magnetism in MRI quiz

What type of current is used with most MRI systems currently manufactured?

Superconducting

What is defined as the excess number of hydrogen protons aligned with the static magnetic field direction (B0)?

Longitudinal magnetization

The energy used to form MRI images is _______ the patients tissues

Emitted from

All of the following are non ferrous substances:

• Plastic

• Titanium

• Copper

The extent to which a material or tissue becomes magnetized in an external magnetic field is called:

Magnetic susceptibility

If a technologist applies a gradient to create a magnetic field of 0.995T at a specific slice location, what RF frequency is needed to excite that slice?

0.995 × 42.57 = 42.36

Which type of magnet can be shut off the quickest in case of an emergency, such as a person being pinned by a ferromagnetic object?

Resistive

The _______ is defined as the resonant frequency, and is equal to the product of the magnetic field and the gyromagnetic ratio

Precessional frequency

All of the following are true regarding RF pulse EXCEPT:

RF converts FID into an echo

The force that an object can be attracted to the magnetic field is reliant upon:

• strength of the main magnetic field

• Spatial gradient of the field

• Mass and specific magnetic properties of the object itself

________ is the term used to describe the degree of magnetization of an object

Susceptibility

What element in the body is the principal nucleus utilized in clinical MR imaging?

Hydrogen

A ferromagnetic oxygen tank is accidentally brought near the MRI scanner. The immense force pulling the object toward the magnet depends on which of the following factors?

I. Mass of the object

II. Strength of the magnetic field

III. Strength of the RF field

IV. Ferromagnetic properties of the object

I, II, and IV

A magnetic vector possesses attributes of both ______ and ______

Magnitude; direction

Hydrogen is used in MR imaging because

Of its abundance in the body

Calculate the Larmor frequency for H at 0.5 Tesla

42.57 × 0.5 = 21.28 MHz

Hydrogen protons in the anti parallel state are referred to as:

• spin down

• High energy

Immediately following the application of the 90 deg RF pulse, the precessing protons:

• causes them to tip into the transverse plane

• Forces them to precess together coherently or in phase

Immediately following the application of the 90 deg RF pulse, the transverse magnetization is:

Non zero

In one T2 relaxation time:

63% of the transverse magnetization has decayed

In one T1 relaxation time:

63% of the longitudinal magnetization has recovered

A free induction decay (FID) is produced from a:

RF pulse

The precessional frequency of hydrogen, according to the Larmor equation, a 3 Tesla is

42.57 × 3 = 127.71 MHz

When a patient is first placed in the MRI scanners main magnetic field, the hydrogen protons align and a state of thermal equilibrium is reached. At this point:

There are more hydrogen protons in the low energy state

At 1.5 Tesla the chemical shift between fat and water is:

220 Hz

Image 59 is an example of a

Free induction decay

Which of the following most accurately defines what image 59 is?

The decaying, oscillating signal induced after 90 deg pulse

Image 60 represents the:

Larmor equation

Image 61 represents:

T1 recovery

Image 62 represents:

T2 decay

Image 82 was acquired at what field strength?

1.5 tesla

Aside from the center frequency what other indicator in image 82 signifies it was acquired at 1.5 Tesla

The chemical shift between fat and water is 220 Hz

Image 91 was acquired at what field strength?

1.5 Tesla

A system operating at 30,000 gauss has a field strength of:

30,000/10,000 =3 Tesla

Image 92 was acquired at what field strength?

1.0 tesla

The net magnetization vector (NMV) when aligned with the magnetic field direction, is aligned

Along the longitudinal axis

The fringe magnetic field:

Can cause nearby medical devices to malfunction

______ states that a changing magnetic field will induce a voltage

Faradays law of induction

What has a higher precessional frequency?

Water

A FID is produced from:

An RF pulse

How many radiofrequency pulses produce a FID?

1

How well a material attracts the imaginary lines of the magnetic field is defined as:

magnetic permeability

_____ occurs after initial RF application, causing phase differences to appear between precessing spins, resulting in decay of transverse magnetization

Dephasing

The difference in chemical shift is approximately ______ parts per million

3.5

The protons that align themselves with the direction of the static magnetic field exist in a energy state ________ than those anti parallel to the magnetic field

Lower

At 1 Tesla the frequency difference between that of fat and water is approximately

147 Hz

_______ substances have strong magnetic properties and can be pulled into the magnetic field

Ferromagnetic

All of the following are ferromagnetic substances

• steel

• Iron

• Nickel

The first documented human MR image was obtained on a 15 MHz RF system, what field strength did it operate at?

0.352 Tesla

All of the following are true except:

The RF field oscillates at the Faraday frequency