MEGA-SPECIAL (MSpc) is a magnetic resonance spectroscopy (MRS) sequence comprising of longer frequency selective editing pulses, allowing γ-Aminobutyric acid (GABA) acquisition without macromolecules (MM) at TE of 68 ms^(1,2). Unlike the ubiquitous MEGA-PRESS sequence⁽³⁾, MSpc requires four acquisitions per localized edited spectrum, rendering it more sensitive to subject motion and magnetic field (B₀) inhomogeneity. Moreover, the MM-suppression technique is highly dependent on B₀ field stability, necessitating real-time frequency update to ensure frequency selective pulses are applied consistently at the resonance of 1.7 ppm⁽¹⁾. The aim of this work is to measure and correct simultaneously in real-time for head position and magnetic field inhomogeneity in terms of zero and first order shim gradients using volumetric navigators (vNav)⁽⁴⁾. A pair of 3D multishot EPI vNav was added to the standard MSpc sequence (vNavMSpc). Motion parameters were estimated from the magnitude images of vNav, while shim parameters were measured from EPI field map, which was reconstructed from magnitude and phase images of vNav. The MSpc sequence receives in real time these parameters to update for subject motion and B₀ distortion to all pulses including the localization, MEGA-editing, OVS and VAPOR pulses⁽¹⁾. All scans were performed on a Siemens Allegra 3T scanner. Three subjects were scanned with the vNavMSpc sequence as follows: i) Reference (no intentional motion) with no correction (NoCo), ii) Reference with shim and motion correction (ShMoCo), iii) intentional motion with ShMoCo, and iv) intentional motion with NoCo. The vNav protocol was as follows: 3D encoded EPI, 32 x 32 x 28, flip angle 2°, TR 16 ms, TE 6.6/9 ms. The vNavMSpc parameters were: (3 cm)³ voxel positioned in a mid-parietal, 2048 points, bandwidth 2kHz, 148 averages and TR/TE 4000/68 ms. GABA was acquired without MM contamination. The duration of every scan was 10 minutes 8 seconds. The motion involved chin up-down and chin left-right rotations of about 5°­, which also resulted in translations of about 4 mm (Figure 1). After every data acquisition involving motion, subjects were instructed to return to their original positions. All data were processed using the Gannet toolkit⁽⁵⁾. Residual fitting error (FitErr) and GABA/Cr concentration – measured by Gannet – were compared between data acquired in the absence and presence of intentional motion.Figure 2 shows spectra from the four different acquisitions of one subject. The edited spectra from the NoCo and ShMoCo reference scans have comparable and excellent spectral quality. Motion caused extreme frequency drifts, which led to overestimated GABA amplitude (arrow A in Fig 2) and insufficient suppression of the NAA peak (arrow B in Fig 2) of the edit-on spectrum. The NoCo motion scans show increases in all parameters (FitErr: 15.22 ± 2.43; GABA/Cr: 0.22 ± 0.17), while ShMoCo recovers the data yielding estimates similar to the reference scans (FitErr: 9.98 ± 1.92; GABA/Cr: 0.037 ± 0.01). Head pose and shim estimates were estimated in each TR using the vNav and if any motion was detected, the correction was applied in the following TR. The NoCo scans during motion led to lower spectral quality and overestimated GABA/Cr concentrations. The ShMoCo scans effectively reduced the artefacts and acquired well edited GABA peaks. The ubiquitous technique for correction is retrospective frequency and phase correction⁽⁶⁾. Although this method reduces subtraction artefacts, localization errors remain uncorrected and corrupted signal arising from poor shimming cannot be corrected retrospectively. Keating et al.⁽⁷⁾ implemented PROMO and a navigator as an efficient alternative method to simultaneously correct in real-time for subject motion and B₀ inhomogeneity. However, this technique requires cameras and a mouthpiece affixed to the subject, necessitating subject compliance. Real-time motion and shim correction have been applied in MRSI MEGA-LASER sequence for GABA+MM acquisition using volumetric navigators⁽⁸⁾. Our implementation involves MM-suppression technique, demanding stronger B₀ stability, which can be impaired by the presence of motion especially when using motion sensitive MSpc sequence. There are no direct comparisons between MEGA-LASER or MEGA-sLASER and MSpc sequences, but when referenced to MEGA-PRESS⁽³⁾, MEGA-LASER and MEGA-sLASER demonstrate lower spatial variations, are less sensitive to motion and yield more GABA signal than MSpc^(1,8-9). This suggests that the real-time motion and shim correction is a necessity for MSpc sequence to ensure proper C4-GABA acquisition. The vNav performed accurate motion and shim correction in real-time without increasing the scan time and resulted in well edited GABA spectra. This technique can greatly benefit GABA MRS, which is challenging due to low signal often necessitating long acquisition times.