Chirp as test gradient for MRI gradient system characterization

Hi ! i wanted to generate gradient pulse for MRI gradient system characterization using chirp,For a chirp function linearly sweeping the frequency range f1 to f2 over a duration T

f0=100hz

f1=10khz

Time duration=80ms

The maximum gradient amplitude is between 20 and 31 mT/m

the instantaneous frequency f is f (t) = f1 + (f2 − f1)t/T

The chirp gradient waveform Gc with amplitude A is

Gc(t) = A sin(2π[f1t + (f2 − f1)t^2/2T])

The slew rate s(t) = dGc/dt = 2πAf (t) cos(2π[f1t + (f2 − f1)t^2/2T])

has an envelope se(t) = 2πAf (t)

The slew-rate-limited chirp gradient waveform,

Gsrlc, for a maximum slew rate, smax, is then calculated as Gsrlc(t) = min{smax/se(t), 1}Gc(t)

Please guide me how to proceed with the code.

Thank you for your valuable time and guidance.Any answers would be great to discuss.

Answer 1

[Kaashyap Pappu]

A similar question has been addressed here. Modifying the ‘f1’ and ‘f2’ values, and changing the sample rate to accommodate the different frequencies to adhere to Nyquist theorem will probably be a solution.

Hope this helps!