Dr Fang-- the details of your phantom acquisition are helpful-- although
some parts are not in my lexicon [CCW?]. However, my point remains, even
more so: you are saying that with a uniform phantom in the camera you get
5-7% assymetry-- with NO actual assymetry in the underlying medium. so I
view this number as the *minimum* expected assymtery, not an upper limit.
My concern is this: the living brain certainly has assymetries
[flow/metabolism and volume], which vary according to what sturcture you
are looking at. These same assymetries are what give rise to, for example,
regional covariance patterns in any imaging modality. these patterns are
rarely symmetric.
So, if there are data about the range of assymetries across defined brain
structures in normal controls using SPECT flow data, I would like to have
those numbers-- i think they are valuable to us all. I define controls only
by history and interview, not by the results of their scan-- to me, their
scans represent by definition *the range of variability in this measure*,
and to select out scans I don't "like" because they are too much like what
I think I;m looking for in my patients seems to me to be artificially
hedging my bet- biasing my assessment of variance in my refernce population.
********************************************************
Christopher Gottschalk, MD *
Assistant Professor of Neurology & Psychiatry *
Yale School of Medicine *
*
Mailing Adress: *
VAMC [116-A] tel [203] 932-5711 x4329*
950 Campbell Avenue FAX 937-4791*
West Haven, CT 06516 *
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