physics question 9
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MPHY501HomeworkLecture91.docxHomework
MPHY 501 Part 1 Lecture 9 Ch 10
Fluoroscopy
1) What is slip ring technology
2) Thinking about CT multichannel detectors what is a “Ray”?
3) Thinking about CT multichannel detectors what is a projection?
4) Using an illustration define the:
a. Fan Beam
b. Cone Beam
5) What is the major problem with cone beam geometries?
6) Why is it important for the axis of rotation of the anode to be perpendicular to the plane of gantry rotation?
7) Assume a sample dwell time of 0.7 milliseconds how many projections can be acquired if the gantry rotation time is 0.5 seconds?
8) How long is an x-ray tube trajectory if the gantry is 120cm?
9) What is the name of the technology that allows to correct for focal spot/detector mis-alignment during rotation?
10) What is the effective energy of a 140keV x-ray beam
11) Why is the effective energy lower that the 140keV?
12) How is it helpful to have effective energies in that range in terms of image contrast?
13) Compton scatter:
a. What is the mathematical formula for the linear attenuation coefficient of Compton scatter? As it related to density , Z and A?
b. Define the terms in the formula
c. What does the formula tell you about the
d. Why is Z/A almost always ½?
14) What is a HU unit?
15) What is the formula to calculate HU units?
16) What are the two points where HU is defined?
17) What is the density of:
a. Bone
b. Water
c. air
18) Show your calculation (using units and a formula) for the HU of:
a. Water
b. Air
c. Bone (assume bone is 100% Calcium)
19) What does a bowtie filter do in CT scanning.
20) What happens when a bowtie filter that is too small is used, in terms of dose and image linearity?
21) What are the differences between single array CT, Multiple detector CT and Cone Beam CT.
22) What is the numerical change in signal to noise when slice thickness goes from 1cm to 1mm?
23) What is the efficiency of a 4-array detector
24) What percent increase or decrease to the current is needed to correct the effencicy issue in question 18?
25) What are 4 other names for Scout View?
26) How is a scout view created?
27) If a detector element is 0.5 mm wide what is the width in of a 128 channel detector?
28) If the detector in question 22 needs to cover 25 inches, show your math and express units with the math all the way through?
29) What is the main reason that low channel count (narrow beam) system give patients more dose than high channel count (wide beam) systems?
30) What can be done to eliminate the extra dose typically given by helical scanning at the extreme at the ends of the helical scan (helical scan requires 220 mm acquisition to reconstruct 200 mm of image data).
31) What is the geometry of the detector in cone beam CT?
32) How does retrospective cardiac gating save dose?
33) Duel Source CT:
a. Why do we need Duel Source CT
b. How is Duel Source CT different from Duel energy CT/
34) Dose Modulation
a. How does dose modulation work for any given slice?
b. When moving to the next table position in an axial acquisition?
