Coregistration of diffuse optical spectroscopy and magnetic resonance imaging in a rat tumor model

We report coregistration of near-infrared diffuse optical spectroscopy (DOS) and magnetic resonance imaging (MRI) for the study of animal model tumors. A combined broadband steady-state and frequency-domain apparatus was used to determine tissue oxyhemoglobin, deoxyhemoglobin, and water concentration locally in tumors. Simultaneous MRI coregistration provided structural (T2-weighted) and contrast-enhanced images of the tumor that were correlated with the optical measurements. By use of Monte Carlo simulations, the optically sampled volume was superimposed on the MR images, showing precisely which tissue structure was probed optically. DOS and MRI coregistration measurements were performed on seven rats over 20 days and were separated into three tumor tissue classifications: viable, edematous, and necrotic. A ratio of water concentration to total hemoglobin concentration, as measured optically, was performed for each tissue type and showed values for edematous tissue to be greater than viable tissue (1.2 +/- 0.49 M/microM versus 0.48 +/- 0.15 M/microM). Tissue hemoglobin oxygen saturation (StO2) also showed a large variation between tissue types: viable tissue had an optically measured StO2 value of 61 +/- 5%, whereas StO2 determined for necrotic tissue was 43 +/- 6%.     

In vivo breast imaging with diffuse optical tomography based on higher-order diffusion equations

We report on in vivo absorption and scattering imaging of a human breast cyst and implant, using a reconstruction algorithm based on our third-order diffusion equations. To validate these in vivo images, a series of phantom experiments were conducted, in which we used low-absorbing and low-scattering heterogeneities to mimic a breast cyst or implant. These heterogeneities or targets were composed of pure water or a mixture of water and very dilute Intralipid (0.05% and 0.1%). The phantom experiment confirmed the quantitative imaging capability of our improved algorithm for reconstructing heterogeneities where the conventional diffusion approximation is inadequate. Pilot clinical results from female volunteers indicate that enhanced diffuse optical tomography can quantitatively image findings such as breast cysts or implants in which the absorption and scattering coefficients are usually low.     

Fast multispectral diffuse optical tomography system for in vivo three-dimensional imaging of seizure dynamics

We describe a multispectral continuous-wave diffuse optical tomography (DOT) system that can be used for in vivo three-dimensional (3-D) imaging of seizure dynamics. Fast 3-D data acquisition is realized through a time multiplexing approach based on a parallel lighting configuration--our system can achieve 0.12 ms per source per wavelength and up to a 14 Hz sampling rate for a full set of data for 3-D DOT image reconstruction. The system is validated using both static and dynamic tissue-like phantoms. An initial in vivo experiment using a rat model of seizure is also demonstrated.     

Gold-coated iron oxide nanoparticles as a T2 contrast agent in magnetic resonance imaging

Gold-coated iron oxide (Fe3O4) nanoparticles were synthesized for use as a T2 contrast agent in magnetic resonance imaging (MRI). The coated nanoparticles were spherical in shape with an average diameter of 20 nm. The gold shell was about 2 nm thick. The bonding status of the gold on the nanoparticle surfaces was checked using a Fourier transform infrared spectrometer (FTIR). The FTIR spectra confirmed the attachment of homocysteine, in the form of thiolates, to the Au shell of the Au-Fe3O4 nanoparticles. The relaxivity ratio, R2/R1, for the coated nanoparticles was 3-fold higher than that of a commercial contrast agent, Resovist, which showed the potential for their use as a T2 contrast agent with high efficacy. In animal experiments, the presence of the nanoparticles in rat liver resulted in a 71% decrease in signal intensity in T2-weighted MR images, indicating that our gold-coated iron oxide nanoparticles are suitable for use as a T2 contrast agent in MRI.     

