CT with IV contrast

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File:Contrast CT.jpg
A woman undergoing CT with IV contrast.

Author: Mikael Häggström [notes 1]
Contrast CT is CT scan using radiocontrast, and in Radlines it refers to a CT scan using IV contrast except otherwise noted.

Bolus tracking is where a specified location within the circulatory system is monitored during IV contrast infusion, and the timing of the main imaging is counted from when the contrast reaches this location (sufficiently to achieve a specified threshold).

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.[1]

Contrast-induced nephropathy

Decreased renal function and several other conditions increase the risk of contrast-induced nephropathy, which is a potentially lethal renal injury to the kidney following intravenous radiocontrast.[2]

File:Contrast CT in low GFR.png
In case of low GFR, the procedure depends on whether the dose that can be given is larger or less than the needed dose.

The main alternatives in people with a risk of contrast-induced nephropathy are:

  • Adjustment of the radiocontrast dose
  • Treating or mitigating risk factors
  • Using no intravenous contrast for the investigation.
  • Switching to another modality such as ultrasonography or MRI

Risk factors

The Roxana Mehran score predictor applies the following ten variables:[3]

  • Age (4 points if older than 75 years old)
  • Anemia (3 points)
  • Use of an intra-aortic balloon pump (5 points)
  • Decreased real function. In terms of estimated glomerular filtration rate in ml/min:
  • eGFR 60 to 40 (2 points)
  • eGFR 40 to 20 (4 points)
  • eGFR less than 20 (6 points)
  • Hypotension (5 points, if systolic BP less than 80 mmHg for at least one hour requiring inotropic support)
  • Contrast media volume (1 point per 100 ml)
  • Congestive heart failure (5 points)
  • Diabetes (3 points).

A risk score of less than 6 carries a risk of 7.5% to score more than 16 carries up to 57% risk.[3]

Adjustment of dose

If and how to adjust the dose depends on supply and demand:

How much contrast can be given?

In some emergent conditions such as CT of aortic aneurysm with suspected rupture, the need for contrast is greater than the risk of contrast-induced nephropathy.

For the rest of the investigations, evidence suggests that contrast doses should be limited to a ratio of grams of iodine to glomerular filtration rate (Igram / GFRml/min) of a maximum of 1 g/(ml/min).[4] According to European guidelines, the ratio should be less than 1.1 g/(ml/min) for intra-arterial contrast medium administration with first-pass renal exposure (not passing lungs or peripheral tissue before reaching the kidneys).[5] Swedish guidelines are more restrictive, recommending a ratio of less than 0.5 g/(ml/min) in patients with risk factors and irrespective of route of administration, and even more caution in first-pass renal exposure.[5]

Volume for various Iodine concentrations
Igram / GFRml/min
ratio		 240 mg/ml 350 mg/ml 370 mg/ml
0.5 2.1 ml *GFRml/min 1.4 ml *GFRml/min 1.4 ml *GFRml/min
0.7 2.9 ml *GFRml/min 2.0 ml *GFRml/min 1.9 ml *GFRml/min
1 4.2 ml *GFRml/min 2.9 ml *GFRml/min 2.7 ml *GFRml/min

How much contrast is needed

Preferable volume for normal weight adults
Exam Iodine concentration Comments
350 mg/ml 370 mg/ml
Brain 80 ml[6] 75 ml[6]
Thorax Overall 60 - 80 ml[notes 2] 55 - 75 ml[notes 2] Parenchymal changes of the lung can often be evaluated adequately without the use of intravenous contrast.
CT of pulmonary embolism 17 ml[notes 3] 15 ml[notes 3] Minimal amount when using specific low-contrast protocol.[notes 3]
Abdomen Overall 60 ml[6] 55 ml 60 ml[6]
Liver 45 ml[notes 4] 40-45 ml[notes 4] Minimal required amount.[notes 4]
Angiography 20 ml[notes 5] When using specific low-contrast protocol.[notes 5]

Departments often have formulas that give the amount of contrast needed for various investigations, using patient sex and weight as main parameters. These may include creatitine levels as well, and in such cases it can help to get a value of of much contrast would hypothetically have been given if the creatinine level was normal, such as for example 80 μmol/L or 0.9 mg/dL. This value can be compared to how much can actually be given in order to determine if it is worth doing the exam with contrast.

Treating risk factors

Risk factors can sometimes be treated or at least mitigated, especially if having suddenly appeared, such as a decreased renal function when it was previously normal. In such cases a common easily treated cause is dehydration.

Hydration by drinking or intravenous volume expander, either before or after contract administration, decreases the risk of contrast-induced nephropathy.[7]

Allergy

Contrast medium reaction

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Main article: Contrast medium reaction

In a more severe reaction:[8]

  • Adrenaline shot, 0.3-0.5mg in adults, given intramuscularly.
  • Summon an anesthesiologist

Pre-medication

Before a contrast CT of a patient with known allergic-like or unknown-type of contrast reaction to the same class of contrast medium (such as iodinated), the American College of of Radiology recommends premedication with a glucocorticoid, preferably starting 12 or 13 hours before contrast administration.[9]

Asthma, atopy, and drug or food allergy have been regarded as generally not conferring enough risk to motivate glucocorticiod premedication.[10]

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.[11] The main phases thereof are as follows:[12]

Phase Time from injection[12] Time from bolus tracking in proximal aorta[12] Targeted structures and findings[12]
Non-enhanced CT (NECT) - -
Pulmonary arterial phase 6-13 sec[13] -
Pulmonary venous phase 17-24 sec[13] -
Early systemic arterial phase 15-20 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 phase 30[14] or 40[15] - 50[15] sec 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[16] 160 sec
Delayed phase
Sometimes called "wash out phase" or "equilibrium phase" 		6[12]-15[16] minutes 6[12]-15[16] minutes
  • Disappearance of contrast in all abdominal structures except for tissue with fibrosis, which appears more radiodense.

