Nonuniform Fourier‐decomposition MRI for ventilation‐ and perfusion‐weighted imaging of the lung

Abstract

Purpose To improve the robustness of pulmonary ventilation‐ and perfusion‐weighted imaging with Fourier decomposition (FD) MRI in the presence of respiratory and cardiac frequency variations by replacing the standard fast Fourier transform with the more general nonuniform Fourier transform. Theory and Methods Dynamic coronal single‐slice MRI of the thorax was performed in 11 patients and 5 healthy volunteers on a 1.5T whole‐body scanner using a 2D ultra‐fast balanced steady‐state free‐precession sequence with temporal resolutions of 4‐9 images/s. For the proposed nonuniform Fourier‐decomposition (NUFD) approach, the original signal with variable physiological frequencies that was acquired with constant sampling rate was retrospectively transformed into a signal with (ventilation or perfusion) frequency‐adapted sampling rate. For that purpose, frequency tracking was performed with the synchro‐squeezed wavelet transform. Ventilation‐ and perfusion‐weighted NUFD amplitude and signal delay maps were generated and quantitatively compared with regularly sampled FD maps based on their signal‐to‐noise ratio (SNR). Results Volunteers and patients showed statistically significant increases of SNR in frequency‐adapted NUFD results compared to regularly sampled FD results. For ventilation data, the mean SNR increased by 43.4%±25.3% and 24.4%±31.9% in volunteers and patients, respectively; for perfusion data, SNR increased by 93.0%±36.1% and 75.6%±62.8%. Two patients showed perfusion signal in pulmonary areas with NUFD that could not be imaged with FD. Conclusion This study demonstrates that using nonuniform Fourier transform in combination with frequency tracking can significantly increase SNR and reduce frequency overlaps by collecting the signal intensity onto single frequency bins.

Analysis of different image-registration algorithms for Fourier decomposition MRI in functional lung imaging

“…Various image registration algorithms for pulmonary FD-MRI have been described in the existing literature (2,3,9,11,12,14,19,28). In the current study, the performance of three different image-registration algorithms for FD-MRI was analyzed.…”

“…The settings used in the present study were: number of iterations per pyramid level = 16, 16, 8, 8; strength of regularization = 6.0. Employment of this program for image registration in pulmonary FD-MRI has been frequently described in the literature (2,3,7–9).…”

Repeatability of dynamic 3D phase‐resolved functional lung (PREFUL) ventilation MR Imaging in patients with chronic obstructive pulmonary disease and healthy volunteers

“…In recent years, extensive development of FD MRI has included improving spatial/temporal resolution, sequence design and postprocessing, and developing a whole-lung technique. [13][14][15][16][17][18][19] Two-dimensional phase-resolved functional lung (PREFUL) MRI 15 is an FD-based technique that was introduced to assess regional ventilation and perfusion dynamics within a single acquisition. Repeatability and validation studies of 2D PREFUL to reference standards have been performed to facilitate the use of 2D PREFUL in clinical routine.…”

Proton MRI of the Lung: How to Tame Scarce Protons and Fast Signal Decay

“…Although respiratory and cardiac frequencies are not stationary and can lead to low repeatability or SNR, different methods were developed to achieve a more robust postprocessing algorithm, including: 1) wavelet decomposition 58,59 and nonuniform Fourier decomposition, 60 which can account for temporal changes in frequency; 2) adapted filter design and/or gated amplitude calculation 51,61 ; 3) an optimized registration to account for large deformation steps 51 ; 4) matrix pencil decomposition for more accurate amplitude calculation 62 …”