Clinical Value of Hybrid TOF-PET/MR Imaging-Based Multiparametric Imaging in Localizing Seizure Focus in Patients with MRI-Negative Temporal Lobe Epilepsy

Abstract

Background and purpose: Temporal lobe epilepsy is the most common type of epilepsy. Early surgical treatment is superior to prolonged medical therapy in refractory temporal lobe epilepsy. Successful surgical operations depend on the correct localization of the epileptogenic zone. This study aimed to evaluate the clinical value of hybrid TOF-PET/MR imaging-based multiparametric imaging in localizing the epileptogenic zone in patients with MR imaging-negative for temporal lobe epilepsy.

Materials and methods: Twenty patients with MR imaging-negative temporal lobe epilepsy who underwent preoperative evaluation and 10 healthy controls were scanned using PET/MR imaging with simultaneous acquisition of PET and arterial spin-labeling. On the basis of the standardized uptake value and cerebral blood flow, receiver operating characteristic analysis and a logistic regression model were used to evaluate the predictive value for the localization. Statistical analyses were performed using statistical parametric mapping. The values of the standardized uptake value and cerebral blood flow, as well as the asymmetries of metabolism and perfusion, were compared between the 2 groups. Histopathologic findings were used as the criterion standard.

Results: Complete concordance was noted in lateralization and localization among the PET, arterial spin-labeling, and histopathologic findings in 12/20 patients based on visual assessment. Concordance with histopathologic findings was also obtained for the remaining 8 patients based on the complementary PET and arterial spin-labeling information. Receiver operating characteristic analysis showed that the sensitivity and specificity of PET, arterial spin-labeling, and combined PET and arterial spin-labeling were 100% and 81.8%, 83.3% and 54.5%, and 100% and 90.9%, respectively. When we compared the metabolic abnormalities in patients with those in healthy controls, hypometabolism was detected in the middle temporal gyrus (P < .001). Metabolism and perfusion asymmetries were also located in the temporal lobe (P < .001).

Conclusions: PET/MR imaging-based multiparametric imaging involving arterial spin-labeling may increase the clinical value of localizing the epileptogenic zone by providing concordant and complementary information in patients with MR imaging-negative temporal lobe epilepsy.

Fig 1.

Receiver operating characteristic curves for SUVr, CBF, and combined SUVr and CBF to predict EZ. The combined PET and ASL obtain the highest area under the curve (0.970) with high sensitivity (100%) and specificity (90.9%). PET has more diagnostic information with an area under the curve of 0.926, compared with ASL (area under the curve of 0.679). The combined PET and ASL show the best performance in specificity for predicating EZ.

Fig 2.

FCD type Ib in a 23-year-old patient with a history of seizures, onset at 14 years of age. A, T1-weighted axial image has normal findings. B and C, PET and PET-T1WI fused images (arrow) indicate a well-defined area of focal hypometabolism in the left temporal lobe region. D and E, ASL and ASL-T1WI fused images (arrow) show hypoperfusion in the same brain region. After a left anterior temporal lobectomy, histopathologic findings showed FCD type Ib. After a postoperative follow-up of at least 1 year, the patient was classified as having an Engel class I outcome.

Fig 3.

FCD type IIIa–HS in a 29-year-old patient with a history of seizures, onset at 15 years of age. A, T1-weighted axial image has normal findings. B and C, PET and PET-T1WI fused images (arrows) indicate a well-defined area of focal hypometabolism in the left temporal lobe region. However, ASL and ASL-T1WI fused images (D and E, arrows) have normal findings in the same brain region. After a left anterior temporal lobectomy, histopathologic findings of the surgical specimen were consistent with FCD type IIIa–HS. This patient with TLE had an Engel class I outcome after >1 year of follow-up.

Fig 4.

FCD type I in a 26-year-old patient with a history of seizure onset at 14 years of age. The T1-weighted axial image (A), PET image (B), and fused image (C) have normal findings. D and E, ASL and ASL-T1WI fused images (circles) show a well-defined area of focal hypoperfusion in the left temporal lobe region. After a left temporal lobe resection, pathologic findings were consistent with FCD type I. The patient had a follow-up time of >1 year, showing Engel class I outcome.

Fig 5.

Regional comparison across the 20 patients for ROIs with hypometabolism in PET and hypoperfusion in ASL (r = 0.587, P < .001).

Fig 6.

SPM analysis of [¹⁸F] FDG-PET images in localizing the EZ between patients and healthy controls. The hypometabolic region is mainly identified in the middle temporal gyrus. The threshold P value is set at .001.

Fig 7.

Brain regions of metabolism and perfusion asymmetry of patients compared with controls by SPM analysis in PET (A) and ASL images (B), respectively. The regions of metabolism and perfusion asymmetry are mainly identified in the middle temporal gyrus and superior temporal gyrus, respectively. The threshold P value is set at .001.