Amino acid PET and MR perfusion imaging in brain tumours

Abstract

PurposeDespite the excellent capacity of the conventional MRI to image brain tumours, problems remain in answering a number of critical diagnostic questions. To overcome these diagnostic shortcomings, PET using radiolabeled amino acids and perfusion-weighted imaging (PWI) are currently under clinical evaluation. The role of amino acid PET and PWI in different diagnostic challenges in brain tumours is controversial.MethodsBased on the literature and experience of our centres in correlative imaging with PWI and PET using O-(2-[18F]fluoroethyl)-l-tyrosine or 3,4-dihydroxy-6-[18F]-fluoro-l-phenylalanine, the current role and shortcomings of amino acid PET and PWI in different diagnostic challenges in brain tumours are reviewed. Literature searches were performed on PubMed, and additional literature was retrieved from the reference lists of identified articles. In particular, all studies in which amino acid PET was directly compared with PWI were included.ResultsPWI is more readily available, but requires substantial expertise and is more sensitive to artifacts than amino acid PET. At initial diagnosis, PWI and amino acid PET can help to define a site for biopsy but amino acid PET appears to be more powerful to define the tumor extent. Both methods are helpful to differentiate progression or recurrence from unspecific posttherapeutic changes. Assessment of therapeutic efficacy can be achieved especially with amino acid PET, while the data with PWI are sparse.ConclusionBoth PWI and amino acid PET add valuable diagnostic information to the conventional MRI in the assessment of patients with brain tumours, but further studies are necessary to explore the complementary nature of these two methods.

Region-by-region analysis of PET, MRI, and histology in en bloc-resected oligodendrogliomas reveals intra-tumoral heterogeneity

“…Our particular study design might also explain the lack of significant correlation between MET uptake and rCBV. Overall, we clearly demonstrate that MET PET has advantages over PWI, which is in line with previous studies [49,50], but in contrast to others [51].…”

PET imaging of medulloblastoma with an 18F-labeled tryptophan analogue in a transgenic mouse model

“…With regard to tumor uptake, L-amino acid radiotracers in general show remarkable advantages over their corresponding D-isomer due to the preference of amino acid transporters and related enzymes for the L-isomer. As such, most amino acid PET radiotracers currently used in the clinic are L-isomers 39,40 . However, at times, D-amino acid PET radiotracers display a similar tumor uptake as their L-counterparts and in some cases, have superior contrast performance to L-isomers due to their fast clearance from the blood pool [43][44][45] .…”

“…It is common that the L-enantiomer of an amino acid PET tracer has higher tumor uptake than its D-counterpart 39,40 . Consistent with this, in breast cancer, it has previously been shown that L-and D-enantiomers of 1-[ 18 F]FETrp have different uptake profiles 33 .…”

Differentiation of suprasellar meningiomas from non-functioning pituitary macroadenomas by 18F-FDG and 13N-Ammonia PET/CT

“…However, the inherent limitation of high physiologic uptake in the normal brain tissue necessitates the search for other newer PET tracers. Although 13 Nammonia has a short half-life time, it is rapidly spreading in recent years because of its diagnostic power (perfusion-metabolism coupling tracer) and the easier interpretation for clinicians owing to the higher tumor to back-ground contrast compared to PWI and other PET tracers [31] . On the other hand, the short half-life time has the advantage of reducing the radiation.…”