissue density. Although from a limited patient dataset, these results suggest that DOSI may provide new functional indices of breast density based on hemoglobin and water that could be used at the bedside to assess response to therapy.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-12.

Impact of phenylephrine administration on cerebral tissue oxygen saturation and blood volume is modulated by carbon dioxide in anaesthetized patients

BACKGROUND

Multiple studies have shown that cerebral tissue oxygen saturation (Sct(O(2))) is decreased after phenylephrine treatment. We hypothesized that the negative impact of phenylephrine administration on Sct(O(2)) is affected by arterial blood carbon dioxide partial pressure (Pa(CO(2))) because CO(2) is a powerful modulator of cerebrovascular tone.

METHODS

In 14 anaesthetized healthy patients, i.v. phenylephrine bolus was administered to increase the mean arterial pressure ~20-30% during hypocapnia, normocapnia, and hypercapnia. Sct(O(2)) and cerebral blood volume (CBV) were measured using frequency domain near-infrared spectroscopy, a quantitative technology. Data collection occurred before and after each treatment.

RESULTS

Phenylephrine caused a significant decrease in Sct(O(2)) during hypocapnia [ΔSct(O(2)) =-3.4 (1.5)%, P<0.001], normocapnia [ΔSct(O(2)) =-2.4 (1.5)%, P<0.001], and hypercapnia [ΔSct(O(2)) =-1.4 (1.5)%, P<0.01]. Decreases in Sct(O(2)) were significantly different between hypocapnia, normocapnia, and hypercapnia (P<0.001). Phenylephrine also caused a significant decrease in CBV during hypocapnia (P<0.01), but not during normocapnia or hypercapnia.

CONCLUSION

The negative impact of phenylephrine treatment on Sct(O(2)) and CBV is intensified during hypocapnia while blunted during hypercapnia.

P2-09-15: Functional Measurements of Tumor Response during Neoadjuvant Chemotherapy Infusion and Early during Treatment Using Diffuse Optical Spectroscopic Imaging

Background: Non-invasive markers of neoadjuvant chemotherapy response early during treatment would provide physicians a valuable tool to make evidence-based changes to treatment strategies. In a retrospective study of 23 patients presented at SABCS 2011 we demonstrated that Diffuse Optical Spectroscopic Imaging (DOSI) can discriminate non-responding from responding subjects on the first day after the start therapy based on the presence or absence of an oxyhemoglobin flare. Here we present results of an ongoing prospective study designed to confirm the predictive nature and biological origins of oxyhemoglobin flare and to determine if similar functional changes occur at even earlier timepoints such as during infusion.

Methods: DOSI was used to measure hemodynamic and metabolic information from tumors and surrounding normal tissue in patients prior to neoadjuvant chemotherapy, during chemotherapy infusion, and daily for the first week of treatment. DOSI uses temporally modulated near-infrared light to determine absolute tissue concentrations of oxyhemoglobin, deoxyhemoglobin, water and lipid content and requires no exogenous contrast agent. Measurements are made using a simple handheld probe placed on the skin. Blood samples were also collected at baseline and daily for seven days after the first infusion and tested for a panel inflammatory cytokines. Patients received paclitaxel + carboplatin + bevacizumab. Overall response to therapy was determined by the decrease in anatomic tumor size.

Results: To date three subjects have been measured, two of which have completed neoadjuvant chemotherapy and undergone surgery. One subject was a pathologic complete responder (pCR) and the other a non-responder (NR). In both the pCR subject and the subject still undergoing therapy there were significant functional changes measured in the tumor during infusion. A decrease in oxyhemoglobin and oxygen saturation occurred after paclitaxel infusion (saturation changes: −4.8% and −9.7% for each subject respectively), followed by an increase in these quantities after carboplatin infusion (saturation: 3.8% and 5.9% respectively). In the NR subject both oxyhemoglobin and oxygen saturation had only small fluctuations during infusion (saturation: 1.1%). Oxyhemoglobin flare was also observed 24 hours after infusion for each of the patients. Plasma levels of several inflammatory cytokines including G-CSF, MIP-1α, and C-reactive protein increased 24 hours after infusion for the first two subjects and subsequently decreased at 48 hours.

