CT Imaging Issues in the Critically Ill E. Wiebe, MD, FRCPC Department of Radiology University of Alberta

I have no financial or other disclosures CT Imaging Issues in the Critically Ill

Imaging Issues and Strategies  Patient selection  Region of interest  Use of contrast IV contrast  Use of oral contrast  Contrast risk  Radiation risk

Imaging Issues and Strategies  Patient selection  Clinical findings  Prior imaging findings  Imaging limitations and access  Relative contraindications

Imaging Issues and Strategies  Patient selection  Region of interest  Clinical findings  Mechanism of injury  Previous imaging findings

Imaging Issues and Strategies  Noncontrast exam  Acute retroperitoneal hemorrhage  Bone injuries  Aortic dissection or rupture  IV Contrast use  Vascular injuries and diseases  Solid organ assessment  Bowel wall assessment

Imaging Issues and Strategies  Oral contrast use  Positive contrast (eg. Telebrix or Gastrografin  Demonstates bowel leak  Impairs bowel wall assessment  Variable lumen distention  Negative contrast (eg. Water or Polyethylene glycol solution)  Better assessment of bowel wall  Cannot identify bowel leak

Imaging Issues and Strategies  Contrast risk  Anaphylactoid reaction  Nephrotoxicity

Imaging Issues and Strategies  Anaphylactoid reaction  Dose and concentration independent  Screen patients for increased risk  Preventative premedication with corticosteroids and antihistamines  No correlation or association with shellfish allergy and povidone-iodine skin cleansing solution

Imaging Issues and Strategies  Nephrotoxicity  recent meta-analysis suggested that the risk of contrast-induced nephrotoxicity is less than previously suggested (Radiology 2010; 256:21–28)  Most recent study concludes that there is increased risk in patients with estimated GFR of <40ml/min (Radiology 2013: 268:719-28)

Imaging Issues and Strategies  Nephrotoxicity  Dose dependent  Intravenous hydration is most important preventative measure  Consider benefit of noncontrast scan

Imaging Issues and Strategies  Radiation dose and risk  Main concern is induction of cancer  ALARA principle  Recognize the relative risk of CT and radiography  Use technology advances made to decrease dose

Imaging Issues and Strategies  Radiation dose  Measured as effective dose in mSV  Background radiation dose: 3mSv/yr  Standard CT abdomen dose: 8-10mSv for single scan  Low dose exams decrease dose to 2- 4mSv/scan

Imaging Issues and Strategies  Radiation dose  Dose estimate based on dose-length product (DLP) which is given with each scan  Chest CT dose = x DLP  Abdomen CT dose = x DLP  Head CT dose = x DLP  Neck CT dose = x DLP

625 x = 9.37 mSv 659 x = 9.88 mSv 630 x = 9.45 mSv Total effective dose = 28.7 mSv Imaging Issues and Strategies

Total effective dose = 166 x = 2.82 mSv Imaging Issues and Strategies

 Tailor exam to clinical situation  Use intravenous and oral contrast when necessary but not always  Be aware of risks of imaging

Questions?