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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.

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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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