In MRI, the concept of T1 recovery (longitudinal relaxation) refers to:
- A Time taken for the transverse magnetisation to decay to 37% of its maximum
- B Time taken for the longitudinal magnetisation to recover to 63% of its equilibrium value after a 90° RF pulse ✓
- C The time between the RF excitation pulse and the echo signal
- D The repetition time between successive RF pulses
Correct answer: B. Time taken for the longitudinal magnetisation to recover to 63% of its equilibrium value after a 90° RF pulse
Explanation
T1 (spin-lattice relaxation time) is the time constant for recovery of longitudinal magnetisation (Mz) to 63% of its equilibrium value after a 90° radiofrequency pulse disturbs the spin system. Fat has a short T1 (bright on T1-weighted images) because its protons exchange energy efficiently with the lattice. Free water has a long T1 (dark on T1). T2 (spin-spin relaxation) refers to decay of transverse magnetisation to 37% — which is the definition confusable with T1. Echo time (TE) is the time between excitation and signal readout. TR is repetition time.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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