Tuesday, November 1, 2011

Paper Published: CCA Geometry and Hemodynamics

The common carotid artery is, er, commonly assumed to be long and straight, which justifies the, er, common assumption of fully-developed flow in this artery.

On the other hand, in the latest issue of Physiological Measurement, we show the typical CCA possesses a compound curvature that, while modest, is sufficient to explain our prior observation of velocity profile skewing in this artery.

Tuesday, October 4, 2011

SBC2012 CFD Challenge

After years of talking about it, Frank Loth and I are finally running a CFD Challenge, at the 2012 ASME Summer Bioengineering Conference.  Details are available here, and you can email me for data/instructions on how to proceed with the first phase.

Comings and Goings

Some recent personnel changes at the BSL, celebrated as shown to the left:

Kristian Valen-Sendstad, who joins the BSL as a postdoc from Simula Research Labs in Norway, to continue his work on cerebral aneurysm hemodynamics.

Muhammad Owais Khan, who joins the BSL as a Master's student, investigating the role of curvature on arterial flow patterns.

And, finally, Yiemeng Hoi, who leaves the BSL for bigger and better (or at least more lucrative :-) things at Toshiba.

Sunday, August 21, 2011

Book Chapter Published: Imagery in the 21st Century

Oliver Grau, Sean Cubitt, James Elkins, Martin Kemp ... and us?!?  Congratulations to Dolores Steinman, whose paper "Toward New Conventions for Visualizing Blood Flow in the Era of Fascination with Visibility and Imagery" has been published in Oliver Grau's latest book, Imagery in the 21st Century.

This chapter had a long incubation, starting from an email sent to Dolores in August 2007 by Jim Ruxton about a call for papers he'd received on "Gazing into the 21st Century: Confronting Image Naivete, The Second international Conference on Image Science in Goettweig, April 24th - 26th 2008".  (This is the same Jim Ruxton who, having come across our paper in Leonardo, had invited us to his Subtle Technologies Festival, the beginning of a beautiful friendship, to coin a phrase :-)

Following a postponement of the Goettweig conference, ticket cancellations (thank you Mastercard travel insurance), and then a rescheduling, we embarked in October 2008 on a month-long tour of conferences from Lisbon (SHOT) to Graz (MRA Club) to Goettweig to London (CHArt).  And speaking of incubation, Dolores was sick on and off throughout (having caught what we later found out to be walking pneumonia) but gamely gave her three talks (mine was at the MRA Club, in case there was any doubt). 

We were then invited by Oliver Grau to contribute a chapter to the book he was planning based on the Goettweig conference -- Oliver's earlier book, Media Art Histories, is a landmark in the field -- and the end result is now published for all to see.  Thanks to Oliver Grau and Thomas Veigl for generously allowing us interlopers into their world; and the indomitable F. Scott Taylor (aka Scotus Dawgus aka Rabbi Scott) for encouraging us and ensuring that our chapter made sense.

Saturday, August 6, 2011

Welcome Yuji Shimogonya

Yuji Shimogonya from the University of Hyogo will be working as a visiting scientist at the BSL for the next couple of months.  Dr. Shimogonya will be investigating various aspects of the Gradient Oscillatory Number (GON) hemodynamic factor that he recently proposed for predicting sites of aneurysm formation.

Thursday, June 30, 2011

Paper Published: High Resolution Intracranial Wall Imaging

Imaging of the normally-thin artery wall remains a major challenge in MRI. Usually we must sacrifice axial slice thickness to achieve high in-plane spatial resolution, under the assumption that geometry and thickness changes through the ~2-mm-thick slices are negligible.  As we recently demonstrated, however, such thick slice acquisitions may be prone to appreciable artifacts if the slices cannot be perfectly aligned with the vessel.

In the latest issue of JMRI, my colleagues at Johns Hopkins and I report on an approach to achieving isotropic spatial resolutions of 0.4 - 0.5 mm with black blood MRI. Not only does this allow us to resolve Italy (see above); it also allows us to resolve smaller changes or differences in wall thickness while avoiding the abovementioned obliqueness artifacts.

Saturday, June 18, 2011

Nerd Alert

Computational modeling of cerebral aneurysms in popular culture!  -- well, popular nerd culture anyway: http://nerd-alert.net/blog/2011/06/phd-nightmares/.  Thanks to BSL alumna Keri Moyle for pointing me to this.

