6.4 QC Programs, PACS & Reject/Repeat Analysis

6.4 QC Programs, PACS & Reject/Repeat Analysis

Quick Answer: Digital radiography lives in a network: the RIS orders and schedules, the modality acquires DICOM images, and PACS stores and distributes them. QC proves the chain still works—from tube output to detector to monitor. Reject/repeat analysis measures preventable failures so teams improve technique, training, and equipment. When performance fails limits, the RTR stops unsafe use, escalates, and documents.

RTR.2.5, RTR.2.7, and RTR.2.8 complete the “manage imaging systems” competency. Physics and technique mean little if images never reach the right study, monitors lie about contrast, or the same positioning error is repeated fifty times without feedback.

Digital Networking & Archiving (RTR.2.5)

RIS, modality, PACS, EHR

Typical flow: Physician order → RIS validates/schedules → modality worklist query → technologist selects correct patient/study → acquire → QC on acquisition workstation → send to PACS → radiologist interprets → report returns via RIS/EHR.

DICOM essentials

DICOM (Digital Imaging and Communications in Medicine) standardizes:

• File/object structure (pixel data + metadata tags).
• Network services (C-STORE, C-FIND, C-MOVE, modality worklist, MPPS, storage commitment).
• Identity of patient, study, series, and equipment in headers.

Operational risks for the RTR:

• Selecting the wrong worklist entry misfiles images under another patient—critical safety event.
• Manual entry typos when worklist unavailable.
• Failure to complete MPPS / exam end steps can leave studies “open” or incomplete in RIS.
• Burning media or exporting outside PACS must follow privacy law (PIPEDA federally, plus provincial health privacy statutes) and facility policy.

Accession numbers, study UIDs, and markers must match the correct exam. Laterality and annotation remain the technologist’s responsibility even in digital systems.

Archiving and retrieval

PACS retention policies follow legal/regulatory and facility rules (often years for adult imaging; longer for pediatrics in many jurisdictions). From the floor:

• Confirm images arrived (send success, PACS thumbnail check when required).
• Use correct destination (primary PACS vs teaching file vs outside burn).
• Understand that lossy compression policies are organizational decisions—do not invent nonstandard compression for clinical interpretation studies.

Repeat / Reject Analysis (RTR.2.7)

A reject (or repeat) is an image not accepted for diagnosis that required additional exposure or did not meet standards. Digital systems make “reject” electronic (tagged, not necessarily film in the bin), but the dose and workflow costs remain.

Why programs exist

1. Patient dose — every unnecessary repeat adds exposure.
2. Quality improvement — common causes cluster by room, shift, or exam type.
3. Education — patterns guide coaching (e.g., lateral knees consistently rotated).
4. Equipment signals — sudden reject spikes may indicate grid, AEC, or detector faults.

Typical reject categories

Analysis metrics: reject rate = rejected images ÷ total images (definitions vary—know your department’s numerator/denominator). Track by cause, room, technologist (confidentially), and exam type. Target rates are facility-set; the exam cares that you know purpose, categorization, and response, not a single universal percentage.

Professional note: Reject analysis is a QI tool. Honest tagging beats hiding repeats. Deliberately deleting rejects without coding undermines safety culture and may violate policy.

QC Programs & Assessing Performance (RTR.2.8)

Quality control verifies that equipment and processes meet defined standards. Quality assurance is the broader program (policies, training, audits). Entry-level RTRs perform or assist with routine checks and recognize out-of-tolerance results.

Daily / start-of-day themes

Exposure index (EI) accuracy awareness

Digital systems report an exposure index (or deviation index relative to a target). Exact scales differ by vendor (IEC standardized EI exists, but departments may still show vendor-specific numbers).

RTR responsibilities:

• Know the target range for common exams on your equipment class.
• Investigate systematic drift (all chests suddenly high EI → AEC density, grid, or calibration issue).
• Do not “fix beauty” alone—brightness is windowed; EI tells dose history better than appearance.

Monitors and TG18-type testing (entry-level depth)

Radiologist and primary diagnostic displays undergo periodic QC using patterns such as AAPM TG18 (or successor protocols). Technologist-level awareness:

• QC patterns assess luminance, contrast (e.g., low-contrast objects), uniformity, and resolution.
• Primary diagnostic monitors differ from hallway review screens—do not make final reject decisions on grossly uncalibrated consumer displays when policy requires a QC workstation.
• Report failures: inability to see required TG18 objects, severe nonuniformity, or broken calibration schedules.

You are not expected to be a medical physicist, but you are expected to know that display QC exists and matters for soft-copy diagnosis.

Detector calibration and related periodic QC

Manufacturers require gain/offset/flat-field calibrations, bad-pixel maps, and sometimes dark calibrations on a schedule or after service. Related periodic tests (often by QC technologist or physics):

• Beam alignment / collimator congruence.
• kVp and timer accuracy, mA linearity (generator).
• AEC reproducibility and backup timer function.
• Grid condition and lead apron fluoroscopic checks.
• Lead PPE inspection programs.

When a calibration is overdue or software warns uncalibrated detector, do not ignore the flag—follow downtime procedure.

Respond When Performance Is Unacceptable

Assess → stop if unsafe → notify → document → use alternative pathway.

Examples:

Incident reporting (wrong patient, wrong site, significant accidental exposure) follows facility and provincial processes—separate from routine reject coding but equally part of professional accountability.

Connecting QC to the Rest of RTR.2

• Physics (6.1) explains why scatter, kVp, and mAs change EI and contrast.
• Systems (6.2) explain what can break and how to run the chain.
• Grids/AEC (6.3) are common root causes in reject data.
• QC/PACS/rejects (6.4) close the loop so the imaging system remains safe, diagnostic, and networked correctly.

For CAMRT preparation, practice scenario questions: Images are sending to the wrong study—what failed?; Reject analysis shows 40% positioning errors on mobile chests—what interventions?; TG18 low-contrast objects invisible—what do you do before hanging cases for final read? Those application patterns match the exam’s emphasis on managing imaging systems as a Clinical Expert.