Single voxel (SV) localization for hyperpolarized ¹³C MRS acquisition is uncommon and difficult because the non-equilibrium magnetization can be easily saturated by the transitions of the refocusing pulses or outer volume suppression pulses. Thus for most of the dynamic hyperpolarized ¹³C MRS experiments to date, localization of the data has been accomplished by pulse-acquire method with just small tip selective RF excitation of large slabs through the subject (1). Single voxel localization using a modified PRESS sequence with ‘notch’ spectral-spatial refocusing pulses has been demonstrated recently for dynamic hyperpolarized ¹³C experiments (2). However, the relatively high B₁ and long pulse duration required for notch refocusing pulses that have good spatial and spectral profiles, and hyperpolarized substrates may still be saturated if there are large B₀ inhomogeneities within the coil volume. Spectroscopic Imaging Acquisition Mode (SIAM) was proposed previously to eliminate out of slice artifact for SV MRS acquisitions (3). In this method, spectroscopic data can be localized to the center slice or voxel of the FOV if k-space samples are acquired in the typical pattern for CSI and summed, recovering the single voxel at the center of the FOV. Here, a spiral gradient trajectory is used to acquire 2D k-space and spectroscopic data during a single readout, after a slice selective RF excitation pulse. It is shown that ¹³C MRS data may be localized to a single volume from just one pulse-acquire acquisition using this approach. By confining the net duration of each 2D trajectory to a single dwell period of the spectroscopic readout (see Fig. 1), the raw data sampled during the trajectory / dwell are averaged by the digital filter and the output data represent only the center voxel of the image with no k-space data sorting and reconstruction are required. The proposed sequence can be used practically in the same way as a standard pulse-acquire MRS acquisition for HP ¹³C experiments, but the spectrum from the experiment will be localized to a single 3D voxel. Readout Trajectory Design: The 2D SIAM gradient readout trajectory was designed in MATLAB (MathWorks). A 4-turn constant velocity spiral trajectory was designed for 26 cm FOV and 3.3 cm nominal resolution. The trajectory has max gradient slew rate of 18.6 G/cm/ms and max gradient amplitude of 1.62 G/cm. The gradient was rewound to zero using the bisection method. The total duration of the trajectory and thus the spectral acquisition dwell time was 1.76 ms (568 Hz spectral bandwidth). The trajectory was repeated 72 times for a total readout duration of 126.72 ms. The k-space trajectory, the gradient waveform as well as simulated point-spread-function are shown in Fig. 1. Phantom experiments: The study was performed using a 3T GE MR750 scanner (GE Healthcare) with a dual-tuned ¹H/¹³C birdcage rat coil (GE). A 38 mm OD HDPE sphere filled with 1.0 M ¹³C bicarbonate solution and an 18 mm OD sphere filled with 8.0 M ¹³C urea solution were used in the phantom experiments. MR spectroscopy experiments were performed using a slice selective pulse-acquire pulse sequence with and without the 2D SIAM readout trajectory (from a 1.5 cm slab through both phantoms, flip angle = 10°, 32 averages, TR = 2 s, 568 Hz / 72 pts readout). The FOV was centered on the 13C bicarbonate sphere. Data from ¹³C phantoms acquired with a pulse-acquire pulse sequence with and without the SIAM gradients applied are shown in Fig. 2. Without the readout gradients (Fig. 2, center), no in-plane spatial localization was performed and ¹³C bicarbonate and ¹³C urea have similar signal intensities in the spectrum. With the SIAM spiral readout trajectory (Fig. 2, right), the signal from the urea phantom that is away from the center of the FOV was significantly reduced. The ¹³C urea / ¹³C bicarbonate signal ratio reduced by 89% with the readout gradient as compared to without; and this suppression of the outer volume signal (¹³C urea) is similar to what was predicted by the PSF of the spiral trajectory (the ripples were 10% of the maximum intensity). Since the spiral trajectory was rewound and placed inside each dwell, no k-space gridding and spatial reconstruction was necessary and the time domain data from the scanner was simply Fourier transformed to obtain the in-plane localized spectrum. Non-spiral trajectories would work similarly and may provide different tradeoffs between localization (PSF) and spectral bandwidth (duration of the trajectory), as long as the trajectory starts and ends at k=0 and the k-space density is roughly uniform. Conclusions: A method for single volume dynamic hyperpolarized ¹³C MRS acquisition was demonstrated using a simple slice selective pulse-acquire pulse sequence with 2D SIAM spiral readout. This technique enables acquisition of dynamic ¹³C MRS data from a single voxel within the tissue / organ of interest.