Chapter 8 Creating a MR Signal

Question 1

The magnetization of tissue can be expressed as a ___________as it has both magnitude (strength) and direction (orientation).

Answer 1

vector quantity
along the x,y,z planes

Question 2

what is longitudinal magnetization?

Answer 2

magnetization along the z axis (Mz)
net magnetization of the tissues when aligned along the axis of the B0 is drawn as a vector along the z axis of a graph

Question 3

what is transverse magnetizaton?

Answer 3

orientation of magnetization along the x-y axis (Mxy)

Question 4

Only ______magnetization is detectable.

Answer 4

transverse
-we can detect (measure) a MR signal only when there is magnetization in x-y or transverse plane.
-in order to produce a MR signal, we have to convert some or all of the available longitudinal magnetization to transverse.

Question 5

hydrogen protons have a resonant frequency of

Answer 5

64 MHz

Question 6

to produce a MR signal you need:

Answer 6

2 magnetic fields perpendicular to one another.
-a strong externally applied magnetic field (B0)
-a secondary magnetic field known as the radiofrequency field (B1) its purpose is to apply RF energy to excite the spins (protons)

Question 7

the wavelength of an electromagnetic wave is measured

Answer 7

peak to peak

Question 8

as frequency increases, wavelength

Answer 8

decreases

Question 9

the transverse magnetization is sampled by means of

Answer 9

measuring the signal in receiver coils, that signal is induced by faraday’s law of induction

Question 10

what is faraday’s law of induction

Answer 10

states that moving or changing a magnetic field through a loop of conductive material will induce an electrical current in that conductor

Question 11

Free Induction Decay

Answer 11

FID
the signal induced in a receiving coil immediately following an RF pulse
-the signal is decaying away since the RF or B1 field is no longer present the protons are returning or relaxing back to thermal equilibrium