Phys Rad Tech Exam 3

NMR stands for

Nuclear Magnetic Resonance

MRI stands for

Magnetic Resonance Imaging

MRI uses what types of waves

Radio Waves (NON-ionizing)

Electromagnetic Spectrum

In order of increasing frequency and decreasing wavelength—-

Radio Waves

Microwaves

Infrared waves

Visible Light

Ultraviolet light

X rays

Gamma Rays

Formula for photon energy

E =hf

What are the three types of magnetic materials?

-Ferromagnetic material: strongly attracted by a magnet (examples: iron, nickel)
-Paramagnetic material: weakly attracted by a magnet
-Diamagnetic material: weakly repelled by a magnet (examples: water and most biologic
tissues)

What is precession?

The magnetic moment of a particle with spin, such as an electron, precesses around an external magnetic field due to the torque exerted by the field on the magnetic moment.

The detected signal in MRI is called an…

Echo

SI unit for magnetic Field

Tesla (T)

Why hydrogen in MRI?

hydrogen gives largest signal per atom - relative sensitivity = 1

T1 and T2 weighting do what to fat and CSF+water

T1 weighting: Fat is bright / CSF and water are dark

T2 weighting: Fat is dark / CSF and water and bright

A transducer does what

detects and produces sound waves

A = decay constant * N

A = activity

N = number of atoms

most commonly used radionuclide in the world

Tc-99m

What is used as a Grid in nuclear imaging to reduce scatter?

collimator

What are the names of the
three pulse sequences that are used for the “bulk of” MRI
imaging?

• spin echo

• inversion recovery

• gradient echo

formula for power

power = SAR(mass)

formula for energy

Energy = power (W) * Time (sec)

What are the four types of collimators in Nuclear imaging?

• Parallel multihole collimator

• Pinhole collimator- for imaging small objects

• Converging collimator- image larger than object

• Diverging collimator - image smaller than object

A positron is made up of antimatter (T/F)

True

PET uses positron emitting isotopes

TRUE- does not use a grid/collimator

FDG

Fluorodeoxyglucose - used in PET

Formula for Acoustic Impedance

Z = density of material * speed of sound

(Z= ρc)

Normal range of hearing

20 Hz- 20 kHz (low to high pitch)

Units for frequency

Hz

units for speed

m/s

units for wavelength

meter

MRI scanners are cooled by what

liquid helium

Faradays Law

changing magnetic field creates electrical field

SAR stands for

Specific Absorption Rate = power absorbed per kg of tissue

formula for SAR

SAR = c ∆T/ ∆t

Whats the most common compound contrast agent used in MRI?

Gadolinium (PARAMAGNETIC MATERIAL)

What does GBCA mean

Gadolinium Based Contrast Agent

Gadolinium-diethylenetriamine
pentaacetic acid (Gd-DTPA)

MEMORIZE- a paramagnetic material given by injection as contrast in MRI

What is the piezoelectric effect

Generating an internal electric charge from mechanical stress from certain materials (or vice versa)

What are the X and Y scales for A and B Ultrasound display modes

A mode: X- Time Y- echo amplitude

B mode: X- location of echo Y- location of echo

What are the four different types of ultrasound wave interactions?

Reflection, Refraction, Scattering, Absorption

Compare the peak sound pressure used in Ultrasound Imaging to the Earth’s atmospheric
pressure

Peak pressure in Ultrasound imaging is 10x the earths atmospheric pressure

What do the letters “HVT” stand for

Half Value Thickness

The thickness of tissue necessary to attenuate the incident intensity by 50%

What do the letters “PZT” stand for?
What is PZT used for?

lead-zirconate-titanate

can be used as a source of sound and also as a detector of sound

What are the two types of wave interference

constructive and destructive interference

What does a Photomultiplier Tube detect?

light

What are the two main functions of a Photomultiplier Tube?

detects light and amplifies the signal

What is SAR?

power absorbed per kg tissue

Power is measured in…

Watts (W)

1 W = 1 J/sec

What are the differences between the A mode and B mode ultrasound imaging displays

(Amplitude modulation): single transducer (Brightness modulation): transducer array, 2D scan

what is a radioactive isotope called?

radionuclide

Radioactive Decay

process by which an unstable nuclide becomes more stable
• Emits particles and energy

T

time for half of the radioactive
particles to decay; after a time T,
half are left.

What does HVT stand for and what it does mean

half-value thickness.

The thickness of tissue necessary to attenuate the incident intensity by 50%

piezoelectric materials do what

creates an internal electric charge from an applied mechanical stress

What are the names of the three basic types of radiation detectors as classified by detection
method

Gas Filled Detector, Scintillation detector, semiconductor detector

How does a Geiger counter work?

counts almost every particle that reaches the interior of the detector

How does a scintillation detector work?

Consists of a scintillator and a device, such as a PMT, that convert the light into an electrical signal

Spin-Echo Pulse Sequence
(memorize these steps)

Start at t = 0
Transmit 90 degree radiofrequency (RF) pulse
At t = TE/2, transmit 180 degree RF pulse.
At t = TE, detect signal.
At t = TR, start the process all over again

What causes the loud knocking noises in MRI?

a large force is being applied to the coils, these forces change directions, causing shifting of the coils in their mountings. This movement causes noise.

Units of Activity In SI and Traditional system

SI: becquerel (Bq)

Traditional: curie (Ci)

What is acoustic impedance used for

a measure of tissues stiffness and flexibility. in rayls (kg/m2/sec)

Average US radiation dose (yearly)

360 mrem/year