Radionuclide Imaging to Determine Cardiac Function

Some facts about gating:

• Gating involves the acquisition of images in conjunction with ECG
• Images are synchronised using ECG–R wave as a reference point
• Each cardiac cycle (R-R int) is divided into 16-64 frames (gen-18)
• Each frame is sorted according to the the position in the cardiac cycle

 

Different gating techniques:

• Frame mode: This is where each frame is directly stored in a temporary memory buffer during acquisition. This is averaged over 300-600 cardiac cycles to produce a single cardiac cycle
• List mode: This is where each scintillation event is stored along with x and y co-ordinates, the timing marker in the R-R interval. Sorting is done retrospectively
• Fixed beats: 300-800 beats. The heart rate is initially sampled for 10-20 seconds and mean R-R interval is determined. Any beat which is 10% longer or shorter than the mean is rejected. The window should not exceed 30% if meaningful data is to be acquired
• Fixed counts: Study is acquired for about 4-6 million counts

 

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This image represents the gating acquisition process. The cardiac cycle is between R-R interval. The acquisition during this interval is divided into n number of bins.

 

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