DICOM PS3.3 2021e - Information Object Definitions
A.34.17.4.3 Number of Channels

The value of Number of Waveform Channels (003A,0005) in each Waveform Sequence depends on the measurement type; seeA.34.17.4.4 Channel Source

To encode the patient's position as fixed values a single channel shall be used.

To encode the patient's position as rotation and elevation, two channels shall be used. The first angle is the patient's angle of rotation around the longitudinal axis (head-feet axis). The second angle is the angle of elevation of the patient against horizontal, which could change if the patient sits up in bed, if the head of the bed is elevated, or if the patient stands up.

DICOM PS3.3 2021e - Information Object Definitions