Discussion: We have confirmed the presence of oxyhemoglobin flare on day one after infusion in this small prospective patient cohort. Increased plasma levels of inflammatory cytokines were correlated in time with the presence of oxyhemoglobin flare suggesting a possible link between optical measurements and inflammatory processes induced by chemotherapy. Additionally, we report for the first time significant changes in tumoral oxyhemoglobin and oxygen saturation during chemotherapy infusion. These changes may be of prognostic significance. DOSI allows functional measurements of tumor response at timepoints unachievable with current functional medical imaging modalities.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-09-15.

Effect of phenylephrine and ephedrine bolus treatment on cerebral oxygenation in anaesthetized patients

BACKGROUND

How phenylephrine and ephedrine treatments affect global and regional haemodynamics is of major clinical relevance. Cerebral tissue oxygen saturation (Sct(O2) )-guided management may improve postoperative outcome. The physiological variables responsible for Sct(O2) changes induced by phenylephrine and ephedrine bolus treatment in anaesthetized patients need to be defined.

METHODS

A randomized two-treatment cross-over trial was conducted: one bolus dose of phenylephrine (100-200 µg) and one bolus dose of ephedrine (5-20 mg) were given to 29 ASA I-III patients anaesthetized with propofol and remifentanil. , mean arterial pressure (MAP), cardiac output (CO), and other physiological variables were recorded before and after treatments. The associations of changes were analysed using linear-mixed models.

RESULTS

The CO decreased significantly after phenylephrine treatment [▵CO = -2.1 (1.4) litre min(-1), P<0.001], but was preserved after ephedrine treatment [▵CO = 0.5 (1.4) litre min(-1), P>0.05]. The was significantly decreased after phenylephrine treatment [▵ = -3.2 (3.0)%, P<0.01] but preserved after ephedrine treatment [▵ = 0.04 (1.9)%, P>0.05]. CO was identified to have the most significant association with (P<0.001). After taking CO into consideration, the other physiological variables, including MAP, were not significantly associated with (P>0.05).

CONCLUSIONS

Associated with changes in CO, decreased after phenylephrine treatment, but remained unchanged after ephedrine treatment. The significant correlation between CO and implies a cause-effect relationship between global and regional haemodynamics.

Abstract P5-01-10: Tumor Optic Properties Measured Using Diffuse Optic Spectroscopy Imaging Correlate with Proliferation and Glucose Metabolism in Breast Cancer Patients

(Background) Diffuse Optic Spectroscopy Imaging (DOSI) is non-invasive imaging technology that employs near-infrared (NIR) light to quantitatively characterize the hemodynamic and metabolic properties of breast cancer tumors.

(Methods) We utilized DOSI to measure baseline tumor concentrations of oxy-hemoglobin (ctO2Hb), deoxy-hemoglobin (ctHHb), total hemoglobin (ctTHb), oxygen saturation (stO2), as well as water and lipid content of tumors from sixteen patients with primary breast cancer prior to neoadjuvant chemotherapy. Core-needle biopsy specimens were also collected from these patients and analyzed for Ki67, Glut-1, and Fatty acid synthese (FAS), biomarkers of cancer proliferation, glucose metabolism and fatty acid metabolism, respectively. These optic and biological biomarkers were statistically compared to each other and to overall therapy response. (Results) Ki67 score was positively correlated with baseline levels of ctO2Hb (µM) (r = 0.51, p = 0.04), ctTHb (µM) (r = 0.51, p = 0.05), and stO2 (%) (r = 0.57, p = 0.02), and negatively correlated with lipid content (%) (r = -0.52, p = 0.04). Tumors with positive Glut-1 status (n=8) showed significantly higher baseline levels of ctO2Hb (26.2±12.5 v.s 19.9±10.1, p = 0.04), ctTHb (41±13.3 v.s 27.5±11.7, p = 0.05), and stO2 (81.1±6.6 v.s 70.2±9.9, p = 0.02) and lower baseline levels of lipid (49±17.1 v.s 66.2±10.4, p = 0.03) compared to those with negative Glut-1 status (n = 8). There were no correlation between FAS and the optic properties. Five (31.3%) of 16 tumors achieved pathologic complete response (pCR) after completion of chemotherapy followed by surgery. Tumors with pCR showed higher stO2, higher Ki67 score and higher likelihood of Glut-1 expression than those with non-pCR (p = 0.009, 0.01, 0.03, respectively).

Only p-values with statistical significance were described.

