In MRI physics, the term 'T2* (T2-star) relaxation' refers to which phenomenon?
- A Spin-lattice relaxation due to energy transfer to surrounding molecules
- B Combined effect of true T2 relaxation and magnetic field inhomogeneity causing faster signal decay ✓
- C Rephasing of spins by a 180° radiofrequency pulse in a spin-echo sequence
- D The time constant for longitudinal magnetisation recovery after an RF pulse
Correct answer: B. Combined effect of true T2 relaxation and magnetic field inhomogeneity causing faster signal decay
Explanation
T2* relaxation (T2-star) is a composite decay constant reflecting both intrinsic T2 relaxation (spin-spin) and additional dephasing caused by local magnetic field inhomogeneities (from susceptibility differences between tissues, metal, calcification, blood products). T2* < T2 always. Gradient echo sequences are sensitive to T2* effects (susceptibility-weighted imaging). T1 is spin-lattice (longitudinal) relaxation. The 180° refocusing pulse in spin-echo sequences eliminates field-inhomogeneity effects, measuring true T2 rather than T2*.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.