In MRI, the 'time of repetition' (TR) and 'time of echo' (TE) determine image contrast. A sequence with SHORT TR and SHORT TE produces:
- A T1-weighted image — fat appears bright, water appears dark ✓
- B T2-weighted image — water appears bright, fat appears moderately bright
- C Proton-density image — grey matter/white matter contrast maximised
- D FLAIR image — CSF signal suppressed
Correct answer: A. T1-weighted image — fat appears bright, water appears dark
Explanation
T1-weighted MRI is produced with SHORT TR (300–600 ms) and SHORT TE (10–20 ms). Short TR allows T1 relaxation time differences between tissues to maximise contrast: tissues with short T1 (fat, subacute haemoglobin, gadolinium-enhanced structures, melanin) appear bright (high signal) because they recover longitudinal magnetisation quickly before the next RF pulse. Water/CSF has long T1 and appears dark. T2-weighted images use LONG TR and LONG TE. Proton density uses LONG TR and SHORT TE. FLAIR is T2 with an inversion prepulse to null CSF.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.