Contrast CT explained

Contrast CT, or contrast-enhanced computed tomography (CECT), is X-ray computed tomography (CT) using radiocontrast. Radiocontrasts for X-ray CT are generally iodine-based types.[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 administered, and postcontrast after radiocontrast administration.[2]

Bolus tracking

Bolus tracking is a technique to optimize timing of the imaging. 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.

Washout

"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]

Phases

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 Time from bolus tracking Targeted structures and findings
Non-enhanced CT (NECT)- -
Pulmonary arterial phase6-13 sec[6] -
Pulmonary venous phase17-24 sec -
Early systemic arterial phase15-20 sec immediately
  • Arteries, without enhancement of organs and other soft tissues.
Late systemicarterial 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 phase30[8] or 40[9] - 50 sec 20-30 sec
Hepatic (most accurate) or late portal phase70-80 sec 50-60 sec
  • Liver parenchyma enhances through portal vein supply, normally with some enhancement of the hepatic veins.
Nephrogenic phase100 sec 80 sec
  • All of the renal parenchyma enhances, including the medulla, allowing detection of small renal cell carcinomas
Systemic venous phase180 sec 160 sec
Delayed phase
Sometimes called "wash out phase" or "equilibrium phase"		6-15 minutes 6-15 minutes
  • Disappearance of contrast in all abdominal structures except for tissue with fibrosis, which appears more radiodense.

Angiography

See main article: CT angiography. 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.[10]

Amount

Adults

The following table shows the preferable volume in normal weight adults. However, dosages may need to be adjusted or even withheld in patients with risks of iodinated contrast, such as hypersensitivity reactions, contrast-induced nephropathy, effects on thyroid function or adverse drug interactions.

Exam !!colspan=3
Iodine concentration !Comments
300 mg/ml 350 mg/ml 370 mg/ml
95ml[11] 80 ml 75 ml
Overall 70 - 95 ml[12] 60 - 80 ml 55 - 75 ml Parenchymal changes of the lung can often be evaluated adequately without the use of intravenous contrast.
20 ml[13] 17 ml 15 ml Minimal amount when using specific low-contrast protocol.
Overall 70 ml 60 ml 55 ml
Liver 55 ml[14] 45 ml 40-45 ml Minimal required amount.
25 ml[15] 20 ml When using specific low-contrast protocol.

The dose should be adjusted in those not having normal body weight, and in such cases the adjustment should be proportional to the lean body mass of the person. In obese patients, the Boer formula is the method of choice (at least in those with body mass index (BMI) between 35 and 40):[16]

For men: Lean body mass = (0.407 × W) + (0.267 × H) − 19.2

For women: Lean body mass = (0.252 × W) + (0.473 × H) − 48.3

Children

Standard doses in children:[17]

Exam Concentration of iodine
300 mg/ml 350 mg/ml
Generally 2.0 ml/kg 1.7 ml/kg
1.5 ml/kg 1.3 ml/kg

Adverse effects

Iodinated contrast agents may cause allergic reactions, contrast-induced nephropathy, hyperthyroidism and possibly metformin accumulation. However, there are no absolute contraindications to iodinated contrast, so the benefits needs to be weighted against the risks.[18]

As with CT scans in general, the radiation dose can potentially increase the risk of radiation-induced cancer.

The injection of iodinated contrast agents may sometimes lead to its extravasation.[19]