(Conclusion) Higher tumoral expression levels of Ki67 and Glut-1 were correlated with higher oxygenation and lower lipid concentration and associated with a pathologic complete response to chemotherapy. Non-invasive optic properties measured using DOSI are potential surrogate markers for tumor proliferation and glucose metabolism.

Abstract P5-01-12: Specific Tumor Component Spectrum as a Predictor of Response to Neoadjuvant Chemotherapy in Breast Cancer

BACKGROUND: Monitoring individual tumor response to neoadjuvant chemotherapy could provide surrogate markers for oncologists to adjust therapeutics in order to minimize collateral damage from ineffective therapies. Diffuse optical spectroscopy imaging (DOSI), by increasing the wavelength range and resolution, has been employed to characterize malignant tumor and its response to neoadjuvant chemotherapy since it measures the abundance in the four major chromophores (lipid, oxy-hemoglobin, deoxy-hemoglobin and water). Through the application of a spectral analysis method, Self-Referencing Differential Spectroscopy (SRDS) analysis, which accounts for only intersubject variability, a novel optical intrinsic biomarker which is unique to cancer was revealed. By fitting the difference spectrum between tumor and normal tissues to the four component basis spectra, the residuals disclose a spectral fingerprint called specific tumor component (STC) spectrum which contains specific absorption bands which separate normal from abnormal tissue and benign from malignant tumors.

PATIENTS AND METHODS: 14 patients were enrolled in this study and all the subjects provided informed written consent according to an institution-approved protocol. Measurements were taken pre-, post-neoajuvant chemotherapy and the midpoint in the treatment. The chemotherapy regimen is 2-4 cycles of doxorubicin-cyclophosphamide (A/C), followed by 2-4 cycles of carboplatin-taxol/abraxane-avastin (nabTC). Tumor classification was confirmed by pathology reports and 8 out of 14 patients were classified as complete responders (CR); the rest as noneresponders (NR). Pre and post-treatment STC spectra were compared in different pathological responding categories. Data were analyzed by using custom software designed for Matlab. The concentrations of NIR absorbers will be calculated from a spectral model of tissue absorption by using the basis spectra. For the SRDS method, the absorption spectra will be further analyzed by using custom software (Elantest; Laboratory for Fluorescence Dynamics, Irvine, Calif, www.lfd.edu). Details of SRDS method has been described previously.

RESULTS: The shape of STC spectra for non-responders was well preserved since insusceptible tumor structure will remain basically unaffected during the chemotherapy. Whereas in the completed responders, the therapy-induced changes in tumor microvasculature, edema, and necrosis lead to a significant dissimilarity in STC spectra.

CONCLUSION: STC spectrum, as an endogenous in vivo biomarker, can predict pathological response in breast tumors treated with neoadjuvant chemotherapy.

Non-invasive tissue temperature measurements based on quantitative diffuse optical spectroscopy (DOS) of water

We describe the development of a non-invasive method for quantitative tissue temperature measurements using Broadband diffuse optical spectroscopy (DOS). Our approach is based on well-characterized opposing shifts in near-infrared (NIR) water absorption spectra that appear with temperature and macromolecular binding state. Unlike conventional reflectance methods, DOS is used to generate scattering-corrected tissue water absorption spectra. This allows us to separate the macromolecular bound water contribution from the thermally induced spectral shift using the temperature isosbestic point at 996 nm. The method was validated in intralipid tissue phantoms by correlating DOS with thermistor measurements (R=0.96) with a difference of 1.1+/-0.91 degrees C over a range of 28-48 degrees C. Once validated, thermal and hemodynamic (i.e. oxy- and deoxy-hemoglobin concentration) changes were measured simultaneously and continuously in human subjects (forearm) during mild cold stress. DOS-measured arm temperatures were consistent with previously reported invasive deep tissue temperature studies. These results suggest that DOS can be used for non-invasive, co-registered measurements of absolute temperature and hemoglobin parameters in thick tissues, a potentially important approach for optimizing thermal diagnostics and therapeutics.

