CSB063 TEST WITH COMPLETE
SOLUTION
5 advantages of MRI - Answer No radiation, good spacial resolution, good for brain/ soft
tissue imaging, non invasive
5 disadvantages of MRI - Answer Loud, claustrophobic, expensive, inaccessible,
contraindications
What is B0 - Answer Main magnetic field, net magnetisation in human body
What is B1 - Answer Radio frequency field used to energise the magnetisation,
generated by transmit coils
Define gradient field - Answer Allows for localisation of nucleus due to imhogeneities in
magnetic field
Why is hydrogen used - Answer Lots of hydrogen in the body, they tend to align with the
magnetic field (spin up), free electron and net positive charge
What is the fridge field - Answer Magnetic field extends widely, decreasing in strength
as you travel away
What are the four safety zones - Answer 1) public area
2) screening area
3) post screened patients
4) scan room, restricted and supervised
What is SAR - Answer Specific absorption rate, temp increase during MRI must be
managed <1Cº
How to decrease SAR - Answer Thinner slices, longer TR, include pause, increase fan
speed
Explain net magnetic vector (NMV) - Answer Measure of the net alignment of hydrogen
to magnetic field, spins up positive and spins down negative, as B0 increases, less spins
down
What is resonance - Answer When an object is forced to vibrate at its natural frequency,
happens in magnet
How to get RF pulse to excite hydrogen - Answer The Lamor frequency of the nucleus
must equal the frequency of RF pulse used or wont excite
, What is the Lamor frequency? - Answer The rate that the nucleus is resonating in the
magnetic field
What is longitudinal relaxation (TR) - Answer RF pulse used to knock the align nucleus
90º, the time to relax back to being aligned to magnetic field is TR
What is transverse dephasing - Answer Over time the nuclei don't remain fully aligned to
B0 as some spin faster and slower, different lamor frequency then needed for different
areas
Causes of transverse dephasing - Answer Magnetic field imhogeneities (fixable ish)
Spin-spin (can't be fixed)
What is spin-spin - Answer Happens when each nuclei has its own little magnetic field
which influences the nucleis around it
What is time to echo - Answer Time from 90º RF pulse to when the signal is aquired,
longer TE is less signal due to dephasing
What is spin echo - Answer 180º pulse used to flip the dephasing spins so they realign
with B0 and regain signal, is done at 1/2 TE
What are field gradients - Answer Due to the magnetic field imhogeneities, different
areas have different lamor frequency, so to pick area use that lamor frequency
What is slice gradient - Answer Picks which slice, thinner slice is thinner slice gradient
What is phase and read gradients - Answer Used to split the slice into columns and
rows, phase first
what is k space - Answer How signal is compartmentalised, dictated by phase and read
squares, most signal is center of k space
What is Fourier transformation and how is it used - Answer Converts signal from time
domain to frequency, easier for computer to deal with
What is a diamagnetic susceptibility - Answer Doesn't remain magnetic when field is
removed, spins oppose B0
What is a ferromagnetic susceptibility - Answer Remains strongly magnetic when field is
removed, large moment, generates its own field
what is paramedic susceptibility - Answer Doesn't remain magnetic when field is
removed, spins weakly align
What is a permanent magnet for MRI - Answer Ferromagnetic material, both sides of
patient, very cheap and low power but not strong and v heavy
What is a resistive electromagnet for MRI - Answer Current runs through copper
SOLUTION
5 advantages of MRI - Answer No radiation, good spacial resolution, good for brain/ soft
tissue imaging, non invasive
5 disadvantages of MRI - Answer Loud, claustrophobic, expensive, inaccessible,
contraindications
What is B0 - Answer Main magnetic field, net magnetisation in human body
What is B1 - Answer Radio frequency field used to energise the magnetisation,
generated by transmit coils
Define gradient field - Answer Allows for localisation of nucleus due to imhogeneities in
magnetic field
Why is hydrogen used - Answer Lots of hydrogen in the body, they tend to align with the
magnetic field (spin up), free electron and net positive charge
What is the fridge field - Answer Magnetic field extends widely, decreasing in strength
as you travel away
What are the four safety zones - Answer 1) public area
2) screening area
3) post screened patients
4) scan room, restricted and supervised
What is SAR - Answer Specific absorption rate, temp increase during MRI must be
managed <1Cº
How to decrease SAR - Answer Thinner slices, longer TR, include pause, increase fan
speed
Explain net magnetic vector (NMV) - Answer Measure of the net alignment of hydrogen
to magnetic field, spins up positive and spins down negative, as B0 increases, less spins
down
What is resonance - Answer When an object is forced to vibrate at its natural frequency,
happens in magnet
How to get RF pulse to excite hydrogen - Answer The Lamor frequency of the nucleus
must equal the frequency of RF pulse used or wont excite
, What is the Lamor frequency? - Answer The rate that the nucleus is resonating in the
magnetic field
What is longitudinal relaxation (TR) - Answer RF pulse used to knock the align nucleus
90º, the time to relax back to being aligned to magnetic field is TR
What is transverse dephasing - Answer Over time the nuclei don't remain fully aligned to
B0 as some spin faster and slower, different lamor frequency then needed for different
areas
Causes of transverse dephasing - Answer Magnetic field imhogeneities (fixable ish)
Spin-spin (can't be fixed)
What is spin-spin - Answer Happens when each nuclei has its own little magnetic field
which influences the nucleis around it
What is time to echo - Answer Time from 90º RF pulse to when the signal is aquired,
longer TE is less signal due to dephasing
What is spin echo - Answer 180º pulse used to flip the dephasing spins so they realign
with B0 and regain signal, is done at 1/2 TE
What are field gradients - Answer Due to the magnetic field imhogeneities, different
areas have different lamor frequency, so to pick area use that lamor frequency
What is slice gradient - Answer Picks which slice, thinner slice is thinner slice gradient
What is phase and read gradients - Answer Used to split the slice into columns and
rows, phase first
what is k space - Answer How signal is compartmentalised, dictated by phase and read
squares, most signal is center of k space
What is Fourier transformation and how is it used - Answer Converts signal from time
domain to frequency, easier for computer to deal with
What is a diamagnetic susceptibility - Answer Doesn't remain magnetic when field is
removed, spins oppose B0
What is a ferromagnetic susceptibility - Answer Remains strongly magnetic when field is
removed, large moment, generates its own field
what is paramedic susceptibility - Answer Doesn't remain magnetic when field is
removed, spins weakly align
What is a permanent magnet for MRI - Answer Ferromagnetic material, both sides of
patient, very cheap and low power but not strong and v heavy
What is a resistive electromagnet for MRI - Answer Current runs through copper
