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

CT Imaging Issues in the

Critically Ill

E. Wiebe, MD, FRCPCDepartment 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


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


Patient selection Region of interest

Clinical findings Mechanism of injury Previous imaging findings


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


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


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


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 = 0.017 x DLP Abdomen CT dose = 0.015 x DLP Head CT dose = 0.023 x DLP Neck CT dose = 0.059 x DLP

625 x 0.015 = 9.37 mSv659 x 0.015 = 9.88 mSv630 x 0.015 = 9.45 mSv

Total effective dose = 28.7 mSv


Total effective dose = 166 x 0.017 = 2.82 mSv



Tailor exam to clinical situation Use intravenous and oral contrast

when necessary but not always Be aware of risks of imaging

Questions?

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

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