Friday, June 3, 2011

Welcome to Jonathan Mynard

I've been a bit distracted lately, so was remiss in not announcing the addition of Jonathan Mynard from the University of Melbourne.  Jonathan is a NHMRC postdoctoral fellow, who will be investigating the role of imaging and full- and reduced-order models for studying congenital cardiovascular disease.

Editorial in AJNR

Earlier this year Juan Cebral's group published an interesting paper suggested that rare cases of aneurysm rupture following treatment by flow diverters might be due to treatment-induced pressure increases.  Barry Lieber and colleagues subsequently questioned these CFD-based results, which brought a strong response from Cebral and colleagues.  I was then asked by AJNR's Charlie Strother to help explain the controversy for the AJNR readership.

Who is right?  This remains to be seen, but I see it as a terrific opportunity for our community to demonstrate the clinical value (or lack thereof) of image-based CFD.

Wednesday, February 2, 2011

Paper Published: Hemodynamics of the Mouse Aorta

Congratulations to BSL postdoc Yiemeng Hoi, whose paper "Correlation between local hemodynamics and lesion distribution in a novel aortic regurgitation murine model of atherosclerosis" has been published by the Annals of Biomedical Engineering. (And kudos to Springer: two weeks from acceptance to online-first publication!)

Our co-authors had previously demonstrated that the induction of aortic regurgitation accelerates the formation of atherosclerotic lesions in Ldlr-/- mice -- lesions whose distinct and consistent spatial localization suggested a strong local hemodynamic influence. Building upon this work, and with painstaking care, Yiemeng reconstructed the geometry of the mouse aorta from micro-CT of a cast vessel; derived the necessary flow rate boundary conditions from Doppler ultrasound measurements and literature values; and ensured that the process of mapping the CFD predictions for comparison with en face plaque stainings was fair and unbiased.

Our main result, summarized in the figure above, shows that the distinctive distributions of plaque can indeed be explained by the patterns of high oscillatory shear index (OSI) and/or long relative residence times (RRT).  Control CFD studies using normal flow rates and straightened geometry confirm that these focal hotspots arise from the combination of the anatomical curvatures of the mouse aorta and the strong retrograde flow rates of the AR mice. On the other hand, time-averaged shear magnitude (TAWSS), the usual suspect, does not explain the plaque distributions, showing that, when it comes to "disturbed" flow, "low and oscillatory" need not always go hand in hand. (I know, I know, that's a lot of hands.)

Friday, January 28, 2011

Paper Published: Scan-Rescan Reproducibility of Carotid Geometry

Congratulations to PhD student Payam Bijari, whose first BSL paper, "Scan-rescan reproducibility of carotid bifurcation geometry from routine contrast-enhanced MR angiography", was recently published in the Journal of Magnetic Resonance Imaging.

As suggested by the figure, this paper demonstrates that lumen geometry can be rapidly and reliably segmented from not-always-optimal MR angiograms, in our case from 60 participants in the ARIC Carotid MRI study, each scanned twice on separate occasions. This now sets the stage for our analysis of the full cohort, which seeks to identify whether the geometry of the carotid bifurcation can be considered a "missing" local risk factor for atherosclerosis.

Tuesday, January 25, 2011

Journal of Universal Rejection

A new and prestigious journal (100% rejection rate, talk about selective!). Got me thinking about starting a Journal of Universal Acceptance, which would guarantee a 100% acceptance rate* so you can pad your CV with "Accepted" submissions from the moment you submit them. Even better, maybe a Journal of Anticipated Submissions, so you can focus on padding your CV without wasting precious time actually writing manuscripts. Oooh, the possibilities are endless...

*guaranteed to be accepted before the end of the universe, or around the same time that the editor will reply to author queries regarding the status of their manuscripts.

Update: Starting from an NPR blog entry about the JUR, I came across a brief interview with the editor, which refers to a Journal of Are You Fucking Kidding, which has an entry about the seemingly "legitimate" journal Nature and Science (as in "I've had my work published in Nature and Science"). Indeed, there is a fine line between stupid and clever...

Sunday, January 23, 2011

Welcome to Diego Gallo

The BSL welcomes Diego Gallo, PhD student from the group of Morbiducci and Montevecchi at the Politecnico di Torino, who will be spending the next six months at the BSL. (Sorry about the extreme cold alert, Diego! :-)