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DHA Radiology / Radiographer study materials
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DHA Radiology / Radiographer practice questions

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Question 1Radiation Protection, Dosimetry and Radiation Biology

Which SI unit expresses absorbed dose?

  1. Coulomb per kilogram
  2. Gray Correct answer.
  3. Sievert
  4. Becquerel

Explanation

Absorbed dose is energy deposited per unit mass and is measured in gray (Gy), where 1 Gy equals 1 J/kg. Sievert is used for equivalent and effective dose, becquerel for activity, and coulomb per kilogram for exposure.

Question 2Radiation Protection, Dosimetry and Radiation Biology

For diagnostic X-rays, which radiation weighting factor (wR) is used to calculate equivalent dose?

  1. 5
  2. 1 Correct answer.
  3. 20
  4. 2

Explanation

Photons such as diagnostic X-rays and gamma rays are assigned a radiation weighting factor of 1. Equivalent dose is the absorbed dose multiplied by this factor, so for X-rays the numerical value in mGy and mSv is the same.

Question 3Radiation Protection, Dosimetry and Radiation Biology

What does the ALARA principle require in radiological practice?

  1. Keeping doses below the annual limit only
  2. Applying dose reduction only to staff members who physically hold patients during examinations
  3. Reducing dose only when a dosimeter alarm sounds
  4. Keeping dose as low as reasonably achievable while meeting the clinical purpose Correct answer.

Explanation

ALARA is the optimization principle: exposures should be kept as low as reasonably achievable, taking economic and social factors into account, while still obtaining the required diagnostic information. It applies to patients and staff and goes beyond merely complying with dose limits.

Question 4Radiation Protection, Dosimetry and Radiation Biology

Under ICRP recommendations, what is the occupational annual effective dose limit for a radiation worker?

  1. 50 mSv in every year, with no averaging permitted over a five-year period
  2. 20 mSv/year averaged over five years, 50 mSv maximum in one year Correct answer.
  3. 20 mSv in every year without any five-year averaging
  4. 5 mSv per year when averaged over a five-year period

Explanation

The ICRP occupational effective dose limit is 20 mSv per year averaged over defined five-year periods, and the dose in any single year should not exceed 50 mSv. The limit applies to the sum of external and internal exposures from work.

Question 5Radiation Protection, Dosimetry and Radiation Biology

What is the ICRP annual effective dose limit for a member of the public from man-made sources, excluding medical exposure?

  1. 20 mSv
  2. 1 mSv Correct answer.
  3. 50 mSv
  4. 5 mSv

Explanation

The public effective dose limit is 1 mSv per year, averaged over five years if necessary, for man-made sources other than medical exposures. Higher values such as 20 mSv apply to occupationally exposed workers, not the public.

Question 6Radiation Protection, Dosimetry and Radiation Biology

What is the main purpose of a personal dosimeter worn by a radiographer?

  1. To monitor background radiation in the room only
  2. To measure X-ray tube output
  3. To estimate the individual's radiation dose Correct answer.
  4. To test the integrity of a lead apron

Explanation

A personal dosimeter records the cumulative dose to the wearer over a monitoring period so that occupational exposure can be assessed and compared with limits. It does not measure tube output, room background alone, or apron integrity.

Question 7Radiation Protection, Dosimetry and Radiation Biology

If the distance from a point X-ray source is doubled, what happens to the radiation intensity, assuming no absorption?

  1. It becomes twice the original value
  2. It becomes four times the original value
  3. It falls to one half of the original intensity value
  4. It falls to one quarter of the original value Correct answer.

Explanation

Radiation intensity from a point source follows the inverse square law, so doubling the distance reduces intensity by a factor of four. This is why increasing distance is such an effective protection measure.

Question 8Radiation Protection, Dosimetry and Radiation Biology

Which effect of radiation is classified as stochastic?

  1. Cataract formation above a threshold
  2. Cancer induction Correct answer.
  3. Skin erythema
  4. Sterility after high gonadal dose

Explanation

Stochastic effects, such as cancer induction and heritable effects, have no practical threshold and their probability increases with dose, while severity does not depend on dose. Erythema, cataracts above threshold, and sterility are deterministic effects.

Question 9Radiation Protection, Dosimetry and Radiation Biology

Under current ICRP recommendations, what is the occupational equivalent dose limit for the lens of the eye?

  1. 20 mSv per year averaged over five years Correct answer.
  2. 1 mSv per year with no averaging
  3. 500 mSv per year averaged over five years
  4. 150 mSv in any single year with no averaging

Explanation

The ICRP occupational lens limit is 20 mSv per year averaged over five years, with no more than 50 mSv in any single year. This lower limit reflects evidence that the lens is more radiosensitive than previously assumed.

Question 10Radiation Protection, Dosimetry and Radiation Biology

A procedure delivers 8 mGy to lung tissue (wT = 0.12) and 2 mGy to red marrow (wT = 0.12). What is the approximate effective dose contribution from these two tissues?

  1. 0.24 mSv
  2. 10.0 mSv
  3. 1.2 mSv Correct answer.
  4. 0.96 mSv

Explanation

Effective dose contribution is the sum of each tissue dose multiplied by its tissue weighting factor: (8 × 0.12) + (2 × 0.12) = 0.96 + 0.24 = 1.2 mSv. Adding the unweighted doses would overestimate effective dose.

Question 11Radiation Protection, Dosimetry and Radiation Biology

A monoenergetic X-ray beam has a half-value layer of 2 mm aluminum. What aluminum thickness reduces its intensity to 25% of the original value?

  1. 2 mm
  2. 1 mm
  3. 8 mm
  4. 4 mm Correct answer.

Explanation

Each half-value layer halves the intensity. Reducing to 25% requires two halvings, so the thickness is 2 × 2 mm = 4 mm aluminum.

Question 12Radiation Protection, Dosimetry and Radiation Biology

How does a lead apron mainly protect a radiographer during fluoroscopy?

  1. By removing all Compton scatter from the room
  2. By changing the primary beam quality
  3. By attenuating scattered photons Correct answer.
  4. By increasing the required tube output

Explanation

The apron attenuates scattered X-rays that would otherwise reach the wearer's body. It does not alter the primary beam quality, eliminate all scatter, or require higher tube output.

Question 13Radiation Protection, Dosimetry and Radiation Biology

Dose-area product (DAP) is most useful for:

  1. Directly measuring patient skin entrance dose
  2. Checking X-ray tube filtration
  3. Measuring the occupational lens dose
  4. Estimating stochastic risk from fluoroscopy Correct answer.

Explanation

DAP integrates air kerma over the beam area and is a practical indicator of the total radiation energy delivered to the patient, useful for comparing procedures and estimating stochastic risk. It does not directly give skin entrance dose or staff lens dose.

Question 14Radiation Protection, Dosimetry and Radiation Biology

Reducing the collimated field size during a radiograph primarily:

  1. Increases the volume of tissue irradiated and patient dose
  2. Increases scatter reaching the image receptor
  3. Reduces irradiated tissue volume and scatter production Correct answer.
  4. Has no effect on patient dose or image contrast

Explanation

Tighter collimation reduces the irradiated volume, so less tissue receives dose and less Compton scatter is generated. This usually improves contrast and lowers patient dose.

Question 15Radiation Protection, Dosimetry and Radiation Biology

What is the main purpose of added filtration in an X-ray tube?

  1. To remove all scattered radiation from the room
  2. To increase the useful beam intensity
  3. To absorb low-energy photons before the patient Correct answer.
  4. To remove high-energy photons from the beam

Explanation

Added filtration preferentially absorbs low-energy photons that would increase skin dose without contributing to the image. It hardens the beam and improves the dose-to-image-quality ratio.

Question 16Radiation Protection, Dosimetry and Radiation Biology

Under ICRP recommendations, what is the dose limit to the embryo or fetus for a declared pregnant radiation worker?

  1. 0.5 mSv over the entire gestation period
  2. 50 mSv over the entire gestation period
  3. 1 mSv over the entire gestation period Correct answer.
  4. 5 mSv over the entire gestation period

Explanation

After a pregnancy is declared, ICRP recommends that the embryo/fetus should be protected to a dose limit of 1 mSv over the gestation period. This is additional protection for the conceptus, not a substitute for the mother's own occupational monitoring.

Question 17Radiation Protection, Dosimetry and Radiation Biology

According to the law of Bergonié and Tribondeau, which cell population is most radiosensitive?

  1. Skeletal muscle cells
  2. Lymphocyte precursors Correct answer.
  3. Mature neurons
  4. Mature erythrocytes

Explanation

Radiosensitivity is greatest in cells that are undifferentiated, divide rapidly, and have a long mitotic future, such as lymphocyte precursors. Mature neurons, muscle cells, and mature red cells are relatively radioresistant.

Question 18Radiation Protection, Dosimetry and Radiation Biology

In the linear-quadratic model of cell survival, what does the α/β ratio represent?

  1. The relative biological effectiveness of alpha particles
  2. The dose where linear and quadratic cell-killing components are equal Correct answer.
  3. The maximum radiation dose before any deterministic effects begin to occur
  4. The dose rate below which no cellular repair occurs at all

Explanation

The α/β ratio is the dose at which the linear and quadratic contributions to cell killing are equal. Tissues with a low α/β ratio are generally more sensitive to changes in fractionation.

Question 19Radiation Protection, Dosimetry and Radiation Biology

When a second personal dosimeter is used for a worker wearing a lead apron, where is that second dosimeter normally placed?

  1. Under the apron at waist level Correct answer.
  2. On the wrist outside the apron
  3. Over the apron at collar level
  4. Outside the controlled area

Explanation

The dosimeter under the apron at waist level estimates the dose to the shielded trunk, while a collar dosimeter over the apron estimates dose to the unshielded head and neck, including the lens. The two readings are used together to assess effective dose.

Question 20Radiation Protection, Dosimetry and Radiation Biology

In radiation protection, what is a dose constraint?

  1. The threshold dose at which deterministic injury first appears in tissue
  2. The average population dose from a practice
  3. A legal limit that must never be exceeded under any circumstances
  4. A prospective restriction on individual dose used in optimization Correct answer.

Explanation

A dose constraint is a prospective source-related restriction on the dose to an individual, used to plan and optimize protection below the regulatory dose limit. It is not itself a legal limit and is distinct from a deterministic threshold.

Question 21Radiation Protection, Dosimetry and Radiation Biology

A worker receives 10 mGy from gamma rays (wR = 1) and 2 mGy from alpha particles (wR = 20). What is the equivalent dose?

  1. 50 mSv Correct answer.
  2. 210 mSv
  3. 12 mSv
  4. 30 mSv

Explanation

Equivalent dose is the sum of absorbed dose multiplied by radiation weighting factor for each radiation type: (10 × 1) + (2 × 20) = 10 + 40 = 50 mSv. Absorbed doses from different radiation types cannot simply be added without weighting.

Question 22Radiation Protection, Dosimetry and Radiation Biology

A CT examination of the abdomen and pelvis delivers an estimated fetal dose of 25 mGy. What is the most appropriate interpretation of the risk of deterministic effects?

  1. The dose guarantees a childhood cancer, so urgent counseling is required
  2. The dose is below the threshold for typical deterministic effects, so the main concern is stochastic risk Correct answer.
  3. The dose is too low to produce any stochastic risk, so no discussion is needed
  4. The dose is above the threshold for fetal malformation, so termination of the pregnancy should be strongly advised

Explanation

Typical deterministic fetal effects generally have thresholds around 100 mGy, so 25 mGy is below the threshold for malformation. The stochastic risk is small but not zero, so appropriate counseling and documentation are still needed.

Question 23Radiation Protection, Dosimetry and Radiation Biology

Why does a young child generally have a higher radiation risk than an adult for the same effective dose?

  1. Children receive a lower tissue weighting factor for red marrow
  2. Children are less sensitive to radiation because their cells divide more slowly than those of adults
  3. Children have more rapidly dividing tissues and a longer remaining lifetime for cancer to appear Correct answer.
  4. Children have more efficient DNA repair mechanisms than adults do at every age

Explanation

Children have more rapidly dividing tissues and a greater remaining lifetime in which radiation-induced cancer can appear. These factors increase risk for a given effective dose compared with an adult.

Question 24Radiation Protection, Dosimetry and Radiation Biology

A fluoroscopy operator's collar badge, worn over a lead apron, reads 12 mSv for the month. Which statement about this reading is most accurate?

  1. It is invalid because the badge was worn over the apron
  2. It estimates the dose to the unshielded head and neck, not the whole-body effective dose Correct answer.
  3. It can be taken directly as the operator's whole-body effective dose for that month without any further calculation
  4. It measures only the dose to the shielded trunk

Explanation

A collar badge worn over the apron estimates dose to the unshielded head and neck, including the lens, and may overestimate whole-body effective dose. Effective dose is usually assessed by combining this reading with an under-apron dosimeter.

Question 25Radiation Protection, Dosimetry and Radiation Biology

A radiographer's personal dosimeter records 0.8 mSv for a month. Which statement best reflects the role of this result in an ALARA program?

  1. It proves that no further radiation protection measures are needed anywhere in the department
  2. It measures the total dose received by all patients examined during that month
  3. It is compared with limits and prior readings to identify trends needing optimization Correct answer.
  4. It can replace area monitoring and routine shielding checks for the whole department

Explanation

Personal dosimetry results are reviewed against dose limits and previous readings so that unusual trends or higher exposures can trigger optimization actions. A single result does not prove that protection is adequate everywhere or replace area monitoring.

Question 26Radiation Protection, Dosimetry and Radiation Biology

In diagnostic radiography, what does the ALARA principle primarily require?

  1. Avoid all medical exposures that use ionizing radiation
  2. Deliver an identical radiation dose to every patient of the same age
  3. Keep exposure time fixed while increasing source-to-patient distance
  4. Keep dose as low as reasonably achievable while obtaining needed diagnostic information Correct answer.

Explanation

ALARA is an optimization principle: radiation dose should be kept as low as reasonably achievable while still answering the clinical question. It does not forbid justified medical exposures or require identical doses for all patients.

Question 27Radiation Protection, Dosimetry and Radiation Biology

Under ICRP recommendations, what is the occupational effective dose limit averaged over five consecutive years?

  1. 20 mSv per year averaged over five years Correct answer.
  2. 1 mSv per year averaged over five years
  3. 50 mSv in any single year with no averaging
  4. 500 mSv per year averaged over five years

Explanation

ICRP recommends an occupational effective dose limit of 20 mSv per year averaged over five consecutive years, with no single year exceeding 50 mSv. The five-year averaging corresponds to a cumulative limit of 100 mSv.

Question 28Radiation Protection, Dosimetry and Radiation Biology

Which radiation quantity is measured in gray (Gy)?

  1. Radioactivity
  2. Absorbed dose Correct answer.
  3. Effective dose
  4. Equivalent dose

Explanation

The gray is the SI unit of absorbed dose and equals one joule per kilogram. Equivalent and effective dose are measured in sieverts, while activity is measured in becquerels.

Question 29Radiation Protection, Dosimetry and Radiation Biology

What is the main purpose of diagnostic reference levels (DRLs)?

  1. To promote optimization by comparing typical doses for a given examination Correct answer.
  2. To guarantee that every radiograph has identical image quality
  3. To set a legal maximum dose that must never be exceeded for any patient
  4. To replace personal dosimetry for staff working in fluoroscopy

Explanation

DRLs are advisory benchmark doses for typical examinations and patient groups, used to identify practices that may need optimization. They are not legal limits and do not apply to individual patients.

Question 30Radiation Protection, Dosimetry and Radiation Biology

What does the radiation weighting factor (wR) account for when calculating equivalent dose?

  1. The attenuation of the beam by patient tissue and filtration
  2. The relative biological effectiveness of the radiation type Correct answer.
  3. The radiosensitivity of each tissue and organ in the body
  4. The time over which the radiation dose is delivered

Explanation

The radiation weighting factor wR reflects the relative biological effectiveness of a radiation type for stochastic effects and multiplies absorbed dose to give equivalent dose. Tissue radiosensitivity is handled separately by tissue weighting factors wT.

Question 31Radiation Protection, Dosimetry and Radiation Biology

Compared with continuous fluoroscopy, pulsed fluoroscopy at a lower pulse rate primarily reduces patient dose by:

  1. Decreasing the source-to-skin distance
  2. Increasing the added filtration of the X-ray tube
  3. Reducing the total X-ray beam-on time Correct answer.
  4. Increasing the degree of image magnification

Explanation

Pulsed fluoroscopy switches the beam on only during selected frames, so reducing the pulse rate shortens total beam-on time for a given screening period. Added filtration, geometry, and magnification affect dose through other mechanisms.

Question 32Radiation Protection, Dosimetry and Radiation Biology

What is the main radiation protection advantage of last-image-hold during fluoroscopy?

  1. It improves spatial resolution without changing dose
  2. It permits image review without additional exposure Correct answer.
  3. It reduces scatter reaching the operator during beam-on time
  4. It automatically increases tube current to shorten exposure

Explanation

Last-image-hold stores the final fluoroscopic frame on the monitor so the operator can study it after the beam is off. This avoids additional screening simply to review anatomy or check positioning.

Question 33Radiation Protection, Dosimetry and Radiation Biology

How does automatic exposure control (AEC) contribute to radiation protection in radiography?

  1. It prevents all repeat radiographs caused by positioning errors
  2. It ends exposure once the detector signal is sufficient Correct answer.
  3. It automatically narrows the collimated field to the area of interest
  4. It selects the tube voltage according to the patient's age

Explanation

AEC uses a detector to measure radiation reaching the image receptor and ends the exposure once a preset signal is reached. This reduces unnecessary exposure from overexposure and helps make exposure reproducible.

Question 34Radiation Protection, Dosimetry and Radiation Biology

Which phase of the cell cycle is generally the most radiosensitive?

  1. Mitosis (M phase) Correct answer.
  2. G1 phase
  3. Late S phase
  4. G0 phase

Explanation

Cells are generally most radiosensitive during mitosis and late G2, while late S phase is relatively resistant because of DNA repair and replication. G0 cells are generally less sensitive than actively dividing cells.

Question 35Radiation Protection, Dosimetry and Radiation Biology

A CT examination has a dose-length product (DLP) of 500 mGy·cm. Using an effective dose conversion coefficient of 0.015 mSv/(mGy·cm), what is the approximate effective dose?

  1. 0.75 mSv
  2. 750 mSv
  3. 7.5 mSv Correct answer.
  4. 75 mSv

Explanation

Effective dose is estimated by multiplying DLP by an anatomical conversion coefficient: 500 mGy·cm × 0.015 mSv/(mGy·cm) = 7.5 mSv. The calculation is a straightforward multiplication, with the decimal point placed correctly.

Question 36Radiation Protection, Dosimetry and Radiation Biology

A worker receives an effective dose of 20 mSv. Using a nominal lifetime cancer risk coefficient of 5% per sievert, what is the approximate added lifetime risk?

  1. 1%
  2. 0.1% Correct answer.
  3. 0.05%
  4. 0.01%

Explanation

Convert 20 mSv to 0.02 Sv, then multiply by 0.05 per sievert: 0.02 × 0.05 = 0.001, or 0.1%. This is a nominal population-based risk estimate, not an individual prediction.

Question 37Radiographic Physics, Equipment and Imaging Informatics

In a rotating-anode X-ray tube, what is the primary source of electrons that strike the target?

  1. A heated tungsten filament Correct answer.
  2. A cooled copper anode
  3. A compressed gas reservoir
  4. A photostimulable phosphor plate

Explanation

Thermionic emission occurs when the filament is heated, releasing electrons that are accelerated toward the anode to produce X-rays. The anode conducts heat and provides the target material, but it does not supply the electron beam.

Question 38Radiographic Physics, Equipment and Imaging Informatics

The half-value layer (HVL) of an X-ray beam is the thickness of material that does what?

  1. Halves the beam intensity Correct answer.
  2. Converts half the beam to characteristic radiation
  3. Doubles the beam penetration
  4. Removes all scattered photons from the beam

Explanation

HVL is the thickness of a specified material that attenuates beam intensity to half its original value. It is used as an indicator of beam quality and penetrability, not as a measure of scatter removal or energy conversion.

Question 39Radiographic Physics, Equipment and Imaging Informatics

In film-screen and digital radiography, changing mAs primarily affects which beam property?

  1. Grid ratio
  2. Beam penetrability
  3. Number of X-ray photons produced Correct answer.
  4. Focal spot size

Explanation

mAs is the product of tube current and exposure time and primarily controls the quantity of X-ray photons produced. kVp mainly affects beam quality and penetrability, while focal spot size and grid ratio are separate equipment or geometry factors.

Question 40Radiographic Physics, Equipment and Imaging Informatics

Increasing kVp while other factors are unchanged primarily does what to the X-ray beam?

  1. Reduces the maximum photon energy
  2. Increases the number of pixels in the image
  3. Decreases the beam's average energy
  4. Increases the beam's penetrability Correct answer.

Explanation

kVp sets the peak tube voltage and shifts the X-ray spectrum toward higher energies, increasing penetrability and generally lowering subject contrast. It does not change digital pixel count or reduce the maximum photon energy.

Question 41Radiographic Physics, Equipment and Imaging Informatics

What is the main purpose of the DICOM standard in medical imaging?

  1. To specify occupational dose limits
  2. To calculate half-value layer
  3. To standardize image format and network exchange Correct answer.
  4. To set electrical wiring codes for X-ray rooms

Explanation

DICOM standardizes image file structure, metadata, and network communication so modalities, PACS, and workstations can interoperate. Dose limits and HVL calculations belong to radiation protection and physics rather than to DICOM.

Question 42Radiographic Physics, Equipment and Imaging Informatics

What is the primary function of a picture archiving and communication system (PACS)?

  1. To generate X-rays within the tube
  2. To control the automatic exposure chamber
  3. To store, retrieve, and distribute medical images Correct answer.
  4. To measure patient entrance skin dose

Explanation

PACS archives images and communicates them to viewing workstations across the imaging network. It does not produce radiation or directly control exposure timing.

Question 43Radiographic Physics, Equipment and Imaging Informatics

In a digital radiography image, an 8-bit pixel can display how many distinct gray levels?

  1. 256 Correct answer.
  2. 16
  3. 64
  4. 1024

Explanation

Bit depth n provides 2^n possible values, so 8 bits give 2^8 = 256 gray levels. The other values correspond to different bit depths and do not match an 8-bit pixel.

Question 44Radiographic Physics, Equipment and Imaging Informatics

Tight collimation of the X-ray field mainly achieves which combination of effects?

  1. Higher tube current and longer exposure time
  2. Larger focal spot and lower spatial resolution
  3. Reduced scatter and lower patient dose Correct answer.
  4. Increased scatter reaching the detector and higher patient dose

Explanation

Collimation restricts the beam to the area of interest, reducing the irradiated volume, scatter production, and patient dose. It does not increase tube current or enlarge the focal spot.

Question 45Radiographic Physics, Equipment and Imaging Informatics

Characteristic X-rays are produced when an incident electron does what?

  1. Decelerates in the nuclear field without ionizing an atom
  2. Ejects an inner-shell electron that is then replaced Correct answer.
  3. Strikes the detector and releases light photons
  4. Passes through the anode without interacting

Explanation

Characteristic radiation occurs after an inner-shell electron is ejected and an outer-shell electron fills the vacancy, emitting a photon with energy equal to the shell energy difference. Simple deceleration in the nuclear field produces bremsstrahlung instead.

Question 46Radiographic Physics, Equipment and Imaging Informatics

If the source-to-image distance is doubled and no other factor is changed, the X-ray intensity at the image receptor becomes what?

  1. Twice the original intensity
  2. One quarter of the original intensity Correct answer.
  3. One half of the original intensity
  4. Four times the original intensity

Explanation

X-ray intensity follows the inverse square law, so intensity is proportional to 1 divided by distance squared. Doubling the distance gives 1/2², which is one quarter of the original intensity.

Question 47Radiographic Physics, Equipment and Imaging Informatics

A grid with a higher ratio, compared with a lower-ratio grid of the same material, generally does what?

  1. Removes more scatter but requires higher mAs Correct answer.
  2. Eliminates the need for collimation
  3. Removes less scatter and allows a lower mAs
  4. Increases focal spot size

Explanation

A higher grid ratio improves scatter cleanup but also absorbs more primary photons, so mAs usually must increase to maintain receptor exposure. Grid ratio does not change focal spot size or replace beam collimation.

Question 48Radiographic Physics, Equipment and Imaging Informatics

When imaging a long body part such as the femur, how should the anode heel effect be used?

  1. Place the cathode end toward the thinner part of the patient
  2. Place the anode end toward the thicker part of the patient
  3. Center the thickest part exactly under the anode
  4. Place the anode end toward the thinner part of the patient Correct answer.

Explanation

X-ray intensity is lower toward the anode because of the heel effect, so the anode should be positioned over the thinner portion and the cathode over the thicker portion. This helps produce a more uniform receptor exposure along the long axis.

Question 49Radiographic Physics, Equipment and Imaging Informatics

Increasing the focal spot size while keeping all other geometric factors constant will do what to the image?

  1. Eliminate scatter radiation
  2. Increase geometric unsharpness Correct answer.
  3. Increase spatial resolution
  4. Reduce patient motion blur

Explanation

A larger focal spot increases the penumbra and therefore geometric unsharpness, reducing spatial resolution. Motion blur and scatter are influenced by exposure time, patient motion, collimation, and grid use rather than focal spot size alone.

Question 50Radiographic Physics, Equipment and Imaging Informatics

What is the main function of automatic exposure control (AEC) in radiography?

  1. To adjust the grid ratio during exposure
  2. To select the kVp automatically for the examination
  3. To measure the focal spot size
  4. To stop exposure at a preset detector dose Correct answer.

Explanation

AEC uses ionization chambers or solid-state detectors to terminate the exposure when the desired receptor dose is reached, improving exposure consistency. It does not choose kVp or alter grid ratio during the exposure.