Haoyang Xing PhD, Presenter: Nothing to Disclose

Hao Shen PhD, Abstract Co-Author: Nothing to Disclose

Hehan Tang BS, Abstract Co-Author: Nothing to Disclose

Qi-Yong Gong MD, PhD, Abstract Co-Author: Nothing to Disclose

Xiaohong Joe Zhou PhD, Abstract Co-Author: Nothing to Disclose

To demonstrate that spectrally selective 2D multi-slice phosphorous (31P) MRI can be achieved using a tailored spatial-spectral (SPSP) radiofrequency (RF) pulse on a human scanner at 3 Tesla. 

Despite its high time-efficiency, 2D multi-slice 31P MRI on a specific metabolite has been difficult due to the need to simultaneously perform spatial and spectral selection. To address this problem, a 2D SPSP RF pulse was designed to achieve spatial localization in one dimension and phosphorous spectral selection in the other. The pulse consisted of 24 sub-pulses, each designed using a Shinnar Le-Roux algorithm with a pulse width of 0.584 ms. All sub-pulses were placed under a spectrally-selective RF pulse envelope with a minimal phase and a time-bandwidth product of 2. On the ramps of the slice-selection gradient, a VERSE technique was used to reduce the minimal TE and improve the pulse performance. After extensive computer simulations to optimize the spatial and spectral responses, the SPSP pulse was implemented in a 2D gradient-echo sequence on a commercial 3T scanner. Experiments were conducted on a 6 cm spherical phantom containing phosphorous compounds (Na2HPO4, etc.) using a 7 inch surface coil tuned to 51.7 MHz. The TR/TE  was 2500/15 ms and voxel size was 140 mm3.

Computer simulations confirmed that the SPSP pulse produced an effective spectral bandwidth of 150 Hz, suitable for selective PCr imaging. The remaining major phosphorous metabolites were placed at true nulls or opposed nulls. The pass-band transition width was ~100 Hz. The 31P images (SNR ~ 12) were artifact-free and clearly showed the shape of the object as well as shading introduced by the surface coil sensitivity profile.

Using a custom-designed and optimized SPSP pulse, 2D multi-slice phosphorous imaging with good spectral selectivity and spatial localization has been demonstrated on a human scanner at 3T. This technique has considerably improved data acquisition efficiency as compared to spectroscopic imaging or 3D spectrally selective imaging techniques. With further improvements in SNR, low-resolution (e.g., 16x16) phosphorous MRI based on a specific metabolite is feasible on human subjects at 3T.

MRI based on specific phosphorous metabolites can have profound applications in understanding the metabolic and physiologic processes in disease progression, intervention, and regression.

Xing, H, Shen, H, Tang, H, Gong, Q, Zhou, X, Spectrally Selective ³¹P MR Imaging at 3 Tesla.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8006835.html