Contrast Media- methods

Flashcards on Contrast Media in CT Scanning

Contrast Media (CM)

Used to distinguish anatomical structures, detect pathologies, and classify pathologies in CT scanning.

Types of Contrast Media

Intravenous (iodinated), Oral/Rectal (Barium sulfate, Iodine), Water, Air

Examples of Intravenous Contrast Media

Omnipaque, Biliscopin

Example of Oral Barium Sulfate Contrast Media

Readi-Cat

Example of Oral Iodine Contrast Media

Ioscan, Gastrografin

eGFR Guidelines for IV Contrast

eGFR >45: no special precautions, eGFR 30-45: pre-hydration recommended, eGFR <30: risk vs benefit assessment

Lactic Acidosis Risk

Patients with stable renal function and eGFR> 30mL/min/1.76m2 are at low to no risk of developing lactic acidosis

Untreated Hyperthyroidism and Contrast Media

Risk of developing thyrotoxicosis following ICM administration

Radioisotope Scanning of the Thyroid

Isotope uptake will be prevented for 8 weeks post ICM administration

Breastfeeding and Contrast Media

Cessation of breastfeeding after ICM is not required.

Body Weight Impact on Contrast Enhancement

Larger patients have a larger blood volume, leading to more dilution of contrast and decreased enhancement.

Body Composition Impact on Contrast

Adipose tissue is less perfused than muscle, requiring a greater contrast volume for muscular individuals to achieve the same enhancement.

Cardiac Output Impact on Contrast Timing

Cardiac output affects the timing of contrast enhancement; low cardiac output delays contrast arrival and slightly increases peak enhancement.

Phases of Tissue Enhancement

Non-contrast, Arterial, Portal Venous, Delayed

Arterial Phase

Aorta brighter than IVC

Portal Venous Phase

Both venous and arterial system enhanced; organ parenchyma enhanced

Delayed Phase

Dilute contrast throughout veins, arteries and organs

High Contrast Density

Needed for CT angiography (CTA), short scan <10s, injection rates ≥ 4ml/s

Medium Contrast Density

Majority of CT (e.g. CT of abdomen), injection rates 2-3ml/s

Saline Flush

Increases the iodine load, reduces mixing of CM in blood, reduces artifact from SVC and subclavian veins, recommended for all CT angiograms.

Tube Voltage (kVp) and Contrast Enhancement

Decreasing tube voltage increases contrast enhancement for a given iodine blood concentration, but affects radiation dose and image quality.

Test Bolus

A small amount of contrast is injected, and repeated low-dose scans are taken to create a timing vs density graph to determine peak enhancement time.

Bolus Tracking

A low-dose single scan is taken over the key vessel, and repeated scans are performed to monitor HUs increase until peak enhancement is reached, triggering the scan.

Adverse Effects of Contrast Media

Warm sensation, metallic taste, flushing, nausea, pruritis, vomiting, headache, mild urticaria.

Moderate Adverse Effects of Contrast Media

Severe vomiting, marked urticaria, bronchospasm, facial/laryngeal oedema, vasovagal attacks.

Severe Adverse Effects of Contrast Media

Hypovolaemic shock, respiratory arrest, cardiac arrest, convulsions

Patient Prep for Contrast Media

Patients alerted to sensations of CM administration and that sensations will pass quickly

Structure of Contrast Media

Iodine-based CM consists of a benzene ring with 3 iodine atoms, can be monomeric or dimeric.

Charge of Contrast Media

Ionic CM dissociate into ions and have higher toxicity; non-ionic CM do not dissociate and are most commonly used.

Osmolality of Contrast Media

Iso-osmolal is ideal (similar to blood); high and low are relative to each other, not to blood; monomeric CM have higher osmolality.

Viscosity of Contrast Media

Increases with contrast concentration, decreases with increased temperature; dimers are more viscous than monomers.

Concentration of Contrast Media

Ranges from 240-400mg of iodine per ml; higher concentration increases risk of negative outcomes like CI-AKI.

Distribution of Contrast Media

CM consists of large molecules; primarily distributed in the bloodstream; BBB prevents distribution into brain tissue and normal CNS.