A Low-Cost, Microcontroller-Based Gas Delivery System for Respiratory Stimuli in MRI Studies

The design and validation of a low-cost, microcontroller-based gas delivery system that automates fixed inspired respiratory stimuli for MRI experiments.

The system uses three solenoid valves controlled by an Arduino-based circuit to switch between premixed medical gases according to predefined timings. By using the MRI scanner external timing signal, gas delivery can be synchronized with image acquisition. The system was constructed using commercial components, with a material cost ∼£650 GBP (∼$880 USD). The system was integrated with a single-use breathing circuit and evaluated using hypercapnic and hyperoxic stimuli. End-tidal oxygen (O₂) and carbon dioxide (CO₂) were measured using a respiratory gas analyzer and physiological responses were assessed using BOLD MRI at 3 T.

The system delivered reliable, repeatable gas transitions during MRI-triggered protocols. During hypercapnia (elevated carbon dioxide level, 5% CO₂) (n = 15), the mean increase in end-tidal CO₂ was 8.7 ± 1.8 mmHg from a baseline of 32.2 ± 3.1 mmHg, producing a mean gray matter BOLD signal increase of 3.2% ± 1.7%. During hyperoxia (elevated oxygen level, 60.5% O₂) (n = 15), the mean increase in end-tidal O₂ was 292.3 ± 59.0 mmHg from a baseline of 114.5 ± 10.7 mmHg, with an associated BOLD signal change of 1.2% ± 1.7%. Across both protocols, respiratory and BOLD responses were consistent across participants.

This microcontroller-based system provides an inexpensive and reliable method for administering fixed inspired respiratory stimuli with automated MRI synchronization. It offers an intermediate option between manual systems and commercial gas blenders, making it well suited for technical and methodological studies in cerebrovascular reactivity, hyperoxia-BOLD, and related applications.