CT of pulmonary embolism

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Author: Mikael Häggström [notes 1]


Need for investigation

The indication can effectively be determined by clinical scoring, followed by D-dimer in those less likely to have pulmonary embolism.[1] By Well's score, CT is indicated at a score over 4:[1]

Feature Points
Signs and symptoms of deep vein thrombosis, at least with leg swelling and pain upon palpation of deep veins. 3
No alternative diagnosis better explains the presentation 3
Heart rate over 100/min 1.5
Immobilization >3 days or surgery in past 4 weeks 1.5
Previous pulmonary embolism or deep vein thrombosis 1.5
Hemoptysis 1
Malignancy (current or treated in the past 6 months) 1

Choice of modality

Radiologist algorithm for pulmonary embolism.png

The threshold for normal versus high D-dimer is generally 500 ng/mL or 0.5 mg/L.[2] In pregnant or elderly patients, corresponding D-dimer ranges need to be used.[notes 2]

CT configuration

CT of pulmonary embolism needs to be done as a CT angiography in pulmonary arterial phase.
The standard amount of contrast is generally 30 to 40g of iodine (such as 20-30 cc of 370 mg/ml of iodine).[3] In case of low renal function, dual energy CTA (such as 90/150SnkVp) is feasible even at iodine doses of 6g (such as 15 ml of 370 mg/ml of iodine).[4]

For general notes on contrast dosage, see Contrast CT

Timing can use bolus tracking in the pulmonary trunk + 6 seconds.[5]


Severity of pulmonary embolism is determined by the level of the embolism along the pulmonary arterial tree, as well as how many such vessels are involved, and how much of the area is covered in each vessel.

In case of severe pulmonary embolism, also measure the diameter of the pulmonary trunk at its bifurcation. A diameter of more than 27 mm for women and 29 mm for men indicates pulmonary hypertension.[notes 3][6]


  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Radlines:Authorship for details.
  2. Pregnant patients
    Upper limit of reference range for D-dimer:
    Units Nonpregnant
    First trimester Second trimester Third trimester
    mg/L or µg/mL < 0.5 < 0.95 < 1.29 < 1.7
    µg/L or ng/mL < 500 < 950 < 1290 < 1700
    nmol/L < 2.7 < 5.2 < 7.1 < 9.3

    Reference: Reference Values During Pregnancy at perinatology.com. Retrieved October 2014.

    Elderly patients

    Patient’s age in years × 10 µg/L (or x 0.056 nmol/L) for patients aged over 50 years for the suspicion of venous thromboembolism (VTE).

    ". J Fam Pract 63 (3): 155–8. March 2014. PMID 24701602. 

    • Raja, Ali S.; Greenberg, Jeffrey O.; Qaseem, Amir; Denberg, Thomas D.; Fitterman, Nick; Schuur, Jeremiah D. (29 September 2015). "Evaluation of Patients With Suspected Acute Pulmonary Embolism: Best Practice Advice From the Clinical Guidelines Committee of the American College of Physicians

    ". Annals of Internal Medicine 163 (9): 701. doi:10.7326/M14-1772. PMID 26414967. 

  3. This measurement is, however, a poor predictor of pulmonary hypertension in patients with interstitial lung disease


  1. 1.0 1.1 Writing Group for the Christopher Study Investigators (2006). "Effectiveness of Managing Suspected Pulmonary Embolism Using an Algorithm Combining Clinical Probability, D-Dimer Testing, and Computed Tomography ". JAMA 295 (2): 172. doi:10.1001/jama.295.2.172. ISSN 0098-7484. 
  2. "Plasma measurement of D-dimer levels for the early diagnosis of ischemic stroke subtypes ". Archives of Internal Medicine 162 (22): 2589–93. 2002. doi:10.1001/archinte.162.22.2589. PMID 12456231. Archived from the original. . 
  3. Janet Cochrane Miller, D. Phil., Author. Raul N. Uppot, M.D., Editor. "Dual Energy CT Imaging for Suspected Pulmonary Embolism Using a Lower Dose of Contrast Agent ". Radiology Rounds, by Massachusetts General Hospital, Department of Radiology 13 (7). Archived from the original. . 
  4. Leroyer, Christophe; Meier, Andreas; Higashigaito, Kai; Martini, Katharina; Wurnig, Moritz; Seifert, Burkhardt; Keller, Dagmar; Frauenfelder, Thomas; et al. (2016). "Dual Energy CT Pulmonary Angiography with 6g Iodine—A Propensity Score-Matched Study ". PLOS ONE 11 (12): e0167214. doi:10.1371/journal.pone.0167214. ISSN 1932-6203. 
  5. Pavan Nandra (2018). Introducing the use of Flash CTPA; how does it compare to standard CTPA?. Postering.
  6. Frank Gaillard. Pulmonary hypertension. Radiopaedia.