Quantitative assessment of renal arterial occlusion in a porcine model using spatial frequency domain imaging.

We present the results of a feasibility study with spatial frequency domain imaging (SFDI) to produce quantitative measurements of optical property and chromophore concentration maps of three porcine kidneys utilizing a renal occlusion model at the near-infrared wavelengths of 658, 730, and 850 nm. Using SFDI, we examined the dynamics of absolute oxygen saturation (StO2). The mean StO2 for the kidneys varied from approximately 60% before occlusion, to 20% during occlusion, to 55% after reperfusion. We also present, for the first time to the best of our knowledge, reduced scattering coefficient (µ(s)') maps of the kidney during occlusion. We observed a substantial decrease in the wavelength dependence of scattering (i.e., scattering power) in the three kidneys, with a mean decrease of 18%±2.6%, which is indicative of an increase in scatterer size, and is likely due to tissue changes such as edema that follow from occlusion and inflammation.

A light emitting diode (LED) based spatial frequency domain imaging system for optimization of photodynamic therapy of nonmelanoma skin cancer: quantitative reflectance imaging.

BACKGROUND: Photodynamic therapy (PDT) offers the potential for enhanced treatment of nonmelanoma skin cancer (NMSC) with minimal scarring. Yet, PDT has not achieved consistent long term effectiveness to gain widespread clinical acceptance for treatment of skin cancer. Therapeutic response varies between practitioners, patients and lesions. One important contributing factor is the absence of quantitative tools to perform in vivo dosimetry. To this end, we have developed a new quantitative imaging device that can be used to investigate parameters related to optimizing dosimetry. METHODS: We present a spatial frequency domain imaging (SFDI) based device designed to: (1) determine the optical properties at the therapeutic wavelength, which can inform variations in light penetration depth and (2) measure the spatially resolved oxygen saturation of the skin cancer lesions and surrounding tissue. We have applied this system to a preliminary clinical study of nine skin cancer lesions. RESULTS: Optical properties vary greatly both spatially [101%, 48% for absorption and reduced scattering, respectively] and across patients [102%, 57%]. Blood volume maps determined using visible wavelengths (460, 525, and 630 nm) represent tissue volumes within ∼1 mm in tissue (1.17 ± 0.3 mm). Here the average total hemoglobin concentration is approximately three times greater in the lesion than that detected in normal tissue, reflecting increased vasculature typically associated with tumors. Data acquired at near infrared wavelengths (730 and 850 nm) reports tissue blood concentrations and oxygenations from the underlying dermal microvasculature (volumes reaching 4.36 ± 1.32 mm into tissue). CONCLUSIONS: SFDI can be used to quantitatively characterize in vivo tissue optical properties that could be useful for better informing PDT treatment parameters. Specifically, this information provides spatially resolved insight into light delivery into tissue and local tissue oxygenation, thereby providing more quantitative and controlled dosimetry specific to the lesion. Ultimately, by optimizing the execution of PDT, this instrument has the potential to positively improve treatment outcomes.

Noninvasive clinical assessment of port-wine stain birthmarks using current and future optical imaging technology: a review.

Port-wine stain (PWS) birthmarks are one class of benign congenital vascular malformation. Laser therapy is the most successful treatment modality of PWS. Unfortunately, this approach has limited efficacy, with only 10% of patients experiencing complete blanching of the PWS. To address this problem, several research groups have developed technologies and methods designed to study treatment outcome and improve treatment efficacy. This article reviews seven optical imaging techniques currently in use or under development to assess treatment efficacy, focusing on: reflectance spectrophotometers/tristimulus colorimeters; laser Doppler flowmetry and laser Doppler imaging; cross-polarized diffuse reflectance colour imaging system; reflectance confocal microscopy; optical coherence tomography; spatial frequency domain imaging; and laser speckle imaging.

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.

In vivo fluorescence spectroscopy of nonmelanoma skin cancer.

In vivo and ex vivo tissue autofluorescence (endogenous fluorescence) have been employed to investigate the presence of markers that could be used to detect tissue abnormalities and/or malignancies. We present a study of the autofluorescence of normal skin and tumor in vivo, conducted on 18 patients diagnosed with nonmelanoma skin cancers (NMSC). We observed that both in basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) the endogenous fluorescence due to tryptophan residues was more intense in tumor than in normal tissue, probably due to epidermal thickening and/or hyperproliferation. Conversely, the fluorescence intensity associated with dermal collagen crosslinks was generally lower in tumors than in the surrounding normal tissue, probably because of degradation or erosion of the connective tissue due to enzymes released by the tumor. The decrease of collagen fluorescence in the connective tissue adjacent to the tumor loci was validated by fluorescence imaging on fresh-frozen tissue sections obtained from 33 NMSC excised specimens. Our results suggest that endogenous fluorescence of NMSC, excited in the UV region of the spectrum, has characteristic features that are different from normal tissue and may be exploited for noninvasive diagnostics and for the detection of tumor margins.

