Pulse Oximetry

SA Instruments, Inc. is developing pulse oximetry monitoring capability as an option for the MR-compatible Model 1025 small animal monitoring and gating system. Beta site evaluation of pulse oximetry began in January 2008. Product release is anticipated early this summer.

Pulse Oximetry allows noninvasive monitoring of arterial blood oxygen saturation. Fiber optic oximetry sensors are used to transmit pulses of red and infrared light through the animal’s peripheral vascular region. Oxygen saturation is determined by measuring the differential absorption of the red and infrared light. In addition to oxygen saturation, the module measures the cardiac plethysmogram waveform, generates a plethysmogram gate and measures the animal’s heart rate

The Pulse Oximeter Module is located next to the magnet bore and near the Respiration or Respiration/IBP Module. A fiber optic sensor extends into the bore and attaches to the animal. The module has bi-directional fiber optic communication to the Respiration and Control/Gating Modules.

Small and large fiber optic clip on sensors are available. The sensors are typically attached to the foot, but other useful locations include the thigh, ankle, paw, wrist, tail, etc. For rabbits, the ear is often the location of choice. For animals with black hair, the signal can be improved by shaving the sensor site.

A white rat is shown below prepared for MR with pulse ox, respiration and temperature sensors. The large pulse ox clip sensor is attached to the rat’s foot.

A white rat is shown below prepared for MR with pulse ox, respiration and temperature sensors. The large pulse ox clip sensor is attached to the rat’s foot.

The PC-sam main display is shown above with ECG, pulse oximetry, respiration and temperature measurements. In this case, data was being collected for retrospective cardiac and respiratory gating on a 9.4T horizontal MR scanner. The animal’s temperature was being regulated using the SAII warm air Heater System with a set point of 37 ºC.

A white dot in the Cardio Sweep display indicated the detection of the R-wave from ECG. The Plet Gate was displayed as a red dot when a gate was generated from the plethysmogram waveform. Note the following:

• There is a delay between the ECG and plet gates, because blood flows to a peripheral site after the heart beats.

• There is continuous presence of baseline interference in the ECG waveform, because the MR scanner is running continuously. i.e. not being triggered.

• The plethysmogram waveform has no interference from the MR scanner.

• There is a small modulation of the plethysmogram waveform from respiration.