BME 520 Multiple Choice - Final

The anode angle (degrees) in an x-ray tube used for chest radiography is most likely: a. 15 b. 30 c. 45 d. 60 e. 75

a- 15 degrees is a typical anode angle.

When a secondary coil has 500 more turns than a primary coil, the ratio of the secondary voltage to the primary voltage is most likely: a. 500 b. 500^0.5 c. 1/500 d. 1/500^0.5 e. Depends on AC frequency

a- 500. The increase in voltage is directly proportional to the increase in the number of turns.

The energy (E) dependence of photo- electric absorption above the K edge varies as: a. 1/E^3 b. 1/E^2 c. 1/E d. E^2 e. E^3

a- Above the K edge, the photoelectric effect is proportional to 1/E^3.

CT collimation is most likely used to change the x-ray beam: a. width b. intensity c. HVL d. FOV e. isocenter

a- CT collimation changes the x-ray beam width.

If the distance from a radiation source is halved, the radiation intensity increases by a factor of: a. 2^−2 b. 2^−1 c. 2^0 d. 2^+1 e. 2^+2

e- 2^2 (i.e., 4). Halving the distance quadruples the radiation intensity (inverse square law).

A chest x-ray examination on a dedicated chest unit would be least likely to use: a. 60-kV voltage b. 800-mA tube current c. 10-ms exposure time d. 1-mm focus e. 5-mm Al filtration

a- Chest x-rays are performed at high voltage (120 kV).

The most likely percentage (%) of coherent scatter photons in an x-ray beam emerging from a patient having a chest x-ray is: a. <5 b.5 c. 10 d. 20 e. >20

a- Coherent scatter never accounts for more than 5% of all interactions in diagnostic radiology.

At the same peak voltage, which generator likely deposits most energy into an anode? a. Constant potential b. High frequency c. Three phase (12pulse) d. Three phase (6 pulse) e. Single phase

a- Constant potential, since it has negligible ripple and the voltage across the x-ray tube is always the maximum possible value.

Which examination would most likely be performed without a scatter removal grid? a. Extremity b. Skull c. Abdomen d. Mammogram e. Fluoroscopy

a- In extremity radiography, use of low kVs means that most interactions (in bone) will be photoelectric absorption and not Compton scatter.

Which of the following refers to the number of nucleons in a nucleus? a. Mass number b. Atomic number c. Avogadro's number d. Atomic mass unit e. Nuclear density

a- The mass number is the total number of protons and neutrons (i.e., nucleons) in the atom's nucleus.

The average photon energy of an x-ray beam is least likely to be affected by changes in the: a. tube current b. tube voltage c. voltage waveform d. target composition e. beam filtration

a- The tube current does not affect the average (or maximum) photon energy in x-ray beams.

X-ray tube output would likely in- crease the most when increasing the x-ray tube: a. voltage b. anode angle c. target Z d. current e. exposure time

a- The x-ray tube output is (approximately) proportional to the square of the x-ray tube voltage.

At 65 kV and with a tungsten target, the percentage (%) of K-shell x-rays in the x-ray beam is most likely: a. 0 b. 1 c. 10 d. 50 e. 99

a- There will be no characteristic x-rays, as the electron kinetic energy (65 keV) is insufficient to eject W K-shell electrons that have a binding energy of 70 keV.

Actual vertical resolution (line pairs) achieved with a 525-line TV monitor is: a. 180 b. 262 c. 370 d. 425 e. 525

a-A TV with 525 lines can display 262.5 line pairs, but TV achieves only 70% of this value, so actual vertical TV resolution is 180 line pairs.

The most important factor for maximizing film contrast is most likely the film: a. optical density b. base thickness c. exposure time d. processing time e. fog level

a-Film optical density is critical (light and dark films have very little image contrast).

The most likely limitation of geometric magnification is an increase in: a. focal blur b. screen blur c. scattered photons d. quantum mottle e. detector exposure

a-Focal blur is extremely important in magnification imaging.

