Radiological contrast media

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Many radiological imaging modalities depend on the inherent contrast in the physical properties of biological tissues. Where insufficient contrast exists, this can be artificially augmented with a contrast agent.

Most are designed to be removed from the body within hours to days, but sometimes contrast material can be deployed for longer periods of time. For instance, hydrogel markers can be injected at the same time into the same area as a biopsy, for subsequent easy localisation (as a so-called fiducial markers). Some are combined with a metal coil so as to be visible across radiological imaging modalities (e.g. HydroMARK®).

Contents

Ultrasound

Microbubble contrast media. These are small bubbles that reflect ultrasound waves, but are too small to cause air embolism.

X-ray

  • Rely on the heavier chemical elements like iodine and barium.
  • Iodine-based media can be classified into ionic/non-ionic and low/high osmolar.

Applications:

Complications of X-ray Contrast Agents

LogoKeyPointsBox.pngPrior to intravascular contrast check for history of:
  1. Previous contrast reaction
  2. Asthma
  3. Renal problems (know current renal function usually)
  4. Diabetes mellitus
  5. Metformin therapy

Please see appropriate current guidelines for prevention[1]. Generally:

  1. Non-ionic, low or iso-osmolar iodinated intravascular media are much safer than the older, high osmolar ionic contrast media
  2. Personnel and facilities should be available to assess and treat an allergic reaction where intravascular contrast agents are used
  3. If a previously reported severe reaction to intravascular contrast, caution should be exercised and the need for the use of contrast should be reassessed
  4. Dose of non-ionic iodine-based contrast medium should be minimised
  • Intravascular low osmolar iodine contrast has a complication rate of 0.15% (very severe 0.004%)[1]
  • Contrast-induced acute kidney injury (CI-AKI, contrast nephrotoxicity, contrast-induced nephropathy (CIN),radiocontrast nephropathy (RCN), particularly in patients with pre-existing renal impairment or diabetes mellitus.[2][3] Local guidelines vary, but the FCR 2015 guidance mentions a eGFR of less than 40 ml/min/1.73 m2
  • Allergic reactions are also recognised, ranging from mild wheeze to full blown anaphylaxis.[4][5]. However, given the relative rarity of serious anaphylactic reactions, pre-medication to prevent such occurances are difficult to justify, particularly on the basis of number needed to treat.[6]
  • Formerly metformin was with held for up to 48 hours after[7][8]. However the current advice is "There is no need to stop metformin after contrast in patients with serum creatinine within the normal reference range and/or eGFR > 60ml/min/1.73 m2. If serum creatinine is above the normal reference range or eGFR is below 60, any decision to stop metformin for 48 hours following contrast medium administration should be made in consultation with the referring clinic."[1]
  • Extravasation injuries - see guidelines for treatment: [9].

MRI

  • Gadolinium-based contrast agent(GBCA)
    • Adverse events in 0.04% (severe in 0.0025%)[1]
    • Renal function must be known for all patients receiving agents deemed as high risk
    • High risk GBCAs for the development of nephrogenic systemic fibrosis (NSF) are contraindicated in patients with severe chronic or acute renal impairment, patients in the peri-operative liver transplantation period and in neonates.

External links

References

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