PHASE AND FREQUENCY & FAST IMAGINING TECHNIQUES Flashcards
The main function of Fourier transform in MR image reconstruction is to:
Convert time domain to frequency domain
Frequency can be defined as:
The rate of phase change
A magnetic field that varies over distance is known as:
A gradient magnetic field
The steepness or amount of slope of a gradient magnetic field is the
Amplitude
The physical gradient that varies the magnetic field in the head to foot direction is the:
Z-gradient
The physical gradient that varies the magnetic field in the right to left direction is:
X-gradient
The physical gradient that varies the magnetic field in the anterior to posterior direction is the:
Y-gradient
Along a gradient magnetic field, the highest frequencies would:
At the ends
Using the logical notation, the gradient performing phase encoding would be annotated with the letter
Y
Using the logical notation, what is the order in which the gradients are applied in a standard acquisition?
Z,Y,X
Slice thickness is affected by the _______ of the slice selecting gradient:
Amplitude
What affects slice thickness?
Transmit bandwidth
What will result in a thinner slice?
Higher amplitude of the slice selecting gradient
What physical gradient would be utilized to selectively excite a sagittal slice?
X
To produce a single axis oblique:
Two gradients would be used in combination
The readout gradient is also known as the what gradient?
Frequency encoding
Selecting a 256 frequency matrix would result in how many data points being collected or sampled during the formation of the echo?
256
The gradient which steps through different amplitudes during the scan is the:
Phase encoding
Increasing what will result in a direct decrease in scan time?
Phase matrix
The number of times each phase line of K-space is samples is:
NSA
Increasing the NSA will result in:
Reduction in noise
The method of filling K-space which begins with the maximum negative phase steps through zero then through positive steps is known as:
Linear
Which of the following K-space filling methods would likely preferred when performing a contrast enhance MRA:
Centric
With regard to MR raw data, the data points which provide the greatest signal contribution are:
Low frequencies
Where in K-space is high frequency date:
Outer
With regard to MR raw date, edge detail is provided by:
High frequencies
Using a conventional spin echo sequence, increasing the TE from 20msec to 80 msec will have what effect on the number of slices allowed?
Decrease
Using a conventional 2DFFT acquisition, what would result in the least amount of cross-talk?
Bigger slice gap
For a typical 2DFFT acquisition of 6 slices, the order in which the slices will be excited are:
1,3,5,2,4,6
In a 3DFFT acquisition, the slices are:
Reconstructed
In a 3DFFT acquisition, SNR is proportional to the:
The square root of the number of slices
Acquired voxels which are equal in all three dimensions are referred to as:
Isotropic
Reformatting image date into another plane is done through a process known as:
MPR
A technique used to reduce scan time which does not fully sample high frequency data but rather replaces it with zeros is known as:
Zero-fill
A scan time reduction technique which reduces the phase matrix and phase FOB by the amount is referred to as:
Rectangular FOV
Which scan time reduction technique may require a reference or calibration scan prior to the actual acquisition?
Parallel imaging
In a FSE sequence what parameter determines how many lines of K-space data will be acquired in a single TR period?
ETL
In FSE the effective TE is associated with:
Low frequency data
Spin echo EPI is most often used to acquire what type of MRI studies?
Diffusion weighted images
When acquiring a single shot EPI what matrix selection will have least distortion artifacts?
128 X 128