Photoacoustic tomography of a rat cerebral cortex in vivo with au nanocages as an optical contrast agent

Poly(ethylene glycol)-coated Au nanocages have been evaluated as a potential near-infrared (NIR) contrast agent for photoacoustic tomography (PAT). Previously, Au nanoshells were found to be an effective NIR contrast agent for PAT; however, Au nanocages with their more compact sizes (<50 nm compared to >100 nm for Au nanoshells) and larger optical absorption cross sections should be better suited for in vivo applications. We sequentially injected Au nanocages into the circulatory system of a rat in three administrations and in vivo PAT was conducted immediately prior to the first injection and continued until 5 h after the final injection. A gradual enhancement of the optical absorption in the cerebral cortex, by up to 81%, was observed over the course of the experiment.     

Properties of a versatile nanoparticle platform contrast agent to image and characterize atherosclerotic plaques by magnetic resonance imaging

The need for more specific and selective contrast agents for magnetic resonance imaging motivated us to prepare a new nanoparticle agent based on high-density lipoproteins (HDL). This second generation contrast agent can be prepared in three different ways. The HDL nanoparticles (rHDL) were fully characterized by FPLC and gel electrophoresis. The flexibility of the platform also allows us to incorporate optical probes into rHDL for localization ex vivo by confocal fluorescence microscopy. The contrast-agent-containing nanoparticles were injected into mice that develop atherosclerotic lesions. Magnetic resonance imaging of the animals showed clear enhancement of the atherosclerotic plaques.     

Time-resolved fluorescence polarization dynamics and optical imaging of Cytate: a prostate cancer receptor-targeted contrast agent

Cypate-octreote peptide analogue conjugate (Cytate) was investigated as a prostate cancer receptor-targeted contrast agent. The absorption and fluorescence spectra of Cytate were ranged in the near-infrared "tissue optical window." Time-resolved investigation of polarization-dependent fluorescence emitted from Cytate in solution as well as in cancerous and normal prostate tissues was conducted. Polarization preservation characteristics of Cytate in solution and tissues were studied. Fluorescence intensity emitted from the Cytate-stained cancerous prostate tissue was found to be much stronger than that from the Cytate-stained normal prostate tissue, indicating more Cytate uptake in the former tissue type. The polarization anisotropy of Cytate contained in cancerous prostate tissue was found to be larger than that in the normal prostate tissue, indicating a larger degree of polarization preservation in Cytate-stained cancerous tissue. The temporal profiles of fluorescence from Cytate solution and from Cytate-stained prostate tissue were fitted using a time-dependent fluorescence depolarization model. The photoluminescence imaging of Cytate-stained cancerous and normal prostate tissues was accomplished, showing the potential of Cytate as a fluorescence marker for prostate cancer detection.     

SURF imaging: in vivo demonstration of an ultrasound contrast agent detection technique

A dual-band method for ultrasound contrast agent detection is demonstrated in vivo in an animal experiment using pigs. The method is named Second -order UltRasound Field Imaging, abbreviated SURF Imaging. It relies on simultaneously transmitting two ultrasound pulses with a large separation in frequency. Here, a low-frequency pulse of 0.9 MHz is combined with a high-frequency pulse of 7.5 MHz. The low-frequency pulse is used to manipulate the properties of the contrast agent, and the high frequency pulse is used for high-resolution contrast detection and imaging. An annular array capable of transmitting the low- and high-frequency pulses simultaneously was constructed and fitted to a mechanically scanned probe used in a GE Vingmed System 5 ultrasound scanner. The scanner was modified and adapted for the dual-band transmit technique. In-house software was written for post-processing of recorded IQ-data. Contrast-processed B-mode images of pig kidneys after bolus injections of 1 mL of Sonovuer are presented. The images display contrast detection with contrast-to-tissue ratios ranging from 15-40 dB. The results demonstrate the potential of SURF Imaging as an ultrasound contrast detection technique for clinically high ultrasound frequencies. This may allow ultrasound contrast imaging to be available for a wide range of applications.     

