Development of high resolution 3D hyperpolarized carbon-13 MR molecular imaging techniques

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Hyperpolarized Carbon-13 (¹³C) Spectroscopy
• Medical Physics

Background:

• Hyperpolarized (HP) probes offer enhanced sensitivity for in vivo metabolic imaging.
• High-resolution imaging is crucial for detailed anatomical and functional assessments.
• Optimizing imaging sequences for HP ¹³C probes is essential for maximizing signal-to-noise ratio (SNR) and temporal resolution.

Purpose of the Study:

• To develop and apply techniques for T₂ mapping and 3D high-resolution (1.5mm isotropic) ¹³C imaging of various HP probes in vivo.
• To obtain the first high-resolution T₂ maps of HP compounds in rats and tumor-bearing mice.
• To extend 3D imaging to serial dynamic acquisitions with compressed sensing for improved temporal resolution.

Main Methods:

• Implementation of a specialized 2D balanced Steady-State Free Precession (bSSFP) sequence on a clinical 3T scanner.
• Acquisition of T₂ maps for [1-¹³C]lactate, [1-¹³C]pyruvate, [2-¹³C]pyruvate, and [¹³C,¹⁵N₂]urea in rats and tumor-bearing mice.
• Optimization of imaging parameters using T₂ maps for single time-point 3D bSSFP acquisitions and serial dynamic imaging with compressed sensing.

Main Results:

• High-resolution T₂ maps revealed T₂ values >1s for most HP compounds in rat kidneys/vasculature and TRAMP tumors, with [2-¹³C]pyruvate showing shorter T₂ values.
• 3D imaging successfully visualized the biodistribution of HP [1-¹³C]lactate, [1-¹³C]pyruvate, and [2-¹³C]pyruvate within different kidney compartments and vasculature.
• The developed 3D sequence with compressed sensing achieved 1.5mm isotropic spatial resolution and 2s temporal resolution, comparable to ¹H imaging.

Conclusions:

• The specialized 3D bSSFP sequence enables high-resolution, high-SNR in vivo imaging of HP ¹³C substrates by leveraging their long T₂ values.
• This approach provides improved structural and functional assessments, visualizing biodistribution and potentially metabolism and perfusion.
• The technique holds promise for future studies in cancer and other disease models, with potential clinical applications.