Influence of RF spoiling on the stability and accuracy of T₁ mapping based on spoiled FLASH with varying flip angles

Abstract

There is increasing interest in quantitative T 1 mapping techniques for a variety of applications. Several methods for T 1 quantification have been described. The acquisition of two spoiled gradient-echo data sets with different flip angles allows for the calculation of T 1 maps with a high spatial resolution and a relatively short experimental duration. However, the method requires complete spoiling of transverse magnetization. To achieve this goal, RF spoiling has to be applied. In this work it is investigated whether common RF spoiling techniques are sufficiently effective to allow for accurate T 1 quantification. It is shown that for most phase increments the apparent T

Optimal radiofrequency and gradient spoiling for improved accuracy of T1 and B1 measurements using fast steady‐state techniques

“…Due to its time efficiency, AFI is useful for correction of errors caused by B 1 nonuniformities in quantitative in vivo imaging applications, and particularly, in VFA T 1 mapping (4,(13)(14)(15). Incomplete spoiling in AFI also was identified as a cause of B 1 measurement errors, and the use of diffusion-based gradient spoiling was shown to improve accuracy of this method (16,17).…”

“…Technically, RF spoiling is achieved by linearly incrementing the phase of an RF pulse between successive TR with a specific value of the phase increment. After the initial publication (1) suggested optimal phase increments of 117 or 123 , several other values were proposed (2)(3)(4). Default settings of the RF phase increment also vary between MRI equipment manufacturers (5).…”

“…In modern implementations, the VFA method takes advantage of a very short TR achievable due to RF spoiling, which allows time-efficient three-dimensional implementation with large anatomic coverage (8)(9)(10). Accuracy of VFA T 1 measurements was extensively studied in aspects of optimal flip-angle sampling (7)(8)(9)(10) and correction of amplitude of RF field (B 1 ) nonuniformities (4,9,10). Recently, incomplete spoiling was identified as a critical source of errors in the VFA method (4,5,11).…”

Synthetic quantitative MRI through relaxometry modelling

“…To address this, we simulated the FLASH acquisitions using Bloch‐Torrey equations for a range of expected transmit field efficiency. The correction parameters describing the linear dependence of the actual T 1 value on the apparent T 1 were derived from these simulations as described in Reference 23 and used to correct for imperfect spoiling of transverse magnetization. Semi‐quantitative maps of the percentage loss of magnetization resulting from the pre‐pulse in the MT‐weighted acquisition were calculated as described by Helms et al17 accounting for spatially varying T 1 times and flip angle inhomogeneities 1…”

Automatic brain segmentation using fractional signal modeling of a multiple flip angle, spoiled gradient-recalled echo acquisition

“…In particular, VFA is more sensitive to variations in excitation flip angle, whereas IR T1 mapping rely on robust inversion efficiency. However, example, it has been suggested that absolute T1 mapping by the VFA method requires absolute FA calibration [26], correction for RF pulse shape [28], and correction for incomplete RF spoiling [29].…”