Spatial resolution in a gamma camera is determined by several physical factors, including collimator design, intrinsic detector resolution, photon energy, and source-to-collimator distance.

Resolution testing typically involves imaging:

• A bar phantom, containing sets of parallel bars at decreasing separations

• A line source, producing a narrow activity profile

At it’s most basic, if the system can clearly distinguish the smallest bar spacing or produce a narrow line image, spatial resolution is adequate.

There are two types of resolution testing:

Intrinsic resolution is measured without the collimator. It reflects the performance of the scintillation crystal and photomultiplier electronics alone.

System resolution includes the collimator and therefore reflects real clinical performance.

Collimator resolution is often the dominant limiting factor. As the distance between the source and collimator increases, geometric blurring increases, and spatial resolution degrades.

Mechanical damage to the collimator, crystal degradation, or electronic instability may all reduce resolution.

In SPECT systems, spatial resolution is also influenced by reconstruction parameters and centre of rotation accuracy. Poor resolution can result in partial volume effects and loss of small lesion conspicuity.

Resolution is typically quantified as the full width at half maximum (FWHM) of a line spread function.