Steady-State Free Precession in Nuclear Magnetic Resonance

Purpose: To examine the spoiled steady-state (spoiled gradient-recalled echo sequence [SPGR]) signal arising from two-compartment systems and the role of experimental parameters, in particular TR for resolving signal from each compartment. Materials and Methods:Using Bloch-McConnell simulations, we examined the SPGR signal from two-component systems in which T 1 is much greater than the mean residence time ( m ) of proton spins in each component. Specifically, we examined the role of TR on the ability to resolve each components signal, as well as the influence of experimental parameters on derived DESPOT1 T 1 values. Results:Results revealed that when TR Յ 0.01 m , the measured SPGR signal may be modeled as a summation of signal from each species using a no-exchange approximation. Additionally, under this short TR condition, the driven equilibrium single pulse observation of T 1 (DESPOT1) mapping approach provides T 1 values preferentially biased toward the short or long T 1 species, depending on the choice of flip angles. Conclusion:The ability to model the SPGR signal using a no-exchange approximation may permit the quantification multicomponent T 1 relaxation in vivo. Additionally, the ability to preferentially weight the DESPOT1 T 1 value toward the short or long T 1 may provide a useful window into these components.

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“…Assuming a single T 1 , the measured SPGR signal immediately prior to each RF pulse is given by (11,27):…”

Section: Theorymentioning

confidence: 99%

Investigating the effect of exchange and multicomponent T₁ relaxation on the short repetition time spoiled steady‐state signal and the DESPOT1 T₁ quantification method

Deoni

Rutt

Jones

2007

Magnetic Resonance Imaging

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“…However, the analysis of tagged images requires sufficient myocardial signal-to-noise ratio (SNR) and tag-myocardium contrast-to-noise ratio (CNR) for accurate tag detection (9 -12). Refocused steady-state free precession (SSFP) (13), also known as fast imaging with steady precession (FISP or TrueFISP) (14,15), has proven valuable for in vivo cardiac functional MRI because of its high tissue SNR and excellent myocardium-to-blood CNR (16,17). Therefore, the analysis of tagged images may be improved with the increased SNR and inherent contrast of an SSFP acquisition.…”

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confidence: 99%

Myocardial tagging with SSFP

Herzka

Guttman

McVeigh

2003

Magnetic Resonance in Med

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This work presents the first implementation of myocardial tagging with refocused steady-state free precession (SSFP) and magnetization preparation. The combination of myocardial tagging (a noninvasive method for quantitative measurement of regional and global cardiac function) with the high tissue signalto-noise ratio (SNR) obtained with SSFP is shown to yield improvements in terms of the myocardium-tag contrast-to-noise ratio (CNR) and tag persistence when compared to the current standard fast gradient-echo (FGRE) tagging protocol. Myocardium-tag CNR and tag persistence were studied using numerical simulations as well as phantom and human experiments. Both quantities were found to decrease with increasing imaging flip angle (␣) due to an increased tag decay rate and a decrease in myocardial steady-state signal. However, higher ␣ yielded better blood-myocardium contrast, indicating that optimal ␣ is dependent on the application: higher ␣ for better blood-myocardium boundary visualization, and lower ␣ for better tag persistence. SSFP tagging provided the same myocardium-tag CNR as FGRE tagging when acquired at four times the bandwidth and better tag-and blood-myocardium CNRs than FGRE tagging when acquired at equal or twice the receiver bandwidth (RBW). The increased acquisition efficiency of SSFP allowed decreases in breath-hold duration, or increases in temporal resolution, as compared to FGRE.Magn Reson Med 49: 329 -340,

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“…This is in contrast to finite RF pulses, which are now considered to be composed of series of an equidistant series of quasi-instantaneous RF (as illustrated for the rectangular RF pulse envelope in Fig. 2b) (23): here, the magnetization evolves for bSSFP under ideal conditions (i.e., at on-resonance and for alternating flip angles, 6a) through a complete zenithal alignment (reached at a/2). As a result, the amount of transverse magnetization M xy decreases continuously to reach zero (for a symmetric RF pulse, at t ¼ T RF /2) before it starts to increase again.…”

