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ABR Part III > Imaging > Flashcards

Imaging Flashcards

1
Q

How far does an F18 positron travel in water?

A

0.5 mm

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2
Q

What is the post-injection uptake period for FDG PET?

A

1 hr

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3
Q

What is a typical dose of FDG PET?

A

10-20 mCi

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4
Q

What are the 2 broad techniques for automated image registration?

A

geometry (detects/aligns edges of objects) and intensity (compares the intensity of the voxels themselves) -based metrics

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5
Q

What kind of image registration metric is best for aligning CT to MRI?

A

mutual information - a special type of intensity-based metric needed because the absolute intensity of MRI and CT differ greatly, and the greater soft-tissue contrast in MRI creates more/different edges making geometry-based registration hard

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6
Q

How does a mutual information registration algorithm work?

A

tries to minimize the number of voxel-intensity pairings rather than trying to minimize the difference between the voxel intensities themselves

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7
Q

What is the pulse sequence for T1 MRI imaging?

A

short-short (TR ~ 500 ms, TE < 15 ms)

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8
Q

what is T1 imaging used for in radiotherapy?

A

to assess nodal invasion

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9
Q

What is the pulse sequence for T2 MRI imaging?

A

long-long (TR ~ 2000 ms, TE ~ TR)

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10
Q

How to tumors appear on a T2 image?

A

they tend to be bright (not always, but usually)

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11
Q

What is the pulse sequence for proton density weighted MRI?

A

long-short

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12
Q

What is T1 relaxation in MRI?

A

longitudinal relaxation - spin-lattice - the amount of time it takes the protons to realign with the magnetic field (to regrow to 63% of the max value)

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13
Q

What is T2 relaxation in MRI?

A

transverse relaxation - the amount of time it takes the transverse signal to fade away (to decay to 37% of the max value) after relaxation

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14
Q

What is TR in MRI?

A

the amount of time between excitation RT pulses

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15
Q

What is TE in MRI?

A

the time between excitation and signal acquisition

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16
Q

What does TR control in MRI?

A

T1 weighting

17
Q

What does TE control in MRI

A

T2 weighting

18
Q

How does imaging dose vary with kVp, mAs, and pitch?

A

proportional to kVp^2, mAs, and 1/pitch

19
Q

What is the Rose criteria?

A

SNR must be at least 5 to resolve an object in an image

20
Q

What is the nyquist frequency?

A

principle that says you must sample at least 2x the frequency you want to resolve, so in imaging, you need at least 2 pixels per dimension you want to see - so 1 cycle/ 2 pixels

21
Q

What is the MTF limit of detectability by humans?

A

0.1

22
Q

Draw the Noise Power Spectrum triangle thing

A
23
Q

What is QDE in imaging?

A

Quantum Detective Efficiency - how good the imager is at collecting information - n collected / n incident

24
Q

What is DQE in imaging?

A

Detective Quantum Efficiency - how good it is at converting information carriers into an image - SNRout^2/SNRin^2

25
Q

What are some advantages/disadvantages of radiochromic film as a dosimeter?

A
  • better dosimetric accuracy
  • tissue equivalent
  • energy independent
  • no chemical processing (gives you the better accuracy)
    X - requires higher minimum dose
26
Q

What are some advantages/disadvantages of radiographic film?

A
  • highest spatial resolution
  • more sensitive (higher minimum dose requirement)
    X- only energy independent for MV beams
    X- higher uncertainty (because of development error, fogging in visible light)
    X- strong energy dependence in kV range
27
Q

what is CTDI vol?

A

CTDI_w / pitch

28
Q

What is the dose-length product (DLP)?

A

CTDI_vol * L_scan

29
Q

What is regularization in image registration?

A

like a penalty function to prevent overfitting, restricts unrealistic motion (like bending of bones)

30
Q

About how much dose do the staff get for an FDG-PET imaging procedure?

A

~25 microGy

ABR Part III (13 decks)

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