Nighthawk™
Nighthawk™
In the summer of 2006, the Foxhollow Technologies Nighthawk™ team successfully performed the first real-time optical coherence tomography (OCT) guided intravascular surgical procedure in humans at the American Heart of Poland Clinic in Bielsko-Biala [1,2]. Like LIGO [3], but on a massively different scale, Nighthawk™ used optical interferometry [4] to look into the wall of a blood vessel at almost cellular level resolution, with the goal of giving the surgeon a histology-like, real-time cross-sectional snap-shot of the inside of the blood vessel to allow a treatment decision to be made in real time.
The picture above shows an OCT cross-section of healthy coronary artery and next to it a cartoon of what one would see in an idealized histology slide. OCT clearly differentiates the intima (endothelium and internal elastic lamina), media (smooth muscle cells) and adventitia (connective tissue) in a manner that a surgeon can interpret, in real-time, with no post-processing. More interesting however are the images of diseased tissue. Early-stage arterial disease starts as intimal hyperplasia [5], where the intima, normally a single-cell thickness at the resolution limit of the device, has started to thicken in response to inflammation or lumen surface injury / insult. The picture below shows this intimal hyperplasia – the slight thickening of the intima compared to the healthy case above is clear but subtle. A saline-filled collateral branch is visible in the center of the image.
As the disease progresses the connection between the endothelium and internal elastic lamina (IEL) “unzippers” and a “plaque” develops in the interstitial space:
LDL (bad cholesterol) from the lumen penetrates through the endothelium, in response to which the lumen lining expresses VCAM (vascular cell adhesion molecule) which in turn recruits macrophages from the blood. Smooth muscle cells proliferate through the internal elastic lamina, and a plaque develops from the foam cells and apoptosis that results.
In the image above, the medial-adventitial boundary can just be made out under the hyperintense (bright) plaque signal.
The voids (hypointense (dark) holes with hyperintense streaks below them) in the image at the IEL / medial boundary are calcium hydroxyapatite (similar to tooth enamel) nodules, “spotty calcifications”, leading to the so-called (and physiologically quite real) hardening of arteries in advanced disease.
Nighthawk™ was an OCT-enabled atherectomy catheter with a rotating cutter that could shave off disease from the inside of the artery in thicknesses of approximately 250 microns and store the debris in the nosecone of the device, preventing embolization. A picture of the device with a red pilot laser beam (where the OCT beam would appear) is shown below. The cutter aperture is just to the right of the laser aperture, and the nose-cone (brown-silver spiral) where the tissue is packed is to the right of the cutter.
Rotating the catheter around inside the vessel gives a 360-degree view of the health of the vessel wall at clinically-relevant, intuitively-understandable, near-histological resolution, in real time, and with minimal clutter on the catheter.
The image below shows a picture of a silicone vessel phantom made using the NRC Canada technique [6] and where the Nighthawk™ has shaved a ~250-micron cut out of the inner wall (7- to 8-oclock position). It is immediately obvious that an OCT-guided cutter can make precision alterations to the wall of a vessel without perforating it, a critical advantage when performing coronary artery atherectomy.
The good news is that (a) the difference between healthy and unhealthy tissue is quite clear in OCT, so it can therefore reliably guide surgery, and (b) that the artery can re-endothelialize normally under the right conditions if the plaque is removed [5]. The bad news is that OCT images are unforgiving, to the point that a therapeutic result that looks good (great?) angiographically still shows plenty of disease in OCT! In addition to being one of the very earliest examples of the use of OCT to guide a therapeutic procedure in humans, Nighthawk™ was also an excellent technology platform. It demonstrated unambiguously that it was possible to incorporate fiber optics into a surgical tool with a reasonable impact on COGs and marginal impact on the profile and functionality of the tool, and return information from the tool in real-time, and present interpretable context to the surgeon in real time with clinically relevant image quality.
2) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3036404/
3) http://www.rle.mit.edu/boib/
4) Link to OCT article in this web site in the Optically-Guided Surgery section.
6) Proc. SPIE “Durable phantoms of atherosclerotic arteries for optical coherence tomography”, Charles-Etienne Bisaillon, Marc L. Dufour, and Guy Lamouche, Industrial Materials Institute, National Research Council, 75 bd. De, Mortagne, Boucherville, Quebec, J4B 6Y4, Canada
End-tidal CO2 Monitoring
End-tidal CO2 Monitoring
We were recently part of a project to develop a compact diode-pumped solid-state (DPSS) laser as part of an airborne CO2 monitoring system. A SWIR laser tunable over two CO2 absorption lines was successfully developed using a commonly-available gain medium. [1] This platform could also be used in the development of saturated CO2 absorption cells for kilohertz-accuracy frequency standards in the 1.34 range. [2]
Coming soon! Adaptation of this DPSS platform technology to CO2 monitoring in critical care situations including end-tidal sensors on intubation systems to prevent accidental esophageal entry.
- CO2 sensing with a 1.432 μm Nd:YAlO3 laser, Simon Vana, William M Grossman, Kenneth L Schepler, Dennis K Killinger, Steven M Jarrett, John F Black, and Larry Myers, Optical Engineering 54 (10), 106104 (2015).
- Burkhart et al. Saturated CO2 absorption near 1.6 μm for kilohertz-accuracy transition frequencies J. Chem. Phys. 142, 191103 (2015); http://dx.doi.org/10.1063/1.4921557