6. Contrast media

Question 1

What is the effective atomic number of soft tissue, Barium, Iodine and Gadolinium?

Answer 1

ST = 7

Ba = 56

I = 53

Gd = 64

Question 2

What advantages make barium a good GI contrast medium? what is one downside of pure barium?

Answer 2

• Pros: Inert, not absorbed by GI, highly attenuating
• Pure barium FLOCULATES - poor mucosal coverage

Question 3

What complications / contraindications are associated with barium administration?

Answer 3

• 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

Question 4

If perforation likely, what agent should be used?

Answer 4

• Non-ionic iodinated

Question 5

Features of BIPs

Answer 5

• 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.

Question 6

Describe the effect of ionisation, osmolality and dimerisation on IODINATED contrast media

Answer 6

• 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

Question 7

Descrive contrast agent ratio

Answer 7

Contrast agent ratio = number of iodine atoms / number of particles in solution

=> DIMERS have 2 x ratio of non-ionic monomer, but more viscous

Question 8

Iodinated contrast media adverse effects - OSMOLALITY ASSOCIATED

Answer 8

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

Question 9

What % of dogs and cats demonstrate >10% change in HR, RR or MAP following IV iodinated contrast admin?

Answer 9

Dogs :37.1%

Cats: 31%

Question 10

What CATIONS are present in ionic contrast media

Answer 10

Either SODIUM or MEGLUMINE

Question 11

What role does protein binding have on ionic contrast media? Give an example

Answer 11

• Increased protein binding delays renal excretion and increased hepatic excretion

=> USE IN BILIARY CONTRAST e.g. meglumine iotroxate (Biloscopin)

Question 12

What specific effect can ionicity have on local tissues (besides increased osmolaltiy)?

Answer 12

• Effects e.g. nerve condution, so no good for myelography

Question 13

Features of Ionic Monomers x 4. WHAT IS THE IP RATIO?

Answer 13

Question 14

Features of Nonionic Monomers x 8. WHAT IS THE IP RATIO?

Answer 14

Question 15

Features of Ionic Dimers x 1 WHAT IS THE IP RATIO

Answer 15

Question 16

Features of Non-ionic Dimers x 2. WHAT IS THE IP RATIO?

Answer 16

Question 17

Learn overall trends of iodinate contrast media table

Answer 17

Question 18

Learn contrast agent ratios for different groups of iodinated contrast

Answer 18

Question 19

Define and detail ACUTE / ANAPHYLACTOID contrast reactions

Answer 19

• <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!!!!!

Question 20

Define and detail LATE adverse contrast reactions

Answer 20

>1 hr - < 1 week

-> T cell mediated skin reactions.

Question 21

Define and detail Contrast Induced Nephropathy (CIN)

Answer 21

• 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

Question 22

Detail the effects of iodinated contrast on thyroid function

Answer 22

• 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

Question 23

What adverse effect is reported with negative contrast?

Answer 23

• Air embolism
• CO2 or NO2 (MORE SOLUBLE) preferred over room air

Question 24

What effect do paramagnetic contrast agents have on T1 and T2 relaxation times?

Answer 24

• 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

Question 25

What toxic effects does Gad have? How is this avoided?

Answer 25

- Hepatic necrosis! Highly toxic - Chelated to limit tox

Question 26

What are the two broad categories of Gad based agents?

Answer 26

- Non-specific extracellular -\> act like nonionic iodine and excreted by kidney - Hig relaxivity / Organ specific -\> protein bound, excreted e.g. by hepatobiliary system

Question 27

What are linear Gad agents, and Features of linear Gad agents x 6

Answer 27

- Linear vs cyclic refers to ligand bound to Gad. Linear less stable

Question 28

What are macrocyclic gad agents? Details of x 3

Answer 28

Macrocyclic -\> surround gad ion, more stable than linear

Question 29

List adverse effects associated with Gad

Answer 29

- 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

Question 30

What is nephrogenic systemic fibrosis (NSF)?

Answer 30

- 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

Question 31

How is a bubble study performed?

Answer 31

- 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.

Question 32

Compare and contrast CEUS agents -\> 0, 1st and 2nd gen

Answer 32

- 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!

Question 33

What parameters affect microbubble behaviour? Which one is most important, and how do the bubble behave at different settings?

Answer 33

- 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

Question 34

List adverse reactions reported with CEUS

Answer 34

- Very uncommon: nausea, headaches reported in people - In dogs: collapse, vomiting reported. 1 severe adverse reactiont to Opitson -\> likley due to human albumin content