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NCCT vs. CTA/CTP vs. MRI/dwMRI for acute onset stroke

Discussion in 'Radiology' started by MS05', Feb 14, 2007.

  1. MS05'

    MS05' Senior Member
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    Hi Guys. I'm an EM resident and am trying to put together a grand rounds presentations on head CT vs. CTA/CTP vs. MRI/dwMRI for acute onset stroke which is better, easier, more feasible etc etc etc. I wondered what you radiologist folk thought. Do you have a preference? Also, could anyone supply me with the average costs for the above?...

    Thanks in advance
     
  2. f_w

    f_w 1K Member
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    Best:

    MRI/dwMRI

    Useful:

    CTA/CTP

    Standard of care:

    NCCT

    It depends on what level of clinical skill you have and what treatment modalities you have available.
    If you are in podunk community memorial hospital and all you have to offer for stroke is IV lysis, the only question you need answered is bleed/no-bleed and swelling/no-swelling. That is where the NCCT will give you all the answers you need.

    If you are at a place with interventional stroke treatment, you want to have an answer (quick) whether this is one of the 5% of patients that might potentially benefit from agressive intervention. This is where CTA/CTP really shines, in a 5 minute scan you can answer:
    - major vessel involvement
    - approximate extent of ischemic territory
    All this on equipment readily available and with technical staff that is routinely in house (CT techs). The only downsides are that CTP can be a bit finicky and you blow 100+ ccs of contrast into a patient that potentially will see a couple of 100cc during his intervention.

    A dw MRI otoh will give you a 3D delineation of the ischemic territory, the most sensitive tool to look for hemorrhagic conversion and when combined with a 3D-TOF MRA will give you the answer for the major vessel involvement. All that without potentially nephrotoxic contrast. The downside is mainly logistics. Your MR techs are rarely in-house, the limited MRI/MRA will take longer than a CTA/CTP, the patient needs to be moved on a MRI compatible stretcher, EKG electrodes have to be switched for MRI compatible stock etc. Also, often stroke patients have pacemakers limiting your ability to do MRI (and if they are not awake or able to talk to you, you can't screen them for MR contraindications like pacers/pumps/clips).

    So, if I had unlimited resources to set up a stroke protocol, I would have:
    - an in-house MRI tech
    - all patients with stroke symptoms in triage would be put in the 'stroke room' where only MR compatible equipment is available
    - I would x-ray head/chest/1view l-spine to r/o hard contraindications to MRI on all comers.
    - from the 'stroke room' where a trained nurse-specialist would do the NIH and whatever other stroke scales, the patient would be shipped right into the scanner next door and get his/her dwMRI/MRA.

    Now, 'cost' in medicine is a very fluid concept. If you want to know the charges for the various modalities, check on the AMA website:
    https://catalog.ama-assn.org/Catalog/cpt/cpt_search.jsp?checkXwho=done
    (strictly speaking those charges which are given in medicare funny-money don't really apply to inpatient medicine as those are billed under a different system. but it gives you an idea as to the relative values)

    After you already own a MRI scanner (which will depreciate whether you use it or not and boil off helium whether you scan or not), the proportional variable cost of doing another MRI is purely limited to the electricity it takes to run the scanner and the personnel cost of calling in a very qualified staff member.
    In CT otoh, your proportional variable cost includes a tech that is already there (and as such costs you nothing) but you have to pay for every second the beam is on (tube-time) and you have expenses for IV contrast.
    So the cost equation is different whether you are in a private hospital setting, a university, a different country like the UK etc. Any time someone publishes a paper about relative cost of different modalities you have to ask hard questions as to what agenda that person is trying to pursue. Especially if people base their fuzzy math on charges. Reimbursement for medical services is the most f-ed up system you can think of. An evil genious couldn't come up with a more ******ed setup. (imagine you bring your car to the shop and they tell you 'well, if you pay cash, that new oxygen sensor is going to be $600, if your boss pays for the repair its going to be $200 and if you give us a phantasy name and just drive off after we do the work you'll get it for free and we'll put it on the bill for the next guy').
     
