[18F]-Fluorodeoxyglucose PET/CT imaging as a marker of carotid plaque inflammation: Comparison to immunohistology and relationship to acuity of events

BACKGROUND

[18F]-fluorodeoxyglucose (¹⁸FDG) uptake imaged with positron emission tomography (PET) and computed tomography (CT) may serve as a biomarker of plaque inflammation. This study evaluated the relationship between carotid plaque ¹⁸FDG uptake and a) intraplaque expression of macrophage and macrophage-like cellular CD68 immunohistology; b) intraplaque inflammatory burden using leukocyte-sensitive CD45 immunohistology; c) symptomatic patient presentation; d) time from last cerebrovascular event.

METHODS

54 patients scheduled for carotid endarterectomy underwent ¹⁸FDG PET/CT imaging. Maximum 18FDG uptake (SUV_max) and tissue-to-blood ratio (TBR_max) was measured for carotid plaques. Quantitative immunohistological analysis of macrophage-like cell expression (CD68) and leukocyte content (CD45) was performed.

RESULTS

¹⁸FDG uptake was related to CD68 macrophage expression (TBR_max: r = 0.51, p < 0.001), and total-plaque leukocyte CD45 expression (TBR_max: r = 0.632, p = 0.009, p < 0.001). ¹⁸FDG TBR_max uptake in carotid plaque associated with patient symptoms was greater than asymptomatic plaque (3.58 ± 1.01 vs. 3.13 ± 1.10, p = 0.008). ¹⁸FDG uptake differed between an acuity threshold of <90 days and >90 days (SUV_max:3.15 ± 0.87 vs. 2.52 ± 0.45, p = 0.015).

CONCLUSIONS

In this CAIN cohort, ¹⁸FDG uptake imaged with PET/CT serves a surrogate marker of intraplaque inflammatory macrophage, macrophage-like cell and leukocyte burden. 18FDG uptake is greater in plaque associated with patient symptoms and those with recent cerebrovascular events. Future studies are needed to relate ¹⁸FDG uptake and disease progression.

P53 deficiency produces fewer regenerating spermatogenic tubules after irradiation

The survival of clonogenic spermatogonia was assessed by scoring regenerating tubules at 35 days after irradiation, in the p53 null, heterozygote and wild-type mouse. Survival levels in the p53 null mouse after doses between 6 and 16 Gy were reduced by a factor of 3-4 compared with the levels in the heterozygote or wild-type mouse, which responded similarly. However the radiosensitivity of the cells was similar in all three types of mice, and was characterised by a D0 = 1.7 Gy. A two-dose experimental protocol was used to show that the reduced level of survival in the null mouse at day 35 after irradiation was compatible with the interpretation that there were fewer functional radioresistant clonogenic spermatogonia in the testis of the unirradiated null mouse by about a factor of 3 compared with that in the testis of the wild-type. The lower cell number was similar to the number deduced in other mice (BDF1), where the cells were much more resistant (D0 = 3.2 +/- 0.2 Gy). It is concluded that the lack of p53 causes a reduced level of tubule regeneration at 35 days after irradiation. This is probably not due to cellular radiosensitization, but possibly to a change in the stem cell cycle phase distribution resulting in a smaller proportion of resistant stem cells, which are assayed after high doses.