Cerenkov excited fluorescence tomography using external beam radiation.

Radiation treatment of cancer induces an optical Cerenkov emission throughout the treated volume, which could be used to excite molecular reporters in vivo, allowing molecular sensing of tissue response during fractionated therapy. In this Letter, the idea that spatial mapping of this signal can be achieved with tomographic recovery of the fluorophore distribution is tested for the first time using 6 MV photons from a linear accelerator in a heterogeneous tissue phantom. Cerenkov light excited fluorophores throughout the tissue phantom, and diffuse tomography was used to recover images. Measurements from 13 locations were used, with spectrometer detection and spectral fitting, to separate the fluorophore emission from the Cerenkov continuum. Fluorescent diffuse tomographic images showed a linear response between the concentration and the reconstructed values. The potential to apply this molecular imaging in treatment with molecular reporters appears promising.

Tomography of epidermal growth factor receptor binding to fluorescent Affibody in vivo studied with magnetic resonance guided fluorescence recovery in varying orthotopic glioma sizes.

The ability to image targeted tracer binding to epidermal growth factor receptor (EGFR) was studied in vivo in orthotopically grown glioma tumors of different sizes. The binding potential was quantified using a dual-tracer approach, which employs a fluorescently labeled peptide targeted to EGFR and a reference tracer with similar pharmacokinetic properties but no specific binding, to estimate the relative bound fraction from kinetic compartment modeling. The recovered values of binding potential did not vary significantly as a function of tumor size (1 to 33 mm3), suggesting that binding potential may be consistent in the U251 tumors regardless of size or stage after implantation. However, the fluorescence yield of the targeted fluorescent tracers in the tumor was affected significantly by tumor size, suggesting that dual-tracer imaging helps account for variations in absolute uptake, which plague single-tracer imaging techniques. Ex vivo analysis showed relatively high spatial heterogeneity in each tumor that cannot be resolved by tomographic techniques. Nonetheless, the dual-tracer tomographic technique is a powerful tool for longitudinal bulk estimation of receptor binding.

Next-generation Raman tomography instrument for non-invasive in vivo bone imaging.

Combining diffuse optical tomography methods with Raman spectroscopy of tissue provides the ability for in vivo measurements of chemical and molecular characteristics, which have the potential for being useful in diagnostic imaging. In this study a system for Raman tomography was developed and tested. A third generation microCT coupled system was developed to combine 10 detection fibers and 5 excitation fibers with laser line filtering and a Cytop reference signal. Phantom measurements of hydroxyapatite concentrations from 50 to 300 mg/ml had a linear response. Fiber placement and experiment design was optimized using cadaver animals with live animal measurements acquired to validate the systems capabilities. Promising results from the initial animal experiments presented here, pave the way for a study of longitudinal measurements during fracture healing and the scaling of the Raman tomography system towards human measurements.

Oxygen tomography by Cerenkov-excited phosphorescence during external beam irradiation.

The efficacy of radiation therapy depends strongly on tumor oxygenation during irradiation. However, current techniques to measure this parameter in vivo do not facilitate routine monitoring in patients. Herein, we demonstrate a noninvasive method for tomographic imaging of oxygen partial pressure (pO(2)) in deep tissue using the phosphorescence decay of an oxygen-sensitive probe excited by Cerenkov radiation induced by external beam radiotherapy. Tissue-simulating scattering phantoms (60 mm diameter with a 20 mm anomaly) containing platinum(II)-G4 (PtG4), a dendritic porphyrin-based phosphor, whose phosphorescence is quenched in the presence of oxygen, were irradiated with a clinical linear accelerator. The emitted phosphorescence was measured at various positions on the phantom boundary using a spectrograph coupled to an intensified charge-coupled device (ICCD). At each position, PtG4 phosphorescence decay curves were measured by synchronizing the ICCD to the linear accelerator pulses. Tomographic images of phosphorescence yield and lifetime were recovered for phantoms with homogenous PtG4 concentrations and heterogeneous pO(2). Since PtG4 lifetime is strongly and predictably dependent on pO(2) through the Stern-Volmer relationship, tomographic images of pO(2) were also reported, and showed excellent agreement with independent oxygenation measurements. Translating this approach to the clinic could facilitate direct sensing of pO(2) during radiotherapy.

Multichannel diffuse optical Raman tomography for bone characterization in vivo: a phantom study.

Raman spectroscopy is used to gather information on the mineral and organic components of bone tissue to analyze their composition. By measuring the Raman signal of bone through spatially offset Raman spectroscopy the health of the bone can be determined. We've customized a system with 8 collection channels that consist of individual fibers, which are coupled to separate spectrometers and cooled CCDs. This parallel detection system was used to scan gelatin phantoms with Teflon inclusions of two sizes. Raman signals were decoupled from the autofluorescence background using channel specific polynomial fitting. Images with high contrast to background ratios of Raman yield and accurate spatial resolution were recovered using a model-based diffuse tomography approach.