Circumferential measurement of thoracic wall using a standard respiratory belt

Respiratory gating during imaging to reduce imaging artifacts involves the gathering of image data only at the end of the respiratory cycle. This is commonly performed by a pneumatic respiratory belt to monitor thoracic wall motion during respiration. Such gating has been used for magnetic resonance, computerized tomographic, and nuclear medicine imaging. The goal of this study was to measure the performance of a standard belt used for gating imaging studies. The standard respiratory belt system provided with the Magnetom 42 SP MRI scanner (Siemens AG, Erlangen, Germany) was selected. The belt was connected to a microcontroller-based pressure measurement unit that was connected, to the standard RS-232C serial port of a computer. The signal was compared with that of a strain gauge respiration transducer. The response of the system was tested in vitro both for isometric and isotonic loading. The data measured from the pneumatic belt was linear with different weights of 50 to 1,400 grams with a coefficient of determination (R2) of 0.999. The system was linear for different amounts of stretching (R2 of 0.998) within the first 45mm, which is enough for normal breathing. In vivo the pneumatic system seemed more accurate in measuring the constant stretching in apnea than the strain gauge respiratory belt. The results show that it is possible to use a standard pneumatic belt for accurate measurement of thoracic wall movement during imaging and for other purposes as well.