An image sensor comprising one or more pixels, each pixel (Pi) including: - a photosensitive region formed in a semiconductor substrate ; - a peripheral isolation trench extending vertically in the semiconductor substrate and laterally delimiting the photosensitive region ; - a sense node (SN) including a region for collecting photogenerated charges arranged at a top face of the substrate , the charge-collecting region being doped and having a first conductivity type, in particular p type; - a charge-transfer gate (TG) extending vertically in the semiconductor substrate around the charge-collecting region ; - a well interposed between the peripheral isolation trench and the vertical transfer gate (TG), and arranged around the sense node (SN), the well being doped and having a second conductivity type, opposite to the first conductivity type, in particular n type, the photosensitive region being formed by a first doped region that is of the first conductivity type, in particular p type, and which extends under the charge-collecting region and under the well and forms a diode with the well , the sensor being provided with at least one pixel (Pi) integrating a so-called "detection acceleration" transistor (M1), said so-called "detection acceleration" transistor (M1) having a gate arranged on said top face of the substrate and which is connected to the sense node (SN), the "detection acceleration" transistor (M1) being configured to, during a so-called "charge overflow detection" operation during which a biasing of the transfer gate (TG) is applied so as to form a potential barrier then maintained and following an illumination of the photosensitive region during said operation causing a transfer of photogenerated charges from the photosensitive region to the sense node (SN) and a variation in potential at this sense node (SN), be switched on, the switched-on "detection acceleration" transistor weakening the potential barrier and favouring a transfer of photogenerated charges to the sense node (SN) of the photosensitive region, the "detection acceleration" transistor (M1) including a channel region formed in a doped part of the substrate having the first conductivity type and belonging to said first region . - a photosensitive region formed in a semiconductor substrate ; - a peripheral isolation trench extending vertically in the semiconductor substrate and laterally delimiting the photosensitive region ; - a sense node (SN) including a region for collecting photogenerated charges arranged at a top face of the substrate , the charge-collecting region being doped and having a first conductivity type, in particular p type; - a charge-transfer gate (TG) extending vertically in the semiconductor substrate around the charge-collecting region ; - a well interposed between the peripheral isolation trench and the vertical transfer gate (TG), and arranged around the sense node (SN), the well being doped and having a second conductivity type, opposite to the first conductivity type, in particular n type, the photosensitive region being formed by a first doped region that is of the first conductivity type, in particular p type, and which extends under the charge-collecting region and under the well and forms a diode with the well , <EOS>