Imaging of Acute Pulmonary Embolism

MidEssexRay Home 

MidEssexRay Protocols and Guidelines

  • Patients with suspected acute pulmonary embolism are imaged, where indicated,  by CT Pulmonary Angiography (CTPA) unless contraindicated.
  • Ventilation-Perfusion (VQ) scanning is used when CTPA is contraindicated, and sometimes for follow-up.
  • Note: in pregnant patients, CTPA delivers less radiation to the fetus compared to a VQ scan (see reference 3 and


In order to facilitate processing of your request, please include the following information:

1. Wells score and Clinical probability (high, moderate or low)
2. D-dimer level if Wells score is 6 or less

If clinical probability of pulmonary embolism is low or intermediate, (Wells score 6 or less) and the D-dimer level is normal, imaging is not indicated routinely.

Clinical probability is essential for proper interpretation of VQ scan results.

Criteria for calculation of Wells score

Clinical signs of DVT (3 points)
Alternative diagnosis less probable than PE (3 points)
Heart rate >100 bpm (1.5 points)
Immobilization or surgery-4 weeks ago (1.5 points)
Previous DVT or PE (1.5 points)
Haemoptysis (1 point)
Cancer (1 point)
Total score:
<2   indicates a low probability of PE;
2–6  indicates a moderate probability of PE
>6   indicates a high probability of PE.


1) Wells PS, Anderson DR, Rodger M, Stiell I, Dreyer JF, Barnes D, Forgie M, Kovacs G, Ward J, Kovacs MJ.
Excluding pulmonary embolism at the bedside without diagnostic imaging: management of patients with suspected pulmonary embolism presenting to the emergency department by using a simple clinical model and d-dimer.
Ann Intern Med. 2001 Jul 17;135(2):98-107.

2) British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group.
British Thoracic Society guidelines for the management of suspected acute pulmonary embolism.
Thorax. 2003 Jun;58(6):470-83.

3) Groves AM, Yates SJ, Win T, Kayani I, Gallagher FA, Syed R, Bomanji J, Ell PJ.
CT pulmonary angiography versus ventilation-perfusion scintigraphy in pregnancy: implications from a UK survey of doctors’ knowledge of radiation exposure.
Radiology. 2006 Sep;240(3):765-70. Abstract

4) Stein PD,Woodard PK,Weg JG,Wakefield TW,Tapson VF,Sostman HD,Sos TA,Quinn DA,Leeper KV Jr,Hull RD,Hales CA,Gottschalk A,Goodman LR,Fowler SE,Buckley JD.
Diagnostic Pathways in Acute Pulmonary Embolism: Recommendations of the PIOPED II Investigators.
Radiology. 2007 Jan;242(1):15-21.