Question

What is the ratio of cost of a “typical” MRI vs. CT scan for the same region (head, chest, etc.)?

What is MRI— what kind of image does it create and how?

Who invented MRI and when?

What are two reasons on why use a MRI instead of a CT scan?

If you get more information from MRI, why are CT scans still used?

What are T1 and T2 and what role do they play in imaging?

What sort of radiation is involved? Are MRIs “perfectly safe”? If not, what are the dangers?

Answer 1

1. The average cost for an MRI scan in USA is about $2611 wheras average cost for a CT scan is about $1200. Therefore, the ratio of cost for an MRI scan to that of an CT scan is about 2.2:1.

2. MRI stands for Magnetic Resonance Imaging. It is an non-invasive technique used in the diagnostics to create detailed images of organs in the body. MRI creates 3-dimensional images of any part of the body using the technique of magnetic resonance.

Hydrogen atoms in our body (eg. in water molecules) has a certain nuclear magnetic momentum due to the proton present in the nucleus. When undisturbed all the magnetic moments are in random directions, effectively cancelling out the overall effect. However, when a magnetic field of about 1.5 Tesla(as in cases of MRIs) are applied, all the magnetic moments are aligned in the direction of magnetic field. If a small extra energy is provided, in the form of radio frequency waves, these protons reacha state of resonance. This extra energy required to reach resonance is dependant on the applied magnetic field.

If the radio frequency waves are switched off, protons come to ground energy by emitting out a radiation. The emitted rays are collected and analysed to create a 3-dimensional image of the body part.

3.Raymond Vahan Damadian invented MRI in the year 1977.

4. (i) MRI uses magnetic field and low energy radio waves for imaging instead of ionising radtions used in CT scan.

(ii) The contrast agents used in MRI is much safer than that of CT scan.

(iii) MRI can image organs that are obscured by bones (eg. brain), whereas CT scan cannot.

5. (i) CT scans give accurate informationon calcification.

(ii) CT scans happen very rapidly, making it extremely usefulin cases of trauma.

(iii) It is a better option for patients with claustrophobia.

(iv) Ct scans are cost effective.

6. T1 (longitudinal relaxtaion time) is the time taken by protons to align themselves in the direction of applied magnetic field. T1 weighted imaging uses T1 values to differntiate betwwen tissues. Tissues with fat molecules appear bright and spaces with water molecules appear dark in T1 weighted images.

T2(transverse relaxtaion time) is the time taken by aligned protons to lose thier coherence (or alignment). T2 weighted imaging uses T2 values to differntiate betwwen tissues. Tissues with fat molecules appear dark and spaces with water molecules appear bright in T2 weighted images.

7. Radiation used in MRI is low energy radio frequency waves. As high energy ionising waves are not used MRIs are completely safe in the radiation crieteria. The only side effect MRI can have is very rare occasions of allergy due to contrasting material used. The allergy is mild and can result in headache or nausea.