Enhanced in-vivo C13 spectroscopy using adiabatic INEPT sequences and custom-made RF coils

Introduction: C spectroscopy offers several advantages compared to H MRS, including increased spectral dispersion, and eliminates the need for water suppression, though it suffers from inherently low sensitivity. In addition, C spectroscopy is important from a physiological point of view because it offers the ability to measure metabolic fluxes such as those of the TCA cycle [1]. In this abstract, we report results obtained with a high-quality custom-made RF coil and optimized sequences including INEPT [2] (with square pulses) and adiabatic INEPT with BIR-4 pulses (BINEPT) [3, 4]. Materials and Methods: All experiments were performed on a 9.4 T horizontal bore (20 cm) animal scanner. We employed a high-quality custom-made RF probe, custom made by the third author, with an inner solenoid for C detection and an outer saddle for H detection. To increase C signal we employed INEPT [2] and adiabatic INEPT with BIR-4 pulses [3, 4]. BIR-4 pulses of 400 μs having maximum amplitude of 16 kHz and 4 kHz for C and H, respectively, were synthesized on a Bruker Avance console. The intra and inter-pulse delays were set according to the C-H scalar coupling of acetate (130 Hz). Both BINEPT with direct C detection and double BINEPT for indirect C detection via 1H were designed and tested. H decoupling with adiabatic WALTZ-16 sequence was employed during acquisition. Results: In phantoms our BINEPT sequence (Figure 1) resulted in increased sensitivity by a factor of 2.8 for C, when compared with direct excitation following a 90° pulse (Figures 2 and 3a). Similar results were obtained in vivo on a mouse (natural-abundance C spectra shown in Figure 3b). The optimized BINEPT sequence showed significant signal increase over INEPT and direct excitation (H decoupled). The BINEPT sequence also acted as a spectral editing sequence suppressing the carbons that do not have a direct proton attached, such as COOH (Figures 2b and 3b).