Flood Field Uniformity

A Co-57 flat source-circular or rectangular, depending on detector head shape- of 80-200 MBq (~2-5mCi) activity, for a gamma camera with small or large FOV respectively.
A flood phantom, in the size of the FOV, filled with Tc-99m of the same activity could also be used.

With the low energy collimator attached on the head detector, turn the camera to face vertically upward.
Place the flat source upon the collimator.
Center the 20% energy window on the nuclide photopeak.
Acquire an image of 10⁶ or 2x10⁶ counts for a small or a large FOV detector.

Daily- Qualitative (visual) method

Visually inspect the image for non-uniformities.
The test should be performed on a daily basis to check the condition of the gamma camera for clinical studies. Keep a log book and a file with images with suspended non uniformities.

Weekly- Quantitative method

Use the quality software of the system, to calculate the differential and the integral uniformity values or estimate uniformity values by creating region of interest (ROI) for max and min counts regions, recording the counts per pixel in each area.

Comparing images with the reference ones, any detectable changes in uniformity should be further investigated
Regions with obvious lack of homogeneity must be examined and corrective action should be taken.

Note:
• If a refilled flood phantom is used, it should be checked that the content is thoroughly mixed to provide a uniform source
• If the camera has a uniformity correction circuit, the daily test should be, if possible, performed with the circuit enabled.
• In a weekly basis, test should be performed with the correction circuit disabled, to monitor defects that may be hidden by correction. (For example, early failure of photomultiplier).