腹主动脉瘤的近红外荧光成像

Near-infrared fluorescence imaging is an optical technique using fluorescent probes to visualize biomolecular assemblies in tissues. Unlike SPECT and PET imaging, NIRF is rapid, high-throughput, and does not involve ionizing radiation. It uses light wavelengths between 650 and 900 nanometers that penetrate deep into tissue, enabling noninvasive disease visualization.

Fluorophores absorb near-infrared photons, raising their energy from ground state S0 to unstable excited state S1 prime. The molecules relax to the lowest vibrational level within the excited state, releasing energy as heat. They then return to ground state, emitting light with a longer wavelength than the excitation light, a phenomenon called the Stokes shift.

The Stokes shift is the difference in nanometers between peak absorption and peak emission wavelengths for a fluorophore. Each fluorophore has a distinct Stokes shift, allowing emitted light to be distinguished from exciting light. This property makes imaging techniques like NIRF possible by preventing interference between excitation and emission signals.

Anesthetize the animal using isoflurane in a knockdown chamber, then transfer it to a nose cone on the imaging stage. Secure the paws to minimize motion artifacts, apply depilatory cream to remove hair from the area of interest, and apply ophthalmic ointment to prevent corneal drying. Finally, inject the activatable fluorescent molecular probe into the animal.

Ex vivo imaging involves euthanizing the animal after fluorescent probe injection, then surgically extracting and rinsing tissue in phosphate buffered saline to remove residual blood. The tissue is then placed directly on the imaging stage and imaged using the same protocol as in vivo imaging, allowing detailed examination of specific organs or tissues.

NIRF imaging with activatable probes targeting matrix metalloproteinase-2 reveals increased MMP2 activity in aneurysmal regions of the abdominal aorta. The technique visualizes vasculature as tubular structures with high fluorescent signals, helping researchers study disease progression in different rodent models of abdominal aortic aneurysms.

NIRF imaging can detect tumor-like inclusions up to approximately two centimeters depth in breast tissue. After incisions are made, deeper inclusions become detectable. Surgeons use NIRF images to evaluate tissue after removal; remaining fluorescence indicates incomplete tumor removal, guiding further excision to ensure complete resection.