SU-E-I-65: Magnetic Resonance Spectroscopy of the Prostate: A Phantom Study of Metabolite Concentrations.

PURPOSE Magnetic Resonance Spectroscopy (MRS) of the prostate is not used in radiotherapy departments on a regular basis due to a number of issues. The indication and severity of prostate cancer is related to the presence of choline in the prostate, in particular, the ratio of choline (plus creatine) to citrate. In-vivo data supports this theory only marginally but lacks strong correlation with biopsy data. The situation is further complicated by the lack of precise spatial information in biopsy, variation of magnetic susceptibility, and spatial dependence of MRS data on the distance from the endo-rectal coil. The latter also cause low signal-to-noise ratio (SNR). We intend to understand how the level of metabolite concentrations and spatial dependences determine what is observed in MRS. METHODS A spherical phantom is filled with water solutions containing various amounts of metabolites. It is placed on top of an endo-rectal coil with the balloon filled with per fluorocarbon. MRS data is acquired on a GE 1.5 T MR scanner. The metabolite values, their ratios etc as reported in GE software, FuncTool are studied as functions of metabolite concentrations in the phantom. RESULTS Analysis of the phantom data indicates that the metabolite ratio reported in FuncTool is approximately linearly correlated to the metabolite concentrations used in the phantom to a certain point and then saturates whereas the largest metabolite value is well correlated with its concentration in the phantom. All metabolite values become weaker and SNR lower as we move away from the coil. CONCLUSIONS This work indicates the potential of using metabolite values directly provided their spatial dependences on the distance of the voxels from the endo-rectal coil can be accommodated.