High‐resolution hyperpolarized metabolic imaging of the rat heart using k–t PCA and k–t SPARSE

Abstract

The purpose of this work was to increase the resolution of hyperpolarized metabolic imaging of the rat heart with accelerated imaging using k–t principal component analysis (k–t PCA) and k–t compressed sensing (k–t SPARSE). Fully sampled in vivo datasets were acquired from six healthy rats after the injection of hyperpolarized [1‐13C]pyruvate. Data were retrospectively undersampled and reconstructed with either k–t PCA or k–t SPARSE. Errors of signal–time curves of pyruvate, lactate and bicarbonate were determined to compare the two reconstruction algorithms for different undersampling factors R. Prospectively undersampled imaging at 1 × 1 × 3.5‐mm3 resolution was performed with both methods in the same animals and compared with the fully sampled acquisition. k–t SPARSE was found to perform better at R < 3, but was outperformed by k–t PCA at R ≥ 4. Prospectively undersampled data were successfully reconstructed with both k–t PCA and k–t SPARSE in all subjects. No significant difference between the undersampled and fully sampled data was found in terms of signal‐to‐noise ratio (SNR) performance and metabolic quantification. Accelerated imaging with both k–t PCA and k–t SPARSE allows an increase in resolution, thereby reducing the intravoxel dephasing of hyperpolarized metabolic imaging of the rat heart.

Production of highly polarized [1‐13C]acetate by rapid decarboxylation of [2‐13C]pyruvate – application to hyperpolarized cardiac spectroscopy and imaging

“…Signal in the myocardial muscle was low but present, possibly displaying perfusion. To reduce partial volume effects, higher spatial resolution could be used as recently shown by Wespi et al In line with literature, [1‐ 13 C]acetate signal was observed when the imaging slice covered larger fractions of the chest muscle. [1‐ 13 C]acetylcarnitine signal appeared in a ring like shape, located in the area of myocardial muscle, a feature that could not be resolved by images obtained with directly polarized sodium [1‐ 13 C]acetate, because of coarser spatial resolution.…”

Extended quantitative dynamic contrast‐enhanced cardiac perfusion imaging in mice using accelerated data acquisition and spatially distributed, two‐compartment exchange modeling

“…Based on the results presented in the supporting information, the undersampled data were reconstructed with k-t SPARSE, which outperforms k-t PCA for small acquisition matrix sizes and moderate acceleration factors R . 29 A gradient echo-based readout was used similarly to work by Naresh et al 13 Although balanced steady state free precession (bSSFP) sequences could potentially offer improved contrast and sensitivity, 36 gradient-echo sequences offer a straightforward solution to map signal enhancement to CA concentration. In this study, the readout of each of the two slices was segmented over two consecutive heartbeats, resulting in an overall temporal footprint of 200-220 ms (depending on the heart rate).…”

“…A dual‐contrast, saturation‐recovery, gradient‐echo sequence with a Cartesian readout was used. The acquisition scheme was undersampled in both k y and time domain using a Poisson weighting . The net undersampling factor was R = 4 (resulting in a total acquisition of 16 phase‐encoding steps per slice per dynamic).…”

“…The acquired data were reconstructed separately for each coil element and the final data set was obtained as a sum of squares from the four coil elements. The data were reconstructed using k‐t SPARSE as described previously using the Fourier transformation over time as transform domain . Residual respiratory motion was minimized using image registration of the reconstructed data based on isotropic total variation regularization .…”

“…The acquisition scheme was undersampled in both k y and time domain using a Poisson weighting. 29 The net undersampling factor was R = 4 (resulting in a total acquisition of 16 phase-encoding steps per slice per dynamic). The sequence consisted of a saturation block based on a hyperbolic secant pulse triggered to an ECG-derived R-wave, followed by an acquisition of two midventricular short-axis slices.…”