Combined application of 18F-fluorodeoxyglucose positron emission tomography/computed tomography and magnetic resonance imaging in early diagnosis of vulnerable carotid atherosclerotic plaques

Association Between 18-FDG Positron Emission Tomography and MRI Biomarkers of Plaque Vulnerability in Patients With Symptomatic Carotid Stenosis

Purpose: Pathologic studies suggest that unstable plaque morphology and inflammation are associated with cerebrovascular events. ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸FDG-PET) is a validated technique for non-invasive imaging of inflammation-related plaque metabolism, and MRI can identify morphologic features of plaque instability. The aim of this study was to investigate the association of selected imaging characteristics of plaque vulnerability measured with MRI and PET in patients with symptomatic carotid stenosis.

Methods: Patients from the BIOVASC study were selected based on the following inclusion criteria: (1) age ≥ 50 years; (2) recent (<30 days) ischaemic stroke (modified Rankin scale ≤3) or motor/speech/vision TIA; (3) ipsilateral internal carotid artery stenosis (≥5 0% lumen-narrowing); (4) carotid PET/CTA and MRI completed. Semi-automated plaque analysis of MRI images was performed to quantify morphologic features of plaque instability. PET images were co-registered with CTA and inflammation-related metabolism expressed as maximum standardised uptake value (SUV_max).

Results: Twenty-five patients met inclusion criteria (72% men, mean age 65 years). MRI-measured plaque volume was greater in men (1,708–1,286 mm³, p = 0.03), patients who qualified with stroke (1,856–1,440 mm³, p = 0.05), and non-statin users (1,325–1,797 mm³, p = 0.03). SUV_max was associated with MRI-measured plaque lipid-rich necrotic core (LRNC) in the corresponding axial slice (r_s = 0.64, p < 0.001) and was inversely associated with whole-plaque fibrous cap thickness (r_s = −0.4, p = 0.02) and calcium volume (r_s = −0.4, p = 0.03).

Conclusion: This study demonstrated novel correlations of non-invasive imaging biomarkers of inflammation-related plaque metabolism with morphological MRI markers of plaque instability. If replicated, our findings may support the application of combined MRI and PET to detect vulnerable plaque in future clinical practise and randomised trials.

Diffusion-weighted and PET/MR Imaging after Radiation Therapy for Malignant Head and Neck Tumors

Interpreting imaging studies of the irradiated neck constitutes a challenge because of radiation therapy-induced tissue alterations, the variable appearances of recurrent tumors, and functional and metabolic phenomena that mimic disease. Therefore, morphologic magnetic resonance (MR) imaging, diffusion-weighted (DW) imaging, positron emission tomography with computed tomography (PET/CT), and software fusion of PET and MR imaging data sets are increasingly used to facilitate diagnosis in clinical practice. Because MR imaging and PET often yield complementary information, PET/MR imaging holds promise to facilitate differentiation of tumor recurrence from radiation therapy-induced changes and complications. This review focuses on clinical applications of DW and PET/MR imaging in the irradiated neck and discusses the added value of multiparametric imaging to solve diagnostic dilemmas. Radiologists should understand key features of radiation therapy-induced tissue alterations and potential complications seen at DW and PET/MR imaging, including edema, fibrosis, scar tissue, soft-tissue necrosis, bone and cartilage necrosis, cranial nerve palsy, and radiation therapy-induced arteriosclerosis, brain necrosis, and thyroid disorders. DW and PET/MR imaging also play a complementary role in detection of residual and recurrent disease. Interpretation pitfalls due to technical, functional, and metabolic phenomena should be recognized and avoided. Familiarity with DW and PET/MR imaging features of expected findings, potential complications, and treatment failure after radiation therapy increases diagnostic confidence when interpreting images of the irradiated neck. Online supplemental material is available for this article.