Evaluation of early-phase [18F]-florbetaben PET acquisition in clinical routine cases

Abstract

Objectives: In recent years several [¹⁸F]-labelled amyloid PET tracers have been developed and have obtained clinical approval. There is accumulating evidence that early (post injection) acquisitions with these tracers are equally informative as conventional blood flow and metabolism studies for diagnosis of Alzheimer's disease, but there have been few side-by-side studies. Therefore, we investigated the performance of early acquisitions of [¹⁸F]-florbetaben (FBB) PET compared to [¹⁸F]-fluorodeoxyglucose (FDG) PET in a clinical setting.

Methods: All subjects were recruited with clinical suspicion of dementia due to neurodegenerative disease. FDG PET was undertaken by conventional methods, and amyloid PET was performed with FBB, with early recordings for the initial 10 min (early-phase FBB), and late recordings at 90-110 min p.i. (late-phase FBB). Regional SUVR with cerebellar and global mean normalization were calculated for early-phase FBB and FDG PET. Pearson correlation coefficients between FDG and early-phase FBB were calculated for predefined cortical brain regions. Furthermore, a visual interpretation of disease pattern using 3-dimensional stereotactic surface projections (3D-SSP) was performed, with assessment of intra-reader agreement.

Results: Among a total of 33 patients (mean age 67.5 ± 11.0 years) included in the study, 18 were visually rated amyloid-positive, and 15 amyloid-negative based on late-phase FBB scans. Correlation coefficients for early-phase FBB vs. FDG scans displayed excellent agreement in all target brain regions for global mean normalization. Cerebellar normalization gave strong, but significantly lower correlations. 3D representations of early-phase FBB visually resembled the corresponding FDG PET images, irrespective of the amyloid-status of the late FBB scans.

Conclusions: Early-phase FBB acquisitions correlate on a relative quantitative and visual level with FDG PET scans, irrespective of the amyloid plaque density assessed in late FBB imaging. Thus, early-phase FBB uptake depicts a metabolism-like image, suggesting it as a valid surrogate marker for synaptic dysfunction, which could ultimately circumvent the need for additional FDG PET investigation in diagnosis of dementia.

Keywords: 3D-SSP, 3-dimensional stereotactic surface projections; AD, Alzheimer's disease; Alzheimer's disease; CBF, cerebral blood flow; CBL, cerebellum; CN, cognitively normal; FBB, [18F]florbetaben; FDG Pet; FDG, [18F]-fluorodeoxyglucose; FTLD, frontotemporal lobar degeneration; GLM, global mean; L, left; MCI, mild cognitive impairment; MNI, Montreal Neurological Institute; Metabolism; PCC, posterior cingulate cortex; PET, Positron emission tomography; Perfusion; R, right; SPECT, single photon emission computed tomography; SUVR, standardized uptake value ratio; VOI, volume of interest; [18F]-florbetaben PET; p.i., post injection; ß-amyloid.

Fig. 1

Correlation charts of early-phase FBB_0–5 and FDG SUVRs (global mean normalization). R: right; L: left; PCC: posterior cingulate cortex; **p < 0.01.

Fig. 2

3D-SSP images of a 79 year old male person with clinical presentation of AD (A) and an 81 year old male person with clinical presentation of FTLD (B). Normalized count and Z-maps for FDG (upper row) and FBB_0–5. The map depicts areas with less uptake compared to normal controls. R: right; L: left; PCC: posterior cingulate cortex

Fig. 3

Correlation of visual scores for hypoperfusion/hypometabolism severity by three readers in early-phase FBB_0–5 and FDG images.

Fig. 4

Agreement and mismatch of individual PET diagnosis in visual interpretation of early-phase FBB_0–5 and FDG 3D–SSP images. AD: Alzheimer's disease; FTLD: Frontotemporal lobar degeneration.