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............................................................. specificity of 96% for (mainly four-detector) CTPA in PE diagnosis.115

PIOPED II also highlighted the influence of pre-test clinical probability on the predictive value of multidetector CTPA. In patients with a low or intermediate clinical probability of PE, a negative CTPA had a high negative predictive value for PE (96 and 89%, respectively), but its negative predictive value was only 60% if the pre-test probability was high. Conversely, the positive predictive value of a positive CTPA was high (9296%) in patients with an intermediate or high clinical probability, but much lower (58%) in patients with a low pre-test likelihood of PE.115 Therefore, clinicians should consider further testing in case of discordance between clinical judgement and the CTPA result. Several studies have provided evidence in favour of CTPA as a stand-alone imaging test for excluding PE. Taken together, the available data suggest that a negative CTPA result is an adequate criterion for the exclusion of PE in patients with low or intermediate clinical probability of PE. On the other hand, it remains controversial whether patients with a negative CTPA and a high clinical probability should be further investigated. Chronic thromboembolic pulmonary hypertension (CTEPH) is a potentially fatal late sequela of PE, but pre-existing CTEPH should not be missed in patients investigated for suspected acute PE. Signs of preexisting CTEPH on CTPA are listed in Supplementary Data Table 2; the diagnosis and management of CTEPH is discussed in section 10.

The major strengths, weaknesses/limitations, and radiation issues related to the use of CTPA in the diagnosis of PE are summarized in Table 6.

4.6 Lung scintigraphy

The planar ventilation/perfusion [V/Q (lung scintigraphy)] scan is an established diagnostic test for suspected PE. Perfusion scans are combined with ventilation studies, for which multiple tracers such as xenon-133 gas, krypton-81 gas, technetium-99m-labelled aerosols, or technetium-99m-labelled carbon microparticles (Technegas) can be used. The purpose of the ventilation scan is to increase specificity: in acute PE, ventilation is expected to be normal in hypoperfused segments (mismatched). Being a lower-radiation and contrast mediumsparing procedure, the V/Q scan may preferentially be applied in outpatients with a low clinical probability and a normal chest X-ray, in young (particularly female) patients, in pregnant women, in patients

Table 6 Imaging tests for diagnosis of pulmonary embolism

Strengths Weaknesses/limitations Radiation issuesa

CTPA • Readily available around the clock in most

centres • Excellent accuracy • Strong validation in prospective manage-

ment outcome studies • Low rate of inconclusive results (35%) • 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 310

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’ vs. ‘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 1020 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 foetus. bFor comparison, the whole-body effective dose of a chest X-ray examination is 0.1 mSv.141 Downloaded from academic.oup.com/eurheartj/article/41/4/543/5556136 by guest on 07 October 2026