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]
Contents
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]
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.[4] A Swedish practice is to have a Igram/GFR ratio of maximum 0.7 in patients with GFR ≥45 ml/min.[5] It recommends a ratio of maximum 0.5 if GFR is lower, or in the presence of risk factors.[5]
| Iodine concentration |
1 | 0.7 | 0.5 |
|---|---|---|---|
| 240 mg/ml | 4.2 ml *GFRml/min | 2.9 ml *GFRml/min | 2.1 ml *GFRml/min |
| 350 mg/ml | 2.9 ml *GFRml/min | 2 ml *GFRml/min | 1.4 ml *GFRml/min |
How much contrast is needed
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.
Examples of how much contrast is needed for particular exams are:
- Liver: 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.[6] For example, a body weight of 70 kg and 125 ml of iodine at a concentration of 350 mg/ml confers an expected enhancement of 83 HU.
- Thorax:
- For CT of pulmonary embolism in patients with risk factors, 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).[7]
- Other diseases of the thorax, such as parenchymal changes, can often be evaluated adequately without the use of intravenous 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.[8]
Allergy
Contrast medium reaction
- Main article: Contrast medium reaction
In a more severe reaction:[9]
- 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.[10]
Asthma, atopy, and drug or food allergy have been regarded as generally not conferring enough risk to motivate glucocorticiod premedication.[11]
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.[6] 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 |
|
| Late systemicarterial phase Sometimes also called "arterial phase" or "early venous portal phase" |
35-40 sec | 15-20 sec |
|
| 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 |
|
| Nephrogenic phase | 100 sec | 80 sec |
|
| 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 |
|
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]
References
- ↑ 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:. ISSN 0033-8419. PMID 25247563.
- ↑ 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:. ISSN 1555-9041.
- ↑ 3.0 3.1 Kalgi Modi, Scott C. Dulebohn (2017). Contrast-Induced Nephropathy. StatPearls Publishing. CC-BY-4.0
- ↑ 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:. ISSN 0931-0509.
- ↑ 5.0 5.1 NU Hospital Group, Sweden
- ↑ 6.0 6.1 Bae, Kyongtae T. (2010). "Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches ". Radiology 256 (1): 32–61. doi:. ISSN 0033-8419.
- ↑ 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:. ISSN 1932-6203.
- ↑ 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:. ISSN 1932-6203.
- ↑ 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].
- ↑ 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
- ↑ . Guidelines for contrast media pre-medication. Nova Scotia Department of Health and Wellness. Retrieved on 2018-08-25. October 2014
- ↑ 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.
- ↑ 13.0 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.
- ↑ 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. .
- ↑ 15.0 15.1 15.2 Otto van Delden and Robin Smithuis. Pancreas - Carcinoma. Radiology Assistant. Retrieved on 2017-12-15.
- ↑ 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
- ↑ Stephen Ledbetter and Robin Smithuis (2007-08-02). Acute Abdomen - Role of CT in Trauma. Radiopaedia.
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