Comparison between 3t and 7t mri

1. 3t & 7t MRI
MELWIN AUGUSTINE
3RD YEAR BSC RADIOGRAPHY
NIMHANS

2. 1 TESLA = 10000 GAUSS
3 TESLA = 30000 GAUSS
7 TESLA = 70000 GAUSS

3. WHAT IS 7 TESLA ????
# Its a new revolution in the field of
MRI
# UhFMRI → Ultra High Field MRI
# Developed to achieve goals like
better resolution,improve SNR,CNR etc

4. 7 t mri :oppurtunities
# Enhancement of SNR
# Spatial Resolution
# Enhancement of T1 Relaxation
# Reduction of T2 Relaxation
# Enhancement of Chemical Shift
# Magnetic Susceptibility Effects

5. Enhancement of SNR
# SNR = Ratio of the average signal intensity over the
standard deviation of noise
# SNR is directly proportional to the field strength B0
# Under such an assumption, the difference between parallel and antiparallel
spins, calculated using the Boltzmann probability distribution, is as small as 10
spins in one million at B0=3T that implies around 2.3 times (i.e.,≈23 spins in one
million) more spins per million at7T.1,3Such an increase in SNR with B0implies
morerefined spin manipulation and image reconstructionwith fewer spins
# Greater SNR provides a signal enhancement to nuclei other than protons, such
as sodium-23 (23Na) and phosphorus-31 (31 P)

6. Spatial Resolution
# The UhFMRI provides SNR that can be spent on resolution. It has been
theorized that the spatial resolution is related to a factor N by which field B0is
increased as:5
Spatial Resolution ∝N1/3
# The above relationship implies about 30% improvement in resolution when B0 is
changed from 3T to 7T.

7. Enhancement of T1 Relaxation
#T1 = time taken by LM to recover its
original value after RF pulse is switched
off
# Prolongation of T1 → disadvantage -->leads
to lesser SNR recovery
# Still advantage in ASL,cardiac imaging,TOF

8. Reduction of T2 Relaxation
# T2= time taken by TM to disappear.
# The shortening of T2 at UhFMRI makes it more sensitive to
presence of calcium and iron in microbleeds and
haemorrhages.This leads to an improved depiction of
microbleeds in patients,detection of small venules
# Also increased BOLD contrast & better visualisation of
capillary beds ,enables high resolution FMRI

9. Enhancement of Chemical Shift
The difference in molecular distribution of different compounds results in
different resonance frequencies for the compounds. This molecular
distribution based variation of resonance frequencies is known as chemical
shift. The extent of resonance frequency spread, is directly proportional to field
strength B0.
Molecular distribution based spectral changes become more pronounced at higher
field and provide higher spectral resolution in applications involving MR
spectroscopy in UhFMRI.Higher spectral resolution and increased SNR would
result in a greater number of metabolites detected at 7T compared to lower
field strengths.

10. Magnetic Susceptibility Effects

11. CHALLENGES of 7T MRI
# B0 inhomogeneity
# Susceptibility related artifacts
# Chemical shift Error
# Peripheral Nerve Stimulation
# Patient safety challenge
# Physiological Effects
# Metal Implants

12. 7T in Neuro Imaging
# Epilepsy
# Degenerative Braim Diseases (AD, PD)
# Multiple Sclerosis (white matter lesions)
## Cerebral Vascular Disease (Aneurysm)
# Brain Tumours
# Functional Brian imaging

17. SWI

24. PARAMETERS 3T 7 T
Larmor frequency 127.8 MHz 298 MHz
Chemical shift 440 MHz 1026 MHz
Susceptibility Less More
Field Inhomogeneity Less Difficulty to achieve
homogeneous magnetic
field
T1 relaxation time Less More
T2 relaxation time More Less
SAR Less More
SNR Less More
COMPARISON BETWEEN 3 TESLA & 7 TESLA

25. Thank you