Physics Flashcards by Ashley Phelps

What is letter A?

Magnetic field strength

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What is letter B?

Gyromagnetic ratio

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10,000 Gauss= ❓Tesla

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Iron & Iron-like substances that can generate a relatively strong magnetic field are?

Ferromagnetic

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Substances with a very weak magnetic field are?

Paramagnetic

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Substances that have no magnetic field are?

Diamagnetic

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Hydrogen protons in the anti-parallel state are referred to as….?

Spin down and/or high energy spins

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T1 relaxation is also known as…?

Spin lattice relaxtion

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Pixel Area x Slice Thickness= ?

Voxel volume ³

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Phase pix size X Freq. pixel size= ?

Pixel Area²

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FOV/Matrix=?

Pixel Size

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TR x Phase Matrix x NEX x #Slices= ?

3D gradient echo scan time

Divide by 1,000 to convert to seconds

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TR x Phase Matrix x NEX / ETL = ?

FSE scan time

Divide by 1,000 to convert to seconds

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TR x Phase Matrix x NEX= ?

Spin Echo scan time

Divide by 1,000 to convert to ms to seconds

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FOV/Phase Matrix= ?

Pixe size dimensions
(Phase encoding direction)

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FOV/Freq. Matrix= ?

Pixe size dimensions
(Freq. encoding direction)

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T2 weighting & contrast are controlled by ____

TE (Echo Time)

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Spatially locating (encoding) signal along the short axis of the slice is known as_____

Phase Encoding

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Spatially locating (encoding) signal along the long axis of the slice is know as____

Freq. Encoding

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How do T2 contrast agents work?

By shortening T2 decay time

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How do T1 contrast agents work?

By shortening T1 recovery time

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Proton density is____

the # of mobile hydrogen protons per unit volume of a tissue

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Parameters that can be change/under our control are called___

Extrinsic contrast parameters

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List the extrinisic contrast parameters

TR
TE
TI
ETL
Flip Angle
b-value

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Parameters that cannot be chaged; are inherent to body tissue are called_

Intrinisic contrast parameters

List the intrinsic contrast parameters

* T1 recovery time * T2 decay time * Proton density * Flow * Apparent diffusion coefficient (ADC)

T1 weighting/contrast are controlled by___

A range of frequencies is known as__

Bandwidth

A range of freq. transmitted in an RF excitation pluse are known as___

Transmit Bandwidth

A range of freq. that are sampled during readout are known as___

Receive Bandwidth

The center of the bore of the magnet in all planes is known as___

Magnetic Isocenter

Magnetic homogeneity is___

Eveness of the magnetic field

Nuclei that possess an odd mass # are considered___

MR Active nuclei

an event in a superconducting MR system causing a loss of superconductivity, a rapid loss of the magnet cryogens, potentially creating a hazard for patients / operators in the magnet room

Quench

A Flair sequenc is used to.....

Suppress CSF/Fluid

A STIR sequence is used to...

Suppress fat

Based on this info what will your image be? Slice selection- Z Gradient Phase encoding- Y Gradient Freq. encoding- X Gradient

Axial (body)

Based on this info what will your image be? Slice selection- Z Gradient Phase encoding- X Gradient Freq. encoding- Y Gradient

Axial (head)

Based on this info what will your image be? Slice selection- X Gradient Phase encoding- Y Gradient Freq. encoding- Z Gradient

Sagittal

Based on this info what will your image be? Slice selection- Y Gradient Phase encoding- X Gradient Freq. encoding- Z Gradient

Coronal

TR (repetition time) is...

the time from one RF excitation pulse to the next

What is the Gyromagnetic ratio of hydrogen is...

42.5774

TE (echo time) is....

Time from RF excitation pulse to the peak signal induced in the receiver coil.

What gradient runs from head-toe of the patient?

Z-Gradient

What gradient runs from RT-LT of the patient?

X-Gradient

What gradient runs from anterior-posterior of the patient?

Y-Gradient

What are the trade offs of decreasing TR?

* Lower SNR * Decrease scan time * Enhance T1 weighting * Decrease # of available slices

What are the trade offs of increasing TR?

* Improve SNR * Increase scan time * Reduce T1 weighting * Increase # of available slices

On T2 weighted images how do fat and water appear?

Fat=Dark Water=Bright

On T1 weighted images how do fat and water appear?

Fat=Bright Water=Dark

What is this formula?

Larmor equation

What is letter C?

Precessional Freq.

The outter lines of K-space are filled with...?

High Resolution Date

The central lines of K-space are filled with...?

Signal & Contrast Data

K-space is...?

Storage location of MR signal data

T1 relaxtion time is the time it takes for...?

63% of the longitudinal magnetisation to recover.

T2 relaxtion time is the time it takes for...?

63% of the transverse mag. to decay or 37% of spins to de-phase

T1 relaxation is also knows as...

Spin-Lattice relaxtion

T2 relaxtion is also known as...

Spin-Spin relaxation

A scan with a short TR and short TE will have what weighting?

T1 weighted

TR range for a T1 weighted image is...

300-750ms

TE range for a T1 weighted image is...

10-30ms

A scan with a long TR and short TE will have what weighting?

Proton Density (PD)

TR range for a PD weighted image is...

1600-4000ms

TE range for a PD weighted image is...

10-30ms

A scan with a long TR and long TE will have what weighting?

TR range for a T2 weighted image is...

2000-6000ms

TE range for a T2 weighted image is...

80-120ms

What are the 3 factors that control contrast for an inversion recovery squence?

* TR * TE * TI

A spin echo pulse sequence preceded by a 180 RF pulse is.....

An inversion recovery pulse sequence

An inversion recovery sequence with a ***short*** TI is...

A STIR

An inversion recovery sequence with a ***long*** TI is...

A FLAIR

The time between 180° preparation pulse and the 90° excitation pulse during an inversion recovery sequence is known as...

TI (inversion time)

A 90° RF followed by 180° RF produces what type of pulse sequence?

Spin Echo

A 90° RF followed by train of 180° RF pulses produces what type of pulse sequence?

Fast Spin Echo (FSE)

A 180° RF followed by 90°RF produces what type of pulse sequence?

Inversion Recovery

A variable° RF followed by gradient to produce echo produces what type of pulse sequence?

Gradient Echo

____ corresponds to the amount of radiofrequency energy deposited in the patient, which may result in heating.

SAR

As the flip angle is doubled, the RF absorption increases by a factor of __________.

The pulse sequence that should be utilized the least in a patient with implanted metallic hardware is:

Gradient echo ## Footnote Gradient echo sequences lack a 180° RF pulse that aids in correcting local magnetic field inhomogeneities, found in metallic implants.