12.2 Quality Control

ARRT Radiography Primary

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1 Introduction & Exam Strategy

1.1 Exam Facts, Format & Scoring 1.2 How to Study & Test-Taking Strategy

2 Ethics, Law & Professional Practice

2.1 Ethical Principles & Patient Rights 2.2 Legal Doctrines & HIPAA 2.3 ARRT Standards of Ethics & Scope of Practice

3 Communication, Assessment & Emergencies

3.1 Patient Communication & Education 3.2 Patient Assessment & Monitoring 3.3 Medical Emergencies & Support Equipment

4 Infection Control, Pharmacology & Venipuncture

4.1 Infection Control & Asepsis 4.2 Pharmacology & Contrast Media 4.3 Venipuncture & Sterile Technique

5 Radiation Physics: X-ray Production

5.1 Atomic Structure & Electromagnetic Radiation 5.2 The X-ray Tube & X-ray Production 5.3 Beam Quality/Quantity & Interactions with Matter

6 Radiobiology

6.1 Cell & Tissue Radiosensitivity 6.2 Dose-Response & Radiation Effects 6.3 Units, Measurement & Dose Quantities

7 Radiation Protection: Patient

7.1 ALARA & Minimizing Patient Dose 7.2 Exposure Factors & Dose 7.3 Shielding, Collimation & Gonadal Protection 7.4 Pediatric, Pregnant & Repeat-Exposure Considerations

8 Radiation Protection: Personnel & Regulation

8.1 Time, Distance, Shielding & Protective Apparel 8.2 Dosimetry, Dose Limits & Regulations

9 Exposure Factors & Image Formation

9.1 Prime Exposure Factors 9.2 Image Brightness, Density & Receptor Exposure 9.3 Radiographic Contrast 9.4 Spatial Resolution & Distortion

10 Digital Image Acquisition

10.1 CR vs DR Systems 10.2 Digital Image Characteristics & Exposure Index 10.3 Image Processing & Post-processing

11 Image Quality, Grids & Beam Restriction

11.1 Evaluating Image Quality 11.2 Grids 11.3 Beam Restriction & Scatter Control

12 Artifacts, QC & Image Management

12.1 Digital & Processing Artifacts 12.2 Quality Control 12.3 PACS, Display & Image Management

13 Positioning Fundamentals & Thorax

13.1 Positioning & Projection Terminology 13.2 Chest & Thorax 13.3 Ribs, Sternum & Soft-Tissue Neck/Airway

14 Abdomen & Upper Extremity

14.1 Abdomen 14.2 Hand, Wrist & Forearm 14.3 Elbow & Humerus 14.4 Shoulder Girdle

15 Lower Extremity & Pelvis

15.1 Foot, Toes & Ankle 15.2 Leg, Knee & Patella 15.3 Femur & Hip 15.4 Pelvis & SI Joints

16 Vertebral Column & Skull

16.1 Cervical Spine 16.2 Thoracic & Lumbar Spine, Sacrum & Coccyx 16.3 Skull, Facial Bones, Sinuses & Mandible

17 Contrast, Trauma, Mobile & Special

17.1 Contrast Studies 17.2 Trauma, Mobile, Surgical & Special Populations

12.2 Quality Control

Key Takeaways Explain This Topic AI

kVp accuracy QC requires measured kVp within about ±5% (roughly ±4-5 kVp) of the selected value.

Exposure reproducibility requires repeated identical exposures to vary by no more than 5% in output (mR/mAs); coefficient of variation ≤ 0.05.

Exposure linearity requires the mR/mAs output between adjacent mAs stations to agree within 10% (coefficient ≤ 0.10).

Collimator light-field/radiation-field congruence must be within 2% of the SID, and central-ray perpendicularity within about 1 degree.

Repeat/reject-analysis programs typically target a repeat rate under about 5-8%, with positioning errors the most common cause.

Last updated: July 2026

Quality Assurance vs Quality Control

Quality assurance (QA) is the broad management program that ensures optimal images at the lowest reasonable dose; quality control (QC) is the concrete set of measurements performed on equipment to verify it meets tolerances. QC has three tiers: non-invasive (technologist checks), intermediate (physicist checks), and invasive (service engineering). The ARRT exam expects you to know which QC test detects which problem, the approximate tolerance , and how often it is done. Memorizing a handful of numeric tolerances pays off directly.

