6. Contrast media Flashcards
What is the effective atomic number of soft tissue, Barium, Iodine and Gadolinium?
ST = 7
Ba = 56
I = 53
Gd = 64
What advantages make barium a good GI contrast medium? what is one downside of pure barium?
- Pros: Inert, not absorbed by GI, highly attenuating
- Pure barium FLOCULATES - poor mucosal coverage
What complications / contraindications are associated with barium administration?
- Leakage into abdomen / mediastinum-> Severe complication - forms fibinous adhesive peritonitis, with associated exudative process whitch results in hypovolameia and hypoalbuminaemia
- Aspiration: Small volume likely Ok (used to do bronchography), but large volume can be fatal. May persist -> incorporation into macrophages, interstitium and regional nodes => TIME AND VOLUME DEPENDENT
- Others: retention in colon (barolith), IV migration, allergic reactions
If perforation likely, what agent should be used?
- Non-ionic iodinated
Features of BIPs
- 1.5 and 5mm sizes
- CANNOT assess mucosa
- Primarly used for : pyloric or intestinal obstruction. May be useful in partial, as smaller BIPS pass and larger BIPs cannot.
Describe the effect of ionisation, osmolality and dimerisation on IODINATED contrast media
- Ionisation -> greater osmolality as dissociate in solution
- Osmolality -> effect on osmosis, resulting on more adverse reaction
- Dimerisation -> adding additional iodine containing benzene rings into molecule = more iodine with less solute -> less osmolar. HOWEVER larger molecule, more viscous
Descrive contrast agent ratio
Contrast agent ratio = number of iodine atoms / number of particles in solution
=> DIMERS have 2 x ratio of non-ionic monomer, but more viscous
Iodinated contrast media adverse effects - OSMOLALITY ASSOCIATED
RBC dessication / small vessel obstrucion and hypoxia
Leukocyte dysfunction
Endothelial disturbance -> TE +- pulmonary oedema
Anticoagulant properties
Haemodynamic: vasodilation / osmotic hypervolaemia
Cardiac rhythm disturbances, HR and BP
What % of dogs and cats demonstrate >10% change in HR, RR or MAP following IV iodinated contrast admin?
Dogs :37.1%
Cats: 31%
What CATIONS are present in ionic contrast media
Either SODIUM or MEGLUMINE
What role does protein binding have on ionic contrast media? Give an example
- Increased protein binding delays renal excretion and increased hepatic excretion
=> USE IN BILIARY CONTRAST e.g. meglumine iotroxate (Biloscopin)
What specific effect can ionicity have on local tissues (besides increased osmolaltiy)?
- Effects e.g. nerve condution, so no good for myelography
Features of Ionic Monomers x 4. WHAT IS THE IP RATIO?
Features of Nonionic Monomers x 8. WHAT IS THE IP RATIO?
Features of Ionic Dimers x 1 WHAT IS THE IP RATIO
Features of Non-ionic Dimers x 2. WHAT IS THE IP RATIO?
Learn overall trends of iodinate contrast media table
Learn contrast agent ratios for different groups of iodinated contrast
Define and detail ACUTE / ANAPHYLACTOID contrast reactions
- <1 hour after admin
- Less severe: Vomiting, urticaria
- More severe: Bronchospasm, layrngeal oedema, hypotensive shock, pulmonary oedema, respiratory or cardiac arrest
E.g. Horses with distal limb CT: 5% urticaria / oedema, 4% HR / BP changes
FATALITY ESTIMATED AT 1 in 80 PATIENTS!!!!!
Define and detail LATE adverse contrast reactions
>1 hr - < 1 week
-> T cell mediated skin reactions.
Define and detail Contrast Induced Nephropathy (CIN)
- Definition: Increase in serum creat > 25% / >44micmol/L / 0.5mg/dl WITHIN 3 DAYS, where other causes ruled out
- Rx features: persistent nephrogram 24-48hrs post
- Risk factors: Renal impairment (particularly diabetic neprhopathy in people), dehydration, CHF, nephrotoxic drugs (NSAIDS, aminoglycosides), Metformin administration
=> increased creat seen within 1 week in 7.6% of dogs in one study
Detail the effects of iodinated contrast on thyroid function
- Iodine induced thyrotoxicosis - advised to not give to HyperT people. NOT REPORTED IN ANIMALS
- Small amount of free iodine -> may interfere with uptake of radioactive iodine
=> Advise delay (circa 14 days) between contrast and RI
What adverse effect is reported with negative contrast?
- Air embolism
- CO2 or NO2 (MORE SOLUBLE) preferred over room air
What effect do paramagnetic contrast agents have on T1 and T2 relaxation times?
- SHORTEN BOTH T1 AND T2
=> Increased T1 signal, decreased T2 signal
E.g. Gad, manganese
Gad (heavy metal) used as has most pronounced shortening effect on T1 relaxation times
What toxic effects does Gad have? How is this avoided?
- Hepatic necrosis! Highly toxic
- Chelated to limit tox
What are the two broad categories of Gad based agents?
- Non-specific extracellular -> act like nonionic iodine and excreted by kidney
- Hig relaxivity / Organ specific -> protein bound, excreted e.g. by hepatobiliary system
What are linear Gad agents, and Features of linear Gad agents x 6
- Linear vs cyclic refers to ligand bound to Gad. Linear less stable
What are macrocyclic gad agents? Details of x 3
Macrocyclic -> surround gad ion, more stable than linear
List adverse effects associated with Gad
- Rarer than iodine
- Acute: renal / CIN (uncommon), mild haemotdynamic, anaphlyaxis reported
=> Non renal effects less common because, despite potential high osmolality of some agents, LOWER DOSES of agent
What is nephrogenic systemic fibrosis (NSF)?
- Gad associated adverse effect in reduced renal function -> NOT DESCRIBED IN ANIMALS
- Longer retention of gad in body -> more free gad -> Macrophages -> fibrotic changes => thickenign / hardening of skin, muscle weakness, bone pain, joint contractures, major involvement of lower extremitites
- Occurs weeks to years after
- ASSOCIATED WITH LESS STABLE LINEAR AGENTS -> tend to use cyclic agents now
How is a bubble study performed?
- Injection of agitated saline in venous catheter -> Visualised in R SIDE of heart
- Will pass into pulmonary circulation, and not reach L side as break down (large bubbles cannot pass through capillary bed)
- Should not arrive in L side unless R-> L shunt.
Compare and contrast CEUS agents -> 0, 1st and 2nd gen
- Agitated saline -> large air bubbles, cannot pass through pulmonary circulation (cardiac bubble studies)
- 1st gen (e.g. Levovist) -> Smaller air bubbles, stabilised by surfactant. More stable, longer window. BUT still dissolution into blood so reduced SNR
- 2nd gen (e.g. Sonovue) -> smaller iner gas bubbles, more stable, longer window, insoluble!
What parameters affect microbubble behaviour? Which one is most important, and how do the bubble behave at different settings?
- ACOUSTIC POWER, resonance frequency, depth, properties of agent
- POWER MOST IMPORTANT
Mechanical index (MI) = summarises contribution of factors to power e.g. output, transmitted freq, attenuation with depth.
MI < 0.2 = bubbles oscillate in linear fasion, similar to surrounding tissue
MI 0.2-0.5 = non-linear oscillation, generate harmonics -> differentiate from tissue
MI >0.5 = expand and destroyed -> transient strong non linear echo
List adverse reactions reported with CEUS
- Very uncommon: nausea, headaches reported in people
- In dogs: collapse, vomiting reported. 1 severe adverse reactiont to Opitson -> likley due to human albumin content
