8: Data Manipulation

Question 1

Slice Select Gradient (SSG)

Answer 1

produces a linear shift of the magnetic field resulting in a positive and negative tilt.

Question 2

Slice Select Gradient Amplitude

Answer 2

The strength of the energy used to create the variation

Question 3

Increasing Slice Select Gradient Amplitude will result in:

Answer 3

a steeper tilt allowing the ability to scan thinner slices.

Question 4

After the SSG selects the slice:

Answer 4

fill in frequency and phase information (encoding) with the echoes gathered from the pulse sequence

Question 5

Raw data

Answer 5

K space image, no anatomy
Center - Contrast
Peripheral - Resolution

Question 6

K Space

Answer 6

raw data storage, collection of a variety of numerical values corresponding to the spatial frequency and phase values of the resultant pulse.
Data is scattered and not identical to an MR image.

Question 7

K Space Center

Answer 7

Contrast

Question 8

K Space Peripheral (boundry)

Answer 8

Resolution, Frequency, Phase, Matrix

Question 9

What is the most essential contributor to image contrast?

Answer 9

effective TE

Question 10

Where is TE located in K Space?

Answer 10

Closest to the center

Question 11

K Space filling

Answer 11

occurs when high and low spatial frequencies fill empty k space.

Question 12

Where are lower spatial frequencies found in K space?

Answer 12

Middle

Question 13

Where are higher spatial frequencies located in K space?

Answer 13

Boundaries, Peripheral

Question 14

The lines of K Space filled during each TR period is (directly or indirectly) related to the number of echoes collected per TR.

Answer 14

Directly

Question 15

What is found in the center of K Space? (3)

Answer 15

1. High amplitude
2. Lower spatial frequency
3. Contrast

Question 16

What is found in the peripheral of K Space? (3)

Answer 16

1. Low amplitude
2. Higher spatial frequency
3. Resolution

Question 17

3 Types of K Space Filling:

Answer 17

1. Cartesian
2. Spiral
3. Keyhole

Question 18

Cartesian K Space filling:

Answer 18

traditional, Fills data row by row from left to right or left to right

Question 19

Spiral K Space filling:

Answer 19

beginning in the center, raw data is filled like a backwards maze beginning with contrast data

Question 20

Keyhole K Space filling:

Answer 20

Normally used for dynamic studies, in which lower spatial frequency data (contrast) is filled to show infiltration of contrast - higher spatial frequency is filled once. Repetitively fills the contrast over time, gets brighter.

Pituitary, Prostate

Question 21

Spiral K Space filling is also called:

Answer 21

Elliptical filling

Question 22

MaxIP (Maximum Intensity Projection)

Answer 22

Post processing technique which allows:
1. Cutting of subtracted (dark) background
2. Highlighting of high intensity blood vessels
3. Manipulation of images to visualize blood vessels in various projections and positions

Question 23

MinIP (Minimum Intensity Projection)

Answer 23

MRA or CT Post-processing technique which allows for cutting of hyperintense or bright structures.

Ideal application for hypodense structures such as the lungs, biliary tree, and pancreatic duct.

Question 24

MPR (Multiplanar Reconstruction)

Answer 24

3D post-processing technique which allows for reformatting of in both slice and acquisition planes.

Question 25

MPR is only possible if the image is a _______ due to: (3)

Answer 25

3D Isotropic volume due to
1. High SNR
2. Thin slices
3. No gaps

unlike 2D.

Question 26

Isotropic:

Answer 26

Volumetric ROI that has EQUAL width, height, and depth of each voxels

Rubix cube

Question 27

Anisotropic

Answer 27

Volumetric ROI that has UNEVEN width, height, and depth of each voxels

Question 28

During 3D acquisitions, voxels can be configured to be: (2)

Answer 28

1. Rectangular - linear anatomical structures
2. Square - routine anatomy

Question 29

To maintain isotropic volume, 4 categorizes need to be accounted for:

Answer 29

1. volume thickness (mm)
2. number of slices
3. FOV (mm)
4. Matrix (phase only)

Question 30

Formula for maintaining Isotropic Volume:

Answer 30

Slice Thickness FOV
___________________ = ________________
Number of slices Matrix (phase)

Question 31

If a technologist selects a 3D volume slab with a FOV of 20cm, a matrix of 512 x 288 and a volume with a 24mm thickness. How many slices are needed to maintain an isotropic 3D sequence?

Answer 31

Slice Thickness FOV
___________________ = ________________
Number of slices Matrix (phase)

24mm 200mm
__________ = _________________
solve for x 288 phase lines

cross multiply
200x = 24 x 288
200x = 6,912
6,912 / 200 = 34.56 slices

Answer = 35 slices

Question 32

Subtraction

Answer 32

technique where pre-contrast T1 is digitally subtracted from identical post-contrast T1 images.

Question 33

Apparent Diffusion Coefficient (ADC)?How is it measured?

Answer 33

Diagnostic assessment tool used to evaluate diffusion of water within a specific area of tissue by mapping acquisitions with different b-values. mm2/s (millimeters squared per second)

Question 34

Diffusion coefficients:

Answer 34

a set of true numerical values for certain diffusivity rates