CT pulmonary angiogram
Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
CT pulmonary angiogram (CTPA) is a medical diagnostic test that employs computed tomography to obtain an image of the pulmonary arteries. Its main use is to diagnose pulmonary embolism (PE).
CTPA was introduced in the 1990s as an alternative to ventilation/perfusion scanning, which relies on radionuclide imaging of the blood vessels of the lung. It is regarded as a highly sensitive and specific test for pulmonary embolism.
CTPA is typically only requested if pulmonary embolism is suspected clinically. If the probability of PE is considered low, a blood test called D-dimer may be requested. If this is negative, risk of a PE is considered negligible and CTPA or other scans are generally not performed. Most patients will have undergone a chest X-ray before CTPA is requested.
After initial concern that CTPA would miss smaller emboli, a 2007 study comparing CTPA directly with ventilation/perfusion scanning found that CTPA identified more emboli without decreasing the risk of long-term complications compared to V/Q scanning.
CTPA is generally avoided in pregnancy due to the amount of ionizing radiation required, which may damage the fetus.
CTPA is contraindicated in known or suspected allergy to contrast media or in renal failure (where contrast agents could worsen the renal function).
The best results are obtained using multidetector computed tomography (MDCT) scanners.
An intravenous cannula is required for the administration of the 50-150 ml of radiocontrast. This is injected, usually automatically, by a syringe driver, at a rate of 4 ml/second. Many hospitals use bolus tracking, where the scan commences when the contrast is detected at the level of the proximal pulmonary arteries. If this is done manually, scanning commences about 10-12 seconds after the injection has started. Slices of 1-3 mm are performed are 1-3 mm intervals, depending on the nature of the scanner (single- versus multidetector).
State of the art CT machines can complete a scan in approximately five seconds and it is possible to complete the entire procedure (set-up, injection and scanning) in the space of five minutes.
On CTPA, the pulmonary vessels are filled with contrast, and appear white. Any mass filling defects (embolus or other matter such as fat or amniotic fluid) appears darker. Generally, the scan should be complete before the contrast reaches the left side of the heart and the aorta, which could result in artifacts.
The diagnostic accuracy of CT pulmonary angiogram for the detection of pulmonary embolism has been reported in a meta-analysis as the following:
- Sensitivity: 86%
- Specificity : 94%
Subsequently, the PIOPED II study provided similar results. PIOPED II used a mixture of 4 slice and 16 slice scanners and reported a sensitivity of 83% and a specificity of 96%.
Standards for reporting of the findings of CTPA have been studied.
The inter-rater reliability of interpretations of the CTPA by radiologists has been studied. While there is excellent inter-rater reliability between radiologists in detecting massive pulmonary emboli, the inter-rater reliability is only moderate for segmental or smaller emboli.
- ↑ 1.0 1.1 1.2 Fedullo PF, Tapson VF (2003). "Clinical practice. The evaluation of suspected pulmonary embolism". N. Engl. J. Med. 349 (13): 1247–56. doi:10.1056/NEJMcp035442. PMID 14507950.
- ↑ 2.0 2.1 2.2 Anderson DR, Kahn SR, Rodger MA; et al. (2007). "Computed tomographic pulmonary angiography vs ventilation-perfusion lung scanning in patients with suspected pulmonary embolism". JAMA. 298 (23): 2743–53.
- ↑ Scarsbrook AF, Gleeson FV (2007). "Investigating suspected pulmonary embolism in pregnancy". BMJ. 334 (7590): 418–9. doi:10.1136/bmj.39071.617257.80. PMID 17322258.
- ↑ Schoepf UJ, Goldhaber SZ, Costello P (2004). "Spiral computed tomography for acute pulmonary embolism". Circulation. 109 (18): 2160–7. doi:10.1161/01.CIR.0000128813.04325.08. PMID 15136509.
- ↑ Hayashino Y, Goto M, Noguchi Y, Fukui T (2005). "Ventilation-perfusion scanning and helical CT in suspected pulmonary embolism: meta-analysis of diagnostic performance". Radiology. 234 (3): 740–8. doi:10.1148/radiol.2343031009. PMID 15734930. Review in: ACP J Club. 2005 Sep-Oct;143(2):52
- ↑ Stein PD, Fowler SE, Goodman LR; et al. (2006). "Multidetector computed tomography for acute pulmonary embolism". N. Engl. J. Med. 354 (22): 2317–27. doi:10.1056/NEJMoa052367. PMID 16738268.
- ↑ Abujudeh HH, Kaewlai R, Farsad K, Orr E, Gilman M, Shepard JA (2009). "Computed tomography pulmonary angiography: an assessment of the radiology report". Acad Radiol. 16 (11): 1309–15. doi:10.1016/j.acra.2009.06.012. PMID 19692272.
- ↑ Shaham D, Heffez R, Bogot NR, Libson E, Brezis M (2006). "CT pulmonary angiography for the detection of pulmonary embolism: interobserver agreement between on-call radiology residents and specialists (CTPA interobserver agreement)". Clin Imaging. 30 (4): 266–70. doi:10.1016/j.clinimag.2006.01.001. PMID 16814143.
- ↑ 9.0 9.1 Brunot S, Corneloup O, Latrabe V, Montaudon M, Laurent F (2005). "Reproducibility of multi-detector spiral computed tomography in detection of sub-segmental acute pulmonary embolism". Eur Radiol. 15 (10): 2057–63. doi:10.1007/s00330-005-2844-4. PMID 16021452.
- ↑ Lucassen WA, Beenen LF, Büller HR, Erkens PM, Schaefer-Prokop CM, van den Berk IA; et al. (2013). "Concerns in using multi-detector computed tomography for diagnosing pulmonary embolism in daily practice. A cross-sectional analysis using expert opinion as reference standard". Thromb Res. 131 (2): 145–9. doi:10.1016/j.thromres.2012.11.027. PMID 23245652.
- ↑ 11.0 11.1 Costantino G, Norsa AH, Amadori R, Ippolito S, Resta F, Bianco R; et al. (2009). "Interobserver agreement in the interpretation of computed tomography in acute pulmonary embolism". Am J Emerg Med. 27 (9): 1109–11. doi:10.1016/j.ajem.2008.08.019. PMID 19931759.
- ↑ Hochhegger B, Alves GR, Chaves M, Moreira AL, Kist R, Watte G; et al. (2014). "Interobserver agreement between radiologists and radiology residents and emergency physicians in the detection of PE using CTPA". Clin Imaging. 38 (4): 445–7. doi:10.1016/j.clinimag.2014.03.001. PMID 24667043.
- ↑ 13.0 13.1 Ruiz Y, Caballero P, Caniego JL, Friera A, Olivera MJ, Tagarro D; et al. (2003). "Prospective comparison of helical CT with angiography in pulmonary embolism: global and selective vascular territory analysis. Interobserver agreement". Eur Radiol. 13 (4): 823–9. doi:10.1007/s00330-002-1588-7. PMID 12664123.