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Investigation of inter-slice magnetization transfer effects as a new method for MTR imaging of the human brain.

Barker JW, Han PK, Choi SH, Bae KT, Park SH - PLoS ONE (2015)

Bottom Line: The effects of varying flip angle and phase encoding (PE) order were investigated experimentally in normal, healthy subjects.Simulations were also used to investigate the effects of varying acquisition parameters, and the effects of varying flip angle, PE steps, and interslice delay are discussed.Lastly, we demonstrated reduced banding with a non-balanced SSFP-FID sequence and showed preliminary results of interslice MTR imaging of meningioma.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America; Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.

ABSTRACT
We present a new method for magnetization transfer (MT) ratio imaging in the brain that requires no separate saturation pulse. Interslice MT effects that are inherent to multi-slice balanced steady-state free precession (bSSFP) imaging were controlled via an interslice delay time to generate MT-weighted (0 s delay) and reference images (5-8 s delay) for MT ratio (MTR) imaging of the brain. The effects of varying flip angle and phase encoding (PE) order were investigated experimentally in normal, healthy subjects. Values of up to ∼50% and ∼40% were observed for white and gray matter MTR. Centric PE showed larger MTR, higher SNR, and better contrast between white and gray matter than linear PE. Simulations of a two-pool model of MT agreed well with in vivo MTR values. Simulations were also used to investigate the effects of varying acquisition parameters, and the effects of varying flip angle, PE steps, and interslice delay are discussed. Lastly, we demonstrated reduced banding with a non-balanced SSFP-FID sequence and showed preliminary results of interslice MTR imaging of meningioma.

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Related in: MedlinePlus

Saturation of the longitudinal magnetization accumulates over multiple prior slices with the majority of saturation due to the first prior slice.For white (a) and gray (b) matter, simulations show the longitudinal magnetization as a function of the number of prior slices for varying number of phase encoding steps per slice and for varying flip angles. One prior slice = saturation at 3840 Hz, two prior slices = saturation at 7680 Hz followed by 3840 Hz, three prior slices = saturation at 11520 Hz, 7680 Hz, and 3840 Hz, etc.
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pone.0117101.g006: Saturation of the longitudinal magnetization accumulates over multiple prior slices with the majority of saturation due to the first prior slice.For white (a) and gray (b) matter, simulations show the longitudinal magnetization as a function of the number of prior slices for varying number of phase encoding steps per slice and for varying flip angles. One prior slice = saturation at 3840 Hz, two prior slices = saturation at 7680 Hz followed by 3840 Hz, three prior slices = saturation at 11520 Hz, 7680 Hz, and 3840 Hz, etc.

Mentions: Fig. 6 shows simulations of the longitudinal magnetization (Mz, f) for WM and GM for varying number of PE steps (RF-pulses) per slice, and two different flip angles. In agreement with the results in Fig. 3, the majority of saturation was generated by the first prior slice; however, a few dummy slices are needed to account for the contributions of earlier (2nd, 3rd, etc.) prior slices to reach a steady value of longitudinal magnetization across slices. More dummy slices are needed for lower flip angles and for lower number of PE steps per slice. The value of magnetization reached depended on the number of PE steps per slice and appeared to asymptotically approach true steady-state MT effects (i.e., the state that would be achieved after an infinite chain of saturation pulses at off-resonance frequency δ−1). For 128 PE steps, 5–6 dummy slices should be included to reach steady MT effects. For 256 or more PE steps, 3–4 dummy slices appeared to be sufficient. Including more dummy slices than needed would have minimal impact on scan time (∼1–3 s per dummy slice).


Investigation of inter-slice magnetization transfer effects as a new method for MTR imaging of the human brain.

Barker JW, Han PK, Choi SH, Bae KT, Park SH - PLoS ONE (2015)

Saturation of the longitudinal magnetization accumulates over multiple prior slices with the majority of saturation due to the first prior slice.For white (a) and gray (b) matter, simulations show the longitudinal magnetization as a function of the number of prior slices for varying number of phase encoding steps per slice and for varying flip angles. One prior slice = saturation at 3840 Hz, two prior slices = saturation at 7680 Hz followed by 3840 Hz, three prior slices = saturation at 11520 Hz, 7680 Hz, and 3840 Hz, etc.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4321840&req=5

pone.0117101.g006: Saturation of the longitudinal magnetization accumulates over multiple prior slices with the majority of saturation due to the first prior slice.For white (a) and gray (b) matter, simulations show the longitudinal magnetization as a function of the number of prior slices for varying number of phase encoding steps per slice and for varying flip angles. One prior slice = saturation at 3840 Hz, two prior slices = saturation at 7680 Hz followed by 3840 Hz, three prior slices = saturation at 11520 Hz, 7680 Hz, and 3840 Hz, etc.
Mentions: Fig. 6 shows simulations of the longitudinal magnetization (Mz, f) for WM and GM for varying number of PE steps (RF-pulses) per slice, and two different flip angles. In agreement with the results in Fig. 3, the majority of saturation was generated by the first prior slice; however, a few dummy slices are needed to account for the contributions of earlier (2nd, 3rd, etc.) prior slices to reach a steady value of longitudinal magnetization across slices. More dummy slices are needed for lower flip angles and for lower number of PE steps per slice. The value of magnetization reached depended on the number of PE steps per slice and appeared to asymptotically approach true steady-state MT effects (i.e., the state that would be achieved after an infinite chain of saturation pulses at off-resonance frequency δ−1). For 128 PE steps, 5–6 dummy slices should be included to reach steady MT effects. For 256 or more PE steps, 3–4 dummy slices appeared to be sufficient. Including more dummy slices than needed would have minimal impact on scan time (∼1–3 s per dummy slice).

Bottom Line: The effects of varying flip angle and phase encoding (PE) order were investigated experimentally in normal, healthy subjects.Simulations were also used to investigate the effects of varying acquisition parameters, and the effects of varying flip angle, PE steps, and interslice delay are discussed.Lastly, we demonstrated reduced banding with a non-balanced SSFP-FID sequence and showed preliminary results of interslice MTR imaging of meningioma.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America; Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.

ABSTRACT
We present a new method for magnetization transfer (MT) ratio imaging in the brain that requires no separate saturation pulse. Interslice MT effects that are inherent to multi-slice balanced steady-state free precession (bSSFP) imaging were controlled via an interslice delay time to generate MT-weighted (0 s delay) and reference images (5-8 s delay) for MT ratio (MTR) imaging of the brain. The effects of varying flip angle and phase encoding (PE) order were investigated experimentally in normal, healthy subjects. Values of up to ∼50% and ∼40% were observed for white and gray matter MTR. Centric PE showed larger MTR, higher SNR, and better contrast between white and gray matter than linear PE. Simulations of a two-pool model of MT agreed well with in vivo MTR values. Simulations were also used to investigate the effects of varying acquisition parameters, and the effects of varying flip angle, PE steps, and interslice delay are discussed. Lastly, we demonstrated reduced banding with a non-balanced SSFP-FID sequence and showed preliminary results of interslice MTR imaging of meningioma.

Show MeSH
Related in: MedlinePlus