Envision that you are sailing in your bloodstream. You are driftwood, propelled effortlessly by the thrust of every heartbeat…
For most of their medical careers, Farouc Jaffer
and Guillermo Tearney
have designed microscopic cameras that chart topographical maps of the cardiovascular system. Their latest innovation could revolutionize the way doctors monitor the artery clogging disease, atherosclerosis.
Unveiled in Nature Medicine last month, their study combines two preexisting techniques:
|Optical Coherence Tomography (OCT)
|Near-Infrared Fluorescence (NIRF)
(Overlaid on OCT scan)
Optical Coherence Tomography (OCT)* operates like sonar in a submarine, except it measures light rather than sound. First, a fiber optic probe connected to a laser is inserted into the bloodstream. Light is emitted from the probe, which reflects off the vessel walls. This lucent echo is recorded by a sensor in the probe, and this info is used to map the surface of the blood vessel.
While OCT surveys texture, Near-Infrared Fluorescence (NIRF) imaging explores the health of the tissue. In particular, it can locate atheroscelerotic plaques. Plaques stem from a vicious cycle of inflammation. Rather than fix an injured vessel, macrophages and T-cells establish a lesion within the arterial wall that gradually thickens. If left unabated, the lesion ruptures and can clog an artery.
NIRF hunts down plaques susceptible to rupture by assessing their molecular architecture. These attributes include unique structural components of the plaque along with the activities of inflammatory cells residing inside. Special light-sensitive dyes are injected into the body to label these different characteristics.
Jaffer and Tearney designed a fiber optic imaging probe – thinner than a dime! – that could simultaneously record OCT and NIRF signals. The result: gorgeous images of the body’s vascular labyrinth that can be used to guide surgery and treat atherosclerosis (Vid 1).
Video Description (paraphrased from paper)
Three-dimensional rendering of an OFDI-NIRF of a stent and plaque from a rabbit iliac artery in vivo.
Artery wall (red); stent (white); thrombus (purple).
The NIRF signal (flashing yellow; tagging fibrin) was overlaid on the luminal surface of the artery wall prior to volume rendering.
Yoo, H., Kim, J., Shishkov, M., Namati, E., Morse, T., Shubochkin, R., McCarthy, J., Ntziachristos, V., Bouma, B., Jaffer, F., & Tearney, G. (2011). Intra-arterial catheter for simultaneous microstructural and molecular imaging in vivo Nature Medicine, 17 (12), 1680-1684 DOI: 10.1038/nm.2555
Images and Video from Main Citation.
In truth, they used a faster version of OCT called optical frequency domain imaging (OFDI). High-resolution 3D images of the arterial wall can be collected within seconds. OFDI’s spatial resolution is also superior (~7 microns), which is 100 times finer than other conventional imaging techniques, such as MRI or ultrasound. Some of the light from the OFDI probe can penetrate the tissue before it is reflected back to the probe. Thus, OFDI can measure structural information beneath the surface of the vessel wall to a depth of 4-5 mm, which is really cool.