Radiographic Imaging and Radiation Protection Lecture

Question-and-Answer flashcards covering image production, quality factors, digital imaging concepts, and radiation protection limits, derived from the provided lecture notes.

What is the primary controlling factor of receptor exposure in radiography?

mAs (mass), which determines the quantity of x-ray photons in the beam.

Which technical factor is the secondary controller of receptor exposure, and what does it govern?

kVp, which primarily controls the energy (quality) of the x-ray beam.

For most radiographic exams, what general combination of kVp and mAs should be selected?

High kVp with low mAs to achieve desired exposure while minimizing patient dose.

What does SID stand for and what does it represent?

Source-to-Image-Receptor Distance—the distance from the x-ray tube focal spot to the image receptor.

When is use of a physical grid recommended?

When imaging a body part thicker than 4 inches (≈10 cm).

What is the primary purpose of an antiscatter grid?

To reduce the amount of scatter radiation reaching the image receptor and improve image contrast.

How does a virtual grid differ from a physical grid?

It is scatter-correction software that suppresses scatter in the image without a physical grid, thereby reducing patient dose.

In digital imaging, what does the Exposure Indicator (EI) represent?

A numeric value proportional to the radiation exposure received by the image receptor.

If the EI value increases, what does that signify about IR exposure?

The image receptor received more radiation exposure.

What is the greatest deterrent to image sharpness related to patient positioning?

Motion of the patient or anatomy.

Define voluntary motion and give an example.

Motion a patient can control, such as breathing or purposeful movement.

Define involuntary motion and give an example.

Motion the patient cannot control, e.g., peristalsis, tremors, or chills.

How can voluntary motion be minimized during an exposure?

Use short exposure times and provide clear patient instructions/cooperation.

What focal-spot size provides the highest spatial resolution?

A small focal spot.

Name two geometric factors that most directly affect spatial resolution.

SID (Source-to-Image-Receptor Distance) and OID (Object-to-Image-Receptor Distance).

What is distortion in radiography?

Misrepresentation of the true size or shape of the object being imaged.

Where in the x-ray beam is distortion minimized?

At the central ray (CR).

List the four primary factors that influence distortion.

SID, OID, object–IR alignment, and CR alignment/centering.

How does increasing SID affect magnification?

Greater SID reduces magnification.

What happens to magnification when the object is placed closer to the IR?

Magnification decreases and spatial resolution improves.

Contrast in a radiographic image is defined as what?

The difference in brightness (or optical density) between adjacent areas on the image.

What bit-depth characteristic improves contrast resolution?

Greater bit depth provides more available shades of gray and higher contrast resolution.

Define Detective Quantum Efficiency (DQE).

A measure of how efficiently an image receptor converts incoming x-ray photons into a useful image signal; a perfect DQE would be 1.0 (not attainable in practice).

How does close collimation affect contrast?

Reduces tissue irradiated, thereby decreasing scatter and increasing image contrast.

Name three primary methods to control scatter radiation.

Use of grids, tight collimation (reduced field size), and optimal selection of kVp.

What does SNR stand for, and why is a high SNR desirable?

Signal-to-Noise Ratio; a high SNR means the image signal is much greater than background noise, resulting in clearer images.

What storage medium does Computed Radiography (CR) use?

A photostimulable phosphor (PSP) plate.

After a CR plate is read, how is any residual latent image cleared?

By exposing the plate to bright white light (plate erasure).

In direct digital radiography, what material directly converts x-rays to electrical charge?

Amorphous selenium (a-Se).

What additional component does an indirect DR system require to convert x-rays to light?

A scintillator (e.g., cesium iodide) that produces light which is then converted to an electronic signal.

How is the IR positioned in portrait orientation relative to the long axis of the body part?

The longer dimension of the IR is parallel to the long axis of the body part.

Which post-processing control adjusts image contrast?

Window width.

Which post-processing control adjusts image brightness?

Window level.

What does PACS stand for?

Picture Archiving and Communication System.

What does RIS stand for?

Radiology Information System.

Define ALARA.

As Low As Reasonably Achievable—a guiding principle to minimize radiation exposure.

What are the three cardinal principles of radiation protection?

Time, distance, and shielding (with distance being the most effective).

What is the annual occupational dose limit for whole-body exposure?

50 mSv per year.

What is the cumulative lifetime occupational dose limit?

10 mSv multiplied by the worker’s age in years.

State the monthly and total gestational dose limits for a pregnant technologist.

0.5 mSv per month and 5 mSv for the entire pregnancy.

What is the annual dose limit for the general public?

1 mSv per year.

Why is filtration added to an x-ray tube housing?

To remove low-energy photons, thereby reducing unnecessary skin dose to the patient.

What minimum total filtration is required for tubes operating at 70 kVp or higher?

2.5 mm aluminum (Al) equivalent.

Within what accuracy must the light field match the x-ray field?

Within 2 % of the selected SID.

Properly placed gonadal shielding can reduce gonadal dose by what range?

Approximately 50 % to 90 %.

What is the tabletop exposure rate limit for routine fluoroscopy?

10 R/min (≈100 mGy/min).

What is the maximum tabletop exposure rate for high-level fluoroscopy (HLF)?

20 R/min (≈200 mGy/min).

What lead-equivalent thickness is required for protective aprons used in fluoroscopy?

At least 0.5 mm lead equivalent.

Define Dose-Area Product (DAP).

A quantity combining absorbed dose and the area irradiated, reflecting total energy imparted to the patient.

What is the principal cause of repeat radiographs related to communication?

Poor communication between technologist and patient.