Translation of Carbon‐13 EPI for hyperpolarized MR molecular imaging of prostate and brain cancer patients

Abstract

Purpose To develop and translate a metabolite‐specific imaging sequence using a symmetric echo planar readout for clinical hyperpolarized (HP) Carbon‐13 (13C) applications. Methods Initial data were acquired from patients with prostate cancer (N = 3) and high‐grade brain tumors (N = 3) on a 3T scanner. Samples of [1‐13C]pyruvate were polarized for at least 2 h using a 5T SPINlab system operating at 0.8 K. Following injection of the HP substrate, pyruvate, lactate, and bicarbonate (for brain studies) were sequentially excited with a singleband spectral‐spatial RF pulse and signal was rapidly encoded with a single‐shot echo planar readout on a slice‐by‐slice basis. Data were acquired dynamically with a temporal resolution of 2 s for prostate studies and 3 s for brain studies. Results High pyruvate signal was seen throughout the prostate and brain, with conversion to lactate being shown across studies, whereas bicarbonate production was also detected in the brain. No Nyquist ghost artifacts or obvious geometric distortion from the echo planar readout were observed. The average error in center frequency was 1.2 ± 17.0 and 4.5 ± 1.4 Hz for prostate and brain studies, respectively, below the threshold for spatial shift because of bulk off‐resonance. Conclusion This study demonstrated the feasibility of symmetric EPI to acquire HP 13C metabolite maps in a clinical setting. As an advance over prior single‐slice dynamic or single time point volumetric spectroscopic imaging approaches, this metabolite‐specific EPI acquisition provided robust whole‐organ coverage for brain and prostate studies while retaining high SNR, spatial resolution, and dynamic temporal resolution.

Hyperpolarized 13C-pyruvate MRI detects real-time metabolic flux in prostate cancer metastases to bone and liver: a clinical feasibility study

“…This study utilized a 2D single-slice imaging strategy. Future advancement in array receiver hardware [42] and MR acquisition sequences [21,43] will enable full 3D coverage of the abdomen/pelvis and seamless integration with standard-of-care restaging scans. Dissemination of this technology, in terms of infrastructure and instruments, requires a clinical 13 C polarizer and specialized MRI hardware.…”

Molecular imaging of the prostate: Comparing total sodium concentration quantification in prostate cancer and normal tissue using dedicated 13C and 23Na endorectal coils

“…Following the intravenous injection of hyperpolarized 13 C-labeled pyruvate, 13 C-labeled lactate and bicarbonate can be imaged in tissue and this has been demonstrated in the normal human brain and heart, as well as in prostate and brain tumors. [15][16][17][18][19][20] In the prostate, lactate has been demonstrated in high-grade tumors, but also in lesions that were occult to conventional imaging and were subsequently shown to represent low-tointermediate grade tumor on biopsy. 15 There is also preliminary evidence to show that lactate may decrease following response to treatment following androgen deprivation therapy.…”

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

“…Flip angles shown in Table 1 were chosen based on previous studies. 31 A flip angle of 20 • was large enough to see pyruvate signals at a reasonable spatial resolution. A flip angle of 30 • for lactate and alanine imaging aimed to maintain sufficient SNR for multiple time points.…”