Section: Superbalanced Ssfpmentioning

confidence: 99%

Superbalanced steady state free precession

Bieri

2011

Magnetic Resonance in Med

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Steady state free precession (SSFP) signal theory is commonly derived in the limit of quasi-instantaneous radiofrequency (RF) excitation. SSFP imaging protocols, however, are frequently set up with minimal pulse repetition times and RF pulses can thus constitute a considerable amount to the actual pulse repetition time. As a result, finite RF pulse effects can lead to 10-20% signal deviation from common SSFP theory in the transient and in the steady state which may impair the accuracy of SSFP-based quantitative imaging techniques. In this article, a new and generic approach for intrinsic compensation of finite RF pulse effects is introduced. Compensation is based on balancing relaxation effects during finite RF excitation, similar to flow or motion compensation of gradient moments. RF pulse balancing, in addition to the refocusing of gradient moments with balanced SSFP, results in a superbalanced SSFP sequence free of finite RF pulse effects in the transient and in the steady state; irrespective of the RF pulse duration, flip angles, relaxation times, or off-resonances. In multipulse experiments, the time evolution of spins is commonly analyzed in the limit of quasi-instantaneously acting radiofrequency (RF) pulses. This concept separates the Bloch equations (1) into repetitive units of RF excitation and interpulse delays (2) and thereby allows the derivation of closed form solutions to steady state free precession (SSFP) sequences in the steady state (3-7) and the transient phase (8-11). In practice, however, RF pulses have a finite duration (T RF ) and may cause systematic deviations from the solutions derived in the limit of quasi-instantaneous RF pulses (12,13). An introductory example of this behavior is presented in Fig. 1 for balanced SSFP (bSSFP). The range of finite RF pulse effects is illustrated for the steady state amplitude (Fig. 1a) and for the decay factor of the transient (Fig. 1b) as a function of the flip angle (a) for the two extremes of quasi-instantaneous (T RF ! 0) and quasi-continuous (T RF ! pulse repetition time [TR]) excitation. Generally, finite RF pulse effects increase with increasing flip angle and relaxation time ratio (L :¼ T 1 /T 2 ) and show a smooth transition with the fractional RF pulse duration (l :¼ T RF /TR) (12). However, neither bSSFP contrast nor its spin-echo nature is affected by finite RF pulse effects (13).Following the common doctrine, SSFP imaging protocols have minimal TR and short excitation periods. Short RF pulses, however, lead to pronounced magnetization transfer (MT) effects in tissues (14) which may impair the accuracy of common SSFP-based quantitative MR imaging techniques, such as fast relaxation time mapping with inversion recovery SSFP (15,16) or variable nutation SSFP (17). Thus, long RF pulses were proposed to be used with these techniques to suppress MT effects (18,19), but it also became evident that signal modulations from finite RF pulses can no longer be neglected (18,20,21). In principle, signal models of quantitative SSFP imaging techniques c...

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Steady-State Free Precession in Nuclear Magnetic Resonance

Cited by 443 publications

References 12 publications

Investigating the effect of exchange and multicomponent T₁ relaxation on the short repetition time spoiled steady‐state signal and the DESPOT1 T₁ quantification method

Investigating the effect of exchange and multicomponent T₁ relaxation on the short repetition time spoiled steady‐state signal and the DESPOT1 T₁ quantification method

Myocardial tagging with SSFP

Superbalanced steady state free precession

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Steady-State Free Precession in Nuclear Magnetic Resonance

Cited by 443 publications

References 12 publications

Investigating the effect of exchange and multicomponent T1 relaxation on the short repetition time spoiled steady‐state signal and the DESPOT1 T1 quantification method

Investigating the effect of exchange and multicomponent T1 relaxation on the short repetition time spoiled steady‐state signal and the DESPOT1 T1 quantification method

Myocardial tagging with SSFP

Superbalanced steady state free precession

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Product

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Investigating the effect of exchange and multicomponent T₁ relaxation on the short repetition time spoiled steady‐state signal and the DESPOT1 T₁ quantification method

Investigating the effect of exchange and multicomponent T₁ relaxation on the short repetition time spoiled steady‐state signal and the DESPOT1 T₁ quantification method