CT with IV contrast
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.
In Swedish practice the standard risk factor questions include presence or absence of:
- Renal or urinary disease
- Thyroid disorders
- Myasthenia gravis: Older forms of iodinated contrast have caused an increased risk of exacerbation of the disease, but modern forms have no immediate increased risk.
- Diabetes and heart disease: These are aggravating factors in low renal function (see CT with IV contrast in low renal function)
Low renal function
- Main article: CT with IV contrast in low renal function
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.
- When it matters
According to European guidelines, the main risk factors of contrast-induced nephropathy:
- Estimated glomerular filtration rate (eGFR) of less than 30 ml/min/1.73 m2 before intra-venous or intra-arterial radiocontrast administration with second-pass renal exposure (passing lungs or other tissues before the kidneys).
- eGFR of less than 45 ml/min/1.73 m2 before intra-arterial administration with first-pass renal exposure or in ICU patients
- Known or suspected acute renal failure
- Large doses of radiocontrast given IA with first-pass renal exposure
- Multiple radiocontrast injections within 48-72 h
Further reading: CT with IV contrast in low renal function
- Main article: Contrast medium reaction
In a more severe reaction:
- Adrenaline shot, 0.3-0.5mg in adults, given intramuscularly.
- Summon an anesthesiologist
- Main article: Prevention of contrast medium reaction
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.
Patients at risk for contrast-induced hyperthyroidism are mainly those with diagnosed yet untreated hyperthyroidism, which may motivate contrast-free alternatives such as using a different modality.
In older patients with multinodular goiter and borderline low or subnormal TSH concentrations, a suggested measure is measurement of thyroid function tests three to four weeks after contrast administration. Limited evidence suggests that antithyroid agents before the investigation may blunt or prevent hyperthyroidism.
Iodinated contrast in pregnancy, when orally administered, is harmless. Intravenous administration of iodinated radiocontrast agents can cross the placenta and enter the fetal circulation, but animal studies have reported no teratogenic or mutagenic effects from its use. There have been theoretical concerns about potential harm of free iodide on the fetal thyroid gland, but multiple studies have shown that a single dose of intravenously administered iodinated contrast medium to a pregnant mother has no effect on neonatal thyroid function. Nevertheless, it generally is recommended that radiocontrast only be used if absolutely required to obtain additional diagnostic information that will improve the care of the fetus or mother.
American College of Radiology guidelines state that iodinated contrast administration to a breastfeeding mother is considered safe for both the mother and child. Still, mothers who remain concerned about any potential adverse effects to the child are recommended to have the option of abstaining from breastfeeding for 24 hours, with continued milk extraction such as by a breast pump during that period. Mothers that opt for this for non-emergent exams may also use a breast pump to obtain milk before the exam in order to feed the child during the 24-hour abstinence period.
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. The main phases thereof are as follows in table below.
CT angiography is a CT scan corresponding with contrast filling one or more blood vessels of interest.
|Phase||Time from injection||Time from bolus tracking in proximal aorta||Targeted structures and findings|
|Non-enhanced CT (NECT)||-||-|
|Pulmonary arterial phase||6-13 sec||-|
|Pulmonary venous phase||17-24 sec||-|
|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 or 40 - 50 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||160 sec|
Sometimes called "wash out phase" or "equilibrium phase"
|6-15 minutes||6-15 minutes||
See CT#By location (CT with IV contrast, including CT angiography, is organized as other CT examinations).
- For a full list of contributors, see article Radlines:Authorship for details. . Creators of images are attributed at the image description pages, seen by clicking on the images. See
- 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.
- NU Hospital Group, Sweden
- Mehrizi, Mehyar; Pascuzzi, Robert M. (2014). "Complications of radiologic contrast in patients with myasthenia gravis ". Muscle & Nerve 50 (3): 443–444. doi:10.1002/mus.24254. ISSN 0148639X. PMID 24677227.
- 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.
- 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.
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- Martin I Surks, MD. Iodine-induced thyroid dysfunction. UpToDate. This topic last updated: Apr 02, 2019.
- . Guidelines for Diagnostic Imaging During Pregnancy and Lactation. American Congress of Obstetricians and Gynecologists. February 2016
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