  3. OP
    OP
    MS05'

    MS05' Senior Member
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    Thanks f_w, the information really helped.

    Re: the $ question...I did come accross those medicare/aid numbers, however it seemed a bit low, especially whe compared to the costs of a abd/pelv CT.


    anyway, thanks!
     
  4. f_w

    f_w 1K Member
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    A non-contrast head CT is indeed a lot cheaper than a abd/pelvis. Part of the reason is that a A/P is actually two studies rather than one.

    And again, cost, medicare reimbursement and actual charges are only very loosely related to each other. So, the number you see on a bill has not much to do with the actual cost to get this study done.
     
  5. OP
    OP
    MS05'

    MS05' Senior Member
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    Okay, I have another one for you guys. Traditionally we use NCCT to eval for sub arachnoid hemorrhage. The sensitivity of CT findings are extremely variable and depend on the time from headache onsent.

    I got to thinking the other day...what about doing CTA in these patients? There have been several times I would've sworn the patient had a SAH, but NCCT and lumbar puncture were negative. It seems we leave out a huge section of patients, those with aneurysms or vasospasm which can present with the typical thunderclap headache. Even carotid and vertebral dissections can cause severe/thunderclap headaches from what I've read.

    ..so why not just skip NCCT and do CTA instead? I imagine that the sensitivity and specificity for SAH by CTA would be much better and you get the additional benefit of looking for aneurysms and dissections...

    what do you guys think?


    Thanks in advance!
     
  6. f_w

    f_w 1K Member
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    Actually, NCCT and lumbar puncture. If you order a head-CT for 'thunderclap headache' but then you are not willing to follow-through with an LP, you are accepting a 10% chance of committing malpractice (it is miraculous how 10millisievert of radiation to the brain downgrades lots of 'worst HA of life' turn into 'oh yeah, she has a longstanding history of migraine')

    The NCCT in the setting of suspected SAH has a two-fold mission:
    - rule out a compressive lesion that precludes LP
    - rule in a SAH with a 90% or so sensitivity

    Vasospasm in the setting of SAH doesn't usually show up before 48hrs, so I don't think it is a big issue at presentation. Rather than a 'huge' proportion, we might miss that fraction who are indolent enough to sit on a SAH for 2-3 days.

    So can a meteorite hitting your head (sorry, I just had to put this in here. this contingency is just part of the pre-op consent from one of our surgeons here).

    Actually, you wouldn't want to skip the NCCT in any scenario, I would certainly do it with a CTA.

    The reasons not to just CTA everyone who shows up with a headache:
    - CTA has a considerable radiation dose, particularly to the thyroid in a typically rather young population
    - You are using a contrast agent that while exceedingly safe, still has a potential to cause morbidity and mortality (e.g. a single digit likelihood of contrast induced transient nephropathy).

    My first choice would be a MRI including:

    - gradient echo
    - FLAIR
    - 3D-TOF MRA
     
  7. OP
    OP
    MS05'

    MS05' Senior Member
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    Ya, at my institution all negative CTs (while entertaining a SAH diagnosis) get LPs...although as of recently we're thinking of changing this as the 64 slice approaches a 99% specificity.

    Old school is still do the LP, new school is 64 slice alone is the standard of care.

    As far as vasospasm is concerned, I was thinking of vasospasm not in the setting of SAH, rather it's own entity, perhaps related to migraines.

    Contrast aside, I understand going for CTA first requires a leap of faith, but considering patients who have a negative NCCT, if the headache persists we've r/o SAH (perhaps), but have missed out on other intracranial pathologies> Rather than send the pt. back to radiology for a CTA, why not just do the CTA first?...it's less radiation than a NCCT and repeat CTA...

    I suppose you would need to look at the number needed to treat (and number needed to harm) data.

    MRI/MRA first, huh. I hadn't thought of that. What kind of time frame does it take to get MRI/MRA done?
     
  8. f_w

    f_w 1K Member
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    Do you mean a CTA using a 64slice scanner or a NCCT ? (btw. standard of care is to 'go to the extreme and actually look at the patient'. with every new test we introduce, it seems that we allow the ED to move closer to push-button medicine)

    But does that patient require a clip in is brain or a couple K worth o platinum wires ?

    In a setting of suspected SAH, you wouldn't want to do away with the non-contrast study.

    Yep, if I see that data, I'll gladly blast every headache that walks through the door with contrast and .6 mm slices.

    Depends on your logistics. It goes back to what I said earlier. 'cost' and getting things done are very fluid concepts.
    If you have the MRI scanner sitting around and a tech available, getting a patient in and out for that kind of limited study shouldn't take more than 15minutes. If the MRA is equivocal, you can still go to CTA or angio.
     
  9. Docxter

    Docxter Senior Member
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    Can you reference the data for this? Also, I'm assuming that you are not in radiology, since you think 64 slice scanners are so much different. How is a 64 slice different than for example a 16 slice? For either NCCTs and CTA? The 64s are certainly better for CTP since they can provide better brain coverage (still not the whole brain). In fact up until a few months ago, the NCCT images from both GE and Siemens scanners were noticeably worse than 16 or 4 detector scanners because of problems with the wide cone beam image reconstruction algorithm. Note that 64s have been clinically around for more than three years. We could all tell if a head CT was done on a 64 because of its poor quality. The recent software upgrades fixed this problem and now they look as good as the 16s.

    In any case, the detection of SAH on a NCCT should be no different on a 8, 16 or 64 scanner.


    In the majority of patients, the vasospasm is in the scalp not in the brain, especially in simple or common migraine. My institution has been a pioneer in neuro CTA/CTP applications and we probably have done more neuro CTA than anywhere else in the last 10 years, averaging now 20-25/day on a weekday and about 10-15/day on weekends. I have asked our people if anyone here has confidently seen migraine vasospasm and no one had.

    There are, however, migraine mimics that you may see on CTA like postpartum angiopathy, Call-Fleming syndrome, ergotism, other drug-induced vasoconstriction syndromes, some vasculitides, etc.

    Even in cases of complicated migraine leading to infarct in the brain, we haven't been able to demonstrate the vasospasm with any confidence.

    Most of this has to do with the confidence of ED physicians, and their time or will to pursue a final diagnosis. Some are content that the emergent causes like SAH, mass, other, hemorrhage, herniations, etc. are excluded by available neuroimaging in the ED, LP, lab tests, and history/physical exam, and that the patient can then safely be transferred to the care of their primary care, a neurologist, or an inpatient team.

    Time to MRI depends on the availability of MRI. At our place we have 24/7 active MRI and about 10 are done every night after midnight. Some places can't afford to, or don't have the need to have such coverage. Plus, availability of overnight MRI always leads to abuse for nonurgent cases, so some places purposefully limit its availability. Even if MRI is not readily available at night, if the emergent things are excluded, the MR can always be done the next day or so.

    2 other things:
    1. A CTA should always by default include a non-contrast head in cases of headache workup.
    2. A CTA is not adequate to evaluate for enhancing parenchymal lesions; the timing on a CTA is too early to assess for that.
     
  10. f_w

    f_w 1K Member
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    What a remote concept, outpatient follow-up for ER patients !

    And how many of those are cases that had to be done on 3rd shift ?

    Well, once you have made the investment into having 24hr staffing, you might as well crank them out.
    However, inpatient MRIs are not reimbursed as they are for the most part included in the DRG for the hospital stay. Emergency room related work is often unreimbursed based on the typically spotty insurance mix of the ERs customer base (at least in inner-city and rural hospitals, some suburban hospitals have very good collections on their ER work). So, while it might seem tempting to maximize utilization during off hours, in the end it only pays off for few hospitals.

    Whenever I do a CTA, I do the NC head followed by the CTA and then another regular run through the head at 60sec (when they walk out, they have a faint blue halo of Cherenkov radiation, but heck we have ruled out any ill that can befall the brain).
     
  11. danielmd06

    danielmd06 Neurosomnologist
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    Excellent subject! Thanks for the comments, guys.
     
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