Factors affecting the repeatability of gamma camera calibration for quantitative imaging applications using a sealed...

Area of Science:

• Medical Physics
• Nuclear Medicine Imaging

Background:

• Accurate absolute activity quantification in single photon emission computed tomography (SPECT) is vital for nuclear medicine applications.
• Repeatable calibration factors are essential for converting image voxel values to activity units.
• Variability in source preparation and activity measurement can impact calibration accuracy.

Purpose of the Study:

• To investigate instrumentation and acquisition factors influencing the repeatability of calibration factors using planar acquisition of sealed sources.
• To evaluate the impact of source size, lateral position, source-to-camera distance (SCD), and temporal variability on calibration factor reproducibility.
• To identify optimal conditions for achieving high-precision calibration in SPECT imaging.

Main Methods:

• Utilized sealed Barium-133 (Ba-133) sources for planar acquisitions under varying geometric conditions.
• Calculated calibration factors by analyzing different source sizes, lateral positions within the field-of-view (FOV), and source-to-camera distances (SCD).
• Employed a small region of interest (ROI) and mixed-effects statistical modeling to assess variable impacts and residual errors.

Main Results:

• A 1 cm variation in SCD caused 1-2% calibration factor change for small sources and <1% for larger sources.
• Lateral source position and temporal variability had minimal effects on calibration factor reproducibility.
• Residual error was primarily attributed to Poisson noise, indicating good statistical predictability.

Conclusions:

• Repeatability better than 1% for calibration factor measurements is achievable with planar acquisition of sealed sources.
• Optimal reproducibility is achieved using larger sources with high count rates and precise SCD positioning (within 5 mm).
• Quantum noise limits calibration source variability under optimal conditions, highlighting the importance of source characteristics and geometry.