Magnetization transfer effects in multislice MR imaging

doi:10.1016/0730-725X(93)90471-O

Magnetic Resonance Imaging

Volume 11, Issue 4, 1993, Pages 521-532

https://doi.org/10.1016/0730-725X(93)90471-O Get rights and content

Abstract

A theoretical model is presented which describes the effects of magnetization transfer in multislice MR imaging of a tissue-mimicking phantom composed of cross-linked agar gel. The model is successful in explaining differences between single and multislice image signal intensities observed for the agar gel but not seen in a simple aqueous solution. Magnetization transfer leads to a reduction in the image signal intensity of a slice of interest due to off-resonance RF irradiation arising from 90° and 180° pulses intended for neighboring slices. The contribution of magnetization transfer to multislice MR imaging depends on the amount of off-resonance RF irradiation during the imaging sequence repetition interval. For the tissue-mimicking agar gel, conventional spin-echo multislice imaging gave rise to a negligible image signal intensity reduction (≤2%); however, fast spin-echo (FSE) imaging, which employs up to 16 times as many RF pulses per slice, exhibited as much as a 13% reduction in image signal intensity (13 slices). The reduction in multislice image signal intensity due to magnetization transfer is sample specific and is shown to be more dramatic for in vivo human leg muscle (10% for conventional spin echo, 40% for FSE) where magnetization transfer rates are greater than in the cross-linked agar gel.

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Citation Excerpt :
Data matching with a dictionary created by Bloch simulation of the QRAPMASTER sequence can be a promising solution for the above signal analysis problem. On the other hand, although many studies have been reported on the MT effect on multislice imaging [16–19], to the best of our knowledge, no studies have been reported on the MT effect on the QRAPMASTER sequence. In this study, to clarify the MT effect, a QRAPMASTER sequence was implemented on a specially designed 1.5 T MRI system and phantom experiments were performed.
To clarify the magnetization transfer (MT) effect on T₁ and T₂ values obtained with the QRAPMASTER sequence.
A phantom consisting of MnCl₂ aqueous solution with various proton relaxation times and a chicken breast sample was imaged with the QRAPMASTER sequence and a multislice multiple spin-echo (MSMSE) sequence that was the basis of the QRAPMASTER sequence using a 1.5 T MRI system. T₁ values were calculated by data matching using the dictionary dataset created by a Bloch image simulation of the QRAPMASTER sequence. T₂ values were calculated by data matching using the dictionary dataset created by a Bloch image simulation of the MSMSE sequence. The MT effect on the images acquired with the QRAPMASTER and MSMSE sequences was calculated by numerically solving Bloch equations using a two-pool model.
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This study demonstrated that the T₁ value of a biological sample obtained by the QRAPMASTER sequence was shortened by the MT effect.
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Citation Excerpt :
The longitudinal relaxation (T1) is a consequence of the combination of the equilibrium between the two pools. However, if the restricted pool is saturated by off-resonance pulses, there is less longitudinal magnetization available, and in consequence, this could cause an apparent T1 that is shorter than the T1 of the free water pool [49], especially when multiple inversion-recovery pulses are played out in multi-slice sequences [50]. In the case of MRF-vFA, each slice is acquired using an initial inversion recovery pulse which could induce a magnetization transfer effect in adjacent slices.
Our purpose is to evaluate bias and repeatability of the quantitative MRI sequences QRAPMASTER, based on steady-state imaging, and variable Flip Angle MRF (MRF-VFA), based on the transient response.
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In the phantom, the mean bias±95% confidence interval for T1 values with QRAPMASTER was 10 ± 10% on 1.5 T and 4 ± 13% on 3.0 T. The mean bias for T1 values with MRF-vFA was 21 ± 17% on 1.5 T and 9 ± 9% on 3.0 T. For T2 values the mean bias with QRAPMASTER was 12 ± 3% on 1.5 T and 23 ± 1% on 3.0 T. For T2 values the mean bias with MRF-vFA was 17 ± 1% on 1.5 T and 19 ± 2% on 3.0 T. QRAPMASTER estimated lower T1 and T2 values than MRF-vFA. Repeatability was good with low coefficients of variation (CoV). Mean CoV ± 95% confidence interval for T1 were 3.2 ± 0.4% on 1.5 T and 4.5 ± 0.8% on 3.0 T with QRAPMASTER and 2.7% ± 0.2% on 1.5 T and 2.5 ± 0.2% on 3.0 T with MRF-vFA. For T2 were 3.3 ± 1.9% on 1.5 T and 3.2 ± 0.6% on 3.0 T with QRAPMASTER and 2.0 ± 0.4% on 1.5 T and 5.7 ± 1.0% on 3.0 T with MRF-vFA.
The in-vivo T1 and T2 are in the range of values previously reported by other authors.
The in-vivo mean CoV ± 95% confidence interval in gray matter were for T1 1.7 ± 0.2% using QRAPMASTER and 0.7 ± 0.5% using MRF-vFA and for T2 were 0.9 ± 0.4% using QRAPMASTER and 2.4 ± 0.5% using MRF-vFA. In white matter were for T1 0.9 ± 0.3% using QRAPMASTER and 1.3 ± 1.1% using MRF-vFA and for T2 were 0.7 ± 0.4% using QRAPMASTER and 2.4 ± 0.4% using MRF-vFA. A GLM analysis showed that the variations in T1 and T2 mainly depend on the field strength and the subject, but not on the follow-up repetition in different days. This confirms the high repeatability of QRAPMASTER and MRF-vFA.
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Citation Excerpt :
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However, the quantitative accuracy was compromised by MT effects largely due to fat saturation pulses. In addition, the (off-resonance) slice-selective excitations of slices other than the one being scanned (Santyr, 1993) contribute to biased T1 estimates. To improve the quantitative usability, fat saturation should be disabled or the spectral saturation should be replaced by some other suppression method.
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Original contributionMagnetization transfer effects in multislice MR imaging

Abstract

Magn. Reson. Imaging

Magn. Reson. Imaging

J. Magn. Reson.

J. Magn. Reson.

Magn. Reson. Imaging

J. Magn. Reson.

Magn. Reson. Imaging

Pulse sequences for magnetic resonance imaging

Effect of multislice interference on image contrast in T2- and T1-weighted MR images

AJNR

Effect of intersection spacing on MR image contrast and study time

Radiology

A stimulated echo artifact from slice interference in magnetic resonance imaging

Med. Phys.

Errors in the measurements of T2 using multiple-echo MRI techniques

Magn. Reson. Med.

Errors in T2 estimation using multislice multiple-echo imaging

Magn. Reson. Med.

Variations in slice shape and absorption as artifacts in the determination of tissue parameters in NMR imaging

Magn. Reson. Med.

MR imaging section profile optimization: Improved contrast and detection of lesions

Radiology

Quantitative studies of hydrodynamic effects and cross-relaxation in protein solutions and tissues with proton and deuteron longitudinal relaxation times

Magn. Reson. Med.

Original contribution
Magnetization transfer effects in multislice MR imaging

Effect of multislice interference on image contrast in T₂- and T₁-weighted MR images

Errors in the measurements of T₂ using multiple-echo MRI techniques

Errors in T₂ estimation using multislice multiple-echo imaging