MRI worksheet

Question 1

1. What properties do Hydrogen-1 nuclei have that make them ideal for imaging in MRI

Answer 1

Hydrogen nuclei only have 1 proton and are abundant in the human body.

Question 2

2. Explain in detail, what happens to the Hydrogen nuclei when placed in a magnetic field

Answer 2

When the hydrogen nuclei are placed in a magnetic field, their moment align parallel to spin up because of the direction of the magnetic field. The Hydrogen nuclei then start to precess.

Question 3

3. What happens to the precessional frequency of our Hydrogen nuclei as we increase the magnetic field strength?

Answer 3

The precessional frequency of the Hydrogen nuclei will increase in direct proportion to the increase in direct proportion to the external magnetic field strength.

Question 4

4. Explain what happens when we apply a radiofrequency at the resonant frequency of our precessing Hydrogen nuclei?

Answer 4

When a radiofrequency is applied at the resonant frequency of our precessing Hydrogen nuclei the nuclei start to spin in phase with each other

Question 5

5. Explain what is meant by the term longitudinal relaxation (or longitudinal recovery)

Answer 5

Longitudinal relaxation occurs when the spins of the hydrogen nuclei relax back to a lower energy state.

Question 6

6. Explain what is meant by the term transverse relaxation (or transverse decay)

Answer 6

Transverse relaxation occurs when the radiofrequency pulse is turned off and the hydrogen nuclei go back to spinning out of phase.

Question 7

7. Explain what happens during the pulse sequence “spin echo”

Answer 7

In the spin echo pulse sequence the time to echo (TE) and time between repetitions (TR) can be manipulated to alter the weighting between T1 and T2 relaxation to alter the appearance of the image overall

Question 8

8. What do the terms TE and TR stand for?

Answer 8

TE is time to echo while TR is time between repetitions

Question 9

9. Which tissue weighting is best at showing common pathologies and why?

Answer 9

T2 is best for showing common pathologies as pathologies are high in water content. T2 shows water as very bright meaning the pathologies will be more easily detectable.

Question 10

10. Which tissue weighting is achieved by using a long TE and long TR?

Answer 10

T2 tissue weighting

Question 11

11. What are the advantages and disadvantages of superconducting magnets used in MRI?

Answer 11

Superconducting magnets are good at creating intense magnetic fields but can be very expensive because of the energy required to operate them.

Question 12

12. What are the risks of the main magnetic field in MRI and how can these be minimised?

Answer 12

The risks of the main magnetic field in MRI include ferromagnetic objects. Due to the strong magnetic field used in MRI these ferromagnetic objects will be extremely attracted and can potentially turn into dangerous projectiles while in the magnetic field. These risks can be minimised by thoroughly making sure that there are no ferromagnetic objects in the room of the MRI scanner and that the patient doesn’t have any metal objects near them.

Question 13

13. What do the gradient coils do?

Answer 13

Gradient coils allow a linear variation of magnetic field strength over a distance.

Question 14

14. What are the risks of the gradient magnetic fields in MRI and how can these be minimised?

Answer 14

The risks of gradient magnetic fields in MRI mainly concern the effects of the noise produced which can damage hearing. These risks can be minimised by giving the patient ear plugs to wear during their MRI to protect their ears

Question 15

15. What do the Radiofrequency coils do?

Answer 15

Radiofrequency coils broadcast the radiofrequency signal to the patient and also receive the return signal.

Question 16

16. What are the main risks of the radiofrequency fields in MRI?

Answer 16

Radiofrequency fields can potentially induce currents in wires close to the patient which can cause skins burns and induce currents in intracardiac leads causing the cardiac pacing to not function properly.

Question 17

17. What are the main concerns with gadolinium?

Answer 17

The main concerns with gadolinium are its side effects which include pain on the point in which it was injected, nausea, itching, rashes, headaches and dizziness.

Question 18

18. What is meant by the term quench and when would you press the quench button?

Answer 18

The term quench is used to refer to stop the MRI machine from continuing to function. When the quench button is pressed the magnetic field strength goes down to zero.

Question 19

19. List the main advantages and disadvantages of MRI

Answer 19

The main advantages of MRI include no radiation being needed, high quality images to distinguish different parts of the body and being able to construct three dimensional detailed images of the patient. The disadvantages include the expensive cost of MRI machines, the risks associated with metal items close to the MRI machine and the potential harm that can be inflicted upon the patient due to metallic objects or the sounds coming from the MRI machine

Question 20

20. What questions would you expect to find on a patient safety checklist in MRI?

Answer 20

The patient would be asked if they have had any surgery, implants, if they are wearing hair accessories like wigs and hair pins, if they have had any other procedures that need penetration into the body by metal surgical tools, the date of the patient’s LMP, if the patient is pregnant or breast feeding, if they are wearing removable braces or hearing aids and if they have any drug allergies.