This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Non-Iodine containing contrast is 
Select and explain. 
A. Gd DTP A, B. Visipaque, C. Iohexol, D. Diatrizoate
A: Gd DTP A
Answer: A: Gd DTP A 
Explanation: Ans is 'a' i.e. Gd DTPA Gadolinium DTPA is a contrast agent for MRI. It contains paramagnetic metal ions Gadolinium and not iodine. Gadolinium affects MR signal properties of surrounding tissues. It reduces the T1 and T2 relaxation time. This increases tissue signal intensity on T1-weighted MR images and has almost no effect on T2-weighted images. All the other options are iodine-containing contrast agents. Iodine in these contrast agents provides radio-opacity needed for visualization of structures on x-ray or CT. Iodine is the only element that has proved satisfactory for general use as an intravascular radiological contrast medium.