Clinical 1H magnetic resonance spectroscopy of brain metastases at 1.5T and 3T

To investigate whether improvements in signal-to-noise ratio (SNR) and spectral resolution are found in spectra from patients with brain metastases obtained at higher magnetic field strengths using standard clinical instrumentation.

Six patients with brain metastases, 13 healthy volunteers, and a phantom containing brain metabolites were examined using two clinical MR instruments operating at 1.5T (Siemens) and 3T (Philips) with standard clinical head coils. Spectra were obtained using a point resolved spectroscopy pulse sequence, echo times (TE) 32 ms and 144 ms, and repetition time 2000 ms from a volume-of-interest (VOI) of size 15 x 15 x 15 mm3. SNR and spectral resolution of the metabolites N-acetylaspartate, choline, and creatine compounds in spectra from 3T were compared to the 1.5T spectra.

In general, spectral resolution was improved by 25-30% at higher magnetic field strength. Only minor improvements in SNR were obtained at 3T using short echo time and 20-50% at long echo time.

SNR and spectral resolution were improved at higher magnetic field strength, especially with TE 144 ms, including spectra from patients with heterogeneous brain tumors. However, differences in the defined effective VOI, particularly at short echo time, reduced the expected effect of increased magnetic field strength on the measured SNR.