A metabolite‐specific 3D stack‐of‐spiral bSSFP sequence for improved lactate imaging in hyperpolarized [1‐¹³C]pyruvate studies on a 3T clinical scanner

Abstract

Purpose:The balanced steady-state free precession sequence has been previously explored to improve the efficient use of nonrecoverable hyperpolarized 13 C magnetization, but suffers from poor spectral selectivity and long acquisition time.The purpose of this study was to develop a novel metabolite-specific 3D bSSFP ("MS-3DSSFP") sequence with stack-of-spiral readouts for improved lactate imaging in hyperpolarized [1-13 C]pyruvate studies on a clinical 3T scanner. Methods: Simulations were performed to evaluate the spectral response of the MS-3DSSFP sequence. Thermal 13 C phantom experiments were performed to validate the MS-3DSSFP sequence. In vivo hyperpolarized [1-13 C], pyruvate studies were performed to compare the MS-3DSSFP sequence with metabolite-specific gradient echo ("MS-GRE") sequences for lactate imaging. Results: Simulations, phantom, and in vivo studies demonstrate that the MS-3DSSFP sequence achieved spectrally selective excitation on lactate while minimally perturbing other metabolites. Compared with MS-GRE sequences, the MS-3DSSFP sequence showed approximately a 2.5-fold SNR improvement for lactate imaging in rat kidneys, prostate tumors in a mouse model, and human kidneys. Conclusions: Improved lactate imaging using the MS-3DSSFP sequence in hyperpolarized [1-13 C]pyruvate studies was demonstrated in animals and humans. The MS-3DSSFP sequence could be applied for other clinical applications such as in the brain or adapted for imaging other metabolites such as pyruvate and bicarbonate. K E Y W O R D S13 C, bSSFP, hyperpolarized, lactate, metabolic imaging, MRI, pyruvate 1114 | TANG eT Al.

Metabolic imaging with hyperpolarized 13C pyruvate magnetic resonance imaging in patients with renal tumors—Initial experience

“…In our study, a sufficient metabolite SNR was obtained in both AUC and dynamic images for pyruvate and lactate at a resolution of 1.5 × 1.5 × 2.1 cm. Use of the metabolite‐specific bSSFP sequence 36 enabled a 2.3‐fold SNR improvement in lactate compared with the GRE sequence. The bSSFP sequence may be applied in future studies to other lower signal metabolites, such as alanine and bicarbonate, to improve their SNR.…”

“…For future studies, voxel shifting can be performed to achieve the maximum number of voxels that are entirely within the tumor. As discussed above, recent development in acquisition and coil combination strategies has enabled improved resolution 36,38 . Because HP 13 C MRI is rapidly improving, it is anticipated that a further improvement in resolution can be achieved for future studies.…”

“…13 C pyruvate and 13 C lactate images through the kidney and tumor were acquired dynamically using a metabolite‐specific imaging sequence comprised of spectral‐spatial excitation and multislice, 2‐dimensional, spiral gradient echo (GRE) readouts, 34 with a Helmholz pair clamshell transmit coil around the torso and an 8‐channel receive array consisting of 2 paddles placed posterior to the kidneys 35 . For 4 patients, a metabolite‐specific, balanced steady‐state free precession (MS‐bSSFP) sequence, which has been shown to provide approximately 2.5‐fold increases in metabolite signal, 36 was used to acquire 13 C lactate images. 13 C alanine images were also acquired in 6 patients.…”

Cardiac measurement of hyperpolarized 13C metabolites using metabolite‐selective multi‐echo spiral imaging

“…Because HP pyruvate is utilized to study metabolism in various in vivo applications, 30‐32 s of HP 13 C metabolites in other organs and tissue types will be beneficial for establishing optimized k‐space sampling patterns. In particular, large variation of magnetic susceptibility is expected in pathological states such as glioblastoma 33 due to blood depositions and calcifications, leading to potential underestimation of HP signals.…”

Clinical translation of hyperpolarized13C pyruvate and urea MRI for simultaneous metabolic and perfusion imaging

“…Dynamic MR images of pyruvate, alanine, lactate, and urea were acquired with volumetric coverage of the rat’s body. Pyruvate, lactate, and alanine images were acquired using a metabolite‐selective spiral gradient echo (GRE) sequence as previously reported, 25 with the following design parameters: 80 Hz RF pulse passband, 25.17 ms pulse length, 22 ms readout duration, and 88 ms repetition time (TR). Urea images were acquired using a balanced steady state free precession (bSSFP) sequence, with a non‐spatially selective RF pulse with a 40 Hz passband and stopband, a 6 ms pulse length, and a 12.26 ms TR.…”