Achieving uniform fat suppression is an important diagnostic requirement for body and musculoskeletal MR examinations. The most commonly used approaches distinguish water from fat based on differences in frequency, *T*_{1}, or both. *T*_{1}-based methods (1) use an inversion pulse followed by a short delay so that fat, which has a short *T*_{1}, is suppressed. Such approaches are robust with respect to static magnetic field (*B*_{0}) inhomogeneity and radiofrequency (RF) field (*B*_{1}) inhomogeneity if adiabatic pulses are used but tend to be slow and inefficient in terms of signal-to-noise ratio due to the inversion pulses. A number of different frequency-based methods exist, which rely on the chemical shift between water and fat resonances (Δf ≈ 435 Hz at 3 T). Methods include frequency-selective saturation of the fat signal (2), water-selective imaging using spectral-spatial (spsp) pulses (3), and signal-phase-based water-fat separation (4, 5). Methods that rely on selective excitation can be efficient and flexible but require a homogenous *B*_{0} field to work well, which is hard to achieve for large fields of view. The phase-based methods can be more robust to *B*_{0} field variation but generally require extra data, with information from multiple images acquired at offset echo times being combined to determine and correct for local frequency offsets.

Spsp RF pulses are commonly used to excite only protons from water or fat within a spatially local region, typically a slice or slab. Slice-selective spsp pulses consist of trains of slice selective subpulses with different amplitudes; a commonly used example is the binomial excitation pulse (6), where the relative amplitudes are given by binomial coefficients. Pulses of this type can be described straightforwardly using the small tip angle approximation (3, 7), which establishes a Fourier relationship between the resulting transverse magnetization (m(**x**)) and the applied RF pulse (b(t)):

In this formalism ** x** = (

*x*,

*y*,

*z*,ω) and so

*m*(

**) is the resulting transverse magnetization as a function of space and (angular) frequency. The transmit sensitivity of the RF coil and static field inhomogeneity are represented by**

*x**S*(

**) and**

*x**B*

_{0}(

**), respectively, and γ is the gyromagnetic ratio. Fourier transform variable**

*x***(**

*k**t*) = (

*k*

_{x},

*k*

_{y},

*k*

_{z},

*k*

_{ω}) has components corresponding to both spatial and temporal frequencies; the spatial components are given by integrals of the applied magnetic field gradients where, for example,

*G*

_{x}is the

*x*gradient strength and the temporal term is given by

*k*

_{ω}(

*t*) =

*t*–

*T*where

*T*is the total pulse duration. Simultaneous slice and frequency selection (i.e., selection in z-

_{ω}) are achieved by applying RF energy while traversing a trajectory in

*k*

_{z}-

*k*

_{ω}(3). For the slice-selective spsp pulses used, the

*k*-space trajectory is such that the spatial and spectral responses are independent to first approximation as the subpulse duration is much shorter than the interval between them. In this case, spatial selection is determined from the individual subpulses while spectral selectivity comes from the pattern of amplitude and phase variation of the pulse train (8, 9). A binomial pulse train with

*N*subpulses separated in time by period τ has frequency response giving strong fat suppression if τ = 1/(2Δ

*f*) = 1.15 ms at 3 T. Use of higher

*N*provides broader stop bands at the expense of longer RF pulse durations. Inhomogeneity of the static magnetic field causes the water and fat resonant frequencies to vary in space so that they may move out of the frequency bands defined by the RF pulse's structure. The result can be poor fat suppression or even fat selection with water suppressed in regions where the effect is severe. Pulses with a broader stop band are less vulnerable to this effect, and for this reason at 3 T the

*N*= 4 binomial sequence (1-3-3-1) is commonly used; however, failure of fat suppression is still often seen. This clinically used

*N*= 4 binomial pulse has been used as an exemplar in this work.

The recent advent of parallel transmission has provided more direct control of the RF field in space, as well as time; we can describe these extra degrees of freedom by modifying Eq. 1 (10):

where *S*_{c} and *b*_{c}(*t*) are the spatial transmit sensitivity and RF pulse waveform, respectively, of coil c and *N*_{c} is the number of coils. Much interest has been placed on using these degrees of freedom to improve spatial homogeneity of excitation, particularly at high field strengths (11, 12). RF shimming (13) is a straightforward method of achieving this by adjusting the relative amplitudes and phases of each channel such that the overall RF field is more uniform. Alternatively, the entire waveform and *k*-space trajectory can be redesigned to gain more control. In this vein, there is a body of work exploring use of composite RF pulses (referred to as “fast *k*_{z}” or “spokes” (14, 15)) in which subpulses played out along a *k*_{z} trajectory are offset in *k*_{x}-*k*_{y} in order to achieve modulation of in-plane excitation. Recently, it has been recognized that spectral properties of these pulses can be optimized to improve wideband uniformity (16–18). There is thus a close link with conventional water-selective binomial pulses in which each subpulse can be seen as a spoke at (*k*_{x},*k*_{y}) = 0. In this work, we explored the potential for using extra degrees of freedom available from parallel transmission to improve performance of binomial-style pulses by correcting for *B*_{0} inhomogeneity. Fat-suppressed images of the pelvis acquired in healthy volunteers are presented, demonstrating the application of this method to a large field of view.