MPI measurement of fCBV modulated by hypercapnic paradigm in a rat model. The drive field at the surface of the detection was a 25 kHz sinusoid at 14 mT. The 3rd harmonic (75 kHz) response of the particles is shown. A 1st order linear trend was removed from the data and the digital low-pass filter with fc = 0.1 Hz was applied. Ventilation properties controlled for alternating hypo/hypercapnia in 5 min. periods. The MPI signal shows a 9.9% signal modulation with the expected CBV trend and CNR = 50. Representative blood-gas measurements were recorded for each condition: Hypocapnia: resp rate = 55 BPM, paCO2 = 28 mmHg, paO2 = 57 mmHg. Hypercapnia: resp rate = 32 BPM with 5% CO2 gas mixture paCO2 = 49 mmHg, paO2 = 47 mmHg. Baseline: resp rate = 34 BPM, paCO2 = 35 mmHg, paO2 = 79 mmHg.