Everything you need to know about Computed Tomography (CT)

Ask the Fish


IV Contrast

question1. Why do we use IV contrast material?
question2. Do you use serum creatinine levels or GFR in your practice for establishing risk prior to CT scanning?
question3. What is GFR and why is it a more accurate measure than simply getting a creatinine level?
question4. Why are GFR numbers different for Caucasians and African Americans?
question5. Are all CT scans with IV contrast done the same way?
question6. What type of IV contrast material do we use and why?
question7. At what temperature do we store IV contrast material?
question8. Why do you warm IV contrast?
question9. What is the advantage of Visipaque as written in the literature?
question10. When do you use Visipaque-320 and when Omnipaque-350?
question11. Does the concentration of contrast mean that higher concentrations are better (AKA-isn’t a higher number better)?
question12. What is the volume of IV contrast material we use?
question13. What patients are considered high risk patients for IV contrast for CIN?
question14. Do we have set cutoffs for creatinine levels and if so what are they?
question15. Can we pretreat patients who have borderline renal function? If yes then how?
question16. Should patients be NPO for CT scanning? If yes for how long?
question17. What are the common volumes of contrast used for IV injection?
question18. What kind of IV access is ideal for use for IV contrast injection?
question19. Has there been any new developments in technology that may help us high injection rates in patients who can not tolerate an 18g needle (or at times even a 20g)?
question20. Can any IV the patient has in place be used to inject the contrast material?
question21. Can we use a central line or a PICC line for injection?
question22. What about the new “purple PICC/central lines” I hear about?
question23. What are some of the common normal “side effects” of IV contrast agents?
question24. Is there a relationship between patients receiving chemotherapy and CIN?
question25. Is it ok for patients to have both an MR and a CT with contrast on the same day?
question26. Have you ever seen a patient develop diffuse erythema distal to the IV injection site in the absence of extravasation?
question27. Patients often report a metallic taste in their mouth following use of IV iodinated contrast. Is there an explanation?
28. Are there any contrast volume limitations for the use of IV contrast?
question

Indeed there is and here are some rules for Omnipaque and Visipaque courtesy of Rich Vitti MD from GE Healthcare.

The recommended doses of Omnipaque™1 and Visipaque™2 for CT body imaging are:

  • Omnipaque 300 50ml to 200ml (15gI to 60gI)
  • Omnipaque 350 60ml to 100ml (21gI to 55gI)
  • Visipaque 270 100ml to 150ml (27gI to 40gI)
  • Visipaque 320 100ml to 150ml (32gI to 48gI)

The maximum total doses of iodine are as follows:

Omnipaque

  • 87.5gI (87500mgI) with a clearance of 90% of injected dose within the first 24hrs

Visipaque

  • 80gI (80000mgI) with a clearance of 97% of injected dose within the first 24hrs

GE Healthcare does not recommend the use of its products outside of the package labeling. Please refer to the package insert for full prescribing information.

Please keep in mind that the doses described below may not have been approved or cleared by the FDA.

Traditionally contrast dose for adult body CT is given in ranges of 50ml – 200ml, depending on procedure (hepatic, renal…) and iodine concentration (270mgI/ml to 400 mgI/ml). With increasing awareness of CIN and radiation dose, the trend has started to shift toward contrast dose by body weight. Some device manufacturers like Medrad (P3T) have introduced power injectors that follow a dose by weight protocol. There are a few studies published on weight-based dose for adults. Below are several examples.

Yanaga gives recommendations for specific exams:

  • Hypervascular HCC
  • Injection duration rate 30 sec
  • Total iodine dose of 525mg or more per kilogram of patient body weight
  • CTA using estimated lean patient body weight instead of total body weight
  • Pancreatic & hepatic enhancement tailored to patient weight with a fixed injection rate

Ichikawa recommends the following for hepatic imaging:

  • Scan duration throughout whole liver with a MDCT scanner: 10 sec;
  • Dose and concentration of contrast material: 2 mL/kg with 300 mg I/mL;
  • Injection duration: fixed, 30 sec (corresponds to 4 mL/s as fixed injection rate);
  • Injection rate: variable (depends on patients’ body weight);
  • Scan start time after the beginning of injection of contrast material for each phase:
    • Hepatic arterial-dominant phase (HAP): 40 sec;
    • Hepatic parenchymal phase (HPP): 55 sec;
    • Delayed phase (DP): 3 min;

Exceptional patients: with severe cardiac dysfunction/abnormal circulation (we recommend a use of double arterial-phase imaging or any bolus tracking techniques, such as manual mini-bolus or automatically computer-assisted bolus tracking techniques).

Megibow7 recommends the following for abdominal CT:

  • Weight-based dose of 1.5ml/kg for most patients

References:

1. Omnipaque™ prescribing information.

2. Visipaque™ prescribing information.

3. Yanaga Y, Awai K, Nakaura T, Namimoto T, et al. Optimal contrast dose for depiction of hypervascular hepatocellular carcinoma at dynamic CT using 64-MDCT. AJR. 2008;190:1003-1009.

4. Yanaga Y, Awai K, Nakaura T, Oda S, et al. Effect of contrast injection protocols with dose adjusted to the estimated lean patient body weight on aortic enhancement at CT angiography. AJR. 2009;192:1071-1078.

5. Yanaga Y, Awai K, Nakayama Y, Nakaura T, et al. Páncreas: Patient body weight-tailored contrast material injection protocol versus fixed dose protocol at dynamic CT. Radiol. 2007;245:475-482.

6. Ichikawa T, Erturk SM, Araki T. Multiphasic contrast-enhanced multidetector-row CT of liver: Contrast-enhancement theory and practical scan protocol with a combination of fixed injection duration and patients’ body-weight-tailored dose of contrast material. EJR. 2006;58:165-176.

7. Megibow AJ, Jacob G, Heiken JP, Paulson EK, et al. Quantitative and qualitative evaluation of volume of low osmolality contrast medium needed for routine helical abdominal CT. AJR. 2001;178:583-589.  

question29. Can you tell me a bit more about GFR and what it really means?

 

All images on this site are © 2016 Elliot K. Fishman, MD.