PETCT Imaging of Unstable Carotid Plaque with Ga-68 labelled Somatostatin Receptor Ligand.

Wan, Ming Young Simon; Endozo, Raymond; Michopoulou, Sofia; Shortman, Robert; Rodriguez-Justo, Manuel; Menezes, Leon; Yusuf, Syed; Richards, Toby; Wild, Damian; Waser, Beatrice; Reubi, Jean Claude; Groves, Ashley (2017). PETCT Imaging of Unstable Carotid Plaque with Ga-68 labelled Somatostatin Receptor Ligand. Journal of nuclear medicine, 58(5), pp. 774-780. Society of Nuclear Medicine 10.2967/jnumed.116.181438

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BACKGROUND

Ga68 labelled somatostatin receptor ligand PET imaging has recently been shown in preclinical and early human studies to have a potential role in the evaluation of vulnerable arterial plaques. We prospectively evaluated carotid plaque Ga68-DOTATATE uptake in patients with recent carotid events, assessed inter- and intra- observer variability of such measurements, and explored the mechanism of any plaque DOTATATE activity with immunohistochemistry in resected specimens.

MATERIALS & METHODS

20 consecutively consenting patients with recent symptomatic carotid events (transient ischaemic attack [TIA], stroke or amaurosis fugax), due for carotid endarterectomy were prospectively recruited. Ga68-DOTATATE PET/CT of the neck was performed prior to surgery. Ga68-DOTATATE uptake was measured by drawing regions of interest (ROI) along the carotid plaques and contralateral plaques/carotid arteries by experienced radionuclide radiologist and radiographer. Two PET quantification methods with inter- and Intra-observer variability were assessed. Resected carotid plaques were retrieved for sst-2 immunohistochemical stain.

RESULTS

Median time delay between research PET and surgery was 2days. SUV and TBR values for the symptomatic plaques and the asymptomatic contralateral carotid arteries/plaques show no significant difference (n = 19, p-value >0.10), regardless of quantification method. Intraclass correlation coefficient was >0.8 in all measures of carotid artery/plaque uptake (SUV) and >0.6 in almost all measures of target-to-background ratio (TBR). None of the excised plaques were shown to contain cells (macrophages, lymphocytes, vessel-associated cells) expressing sst2 on their cell membrane.

CONCLUSION

Ga68 DOTATATE activity on PET in recently symptomatic carotid plaques is not significantly different to contralateral carotids/plaques. Any activity seen on PET is not shown to be from specific sst2 receptor-mediated uptake in-vitro. It is therefore unlikely that sst2 PET/CT imaging will have a role in the detection and characterization of symptomatic carotid plaques.

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