AMRI 300 Week 4 - Mysterious Data and Wild Math

K-space can be described as: -'Raw Data' for an MRI image -K-Yaw Sampling -A collection of data points -Y-Acquisitions -'Raw Data' for an MRI image AND A collection of data points

'Raw Data' for an MRI image AND A collection of data points

Doubling the NSA will increase SNR by a factor of: -2 -4 -1.6 -1.41

1.41

How many phase encoding steps are represented in this figure? -128 -512 -8 -256

256

Only sampling half of an echo and 'guessing' the other side of the data points is called: -Side Interval -A Fractional Echo -Ejection Fraction -Half Side Eliminate Function

A Fractional Echo

K-Space contains: -"Raw data" -Data Points -Spatially Encoded Information -All of the above

All of the above

The contrast and SNR information is located on the _________ of k-space. -Outer lines -Central lines -Center line -Bottom half

Central lines

Fourier Transforms always require/involve: F * W * E Re-uptake X-T Cross Ally Complicated Math Electronic Computers

Complicated Math

Doubling NEX will double the SNR. Select one: True False

FALSE

K-Space is also known as the "Frequency Domain". Select one: True False

FALSE

Strong PEG amplitudes create the highest amplitude echos: Select one: True False

FALSE In k-space, it is the outer lines that contribute to the highest spatial frequency information which results in image contrast. The central lines of k-space provide lower spatial frequency information, affecting image brightness. The PEG (Phase Encoding Gradient) determines the position of each line in k-space and does not directly influence the amplitude of the echoes.

Increasing NSA is the only way to increase SNR. Select one: True False

FALSE While increasing the number of signal averages (NSA) can improve the signal-to-noise ratio (SNR) by reducing noise through signal averaging, other techniques and adjustments, such as increasing voxel size or using stronger field strengths, can also affect SNR.

What's the difference between a Fast Fourier Transform and a Discrete Fourier Transform? -DFT is only used for CT images. -FFT is performed manually by the technologist. -There's no functional difference. -FFT is an optimized mathematical algorithm to speed up the process.

FFT is an optimized mathematical algorithm to speed up the process.

The horizontal axis (logical X), made up of columns, is filled in by the: -Lo-Fi Axel Converter -Phase Encoding Gradient -Slice Encoding Gradient -Frequency Encoding Gradient -Interpolation Stack

Frequency Encoding Gradient

Where in k-space is the effective TE placed when performing FSE pulse sequences? -Throughout k-space -In the central lines of k-space -On the outer lines of k-space -It depends on the effective TE

In the central lines of k-space

Which of these statements is NOT true regarding k-space? -Individual cells in k-space do not correspond one on one with individual pixels in the MR image -K-space corresponds to the echo data obtained from a single phase encoding gradient -There is no direct correspondence between the location of a cell in k-space and location of a pixel in the image -Rows near the center of the k-space grid correspond to high-order phase encode steps, whereas rows near the top and bottom correspond to lower order phase encodes

K-space corresponds to the echo data obtained from a single phase encoding gradient The relationship between k-space and the final image pixels isn't a one-to-one correlation. The Fourier transformation of the data in k-space eventually forms the image, but the relationship between individual cells in k-space and the individual pixels in the image is more complex and not a direct, one-to-one mapping.

A high strength PEG gradient application will tend to put spins: -More In-Phase -In reverse order -No change in phase -More Out-of-Phase

More Out-of-Phase

In K-space, the columns of data are fill by the ____ steps through the ____ , and the columns are filled in a ____ fashion -Nx PEG Vertical -Ny PEG Vertical -Nx PEG Horizontal -Nx FEG Horizontal

Nx FEG Horizontal

In K-space, the rows of data are fill by the ____ steps through the ____ , and the rows are filled in a ____ fashion -Nx FEG Horizontal -Nx PEG Horizontal -Ny FEG Vertical -Ny PEG Vertical

Nx PEG Vertical

In K-space, the column of data are filled by the ____ steps in a/an ______ direction, and the rows of data are filled by the ____ steps in a/an _______ direction -Ny horizontal Nx vertical -Nx vertical Ny horizontal -Nx horizontal Ny vertical

Nx vertical Ny horizontal

How many TR's (and TE's) must be performed in a sequence? -One for each Nx step -One for each Frequency Encoding step -One for each Ny step -One for each slice

One for each Ny step

Why are these central rows of K-Space the highest amplitude echos? -The SEG has little effect on those rows. -FEG turns on more strongly toward the middle. -PEG applications are the strongest near the middle rows. -More processing occurs in the middle (Central Processing) -PEG applications are the weakest to select middle rows.

PEG applications are the weakest to select middle rows.

In K-space, the rows of data are filled by the ____ gradient through its ____ steps called ____ -FEG frequency Nx -PEG frequency Ny -PEG phase Nx -PEG phase Ny

PEG phase Ny

The system can tell every row of K-Space apart because of the: -Frequency -Array Processor -Optimization Protocol -Phase shift -Absention Algorithm

Phase shift

A Fast Fourier Transform is optimized to be performed: -Quickly by a computer algorithm -Quickly on pen and paper -In 1830, before the advent of electronic computers -Quickly by the MRI Physicist

Quickly by a computer algorithm

Reducing the NEX reduces the scan time and causes what effect on SNR? -Reduction -Increase -No effect -Doubling

Reduction

With conventional spin echo one line of k-space is filled in each: -Frequency encoding period -Phase encoding period -TR period -Excitation period

TR period

Why do frequency encoding steps not cost time? -The FEG is supremely fast, about 2 millisecond rise time. -The gradient is simply turned on during read-out and the difference in frequencies are recorded in the echo. -The FEG has a smaller peak amplitude. -The FEG doesn't need to turn on very often.

The gradient is simply turned on during read-out and the difference in frequencies are recorded in the echo.

In a fast spin echo sequence, the effective TE is the echo(s) that is performed with: -The outer views of k-space -The high amplitude phase encoding gradients -The low amplitude phase encoding gradients -The first phase encoding step

The high amplitude phase encoding gradients

Why does every row of K-Space cost time? -Frequency encoding steps add time. -There is lag time to turn on the coil. -The sequence must be repeated for each row sampled. -The sequence must be repeated for each column sampled.

The sequence must be repeated for each row sampled.

Which is another name for K-space? -Time Domain -Ether Space -X(e) = X(t)u -Frequency Domain -Re-admissions Database

Time Domain

The lowest amplitude signal in K-Space tends to be: -Toward the periphery -K-Space signal amplitudes are all about the same -Toward the center -Only at the bottom

Toward the periphery

The center of K-space determines the image _____ of the picture -contrast and detail -details/resolution -none of these -contrast

contrast

The columns of K-space are filled by the Nx steps in a ______ fashion/direction

horizontal

The columns of K-space are filled by the Nx steps in a ______ fashion/direction -diagonal -perpendicular -vertical -horizontal

horizontal

The detail of the image is obtained using data from the ______ of K-space -none of these -all of k-space -center -periphery

periphery

The rows of K-space are filled by the Ny steps in a ____ fashion/direction Select one: -horizontal -diagonal -vertical -perpendicular

vertical