Purpose: Our purpose is to develop and test a molecular probe that can detect the expression of neutropilin-1 receptor
(NPR-1) in vivo using fluorescence imaging and photoacoustic spectroscopy.
Introduction: NPR-1 is expressed on endothelial cells and some breast cancer cells, and binds to vascular endothelial
growth factor VEGF165, a growth factor associated with pathological tumor angiogenesis. This receptor is coexpressed
with VEGFR2 and shown to enhance the binding of VEGF165; therefore, it has the potential to be used as a
marker of angiogenic activity and targeted for therapy.
Material and Methods: A peptide specific to NPR-1 receptor was synthesized and conjugated to a NIR fluorochrome
(IRDye800CW) and was intravenously injected into mice with breast tumors (MCF7VEGF). Probe kinetics was
monitored in vivo via near infrared fluorescence (NIRF) within an optical imager for up to 72 hours within the tumor
and compared to other organs (liver, muscle) for binding specificity. A multivariate fitting algorithm was used to
spectrally deconvolve the IRDye800CW from endogenous hemoglobin signature (hemoglobin concentration and
Results: Dynamics of the NIR fluorescence signal within the first hour after injection indicates specific binding
compared to muscle, with an average tumor-to-muscle ration of 2.00 (+/- 0.27). Spectral analysis clearly indentified
the presence of the NPR-1 probe. Based on calibration data, the average tumor concentration from both NIRF and
PCT-S was measured to be ~200-300nM.
Conclusion: These preliminary results show the capability of PCT to image an exogenous probe in vivo in addition to
its hemoglobin state.
Purpose: The purpose of this study is to monitor in vivo the IR dose dependent response of NF-κB and tumor
hemodynamics as a function of time.
Material and Methods: An MDA-231 breast cancer cell line was stably transfected with a firefly luciferase gene
within the NF-kappaB promoter. Tumors on the right flank irradiated with a single fractionated dose of 5Gy or 10Gy.
Over two weeks, photoacoustic spectroscopy (PCT-S), bioluminescence imaging (BLI), and dynamic contrast
enhanced CT (DCE-CT) was used to monitor hemoglobin status, NF-kappaB expression, and physiology, respectively.
Results: From the BLI, an increase in NF-kappaB expression was observed in both the right (irradiation) and left (nonirradiated)
tumors, which peaked at 8-12 hours, returned to basal levels after 24 hours, and increased a second time
from 3 to 7 days. This data identifies both a radiation-induced bystander effect and a bimodal longitudinal response
associated with NF-κB-controlled luciferase promoter. The physiological results from DCE-CT measured an increase
in perfusion (26%) two days after radiation and both a decrease in perfusion and an increase in fp by week 1 (10Gy
cohort). PCT-S measured increased levels of oxygen saturation two days post IR, which did not change after 1 week.
Initially, NF-κB would modify hemodynamics to increase oxygen delivery after IR insult. The secondary response
appears to modulate tumor angiogenesis.
Conclusions: A bimodal response to radiation was detected with NF-kappaB-controlled luciferase reporter with a
concomitant hemodynamic response associated with tumor hypoxia. Experiments are being performed to increase
Monte Carlo simulation experiments have shown that very high energy electrons (VHEE), 150-250 MeV, have potential
advantages in prostate cancer treatment over currently available electrons, photon and proton beam treatment. Small
diameter VHEE beamlets can be scanned, thereby producing a finer resolution intensity modulated treatment than
photon beams. VHEE beams may be delivered with greater precision and accelerators may be constructed at
significantly lower cost than proton beams. A VHEE accelerator may be optimally designed using laser-plasma
technology. If the accelerator is constructed to additionally produce low energy photon beams along with VHEE, real
time imaging, bioprobing, and dose enhancement may be performed simultaneously. This paper describes a Monte Carlo
experiment, using the parameters of the electron beam from the UCLA laser-plasma wakefield accelerator, whereby dose
distributions on a human prostate are generated. The resulting dose distributions of the very high energy electrons are
shown to be comparable to photon beam dose distributions. This simple experiment illustrates that the nature of the dose
distribution of electrons is comparable to that of photons. However, the main advantage of electrons over photons and
protons lies in the delivery and manipulation of electrons, rather than the nature of the dose distribution. This paper
describes the radiation dose delivery of electrons employing technologies currently in exploration and evaluates potential
benefits as compared with currently available photon and protons beams in the treatment of prostate and other cancers,
commonly treated with radiation.
Purpose: To evaluate photoacoustic CT spectroscopy (PCT-S) and dynamic contrast-enhanced CT (DCE-CT) ability to measure parameters - oxygen saturation and vascular physiology - associated with the intra-tumor oxygenation status.
Material and Methods: Breast (VEGF165 enhance MCF-7) and ovarian (SKOV3x) cancer cells were implanted into the fat pads and flanks of immune deficient mice and allowed to grow to a diameter of 8-15 mm. CT was used to determine physiological parameters by acquiring a sequence of scans over a 10 minute period after an i.v. injection of a radio-opaque contrast agent (Isovue). These time-dependent contrast-enhanced curves were fit to a two-compartmental model determining tumor perfusion, fractional plasma volume, permeability-surface area produce, and fractional interstitial volume on a voxel-by-voxel basis. After which, the tumors were imaged using photoacoustic CT (Optosonics, Inc., Indianapolis, IN 46202). The near infrared spectra (700-910 nm) within the vasculature was fit to linear combination of measured oxy- and deoxy-hemoglobin blood samples to obtain oxygen saturation levels (SaO2).
