MRI

Question 1

Which planes do gradient coils allow spatial encoding in and what plane of images do they produce?

Answer 1

x axis : runs along horizontal axis - sagittal images
y axis: runs along vertical axis - coronal images
z axis: runs along long axis - axial images

Question 2

Identify the pulse sequence

Answer 2

Conventional Spin echo

Question 3

Identify the pulse sequence

Answer 3

Fast Spin echo

Question 4

Identify the pulse sequence

Answer 4

Inversion Recovery (Spin Echo)

Question 5

Identify the pulse sequence

Answer 5

Dual echo spin echo sequence

Question 6

Identify the pulse sequence

Answer 6

FLAIR

Question 7

Identify the pulse sequence

Answer 7

FLAIR

Answer 8

Question 9

What is an MRI pulse sequence?

Answer 9

An MRI pulse sequence is a programmed set of changing magnetic gradients.

Question 10

How are MRI sequences grouped?

Answer 10

MRI sequences can be grouped according to the type of sequence (e.g. spin echo) or by general image weighting (e.g. T1 or T2) and additional features (e.g. fat suppressed or gadolinium enhanced).

Question 11

What is the purpose of multiple sequences in MRI?

Answer 11

Multiple sequences are needed to adequately evaluate a tissue, and the combination of sequences is referred to as an MRI protocol.

Question 12

What is Time to Echo (TE) in MRI pulse sequences?

Answer 12

The echo time (TE) refers to the time between the application of the radiofrequency excitation pulse and the peak of the signal induced in the coil. It is measured in milliseconds. The amount of T2 relaxation is controlled by the TE.

Question 13

What is Time to Repetition (TR) in MRI pulse sequences?

Answer 13

The repetition time (TR) is the time from the application of an excitation pulse to the application of the next pulse. It determines how much longitudinal magnetisation recovers between each pulse. It is measured in milliseconds.

Question 14

What are Spin-echo pulse sequences?

Answer 14

Spin-echo pulse sequences are one of the earliest developed and still widely used of all MRI pulse sequences. They can be adjusted to give T1-weighted, proton density, and T2-weighted images.

Question 15

What is Flip Angle in MRI pulse sequences?

Answer 15

The flip angle is an MRI phenomenon by which the axis of the hydrogen proton shifts from its longitudinal plane to its transverse plane by excitation with radiofrequency pulses.

Question 16

What are Inversion Recovery Pulse Sequences?

Answer 16

Inversion recovery pulse sequences are used to selectively null the signal for certain tissues and can generate heavily T1-weighted images. They involve a preparatory 180° RF pulse to invert longitudinal magnetisation.

Question 17

What is Short tau inversion recovery (STIR)?

Answer 17

Short tau inversion recovery (STIR) is a fat suppression technique with an inversion time that nulls the signal of fat. It cannot be used with gadolinium injection due to T1 shortening effects on tissues.

Question 18

What is Fluid attenuated inversion recovery (FLAIR)?

Answer 18

Fluid attenuated inversion recovery (FLAIR) is a special inversion recovery sequence with a long inversion time to remove signal from cerebrospinal fluid in the resulting images.

Question 19

What does the FLAIR pulse sequence do?

Answer 19

removes signal from the cerebrospinal fluid in the resulting images

Brain tissue on FLAIR images appears similar to T2 weighted images with grey matter brighter than white matter but CSF is dark instead of bright.

Question 20

How is the signal from fluid nulled in the FLAIR pulse sequence?

Answer 20

The inversion time (TI) of the FLAIR pulse sequence is adjusted such that at equilibrium there is no net transverse magnetisation of fluid.

Question 21

What is the purpose of the FLAIR sequence in brain imaging?

Answer 21

It is particularly useful in the detection of subtle changes at the periphery of the hemispheres and in the periventricular region close to CSF.

(Infarction, Multiple Sclerosis, Subarachnoid haemorrhage, head injuries)

Question 22

What is Phase-sensitive inversion recovery (PSIR) in MRI?

Answer 22

refers to an inversion recovery MRI pulse sequence that accounts for the positive and negative polarities and preserves the information of tissue magnetisation during the recovery from the initial 180° inversion pulse and factually doubles the dynamic range.

Question 23

What is Diffusion-weighted imaging (DWI) based on?

Answer 23

measuring the random Brownian motion of water molecules within a voxel of tissue.

Question 24

What is the fundamental idea behind diffusion-weighted imaging?

Answer 24

The attenuation of T2* signal based on how easily water molecules are able to diffuse in that region.

Question 25

What are the key parameters for T1 MRI Pulse Sequence?

Answer 25

TR: <800 TE: <30 flip angle: 90°

Question 26

What are the key parameters for T2 MRI Pulse Sequence?