Generator and Beam Tests

kVp accuracy verifies that the beam quality the generator produces matches the selected value. Measured kVp must be within about ±5% (roughly ±4-5 kVp) of the set value; an inaccurate kVp shifts contrast and dose. Timer accuracy checks that exposure time is correct — critical for single-phase units where a spinning-top test historically counted dots. Exposure reproducibility checks that repeating the same technique gives the same output : repeated identical exposures must vary by no more than 5% in mR/mAs ( coefficient of variation ≤ 0.05 ). Exposure linearity checks that output tracks proportionally as you change mA/time stations: the mR/mAs between adjacent stations must agree within 10% (linearity coefficient ≤ 0.10).

Half-value layer (HVL) measures beam filtration/quality — the thickness of aluminum that halves the beam intensity. A minimum HVL (for example, ≥ 2.3 mm Al at 80 kVp , with 2.5 mm Al total filtration required on units operating above 70 kVp) confirms low-energy photons that only add skin dose are removed. Too low an HVL means inadequate filtration and excess patient dose.

AEC, Focal Spot, and Alignment

Automatic exposure control (AEC) consistency verifies that the AEC terminates at the correct receptor exposure across changes in kVp, part thickness, and field selection, keeping receptor exposure and the exposure index stable. AEC reproducibility should also fall within the ±5% band. Focal-spot size and resolution are checked with a line-pair resolution test tool, star pattern, slit camera, or pinhole ; results are reported in line pairs per millimeter (lp/mm) . Measured focal-spot size is allowed to run somewhat larger than the nominal size (NEMA tolerances permit up to roughly 50% oversize for small spots), and blurring from focal-spot bloom lowers spatial resolution. Collimator (beam-restriction) and beam-alignment testing uses a collimator/beam-alignment test tool: the light field and radiation field must coincide within 2% of the SID , and the central ray must be perpendicular within about 1 degree (the two steel balls of the beam-alignment cylinder superimpose when the CR is truly perpendicular). Positive beam limitation (PBL) is held to the same 2%-of-SID standard.

Image-receptor uniformity (flat-field / gain calibration for DR, or plate sensitivity checks for CR) confirms a uniform exposure produces a uniform image with no shading, banding, or dead-pixel lines. Monitor and display QC is covered in Section 12.3.

QC Test → Tolerance → Frequency

QC test Tolerance Typical frequency
kVp accuracy Within ±5% (≈±4-5 kVp) Annually / at service
Timer accuracy Within ±5% (short times) Annually
Exposure reproducibility ≤ 5% variation (CoV ≤ 0.05) Annually
Exposure linearity ≤ 10% between adjacent mAs stations Annually
Half-value layer (HVL) ≥ 2.3 mm Al at 80 kVp Annually
AEC consistency/reproducibility ≤ 5% receptor-exposure variation Semiannually-annually
Focal-spot / resolution lp/mm within tool spec; ≤ NEMA oversize Annually
Collimator light/radiation field Within 2% of SID Semiannually-annually
Beam-alignment (central ray) Perpendicular within ~1° Annually
Repeat/reject analysis Target < ~5-8% repeat rate Continuous/monthly
Repeat-Analysis Programs

A repeat (reject) analysis program tracks every discarded image and its reason. It is the QC feedback loop that turns error data into training and equipment fixes. Programs usually target a repeat rate under about 5-8% , and the single most common cause is positioning error (rotation, centering, clipped anatomy), followed by exposure/technique errors and motion. Because digital systems hide overexposure, a repeat program must also flag dose creep using exposure-index/deviation-index trends. A worked example: if a department exposes 5,000 images in a month and repeats 350, the repeat rate is 350 ÷ 5,000 = 7% — within range but trending high, prompting a positioning refresher.

QC Program Structure and a Linearity Example

QC duties are tiered: radiographers run daily/weekly checks (plate erasure, artifact review, marker and annotation audits), a medical physicist performs annual measurements (kVp, HVL, linearity, AEC), and service engineers handle invasive repairs. A single-phase timer can still be verified with a spinning-top test , in which each dot represents one useful pulse. A worked linearity example: if 10 mAs yields 30 mR ( 3.0 mR/mAs ) and the adjacent 20 mAs station yields 66 mR ( 3.3 mR/mAs ), the difference is (3.3 − 3.0) ÷ 3.15 ≈ 9.5% , just within the 10% limit — the generator passes. If 20 mAs instead read 75 mR (3.75 mR/mAs), the ≈22% difference would fail linearity and flag a generator or timer fault. Scheduling these numeric checks is what keeps receptor exposure — and the exposure index — stable across the equipment fleet.

Common exam trap: reproducibility and linearity are easy to confuse. Reproducibility = same technique, same output (≤5%); linearity = adjacent mA stations track proportionally (≤10%). If a question stresses repeating identical settings , the answer is 5%; if it stresses changing mAs stations , the answer is 10%.