CTA and CT with iv contrast

[eroicamadeus]

what's the difference between these two? In case of Pulmonary emboli, I always order CTA. But seems like it's the same procedure as CT with iv contrast.

Also, how often do you guys order conventional angiography for diagnosis of mesenteric ischemia? What is the sensitivity of CT with iv contrast in this case?

Last question is, what is your threshold of creatinine level when using iv contrast on pts not on dialysis?

Thanks a lot!

---

Members don't see this ad.

 

[Osteopathology]

The difference is usually the bolus timing of the contrast from the way I see it ....

CTA angio usually is the timing for pulmonary artery flow. Other CT of the ____ with contrast can usually be timed to target those particular areas. Not sure there is too much of a difference besides that.

I am sure some of the super pros who hang out here know better than I do though! Also may be related to selected slice thickness -- I know some of the CTA's have a good deal of slices for remodeling in 3D whereas some of the basic w/ contrast scans do not require more slices.

Osteo

 

[Vince]

what's the difference between these two? In case of Pulmonary emboli, I always order CTA. But seems like it's the same procedure as CT with iv contrast.

Also, how often do you guys order conventional angiography for diagnosis of mesenteric ischemia? What is the sensitivity of CT with iv contrast in this case?

Last question is, what is your threshold of creatinine level when using iv contrast on pts not on dialysis?

Thanks a lot!

The other poster was correct. It depends on the timing from the time of the injection to the time of the scan. If you are ordering a regular Chest CT with contrast, the delay from the time of injection to scanning is about 70 seconds. If you are doing a CTPA(CT Pulmonary Angiogram), then it will probably be a delay of about 15-20 seconds, although most scanners can perform "bolus tracking." In bolus tracking, a region of interest in the main pulmonary artery is selected and once a cutoff Hounsfield Unit value is reached, it triggers the scan, to optimize contrast opacification of pulmonary arteries. This slightly increases the radiation dose, but not by too much. If you want a CTA(CT Angiogram), those are typically to evaluate for aortic aneurysm or dissection, and can be performed with cardiac gating so that cardiac motion is minimized during the scan. These are probably performed at about 30 seconds when the Aorta is maximally opacified. With CTA/CTPA protocols, you need an IV catheter that is at least an 18 or 20 gauge, and AC fossa or more proximal, otherwise you may get suboptimal opacification of the subsegmental pulmonary arteries. A central line may be required...

Modern CTs can be tailored to answer the clinical question. Of course, when the request says "R/O Pathology," the clinicians aren't helping us very much... 👎

You can order a CTA of the abdomen if you are worried about mesenteric ischemia, but most of the time when my hospital's ED orders a CT for R/O mesenteric ischemia, it only rarely is present and we often just do a regular CT of the Abd/Pelvis to find the problem. Often times, CTAs of the abdomen are performed without oral contrast. In standard CTs of the Abd/Pelvis, there is usually enough contrast in the arteries and veins to check for SMA thrombus, etc. Mesenteric ischemia could be related to clot in the SMA, Celiac, IMA, but it could also be related to SMV thrombus, or be occuring at the capillary level and CT cannot exclude the diagnosis of mesenteric ischemia, although we can suggest it in some cases. Our IR dept doesn't usually do conventional angiography in cases of mesenteric ischemia, unless there is something on CT which can be intervened on, such as vascular thrombosis of either the SMA or SMV.

You shouldn't go by Creatinine levels when deciding to use IV contrast. You should calculate the patient's GFR. Above 60, no problem in using IV contrast. Between 30-60, my hospital will usually pretreat with Mucomyst and hydration, unless it is an emergency, and then we may just hydrate, give some bicarb, and possibly decrease contrast dose. If the GFR is less than 30, we don't use IV contrast, unless they are already on dialysis, and if that is the case, we try to have dialysis performed after the CT examination is performed. If the CT can be performed without IV contrast, to answer a particular clinical question, that is also an option.

Vince
PGY5 Radiology Resident

 

[goremachine]

Actually, I was wondering about the CVL for CT angio studies. I'm pretty sure I heard that a CVL is actually not sufficient because the lumen is too narrow to push enough contrast fast enough. I've always heard it has to be an antecubital IV or a PICC can also work. I assume a CVL intro would work, but generally I have had trouble getting CT angios done with a CVL triple lumen. Any input?

 

[colbgw02]

Only certain CVLs, ports, PICCs, etc., are certified for a power injector. I know that our CT techs will only inject through a central line as a last resort, and they do so with the full knowledge that there's a decent likelihood that they'll blow the line.

It depends on the CTPA protocol your hospital uses as well. We switched a few years ago from a test bolus technique to a timing bolus technique. The timing bolus is based off of an antecubital injection, which forces our techs to guess when to initiate the scan if the contrast is delivered through an alternative route. Anecdotally, there has been no change in scan quality, but that may explain why you get bad results with a CVL injection. Intuitively, it would seem like the bolus tracking method (outlined above) would alleviate this issue, but I don't have personal experience to confirm or refute that.

 

[Zweihander]

what's the difference between these two? In case of Pulmonary emboli, I always order CTA. But seems like it's the same procedure as CT with iv contrast.

Also, how often do you guys order conventional angiography for diagnosis of mesenteric ischemia? What is the sensitivity of CT with iv contrast in this case?

Last question is, what is your threshold of creatinine level when using iv contrast on pts not on dialysis?

Thanks a lot!

In addition to other things people have said, CTA involves thinner sections than a standard IV contrast protocol, and you can also get special reformats (MIPs) that don't come standard with a normal ct so that you can illustrate the vascular anatomy more fully.

 

[DutchgirlRN]

Actually, I was wondering about the CVL for CT angio studies. I'm pretty sure I heard that a CVL is actually not sufficient because the lumen is too narrow to push enough contrast fast enough. I've always heard it has to be an antecubital IV or a PICC can also work. I assume a CVL intro would work, but generally I have had trouble getting CT angios done with a CVL triple lumen. Any input?

I am an RN that works in Medical Imaging. For a CTA we require a 20g or larger above the wrist because of the pressure at which the contrast is injected by the power injector, 3ml per sec. PICC's are fine as long as they have a specific port (purple) labeled "CT compatible", I've personally not seen a PICC that couldn't be used. We also use port-a-caths (power ports only) that are designed to with stand the pressure. I have never seen a CVL used for any CT studies not even those that are hand injected such as a CT of the head.

We hydrate any patient that has a GFR of <60. We check the GFR on any patient 60 or older and or any patient with diabetes or renal function issues of any age. We infuse a 250cc bolus of 0.45% with 25mcg of Sod Bi Carb pre scan and give 600 mg of Mucomyst. They get another 250 cc bolus post scan and a script for 2 additional doses of Mucomyst 12 hours post scan and 24 hours post scan. If the patient is stat we can hydrate with 500cc and mucomyst post scan.

Pt's whose GFR is <30 cannot be contrasted without a nephrology consult. Pt's with ESRD are contrasted as long as they will be dialysed within the following 8 hours.

Not sure how I happened into the SDN but saw the Radiology section and couldn't resist. -