Optimized spectrally selective steady-state free precession sequences for cartilage imaging at ultra-high fields

Bieri, Oliver; Mamisch, TC; Trattnig, Siegfried; Kraff, Oliver; Ladd, Mark E.; Scheffler, Klaus

doi:10.1007/s10334-007-0092-0

Cited by 12 publications

(11 citation statements)

References 13 publications

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“…The prominent reverse change in signal from fat (as indicated by the white arrows in Fig. 8a) relates to the spatial spectral selectivity of the RF pulse (8), which becomes at low fields only apparent for considerable pulse durations (T RF ϳ 8 ms).…”

Section: Discussionmentioning

confidence: 98%

SSFP signal with finite RF pulses

Bieri

Scheffler

2009

Magnetic Resonance in Med

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The theoretical description of steady state free precession (SSFP) sequences is generally well accepted and unquestioned, although it is based on instantaneously acting radiofrequency (RF) pulses. In practice, however, all excitation processes are finite, thereby questioning the overall validity of the common SSFP signal description for use with finite RF pulses. In this paper, finite RF pulse effects on balanced SSFP signal formation are analyzed as a function of the RF time (T RF ), the pulse repetition time (TR), the flip angle (␣) and relaxation times (T 1,2 ). The observed signal modulations from finite RF pulses (compared to infinitesimal ones) can range from only a few percent (for T RF /TR Ͻ Ͻ 1, ␣ Ͻ Ͻ 90°, T 2 /T 1 ϳ 1) to over 10% (for T RF /TR Ͻ Ͻ 1, ␣ ϳ 90°, T 2 /T 1 Ͻ Ͻ 1) and may even exceed 100% in the limit of T RF /TR 3 1 (for ␣ ϳ 90°, T 2 /T 1 Ͻ Ͻ 1). As a result, a revision of SSFP signal theory is indicated not only for reasons of completeness but also seems advisable, e.g., for all quantitative SSFP methods. A simple modification for the common balanced SSFP equation is derived that provides an accurate framework for SSFP signal description over a wide variety of practical and physiologic parameters. Magn Reson Med 62: 1232-1241, 2009.

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Section: Discussionmentioning

confidence: 98%

SSFP signal with finite RF pulses

Bieri

Scheffler

2009

Magnetic Resonance in Med

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“…Binomial water excitation pulses have been proven to be beneficial for cartilage imaging (17), where uniform fat suppression with high spatial resolution is required. Cartilage imaging with single frequency selective RF pulses at ultrahigh‐fields has been shown to be easily applicable for fat suppression or fat–water separation (18).…”

Section: Spatial‐spectral Pulses (Water Excitation)mentioning

confidence: 99%

Fat and water magnetic resonance imaging

Bley

Wieben

François

et al. 2009

Magnetic Resonance Imaging

321

291

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A wide variety of fat suppression and water-fat separation methods are used to suppress fat signal and improve visualization of abnormalities. This article reviews the most commonly used techniques for fat suppression and fatwater imaging including 1) chemically selective fat suppression pulses "FAT-SAT"; 2) spatial-spectral pulses (water excitation); 3) short inversion time (TI) inversion recovery (STIR) imaging; 4) chemical shift based water-fat separation methods; and finally 5) fat suppression and balanced steady-state free precession (SSFP) sequences. The basic physical background of these techniques including their specific advantages and disadvantages is given and related to clinical applications. This enables the reader to understand the reasons why some fat suppression methods work better than others in specific clinical settings.

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“…2), but this has to be traded off for a loss of signal intensity. However, the increased chemical shift differences between water and fat at ultra-high fields can also be used; a recent study has shown that it might be used for optimized fat suppression purposes 7 or spectroscopy applications. 8 Another important issue at 7.0 T is that the regulatory limitations for specific SARs should not be exceeded, although RF power deposition is much higher than at 1.5 T or 3.0 T, due to its quadratic dependence on B 0 ; this is especially true for high-duty RF pulse sequences in three-dimensional (3D) mode.…”

Section: Mr Scanner and Radiofrequency Coilmentioning

confidence: 99%

In Vivo 7.0-Tesla Magnetic Resonance Imaging of the Wrist and Hand: Technical Aspects and Applications

Friedrich

Chang²,

Vieira³

et al. 2009

Semin Musculoskelet Radiol

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Magnetic resonance imaging (MRI) at 7.0 T has the potential for higher signal-to-noise ratio (SNR), improved spectral resolution, and faster imaging compared with 1.5-T and 3.0-T MR systems. This is especially interesting for challenging imaging regions like the wrist and the hand because of the small size of the visualized anatomical structures; the increase in SNR could then be directly converted into higher spatial resolution of the images. Practically, imaging at 7.0 T poses a variety of technical challenges such as static (B0) and radiofrequency (B1) homogeneities, shimming, chemical shift artifacts, susceptibility artifacts, alterations in tissue contrast, specific absorption rate limitations, coil construction, and pulse sequence tuning. Despite these limitations, this first experience in anatomical imaging of the wrist and the hand at 7.0 T is very promising. Functional imaging techniques will gain importance at ultra-high-field MRI and need to be assessed in detail in the future.

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Optimized spectrally selective steady-state free precession sequences for cartilage imaging at ultra-high fields

Cited by 12 publications

References 13 publications

SSFP signal with finite RF pulses

SSFP signal with finite RF pulses

Fat and water magnetic resonance imaging

In Vivo 7.0-Tesla Magnetic Resonance Imaging of the Wrist and Hand: Technical Aspects and Applications

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