Review questions rad 113 lecture test 1

When an x-ray photon has a shorter wavelength, what happens to its frequency and energy?

Frequency and energy increase.

Which SI unit measures absorbed dose and what does it mean physically?

Gray (Gy); joule of deposited energy per kilogram of tissue.

Name the three things that reduce occupational exposure.

Time, distance, and shielding.

What does the physical half-life of radioactive material describe?

The amount of time it takes for radioactive material to decay to half of its original activity.

Name the SI unit for equivalent and effective dose.

Sievert (Sv).

Distinguish air kerma from absorbed dose.

Air kerma = energy transferred to charged particles in air; absorbed dose = energy deposited per unit mass of tissue or another material.

CH 2 - What is the relationship between the angle of the anode and the effective focal spot?

The greater the anode angle, the greater the effective focal spot; a smaller angle produces a smaller effective focal spot.

Name the negative electrode and the positive electrode in the x-ray tube.

Negative = cathode; positive = anode.

What is thermionic emission and which two components supply the electrons?

The process of boiling off electrons from a heated filament; the filament produces the electrons, and the focusing cup directs them.

What does milliamperage describe during x-ray exposure?

Tube current; the amount of electron flow from the cathode to the anode.

If kVp and other conditions are unchanged, what is the main effect of increasing mAs on the x-ray beam?

Increases the quantity of x-ray photons produced.

Which part of the tube should be positioned over the thicker part of the patient?

Cathode.

CH 3 - Name the two mechanisms that remove photons from the primary beam and together produce attenuation.

Absorption and scatter.

What happens to an incoming photon during a photoelectric interaction?

The photon is completely absorbed, and an inner-shell electron (usually a K-shell electron) is ejected.

What happens during a Compton interaction?

An outer-shell electron is ejected, and the incoming photon loses some energy and changes direction, producing scatter.

On an x-ray, does bone appear lighter or darker than an air-filled region, and why?

Lighter because bone has a higher density and attenuates (absorbs) more of the x-ray beam.

How is a bremsstrahlung photon produced?

An electron is attracted to the nucleus, slows down or changes direction, and releases energy in the form of an x-ray photon.

Distinguish size distortion from shape distortion.

Size distortion = magnification; shape distortion = elongation or foreshortening.

What is the effect of scatter reaching the image receptor?

It decreases image contrast and overall image quality.

CH 4 - What is an image matrix and what is a pixel?

Matrix = an array of rows and columns; pixel = the smallest individual picture element in the matrix.

If the matrix is fixed, how do smaller pixels affect detail/spatial resolution?

Smaller pixels improve detail and spatial resolution.

What does pixel bit depth mean?

The number of possible shades of gray represented in an image.

What is the difference between indirect and direct conversion in a flat-panel detector?

Indirect conversion changes x-rays into light first, then into an electrical signal; direct conversion changes x-rays directly into an electrical signal without producing light.

What does an analog-to-digital converter do?

Converts the electrical signal into a digital numerical value so the computer can create and display the image.

What happens to a CR latent image if the plate readout is delayed?

The latent image loses signal strength and fades over time, reducing image quality.

An underexposed digital image has acceptable displayed brightness but looks grainy. What is this called and why does it happen?

Quantum mottle (noise); it happens because there are not enough x-ray photons reaching the image receptor.