Inversion recovery TrueFISP: Quantification of T₁, T₂, and spin density

Abstract

A novel procedure is proposed to extract T 1 , T 2 , and relative spin density from the signal time course sampled with a series of TrueFISP images after spin inversion. Generally, the recovery of the magnetization during continuous TrueFISP imaging can be described in good approximation by a three parameter monoexponential function S(t) ‫؍‬ S stst (1-INV exp(-t/T* 1 ). This apparent relaxation time T* 1 ≤ T 1 depends on the flip angle as well as on both T 1 and T 2 . Here, it is shown that the ratio T 1 /T 2 can be directly extracted from the inversion factor INV, which describes the relation of the signal value extrapolated to t ‫؍‬ 0 and the steady-state signal. The balanced SSFP MR imaging technique (1), also named balanced FFE and FIESTA, here referred to as TrueFISP (2), was proposed more than a decade ago and has generated much renewed interest during recent years due to technical advances in gradient and receiver performance. It provides the capability of extremely rapid imaging while preserving a high SNR efficiency. With a fixed flip angle ␣, the steady-state signal is an increasing function of the ratio T 2 /T 1 , so that high signal is generally obtained from fluid compartments with a long T 2 . The resulting image contrast renders the technique beneficial for several different applications, e.g., evaluation of cardiac function (3) or coronary angiography (4,5).In practice, magnetization reaches its steady-state condition after a certain transition period. A smooth signal time course towards steady state can be achieved by preparation with an RF pulse of flip angle -␣/2, preceding the imaging sequence at a time TR/2 before the first ␣ pulse (6). Whereas new elaborate pulse schemes have also been described (7), the ␣/2-based technique is robust and allows the implementation of additional magnetization preparation experiments immediately before a TrueFISP readout. In combination with the ␣/2 prepulse, an inversion recovery TrueFISP sequence has been proposed for magnetization prepared steady-state imaging (6). This approach has recently gained renewed interest as a promising tool for fast T 1 quantification (8). The intensities of a TrueFISP image series acquired after spin inversion and ␣/2 preparation were reported to follow the free longitudinal relaxation curve very closely, even at comparatively high flip angles of 50°.In a subsequent study from our group using numerical simulations and phantom experiments, it was also found that the recovery time course under a train of TrueFISP pulses can be described by monoexponential behavior (9). However, apparent relaxation times T* 1 were measured which strongly depended on the flip angle, T 1 and T 2 . It was demonstrated that this property can be used to quantify both T 1 and T 2 by fitting T* 1 curves measured with different flip angles to theoretical response curves. This numerically described behavior was confirmed by the results of a recent publication wherein an elegant simplifying calculation was presented, yielding a compact mathematical descripti...

FAIR‐TrueFISP imaging of cerebral perfusion in areas of high magnetic susceptibility differences at 1.5 and 3 Tesla

“…The total acquisition time during recovery was 5000 msec and the time between inversion pulses was 10000 msec. T1 values were pixelwise fitted with the use of a previously published method (20).…”

A simple geometrical description of the TrueFISP ideal transient and steady‐state signal

“…[3] and the phase defined in Eq. [6]. This direction is of particular importance for obtaining smooth signal evolution, as will be shown later.…”

“…For magnetization at resonance frequency and for TR Ͻ Ͻ T 1,2 , the transient signal behavior can be described with a simple closed formula (5). Recently, analytic expressions were presented for the calculation of T 1 , T 2 , and spin density from the fit parameters that are obtained by fitting an IR TrueFISP signal time course to a three-parameter monoexponential function (6). The technique works well on the human brain, but the presence of off-resonances poses problems in that it yields modified relaxation parameters and the ␣/2 preparation scheme is suboptimal so that signal fluctuations may impair the early echoes.…”

Dual Contrast - Magnetic Resonance Fingerprinting (DC-MRF): A Platform for Simultaneous Quantification of Multiple MRI Contrast Agents

“…The ability of the MRF data to be acquired in as little as 10 seconds provides the opportunity to dynamically assess a wide variety of contrast agents regardless of the pharmacokinetics making it a more general solution with fewer required assumptions. Further, prior studies have shown that MRF is more temporally efficient than other rapid MRI techniques 37,38 , and has been implemented on both clinical and preclinical MRI scanners. An additional benefit of the simultaneous measurement of T1 and T2 provided by MRF is these two relaxation time maps always being co-registered regardless of subject motion.…”