Characterization of the biocompatible magnetic colloid on the basis of Fe3O4 nanoparticles coated with dextran, used as contrast agent in magnetic resonance imaging

The magnetic resonance imaging contrast agent, the so-called Endorem colloidal suspension on the basis of superparamagnetic iron oxide nanoparticles (mean diameter of 5.5 nm) coated with dextran, were characterized on the basis of several measurement techniques to determine the parameters of their most important physical and chemical properties. It is assumed that each nanoparticle is consisted of Fe3O4 monodomain and it was observed that its oxidation to gamma-Fe2O3 occurs at 253.1 degrees C. The M?ssbauer spectroscopy have shown a superparamagnetic behavior of the magnetic nanoparticles. The Magnetic Resonance results show an increase of the relaxation times T1, T2, and T2* with decreasing concentration of iron oxide nanoparticles. The relaxation effects of SPIONs contrast agents are influenced by their local concentration as well as the applied field strength and the environment in which these agents interact with surrounding protons. The proton relaxation rates presented a linear behavior with concentration. The measured values of thermo-optic coefficient dn/dT, thermal conductivity kappa, optical birefringence delta n0, nonlinear refractive index n2, nonlinear absorption beta' and third-order nonlinear susceptibility |chi(3)| are also reported.     

In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry

Methods for local photon path length and optical properties estimation, based on measured and simulated diffuse reflectance within 2 mm from the light source, are proposed and evaluated in vivo on Caucasian human skin. The accuracy of the methods was good (2%-7%) for path length and reduced scattering but poor for absorption estimation. Reduced scattering and absorption were systematically lower in the fingertip than in the forearm skin (633 nm). A maximum intrasite and interindividual variation of approximately 35% in an average photon path length was found. The methodology was applied in laser Doppler flowmetry, where path-length normalization of the estimated perfusion removed the optical property dependency.     

Quantitative analysis of cerebrospinal fluid flow in complex regions by using phase contrast magnetic resonance imaging

To develop a method for segmenting cerebrospinal fluid (CSF) regions with complex, inhomogeneous pulsatile patterns in phase contrast magnetic resonance imaging (PC‐MRI) sequences. Our approach used various temporal features of flow behavior as input attributes in an unsupervised k‐means classification algorithm. CSF flow parameters for the cervical subarachnoid spaces and the pontine cistern were calculated in 26 healthy volunteers. Background and aliasing corrections were applied automatically. The algorithm's reproducibility was determined by calculating two parameters (area and stroke volume) while varying the initially selected seed point. The influence of background correction on these parameters was also assessed. The method was highly reproducible, with coefficients of variation of 3 and 4% for the cervical stroke volume and area, respectively. In an analysis of variance, background correction did not have a statistically significant effect on either the stroke volume (p = 0.32) or the CSF net mean flow (p = 0.69) at the C2C3 level. The method presented here enables rapid, reproducible, quantitative analysis of CSF flow in complex regions such as the C2C3 subarachnoid spaces and the pontine cistern. © 2011 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 21, 290–297, 2011;     

Fluorescent liposomes as contrast agents for in vivo optical imaging of edemas in mice

