TABLE 6

Imaging tests for diagnosis of pulmonary embolism

StrengthsWeaknesses/limitationsRadiation issuesa
CTPA
  • Readily available around the clock in most centres

  • Excellent accuracy

  • Strong validation in prospective management outcome studies

  • Low rate of inconclusive results (3–5%)

  • May provide alternative diagnosis if PE excluded

  • Short acquisition time

  • Radiation exposure

  • Exposure to iodine contrast:

    • limited use in iodine allergy and hyperthyroidism

    • risks in pregnant and breastfeeding women

    • contraindicated in severe renal failure

  • Tendency to overuse because of easy accessibility

  • Clinical relevance of CTPA diagnosis of subsegmental PE unknown

  • Radiation effective dose 3–10 mSvb

  • Significant radiation exposure to young female breast tissue

Planar V/Q scan
  • Almost no contraindications

  • Relatively inexpensive

  • Strong validation in prospective management outcome studies

  • Not readily available in all centres

  • Interobserver variability in interpretation

  • Results reported as likelihood ratios

  • Inconclusive in 50% of cases

  • Cannot provide alternative diagnosis if PE excluded

  • Lower radiation than CTPA, effective dose ∼2 mSvb

V/Q SPECT
  • Almost no contraindications

  • Lowest rate of non-diagnostic tests (<3%)

  • High accuracy according to available data

  • Binary interpretation (“PE” versus “no PE”)

  • Variability of techniques

  • Variability of diagnostic criteria

  • Cannot provide alternative diagnosis if PE excluded

  • No validation in prospective management outcome studies

  • Lower radiation than CTPA, effective dose ∼2 mSvb

Pulmonary angiography
  • Historical gold standard

  • Invasive procedure

  • Not readily available in all centres

  • Highest radiation, effective dose 10–20 mSvb

CTPA: computed tomographic pulmonary angiography; mGy: milligray; mSv: millisieverts; PE: pulmonary embolism; SPECT: single-photon emission computed tomography; V/Q: ventilation/perfusion (lung scintigraphy). aIn this section, effective radiation dose is expressed in mSv [dose in mSv = absorbed dose in mGy×radiation weighting factor (1.0 for X-rays)×tissue weighting factor]. This reflects the effective doses of all organs that have been exposed, that is, the overall radiation dose to the body from the imaging test. Compare with table 12, in which the absorbed radiation dose is expressed in mGy to reflect the radiation exposure to single organs or to the fetus. bFor comparison, the whole-body effective dose of a chest X-ray examination is 0.1 mSv [141].