Periaqueductal gray matter echogenicity as a marker of migraine chronification : a case control study - Vilas, Dolores (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol) ; Rubio, Sara (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol) ; Gea, Mireia (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol) ; Ríos, José (Universitat Autònoma de Barcelona) ; Ispierto, Lourdes (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol) ; Hernández-Pérez, María (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol) ; Paré-Curell, Martí (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol) ; Millán, Mònica (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol) ; Dorado Bouix, Laura (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol)