Radiography Exam Radiographic Equipment and Maintenance 2 — Questions and Answers

Question 1: The automatic exposure control (AEC) device in a radiographic system terminates the exposure when:

A preset quantity of radiation has reached the image receptor (Correct answer)
The timer reaches its maximum setting
The kVp reaches its peak value
The filament current drops below a threshold

Correct answer: A preset quantity of radiation has reached the image receptor

The AEC (phototimer or ionization chamber) terminates the exposure automatically when a preset amount of radiation has been detected at the image receptor, ensuring consistent image density.

AEC devices use ionization chambers or photomultiplier tubes placed behind the image receptor. When the predetermined charge (representing sufficient radiation for adequate image density) accumulates, the circuit terminates the exposure. AEC ensures consistent image quality regardless of patient size. The radiographer selects the appropriate detector cell(s) to match the anatomy of interest.

Question 2: Which test evaluates the reproducibility of x-ray output from an x-ray generator?

Exposure reproducibility test (Correct answer)
Focal spot resolution test
Beam quality (HVL) test
Grid alignment test

Correct answer: Exposure reproducibility test

The exposure reproducibility test measures the variation in radiation output across multiple identical exposures, verifying that the generator produces consistent output.

Exposure reproducibility is measured by making five or more exposures at identical technique factors and measuring the radiation output with a calibrated dosimeter. The coefficient of variation (CV) of the readings should be ≤0.05 (≤5%) per ACR and AAPM guidelines. Poor reproducibility indicates generator instability and leads to inconsistent image quality, requiring service.

Question 3: The half-value layer (HVL) of an x-ray beam is used to assess:

Beam quality (penetrating ability/energy spectrum) (Correct answer)
Beam quantity (number of photons)
Focal spot size
Tube heat loading capacity

Correct answer: Beam quality (penetrating ability/energy spectrum)

The HVL is the thickness of a specific absorber that reduces the x-ray beam intensity by 50%, and it measures beam quality (average photon energy/penetrability).

The HVL is measured by placing increasing thicknesses of aluminum between the x-ray tube and a dosimeter and finding the thickness that reduces dose rate by 50%. A higher HVL indicates a more penetrating (harder) beam. Federal standards require minimum HVL values at specific kVp settings (e.g., at 80 kVp, HVL must be ≥2.3 mm Al). Adequate HVL ensures unnecessary low-energy photons are filtered before reaching the patient.

Question 4: Which component of the x-ray generator is responsible for converting AC to DC current for the x-ray tube?

Rectifier (Correct answer)
Autotransformer
High-voltage transformer
Timer circuit

Correct answer: Rectifier

Rectifiers (solid-state diodes) convert alternating current (AC) to direct current (DC) so that electrons in the x-ray tube always flow from cathode to anode.

X-ray tubes require DC because electrons must travel only from cathode to anode. Rectifiers (silicon diode bridges) convert the AC from the high-voltage transformer into pulsating DC. Modern x-ray generators use high-frequency inverters to produce near-constant potential, improving efficiency and reducing patient dose. The autotransformer selects the kVp, while the high-voltage transformer steps up the voltage to the required kV range.

Question 5: Timer accuracy in radiographic equipment is verified to be within what tolerance?

±5% or ±1 ms, whichever is greater (Correct answer)
±10% or ±5 ms, whichever is greater
±1% or ±0.5 ms, whichever is greater
±15% or ±10 ms, whichever is greater

Correct answer: ±5% or ±1 ms, whichever is greater

Federal performance standards require that exposure timer accuracy be within ±5% or ±1 ms (whichever is greater) of the indicated exposure time.

Per 21 CFR 1020.31, timer accuracy must be within ±5% of the indicated time, or ±1 ms (whichever is greater). Timer accuracy is especially critical for short exposure times (pediatric, extremity imaging) where a small timing error produces a larger percentage deviation. Timer accuracy is measured using a spinning top or electronic timer test tool.

Question 6: The purpose of added filtration in an x-ray tube is to:

Remove low-energy photons that would increase patient dose without contributing to image formation (Correct answer)
Increase the number of high-energy photons reaching the image receptor
Reduce the overall radiation output of the tube
Improve the spatial resolution of the image

Correct answer: Remove low-energy photons that would increase patient dose without contributing to image formation

Added filtration (typically aluminum) removes low-energy photons that are absorbed by the patient's skin without contributing to the diagnostic image, reducing skin dose.

The x-ray beam contains a spectrum of photon energies. Low-energy photons are absorbed by superficial tissues (increasing patient dose) but are too weak to penetrate and reach the image receptor. Added filtration (typically 1.5–3.0 mm aluminum) selectively removes these photons, 'hardening' the beam. Total filtration (inherent + added) must equal at least 2.5 mm Al equivalent for equipment operating above 70 kVp per federal standards.

Radiography Exam Radiographic Equipment and Maintenance 2

The automatic exposure control (AEC) device in a radiographic system terminates the exposure when: