Nuclear Magnetic Resonance-Bushberg Chapter 14 Diagnostic Radiology Imaging Physics Course Inversion Recovery (IR) Inversion Recovery(IR) Echo amplitude depends on TI.TE.TR and IM.l Emphasizes T1 by expanding the amplitude of M,by 2X ◆Sxp-【1-2e-T+e-T-eTET2 。Initial18o°oulse inverts M2一-M2 .After At=TI (inversion time).a 90 pulse rotates M,into M. ◆AL△t=TI+TE/2.a second180°pulse induces an FID echo at TE 。TR=period between initial18o°pulses .TR<5T1 causes partial saturation 卫中 IR-T2 Short Tau IR IR-T2 Short Tau IR Short Tau Inversion Recovery(STIR) ◆Null point:TI=n(2)-T1 Uses very short Tl and magnitude signal prooessing Example:fat suppression:T1= Materials w short T1 have lower sig.intensity (reverse of std.T1-weighting) 260msec(B。=1.5d）-T1= .All tissues pass through zero amplitude (M=0) 180 msec Judicious TI selection-suppress a given tissue signal (bounce point) .Compared with a T1-weighted sequence,STIR 'fat suppression reduces artifacts Typical STIR:TI=140-180 msec:TR=2,500 msec 9,19and26May2005 14 Nuclear Magnetic Resonance – Bushberg Chapter 14 Diagnostic Radiology Imaging Physics Course 9, 19 and 26 May 2005 14 © UW and Brent K. Stewart, PhD, DABMP 53 Inversion Recovery (IR) Inversion Recovery (IR) ™ Emphasizes T1 by expanding the amplitude of Mz by 2X ™ Initial Initial 180° pulse inverts pulse inverts Mz → - Mz ™ After ∆t = TI ( t = TI (inversion time), a 90° pulse rotates pulse rotates Mz into Mxy ™ At ∆t = TI + TE/2, a second 180° pulse induces an FID echo at TE ™ TR = period between initial 180° pulses ™ TR < 5 T1 causes partial saturation c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 400. (x,y) © UW and Brent K. Stewart, PhD, DABMP 54 Inversion Recovery (IR) Inversion Recovery (IR) ™ Echo amplitude depends on TI, TE, TR and |Mz| ™ S ∝ ρ · [1-2e-(TI/T1)+e-(TR/T1)] · e-(TE/T2) ™ TI controls contrast between tissues ™ Can produce negative Mz (out of phase) when short TI used ™ FID amplitude phase (phase sensitive detection FID amplitude phase (phase sensitive detection – quadrature quadrature receiver coil) can be preserved or the magnitude taken c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 400. © UW and Brent K. Stewart, PhD, DABMP 55 IR - T2 Short Tau IR ™ Short Tau Inversion nversion Recovery (STIR) ecovery (STIR) ™ Uses very short TI and magnitude signal processing ™ Materials w/ short T1 have lower sig. intensity (reverse of std. Materials w/ short T1 have lower sig. intensity (reverse of std. T1-weighting) weighting) ™ All tissues pass through zero amplitude (Mz = 0) ™ Judicious TI selection Judicious TI selection → suppress a given tissue signal (bounce suppress a given tissue signal (bounce point) c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 402. © UW and Brent K. Stewart, PhD, DABMP 56 IR - T2 Short Tau IR ™ Null point: TI = ln(2) Null point: TI = ln(2) · T1 ™ Example: fat suppression; T1 = Example: fat suppression; T1 = 260 msec (B0=1.5T) → TI = 180 msec ™ Compared with a T1-weighted weighted sequence, STIR sequence, STIR ‘fat suppression’ reduces reduces distracting fat signal and distracting fat signal and eliminates chemical shift eliminates chemical shift artifacts ™ Typical STIR: TI = 140-180 msec; TR = 2,500 msec c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 402. FLAIR T2 (TI=2400 TR=10K, TE=150) (TR=2400, TE=90) (TI=150, TR=5520, TE=29) (TR=750, TE=13)