Gastrointestinal contrast

Rectally administered contrast is indicated in cases where a suspicion remains of penetrating trauma to the colon where an initial CT shows no reason for immediate surgery.[17]

Notes

  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. ↑ 2.0 2.1 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; et al. (2017). "Tailoring protocols for chest CT applications: when and how?
    ". Diagnostic and Interventional Radiology 23 (6): 420–427. doi:10.5152/dir.2017.16615. ISSN 13053825. 
  3. ↑ 3.0 3.1 3.2 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; 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. 
  4. ↑ 4.0 4.1 4.2 The liver generally needs an enhancement of at least 30 HU for proper evaluation according to:
    • Multislice CT
    (3 ed.). Springer-Verlag Berlin and Heidelberg GmbH & Co. KG. 2010. ISBN 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. (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.  This example takes the example of a man with a typical weight of 70 kg.
  5. ↑ 5.0 5.1 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:
    • Nyman, Ulf (2012). Contrast Medium-Induced Nephropathy (CIN) Gram-Iodine/GFR Ratio to Predict CIN and Strategies to Reduce Contrast Medium Doses
    . doi:10.5772/29992. 

References

  1. ↑ 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. PMID 25247563. 
  2. ↑ Rudnick, M.; Feldman, H. (2008). "Contrast-Induced Nephropathy: What Are the True Clinical Consequences? ". Clinical Journal of the American Society of Nephrology 3 (1): 263–272. doi:10.2215/CJN.03690907. ISSN 1555-9041. 
  3. ↑ 3.0 3.1 Kalgi Modi, Scott C. Dulebohn (2017). Contrast-Induced Nephropathy. StatPearls Publishing. CC-BY-4.0
  4. ↑ Keaney, J. J.; Hannon, C. M.; Murray, P. T. (2013). "Contrast-induced acute kidney injury: how much contrast is safe? ". Nephrology Dialysis Transplantation 28 (6): 1376–1383. doi:10.1093/ndt/gfs602. ISSN 0931-0509. 
  5. ↑ 5.0 5.1 Nyman, Ulf; Ahlkvist, Joanna; Aspelin, Peter; Brismar, Torkel; Frid, Anders; Hellström, Mikael; Liss, Per; Sterner, Gunnar; et al. (2018). "Preventing contrast medium-induced acute kidney injury ". European Radiology. doi:10.1007/s00330-018-5678-6. ISSN 0938-7994. 
  6. ↑ 6.0 6.1 6.2 6.3 . New Zealand Datasheet. New Zealand Medicines and Medical Devices Safety Authority. Retrieved on 2018-10-16.
  7. ↑ Yang, Xiaoming; Hiremath, Swapnil; Akbari, Ayub; Shabana, Wael; Fergusson, Dean A.; Knoll, Greg A. (2013). "Prevention of Contrast-Induced Acute Kidney Injury: Is Simple Oral Hydration Similar To Intravenous? A Systematic Review of the Evidence ". PLoS ONE 8 (3): e60009. doi:10.1371/journal.pone.0060009. ISSN 1932-6203. 
  8. ↑ Unless otherwise specified in lists and table: . Hypersensitivity reactions against contrast media - Swedish Society of Uroradiology [Swedish: Överkänslighetsreaktioner mot kontrastmedel – SURFs kontrastmedelsgrupp ], 2014-10-17].
  9. ↑ Error on call to Template:cite web: Parameters url and title must be specified. . American College of Radiology, Committee on Drugs and Contrast Media. Retrieved on 2018-08-25. Version 10.3. 2018. ACR
  10. ↑ . Guidelines for contrast media pre-medication. Nova Scotia Department of Health and Wellness. Retrieved on 2018-08-25. October 2014
  11. ↑ 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. 
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 Robin Smithuis. CT contrast injection and protocols. Radiology Assistant. Retrieved on 2017-12-13.
  13. ↑ 13.0 13.1 Page 584 in: Ákos Jobbágy (2012). 5th European Conference of the International Federation for Medical and Biological Engineering 14 - 18 September 2011, Budapest, Hungary. Volume 37 of IFMBE Proceedings . Springer Science & Business Media. ISBN 9783642235085. 
  14. ↑ Raman SP, Fishman EK (2012). "Advances in CT Imaging of GI Malignancies. ". Gastrointest Cancer Res 5 (3 Suppl 1): S4-9. PMID 22876336. PMC: 3413036. Archived from the original. . 
  15. ↑ 15.0 15.1 15.2 Otto van Delden and Robin Smithuis. Pancreas - Carcinoma. Radiology Assistant. Retrieved on 2017-12-15.
  16. ↑ 16.0 16.1 16.2 16.3 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
  17. ↑ Stephen Ledbetter and Robin Smithuis (2007-08-02). Acute Abdomen - Role of CT in Trauma. Radiopaedia.
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