MRA question

[Mohd]

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I was reading a neuroanatomy text and came across the following:

- Injection of the contrast into the right subclavian artery will demonstrate back & front cerebral arteries, whereas injecting it into the left subclavian artery will show the posterior circulation only.
This part was well-explained and I had no problem understanding it, the problem came up next:

- The communicating arteries show no tendency of blood to go one way or the other since blood flows through carotid & vertebral arteries with equal pressure. Hence, contrast material injected into the right carotid artery generally will not cross over to the left side of the brain via the anterior communicating artery or flow back into the basilar artery across the posterior communicating artery.

So here is my question:
If contrast cannot cross through the communicating arteries how does it cross to the left side when the contrast is injected into the right side? 😕
Thanks !🙂

 

[Mohd]

No replies yet?
Then how about this: "one carotid artery is compressed during transfusion of the contrast which leads to a pressure gradient"
Do radiologist really do that?

 

[flux=rad]

I think there are no replies because your questions seem a bit confusing. The subject says Magnetic Resonance Angio, but you are asking about selective contrast injections. In MRA, contrast is injected into a peripheral vein, travels to the heart, and then gets pumped up to the brain. All of the patent arteries are opacified. It sounds like you are reading about catheter angiograms, AKA DSA. The first part refers to the fact that the origin of the left carotid is off the arch, while on the right the carotid and the vert arise from the subclavian. Not sure where you mean by "into the right side" on your question. Carotid compression again refers to a catheter angiogram, not MRA.

 

[Mohd]

Thanks Flux=rad!!
Actually I was confused myself, what I wrote between quotations above was taken from a neuroanatomy text, they didn't mention the procedure's name so I wrongly assumed it was an MRI (you can't blame me I haven't done my Rads rotation yet - although I'm looking forward to it !!!!!)
Thanks again your reply was helpful !!!! 🙂