MRI Basics
WHY DOES MRI USE HYDROGEN PROTONS
BECAUSE THEY ARE THE MOST ABUNDANT IN THE BODY
TO COOL DOWN THE MAGENT WHAT ELEMENT DO THEY USE
HELIUM
Fast spin echo sequences are fast because:
More than 1 line of k-space is acquired in each TR period
DEFINE SLEW RATE
is the speed rate of ascent or descent of a gradient from zero to its maximum amplitude, either positive or negative
The intensity limit for a static magnetic field by the FDA for the entire population is?
4.0 TESLA
WHAT IS THE (Y) IN THE LEMMOUR EQATION
GYROMAGNETIC RATIO
What type of magnet is used with most systems currently manufactured?
SUPERCONDUCTING
The fastest sequence commonly and currently available is:
Echo planar imaging
The gradient rise time is defined as the:
Time it takes for the gradient to reach its full amplitude
FDA guidelines dictate a level of concern when RF energy absorption produces an increase in body temperature of:
1 deg Celsius
repetition time (TR), IS the controlling factor of T1 weighting contrast in an image INCREASING TR WILL DO WHAT, NAME 4 THINGS
*HINT* IT INCREASES 4 THINGS AND REDUCES 1 THING
increases SNR
increaces scan time
increases the availabe # of slices
reduces T1 weighting
In order for energy to be efficiently transferred between a transmitter and receiver, the two must be at the same:
FREQUNCEY
In a spin echo sequence, the time between the 90 RF pulse and the 180 RF pulse is known as the:
1/2 TE
The performance of a gradient, measured as its maximum strength divided by its rise time, is known as the:
SLEW RATE
What type of pulse sequence transmits the most RF to the patient and consequently can potentially have more SAR restrictions?
FAST SPIN ECHO
The slice thickness directly affects:
*HINT* THREE THINGS
• The signal-to-noise ratio of the image
• The image resolution
• The anatomical coverage
Active shielding can be defined as:
Superconducting windings within the MR scanner, reducing the fringe magnetic field
A patient is being scanned for multiple sclerosis. Which sequence is specifically designed to suppress the signal from CSF to aid in the detection of periventricular lesions?
FLAIR
To select a transverse/axial slice plane for a brain MRI, the scanner must energize the gradient that alters the magnetic field along the head-to-foot direction. Which gradient performs this function?
THE Z GRADIENT
FILL IN THE BLANK: To protect the general public and patients with pacemakers from the magnetic field, the FDA recommends posting warning signs to indicate the .......line.
5 GAUSS
FILL IN THE BLANK: Referring to k-space, the data containing ......AND ..... are located along the central lines. Referring to k-space, the data containing ...... are located along the outer lines.
SIGNAL, CONTRAST
HIGH RESOLUTION
The coil construction in an MR system, from the innermost aspect to the outer:
Radiofrequency coils, gradient coils, shim coils, main magnet
A technologist wants to generate a proton density weighted image. To do this, they should select a spin echo sequence with which parameters?
HINT THINK TR/TE
Long TR, Short TE
Magnetic field inhomogeneity is expressed in:
Parts per million
A patient reports seeing flashing lights in their peripheral vision during a fast EPI sequence. This harmless but sometimes startling physiological effect is known as:
Magnetophosphenes