. Author manuscript; available in PMC: 2012 Jun 1.

Published in final edited form as: Magn Reson Med. 2011 Feb 8;65(6):1649–1660. doi: 10.1002/mrm.22755

Table 1.

Optimal MR parameters derived under the small variation assumption.

	Optimal TR	Optimal TE	Optimal θ
T₁ contrast efficiency^a	TR < T₁	TE ≪T₂*	θ = θ_T₁ > θ_Ernst
T₂* contrast efficiency^a	TR < T₁	TE = T₂*	θ = θ_Ernst

IONP contrast efficiency	TR < T₁₀	TE ≪ T₂₀*	θ = θ_T₁ > θ_Ernst
Positive contrast regime (CNR_T₁)	TR < T₁₀	TE ≪ T₂₀*	θ = θ_T₁ > θ_Ernst
IONP contrast efficiency	TR < T₁₀^b	TE = TE_T₂*	θ = θ_T₂* < θ_Ernst
Negative contrast regime (CNRT_T₂*)	TR < T₁₀^b	TE = TE_T₂*	θ = θ_T₂* < θ_Ernst
IONP contrast efficiency	TR < T₁₀	TE = TE_T₁–T₂*	θ = θ_T₁–T₂*
Synergistic T₁-T₂* (CNR_T₁–T₂*)	TR < T₁₀	TE = TE_T₁–T₂*	θ_T₂* < θ_T₁–T₂* < θ_T₁

TR < T₁ means that the optimum is essentially flat, as opposed to TE ≪ T₂* here.

T₁ and T₂* variations treated separately. See (37) for an analytical expression of θ_T₁.

When β < 1, a low flip angle does not reduce T₁ effects enough at short TR, and a longer TR (> T₁) may slightly improve CNR_T₂*. However in such cases T₁ contrast is the dominant mechanism and thus is a better strategy than T₂* contrast.