Medical Imaging Exam 1 Solutions

Name: ______________________

BE 483/583 Molecular Imaging Exam #1

October 3, 2011

1) (5 points) List two things that you could do to increase the quantity (number) of x-rays produced by a radiographic x-ray source without altering the mean energy of the beam.

-

increase the mA (current) increase the exposure time

2) (5 points) (a) Drawn an energy spectrum (x-ray intensity vs. x-ray energy) for an x-ray tube with a gold anode operating at 150 kVp? (b) Drawn an energy spectrum for an x-ray tube with a gold anode operating at 75 kVp?

66.36 keV

x-ray intensity

0

50 75 x-ray energy (keV)

3) (2.5 points) Complete and balance the equation below. Be sure to include both the element and mass number.

223

Rn + alpha particle = __226Ra___ + neutron

4) (2.5 points) A measure of the total risk associated with an x-ray procedure is known as the __effective_______ dose.

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Name: ______________________ 5) (5 points) (a) Suppose a 50 keV x-ray hits a calcium atom in bone and is photoelectrically absorbed. If no characteristic radiation is released when an electron falls from the L-shell to the K-shell, but rather an electron is ejected from the L-shell, what is the velocity of this electron? (Assume the mass of an electron is me). (b) What is the name of this type of electron?

(a)

E ka = ( E bi " E bo ) " E bo

= (4.038 keV – 0.399 keV) – 0.399 keV

!

= 3.24 keV

1 me v 2 = 3.24 keV 2

v=

!

6.48 me

(b) Auger electron

!

6) (2.5 points) Indicate whether the following are directly or indirectly ionizing. a) alpha particle b) neutron c) x-ray d) electron e) proton _______direct___________ _______indirect___________ _______indirect___________ _______direct___________ _______direct___________

7) (2.5 points) How can you increase the maximum photon energy of an x-ray source?

By increasing kVp (accelerating voltage), i.e. maximum potential difference between the cathode and anode

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Name:...