This study assesses if specially designed fluorescent liposomes can be used as contrast agent for near-infrared fluorescence (NIRF) optical imaging of cultured macrophages in vitro and for NIRF imaging of inflammatory processes, like edema, in an in vivo mouse model. Fluorescent liposomes are prepared by the film hydration and extrusion method using cholesterol, L-phosphatidylcholine, and the NIR fluorescent dye DY-676-C(18) ester. Photon correlation spectroscopy and flow cytometry reveal that fluorescent liposomes are structurally stable for up to 133 days. Distinct uptake/labeling of cultured murine J774 macrophages is demonstrated by confocal laser scanning microscopy (CLSM), flow cytometry, and macroscopic NIRF imaging system at wavelengths >670 nm. Moreover, CLSM analysis reveals fluorescence signals within intracellular compartments. Ear edema is induced in mice (n = 16) by subcutaneous injection of zymosan A. Whole-body NIRF imaging is performed after intravenous injection (0-24 h) of fluorescent liposomes (55 nmol dye per kg body weight). Distinctly higher fluorescence intensities (1613.6 +/- 61.7 a.u.) are detected at inflamed areas of diseased mice as compared to controls (892.8 +/- 19.4 a.u.). Furthermore, cell isolated from ear lavage reveals the presence of labeled F4/80 positive tissue macrophages. Taken together, the results indicate both that mouse macrophages labeled with fluorescent liposomes can be detected in vitro with fluoro-optical methods and that in vivo optical imaging of inflammatory processes with fluorescent liposomes as contrast agent is feasible. Possibly, early stages of other inflammatory diseases could also be detected by the proposed diagnostic tool in the long term.     

Targeted nanoparticles for the non-invasive detection of traumatic brain injury by optical imaging and fluorine magnetic resonance imaging

Necrosis is a form of cell death that occurs only under pathological conditions such as ischemic diseases and traumatic brain injury (TBI). Non-invasive imaging of the affected tissue is a key component of novel therapeutic interventions and measurement of treatment responses in patients. Here, we report a bimodal approach for the detection and monitoring of TBI. PEGylated poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs), encapsulating both near infrared (NIR) fluorophores and perfluorocarbons (PFCs), were targeted to necrotic cells. We used cyanine dyes such as IRDye 800CW, for which we have previously demonstrated specific targeting to intracellular proteins of cells that have lost membrane integrity. Here, we show specific in vivo detection of necrosis by optical imaging and fluorine magnetic resonance imaging (¹⁹F MRI) using newly designed PLGA NP(NIR700 + PFC)-PEG-800CW. Quantitative ex vivo optical imaging and ¹⁹F MR spectroscopy of NIR-PFC content in injured brain regions and in major organs were well correlated. Both modalities allowed the in vivo identification of necrotic brain lesions in a mouse model of TBI, with optical imaging being more sensitive than ¹⁹F MRI. Our results confirm increased blood pool residence time of PLGA NPs coated with a PEG layer and the successful targeting of TBI-damaged tissue. A single PLGA NP containing NIR-PFC enables both rapid qualitative optical monitoring of the TBI state and quantitative 3D information from deeper tissues on the extent of the lesion by MRI. These necrosis-targeting PLGA NPs can potentially be used for clinical diagnosis of brain injuries.

Open image in new window

     

In vivo near-infrared spectroscopy of rat skin tissue with varying blood glucose levels

We have performed in vivo measurements of near-infrared rat skin absorption in the 4000-5000-cm(-1) spectral range (2.0-2.5-microm wavelength) during a glucose clamp experiment in order to identify the presence of glucose-specific spectral information. Spectra were collected during an initial 3-h period where the animal's blood glucose concentration was held at its normal value. The blood glucose level was then increased above 30 mM by venous infusion of glucose and held for 2 h, after which it was allowed to return to normal. Spectra were recorded continuously during the procedure and are analyzed to identify spectral changes associated with changes in glucose concentration. Because the change in absorbance due to an increase in glucose concentration is small compared to changes due to other variations (e.g., the thickness of the skin sample), a simple subtraction of absorbance spectra from the hyperglycemic and euglycemic phases is not instructive. Instead, a set of principal components is established from the euglycemic period where the glucose concentration is constant. We then examine the change in absorbance during the hyperglycemic period that is orthogonal to these principal components. We find that there are significant similarities between these orthogonal variations and the net analyte signal of glucose, which suggests that glucose spectral information is present. The analysis described here provides a procedure by which the analytical significance of a multivariate calibration can be evaluated.     

