Glossary of Advanced Imaging Test 3

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Created by huffmajl

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

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

– 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
– 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
– selects certain pixel values for special attention

– display choices
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
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 ______
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

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
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 _____.
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)

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

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

The spinning protons create a ____ and they precess around an axis

magnetic field

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)

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