Magnetic Resonance Imaging

Question 1

What EMR is used in MRI?

Answer 1

Radiowaves (and a Magnetic field is used)

Question 2

T1 Hypo intense is what colour

Answer 2

dark

Question 3

T2 Hyper bright is what colour

Answer 3

White

Question 4

Ferro-magnetic

Answer 4

Strongest force of magnet

Stays magnet

Question 5

SAR

Answer 5

Specific adsorption rate

Heats up patient

Question 6

Homogeneity

Answer 6

All the same
All the magnets are in rows, that’s why it’s 50cm

Radio frequency
We want coils close cause inverse square law

Question 7

Gradient coil

Answer 7

Pairs of the coils

On gradient axes to the patient

Question 8

Paramagnetic

Answer 8

Slightly magnetic

Gadolinium

Question 9

Didgeridoo

Answer 9

Vibration MRI

Same frequency of sound

Question 10

Super-conducting magnet

Answer 10

No resistance
Using liquid helium low temp
So it’s superconducting as there is no resistance

Question 11

Pixel

Answer 11

A picture element
Pixels are bigger in MRI compared to CT
Poor signal to noise frequency

Question 12

Matrix

Answer 12

Made up of pixels
You want a large matrix small pixel
But MRI has large pixel and small matrix

Question 13

Larmour Frequency

Answer 13

Larmour frequency equation

Frequency is equal to magnetic field strength

Question 14

Voxel

Answer 14

Volume element to give pixel

Question 15

M0

Answer 15

Bodies magnetic field

Influence by the MRI to line up

Question 16

1 Tesla is what gauss

Answer 16

10000

Question 17

Missile effect

Answer 17

If you bring metal into MRI room it will launch towards MRI machine

Question 18

Deflection

Answer 18

Twist to follow the MRI scanner

Question 19

MR safe

Answer 19

Safe for MRI

Question 20

MR conditional

Answer 20

You might be able to scan

Question 21

MR unsafe

Answer 21

Not safe for MRI

Question 22

In medical emergency

Answer 22

Take the patient out the room as the cardiac team may have metal equipment
Usually MRI have their own trolley for this reason

Question 23

5 guass

Answer 23

5 guass line is how far the metal field strength is

Always in the MRI room

Question 24

Implant effects the scan how

Answer 24

They are safe
But it makes area dark so you can’t see there

But if you don’t know it’s there smear the artefact across the image

Question 25

Uncontrolled quench | Controlled quench

Answer 25

Is to let the helium gas out safely, warm it up slowly If it was to leak into the room it would cause dissipation of oxygen so you couldn't breathe Could explode

Question 26

How to deal with claustrophobia

Answer 26

Patients with bad claustrophobia will not be able to have MRI Cognitive methods reassurance eye masks mirrors on the head coil so the patient can see you at the scanner mild oral medication such as low dose diazeplam IV sedation is not safe for MRI because it can be magnetic the equipment

Question 27

Radio frequency burns

Answer 27

radio frequency waves raise the patient's temp different sequences in MRI have different SAR levels changes can be made to the MRI protocol to limit the heating but it takes longer radio frequency burns can be caused by skin-to-skin contact that can form a loop which leads to heating ECG and overweight patients are also a risk Sponge pads may be used to prevent skin to skin contact

Question 28

What is the most common element and why is it used for MRI

Answer 28

Hydrogen is chosen because:- 1. It is very abundant in the body (approx 10% of body mass is Hydrogen) 2. It gives the strongest MRI signal ``` Hydrogen has a single spinning proton (+ve) • A moving (spinning) charge creates a magnetic field • This results in the nucleus acting like a small bar magnet ```

Question 29

MRI involves 3 physical principles:-

Answer 29

1. Nuclear - the nuclei of certain atoms behave like small bar magnets 2. Magnetic – when placed in a strong magnetic field, these small bar magnets align with the field and precess 3. Resonance - if a radio frequency pulse is applied to these nuclei, some resonate and absorb energy and re- emit the energy as an MRI signal

Question 30

Protons from M0 change to what

Answer 30

B0 some hydrogens may spin in the opposite direction M0 perpendicular to B0 to measure it

Question 31

Advantages of MRI

Answer 31

No rad Soft tissue contrast resolution safer contrast, fewer contraindications Multimodal- functional, anatomical angiographic in one exam

Question 32

Disadvantages of MRI

Answer 32

``` longer time Claustrophobic metal devices, magnets Noisy Expensive to buy, and less staff, equipment for the MRI ```

Question 33

Pregnancy is a contraindication in what trimester

Answer 33

the first trimester

Question 34

Proton density T1 T2 How long are the tr and te?

Answer 34

long tr short te its proton density short tr and short te its T1 Long tr and long te its T2

Question 35

T1, what colour is water

Answer 35

Water is dark

Question 36

T2, what colour is water

Answer 36

Light

Question 37

TR means what

Answer 37

Time to repeat

Question 38

TE means what?

Answer 38

Time to echo

Question 39

Precessional frequency means what

Answer 39

How fast the hydrogen spins around B0 how fast it wobbles RF pulse has to be the same frequency in order to flip the hydrogen from longitude to transverse plane (to take MRI picture)

Question 40

What is measured?

Answer 40

During excitation using the RF all the atoms are put on the same spin path at the same precession We measure the point of the rotation as it causes a net magnetic field in the direction they are all pointing Same transverse magnetism

Question 41

How do the spins depend on the tissues?

Answer 41

After the RF is stopped the atoms stay to go back to normal and stop spinning again Different tissues return back at different rates Spins recover at different rates depending on the type of tissue

Question 42

T1 recovery curve

Answer 42

Recovery of longitudinal magnetization | Rate of different tissues to go back to normal spin

Question 43

T2 relaxation curve

Answer 43

Transverse magnetization Decay process moving out of phase with each other once the RF is switched off

Question 44

Receiver coils do what?

Answer 44

Have to be close to the part measuring | collects the signal whilst recovery/relaxation takes place

Question 45

FLAIR meaning

Answer 45

Fluid Attenuated Inversion Recovery - Protons in tissue water

Question 46

What different coils are used in MRI?

Answer 46

Y coil Z coil X coil Transceiver coil

Question 47

What does the information that is given on the screen with an MRI image represent?

Answer 47

What T1 or T2 it is

Question 48

Patient prep

Answer 48

Remove all the metal objects from the patient Keys, coins, mobile phone, hair-grips, watch Credit cards and travel cards will be wiped if taken into the room Clothing with metal attached? Artificial limbs or callipers

Question 49

What contra-indications there are to MRI?

Answer 49

``` Pregnant Metal fragments in body e.g gunshot Any metal implants Cardiac pacemaker Claustrophobia (any contradictions to contrast) ```

Question 50

Explain how an MRI image is created.

Answer 50

Magnetic resonance imaging (MRI) uses the movement of protons within a magnetic field to generate an image. The coils send different RFs to the tissues and depending on the coil will affect which way the atoms will face and spin. Then you wait some time as the tissues start to go back to their original spin. Then the Transceiver coil will measure the magnetic field given off the tissues (the tissues will give off different MF depending on which ones it is, some tissues go back to normal faster than others)

Question 51

What must you do if someone has a neurotransmitter device?

Answer 51

Check that its MRI compatible/safe | Will have to use a special low frequency to ensure that the MRI doesn't affect the neurotransmitter device.

Question 52

Recognize the different sequences (T1 and T2) that may be used.

Answer 52

You can tell by what the colour of the water is | or the graphs in the PowerPoint.