Abstract: In an apparatus for determining relaxation parameters T1 and T2, a sample 10 is placed in a constant magnetic field supplied by magnet 12. An rf transmitter/receiver probe 14 is used to apply excitation pulses to the sample 10 and to detect a resonance response signal. The probe 14 is driven by a pulse programmer 16 via a modulator 18, a mixer 20 and a linear power amplifier 22. The resonance response signal is fed to an acquisition computer 24 via a preamplifier 26, a rf amplifier 28, a mixer 30 and phase sensitive detectors 32, 34. An oscillator 36 having a reference frequency synchronises the excitation pulses and the detected signal by means of the mixer 20 and the mixer 30 respectively. Gradient coils 38 provide the gradients necessary for acquiring the resonance response signal, and are driven by the pulse programmer 16 via gradient coil amplifiers 40, 42, 44 using data stored in the waveform memory 46.