Chirp as test gradient for MRI gradient system characterization

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preethi chandrasekarn
preethi chandrasekarn on 14 Jan 2020
Answered: Kaashyap Pappu on 22 Jan 2020
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.

Answers (1)

Kaashyap Pappu
Kaashyap Pappu on 22 Jan 2020
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!

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