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Everything you need to know about Computed Tomography (CT) & CT Scanning


Oral Contrast

question1. Why do we use oral contrast?
question2. What kind of oral contrast do we use?
question3. When do we use positive agents and when do we use neutral agents?
question4. What are the advantages of oral LOCM (Omnipaque)?
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Advantages are:

  • Poorly absorbed from the normal GI tract
  • Rapidly absorbed from the peritoneum
  • Rapidly dissipated from the lungs if aspirated
  • Well-accepted by patients due to neutral taste
  • Stable in bowel secretions
  • Infrequent GI distress

LOCM, low-osmolar CM
Cohen MD. Radiology. 1987;162:447-456; Omnipaque package insert.
Smevik B, et al. Contrast Media in Pediatric Radiology. 1987:79-80.


"Low-osmolar contrast media is an ideal CT oral contrast. It is relatively nonabsorable and of low risk to the patient if aspirated. It can easily be titrated to create the desired density. It is water soluble and of low viscosity which permits uniform distribution."

The Use of Iohexol as Oral Contrast for Computed Tomography of the Abdomen and Pelvis
Horton KM, Fishman EK, Gayler B
J Comput Assist Tomogr 2008; 32:207-209


"We have recently switched completely to LOCM for our oral contrast during CT scanning. Iohexol is the only LOCM with Food and Drug Administration approval for use as an oral contrast at this time."

The Use of Iohexol as Oral Contrast for Computed Tomography of the Abdomen and Pelvis
Horton KM, Fishman EK, Gayler B
J Comput Assist Tomogr 2008; 32:207-209


Horton et al: Taste and Tolerability of Iohexol as Oral Contrast for CT

Results

  • Patients readily accepted oral iohexol
  • 100-110 mL iohexol mixed in 1 gallon of water achieved a contrast density of approximately 200 HU, comparable to that of HOCM
  • The ability to easily titrate the concentration of iohexol can be helpful in situations where it is important to customize intraluminal contrast density
  • Diluted as described, the cost of iohexol was less than that of diatrizoate powder: (Diatrizoate powder = $17.04/gal vs iohexol =$11.95/gal )

"Patients preferred dilute iohexol over dilute diatrizoate sodium for oral contrast for abdominal-pelvic CT. There was no significant difference in bowel opacification or adverse effect profile."
Oral Contrast Media for Body CT: Comparison of Diatrizoate Sodium and Iohexol for Patient Acceptance and Bowel Opacification
McNamara MM et al.
AJR 2010;195:1137-11411


"Of 287 subjects who expressed a preference, 233 patients (81%) preferred dilute iohexol compared with 54 patients (19%) who preferred dilute diatrizoate sodium.ten patients had no preference and 3 did not complete the taste comparison study."
Oral Contrast Media for Body CT: Comparison of Diatrizoate Sodium and Iohexol for Patient Acceptance and Bowel Opacification
McNamara MM et al.
AJR 2010;195:1137-11411


Johns Hopkins Protocol: January 2015

  • For every 10 cc of contrast you get around 20 HU increase in attenuation
  • Add 100 cc of Omnipaque-350 to 1 gallon of water
  • Dilute solutions can be used for CT Angiography (40HU)
question5. Is there any contraindication to the use of oral contrast?
question6. If a patient has had a prior reaction to IV contrast can we still use oral contrast?
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7. Part 1: When does the patient get the oral contrast relative to the time the patients get the actual CT scan?

Part 2: Does this differ between inpatients and outpatients?

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8. Are there any other oral contrasts that are used?

question9. Can you use a single bottle of Omnipaque -350 at multiple time points by drawing 10-20 cc at a time to use to mix oral contrast?
question10. What is VoLumen and when do you use it?

 

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