RF SYSTEM

Question 1

• The electromagnetic components of the RF system may be provided by outside
  suppliers and assembled by the MRI manufacturer. These components are attached
  to the RF coils, which are made with vary designs.

Answer 1

RF system

Question 2

– make the magnetic field homogeneous (they maintain the mri should receive
balanced magnetic fields) in Xray they act as filter

Answer 2

Shim coils

Question 3

– detect the returning radio signals

Answer 3

Receiver coils

Question 4

– are the antenna of MRI system that broadcast the RF signal to the patient and/or
receives the return signal RF coils can be receive only, in which case the body coil is used
as a transmitter, or transmit and receive (transceiver)

Answer 4

RF coils

Question 5

5 RF BODY COILS: SUPAHEBIFA

Answer 5

Surface
Paired saddle
Helmhortz pair
Bird cage
Faraday cage

Question 6

– are the simply a loop of wire either circular or rectangular, that is
placed over the region of interest. The depth of the image of a surface coil is
generally limited or about one radius. Commonly used in spines, shoulders, tmj’s and
other relatively small body parts

Answer 6

Surface coils

Question 7

– provide better homogeneity of the RF in the are of interest and
are used as volume coils, unlike surface coils. Also used of the X and Y gradient
coils. Commonly used for imaging of the knee

Answer 7

Paired saddle coil

Question 8

– consist of two circular coils parallel to each other. They are
use as gradient coils in MRI scanners. They also used occasionally RF coils for
pelvis imaging and spine imaging (dedicated for spina and pelvic imaging, bigger
anatomy or bony structure)

Answer 8

Helmhortz pair coil

Question 9

– provides the best RF homogeneity of all the RF coils. It has the
appearance of a bird cage, hence, its name. This coil is commonly used as a
transceiver coil for imaging of the head. This type of coil is also used occasionally for
imaging of the extremities such as the knees. (For the brain)

Answer 9

Bird cage coil

Question 10

(to prevent radio frequency interference from outside)
- Specification: to provide radio frequency shielding, uses aluminium, or in certain
conditions galvanized steel, to form the shielded faraday cage
-

Answer 10

Faraday Cage

Question 11

is used in MRI to describe the relative contributions to a detected
signal of the true signal and random superimposed signals (background noise)

Answer 11

signal to noise ratio

Question 12

SNR formula

Answer 12

Mean signal/Standard Deviation of Background noise

Question 13

If SNR INCREASE these 4 factors will DECRASE

Answer 13

T1, TE, MATRIX SIZE, RF BANDWIDTH

Question 14

If SNR WILL INCREASE THESE 7 FACTORS WILL INCREASE ALSO

Answer 14

Bo, T2, TR, NEX, Pixel Size, Slice Thickness, FOV

Question 15

If all parameters are constant…the smaller the sensitive volume of a coil, the ___ the noise from the adjacent
structures of the selected slice plane which it can detect, and the better the signal to
noise ratio will be

Answer 15

Lower

Question 16

A ___or better, a ___coil has a higher signal to noise ratio than a body coil

Answer 16

local coil,surface

Question 17

– frequencies associated either with RF-excitation (transmitter bandwidth,
tBW) or signal reception (receiver bandwith, rBW) or the highest or lowest signal

Answer 17

RF bandwidth

Question 18

is the range of frequencies accepted by
the receiver to sample the MR signal. rBW has a direct relationship to the signal to noise
ration (SNR = 1/sqrt (rBW)

Answer 18

receiver (or acquisition) bandwidth (rBW)

Question 19

– RF excitation pulse required for slice selection in a pulse
sequence. The slice thickness is proportional to the bandwidth of the RF pulse (and
inversely proportional to the applied gradient strength) lowering the pulse bandwidth can
reduce the slight thickness

Answer 19

transmit bandwidth

Question 20

Slice thickness in MRI is determined: BS

Answer 20

The band width of the RF (longer BW, lower ST)
Steepness of the slope of the gradient coil (strength)

Question 21

– (mri uses techniques) to acquire images with different tissue contrast
mechanisms. Pulse sequences are a set of specific instructions programmed into the
computer with an expectation as to how the images should appear

Answer 21

Pulse sequence

Question 22

)
- Diffusion movement of molecules due to random motion. If an incident occurs less
than 72 hours prior to the scan, swelling due to edema occurs.
- Used for CVA and CNS
- The combination of actual diffusion values and T2 signal.

Answer 22

DWI (diffusion weighted imaging

Question 23

• Diffusion movement of molecules due to random motion. If an incident occurs less
  than 72 hours prior to the scan, swelling due to edema occurs.
• Used for _____
• The combination of actual diffusion values and T2 signal.

Answer 23

DWI (diffusion weighted imaging)
CVA and CNS

Question 24

DWI is most applicable when the tissue of interest is dominated by isotropic water movement
e.g., grey matter in the cerebral cortex and major brain nuclei, or in the body-where the
diffusion rate appears to be the same when measured along any axis. However, DWI also
remains sensitive to T1 and T2 relaxation

Question 25

was introduced to take
into account the fact that the diffusion process is complex in biological tissues and reflects
several different mechanisms

Answer 25

ADC concept

Question 26

– are images representing the actual diffusion
values of the tissue without T2 effects
- They are therefore much more useful, and objective measures of diffusion values can
be obtained; however, they are much less pretty to look at.
- They appear basically as grayscale or inverted DWI images

Answer 26

Apparent diffusion coefficient maps (ADC)

Question 27

– most widely used. starts with 90 pulse and ends with 180 degrees pulse.

Answer 27

Spin Echo

Question 28

– a gradient to refocus the spins. Gradient echoes are more susceptible to
blood flows. They utilize the flip angles lesser than 90 degrees in addition to TR and TE.
- Are an alternative technique to spin echo sequences
- Utilization of gradient fields to generate transverse magnetization
- Flip angles of less than 90 degrees
- Aka reverse polarity of gradient

Answer 28

Gradient echo

Question 29

– fast gradient imaging technique. For turbulent blood
flow.

Answer 29

Fast gradient echo (FGRE)

Question 30

– is quicker because it covers a wide range of tissue, however it
does increase the specific absorbed rate. FSE starts with a 90 degree pule and
followed with a series of 180-degree pulse.

Answer 30

Fast spin echo