Future Methods in Tumor Imaging

U. Pilatus (*)

Department of Neuroradiology, Goethe University Frankfurt, Schleusenweg 2-16, Frankfurt 60528, Germany

e-mail: u.pilatus@em.uni-frankfurt.de

E. Hattingen

Neuroradiology, Clinic of Rheinische Friedrich-Wilhelms- University, Sigmund-Freud Stra§e 6, 53127 Bonn, Germany e-mail: elke.hattingen@ukb.uni-bonn.de

E. Hattingen, U. Pilatus (eds.), Brain Tumor Imaging, Med Radiol Diagn Imaging (2016),

DOI 10.1007/174_2016_1055, © Springer Berlin Heidelberg

Abbreviations

1Special Editing Methods in 1H MRS

In Chap. MR Spectroscopic Imaging, spectroscopic methods were described which provide biochemical information. In addition to the easily detectable main metabolites (creatine,

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choline, tNAA), other compounds can be detected using more sophisticated technique markers, which may serve as biomarkers for speciÞc questions in tumor diagnosis. These are glycine and 2-hydroxyglutarate (2-HG), which require nonstandard techniques like speciÞc spacing of the refocusing pulses in PRESS or additional RF pulses in the sequence like MEGA PRESS.

1.1Measuring Glycine

At short echo time (TE) of about 30 ms, the glycine (Gly) signal, a singlet at 3.56 ppm, is masked by the main peak of myo-inositol (MI). Since MI represents a strongly coupled spin system (Govindaraju et al. 1998), its pattern is signiÞcantly changing with TE, exhibiting a signal reduction at TE of 135Ð44, which is far beyond the signal decay due to typical T2 relaxation of singlets. This effect can be exploited for differentiation between MI and Gly as has been shown in several studies on brain tumors using either both TE

(Hattingen et al. 2009; Davies et al. 2010) or performing a single spectroscopic measurement with an optimized TE and refocusing pulse spacing in addition to dedicated spectral analysis (Choi et al. 2011; Maudsley et al. 2014). Figure 1 shows the efÞciency of using the long and short TE, comparing tumor spectra for TE at 30 ms to those obtained at 144 ms. It is obvious that there is no signiÞcant decrease in the 3.56 ppm signal between the tumor spectra (b, d). In contrast, rather small signal at TE of 144 ms in normal-appearing tissue (c) indicates the rather low concentration of MI here.

1.2Measuring 2-hydroxyglutarate

About 70 % of WHO grade II and III gliomas have a mutation of isocitrate dehydrogenase (IDH1 and IDH2). These mutations cause an increased formation of 2-hydroxyglutarate (2-HG) from isocitrate, offering the obvious approach to consider increased 2-HG as a tumor marker visible in vivo

Fig. 1 Discriminating glycine from myo-inositol by comparing short and long TE spectra. a shows a spectrum from normal tissue and b from tumor tissue at TE of 30 ms. The signal at 3.56 ppm could be Gly or MI. c shows the normal tissue at a TE of 144 ms, while d shows the repec-

tive tumor voxel. Normal tissue is known to contain MI but rather low concentrations of glycine. The lack of the 3.56 signal in c indicates the sufÞcient suppression of MI at long TE. (Black raw data, red signal estimated by data analyisis, blue residual)