Triple-rule-out CT

Triple-rule-out CT (TRO CT) angiography may be ordered in the setting of acute chest pain to examine the thoracic aorta and the coronary and pulmonary arteries. The protocol helps exclude life-threatening causes of acute chest pain, especially if atypical, or if alternative causes to acute coronary syndrome (ACS) are being entertained (i.e. the patient is thought to be at a low to intermediate risk for ACS).

Causes of acute chest pain to be ruled out using this protocol include:

• aortic dissection
• pulmonary embolism (PE)
• coronary artery disease (CAD)
• non-vascular chest disease

Scan protocol

The exam is essentially an extended coronary CT angiogram:

• patient preparation is the same as for cardiac CTA, including administration of an intravenous β-blocker and sublingual nitroglycerin, unless contraindicated
• the scan should include the thoracic aorta and lungs
• the scan can begin from 1 cm above the aortic arch, excluding the lung apices for the sake of minimizing radiation exposure, as apical emboli are both rare and virtually undetectable at CT angiography
• biphasic contrast injection has been shown to give a more homogeneous enhancement profile compared with monophasic injection :
  • during the first phase, undiluted contrast material is injected for opacifying the left heart, commencing at the plateau phase of peak aortic and coronary enhancement
  • following this, diluted contrast material (1:1) is injected at the same rate for opacifying the right heart
  • contrast material quantities and rates differ between machines