Low Field Vs High Field Mri

Question 1

Low vs high field MRI

Answer 1

• The difference is determined by the tesla energy
• High field mri – 1 tesla or higher
• Mr signal is proportional to the square of the main magnetic field strength
• Mr signal and snr increase with increasing field strength
• Higher field strength = higher snr = increase contrast, spatial and temporal resolution
• Higher field strenth. = more safety considerations

Question 2

Low field MRI

Answer 2

• Open design – smaller physical footprint, wider boars - less chance of claustrophobia
• Imaging takes slightly longer – more chance of movement – motion artefact– pt is longer in the bore- more risks
• More access for interventional procedures with open bores
• Less likely to have artefacts such as chemical shift susceptibility (occurs in the frequency-encoding direction and is due to spatial misregistration of fat and water molecules) and flow motion artefacts (signal changes caused by the movement of fluids)
• Less spatial distortion and isgnal loss for patients with devices
• Up to 3 tesla the application of fat suppressed imaging with chemical shift selective rf is challeneged due to the decreased chemical shift of water and fat spectra- application of fat suppression pulses more difficult
• Lower field strength = lower fringe field=easier and cheaper to shield-requires less shiekding and are more portable
• Equipment can be brought closer
• SAR can cause burning in higher field strengths

Question 3

High and uktra high firld MRI

Answer 3

• 10.5 tesla mainly used for research
• High field mri increases contrast, SNR, spatial resolution almost linearly
• Improved cnr =improve magnetic resonance spectroscopy
• Faster scaning- Motion artefacts are less likely to occur on high resolution mri as sequences are more susceptible to artefacts
• Ultra high field imaging – more susceptible to motion artefacts
• Physiologic effect are time dependent and can be classified as transient or permanent
• Costs are higher – increased shielding

Question 4

Artefacts

Answer 4

Low field - less likely to have flow motion and chemical shift artefacts

High field - less likely to have motion artefacts

Ultra high field - more likely to have motion artefacts

Question 5

Low field mri advantages

Answer 5

• patient comfort
• Reduced acoustic noise
• Opportunity for open settings for claustrophobic and obese patients
• less heating
• Lower risk for electronical devices such as implants
• lower torque and transitional force with ferromagnetic objects

Question 6

Disadvantages

Answer 6

• less visible contrast enhancement

Question 7

Advantages of high field and ultra high field mri

Answer 7

• increased CNR
• longer T1
• increased snr

Question 8

Disadvantages of high and ultra high field mri

Answer 8

• patient discomfort
• metallic taste
• Nausea
  -dizziness
• vertigo
  -sweating
  -magnetophosphenes
• longer duration
  -lying motionless
  -acoustic noise
  -increased sar- more frequent occurances of RF heating
• ecg alterations under high magnetic field systems