As a (white) matter of fact – Different white matter properties of beta-amyloid PET tracers

Ziel/Aim The visual reading of brain beta-amyloid (Aβ) PET images is based on the regional evaluation of the contrast between specific gray and unspecific white matter (WM) uptake. Thus, the degree and homogeneity of the WM uptake might influence the read results. It is known for the approved [¹⁸F]-labeled Aβ tracer Florbetaben (FBB) that its WM uptake is relatively higher than that of [11C]PiB. We argue, however, that the homogeneity of the tracer uptake within the WM is more important than its magnitude, and investigated this feature in the present study.

Methodik/Methods We analyzed the data of (1) two matched (for the Aβ-neg. vs. Aβ-pos ratio, age and gender, n = 67 each) patient cohorts who underwent [11C]PiB and [¹⁸F]Florbetaben PET, and those of (2) a head-to-head PiB vs. FBB comparison (10 young controls: 32.6±9yrs, 3 males; 25 elderly: 71.7 ± 6yrs, 12 males) from the GAAIN database. For both tracers, we assessed the homogeneity, energy and contrast as WM uptake texture characteristics using the Radiomics toolbox in Matlab.

Ergebnisse/Results For (1), homogeneity, energy and contrast showed no tracer differences, but a smaller variance (p < 0.001) for FBB independent of the Aβ status. Here, no age effect on the WM uptake texture parameters was seen. For (2), the FBB WM uptake data showed higher homogeneity (p < 0.001), energy (p < 0.001) and lower contrast (p < 0.001) as compared to the PiB data. Here, the FBB data had a lower variance in homogeneity (young controls: p = 0.02), energy (young controls: p = 0.006) and contrast (elderly: p = 0.009). While, in this cohort, for both tracers the WM uptake homogeneity correlated with age (FBB: r = 0.45, p = 0.007; PiB: r = 0.6, p < 0.001), only in the PiB data the WM uptake energy (r = 0.57, p < 0.001) and contrast (r = -0.59, p < 0.001) was age-correlated.

Schlussfolgerungen/Conclusions For PiB and FBB, the homogeneity, energy and contrast of the WM uptake differ, with favorable results for FBB. Further, an age effect on the WM uptake was evident for the PiB, but not for the FBB data. Further investigations on this expression of this feature over different patients and on its effect on the gray matter Aβ diagnosis are, thus, warranted.