Quality Control & Assurance Flashcards

The purpose of a half-value layer (HVL) measurement in diagnostic radiology QC is to:

Answer: Assess the quality (penetrating ability) of the X-ray beam and verify adequate filtration

HVL measures the thickness of material (typically aluminum) needed to reduce X-ray beam intensity by 50%. It reflects beam quality and verifies that adequate filtration is present to remove low-energy photons that would increase patient dose without contributing to image formation.

In digital radiography, what QC test is performed to detect dead pixels or detector non-uniformity?

Answer: Flat-field uniformity test

The flat-field uniformity test exposes the digital detector to a uniform radiation field and analyzes the resulting image for non-uniformity, dead pixels, or detector artifacts that could mimic pathology.

Which of the following represents the NCRP recommended total filtration for a general-purpose radiographic tube operating above 70 kVp?

Answer: 2.5 mm Al equivalent

NCRP Report 102 and federal regulations (21 CFR 1020.30) require a minimum total filtration (inherent + added) of 2.5 mm Al equivalent for X-ray tubes operating above 70 kVp. This removes low-energy photons that increase skin dose without diagnostic benefit.

The modulation transfer function (MTF) in digital radiography is a measure of:

Answer: Spatial resolution — how faithfully the system reproduces fine detail

MTF quantifies the system's ability to reproduce spatial detail. An MTF of 1.0 means perfect reproduction; values below 1.0 indicate blurring. MTF decreases at higher spatial frequencies (finer detail), and is plotted as a curve to characterize detector resolution performance.

When performing radiographic room QC, which test assesses the accuracy of the collimator light field versus the actual radiation field?

Answer: Light field-radiation field congruence test

The light field-radiation field congruence test verifies that the light projected by the collimator accurately represents the actual X-ray field. Misalignment can result in patient structures outside the intended field being irradiated.

In a quality management program, a control chart with data points outside the ±2 standard deviation range indicates:

Answer: A systematic process problem requiring investigation

Data points outside ±2 SD in a QC control chart trigger a warning (Westgard rules). Points outside ±3 SD or two consecutive points outside ±2 SD indicate process instability requiring investigation and corrective action before clinical use.