An atom is made up of:
P… (… charge)
N… (… charge)
E… (… charge)
An atom is made up of:
PROTONS (POSITIVE charge)
NEUTRONS (NO charge)
ELECTRONS (NEGATIVE charge)
Within the nucleus of the atom, … and … spin in opposite directions
In atoms with the same number of … and …, the nucleus itself has … net spin
However if there is an … amount of … and …, the nucleus itself will have a net …
Within the nucleus of the atom, PROTONS and NEUTRONS spin in opposite directions
In atoms with the same number of PROTONS and NEUTRONS, the nucleus itself has NO net spin
However if there is an UNEQUAL amount of PROTONS and NEUTRONS, the nucleus itself will have a net SPIN
Atoms with an … mass number are said to be MRI a… n…
They have a tendency to align their axis of … to an applied … field
Atoms with an ODD mass number are said to be MRI ACTIVE NUCLEI
They have a tendency to align their axis of ROTATION to an applied MAGNETIC field
Hydrogen atoms have a mass number of …, and contain a … charge proton
This gives a … magnetic moment
It’s used in medical imaging as it is … in the body
Hydrogen atoms have a mass number of -1, and contain a POSITIVELY charge proton
This gives a LARGE magnetic moment
It’s used in medical imaging as it is ABUNDANT in the body
Without a … field, the … moments are random
When placed in a strong … field, the … moments … with this field
Some align … (low energy nuclei) and some …-… (high energy nuclei)
The … nuclei create a net … vector (…)
Without a MAGNETIC field, the MAGNETIC moments are random
When placed in a strong MAGNETIC field, the MAGNETIC moments ALIGN with this field
Some align PARALLEL (low energy nuclei) and some ANTI-PARALLEL (high energy nuclei)
The PARALLEL nuclei create a net MAGNETIC vector (NMV)
Each hydrogen nucleus (…) is spinning on its …
The magnetic field strength (…) causes an … spin- called …
The … at which they spin is called the … frequency
Each hydrogen nucleus (PROTON) is spinning on its AXIS
The magnetic field strength (Bo) causes an ADDITIONAL spin- called PRECESSION
The SPEED at which they spin is called the PRECESSION frequency
R… occurs when an object is exposed to an external … that has a … close to its own
The nucleus gains … and resonates
For the resonance of hydrogen atoms to occur at 1.5T, a frequency of … MHz must be applied
The application of the … pulse that causes resonance to occur is called …
The application of this … pulse results in the … to move out of alignment with Bo
The flip angle is the angle between … and the …
It affects image contrast, signal … and … timing
Another result of resonance is the … moments of the … nuclei move in … with each other
RESONANCE occurs when an object is exposed to an external FORCE that has a FREQUENCY close to its own
The nucleus gains ENERGY and resonates
For the resonance of hydrogen atoms to occur at 1.5T, a frequency of 63.86 MHz must be applied
The application of the RADIOFREQUENCY pulse that causes resonance to occur is called EXCITATION
The application of this RADIOFREQUENCY pulse results in the NMV to move out of alignment with Bo
The flip angle is the angle between Bo and the NMV
It affects image contrast, signal STRENGTH and SCAN timing
Another result of resonance is the MAGNETIC moments of the HYDROGEN nuclei move in PHASE with each other
The MRI signal is produced when the in … magnetism occurs across the … coil
This is due to the moving … magnetisation producing magnetic field … inside the coil which induces an electric … in the coil
The MRI signal is produced when the in PHASE magnetism occurs across the RECEIVER coil
This is due to the moving TRANSVERSE magnetisation producing magnetic field FLUCTUATIONS inside the coil which induces an electric VOLTAGE in the coil
When the MRI signal in the receiver coil is switched off, the … energy nuclei … energy
This results in the … realigning with …- relaxation
When the MRI signal in the receiver coil is switched off, the HIGH energy nuclei LOSE energy
This results in the NMV realigning with Bo- relaxation
What is T1 recovery?
When the amount of magnetisation in the longitudinal plane increases
What is T2 decay?
