Widespread use of ultra-high field ³¹P MRSI in clinical studies is hindered by limited field of view and non-uniform RF field obtained from mostly surface transceivers. The non-uniform RF field necessitates the use of high SAR demanding adiabatic RF pulses, limiting SNR per unit of time. Here we demonstrate the feasibility of using a body size volume RF coil at 7T, which enables uniform excitation and ultra-fast power calibration by pick-up (PU) probes. Performance of the body coil is examined by benchmark tests, and phantom and in vivo measurements. Accuracy of power calibration with PU Probes is analyzed at a clinical 3T MR system with a close to identical (¹H) body coil integrated at the MR system. Finally, we demonstrate full 3D ³¹P MRSI that can be obtained in single breath holds of the human body at 7T or averaged over 5 minutes of acquisition resulting in excellent spectra that includes sub-second RF power calibration.A birdcage coil¹ was constructed with 52 cm inner diameter (121 MHz), sharing the RF shield of the integrated patient tube of a 7T MR system (Philips). Performance was analyzed by transmission (S21) measurements with and without presence of 8 ¹H RF elements on 5 volunteers at different loading positions. Accuracy of RF-power calibration by PU probes is compared to the automatic RF-power adjustment (PO) of a 3T MR system (Philips) with the integrated ¹H body coil (128 MHz) on 5 volunteers including B₁⁺ maps obtained from heart and liver. At 7T, PU probes were calibrated using B₁⁺ maps in phantoms and validated with multi flip-angle CSI in a volunteer. A 3D CSI (block) pulse-acquire sequence was acquired at 7T with T_R = 0.5 s, with a total acquisition time of 4:16 min (FOV=32x32x32 cm³, 8x8x8 acquired resolution, zero-filled to 16x16x8). The sequence was accelerated using EPSI, to facilitate 3D acquisition within a single breath-hold.RF coupling to ¹H elements is low (average 0.3 dB). STD in S21 is 0.6 dB in both bladder and heart loading position (Fig. 1). Difference in PU vs. PO is 0.65 dB (bladder) and 0.17 dB (heart) (Fig. 1). Calibrating PU at 7T (Fig. 2, left) gave a B₁⁺ of 15 µT in the phantom and 10 µT in the body (Fig. 2, middle) when driven with 3700 W. RF-power adjustments based on pick-up probes took less than 1s. Using Ernst-angle excitation of 30 degrees, full bandwidth ³¹P MRSI at 7T could be obtained with the limited RF power of 4 kW. Apart from a subtle N/2 spectral ghost, even full bandwidth (30 ppm ) EPSI could be obtained enabling whole body MRSI within a single breath-hold (Fig. 2, right). Fig. 3 shows MRSI data with characteristic ³¹P spectra of the liver and heart including all phosphorus metabolites. In the liver, all the ATP peaks are present but there is no PCr while the PDEs and PMEs are present. In the (zoomed in) voxel of the heart (yellow), the energy metabolism ³¹P metabolites PCr, γ-ATP, α-ATP are all visible and PCr/ATP-ratio is ~2. The spectrum of the heart contains DPG, which results from signal from blood. Notice the homogeneity in SNR along ATP peaks in the voxels of the liver which is weighted by both transmission (B₁⁺) as well as receive (B₁^-) homogeneity of the body coil due to (block) pulse-acquire acquisition. Moreover their relatively high signal intensities versus PME and PDE is caused by substantial T₁ weighting, demonstrating the high flip angle during the scan.We showed the performance of a RF body coil for ³¹P MRSI at 7T. The in vivo MRSI data represent the homogeneity and efficiency of the RF field for multiple voxels of the heart and liver. In contrast to SAR demanding adiabatic RF pulses with limited bandwidth, we could use simple RF pulses at Ernst angle that not only maximizes SNR per unit of time at low SAR, but also facilitates full bandwidth excitation for ³¹P MRSI at 7T. The required power optimization can be obtained within 0.6 dB of accuracy in less than 1 s. Though SNR is expected to increase even further with local receiver coils and optimized sequences, we have demonstrated that an integrated ³¹P body coil can facilitate body MRSI at acceptable scan times and fast power optimization.