Diagnostic 2 Quiz 1 (MRI, CT, Fluoro)

What is Coupling Factor? (MRI)

Efficiency of energy transfer from RF coil to patient… Effectiveness of coil’s B field responsible for flipping H nuclei into transverse plane

Higher coupling factor means better energy transfer and stronger signal

How is the MRI signal matrix determined? (i.e. what are the axes of the graph?)

Gy Pulse & Frequency.

What is MRI signal?

Voltage induction

What gradient is used when testing for MRI Center Frequency? (Larmor Frequency)

NO GRADIENT. Because it’s the center frequency!

What is Nyquist Frequency?

“Min sampling rate to give correct shape of wave.”

f_N = 1/2D (D is CT detector width)

How to determine scannign time for MRI?

Number of Gy (phase) pulses x TR

Difference between Soft-Copy and Hard-Copy?

Soft-Copy is on the monitor. Hard-Copy is a physical printout

What is the CT QC phantom filled with?

water. density 1g/cm³ to mimic scatter environment

What is the minimum slice thickness for CT?

Detector width, ~0.5mm

How many filters in CT?

at least 3…

2 physical: BHF (Cu), and Bowtie (for uniform field)

1 algorithm: Kernel Filter (smooth & enhance contrast and spatial res)

Does axial or helical scan produce more dose in CT?

Axial. Helical scan is faster

Why is Iodine used in NaI scintillator in CT detector?

Iodine K-edge most effective at converting to light

What are the bounds of the CT phantom scan? Where is the phantom’s air pocket located?

“edge-to-edge"

Air pocket in front, bottom right quandrant

What is first scan performed? (MRI, CT, etc..)

Scout scan

Which body part receives higher kV (dose) in CT?

Head. Have to penetrate skull

How does dose (kV) affect low contrast detectability?

goes down with decreased dose

What is CT unit?

Hounsfield unit

What is CT?

Computed Tomography is a spatial sampling technique that utilizing the Nyquist frequency determined by the detector width.

How can we check accuracy of CT?

MTF (Modulate amplitude Transfer Function) —> determines if LINEAR system, f_in = f_out.

What is MTF? What is condition for MTF?

Modulated Transfer Function. ratio of output amplitude to input amplitude. A_out/A_in…

no noise, highest signal without saturating system, ASSUMED linear system (if MTF > 1, non-linear → false info)

Why does the ratio go down in the graph?

As frequency increases, system has a harder time resolving noise from Amplitude… ELECTRONIC noise

How to calculate total MTF… MTF_system?

just multiply all MTF values together… (MTF_xray)(MTF_detector)(MTF_monitor)

Which MTF value has the highest impact on the system?

MTF_detector from the element , because it is the smallest component… resolution is preserved at the detector element (~140μm) but lost at monitor pixel (~200μm)

REVIEW THE MTF GRAPH NOTES

do it.