Pore structure and sorption properties of silica aerogels studied by magnetic resonance imaging and pulsed-field gradient spectroscopy

Magnetic resonance imaging (MRI) has provided direct visualization of gaseous xenon and methane in the void spaces of aerogels, offering unique information and insights into the pore structure and molecular diffusivities of occluded sorbates. Nuclear magnetic resonance (NMR) pulsed-field gradient (PFG) techniques were used to characterize exchange and diffusive motion of sorbed xenon gas at equilibrium. PFG measurements showed evidence of anisotropic diffusion; nominal self-diffusivity coefficients of xenon on the order of D = 10(-7) m2/s were determined. Based on a mathematical relationship for the restricted diffusion of gases in confined environments, an expression for estimating the mean free path was derived, from which the average pore size could be obtained from the extrapolated value of the diffusion coefficient to low xenon pressures.     

Robust inference of baseline optical properties of the human head with three-dimensional segmentation from magnetic resonance imaging

We model the capability of a small (6-optode) time-resolved diffuse optical tomography (DOT) system to infer baseline absorption and reduced scattering coefficients of the tissues of the human head (scalp, skull, and brain). Our heterogeneous three-dimensional diffusion forward model uses tissue geometry from segmented magnetic resonance (MR) data. Handling the inverse problem by use of Bayesian inference and introducing a realistic noise model, we predict coefficient error bars in terms of detected photon number and assumed model error. We demonstrate the large improvement that a MR-segmented model can provide: 2-10% error in brain coefficients (for 2 x 10(6) photons, 5% model error). We sample from the exact posterior and show robustness to numerical model error. This opens up the possibility of simultaneous DOT and MR for quantitative cortically constrained functional neuroimaging.     

Magnetic resonance imaging contrast agent: cRGD-ferric oxide nanometer particle and its role in the diagnosis of tumor

To construct tumor-targeted nanometer particles as a negative magnetic resonance imaging (MRI) contrast agent. Ultra-small superparamagnetic iron oxide (USPIO) nanometer particles were prepared by one-step chemical precipitation. The covalent bond between cyclic RGD (cRGD) containing an Arg-Gly-Asp sequence targeting integrin-alphavbeta3, and USPIO was conducted by chemical crosslinking. The physico-chemical property of cRGD-USPIO was detected. Prussian blue staining was applied to detect the specific binding capacity of cRGD-USPIO and USPIO to human pulmonary adenocarcinoma A549 cells and human umbilical vein endothelial cells. Subsequently, A549 xenografts in nude mice were established, and intravenous injections of USPIO and cRGD-USPIO into the vena caudalis were performed. The enhancement of cRGD-USPIO against tumor MRI signal was evaluated. The mean hydrodynamic diameter of cRGD-USPIO was 43.97 +/- 10.10 nm and the size of the ferric oxide core was 5-10 nm. The specific saturation magnetization was 59.94 A x m2 x Kg(-1). The cell conjugation assay results indicated that the positive staining of the cRGD-USPIO group was significantly enhanced. The in vivo MRI diagnosis indicated that the cRGD-USPIO tumor signal was significantly reduced compared to that of the USPIO group (P < 0.01). The targeted superparamagnetic iron oxide nanometer particle can be a novel MRI negative contrast agent for more specific tumor early diagnosis.     

Spectroscopic imaging for detection of ischemic injury in rat kidneys by use of changes in intrinsic optical properties

It is currently impossible to consistently predict kidney graft viability and function before and after transplantation. We explored optical spectroscopy to assess the degree of ischemic damage in kidney tissue. Tunable UV laser excitation was used to record autofluorescence images, at different spectral ranges, of injured and contralateral control rat kidneys to reveal the excitation conditions that offered optimal contrast. Autofluorescence and near-infrared cross-polarized light-scattering imaging were both used to monitor changes in intensity and spectral characteristics, as a function of exposure time to ischemic injury. These two modalities provided different temporal behaviors, arguably arising from two different mechanisms providing direct correlation of intrinsic optical signatures to ischemic injury time.