Question

Which of the following is true about contrast radiography?

• A. In conventional monomeric iodinated contrast media, the iodine atom to solute particle ratio is 3:2.
• B. Injection into an artery is associated with three times more complications than injection into a vein.
• C. A test dose should be performed if a contrast reaction is suspected.
• D. Gadolinium-DTPA crosses the intact blood-brain barrier.

Hint:

Count iodine atoms per molecule versus the particles formed on dissociation of an ionic monomer.

Answer 1

The Correct Option is A

Step 1: Analyse option A.
Conventional (first-generation) ionic monomeric contrast media dissociate in solution into one iodine-carrying anion and one cation, giving 2 particles, while each molecule carries 3 iodine atoms. The iodine atom to solute particle ratio is therefore 3:2. This statement is correct.

Step 2: Analyse option B.
There is no fixed rule that arterial injection causes exactly three times more complications than venous injection. This figure is not valid, so the statement is wrong.

Step 3: Analyse option C.
A test dose is not recommended; small test doses do not reliably predict anaphylactoid reactions and may themselves provoke a severe reaction. Prophylaxis and preparedness are advised instead. So this is wrong.

Step 4: Analyse option D.
Gadolinium-DTPA does NOT cross the intact blood-brain barrier. It enhances only where the barrier is broken down (tumour, infection, demyelination), which is precisely why it is useful for detecting such lesions. So this is wrong.

Hence the correct statement is the 3:2 ratio of conventional monomeric contrast media.