Hyperoxic respiratory challenges to monitor chemotherapy effects on Brca1/p53 deficient mice breast tumors

Abstract #5065

Background: Response to cancer treatments such as radiotherapy, chemotherapy, and photodynamic therapy are less effective when tumors are hypoxic. Hyperoxic gas intervention has been shown to improve tumor oxygenation. Here we report how hemodynamic changes due to oxygen intervention are related to the tumor response during cisplatin treatment of spontaneous mammary tumors developed in mice with conditional inactivation of the Brca1 and p53 genes.&#x2028; Materials and Methods: We treated mammary tumors in Brca1/p53 knockout mice (n=8) with 1.2mg/kg of Cisplatin (i. p. daily for a week), and tumor volume and body weight were monitored during treatment. We imaged tumors during chemotherapy using an optical imaging system that quantifies intrinsic light scattering and absorption by projecting spatially modulated, near infrared (NIR) light (650nm to 980nm) onto tissues and calculating oxy-(Ohb), deoxy-(RHb), total hemoglobin (THb) concentrations, tissue oxygen saturation (StO2) values, and scattering values at all wavelengths. During imaging, animals were anesthetized using 1.5% isoflurane and each animal inhaled medical air (33% O2) for 6 min followed by 100% oxygen for an additional 12 min.&#x2028; Results: Among 8 tumors, 5 (volume=0.38±0.1) showed response to Cisplatin treatment while the other 3 tumors (volume=0.56±0.12) did not. Tumors responding to Cisplatin displayed greater than 2-fold increase in [Ohb] and [RHb] during oxygen intervention compared to non responding tumors (p&lt;0.05). (Fig.1) Significant differences in tumor size changes (data not shown) were also observed between responders and non-responders.&#x2028; &#x2028; Discussion: Breast cancers are heterogeneous in their molecular profiles as well as treatment response. Hyperoxic gas intervention during chemotherapy combined with intrinsic signal optical imaging can be used to evaluate vascular reactivity. Our preliminary results indicate that OHb and RHb reactive tumors are significantly more likely to respond to Cisplatin chemotherapy. This general approach can be extended to other tumor therapy models and can be readily translated to patients.&#x2028; Keywords:Breast Cancer, Brca1/p53 Transgenic Mice, Diffuse Optical Imaging, Cisplatin Chemotherapy.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5065.

Diffuse optical spectroscopic imaging measures tumor functional response to bevacizumab: initial studies

Abstract #6056

Background: Diffuse Optical Spectroscopic Imaging (DOSI) is a non-invasive, bedside functional imaging technique that quantifies the concentrations and molecular states of tissue hemoglobin, water, and lipids. Pilot studies have shown that DOSI may be a useful tool for quantifying neoadjuvant chemotherapy response, typically by comparing the degree of change in tumor water and deoxy-hemoglobin concentrations before and after therapy. DOSI may offer a point-of-care measurement of tumor responses to therapeutic intervention. The majority of these DOSI studies have measured responses to Anthracyclines. However, the optical response to Bevacizumab has not been demonstrated in vivo in human subjects.&#x2028; Materials and Methods: Twenty-one patients diagnosed with stage II/III cancers were followed with DOSI prior to and during their two-stage neoadjuvant chemotherapy regimen that featured (a) Anthracyclines (2-4 cycles) and (b) Trastuzumab/Bevacizumab (for HER2+/HER2- status, respectively). Changes between pre-treatment and pre-surgical DOSI-measured parameters were compared against final surgical pathology (complete, partial, or non-responder). A functional tissue optical index (TOI) was calculated that has been shown to discriminate between normal and malignant tissues.&#x2028; Results: Both short-term and long-term changes in tumor physiology were observed. For both therapy strategies (N=21), statistically significant changes were measured in TOI from baseline to pre-surgery between complete (95+/-15%), partial (79+/-11%) and non-responders (38+/-42%). TOI changes after the initial therapy stage were strongest in patients with more favorable pathological responses (78%, 56%, and 12% for complete, partial, and non-responders respectively). For patients receiving Bevacizumab (N=9), more detailed serial image analysis of tumor deoxy-hemoglobin revealed short-term changes (7-14 days) where initial decreases in hemoglobin were soon followed by slow increases back to pre-treatment levels. Two of the patients who received Bevacizumab demonstrated detectible residual disease by DOSI after completion of all neoadjuvant therapy, despite that contrast-enhanced MRI signals had disappeared.&#x2028; Discussion: We have provided evidence that DOSI may be well-suited to monitor the response of different cancer drugs, including anti-angiogenic compounds such as Bevacizumab, in breast cancer patients. While the usage of Bevacizumab in human subjects is still under investigation in breast cancer, we foresee that DOSI may be a useful tool in general for the development of drugs and dosing strategies.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6056.

Assessing the spatial extent of breast tumor intrinsic optical contrast using ultrasound and diffuse optical spectroscopic imaging

Abstract #806

Background: Near infrared (NIR) light is sensitive to several important tissue components and has been used to detect, characterize, and monitor breast tumor functions. However, little is known about the relationship between anatomic and functional contrast derived from intrinsic optical signals. Diffuse Optical Spectroscopic Imaging (DOSI) is a non-invasive, bedside functional imaging technique that quantifies the concentrations and molecular states of tissue hemoglobin, water, and lipids. Pilot studies have shown that DOSI may be a useful tool for breast lesion detection/characterization and therapeutic monitoring.&#x2028; Materials and Methods: DOSI data were compared with theoretical computer simulations to estimate the nature and extent of optical contrast with respect to standard ultrasound imaging. DOSI reflectance measurements were obtained from 10 breast tumor patients, with both malignant (N=5) and benign (N=5) lesions. Patient average ages: 35+/-7.8 years vs. 44.3+/-14.7 years, lesion depth 10.9+/-5.5 mm vs. 15.8+/-5.3 mm, and maximum size 13.0+/-6.0 mm vs. 14.8+/-4.9 mm for benign and malignant, respectively. Two trial tumor models were simulated to model actual tumor optical properties (hemoglobin): (a) a discrete target constrained to ultrasound dimensions, and (b) a distributed target that spatially extended beyond ultrasound dimensions.&#x2028; Results: High optical contrast (i.e., the ratio target to background) was observed for both benign (1.53+/-0.17) and malignant (2.06+/-0.4) lesions, even for this younger population. While the discrete target model could not match experiment and simulation, a distributed model provided excellent agreement. The spatial extent of optical properties in breast tumor was significantly greater than anatomical dimensions reported by ultrasound imaging. The extent of the distribution was greater in the malignant lesions than in the benign ones. Further simulations also suggested that invasive breast tumors in this population with anatomical size 10 mm may still be detectable at depth 30 mm using DOSI in reflectance.&#x2028; Discussion: The spatial extension of tumor optical contrast complicates co-registration of optical functional images with anatomic images. The true optical contrast is significantly higher in breast cancer tumors, likely 4-5x than the hemoglobin levels in normal tissues. Breast tumor optical contrast is more realistically modeled as a spatially distributed target, which facilities a fast 3D imaging scheme in reflectance geometry. Results from these topographic reconstructions will be discussed.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 806.

In vivo water state measurements in breast cancer using broadband diffuse optical spectroscopy

Structural changes in water molecules are related to physiological, anatomical and pathological properties of tissues. Near infrared (NIR) optical absorption methods are sensitive to water; however, detailed characterization of water in thick tissues is difficult to achieve because subtle spectral shifts can be obscured by multiple light scattering. In the NIR, a water absorption peak is observed around 975 nm. The precise NIR peak's shape and position are highly sensitive to water molecular disposition. We introduce a bound water index (BWI) that quantifies shifts observed in tissue water absorption spectra measured by broadband diffuse optical spectroscopy (DOS). DOS quantitatively measures light absorption and scattering spectra and therefore reveals bound water spectral shifts. BWI as a water state index was validated by comparing broadband DOS to magnetic resonance spectroscopy, diffusion-weighted MRI and conductivity in bound water tissue phantoms. Non-invasive DOS measurements of malignant and normal breast tissues performed in 18 subjects showed a significantly higher fraction of free water in malignant tissues (p < 0.0001) compared to normal tissues. BWI of breast cancer tissues inversely correlated with Nottingham-Bloom-Richardson histopathology scores. These results highlight broadband DOS sensitivity to molecular disposition of water and demonstrate the potential of BWI as a non-invasive in vivo index that correlates with tissue pathology.

