Physics Chapter on X-Rays and Radiation

Question 1

• Electricity is the flow of charge, measured in amps (C/s).
• A watt is a unit of power, measured in J/s.
• Electrons are attracted to anodes (positive).

Question 2

• Units of energy include erg, joule, calorie, eV.
• Watt is a unit of power, not energy.

Question 3

• Electrons are negatively charged and attracted to positive charges.

Question 4

• Power is measured in Watts, where 1 Watt = 1 Joule/second.

Question 5

• Radio waves have the longest wavelengths.

Question 6

• Electromagnetic radiation's frequency increases with photon energy.

Question 7

• Halving the distance from a radiation source quadruples the intensity (inverse square law).

Question 8

• X-ray generators typically have a power level of approximately 100 kW.

Question 9

• Double-phase x-ray generators do not exist.

Question 10

• Transformers primarily change electrical voltage.

Question 11

• The voltage ratio of a transformer is equal to the turns ratio.

Question 12

• Single-phase generators have the highest waveform ripple.

Question 13

• Electrons lose energy primarily by producing Bremsstrahlung.

Question 14

• Tungsten is used as an x-ray target due to its high melting point.

Question 15

• The maximum photon energy in an x-ray beam is determined by the anode-cathode voltage.

Question 16

• At 65kV and with a tungsten target, the percentage of k-shell x-rays is not a significant factor.

Question 17

• The average photon energy of an x-ray beam is least affected by tube current.

Question 18

• The number of electrons accelerated across an x-ray tube is most strongly influenced by filament current.

Question 19

• X-ray tube filament current is frequently 4000 mA.

Question 20

• Large focal spots are typically 100% larger than small focal spots in x-ray tubes.

Question 21

• A typical anode angle for chest radiography is 15 degrees.

Question 22

• X-ray tube output increases most when voltage is increased.

Question 23

• A chest x-ray examination is least likely to use a 1 mm focal spot.

Question 24

• One heat unit corresponds to 0.7 joules of energy.

Question 25

• High-frequency generators deposit the most energy per unit time into the target.

Question 26

• Anodes in x-ray tubes primarily lose heat through radiation.

Question 27

• The maximum power loading on a 0.6mm focal spot is 25 kW.

Question 28

• Radiation that is not useful in image formation is called leakage radiation.

Question 29

• Mass number refers to the number of nucleons in an atom's nucleus.

Question 30

• Barium has atomic number 56, and a K-shell binding energy of 37 keV.

Question 31

• Outer shell electrons have low binding energies, typically in the eV range.

Question 32

• Infrared radiation is not ionizing.

Question 33

• The approximate number of atomic ionizations from a 30keV photon is 1000

Question 34

• Coherent scatter in a chest x-ray is likely to be less than 5% of the total scatter.

Question 35

• Photoelectric absorption varies as 1/E^2 above the K-edge.

Question 36

• In photoelectric absorption, the least likely emission is a scattered photon.

Question 37

• The likelihood of Compton interactions is best quantified using electron density.

Question 38

• The Compton attenuation coefficient at 100 keV will be ~ half the value at 50 keV.

Question 39

• Photoelectric and Compton effects are approximately equal in bone at ~40 keV.

Question 40

• If the linear attenuation coefficient is 0.1 cm−1, approximately 10% of the photons are lost in 1 mm.

Question 41

• With an attenuation coefficient of 0.5 cm−1, approximately 70% of photons are transmitted through 1 cm.

Question 42

• The mass attenuation coefficient does not depend on absorber density.

Question 43

• Attenuating a beam by three half-value layers reduces the beam intensity by a factor of 8.

Question 44

• Increasing filtration reduces the average energy and intensity of an x-ray beam.

Question 45

• Decreasing filtration increases the x-ray tube output.

Question 46

• Adding aluminum filters increases beam hardening.

Question 47

• The half-value layer (HVL) is used to evaluate the adequacy of x-ray beam filtration.

Question 48

• Reducing the anode angle increases the heel effect.

Question 49

• Scatter-to-primary ratio in abdominal radiography is generally 5:1.

Question 50

• Increasing the field size or patient thickness increases scattered photons reaching the receptor.

Question 51

• Bucky factor in adult abdominal radiography is usually 2.

Question 52

• Grid use typically improves lesion contrast by 50 – 100%.

Question 53

• Extremity radiography is less likely to use a scatter removal (grid) system.

Question 54

• Air kerma is the kinetic energy released per unit mass.

Question 55

• Measuring charge liberated in air measures exposure

Question 56

• An exposure of 1 R corresponds to approximately 0.01 Gy of air kerma.

Question 57

• An air kerma of 1 mGy absorbed dose to soft tissue of approximately 1.1 mGy (no backscatter).

Question 58

• An air kerma of 1 mGy will likely result in a soft tissue absorbed dose of 1.1 mGy and bone of roughly 4 mGy

Question 59

• X-ray film emulsion contains silver bromide crystals.

Question 60

• The developer in film processing removes unexposed grains and reduces latent images.

Question 61

• A film with an optical density of 2 transmits 1% of the incident light.

Question 62

• Gamma is the slope of the characteristic curve.

Question 63

• Wide latitude films are used for chest radiography to accommodate varying tissue densities.

Question 64

• Film alone absorbs approximately 1% of photons without a screen.

Question 65

• A 20 keV photon absorbed by a screen could generate 1000 light photons.

Question 66

• Radiographic intensifying screen conversion efficiencies are typically 10-20%.

Question 67

• The fraction of 80 keV x-rays absorbed by a standard screen-film cassette is approximately 0.5.

Question 68

• Cassette dimensions are not a significant factor for screen-film imaging system speed, rather phosphor material.

Question 69

• A 200 speed screen-film combination needs approximately 5 uGy (microgray) to adequately expose

Question 70

• Nine bits are needed to represent 512 shades of gray.

Question 71

• Printers are output devices; input devices include keyboards, trackballs, and touchscreens.

Question 72

• A modem with a 56 k baud rate transmits 448 bits per second.

Question 73

• A 2 GB disk can store 1000 * 1024^2 images, based on 2 bytes per pixel.

Question 74

• A 25-cm x 25cm region imaged with a 256 x 256 matrix typically has a pixel size of 1 mm.

Question 75

• Xenon is an appropriate x-ray detector gas due to its high atomic number.

Question 76

• Csl is a common x-ray absorption material for digital x-ray imaging, particularly in flat panel detectors.

Question 77

• Photostimulable phosphors are read out using red light.

Question 78

• The likely dynamic range of a photostimulable phosphor is ~10,000:1

Question 79

• Csl is a common x-ray absorber in indirect detectors.

Question 80

• Selenium (Se) is commonly used as a photoconductor in direct flat panel x-ray detectors.

Question 81

• A typical pixel size in a digital diagnostic chest x-ray image is ~175 µm or 0.175mm.

Question 82

• A typical maximum brightness for a digital image display is 300 cd/m^2.

Question 83

• A radiology diagnostic workstation typically has 3 or 5 megapixel display capabilities.

Question 84

• Unsharp mask enhancement increases the visibility of edges in digital images.

Question 85

• Smoothing the acquired data in digital image processing is most likely to reduce noise.

Question 86

• The Society of Motion Picture and Television Engineers (SMPTE) test patterns are often utilized in evaluating display monitors for radiology applications.

Question 87

• PACS is likely to increase retrieval time in radiology departments.

Question 88

• 19 keV is the optimal photon energy for mammography, balancing penetration and contrast.

Question 89

• A standard focal spot size in mammography is 0.3 mm.

Question 90

• Molybdenum filters used in mammography typically have a thickness of 30µm.

Question 91

• The most common grid ratio used in contact mammography for better contrast and reduce scatter, it's 5:1.

Question 92

• A mammography film gradient is typically around 3

Question 93

• The optimal film density in mammography is typically 1.8

Question 94

• Calcium's high atomic number means it strongly absorbs low-energy x-rays, making calcifications visible in mammograms.

Question 95

• Breast compression in mammography improves x-ray penetration.

Question 96

• The typical power supplied to a mammography X-ray tube is 3 kW.

Question 97

• 25 kV is the most likely x-ray tube voltage used in screening mammography techniques.

Question 98

• Exposure time for magnification film mammograms is typically 1 to 3 seconds.

Question 99

• The luminance of viewboxes used to view mammography films should be 3000 cd/m^2 or higher.

Question 100

• Artifacts such as three masses, four fibres, and minimal micro-calcification are required in PACS verification images for ACR accreditation.

Question 101

• 3 % is the typical repeat rate (%) for screen film mammography.

Question 102

• CsI is the typical input phosphor material for image intensifiers in mammography.

Question 103

• A typical image intensifier flux gain is 50.

Question 104

• A 250 mm diameter II will have a brightness gain of greater than 100.

Question 105

• Exposure time is least influential on image output brightness during fluoroscopy.

Question 106

• Vignetting is the falloff of brightness at the periphery of a fluoroscopic image.

Question 107

• The aspect ratio of a high-definition TV is 16:9

Question 108

• Replacing a TV camera with a CCD will likely improve signal-to-noise ratio due to improved quantum efficiency.

Question 109

• A tube current of 30–100 mA is common in fluoroscopic imaging.

Question 110

• Pulsed fluoroscopy acquisition rates are usually around 15 frames per second

Question 111

• ABC in fluoroscopy aims to keep the II output brightness constant, primarily adjusting tube current.

Question 112

• Switching from a 250-mm to a 125-mm II input diameter with constant technique increases skin dose by 400%.

Question 113

• Tube currents in photospot imaging typically approach 300 mA.

Question 114

• A common matrix size for digital photospot images is 1024 x 1024 pixels.

Question 115

• Temporal filtering in digital fluoroscopy increases image lag.

Question 116

• Increasing the DSA matrix size in CT usually decreases pixel size.

Question 117

• The heat capacity of a modern CT x-ray tube anode is likely ~ 4000 kJ.

Question 118

• The power applied to a modern CT x-ray tube is frequently 100 kW.

Question 119

• Teflon (polytetrafluoroethylene) is a common material used in CT beam shaping filters.

Question 120

• CT collimation primarily controls the x-ray beam width.

Question 121

• A relatively common x-ray beam width in a 64-row CT scanner is around 40 mm.

Question 122

• To measure CTDIc in a head phantom, the x-ray tube usually rotates 1 to 3 times.

Question 123

• CT x-ray detectors capture over 75% of the incident radiation.

Question 124

• In a single slice CT, typically around 1000 projections are taken per rotation of the tube.

Question 125

• Using a bone filter instead of a soft tissue filter improves subject contrast in a CT image.

Question 126

• CT number (HU) is directly proportional to the linear attenuation coefficient of the tissue.

Question 127

• Fat typically has a CT number of -90 HU.

Question 128

• Tube current is less likely to affect CT number, while tube voltage and filtration have significant impacts.

Question 129

• Increasing the CT image window width typically reduces image contrast.

Question 130

• Increasing the CT image matrix from 256^2 to 512^2 improves spatial resolution.

Question 131

• Typical pixel size in a head CT are ~ 0.5mm.

Question 132

• Applying the inverse square law, the pitch is 1.5.

Question 133

• The fastest x-ray tube rotation speed is 0.3 seconds/rotation.

Question 134

• Multislice CT improves utilisation of the x-ray beam.

Question 135

• Temporal resolution in a dual-source CT for cardiac imaging is typically around 80 ms.

Question 136

• The x-ray tube needs to rotate 1-3 times to measure CTDIc in a head phantom.

Question 137

• Peripheral CTDI is typically double or more than the central CTDI in body phantoms.

Question 138

• If peripheral CTDI is 12 mGy and central CTDI is 6 mGy, the weighted CTDIw is 8 mGy.

Question 139

• The dose length product for the given conditions (CTDIw=20 mGy, pitch=2, scan length=100cm) is 1000 mGy-cm.

Question 140

• The ACR (2008) recommends a CTDIvol of 75 mGy for an adult head.

Question 141

• A 1-year-old head CT uses ~85% of the technique as an adult head CT.

Question 142

• CT fluoroscopy is most likely to reduce tube currents to minimize radiation doses.

Question 143

• 80 kV is a common tube voltage for performing CT angiography.

Question 144

• Dual energy CT typically uses 80 kV and 140 kV.

Question 145

• Ring artifacts in CT are most often due to faulty detectors.

Question 146

• Increasing tube voltage tends to reduce the effect of beam hardening.

Question 147

• Tube voltage (kV) is the biggest contributor to image contrast.

Question 148

• Film contrast is determined by its gradient, inversely related to latitude.

Question 149

• Film contrast is inversely related to film latitude.

Question 150

• High gamma in a characteristic curve suggests higher image contrast.

Question 151

• Increased screen thickness improves contrast in screen-film mammography.

Question 152

• Increasing kV in CT usually leads to a decrease in image mottle.

Question 153

• Increased scatter in a radiograph reduces image contrast.

Question 154

• Resolution is often measured by the modulation transfer function (MTF).

Question 155

• High spatial resolution is essential for detecting small and low-contrast lesions.

Question 156

• Geometric magnification increases focal blur.

Question 157

• Reducing detector thickness usually improves spatial resolution of a radiographic image.

Question 158

• Increased detector thickness in imaging systems will increase image mottle.

Question 159

• If the FWHM of an imaged slit is 0.1 mm, the limiting resolution would be 5 or more line pairs/mm (inverse relation).

Question 160

• The MTF value (%) at the lowest spatial frequencies in almost all imaging systems is 100%.

Question 161

• The limit on spatial resolution in a screen-film chest radiographic unit is on the order of ~2.5 lp/mm

Question 162

• A 512 x 512 matrix, using a 25 cm field of view may allow for ~2.0 lp/mm vertical resolution.

Question 163

• The horizontal resolution of a TV system is primarily determined by the bandwidth.

Question 164

• Increasing the image matrix size in digital fluoroscopy improves spatial resolution.

Question 165

• A 1k matrix can achieve 500 line pairs resolution

Question 166

• Using a 512 x 512 matrix with 25 cm field of view achieves ~2 lp/mm.

Question 167

• ~95 % chance of getting 9700-10300 counts with 10,000 photons.

Question 168

• In x-ray imaging, the x-ray air kerma is a measure of the energy in the x-ray beam.

Question 169

• The image receptor with the shortest latency period for radiation-induced cancers is leukemia.

Question 170

• The dominant source of image mottle in a radiographic flat panel detector is quantum mottle.

Question 171

• The air kerma needed to produce a digital fluoroscopy image is likely ≤ 0.01 µGy.

Question 172

•  The air kerma for a single digital fluoroscopy frame image is likely 0.01 µGy.

Question 173

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

Question 174

•  Sensitivity is the number of true positives divided by the total number of actual positives, or 1 - (false negative rate).

Question 175

•  Specificity refers to the proportion of true negatives in relation to the total number of actual negatives.

Question 176

• Relaxing threshold criteria in a ROC analysis increases false-positive rates and reduces test specificity. Overall performance doesn't increase though.

Question 177

•  Direct action accounts for about one third of cell damage during X-ray exposure.

Question 178

•  An LD50 dose kills ~50% of the exposed cells.

Question 179

•  Neuronal cells are highly differentiated and non-dividing, making them generally more resistant to ionizing radiation.

Question 180

•  Linear energy transfer (LET) is a measure of the rate that energy is lost by ionizing radiation per unit distance.

Question 181

•  Radiation weighting factor (Wr) converts absorbed dose (Gy) into equivalent dose (Sv).

Question 182

•  A lung equivalent dose due to 10 mGy from radon daughters is ~200 mSv.

Question 183

•  Acute whole body doses of 1 Gy are potentially associated with the reduction of lymphocytes

Question 184

•  3 Gy is considered the threshold dose for inducing deterministic effects in interventional radiology.

Question 185

•  Temporary hair loss is a likely deterministic effect at a dose in the 3 Gy range.

Question 186

•  Gross developmental abnormalities are most likely to occur during the early organogenesis stage.

Question 187

•  A cataract dose threshold is 2 Gy

Question 188

•  3 Gy (fractionated) is a likely dose for permanent male sterility

Question 189

•  Stochastic effects of radiation include cancer and genetic defects.

Question 190

•  Nuclear medicine (NM) imaging patients are not likely to present elevated risk of childhood cancer.

Question 191

•  The thyroid is relatively sensitive to radiation-induced carcinogenesis.

Question 192

•  Leukemia is likely to have the shortest latency period for radiation-induced cancers in adults.

Question 193

•  The relative cancer radiosensitivity of a child compared to a seventy year old is ~ 10:1

Question 194

•  A-bomb survivors have been likely to demonstrate inherited effects after significant exposure, but not definitively proven.

Question 195

•  The average number of hereditary effects from radiation in two generations following a 1 mGy gonadal dose is likely to be 1 in 50,000.

Question 196

•  Gross malformations are most likely to develop in the early organogenesis stage.

Question 197

•  10 mGy is a typical threshold dose in radiation biology for medical intervention in a fetus. 

Question 198

•  A 10 mGy fetal dose does not likely increases the incidence of childhood cancer by ~0.5%. It accounts for natural incidence.

Question 199

• The backscatter factor is most likely >1.1, not including attenuation due to materials or thickness. It refers to the ratio between backscattered dose and incident dose.

Question 200

•  An air kerma of 1 mGy will likely result in a skin dose of ~0.5–1.5 mGy depending on the source characteristics.

Question 201

•  The air kerma-area product for a PA chest x-ray with an entrance air kerma of 0.1 mGy is likely to be ~100 Gy-cm^−2.

Question 202

• The embryo dose is likely ~5% of the skin dose in a lateral abdominal radiographic examination.

Question 203

•  Fetal dose is least affected by focal spot size in x-ray imaging

Question 204

•  The dose to the brain and other organs is affected by factors like tissue composition, density, and projection type, in addition to distance and beam geometry.

Question 205

•  The liver has a weighting factor of 0.02, not 0.04, in assessing the average glandular dose.

Question 206

•  A photostimulable phosphor is likely the least suitable x-ray detector choice when the operator holds a child during the exposure for an x-ray image.

Question 207

•  Ionisation chambers measure the electrical charge which is formed by x-ray absorption in air.

Question 208

•  A pocket dosimeter is a readily available option for radiation monitoring in x-ray situations.

Question 209

•  A Geiger counter detects ionization in air, which is a key principle in x-ray detection.

Question 210

•  A pocket dosimeter is useful for radiation monitoring in tasks like holding a child during an x-ray examination.

Question 211

•  The regulatory limit for radiation exposure to x-ray technologists is 50 mSv/year.

Question 212

•  The regulatory limit for a patient chest CT scan is not explicitly stated. (Regulatory standards vary by jurisdiction)

Question 213

•  Regulatory dose limits for the public include only doses received from medical exposures, not terrestrial radioactivity, dental radiographs or screening radiographs.

Question 214

• The regulatory limit on dose for the public from medical X-ray procedures is 1 mSv per year.

Question 215

•  Scattered radiation would account for roughly 0.1% of the patient's skin dose at 1 meter.

Question 216

•  Leakage radiation levels at 1 meter from an X-ray tube should not exceed 1 mGy/hr.

Question 217

•  A 0.5mm lead apron in diagnostic radiology will likely transmit ~ 5% of the primary x-ray radiation.

Question 218

•  The use factors and occupancy factors are important components in x-ray room shielding design process

Question 219

•  The annual effective dose for an NM technologist is estimated to be roughly 1 to 5 mSv.

Question 220

•  If a radiologist increases the distance to a fluoroscopic patient from 1 m to 2 m, the radiation dose would likely decrease by a factor of ~four (inverse square law)

Question 221

•  Entrance skin dose (mGy) for a standard AP abdominal X-ray is most likely to be within a range of ~0.5 – 10 mGy

Question 222

•  The average glandular dose in screening mammography is expected to be ~ 1.5 – 3mGy/exposure.

Question 223

•  The percentage change in average glandular dose when moving to a larger breast is roughly 1%.

Question 224

•  The chance of sustaining a deterministic injury in an IR procedure is less than 1%

Question 225

•  Fetal dose in CT is reduced when increasing the patient size (related to increased x-ray attenuation by the patient).

Question 226

• The optimal kV for mammography is 25 to 33 keV, offering sufficient penetration while maintaining adequate contrast

Question 227

•  Typical focal spot size in mammography is 0.3 mm. 

Question 228

•  The most frequent grid ratio in contact mammography (given sufficient scatter reduction properties) is ~5:1.

Question 229

• The average film gradient for mammography is typically ~3.

Question 230

•  The optimum film density in mammography is ~1.8, maximizing image contrast.

Question 231

•  Calcifications in mammograms are readily apparent due to calcium's high atomic number, resulting in strong absorption of low-energy x-rays. 

Question 232

•  Breast compression in mammography augments x-ray penetration through the breast tissue.

Question 233

•  The electrical power supplied to a mammography x-ray tube is usually ~3 kW, providing enough power for the required output.

Question 234

•  The optimal tube voltage for screening film mammography is in the 25 to 30 kV range.

Question 235

•  Exposure times for magnification mammography are relatively longer than for standard projections (typically 1–3 seconds to enable proper magnification).

Question 236

•  Luminance levels for mammography viewboxes are typically 3000 cd/m².

Question 237

•  The most typical repeat rate in a screen-film mammography facility is 3%.

Question 238

•  Photostimulable phosphor (PSP) plates contain cesium iodide (CsI) which is then read by a laser light. 

Question 239

•  A typical image intensifier operating flux gain is ~50.

Question 240

• The brightness gain of a 250-mm-diameter II is greater than 100 given that a typical II brightness gain is approximately 10^−3 to 10^4.

Question 241

• The variable in the question, in most cases, will not significantly affect the fluoroscopic image brightness.

Question 242

• Vignetting is a common artifact in fluoroscopy, resulting in reduced image brightness at the periphery of the image.

Question 243

• Pulsed fluoroscopy refresh rates are typically in the 15–60Hz range.

Question 244

• In digital fluoroscopy, temporal filtering aims to reduce noise and artifacts by averaging the frames.

Question 245

• Increasing the DSA matrix commonly leads to a decrease in pixel size in CT images.

Question 246

•  Matrix size in medical imaging systems is a crucial parameter dictating the image's spatial resolution.  Increasing the matrix size decreases the size of the individual pixels, typically associated with improved spatial resolution.

Question 247

• In most cases, a 512x512 matrix yields ~2 line pairs per mm vertical resolution in a 25cm field of view.

Test your understanding of x-ray concepts and radiation physics with this quiz. Questions cover forces, energy units, power measurement, electromagnetic properties, and the specifics of x-ray generation. Ideal for students studying physics and radiology.