MRI Flashcards
the patient is asked to perform certain activities to help the neurosurgeons map the functional areas of the brain before surgery takes place.
fMRI
types of MRI exams
fMRI
Breast Scans
MRA
MRV
s a non-invasive technique that is used to examine our patients at high risk for breast cancer. Breast MRI can catch areas of concern earlier and in ways not possible with other breast imaging techniques, giving our experts the ability to best diagnosis and treat breast cancers.
Breast Scans
is a non-invasive diagnostic procedure that uses a combination of magnetic resonance technology (MRI) and intravenous (IV) contrast dye to visualize blood vessels. An MRA is often used to examine the heart and other soft tissues and to assess blood flow.
Magnetic Resonance Angiography (MRA)
diagnostic procedure that uses a combination of a large magnet, radio frequencies, and a computer to produce detailed images of organs and structures within the body. An MRV uses magnetic resonance technology and intravenous (IV) contrast dye to visualize the veins.
Magnetic Resonance Venography (MRV)
is measured frequently by calculating the difference in signal intensity between the area of interest and the background (usually chosen from the air surrounding the object).
signal-to-noise ratio
Used to describe the relative contributions to a detected signal of the true signal and random superimposed noise
Signal to Noise Ratio (SNR)
is proportional to the volume of the voxel and to the square root of the number of averages and phase steps (assuming constant-sized voxels).
Signal-to-noise ratio
On MRI, the signal-to-noise ratio can be improved by:
volume acquisition as compared to 2D imaging, but imaging time is increased
spin-echo sequences as compared to gradient echo
decreasing the noise by reducing the bandwidth, using surface coils, and increasing the number of excitations
increasing the signal by decreasing the TE (time to echo) and increasing the TR (time to repeat), slice thickness, or field of view
Additionally, SNR can be improved by tweaking scan parameters. Assuming all other factors remain the same, SNR can be improved by:
increasing the field of view (FOV)
decreasing the matrix size
increasing the slice thickness
is energy delivered to the spins via excitation.
Relaxation Time
The NMV in the transverse plane decreases due to:
relaxation processes;
field in homogeneities and susceptibility effects.
The amplitude of the voltage induced in the receiver coil therefore gradually decreases. This is called
free induction decay or FID
The magnetization in each tissue relaxes at different rates. This is one of the factors that create image contrast.
Relaxation processes
Spins emit energy absorbed from the RF pulse through a process known as
spin lattice energy transfer
Spins emit energy absorbed from the RF pulse through a process known as spin lattice energy transfer and shift their magnetic moments from the high‐energy state to the low‐energy state. The NMV recovers and realigns to B0. This relaxation process is called ___
T1 recovery
The magnetic moments of the spins lose precessional coherence or dephase and the NMV decays in the transverse plane. The dephasing relaxation process is called__
T2 decay.
is also called the longitudinal or spin-lattice relaxation time. The term longitudinal refers to events occurring along the axis of the net magnetization vector, which is parallel to B0. T1 relaxation describes the growth and decay of MZ; therefore it is longitudinal in nature.
T1
is called the transverse relaxation time. Because T2 relaxation represents a loss of net XY magnetization, it represents the loss of phase coherence in a plane perpendicular to or transverse to M0. M0 lies along the Z-axis.
T2
concentration of nuclei in tissue processing at theLarmor frequency in a given region; one of the principal determinants of the strength of theNMR signal from the region.
Spin Density
are very fast bursts of radio waves, provided that the radio waves and nuclear precession are of the same frequency.
RF pulse
The grouping of two or more RF pulses is called a __
pulse sequence.
is the time between the delivery of the RF pulse and the receipt of the echo signal.
Time to Echo (TE)
is the amount of time between successive pulse sequences applied to the same slice.
Repetition Time (TR)
are wave forms of the gradients and RF pulses applied in MR image acquisition
Pulse sequences
is a schema of the timing of instructions sent to the RF generator and gradient amplifiers.
pulse sequence diagram
There are only two fundamental types of MR pulse sequences: __
SE and GRE
MR pulse sequences can be either
2D w/ one section acquired at a time or 3D w/ volume of multiple sections obtained in a single acquision
If a 180° RF pulse follows the 90° RF pulse at some later time, an __ of the FID can be generated.
echo signal
does not follow the 180° RF pulse immediately. The spin echo sequence is the most commonly used two-pulse MRI sequence.
spin echo (SE)
pulse sequence using three RF pulses is the __
inversion recovery (IR).
RF pulse sequence uses a 180° RF pulse before the 90° RF pulse.
inversion recovery (IR)
When three RF pulses are used and if the time between the pulses is less than T2, then a different kind of echo signal, called the
stimulated echo (STE)
is designed to detect the random movements of water protons.
Diffusion weighted imaging (DWI)
is a non-toxic paramagnetic contrast enhancement agent.
Gadolinium (Gad).
