Saturday, July 3, 2010

Shit my dad says about radiology

For those of you disconnected from mainstream media, Shit My Dad Says -- I refuse to sanitize the title -- documents the pearls of wisdom passed down from a father to his son over the years. Being Twitter-free and Facebook-phobic, I only heard about this a few weeks ago from my daughter, who is a devoted follower, and then a few days ago I received the recently-published book, unsolicited, from my father as a birthday present. (Hmm, I wonder what this says about me as a father and as a son, Dr. Freud?)

What does this have to do with Biomedical Simulation? Well, a few minutes on Google and then PubMed reveals that the father, introduced in the book as having worked "in nuclear medicine at the University of California-San Diego", is indeed a former academic radiologist at UCSD, specializing in nuclear and adolescent(!) medicine, with quite a few papers in journals that I read. (OK, it's a stretch, but allow me this tenuous brush with greatness.)

All this to say: if you don't believe there's wit and wisdom behind the media hype, check out Samuel E. Halpern's editorial "Of Models and Men" from 1977. They don't write 'em like that anymore!

All hail Lewis Fry Richardson (1881-1953)

First time I came across his name was indirectly, as an undergrad, learning about something called "Richardson extrapolation", a method for inferring the convergence of a numerical analysis. Then, much (much) later, as I was rethinking turbulence in blood, I came across Richardson as one of the pioneers of modern turbulent flow theory, and as the author of this unsurpassedly clever and concise description of turbulence:
Big whorls have little whorls
that feed on their velocity,
And little whorls have lesser whorls
and so on to viscosity.
Shortly thereafter -- OK, so I didn't pay close attention to my reading of Gleick's "Chaos" many years back -- I learned about Richardson's anticipation of fractals via his musings on the measurement of coastlines, something that arose out of his interest in divining the mathematical rules underlying human conflict; and of his anticipation of chaos theory through his pioneering work in weather prediction. By virtue of what some might call his mania for the latter, he arguably founded modern numerical analysis and finite difference methods.

If that weren't enough, thanks to my reading of Abigail Swillens' fine PhD thesis, I learned that Richardson filed the first patent for underwater echo-ranging (apparently inspired by the sinking of the Titanic), a precursor to sonar and, by extension, medical ultrasound.

In short, virtually everything I do in my research can be traced back, with far fewer than six degrees of separation, to Lewis Fry Richardson. For more about Richardson's life and works, there's the at-your-fingertips Wikipedia of course, but also a nice 1998 review in the Annual Reviews of Fluid Mechanics.

Friday, July 2, 2010

Paper published in J Biomech Eng

Not long ago we reported differences in the characteristic shape of older vs. young adult carotid flow rate waveforms, which got us wondering whether and how such age-related differences might affect predictions of disturbed flow. In "Carotid bifurcation hemodynamics in older adults: effect of measured versus assumed flow waveform", we went a step further by testing the impact of not only waveform shape, but also mean flow rates, using the actual subject-specific measured flow condition as a gold standard. As it turned out, errors in mean flow had a greater impact on nominal metrics of disturbed flow, particularly oscillatory shear index (OSI); however, these effects were on the order of those due other assumptions we typically make regarding, say, blood rheology or inlet velocity profiles. Take-home message: don't sweat the waveform shape, but if you can measure the mean flow rates, go for it!