Performance Assessment / Quality Assurance in Cross Sectional Modalities

MODULE LEARNING OBJECTIVES

• Understand the physical principles behind cross-sectional imaging modalities.
• Assess the acceptability of equipment operation via Quality Assurance (QA), Quality Control (QC), and radiation dosimetry tests.
• Identify hazards and errors in cross-sectional imaging and how to address them.

SESSION LEARNING OBJECTIVES

• Familiarization with QA guidance documents and test procedures for Ultrasound, CT, and MRI.
• Comprehending the importance of QA procedures in clinical practice.

GENERAL PRINCIPLES OF QA

• Ensures system performance is suitable for clinical use.
• Detects changes in system performance over time.
• Standardized testing methods must be employed.
• Needs established standards for measurement.
• Guidelines provided by professional health organizations.

UK GUIDANCE DOCUMENTS

• Ultrasound: IPEM Report 102 & BMUS QA guidelines.
• CT: IPEM Report 91 & 32 (Level A & B tests).
• MRI: IPEM Report 112.
• Focus on user tests rather than physics tests today.

ULTRASOUND QA

Types of Issues to Assess

• Image Dropout: A well-defined vertical line to a blurry area in images, usually due to damage to the acoustic array.
• Acoustic Array Damage: Arrays are fragile (0.5mm thick); careless handling can lead to failures.
• Cable Damage: Can produce artefacts appearing as dark streaks in images.

BMUS QA GUIDANCE

• Level 1: Focus on infection control and scanner damage checks.
• Level 2: Basic scanner and transducer testing for imaging consistency.
• Level 3: In-depth evaluation using simple test tools and performed monthly.

LEVEL 1 TESTS (Daily Tasks)

• Clean transducers and cables after each patient.
• Inspect for damage on a daily/weekly basis.
• Check system functionality and clean filters regularly.

LEVEL 2 TESTS

• Check monitor settings, image quality, and perform various technical assessments monthly.
• Air reverberation tests and electronic noise assessments to ensure operational integrity.

ULTRASOUND SUMMARY

• Approximately 90% of faults detected through visual inspection and sensitivity tests.

CT QA

Routine QA Tests

• Adhere to IPEM Reports 91 and 32 for standards and procedures.

LEVELS OF TESTING

• Level A: Quick, frequent tests done mainly by radiographers.
• Level B: Analytical tests requiring more resources and performed by medical physics staff.

KEY MEASUREMENTS

• Image Noise: Assessed with QA phantoms, the consistency is vital for diagnostic accuracy. Standards for remedial and suspension levels are established.
• CT Number Values: Measured to ensure correct diagnostics based on water CT# and other materials.

TESTING AND MONITORING

• Frequent measurements ensure that the imaging quality and safety remain within the set limits.
• Adjustments are made following QA tests to maintain system performance.

MRI QA

Quality Assurance Guidelines

• Follow IPEM Report 112 for test procedures and tolerances.

PERFORMANCE MONITORING

• Monitor SNR (Signal-to-Noise Ratio), uniformity, and distortion on a monthly basis.
• Identifying abrupt performance changes or systematic deterioration is crucial for maintaining diagnostic integrity.

SNR Measurement Procedure

• Requires a consistent methodology to assess the quality derived from phantoms.

SUMMARY OF MRI

• Regular QA tests essential for maintaining safety and image quality in clinical settings. Monthly assessments of the SNR, uniformity, and distortion are crucial.

OVERALL SUMMARY OF QA

• It is critical for all cross-sectional imaging modalities to implement QA measures with testing frequency defined by the associated risk.
• Focus on imaging quality and determinant safety is key, alongside documentation for adjustment based on adverse findings.