Advanced Imaging Test 3
Terms
undefined, object
copy deck
- Why is MRI such a popular modality?
- because it provides information both anatomical and physiological
- 3 characteristics of MRI?
-
It is non invasive
It is computer-based and produces cross-sectional images like CT
Uses no ionizing radiation
- The MRI image is created by?
-
created by the interaction of the subject with magnetic fields and radiowaves
- What is the principle advantage of MRI?
-
The principle advantage of MRI is its ability to distinguish small anatomical differences – contrast resolution
- MRI was first termed _____.
-
The concept that developed into MRI was first termed Nuclear Magnetic Resonance (NMR)
Nuclear – because the nuclei was where the activity was occurring
Magnetic – because a magnetic field was required
Resonance – the direct frequency depended on the magnetic fields and radiofrequency
- The first successful Nuclear Magnetic Resonance experiment was conducted in
-
1946
- WHo accomplished the first MRI experiment? two people? When were they awarded their Peace Prize
-
By Felix Bloch of Stanford University and Edward Purcell of Harvard University
They were awarded the 1952 Nobel Prize in Physics
-
_____ showed that water inside a tumor had a different relaxation time than did water in normal tissue
- Raymond Damadian
-
In 1973,____ demonstrated the first cross sectional images attained with MRI technology
- Paul Lauterbur
-
The first images were of two test tubes of water
He demonstrated the spatial relationship of the test tubes using the Principles of MRI
- Paul Lauterber
-
______demonstrated that the images could be analyzed mathematically
- Peter Mansfield
-
What discovery made the development of the modern MRI machine possible?
- Peter Mansfields showing that images could be done matematically
-
Images being analyzed matematically...
____ can be imaged quickly and accurately
______ were jointly awarded the Nobel prize in 2003
- Small objects; Mansfield and Lauterbur
- Major components in MRI
-
The Gantry
The Operating Console
The Computer
- Three types of MRI imagers
-
Permanent Magnet
Resistive Electromagnet
Superconducting Electromagnet
- Describe the Superconducting MRI gantry
-
Very large – 3m x 3m x 5 m
The size is due to the insulating chambers that keep the supercooled primary magnet cold
This gantry has three sub-assemblies:
The patient couch
The primary magnet (immersed in liquid helium)
The various secondary magnets (for the RF pulses)
- IN the superconducting MRI gantry: the patient couch has two main functions...
-
Support for the subject
Precise positioning - it must be accurate to +/- 1 mm
-
The secondary magnets (three types) in the gantry...Name the types
-
3. RF probe – used to measure the signal
2. Gradient coils – flip on and off rapidly producing the transient gradient magnetic field
1. Shim coils – help provide a more uniform magnetic field at the patient
-
Which gantry has these characteristics....
Has the gradient coils and the shim coils housed with the permanent magnet
The RF probe is a separate operator changeable assembly
-
Resistive Electromagnet Imager
-
Which gantry?
Is designed similar to a transformer
Has no shim coils
- Permanent Magnet Imager
-
Generally has two sets of controls..Name them.
-
Image Acquisition
Image Processing
- The operating console generally has two sets of controls..
- Image Acquistion and Image Processing
- WIthin the Operating Cosole, the COmmon startup commands are :
-
1. powere on/off
2. emergency stop - Common startup Commands withing the operating console are
-
power on and off
emergency stop- dont use with Superconductor
intercom -
– adjust the resonance frequency to accommodate the subject
- Tuning Controls
-
– the operator has a choice of sequence
- Pulse Sequence
-
– by increasing the Repetition time, more slices per scan can be obtained
- Repetition Time
-
– Used with inversion recovery sequence. As this increases, T1 weighted imaging increases
- Inversion Time
- used with inversion recovery sequences and spin echo pulse. As this time increases, the more T2 weighted the image
- echo time
-
– the more views, the better the spatial resolution, but the longer the scan time
- Number of Views
-
– refers to the number of excitations. As this increases, SNR increases so image quality increases
- Number of Acquisitions
- determines the area of interest. Reducing the FOV increases spatial resolution, increases required number of acquisitions, and increases scan time
- FOV
-
– Reducing slice thickness increases spatial resolution
- Slice Thickness
-
– used to set the contrast and shades of gray for the displayed image
- Window width/level
- allows for image manipulation
- cursor on adn off
- used for calculations of certain areas of the image
- region of interest
- overall evaluation of pixel values
- profile/histogram
-
– selects certain pixel values for special attention
- Highlight
- – display choices
- collage
- The most important thing to note is that it much more powerful than a
-
normal CT computer
- MRI must have a
-
large storage capacity
- What three things must the MRI be able to do?