Amlodipine besylate induced acute interstitial nephritis.

Adverse effects of amlodipine besylate, a widely used antihypertensive medication, include peripheral edema, flushing, headache, pruritus, and rash. An adverse renal effect attributable to the medication has hitherto not been reported in the literature. We herein report a case of amlodipine besylate induced acute interstitial nephritis.

Chemometric analysis of frequency-domain photon migration data: quantitative measurements of optical properties and chromophore concentrations in multicomponent turbid media.

Frequency-domain photon migration (FDPM) is a widely used technique for measuring the optical properties (i.e., absorption, micro(a), and reduced scattering, micro(s)', coefficients) of turbid samples. Typically, FDPM data analysis is performed with models based on a photon diffusion equation; however, analytical solutions are difficult to obtain for many realistic geometries. Here, we describe the use of models based instead on representative samples and multivariate calibration (chemometrics). FDPM data at seven wavelengths (ranging from 674 to 956 nm) and multiple modulation frequencies (ranging from 50 to 600 MHz) were gathered from turbid samples containing mixtures of three absorbing dyes. Values for micro(a) and micro(s)' were extracted from the FDPM data in different ways, first with the diffusion theory and then with the chemometric technique of partial least squares. Dye concentrations were determined from the FDPM data by three methods, first by least-squares fits to the diffusion results and then by two chemometric approaches. The accuracy of the chemometric predictions was comparable or superior for all three dyes. Our results indicate that chemometrics can recover optical properties and dye concentrations from the frequency-dependent behavior of photon density waves, without the need for diffusion-based models. Future applications to more complicated geometries, lower-scattering samples, and simpler FDPM instrumentation are discussed.

Financial status does not predict weight loss after bariatric surgery.

BACKGROUND: Lower socioeconomic status and poor funding are thought to be associated with suboptimal outcome after bariatric surgery. We undertook this study to determine if funding status is a predictor of outcome in patients undergoing bariatric surgery. METHODS: The medical records of 131 consecutive patients who underwent vertical banded gastroplasty (VBG) for clinically severe obesity (BMI >40 kg/m2) were reviewed. Patients were divided into three groups based on insurance status: (1) commercially insured/traditional indemnity programs; (2) entitlement programs (Medicare), and (3) medically indigent (Medicaid or no funding). Data is mean +/- SD. Data was analyzed using ANOVA and Student t-test. RESULTS: The three groups had similar preoperative weight. Mean BMI was 39 +/- 13, 42 +/- 15, 41 +/- 11 at 1 year, and 40 +/- 13, 43 +/- 16, 45 +/- 16 at 2 years postoperatively for the insured, entitlement, and indigent groups, respectively. CONCLUSION: After standard preoperative evaluation and screening, patients loss weight following VBG independent of insurance status. Source of funding should, therefore, not preclude patients from undergoing bariatric surgery. Patients with limited financial resources can expect similar outcomes as patients with commercial insurance.

Comparison of methods to determine chromophore concentrations from fluorescence spectra of turbid samples.

BACKGROUND AND OBJECTIVE: This paper compares the ability of three analytic techniques to predict chromophore concentration from fluorescence emission spectra of homogeneous, turbid samples with optical properties similar to human tissue. STUDY DESIGN, MATERIALS AND METHODS: Two models of light propagation were implemented (exponential attenuation, two flux Kubelka-Munk theory); a priori information about sample optical properties was used to analyze data with the two flux Kubelka-Munk model. The third data analysis technique utilizes the method of partial least squares (PLS) to develop an empirical, linear model of sample fluorescence from a training set with optical properties and known concentrations representative of those to be predicted. This model can be applied to predict chromophore concentrations in the unknown samples. RESULTS: Of the three methods, PLS achieved the most accurate results and was able to predict fluorophore concentration to within +/- 6% of true values. CONCLUSION: We investigated conditions under which PLS predictions were most accurate and find that best results are achieved when predictions are based on fluorescence emission spectra at more than one excitation wavelength with inclusion of the tail of Rayleigh scattering at the excitation wavelength.

Relation between fluorescence spectra of dilute and turbid samples.

We present a method to extend rank-annihilation-factor analysis (RAFA) for the analysis of fluorescence from homogeneous turbid samples. The method is based on a fundamental relationship between the fluorescence of a dilute solution and that of a turbid solution. We have derived this relationship, known as the transfer function, for turbid materials using the two-flux Kubelka-Munk theory. The method is tested with spectroscopic data from optically thin and turbid samples of the media of a human aorta. At 450-nm excitation, agreement between the measured and predicted dilute-solution fluorescence spectra is within 5% at all emission wavelengths; at 340-nm excitation, agreement is within 20% at all wavelengths, with some residual Soret-band absorption. The simulations presented indicate that the transfer function is markedly more sensitive to absorption than to scattering properties.