Results: The PCT-S scanner was first calibrated using different samples of oxygenated blood, from which a statistical error ranging from 2.5-6.5% was measured and a plot of the hemoglobin dissociation curve was consistent with empirical formula. In vivo determination of tumor vasculature SaO2 levels were measurably tracked, and spatially correlated to the periphery of the tumor. Tumor depend variations in SaO2 - 0.32 (ovarian) and 0.60 (breast) - and in vascular physiology - perfusion, 1.03 and 0.063 mL/min/mL, and fractional plasma volume, 0.20 and 0.07 - were observed.
Conclusion: Combined, PCT-S and CED-CT has the potential to measure intra-tumor levels of tumor oxygen saturation and vascular physiology, key parameters associated with hypoxia.
Initial animal study for quantifying myocardial physiology through contrast-enhanced dynamic x-ray CT suggested that beam hardening is one of the limiting factors for accurate regional physiology measurement. In this study, a series of simulations were performed to investigate its deterioration effects and two correction algorithms were adapted to evaluate for their efficiency in improving the measurements.
The simulation tool consists of a module simulating data acquisition of a real polyenergetic scanner system and a heart phantom consisting of simple geometric objects representing ventricles and myocardium. Each phantom component was modeled with time-varying attenuation coefficients determined by ideal iodine contrast dynamic curves obtained from experimental data or simulation. A compartment model was used to generate the ideal myocardium contrast curve using physiological parameters consistent with measured values. Projection data of the phantom were simulated and reconstructed to produce a sequence of simulated CT images. Simulated contrast dynamic curves were fitted to the compartmental model and the resultant physiological parameters were compared with ideal values to estimate the errors induced by beam hardening artifacts.
The simulations yielded similar deterioration patterns of contrast dynamic curves as observed in the initial study. Significant underestimation of left ventricle curves and corruption of regional myocardium curves result in systematic errors of regional perfusion up to approximately 24% and overestimates of fractional blood volume (fiv) up to 13%. The correction algorithms lead to significant improvement with errors of perfusion reduced to 7% and errors of fiv within 2% which shows promise for more robust myocardial physiology measurement.
Purpose. To evaluate photoacoustic spectroscopy as a potential imaging modality capable of measuring intra-tumor heterogeneity and spectral features associated with hemoglobin and the molecular probe indocyanine green (ICG). Material and Methods. Immune deficient mice were injected with wildtype and VEGF enhanced MCF-7 breast cancer cells or SKOV3x ovarian cancer cells, which were allowed to grow to a size of 6-12 mm in diameter. Two mice were imaged alive and after euthanasia for (oxy/deoxy)-hemoglobin content. A 0.4 mL volume of 1 μg/mL concentration of ICG was injected into the tail veins of two mice prior to imaging using the photoacoustic computed tomography (PCT) spectrometer (Optosonics, Inc., Indianapolis, IN 46202) scanner. Mouse images were acquired for wavelengths spanning 700-920 nm, after which the major organs were excised, and similarly imaged. A histological study was performed by sectioning the organ and optically imaging the fluorescence distribution. Results. Calibration of PCT-spectroscopy with different samples of oxygenated blood reproduced a hemoglobin dissociation curve consistent with empirical formula with an average error of 5.6%. In vivo PCT determination of SaO2 levels within the tumor vascular was measurably tracked, and spatially correlated to the periphery of the tumor. Statistical and systematic errors associated with hypoxia were estimated to be 10 and 13%, respectively. Measured ICG concentrations determined by contrast-differential PCT images in excised organs (tumor, liver) were approximately 0.8 μg/mL, consistent with fluorescent histological results. Also, the difference in the ratio of ICG concentration in the gall bladder-to-vasculature between the mice was consistent with excretion times between the two mice. Conclusion. PCT spectroscopic imaging has shown to be a noninvasive modality capable of imaging intra-tumor heterogeneity of (oxy/deoxy)-hemoglobin and ICG in vivo, with an estimated error in SaO2 at 17% and in ICG at 0.8 μg/mL in excised tissue. Ongoing development of spectroscopic analysis techniques, probe development, and calibration techniques are being developed to improve sensitivity to both exogenous molecular probes and (oxy/deoxy)-hemoglobin fraction.
Purpose: The purpose of this study is to evaluate multi-slice computed tomography technology to quantify functional and physiologic changes in rats with pulmonary emphysema. Method: Seven rats were scanned using a 16-slice CT (Philips MX8000 IDT) before and after artificial inducement of emphysema. Functional parameters i.e. lung volumes were measured by non-contrast spiral scan during forced breath-hold at inspiration and expiration followed by image segmentation based on attenuation threshold. Dynamic CT imaging was performed immediately following the contrast injection to estimate physiology changes. Pulmonary perfusion, fractional blood volume, and mean transit times (MTTs) were estimated by fitting the time-density curves of contrast material using a compartmental model. Results: The preliminary results indicated that the lung volumes of emphysema rats increased by 3.52±1.70mL (p<0.002) at expiration and 4.77±3.34mL (p<0.03) at inspiration. The mean lung densities of emphysema rats decreased by 91.76±68.11HU (p<0.01) at expiration and low attenuation areas increased by 5.21±3.88% (p<0.04) at inspiration compared with normal rats. The perfusion for normal and emphysema rats were 0.25±0.04ml/s/ml and 0.32±0.09ml/s/ml respectively. The fractional blood volumes for normal and emphysema rats were 0.21±0.04 and 0.15±0.02. There was a trend toward faster MTTs for emphysema rats (0.42±0.08s) than normal rats (0.89±0.19s) with p<0.006, suggesting that blood flow crossing the capillaries increases as the capillary volume decreases and which may cause the red blood cells to leave the capillaries incompletely saturated with oxygen if the MTTs become too short. Conclusion: Quantitative measurement using CT of structural and functional changes in pulmonary emphysema appears promising for small animals.