-
It must have a large storage capacity
It must be able to perform several million calculations quickly
The operating system must be able to allow several programs to run at once
- WIth MRI,reducing slice thickness, ____SR
- increase
- WIth MRI, reducing the FOV, ____SR, and does what else?
- increases; increases the number of acquisitions and scan time
- As number of image aquistions increases, SNR _____ so what does this do to quality?
- As this increases, SNR increases so image quality increases
- THe more views, the _____SR, but _____
- the more views, the better the spatial resolution, but the longer the scan time
- In MRI, do some atoms display more magnetic characteristics than others?
-
Some atoms display more magnetic characteristics than others
-
The most abundant magnetically active nuclei in the human body
is ______ - hydrogen
-
The hydrogen atom consists of a _____;
The spinning proton produces a ______ -
single proton
magnetic field
-
IN MRI, The magnetic field is called ____ the Hydrogen has a relatively large magnetic moment
-
magnetic moment
- In the magnetic field, the hydrogen protons align in the field according to _____
-
their energy level
- In MRI, Low-energy nuclei align
-
parallel with the external magnetic field
- In MRI, High energy nuclei
-
align against the magnetic field
-
The accumulation of all these fields is called the ______ It is always in the direction of the external field
-
Net Magnetization Vector (NMV)
-
In MRI, ____ is a term that describes the motion of the hydrogen proton
- Precession
- IN MRI, Equilibrium is when the majority of the nuclei
-
are in the low energy state
-
By applying a ______ , low energy nuclei absorb the energy and align with the other high energy nuclei
- radiofrequency pulse to the subject
-
IN MRI, As they return (relax) to their original state, _____which is the signal
-
they emit a signal that can be measured
-
In MRI, In order to follow the motions of the magnetic moments and the NMV a _____ is needed
- standard frame of reference
- WHat is used to follow the motions of the magnetic field and the NMV?
-
The three dimensional Cartesian coordinate system is used
- The signal is a result of ____ in the receiver coil when the net NMV is rotated by the introduction of ______
-
mutual induction;the RF pulse
-
The RF is _____;
It is an _____ electromagnetic field
-
non ionizing EMR
oscillating - IN MRI, When exposing the magnetized tissue to the RF, what happens to the spinning photons and NMV?
-
the spinning protons precess in phase causing the NMV to precess (absorbing energy)
- In MRI production signal, As more energy is absorbed, the NMV spins
-
at 90 degrees from the original axis (flip angle)
- Production signal in MRI, Applying a 90-degree tip angle is also called the ____ is converted to a ____
-
longitudinal magnetization ;transverse magnetization
- In the MRI production signal, Increasing the RF energy will
-
increase the flip angle
- In the production of MRI signal, The amount of energy required to achieve a certain flip angle is determined at____. Once the desired flip angle is achieved, the RF pulse is _____.
-
pre-scan
stopped and the detection begins
-
IN MRI production of signal, Once the RF pulse is ceased, a signal is received in the ____.
_____begins immediately after RF pulses cease
The ____shrinks as individual spinning protons return to the longitudinal axis
-
signal coil
Free Induction Decay (FID)
NMV -
IN MRI relaxation
The ____ excites the spinning protons
Once removed, the ___ relax (give off the energy) in two ways
These are simultaneous actions, but they are ____ of each other
- RF pulse;protons ;independent
-
– the recovery of magnetization along the Z axis
- T1
-
the loss of magnetization in the Transverse axis
- T2 –
-
During Relaxation of MRI,
Once the RF pulse is removed, the spinning protons -
lose phase coherence
-
During relaxation of MRI
_____ is a result of the de-phasing energy shifts between the protons
- T2 (spin-spin)
-
During relaxation of MRI
At the same time T2 is occurring, the NMV returns toward the Z axis as -
high energy precessing protons return to the low energy state
-
Relaxation of MRI
_____ is the rate the longitudinal magnetization increases toward the Z axis
- T1
-
The spinning protons create a ____ and they precess around an axis
- magnetic field
-
IN MRI,
In the magnetic field, the hydrogen atoms align in one of two ways
-
high energy (against the long axis of the external field)
low energy (parallel to the external magnetic field)