Increasing the amount of scatter in a radiograph reduces: a. imagecontrast b. focal blur c. screen blur d. image mottle e. patient dose

a-Image contrast is reduced when scatter increases.

Which of the following is least likely a measure of spatial resolution? a. ROC b. PSF c. LSF d. FWHM e. MTF

a-ROC is receiver operating characteristic, which measures diagnostic performance (PSF is the point spread function; LSF is the line spread function; FWHM is the full width half maximum; and MTF is the modulation transfer function).

Spatial resolution is important when detecting lesions that are characterized as being: a. small size b. low contrast c. high contrast d. less attenuating e. more attenuating

a-Spatial resolution is important for detecting, differentiating, and characterizing lesions that have a small size.

The MTF value (%) at the lowest spatial frequencies is most likely: a. 100 b. 75 c. 50 d. 25 e. 0

a-The MTF value is 100% for all imaging systems; this effectively means that huge objects can very easily be seen.

The II air kerma (μGy) needed to produce a single digital fluoroscopy image (frame) is most likely: a. 0.01 b. 0.03 c. 0.1 d. 0.3 e. 1

a-The air kerma that produces a single digital fluoroscopy frame is 0.01 μGy.

The detector air kerma (μGy) producing a digital photo spot image in a Ba enema examination is most likely: a. 1 b.5 c. 25 d. 100 e. 500

a-The detector air kerma in digital photo spot imaging is 1 μGy.

Specificity is given by the: a. true - negative fraction b. true - positive fraction c. (1- true-positive fraction) d. (1+true-negative fraction) e. truepositives+truenegatives

a-The true-negative fraction is the specificity.

An exposure of 1 R most likely corresponds to an air kerma (Gy) of a. 0.001 b. 0.01 c. 0.1 d. 1 e. 10

b- 1 R equals ∼10 mGy (i.e., 0.01 Gy).

If the linear attenuation coefficient is 0.1 cm^-1 , how many x-ray photons (%) are lost in 1 mm? a. 0.1 b.1 c. 10 d. e^-1 e. e^-0.01

b- 10% are lost in 1 cm, so 1% must be lost in each mm.

The CT number (HU) is directly proportional to the pixel: a. mass attenuation b. linear attenuation c. physical density d. electron density e. atomic number

b- CT numbers are directly proportional to the pixel linear attenuation.

Measuring the charge liberated in a mass of air quantifies: a. dose b. exposure c. equivalent dose d. HVL e. LET

b- Exposure is the charge liberated per unit mass, and in the SI system is measured in C per kg.

For electromagnetic radiation, which increases with increasing photon energy? a. Wavelength b. Frequency c. Velocity d. Charge e. Mass

b- Frequency, which is directly proportional to the photon energy

The number of projections obtained per 360-degree rotation of the x-ray tube in a single-slice CT scanner is most likely: a. 500 b. 1,000 c. 2,000 d. 4,000 e. 8,000

b- In CT, ∼1,000 projections are obtained for a single rotation of the x-ray tube.

The likelihood of Compton interactions is best quantified using: a. physical density b. electron density c. atomic number d. K-shell energy e. outer shell energy

b- The likelihood of Compton interactions is approximately proportional to the electron density.

The outer shell electrons most likely have binding energies (keV) of approximately: a. 0.001 b. 0.005 c. 0.025 d. 0.1 e. 0.5

b- The outer shell binding energy is ∼5 eV (i.e., 0.005 keV).

Which of the following is not a type of x-ray generator? a. Single phase b. Double phase c. Six pulse d. Twelve pulse e. High frequency

b- There are no double-phase generators.

After an x-ray undergoes photoelectric absorption by a K-shell electron, which emission is least likely? a. Photoelectron b. Scattered photon c. K-shell x-ray d. L-shell x-ray e. Auger electron

b- There are no scattered photons in photoelectric absorption; scatter occurs with Compton interactions.

The purpose of x-ray transformers is most likely to change the: a. magnetic field b. electrical voltage c. power level d. waveform frequency e. current intensity

b- Transformers change (increase or decrease) voltages.

Increasing the kV alone in CT scanning would most likely reduce: a. anode loading b. image mottle c. patient dose d. reconstruction time e. scan time

b-Mottle will be reduced at higher kV because more x-rays are produced, and the x-ray beam is more penetrating, which will increase the number of detected photons.

For comparable image mottle in an abdominal radiograph, which image receptor would likely result in the highest patient dose? a. Screen-film b. Photo stimulable phosphor c. Direct flat panel detector d. Indirect flat panel detector e. Digital photo spot

b-Photo stimulable phosphor requires more radiation as it must be thin to minimize light scatter during the readout process.

The horizontal resolution of a TV system is primarily determined by the: a. image lag b. bandwidth c. TV lines d. frame rate e. camera size

b-The TV bandwidth determines the horizontal TV resolution (usually the same as the vertical resolution).

X-ray quantum mottle is best characterized by quantifying: a. x-ray beam filtration b. detector air kerma c. average photon energy d. scintillator conversion efficiency e. image receptor thickness

b-The detector air kerma determines the number of x-ray photons used to make an image.

Sensitivity is given by the: a. true-negative fraction b. true-positive fraction c. (1-true-positive fraction) d. (1 + true-negative fraction) e. truepositives+truenegatives

b-The true-positive fraction is the sensitivity.

For a given absorber, if the Compton attenuation coefficient at 50 keV is 0.1 cm^-1 , its value at 100 keV (cm^-1 ) is most likely: a. 0.01 b. 0.025 c. 0.05 d. 0.1 e. 0.2

c- 0.05 cm^-1, since Compton interactions vary as 1/E, so doubling the photon energy will halve the probability of this interaction.

The total number of atomic ionizations produced following absorption of a 30 keV photon is most likely: a. 10 b. 100 c. 1,000 d. 10,000 e. 100,000

c- 1,000 ionization events are likely since it takes 30 eV or so to produce one ionization and there is 30,000 eV available.

An air kerma of 1 mGy is likely to result in an absorbed dose (mGy) to bone (no back scatter) of: a. 1 b. 2 c. 4 d. 8 e. 16

c- An air kerma of 1 mGy will result in an absorbed dose to bone of ∼4 mGy when there is no backscatter.

An air kerma of 1 mGy will most likely to result in an absorbed dose (mGy) to soft tissue (no backscatter) of: a. 0.5 b. 1.0 c. 1.1 d. 2.0 e. 4.0

c- An air kerma of 1 mGy will result in an absorbed dose to tissue of ∼1.1 mGy when there is no backscatter.

Heat stored in x-ray tube anodes is most likely dissipated by: a. convection b. conduction c. radiation d. air cooling e. oil cooling

c- Anodes get to be white hot and lose energy by radiation (light) to the tube housing.

In bone, at what photon energy are photoelectric and Compton effects approximately equal? a. 4.0 b. 25 c. 40 d. 70 e. 88

c- Compton and photoelectric interactions are equally probable at 40 keV in bone.

Which of the following would most likely be attracted to an anode? a. Proton b. Neutron c. Electron d. Positron e. Alpha particle

c- Electron, since it has a negative charge that is attracted to the positive anode.

Electrons passing through matter lose energy primarily by producing: a. bremsstrahlung b. characteristic x-rays c. atomic ionizations d. Compton electrons e. photoelectrons

c- Electrons lose most of their kinetic energy by knocking out (or exciting) outer shell electrons.

Ionizing radiations are least likely to include: a. x-ray photons b. energetic electrons c. infrared radiation d. alpha particles e. fast neutrons

c- Infrared radiation is non-ionizing, as the photon energy is less than 1 eV.

Which of the following is/are likely to have the longest wavelength? a. Gamma rays b. Microwaves c. Radiowaves d. Ultraviolet e. Visible light

c- Radio waves have the lowest frequencies and longest wavelengths.

The heel effect most likely increases when reducing the: a. tube voltage b. tube current c. anode angle d. filtration e. field size

c- Reducing the anode angle will increase the heel effect.

The most likely characteristic x-ray energy (keV) from x-ray tubes used in chest radiography is: a. 19 b. 33 c. 65 d. 75 e. 140

c- The chest x-ray unit will use a W target; the characteristic x-ray energy is therefore ∼65 keV.

The number of electrons accelerated across an x-ray tube is most strongly influenced by: a. anode speed b. focus size c. filament current d. tube filtration e. tube voltage

c- The filament current affects the temperature of the filament and thereby how many electrons the filament "bubbles off''.

For specification of anode heat capacities, one heat unit corresponds to energy (J) of: a. 0.9 b. 0.8 c. 0.7 d. 0.5 e. 0.3

c- The heat unit is 0.7 joule, and is an anachronism in modern radiology.

The mass attenuation coefficient is least likely to depend on absorber: a. composition b. K-shell energy c. physical density d. electron density e. atomic number

c- The linear attenuation coefficient is directly proportional to density; the mass attenuation coefficient is the linear attenuation coefficient divided by the density, which is therefore independent of density.

Which of the following generators is likely to have the largest waveform ripple? a. Constant potential b. High frequency c. Single phase d. Six pulse e. Twelve pulse

c- The ripple on a single phase generator is 100%.

Which of the following is not a unit of energy? a. Erg b. Joule c. Watt d. Calorie e. eV

c- The watt is a unit of power, measured in J/s.

Which quantity is the best measure of power? a. Joule b. Tesla c. Watt d. Coulomb e. Newton

c- Watt is a unit of power, where 1 W= 1 J/s.

If the attenuation of bone is 0.5 cm^-1, the fraction of x-ray photons transmitted through 1 cm is most likely: a. 0.05 b. 0.5 c. e^-0.5 d. e^+0.5 e. (1 - e^-0.5)

c- e^-0.5 is the fractional transmission of photons through 1 cm, when the attenuation of bone is 0.5 cm^-1

Radiographic spatial resolution performance can be best improved by reducing: a. beam filtration b. detector exposure c. detector thickness d. grid ratio e. tube voltage

c-Detector thickness (e.g., screen thickness) is important for determining the spatial resolution performance.

Film contrast is inversely related to film: a. fog b. noise c. latitude d. speed e. resolution

c-Film contrast (i.e., gradient) is inversely related to film latitude.

Increasing the detector thickness to absorb more x-rays will most likely increase image: a. contrast b. magnification c. blur d. mottle e. brightness

c-Image blur will increase with a thicker x-ray detector.

The best achievable head CT limiting resolution (line pairs/mm) using a 5122 matrix and 25 cm field-of-view is most likely: a. 0.25 b. 0.5 c. 1.0 d. 2.0 e. 4.0

c-One line pair per mm, since the pixel size is 0.5 mm.

Subject contrast is most likely to be affected by the: a. exposure time b. tube current (mA) c. tube voltage (kV) d. focus size e. display window

c-The x-ray tube voltage (average photon energy) is the most important factor that affects subject contrast.

Relaxing the threshold criterion in a ROC study increases false-positive fraction as well as the test: a. performance b. specificity c. ROCarea d. sensitivity e. accuracy

d-Sensitivity will increase as the threshold criterion increases and one moves up the ROC curve from lower left to upper right.

X-ray generators have a power level (kW) of approximately: a. 0.1 b.1 c. 10 d. 100 e. 1,000

d- 100 kW is typical of the power of x-ray generators in radiography and CT.

The total number of individual detector elements on a 64-row CT scanner is most likely: a. 64 × 100 b.64×200 c. 64 × 400 d.64×800 e. 64×1,600

d- 64 × 800 Since each slice would make use of ∼800 individual detectors.

The x-ray tube output most likely in- creases when reducing the: a. mA b. exposure time c. kV d. filtration e. focal spot

d- A reduction in filtration means that more x-rays can get out.

Which element has an atomic number of 56 and a K-shell binding energy of 37 keV? a. Calcium b. Selenium c. Molybdenum d. Barium e. Tungsten

d- Barium has 56 protons and a K-shell binding energy that is slightly higher than that of Iodine (33 keV).

Use of a bone filter, as opposed to a soft tissue filter, to reconstruct CT images would likely improve: a. subject contrast b. image contrast c. scatter rejection d. spatial resolution e. data storage

d- Bone filters improve spatial resolution but also result in higher mottle (noise).

An x-ray beam, attenuated by three half-value layers, is reduced by a factor of: a.3 b. 4 c. 6 d. 8 e. 9

d- Each HVL reduces the beam by 1/2, so three HVL attenuate the beam by a factor of 8.

Adding Aluminum filters to an x-ray beam is most likely to increase x-ray: a. intensity (air kerma) b. air kerma-area product c. maximum energy d. beam hardening e. leakage radiation

d- Increasing (Al) filtration always increases beam hardening in radiology.

Radiation transmitted through the x-ray tube housing is referred to as: a. useful b. secondary c. stray d. leakage e. scattered

d- Leakage radiation escapes through a fully closed collimator (the regulatory limit in the United States is <1 mGy/hr at 1 m).

A CT beam shaping filter (bow tie) is most likely made out of: a. aluminum b. copper c. molybdenum d. Teflon e. tin

d- Teflon (i.e., tissue like) is used as the CT beam shaping filter material to minimize beam hardening artifacts.

The adequacy of the filtration of an x-ray tube is best determined by measuring the: a. tube voltage b. air kerma c. field size d. half-value layer e. leakage radiation

d- The HVL is a good measure of the adequacy of filtration and at 80 kV should be greater than ∼2.5 mm Al.

The maximum photon energy in x-ray beams is determined by the x-ray tube: a. current b. exposure time c. target material d. anode-cathode voltage e. total filtration

d- The voltage across the x-ray tube determines the kinetic energy imparted to the electrons that are accelerated from the cathode (filament) to the anode (target), and thereby the maximum x-ray photon energy.

Tungsten is most likely used as an x-ray target because it has a high: a. physical density b. electron density c. electrical resistance d. melting point e. ionization potential

d- Tungsten can tolerate very high temperatures, which makes it an attractive target material in x-ray tubes.

The most likely Bucky factor in adult abdominal radiography is: a. 0.5 b. 1 c.2 d.5 e. 10

d- Use of a grid will likely increase patient doses fivefold (i.e., Bucky factor).

The maximum number of line pairs that can be observed using a 1k matrix size is: a. 50 b. 100 c. 250 d. 500 e. 1,000

d-A 1k matrix can display 500 line pairs (1 line pair needs two pixels, one that is white and one that is black).

When the full width half maximum of an imaged slit is 0.1 mm, the limiting resolution (line pairs per mm) is most likely: a. 1 b.2 c. 3 d.5 e. 10

d-Five line pairs per mm, since the achievable number of lp/mm is normally taken to be ∼1/(2 × FWHM).

A characteristic curve with a high gamma likely results in images with a high: a. patient dose b. film density c. quantum mottle d. imagecontrast e. fog level

d-Gamma is the maximum film gradient; high gamma produces a high image contrast.

If an average of 10,000 photons are detected per mm2, the chance (%) of detecting between 9,700 and 10,300 counts in any exposed mm2 is: a. 67 b. 90 c. 95 d. 99 e. 99.9

d-Ninety-nine percent, since the standard deviation is 100, and the limits correspond to three standard deviations.

The dominant source of image mottle in a radiographic flat panel detector is most likely: a. detector granularity b. electronic noise c. digitization noise d. quantum mottle e. monitor structure

d-Quantum mottle, as virtually all radiographic and CT imaging is quantum noise limited.

