Fast and High-Resolution T2 Mapping Based on Echo Merging Plus k-t Undersampling with Reduced Refocusing Flip Angles (TEMPURA) as Methods for Human Renal MRI

Hao Li; Andrew N Priest; Ines Horvat-Menih; Yuan Huang; Shaohang Li; Grant D Stewart; Iosif A Mendichovszky; Susan T Francis; Ferdia A Gallagher

doi:10.1002/mrm.30115

Fast and High-Resolution T₂ Mapping Based on Echo Merging Plus k-t Undersampling with Reduced Refocusing Flip Angles (TEMPURA) as Methods for Human Renal MRI

Magn Reson Med. 2024 May 10. doi: 10.1002/mrm.30115. Online ahead of print.

Authors

Hao Li^{1

2}, Andrew N Priest^{2

3}, Ines Horvat-Menih², Yuan Huang^{2

4}, Shaohang Li¹, Grant D Stewart⁵, Iosif A Mendichovszky^{2

3}, Susan T Francis⁶, Ferdia A Gallagher^{2

3}

Affiliations

¹ Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China.
² Department of Radiology, University of Cambridge, Cambridge, UK.
³ Department of Radiology, Cambridge University Hospitals NHS Foundation Trust, Addenbrooke's Hospital, Cambridge, UK.
⁴ EPSRC Cambridge Mathematics of Information in Healthcare Hub, University of Cambridge, Cambridge, UK.
⁵ Department of Surgery, Cambridge University Hospitals NHS Foundation Trust, Addenbrooke's Hospital, Cambridge, UK.
⁶ Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, UK.

PMID: 38730565
DOI: 10.1002/mrm.30115

Abstract

Purpose: To develop a highly accelerated multi-echo spin-echo method, TEMPURA, for reducing the acquisition time and/or increasing spatial resolution for kidney T₂ mapping.

Methods: TEMPURA merges several adjacent echoes into one k-space by either combining independent echoes or sharing one echo between k-spaces. The combined k-space is reconstructed based on compressed sensing theory. Reduced flip angles are used for the refocusing pulses, and the extended phase graph algorithm is used to correct the effects of indirect echoes. Two sequences were developed: a fast breath-hold sequence; and a high-resolution sequence. The performance was evaluated prospectively on a phantom, 16 healthy subjects, and two patients with different types of renal tumors.

Results: The fast TEMPURA method reduced the acquisition time from 3-5 min to one breath-hold (18 s). Phantom measurements showed that fast TEMPURA had a mean absolute percentage error (MAPE) of 8.2%, which was comparable to a standardized respiratory-triggered sequence (7.4%), but much lower than a sequence accelerated by purely k-t undersampling (21.8%). High-resolution TEMPURA reduced the in-plane voxel size from 3 × 3 to 1 × 1 mm², resulting in improved visualization of the detailed anatomical structure. In vivo T₂ measurements demonstrated good agreement (fast: MAPE = 1.3%-2.5%; high-resolution: MAPE = 2.8%-3.3%) and high correlation coefficients (fast: R = 0.85-0.98; high-resolution: 0.82-0.96) with the standardized method, outperforming k-t undersampling alone (MAPE = 3.3-4.5%, R = 0.57-0.59).

Conclusion: TEMPURA provides fast and high-resolution renal T₂ measurements. It has the potential to improve clinical throughput and delineate intratumoral heterogeneity and tissue habitats at unprecedented spatial resolution.

Keywords: T2 mapping; compressed sensing; imaging acceleration; kidney; multi‐echo spin‐echo; quantitative MRI.

Abstract

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