Image Basics

The smallest object that can be resolved in an image acquired with a 20cm FOV and a 224 x 224 matrix is _________ mm.

.89

Calculate the pixel area for the following sequence: TR 450, TE 12, FOV 18cm, 224 x 256 matrix, 4 NEX.

0.56 mm2

Calculate the pixel area for the following sequence: TR 4000, TE 120, FOV 28cm, 304 x 304 matrix, 2 NEX, ETL 12.

0.85 mm2

The pixel size of the images which result from a 3D acquisition using a 240mm FOV, a 272 x 272 matrix, 32 slices and a volume of 64 mm is:

0.88 x 0.88 mm

Choose the correct slice thickness to create an isotropic voxel for the following: TR 2000, TE 90, Matrix 256 x 256, FOV 32cm.

1.25mm

Calculate the voxel volume for the following pulse sequence parameters: TR 450, TE 20, FOV 24cm, 320 x 320 matrix, 3mm slice thickness.

1.69mm3

If the NEX is increased from 2 to 6, the signal-to-noise ratio increase would be:

1.7

Assuming all other parameters are the same, an echo time of ___________ ms provides the best Signal-to-Noise Ratio. A. 15 B. 30 C. 80 D. 110

15

The scan time of a fast spin echo sequence utilizing a TR of 3500ms, a TE of 90ms, a 256x256 matrix, 1NSA, a 220mm FOV and an echo train length of 5 is ______ minutes, approximately.

3

In a fast spin echo sequence with a 28 cm FOV, 256 x 512 matrix, TR 2200, 90 TE, 5mm slice thickness, 8 ETL and 3 NEX, the scan time would be:

3 minutes 31 seconds (Scan time formula: TR x Phase Matrix x NEX ÷ ETL = total in milliseconds, then ÷ 1000 to achieve scan time in seconds. Be careful if you divide by 60 to achieve the scan time in decimal format (This example computes to 211 seconds, if you divide by 60 you get 3.52 seconds, which is 3 minutes 31 seconds, not 3 minutes 52 seconds))

Calculate the voxel volume for the following pulse sequence: TR 2000, TE 85, FOV 28cm, Matrix 272 x 320, 5mm slice thickness, 3 NSA.

4.55 mm3

Which parameter will provide the better spatial resolution? A. 4mm slice thickness; 256 x 192 matrix B. 4mm slice thickness; 256 x 256 matrix C. 6mm slice thickness; 256 x 192 matrix D. 6mm slice thickness; 256 x 256 matrix

4mm slice thickness; 256 x 256 matrix (Thinner slices yield improved spatial resolution, in addition to smaller pixel size (higher matrix))

Which of the following pulse sequence parameter combinations would yield an image with the most blurring? A. 400TR, 25TE, 256 x 256, 5mm slice thickness, 1NSA B. 2000TR, 30TE, 256 x 256, 5mm slice thickness, 6 ETL, 2NSA C. 4000TR, 60TE, 256 x 256, 5mm slice thickness, 12 ETL, 4NSA D. 6000TR, 80TE, 256 x 256, 5mm slice thickness, 16 ETL, 4NSA

6000TR, 80TE, 256 x 256, 5mm slice thickness, 16 ETL, 4NSA

Assuming all other parameters are the same, a ___________ ms TR provides the best signal-to-noise ratio. A. 30 B. 200 C. 500 D. 800

800

What would the scan time be in a 3D volume acquisition as follows: TR 32 ms, TE 4 ms, Flip Angle 15°, FOV 18cm, 2mm slice thickness, 96 slices, 192 x 256 matrix, 1 NEX?

9 min 50 sec (3D scan time formula: TR x Phase Matrix x NEX x # slices)

Acquiring a bit more than half the phase k-space samples, then interpolating the data with zeroes for the remaining half is a technique known as: A. Half Fourier B. Zero fill C. Fast spin echo D. A and/or B

A and/or B

The overall signal-to-noise ratio will increase in 3D volume imaging when there is an increase in: A. Number of slices or partitions B. TE C. Phase Matrix D. Field of View E. A and/or D

A and/or D

Reducing the slice thickness will result in: A. An increase in partial volume averaging B. A decrease in SNR C. An increase in SNR D. A & B only E. None of the above

A decrease in SNR (Reducing the slice thickness will result in a decrease in SNR, but will decrease partial volume averaging.)

