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

PURPOSE: 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. MATERIAL AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Development of an ombrotrophic peat bog (low ash) reference material for the determination of elemental concentrations.

Given the increasing interest in using peat bogs as archives of atmospheric metal deposition, the lack of validated sample preparation methods and suitable certified reference materials has hindered not only the quality assurance of the generated analytical data but also the interpretation and comparison of peat core metal profiles from different laboratories in the international community. Reference materials play an important role in the evaluation of the accuracy of analytical results and are essential parts of good laboratory practice. An ombrotrophic peat bog reference material has been developed by 14 laboratories from nine countries in an inter-laboratory comparison between February and October 2002. The material has been characterised for both acid-extractable and total concentrations of a range of elements, including Al, As, Ca, Cd, Cr, Cu, Fe, Hg, Mg, Mn, Na, Ni, P, Pb, Ti, V and Zn. The steps involved in the production of the reference material (i.e. collection and preparation, homogeneity and stability studies, and certification) are described in detail.

Temporal and spatial trends in Hg deposition monitored by moss analysis.

Results for Hg from a nation-wide survey of atmospheric deposition of heavy metals in Norway in 2000 are presented and compared to similar results from 1985, 1990 and 1995. The study is based on sampling of the naturally growing feather moss Hylocomium splendens at approximately 500 sites all over the country. Cold vapor AAS (1985, 1990) or atomic fluorescence spectrometry (1995, 2000) was used for Hg determinations after HNO(3) digestion of the moss samples. As different from the wet deposition of Hg and several other heavy metals in Norway the Hg concentration in moss shows no significant north-south gradient. This is explained by a considerable supply of Hg to the moss from dry deposition of Hg(0) in addition to the retention of Hg(2+) from wet deposition. Presumably the cool summer climate particularly in the middle and northern parts of the country explains that some of the Hg(0) retained in the moss is not lost by re-volatilisation. Whereas the level and geographic distribution of Hg in moss showed only small differences during 1985-1995 the 2000 data are approximately 30% lower. A satisfactory explanation of this difference remains to be found.