Proton MR spectroscopy of the brain at 3 T: an update

European Radiology, Jul 2007

Proton magnetic resonance spectroscopy (1H-MRS) provides specific metabolic information not otherwise observable by any other imaging method. 1H-MRS of the brain at 3 T is a new tool in the modern neuroradiological armamentarium whose main advantages, with respect to the well-established and technologically advanced 1.5-T 1H-MRS, include a higher signal-to-noise ratio, with a consequent increase in spatial and temporal resolutions, and better spectral resolution. These advantages allow the acquisition of higher quality and more easily quantifiable spectra in smaller voxels and/or in shorter times, and increase the sensitivity in metabolite detection. However, these advantages may be hampered by intrinsic field-dependent technical issues, such as decreased T2 signal, chemical shift dispersion errors, J-modulation anomalies, increased magnetic susceptibility, eddy current artifacts, challenges in designing and obtaining appropriate radiofrequency coils, magnetic field instability and safety hazards. All these limitations have been tackled by manufacturers and researchers and have received one or more solutions. Furthermore, advanced 1H-MRS techniques, such as specific spectral editing, fast 1H-MRS imaging and diffusion tensor 1H-MRS imaging, have been successfully implemented at 3 T. However, easier and more robust implementations of these techniques are still needed before they can become more widely used and undertake most of the clinical and research 1H-MRS applications.

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Proton MR spectroscopy of the brain at 3 T: an update

Eur Radiol Proton MR spectroscopy of the brain at 3 T: an update 0 T. Schirmer GE Healthcare, Applied Science Laboratory , Munich , Germany 1 M. Tosetti Magnetic Resonance Laboratory, Scientific Institute “Stella Maris” , Pisa , Italy 2 F. Trojsi Department of Neurological Sciences, Second University of Naples , Naples , Italy 3 S. M. Lechner GE Global Research , Munich , Germany Proton magnetic resonance spectroscopy (1H-MRS) provides specific metabolic information not otherwise observable by any other imaging method. 1H-MRS of the brain at 3 T is a new tool in the modern neuroradiological armamentarium whose main advantages, with respect to the well-established and technologically advanced 1.5-T 1H-MRS, include a higher signal-to-noise ratio, with a consequent increase in spatial and temporal resolutions, and better spectral resolution. These advantages allow the acquisition of higher quality and more easily quantifiable spectra in smaller voxels and/or in shorter times, and increase the sensitivity in metabolite detection. However, these advantages may be hampered by Magnetic resonance spectroscopy; Brain; Diagnostic imaging - intrinsic field-dependent technical issues, such as decreased T2 signal, chemical shift dispersion errors, J-modulation anomalies, increased magnetic susceptibility, eddy current artifacts, challenges in designing and obtaining appropriate radiofrequency coils, magnetic field instability and safety hazards. All these limitations have been tackled by manufacturers and researchers and have received one or more solutions. Furthermore, advanced 1H-MRS techniques, such as specific spectral editing, fast 1H-MRS imaging and diffusion tensor 1H-MRS imaging, have been successfully implemented at 3 T. However, easier and more robust implementations of these techniques are still needed before they can become more widely used and undertake most of the clinical and research 1H-MRS applications. disorders. The list is very long and includes brain tumors, degenerative diseases such as Alzheimer’s, Huntington’s and Parkinson’s diseases, cerebrovascular diseases, metabolic disorders such as adrenoleukodystrophy and Canavan’s disease, epilepsy, multiple sclerosis and systemic diseases such as hepatic and renal failure [1–3]. Rare diseases also studied include creatine deficiency syndrome [7], variant Creutzfeldt-Jakob Disease [8], pantothenate kinase-associated neurodegeneration [9] and Rasmussen’s encephalitis [10]. Most of these studies have been performed using devices operating at 1.5 T, which has been considered the standard field for years. In the last decade, with the approval of the US Food and Drug Administration for clinical use, MR systems at 3 T are proliferating, particularly at research centers [11]. With respect to the well-established MR technique at 1.5 T, switching to a higher field brings several advantages, such as an increased signal-to-noise ratio, with consequent enhanced spatial and temporal resolutions, and better spectral resolution, but also many limitations, such as installation issues, higher acoustic noise, device compatibility, system inhomogeneity, eddy current artifacts, misregistration errors, J-modulation anomalies, magnetic field instability and safety restrictions. Some technical characteristics, such as changes in relaxation times, chemical shift and susceptibility, can have both benefits and disadvantages [11–15]. These limitations necessitating changes in technical devices and acquisition strategies have led to a debate about the usefulness of higher field strength in clinical settings [14–20]. However, the new generation of 3-T systems presents a number of fundamental technical differences with respect to the first generation, which have reduced the concerns about the limitations as well as the benefits of 3-T over 1.5-T systems and increased the penetration of 3-T scanners into the clinical setting [18– 20]. Furthermore, adapting the imaging procedures to changes produced by the higher field allows obtaining images with quality and/or acquisition speed superior to 1.5 T [21, 22]. A number of recent studies have evidenced the advantages of 3 T over 1.5 T for both conventional MRI and MR applications limited by insufficient sensitivity, such as MR angiography, functional MRI and 1H-MRS [19, 20, 23, 24]. This review focuses on brain 1H-MRS at 3 T, illustrating the advantages, the strategies to overcome the limitations and the advanced techniques. Advantages and disadvantages of 1H-MRS at 3 T Signal-to-noise ratio The intensity of the MR signal is correlated linearly with the strength of the static magnetic field. Thus, in theory, the signal-to-noise ratio (SNR) would double when moving from 1.5 T to 3 T, but in practice the improvement ranges only from 20% to 50% [25–28]. In effect, the SNR depends on several other variables, such as T1 and T2 relaxation times, type of sequence, number of signal averages, size of sample volume, radiofrequency (RF) ef (...truncated)


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Alfonso Di Costanzo, Francesca Trojsi, Michela Tosetti, Timo Schirmer, Silke M. Lechner, Teresa Popolizio, Tommaso Scarabino. Proton MR spectroscopy of the brain at 3 T: an update, European Radiology, 2007, pp. 1651-1662, Volume 17, Issue 7, DOI: 10.1007/s00330-006-0546-1