Artifacts in T1ρ-weighted imaging: Compensation for B₁ and B₀ field imperfections

详细信息    查看全文

• 作者：Walter R.T. Witschey II ; Arijitt Borthakur ; Mark A. Elliott ; Eric Mellon ; Sampreet Niyogi ; Daniel J. Wallman ; Chenyang Wang ; Ravinder Reddy
• 关键词：Spin locking ; T1&#x3c1 ; ; Relaxation ; Off-resonance T1&#x3c1 ; ; Inhomogeneous B₀ and B₁ fields
• 刊名：Journal of Magnetic Resonance
• 出版年：2007
• 出版时间：May 2007
• 年：2007
• 卷：186
• 期：1
• 页码：75-85
• 全文大小：1690 K

文摘

The origin of spin locking image artifacts in the presence of B₀ and B₁ magnetic field imperfections is shown theoretically using the Bloch equations and experimentally at low (ω₁ Δω₀), intermediate (ω₁ Δω₀) and high (ω₁ Δω₀) spin locking field strengths. At low spin locking fields, the magnetization is shown to oscillate about an effective field in the rotating frame causing signature banding artifacts in the image. At high spin lock fields, the effect of the resonance offset Δω₀ is quenched, but imperfections in the flip angle cause oscillations about the ω₁ field. A new pulse sequence is presented that consists of an integrated spin echo and spin lock experiment followed by magnetization storage along the −z-axis. It is shown that this sequence almost entirely eliminates banding artifacts from both types of field inhomogeneities at all spin locking field strengths. The sequence was used to obtain artifact free images of agarose in inhomogeneous B₀ and B₁ fields, off-resonance spins in fat and in vivo human brain images at 3 T. The new pulse sequence can be used to probe very low frequency (0–400 Hz) dynamic and static interactions in tissues without contaminating B₀ and B₁ field artifacts.