Glioma Imaging by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030273590
Publisher: Springer International Publishing

Radionuclide Imaging: Positron Emission Tomography and SPECT

Radionuclide techniques such as PET and single photon emission computed tomography (SPECT) allow specific metabolic and molecular processes to be probed using radiolabelled molecules; a range of such tracers and ligands that probe processes relevant to glioma biology are available [34, 80]. Detection sensitivity is in the nanomoles to micromoles per litre range, and spatial resolution is around 5 mm for PET. Most contemporary PET acquisition uses hybrid PET-CT scanners which provide corresponding structural images for anatomical information and attenuation correction. The relatively recent advent of hybrid PET-MR offers better soft tissue characterisation, and the potential for co-acquisition of quantitative and physiological MR data, but has yet to be applied widely in the clinic.

The first application of PET for glioma stratification involved the use of FDG, a glucose analogue tracer widely used in clinical cancer imaging outside the CNS [81]. Increased standardised uptake value (SUV) of FDG in cancer cells has been related to overproduction of glucose transporters; however, high uptake in normal brain tissue and unspecific uptake of inflammatory benign lesions has limited its sensitivity and specificity in glioma.

Amino acid tracers are more specific and have found greater applicability in neuro-oncology [82].

FET (F-18 fluoro-ethyl-tyrosine) measures the rate of amino acid transport associated with cancer growth; its superior specificity for tumor tissue and the relatively long half-life of the 18F label have contributed to its adoption for clinical assessment of gliomas [83]. An early study by Pöpperl et al. demonstrated in 54 patients that static and dynamic FET-PET uptake measured as maximum tumor SUV and tumor SUV-to-background ratio could significantly differentiate LGG from HGG [84]. While differentiation of individual tumor grades with FET was equivocal in their study, Calcagni et al. later demonstrated that early-to-mid SUV tumor ratio and time-to-peak from dynamic FET-PET could discriminate individual glioma grades with high accuracy, thereby potentially reducing scan time by twofold [85]. Early static FET-PET scans have been furthermore proposed in instances where dynamic imaging cannot be performed; Albert et al. demonstrated highly accurate differentiation between LGG and HGG using a maximum tumor SUV-to-background ratio acquired between 15 and 25 minutes earlier than standard acquisition times [86].

One of few multiparametric studies involving dynamic FET-PET, MR spectroscopy, and diffusion demonstrated significant increases in the accuracy of glioma classification when ADC histogram distributions were combined with tumor time-activity-curves [87]. A recent comparison of dynamic FET-PET and perfusion MRI revealed similar diagnostic accuracy in the distinguishing of LGGs from HGGs [88]. While no individual parameter derived from FET-PET has been identified as a reliable molecular stratifier of gliomas, radiogenomics approaches based on the extraction of many static, dynamic, and textural FET-PET features have been successful in distinguishing IDH mutation status [89]. Stratification of IDH-mutant oligodendrogliomas according to 1p/19q co-deletion status has been achieved using C-11 methionine (MET) [90, 91] (Fig. 9.3). MET-PET targets protein synthesis [83] and, in the assessment of glioma, has been shown to be a better stratifier than FDG-PET [92], though it remains less specific for tumor

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