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J Magn Reson Imaging. 2016 Apr;43(4):789-99. doi: 10.1002/jmri.25076. Epub 2015 Oct 10.

Imaging of the lumbar plexus: Optimized refocusing flip angle train design for 3D TSE.

Author information

1
Department of Diagnostic and Interventional Radiology, Technische Universität München, Munich, Germany.
2
Department of Neuroradiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
3
Philips Healthcare, Hamburg, Germany.
4
Zentralinstitut für Medizintechnik, Technische Universität München, Garching, Germany.

Abstract

PURPOSE:

To study the effects of refocusing angle modulation with 3D turbo spin echo (TSE) on signal and sharpness of small oblique nerves embedded in muscle and suppressed fat in the lumbar plexus.

MATERIALS AND METHODS:

Flip angle trains were generated with extended phase graphs (EPG) for a sequence parameter subspace. Signal loss and width broadening were simulated for a single-pixel nerve embedded in muscle and suppressed fat to prescribe a flip angle modulation that gives the best compromise between signal and sharpness of small nerves. Two flip angle trains were defined based on the simulations of small embedded nerves: design denoted A, predicting maximum global signal, and design denoted B, predicting maximum signal for minimum width broadening. In vivo data of the lumbar plexus in 10 healthy volunteers was acquired at 3.0T with 3D TSE employing flip angle trains A and B. Quantitative and qualitative analyses of the acquired data were made to assess changes in width and signal intensity.

RESULTS:

Changing flip angle modulation from A to B resulted in: 1) average signal losses of 23% in (larger) L5 nerves and 9% in (smaller) L3 nerves; 2) average width reductions of 4% in L5 nerves and of 16% in L3 nerves; and 3) statistically significant sharpness improvement (P = 0.005) in L3 nerves.

CONCLUSION:

An optimized flip angle train in 3D TSE imaging of the lumbar plexus considering geometry-specific blurring effects from both the nerve and the surrounding tissue can improve the delineation of small nerves.

KEYWORDS:

3D turbo spin echo (TSE); extended phase graphs (EPG); flip angle modulation; lumbar plexus; magnetic resonance imaging (MRI); magnetic resonance neurography (MRN)

PMID:
26454005
DOI:
10.1002/jmri.25076
[Indexed for MEDLINE]

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