Image Basics

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

1.7

*Which of the following pulse sequence parameter combinations would yield an image with the most blurring?

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

Reducing the slice thickness will result in:

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

A reduction in FOV will result in:

Decrease in SNR

*Reducing the phase matrix from 256 to 192 will:

All the above *Reducing the phase encoding matrix yields higher SNR, shorter scan times, but decreased spatial resolution due to the increased pixel size.

*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

Both A&B

*Decreasing the TR will:

Both A&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 *The central lines of k-space are associated with contrast information in a fast spin echo sequence.

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

Image contrast

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:

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

_______ 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 affect acquisition time EXCEPT:

TE

*All of the following would aid in reducing scan time EXCEPT:

TE

*Which of the following is NOT affected by changing the slice thickness?

The T1 contrast *Time (TR) is the controlling factor of T1 weighting/contrast in an image; slice thickness does nothing to alter the T1 information.

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

The central lines *Referring 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 *Referring to k-space, the data containing high resolution are located along the outer lines

*Reducing the number of lines filled in k-space will produce an image:

With a decrease in spatial resolution

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

long; long

K-space is typically filled:

one line at a time

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

short; short