Chemical shift separation with controlled aliasing for hyperpolarized ¹³C metabolic imaging

Abstract

Purpose A chemical shift separation technique for hyperpolarized 13C metabolic imaging with high spatial and temporal resolution was developed. Specifically, a fast 3D pulse sequence and a reconstruction method were implemented to acquire signals from multiple 13C species simultaneously with subsequent separation into individual images. Methods A stack of flyback-EPI readouts and a set of multiband excitation RF pulses were designed to spatially modulate aliasing patterns of the acquired metabolite images, which translated the chemical shift separation problem into parallel imaging reconstruction problem. An eight-channel coil array was used for data acquisition and a parallel imaging method based on nonlinear inversion was developed to separate the aliased images. Results Simultaneous acquisitions of pyruvate and lactate in a phantom study and in vivo rat experiments were performed. The results demonstrated successful separation of the metabolite distributions into individual images having high spatial resolution. Conclusion This method demonstrated the ability to provide accelerated metabolite imaging in hyperpolarized 13C MR utilizing multi-channel coils, tailored readout, and specialized RF pulses.

Recent advances in parallel imaging for MRI

“…SENSE has been used to reduce 2D acquisition from 43 seconds to 14 seconds [162], and parallel imaging with EPSI has been used to collect 3D pyruvate and lactate images from rat kidneys in a few seconds [163]. …”

Hyperpolarized 13C spectroscopic imaging using single‐shot 3D sequences with unpaired adiabatic refocusing pulses

“…Others have used single‐band SpSp pulses to image a single metabolite at a time, for example with 2D and 3D echo planar imaging (EPI), which can be accelerated with compressed sensing . The EPI trajectory can also be designed to enable separation of metabolite resonances in the resulting images . Spiral chemical shift imaging (CSI) has been studied extensively, while traditional CSI with compressed sensing has also shown promise for dynamic measurements .…”

“…We recently proposed a single‐shot 3D sequence that makes efficient use of the transverse magnetization after each excitation . The sequence exploits the B 1 insensitivity of adiabatic pulses, following a dual‐spin‐echo (DSE) scheme that is widely used in other hyperpolarized MRI applications . The adiabatic pulses in the DSE scheme result in better refocusing and hence less signal loss due to dephasing, but the pulse sequence is inefficient in its use of spin hyperpolarization, since signal is acquired from only half of the spin echoes.…”

Development and testing of hyperpolarized 13C MR calibrationless parallel imaging

“…For 13 C receive, an 8-channel array coil was used with 2 sets of four coil elements in a linear arrangement as shown in Fig. 1(a) [24,25]. Each rectangular element was approximately 5 × 10 cm and adjacent elements were overlapped to minimize mutual inductance.…”