Answer 26

TR: >2000 TE: >80 flip angle: 90°

Question 27

What are the key parameters for FLAIR MRI Pulse Sequence?

Answer 27

TR: >3000 TE: >80 flip angle: variable inversion time: 1700–2200

Question 28

What properties do nuclei need to have for MRI?

Answer 28

Spin charge

Question 29

What are good MR nuclei?

Answer 29

1H, 13C, 19F, 23Na, 31P

Question 30

What are biological tissues predominantly made of?

Answer 30

12C, 16O

Question 31

What are nuclei made of in MRI?

Answer 31

Nuclei are made of protons and neutrons ## Footnote Both have spin ½. Protons have charge.

Question 32

Which atoms have spin in MRI?

Answer 32

Only atoms with an odd number of protons or neutrons have spin ## Footnote Good MR nuclei are 1H, 13C, 19F, 23Na, 31P.

Question 33

What is the most abundant atom in the body for MRI?

Answer 33

Hydrogen is the most abundant atom in the body ## Footnote The majority of hydrogen is in water (H2O). Essentially all MRI is hydrogen (proton) imaging.

Question 34

What does a moving charged particle generate in MRI?

Answer 34

A moving (spinning) charged particle generates its own little magnetic field ## Footnote Spinning particles with mass have angular momentum. Angular momentum resists attempts to change the spin orientation.

Question 35

What is the purpose of RF electromagnetic fields in MRI?

Answer 35

RF electromagnetic fields are used to manipulate the magnetization of specific types of atoms ## Footnote Some atomic nuclei are sensitive to magnetic fields and their magnetic properties are tuned to particular RF frequencies.

Question 36

What is T1 relaxation in MRI?

Answer 36

T1 relaxation – Flipped nuclei realign with the magnetic field

Question 37

What is T2 relaxation in MRI?

Answer 37

T2 relaxation – Flipped nuclei start off all spinning together, but quickly become incoherent (out of phase)

Question 38

What is T2* relaxation in MRI?

Answer 38

T2* relaxation – Disturbances in magnetic field (magnetic susceptibility) increase the rate of spin coherence T2 relaxation

Question 39

What are the relaxation times used for image contrast in MRI?

Answer 39

Different tissues have different relaxation times. These relaxation time differences can be used to generate image contrast ## Footnote T1 - Gray/White matter. T2 - Tissue/CSF. T2* - Susceptibility (functional MRI). Relaxation time in milliseconds.

Question 40

What are some safety concerns in MRI?

Answer 40

Safety in Magnetic Resonance Imaging. MRI may pose significant hazards to patients and staff due to: 1. Electromagnetic fields. 2. The auditory effects of noise. 3. Inert gas quench. 4. Claustrophobia. 5. I.V. contrast agent.

Question 41

What are the significant hazards to patients and staff during MRI?

Answer 41

1. Electromagnetic fields 2. The auditory effects of noise 3. Inert gas quench 4. Claustrophobia 5. I.V. contrast agent ## Footnote These are potential hazards that may arise during Magnetic Resonance Imaging.

Question 42

What should be ensured before performing MRI on a patient?

Answer 42

Ensure a detailed history of the patient is carried out to check for any ferromagnetic implants such as pins in broken bones or cardiac pacemakers. ## Footnote This precaution is necessary to avoid any complications during the MRI procedure.

Question 43

What happens to radiofrequency above 10MHz during an MRI examination?

Answer 43

It will be converted to heat, which will be distributed by connective heat transfer through blood flow. ## Footnote This explains the process of converting radiofrequency to heat during an MRI.

Question 44

What guidelines are created when using MRI to limit temperature rise?

Answer 44

Guidelines are created to limit the rise in temperature of the skin, body core, and local tissues to levels lower than those that may cause tissue damage (thermal). ## Footnote These guidelines help ensure patient safety during MRI procedures.

Question 45

Why is there noise during an MRI scan?

Answer 45

The noise is due to vibration in the gradient coils and other parts of the scanner caused by varying magnetic fields. ## Footnote This explains the source of noise during MRI scans.

Question 46

What is the noise level that may be achieved during an MRI scan?

Answer 46

Up to 95dB. ## Footnote This noise level is due to the operation of the MRI scanner.

Question 47

How is the MRI unit super cooled?

Answer 47

By using liquid helium and nitrogen. ## Footnote This cooling method is essential for the operation of the MRI unit.

Question 48

What should be done to prevent severe frost bites in case of a breakdown in the MRI unit?

Answer 48

Install a well-ventilated room with an oxygen monitor to raise an alarm. ## Footnote This precaution helps prevent severe frost bites in case of a breakdown.

Question 49

What precaution should be taken when entering the control area of the MRI suite?

Answer 49

Remove all ferromagnetic objects before entering. ## Footnote This precaution is necessary to avoid interference with the MRI equipment.