Broadband diffuse optical spectroscopy measurement of hemoglobin concentration during hypovolemia in rabbits

Serial blood draws for the assessment of trauma patients' hemoglobin (sHgb) and hematocrit (sHct) is standard practice. A device that would allow for continuous real-time, non-invasive monitoring of hemoglobin and tissue perfusion would potentially improve recognition, monitoring and resuscitation of blood loss. We developed a device utilizing diffuse optical spectroscopy (DOS) technology that simultaneously measures tissue scattering and near-infrared (NIR) absorption to obtain non-invasive measurements of oxy- (Hb-O(2)), deoxyhemoglobin (Hb-R) concentrations and tissue hemoglobin concentration (THC) in an animal model of hypovolemic shock induced by successive blood withdrawals. Intubated New Zealand White rabbits (N = 16) were hemorrhaged via a femoral arterial line every 20 min until a 20% blood loss (10-15 cc kg(-1)) was achieved to attain hypovolemia. A broadband DOS probe placed on the inner thigh was used to measure muscle concentrations of Hb-O(2) and Hb-R, during blood withdrawal. THC and tissue hemoglobin saturation (S(T)O(2)) were calculated from DOS [Hb-O(2)] and [Hb-R]. Broadband DOS-measured values were compared against traditional invasive measurements: systemic sHgb, arterial oxygen saturation (S(a)O(2)) and venous oxygen saturation (S(v)O(2)) drawn from arterial and central venous blood. DOS and traditional invasive measurements versus blood loss were closely correlated (r(2) = 0.96) showing a decline with removal of blood. S(T)O(2) and [Hb-O(2)] followed similar trends with hemorrhage, while [Hb-R] remained relatively constant. These measurements may be limited to some extent by the inability to distinguish between hemoglobin and myoglobin contributions to DOS signals in tissue at this time. Broadband DOS provides a potential platform for reliable non-invasive measurements of tissue oxygenated and deoxygenated hemoglobin and may accurately reflect the degree of systemic hypovolemia and compromised tissue perfusion.

Comparison of water and lipid content measurements using diffuse optical spectroscopy and MRI in emulsion phantoms

We present a quantitative comparison of lipid and water signals obtained from broadband Diffuse Optical Spectroscopy (DOS) and Magnetic Resonance Imaging (MRI). DOS and MRI measurements were performed on an identical set of emulsion phantoms that were composed of different water/soybean oil fractions. Absolute concentrations of water and lipid ranging from 35-94% and 63-6%, respectively were calculated from quantitative broadband near-infrared (NIR) absorption spectra (650-1000 nm). MR images of fat and water were separated using the three-point Dixon technique. DOS and MRI measured water and lipid were highly correlated (R(2) = 0.98 and R(2) = 0.99, respectively) suggesting that these techniques are complementary over a broad range of physiologically relevant water and lipid values. In addition, comparison of DOS derived concentrations to the MRI "gold standard" technique validates our quantitation approach and permits estimation of DOS accuracy and sensitivity in vivo.

Spectroscopy enhances the information content of optical mammography

Near-infrared (NIR) diffuse optical spectroscopy and imaging may enhance existing technologies for breast cancer screening, diagnosis, and treatment. NIR techniques are based on quantitative measurements of functional contrast between healthy and diseased tissue. In this study we measured the spectral dependence of tissue absorption (mu(a)) and reduced scattering (mu'(s)) in the breasts of 30 healthy women and one woman with a fibroadenoma using a seven-wavelength frequency-domain photon migration probe. Subjects included pre- and postmenopausal women between the ages of 18 and 64. Multi-spectral measurements were used along with a four-component fit to determine the concentrations of de-oxy and oxy-hemoglobin, water and lipids in breast. The scattering spectral shape was also quantified. Our measurements demonstrate that the measured concentrations of NIR analytes correlate well with known breast physiology. Although the tissue scattering at a single wavelength was found to have little value as a functional parameter, the dependence of the scattering on wavelength provided key insights into breast composition and physiology. Lipids and scattering spectra in the breast were found to increase and decrease, respectively, with increasing body mass index. Simple calculations are also provided to demonstrate potential penalties from ignoring the contributions of water and lipids in breast measurements. Finally, water is shown to be a possible indicator for detecting a fibroadenoma, whereas the hemoglobin saturation was found to be a poor indicator. Multi-spectral measurements, compared to measurements restricted to one or two wavelengths, provide additional information that may be useful in managing breast disease.

Sources of absorption and scattering contrast for near-infrared optical mammography

RATIONALE AND OBJECTIVES

Near-infrared (NIR) diffuse optical spectroscopy and imaging may enhance existing technologies for breast cancer screening, diagnosis, and treatment. NIR techniques are based on sensitive, quantitative measurements of functional contrast between healthy and diseased tissue. In this study, the authors quantified the origins of this contrast in healthy breasts.

