Contrast CT

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A CT pulmonary angiogram is a contrast CT scan of the pulmonary arteries, in this case showing pulmonary embolism of saddle-type, which becomes more radiolucent than the radiocontrast filled blood surrounding it (but it may be indistinguishable without radiocontrast).

Contrast CT is X-ray computed tomography (CT) using radiocontrast. Radiocontrasts for X-ray CT are, in general, iodine-based.[1] This is useful to highlight structures such as blood vessels that otherwise would be difficult to delineate from their surroundings. Using contrast material can also help to obtain functional information about tissues. Often, images are taken both with and without radiocontrast. CT images are called precontrast or native-phase images before any radiocontrast has been administrated, and postcontrast after radiocontrast administration.[2]

Bolus tracking[edit]

Volume Rendered Carotid Angiogram

Bolus tracking is a technique used in computed tomography imaging, to visualise vessels more clearly. A small bolus of radio-opaque contrast media is injected into a patient via a peripheral intravenous cannula. Depending on the vessel being imaged, the volume of contrast is tracked using a region of interest (abbreviated "R.O.I.") at a certain level and then followed by the CT scanner once it reaches this level. Images are acquired at a rate as fast as the contrast moving through the blood vessels.

This method of imaging is used primarily to produce images of arteries, such as the aorta, pulmonary artery, cerebral, carotid and hepatic arteries. The image shown illustrates this technique on a sagittal MPR (multi planar reformat). The image is demonstrating the blood flow through an abdominal aortic aneurysm or AAA. The bright white on the image is the contrast. You can see the lumen of the aorta in which the contrast is contained, surrounded by a grey 'sack', which is the aneurysm. Images acquired from a bolus track, can be manipulated into a MIP (maximum intensity projection) or a volume rendered image.


"Washout" is where tissue loads radiocontrast during arterial phase, but then returns to a rather hypodense state in venous or later phases. This is a property of for example hepatocellular carcinoma as compared to the rest of the liver parenchyma.[3]


Depending on the purpose of the investigation, there are standardized protocols for time intervals between intravenous radiocontrast administration and image acquisition, in order to visualize the dynamics of contrast enhancements in different organs and tissues.[4] The main phases thereof are as follows:[5]

Phase Time from injection[5] Time from bolus tracking[5] Targeted structures and findings[5]
Non-enhanced CT (NECT) - -
Early arterial phase 15-20 sec immediately
  • Arteries, without enhancement of organs and other soft tissues.
Late arterial phase
Sometimes also called "arterial phase" or "early venous portal phase"
35-40 sec 15-20 sec
  • All structures that get their blood supply from the arteries have optimal enhancement.
  • Some enhancement of the portal vein
Pancreatic phase 40-50 sec[6] 20-30 sec
Hepatic (most accurate) or late portal phase 70-80 sec 50-60 sec
  • Liver parenchyma enhances through portal vein supply, normally with some enhancement of the hepatic veins.
Nephrogenic phase 100 sec 80 sec
  • All of the renal parenchyma enhances, including the medulla, allowing detection of small renal cell carcinomas
Systemic venous phase 180 sec[7] 160 sec
Delayed phase
Sometimes called "wash out phase" or "equilibrium phase"
6[5]-15[7] minutes 6[5]-15[7] minutes
  • Disappearance of contrast in all abdominal structures except for tissue with fibrosis, which appears more radiodense.


CT angiography is a contrast CT taken at the location and corresponding phase of the blood vessels of interest, in order to detect vascular diseases. For example, an abdominal aortic angiography is taken in the arterial phase in the abdominal level, and is useful to detect for example aortic dissection.[8]

See also[edit]


  1. ^ Webb, W. Richard; Brant, Wiliam E.; Major, Nancy M. (2014). Fundamentals of Body CT. Elsevier Health Sciences. p. 152. ISBN 9780323263580. 
  2. ^ Dahlman P, Semenas E, Brekkan E, Bergman A, Magnusson A (2000). "Detection and Characterisation of Renal Lesions by Multiphasic Helical Ct". Acta Radiologica. 41 (4): 361–366. doi:10.1080/028418500127345479. PMID 10937759. 
  3. ^ Choi, Jin-Young; Lee, Jeong-Min; Sirlin, Claude B. (2014). "CT and MR Imaging Diagnosis and Staging of Hepatocellular Carcinoma: Part II. Extracellular Agents, Hepatobiliary Agents, and Ancillary Imaging Features". Radiology. 273 (1): 30–50. doi:10.1148/radiol.14132362. ISSN 0033-8419. PMC 4263770Freely accessible. 
  4. ^ Bae, Kyongtae T. (2010). "Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches". Radiology. 256 (1): 32–61. doi:10.1148/radiol.10090908. ISSN 0033-8419. 
  5. ^ a b c d e f Robin Smithuis. "CT contrast injection and protocols". Radiology Assistant. Retrieved 2017-12-13. 
  6. ^ a b Otto van Delden and Robin Smithuis. "Pancreas - Carcinoma". Radiology Assistant. Retrieved 2017-12-15. 
  7. ^ a b c d Dongqing Wang (2013). Selected Topics on Computed Tomography. ISBN 9789535111023.  License: CC-BY-3.0. Chapter 1: "Computed Tomography in Abdominal Imaging: How to Gain Maximum Diagnostic Information at the Lowest Radiation Dose" by Kristie Guite, Louis Hinshaw and Fred Lee. DOI: 10.5772/55903
  8. ^ Page 424 in: Stuart E. Mirvis, Jorge A Soto, Kathirkamanathan Shanmuganathan, Joseph Yu, Wayne S Kubal (2014). Problem Solving in Emergency Radiology E-Book. Elsevier Health Sciences. ISBN 9781455758395.