See also

External links

Notes and References

  1. Book: Webb. W. Richard. Brant. Wiliam E.. Major. Nancy M.. Fundamentals of Body CT. 2014. Elsevier Health Sciences. 9780323263580. 152. en.
  2. Dahlman P, Semenas E, Brekkan E, Bergman A, Magnusson A . Detection and Characterisation of Renal Lesions by Multiphasic Helical Ct . Acta Radiologica . 41 . 4 . 361–366 . 2000 . 10937759 . 10.1080/028418500127345479 . 27758886 .
  3. Choi. Jin-Young. Lee. Jeong-Min. Sirlin. Claude B.. CT and MR Imaging Diagnosis and Staging of Hepatocellular Carcinoma: Part II. Extracellular Agents, Hepatobiliary Agents, and Ancillary Imaging Features. Radiology. 273. 1. 2014. 30–50. 0033-8419. 10.1148/radiol.14132362. 4263770. 25247563.
  4. Bae. Kyongtae T.. Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches. Radiology. 256. 1. 2010. 32–61. 0033-8419. 10.1148/radiol.10090908. 20574084. free.
  5. Web site: CT contrast injection and protocols. Robin Smithuis. Radiology Assistant. 2017-12-13.
  6. https://books.google.com/books?id=oVGjnOLXUgkC&pg=PA584 Page 584
  7. Introducing the use of Flash CTPA; how does it compare to standard CTPA?. Postering. Pavan Nandra. 2018. 10.1594/ecr2018/C-1831.
  8. Raman SP, Fishman EK. Advances in CT Imaging of GI Malignancies. . Gastrointest Cancer Res . 2012 . 5 . 3 Suppl 1 . S4-9 . 22876336 . 3413036 .
  9. Web site: Pancreas - Carcinoma. Otto van Delden and Robin Smithuis. Radiology Assistant. 2017-12-15. 2019-09-26. https://web.archive.org/web/20190926032743/http://www.radiologyassistant.nl/en/p43848b63def9d/pancreas-carcinoma.html. dead.
  10. https://books.google.com/books?id=E3tYBAAAQBAJ&pg=PA424 Page 424
  11. Web site: New Zealand Datasheet. New Zealand Medicines and Medical Devices Safety Authority. 2018-10-16.
  12. 0.3–0.4 gI/kg in a 70kg individual, according to:
    • Iezzi. Roberto. Larici. Anna Rita. Franchi. Paola. Marano. Riccardo. Magarelli. Nicola. Posa. Alessandro. Merlino. Biagio. Manfredi. Riccardo. Colosimo. Cesare. Tailoring protocols for chest CT applications: when and how?. Diagnostic and Interventional Radiology. 23. 6. 2017. 420–427. 1305-3825. 10.5152/dir.2017.16615. 5669541. 29097345.
  13. Using dual energy CTA (such as 90/150SnkVp), according to:
    • Leroyer. Christophe. Meier. Andreas. Higashigaito. Kai. Martini. Katharina. Wurnig. Moritz. Seifert. Burkhardt. Keller. Dagmar. Frauenfelder. Thomas. Alkadhi. Hatem. Dual Energy CT Pulmonary Angiography with 6g Iodine—A Propensity Score-Matched Study. PLOS ONE. 11. 12. 2016. e0167214. 1932-6203. 10.1371/journal.pone.0167214. 5132396. 27907049. 2016PLoSO..1167214M. free.
  14. The liver generally needs an enhancement of at least 30 HU for proper evaluation according to:
    • Book: Multislice CT. 3. 2010. Springer-Verlag Berlin and Heidelberg GmbH & Co. KG. 9783642069680.

    In males at 30 years of age, there is an estimated 0.027 HU of liver parenchymal enhancement per kilogram of body weight and per gram of iodine, when injected at 4 ml per second, according to:

    • Bae. Kyongtae T.. Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches. Radiology. 256. 1. 2010. 32–61. 0033-8419. 10.1148/radiol.10090908. 20574084. free.

    This example takes the example of a man with a typical weight of 70 kg.

  15. CT-angiography in a 70kg person, with 100-150 mg I/kg by using 80 kVp, mAs-compensation for constant CNR, fixed injection duration adapted to scan time, automatic bolus tracking and a saline chaser, according to:
    • Book: Nyman. Ulf. Coronary Interventions. Contrast Medium-Induced Nephropathy (CIN) Gram-Iodine/GFR Ratio to Predict CIN and Strategies to Reduce Contrast Medium Doses. 2012. 10.5772/29992. 978-953-51-0498-8. free.
  16. Caruso. Damiano. De Santis. Domenico. Rivosecchi. Flaminia. Zerunian. Marta. Panvini. Nicola. Montesano. Marta. Biondi. Tommaso. Bellini. Davide. Rengo. Marco. Laghi. Andrea. Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula. BioMed Research International. 2018. 2018. 1–6. 2314-6133. 10.1155/2018/8521893. 30186869. 6110034. free.
  17. Nievelstein. Rutger A. J.. van Dam. Ingrid M.. van der Molen. Aart J.. Multidetector CT in children: current concepts and dose reduction strategies. Pediatric Radiology. 40. 8. 2010. 1324–1344. 0301-0449. 10.1007/s00247-010-1714-7. 2895901. 20535463.
  18. Web site: Iodine-containing contrast medium. Stacy Goergen. InsideRadiology - The Royal Australian and New Zealand College of Radiologists. 2019-02-22. Page last modified on 26/7/2017
  19. Hrycyk J, Heverhagen JT, Böhm I . What you should know about prophylaxis and treatment of radiographic and magnetic resonance contrast medium extravasation . Acta Radiol . 60 . 4 . 496–500 . 2019 . 29896979 . 10.1177/0284185118782000. 48360725 .

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Contrast CT".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2024, A B Cryer, All Rights Reserved. Cookie policy.