MATERIALS AND METHODS

A seven-wavelength frequency-domain photon migration probe was used to perform noninvasive NIR measurements in the breasts of 28 healthy women, both pre- and postmenopausal, aged 18-64 years. A diffusive model of light transport quantified oxygenated and deoxygenated hemoglobin, water, and lipid by their absorption signatures. Changes in the measured light-scattering spectra were quantified by means of a "scatter power" parameter.

RESULTS

Substantial quantitative differences were observed in both absorption and scattering spectra of breast as a function of subject age. These physiologic changes were consistent with long-term hormone-dependent transformations that occur in breast. Instrument response was not adversely affected by subject age or menopausal status.

CONCLUSION

These measurements provide new insight into endogenous optical absorption and scattering contrast mechanisms and have important implications for the development of optical mammography. NIR spectroscopy yields quantitative functional information that cannot be obtained with other noninvasive radiologic techniques.

Broadband absorption spectroscopy in turbid media by combined frequency-domain and steady-state methods

A technique for measuring broadband near-infrared absorption spectra of turbid media that uses a combination of frequency-domain (FD) and steady-state (SS) reflectance methods is presented. Most of the wavelength coverage is provided by a white-light SS measurement, whereas the FD data are acquired at a few selected wavelengths. Coefficients of absorption (mu(a)) and reduced scattering (mu(s)') derived from the FD data are used to calibrate the intensity of the SS measurements and to estimate mu(s)' at all wavelengths in the spectral window of interest. After these steps are performed, one can determine mu(a) by comparing the SS reflectance values with the predictions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined SSFD technique, agree well with expected reference values. All measurements can be performed at a single source-detector separation distance, reducing the variations in sampling volume that exist in multidistance methods. The technique uses relatively inexpensive light sources and detectors and is easily implemented on an existing multiwavelength FD system.

Experimental verification of a theory for the time-resolved fluorescence spectroscopy of thick tissues

Fluorescence spectroscopy provides potential contrast enhancement for near-infrared tissue imaging and physiologically correlated spectroscopy. We present a fluorescence photon migration model and test its quantitative predictive capabilities with a frequency-domain measurement that involves a homogeneous multiple-scattering tissue phantom (with optical properties similar to those of tissue in the near infrared) that contains a fluorophore (rhodamine B). After demonstrating the validity of the model, we explore its ability to recover the fluorophore's spectral properties from within the multiple-scattering medium. The absolute quantum yield and the lifetime of the fluorophore are measured to within a few percent of the values measured independently in the absence of scattering. Both measurements are accomplished without the use of reference fluorophores. In addition, the model accurately predicts the fluorescence emission spectrum in the scattering medium. Implications of these absolute measurements of lifetime, quantum yield, concentration, and emission spectrum from within multiple-scattering media are discussed.

Frequency-domain method for measuring spectral properties in multiple-scattering media: methemoglobin absorption spectrum in a tissuelike phantom

We have measured the optical absorption and scattering coefficient spectra of a multiple-scattering medium (i.e., a biological tissue-simulating phantom comprising a lipid colloid) containing methemoglobin by using frequency-domain techniques. The methemoglobin absorption spectrum determined in the multiple-scattering medium is in excellent agreement with a corrected methemoglobin absorption spectrum obtained from a steady-state spectrophotometer measurement of the optical density of a minimally scattering medium. The determination of the corrected methemoglobin absorption spectrum takes into account the scattering from impurities in the methemoglobin solution containing no lipid colloid. Frequency-domain techniques allow for the separation of the absorbing from the scattering properties of multiple-scattering media, and these techniques thus provide an absolute measurement of the optical absorption spectra of the methemoglobin/lipid colloid suspension. One accurately determines the absolute methemoglob in absorption spectrum in the frequency domain by extracting the scattering and absorption coefficients from the phase shift Φ and average light intensity DC (or Φ and the amplitude of the light-intensity oscillations AC) data with relationships provided by diffusion theory, but one determines it less accurately by using the Φ and modulation M (M ≡ AC/DC) data and the diffusion theory relationships. In addition to the greater uncertainty in the absorption and scattering coefficients extracted from the Φ and M data, the optical parameters extracted from the Φ and M data exhibit systematically inaccurate behavior that cannot be explained by random noise in the system. Possible reasons for the systematically lower accuracy of the methemoglobin absorption spectrum obtained from Φ and M data are discussed.