The limiting spatial resolution (lp/mm) of a (dedicated) chest screen- film unit is likely: a. 0.5 b. 1 c. 2.5 d. 5 e. 10

d-Screen-film (200 speed) should achieve 5 lp/mm.

Air kerma is the kinetic energy released per unit: a. distance(m) b. area (m^2 ) c. volume (m^3 ) d. mass (kg) e. density (kg/m^3 )

d. Mass (energy transferred to electrons per unit mass and measured in Gy).

The number of scattered photons reaching a radiographic imaging receptor most likely decreases with increasing: a. field size b. patient thickness c. tube voltage d. beam filtration e. grid ratio

e- A higher grid ratio will reduce the amount of scatter.

The percentage (%) of incident radiation likely captured by a CT x-ray detector is: a. 30 b. 45 c. 60 d. 75 e. >75

e- CT x-ray detectors are very efficient and capture well over 75% of the incident radiation (e.g., 90%).

Which of the following is not considered a force? a. Electrostatic b. Weak c. Strong d. Gravity e. Electricity

e- Electricity is the flow of charge, and is measured in amps (C/s).

Increasing the filtration of an x-ray beam most likely reduces the: a. exposure time b. average energy c. maximum energy d. half-value layer e. beam intensity

e- Increasing filtration reduces the x-ray tube intensity; 3 mm or so would likely halve the x-ray tube output.

The large focus dimension is most likely larger (%) than that of the small focus by: a. 10 b. 25 c. 50 d. 75 e. 100

e- The large focal spot is typically 1.2 mm, and the small focal spot is 0.6 mm (i.e., 100% larger).

The power (kW) applied to a modern CT x-ray tube is most likely: a. 1 b. 3 c. 10 d. 30 e. 100

e- The most common power level in CT today (2008) is 100 kW.

The most likely x-ray beam width (mm) on a 64-row CT scanner is: a. 0.5 b. 5 c. 10 d. 20 e. 40

e- The most likely x-ray beam width is 40 mm because the detector thickness is comparable to the in-plane pixel size of ∼0.6 mm.

In a standard x-ray tube, the maximum power loading (kW) on the 0.6 mm focal spot is most likely: a. 1 b. 2 c. 5 d. 10 e. 25

e- The small focal spot can tolerate power levels of 25 kW (higher power would require the large focal spot).

The heat capacity of a CT x-ray tube anode (kJ) is most likely: a. 0.4 b. 4 c. 40 d. 400 e. 4,000

e- The typical anode heat capacity of a modern CT x-ray tube anode is 4,000 kJ (4 MJ).

In abdominal imaging, the scatter to primary ratio of photons leaving the patient is most likely: a. 0.2 b. 0.5 c. 1 d. 2 e. 5

e- There are about five scattered photons exiting the patient for every one primary photon.

Changing x-ray tube current (mA) most likely changes the x-ray: a. field of view b. maximum energy c. average energy d. anode angle e. beam intensity

e- Tube current controls the x-ray beam intensity, or the total number of x-ray photons produced.

Improvement of lesion contrast (%) by the use of a grid in abdominal radiography would most likely be: a. 10 b. 25 c. 50 d. 100 e. 200

e- Use of grids improves contrast by a large factor (e.g., 200% or more).

The most likely x-ray tube filament current (mA) is: a. 0.4 b. 4 c. 40 d. 400 e. 4,000

e- X-ray tube filaments are about 4 A, or 4,000 mA.

Screen-film mammography contrast is likely improved by increasing: a. tube voltage b. target atomic number c. screen thickness d. film latitude e. film gradient

e-A high film gradient in mammography (∼3 or more) results in high image contrast.

Digital fluoroscopy spatial resolution would most likely be improved by increasing the: a. grid ratio b. II input diameter c. air kerma d. tube voltage e. image matrix

e-Increasing the image matrix size will normally improve spatial resolution.

CT image mottle is least likely to be affected by changing the: a. section thickness b. reconstruction algorithm c. patient size d. x-ray intensity e. window width

e-The display window width will not affect the image data, only the way it appears on the monitor.