A set of specifically timed instructions to the magnet is known as:

A pulse sequence

Reducing the phase matrix from 256 to 192 will: A. Increase the signal-to-noise ratio B. Decrease imaging time C. Decrease spatial resolution D. All of the above

All of the above

Decreasing the TR will: A. Lower SNR B. Reduce scan time C. Increase SNR D. Both A and B

Both A and B

High amplitude signals are stored in the:

Center portion of k-space

The central lines of k-space are associated with _____________ in a fast spin echo sequence.

Contrast information

A reduction in FOV will result in: A. Decrease in spatial resolution B. Increase in SNR C. Decrease in SNR D. None of the above E. A and C only

Decrease in SNR

An increase in TR will produce all of the following EXCEPT: A. Increase the signal-to-noise ratio B. Decrease T1 weighting C. Decrease the number of available slices D. Increase scan time

Decrease the number of available slices

Reducing the FOV (field of view) only will result in:

Decreased signal-to-noise

As the number of phase encodings is increased from 256 to 512, SNR (signal to noise ratio)

Decreases

SNR increases with all the following adjustments, EXCEPT: A. Increasing FOV B. Decreasing pixel size C. Increasing NEX/NSA D. Decreasing phase matrix

Decreasing pixel size

If the repetition time is doubled, the scan time will:

Double

What formula is used to calculate the size of the pixel?

FOV ÷ matrix

The timing of the RF pulses in an MRI pulse sequence controls:

Image contrast

Increasing NSA will:

Improve SNR

All of the following yield a higher signal-to-noise ratio EXCEPT: A. Increase TR B. Increase TE C. Larger FOV D. Higher NEX E. Decrease Matrix

Increase TE (An increase in TE will yield a decrease in SNR)

K-space is typically filled:

One line at a time

_______ is when only half the views of k-space are filled in the frequency axis.

Partial or fractional echo

Each line of k-space is defined by the:

Phase encoding gradient

With a recFOV that is twice as tall as it is wide, and the phase direction oriented along the smaller "width" dimension of the FOV, which of the following relationships between the frequency and phase steps yields square pixels? A. Frequency steps must be half the phase encoding steps B. Phase steps must equal the number of frequency steps C. Phase steps must be half the number of frequency steps D. The pixels will always be rectangular

Phase steps must be half the number of frequency steps (With a 50% Rectangular FOV, the phase matrix (rectFOV direction) must be exactly half the frequency matrix in order to yield square pixels.)

Another name for a picture element is a:

Pixel

A method of reducing MRI scan time by not filling as many lines of k-space in the phase direction, while maintaining spatial resolution, is known as:

Rectangular FOV

All of the following would aid in reducing scan time EXCEPT: A. Utilizing the coarsest matrix possible B. Reducing NEX C. Reducing TE D. Increasing parallel imaging factor E. Setting TR to shortest

Reducing TE (TE (echo time) has no affect on scan time.)

Which of the following would NOT compensate for the change in signal-to-noise as a result of decreasing the FOV? A. Reducing the image matrix B. Reducing the number of echo train lengths C. Reducing the number of excitations D. Increasing slice thickness

Reducing the number of excitations (A reduction in excitations (NEX/NSA) would reduce SNR, which has the same effect as decreasing the field of view)

All of the following affect acquisition time EXCEPT: A. TR B. TE C. NEX D. Matrix

TE

If a sequence with a matrix of 256 x 512 is adjusted to 512 x 512,

The SNR will decrease and the scan time will increase

Which of the following is NOT affected by changing the slice thickness? A. The signal-to-noise ratio of the image B. The T1 contrast C. The image resolution D. The anatomical coverage

The T1 contrast

With regards to k-space, the data containing signal and contrast information are located along:

The central lines

With regards to k-space, the data containing high resolution are located along:

The outer lines

As the number of excitations (NEX) is increased from 1 to 3, which of the following does NOT occur? A. The scan time triples B. The pixel size is increased C. The image resolution remains the same D. The signal-to-noise ratio is increased

The pixel size is increased

Reducing the number of lines filled in k-space will produce an image: A. With a decrease in spatial resolution B. With an increase in spatial resolution C. With an decrease in overall SNR D. A and C

With a decrease in spatial resolution

Water has a __________ T1 relaxation time and a ________ T2 relaxation time.

long; long

Fat has a _______ T1 relaxation time and a ________ T2 relaxation time.

short; short