imaging for cerebral arteries

  Could you tell me about transcranial doppler(sp?) for imaging of the cerebral arteries?  I have  had the MRA and it indicated some problems in the posterior arteries circulation.  My docs  dont want to do a regular angiogram because of the risks and the problems I am having with the lupus.  I am trying to get some info about  other imaging possiblities ect before I see my new neurologist so I can ask him about all that.
  Also is a SPECT scan useful in this type of problem( cerebral blood flow problems?)  Thanks  once again for all the time  you take to answer all  these questions.
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Thanks for your question.  Transcranial Doppler (TCD) uses ultrasonic waves
to study the blood flow within a vessel.  In a very simplified manner, it
uses the same principle that an approaching car/train/"noisy-object" seems
to have a higher "pitch" than one that is moving away from you.  Under many
circumstances, TCD can provide a more "dynamic" picture of the actual blood
flow inside intracranial vessels, by being able to give the actual "velocity"
of flow within a vessel.  However, MR-Angiograms (MRAs) are much better in
illustrating irregularities/narrowings along the course of a vessel.
The likely reason your regular physicians want an evaluation of your
intracranial arteries, given your diagnosis of lupus, is the concern about
the possibility of vasculatis - inflammation of the blood vessels.  If that
is the case, neither MRA nor TCD will provide suficient resolution to be
helpful.  Only an angiogram will be able to provide the details of the
finer braches of the intracranial arteries to help in the evalution.
I hope this information is helpful.
This information is provided for general medical education purposes only.
Please consult your doctor regarding diagnostic and treatment options.