When the amount of magnetisation in the transverse plane decreases
Free Induction Decay (FID):
As relaxation occurs, the … of transverse magnetisation …
The nuclei also begin to move … of phase with each other- dephase
All of these result in the … of signal in the receiver coil
Free Induction Decay (FID):
As relaxation occurs, the MAGNITUDE of transverse magnetisation DECREASES
The nuclei also begin to move OUT of phase with each other- dephase
All of these result in the LOSS of signal in the receiver coil
Image contrast:
Different tissues in the body have different … times
These are dependent on:
The inherent energy of the tissue; tissue with … inherent energy can … absorb energy from hydrogen nuclei during … and vice versa
How closely packed the modules are; in tissues where the molecules are closely packed, there’s more … interaction between the … fields of … hydrogen nuclei. And vice versa
mage contrast:
Different tissues in the body have different RELAXATION times
These are dependent on:
The inherent energy of the tissue; tissue with LOW inherent energy can EASILY absorb energy from hydrogen nuclei during RELAXATION and vice versa
How closely packed the modules are; in tissues where the molecules are closely packed, there’s more EFFICIENT interaction between the MAGNETIC fields of NEIGHBOURING hydrogen nuclei. And vice versa
Example of longitudinal magnetisation:
Fat are … molecules that are … packed together
They have a … inherent energy (can easily give it up)
Therefore, fat molecules regain longitudinal magnetisation fairly …
Water molecules are spaced …
They have a … inherent energy (take longer to give it up)
Therefore, water molecules regain longitudinal magnetisation fairly …
Example of longitudinal magnetisation:
Fat are LARGE molecules that are CLOSELY packed together
They have a LOW inherent energy (can easily give it up)
Therefore, fat molecules regain longitudinal magnetisation fairly QUICKLY
Water molecules are spaced APART
They have a HIGH inherent energy (take longer to give it up)
Therefore, water molecules regain longitudinal magnetisation fairly SLOWLY
Example of transversal magnetisation:
Fat molecules are closely … together
Therefore they can easily … up their energy
Transverse magnetisation will be lost …
Water molecules are spaced far … so therefore loss of transverse magnetisation will be …
Example of transversal magnetisation:
Fat molecules are closely PACKED together
Therefore they can easily GIVE up their energy
Transverse magnetisation will be lost RAPIDLY
Water molecules are spaced far APART so therefore loss of transverse magnetisation will be SLOW
To distinguish contrast on an image, the image needs to be weighted towards one contrast mechanism- either … or …
This is done by selecting the appropriate TR and TE
To distinguish contrast on an image, the image needs to be weighted towards one contrast mechanism- either T1 or T2
This is done by selecting the appropriate TR and TE
Repetition time (TR):
The time from the application of one … pulse to another
It determines the amount of … relaxation that is allowed to occur
Echo time (TE):
Time from the application of the … pulse to the … of the signal induced in the received coil
It determines the amount of decay in the … plane
Repetition time (TR):
The time from the application of one RADIOFREQUENCY pulse to another
It determines the amount of LONGITUDINAL relaxation that is allowed to occur
Echo time (TE):
Time from the application of the RADIOFREQUENCY pulse to the PEAK of the signal induced in the received coil
It determines the amount of decay in the TRANSVERSE plane
Image contrast:
The … can be separated into individual … of different tissues
Areas of high signal (… on image) are tissues that have a large component of … magnetism at the time of TE
Tissues with a low signal component of … magnetisation at the time of TE will appear …
Image contrast:
The NMV can be separated into individual VECTORS of different tissues
Areas of high signal (WHITE on image) are tissues that have a large component of TRANSVERSE magnetism at the time of TE
Tissues with a low signal component of TRANSVERSE magnetisation at the time of TE will appear DARK
T1 weighted:
An image where the contrast depends predominantly on the differences in the T1 … times between tissues
The TR controls how far each … recovers before the next slice is excited by the next radiofrequency pulse
T1 weighted:
An image where the contrast depends predominantly on the differences in the T1 RELAXATION times between tissues
The TR controls how far each VECTOR recovers before the next slice is excited by the next radiofrequency pulse
T1 weighted image:
… time (TR) is crucial for T1 contrast
TR controls how far each vector can recover before it is excited by the next … pulse
For T1 weighting, the TR must be … enough so that neither fat nor water have … time to fully return to Bo
If the TR is too long, then both fat and water will fully recover to the … magnetisation
In that case, the difference in T1 contrast can’t be demonstrated in the image
(Short TR = strong T1 weighting
Long TR = low T1 weighting)
T1 weighted image:
REPETITION time (TR) is crucial for T1 contrast
TR controls how far each vector can recover before it is excited by the next RADIOFREQUENCY pulse
For T1 weighting, the TR must be SHORT enough so that neither fat nor water have SUFFICIENT time to fully return to Bo
If the TR is too long, then both fat and water will fully recover to the LONGITUDINAL magnetisation
In that case, the difference in T1 contrast can’t be demonstrated in the image
(Short TR = strong T1 weighting
Long TR = low T1 weighting)
T2 weighted:
An image where the contrast depends predominantly on the differences in the T2 … times between tissues
The TE controls the amount of T2 decay that occurs before the signal is received
T2 weighted:
An image where the contrast depends predominantly on the differences in the T2 DECAY times between tissues
The TE controls the amount of T2 decay that occurs before the signal is received
T2 weighted image:
… times between tissues (TE) is crucial for T2 weighting
If a short echo time (25ms) is used, the signal differences between tissues are …
T2 relaxation has only just started and there has only been … signal decay at the time of echo collection
The resulting image has … T2 weighting
T2 weighted image:
ECHO times between tissues (TE) is crucial for T2 weighting
If a short echo time (25ms) is used, the signal differences between tissues are SMALL
T2 relaxation has only just started and there has only been LITTLE signal decay at the time of echo collection
The resulting image has LOW T2 weighting
