A microwave ablation probe having a longitudinal axis and comprising: a probe body comprising a shielded portion and a radiation window that is at least partially transparent to microwave energy, wherein the shielded portion comprises a cannula; a coaxial cable disposed within the probe body; and an antenna comprising a radiating portion for emission of microwave energy at a distal portion (115, 296) of the probe body, wherein the radiating portion is aligned with the radiation window; wherein the probe body defines an irrigation path configured to carry cooling fluid to and from the distal portion of the probe body, wherein at least one wall defining the irrigation path comprises a heat exchange surface (224, 226); wherein the heat exchange surface has an average radius, wherein a surface area of the heat exchange surface is larger than a surface area of a smooth surface with a radius equal to the average radius; wherein: a) the heat exchange surface (224, 226) is located on at least a portion of an inner surface of the cannula or on at least a portion of an outer surface of an outer conductor of the coaxial cable; and b) the distance between the heat exchange surface (224, 226) and the longitudinal axis of the probe body varies around the circumference of the heat exchange surface, or the heat exchange surface (224, 226) includes corrugations, undulations, fins, or one or more ridges. a probe body comprising a shielded portion and a radiation window that is at least partially transparent to microwave energy, wherein the shielded portion comprises a cannula; a coaxial cable disposed within the probe body; and an antenna comprising a radiating portion for emission of microwave energy at a distal portion (115, 296) of the probe body, wherein the radiating portion is aligned with the radiation window; wherein the probe body defines an irrigation path configured to carry cooling fluid to and from the distal portion of the probe body, wherein at least one wall defining the irrigation path comprises a heat exchange surface (224, 226); wherein the heat exchange surface has an average radius, wherein a surface area of the heat exchange surface is larger than a surface area of a smooth surface with a radius equal to the average radius; wherein: a) the heat exchange surface (224, 226) is located on at least a portion of an inner surface of the cannula or on at least a portion of an outer surface of an outer conductor of the coaxial cable; and b) the distance between the heat exchange surface (224, 226) and the longitudinal axis of the probe body varies around the circumference of the heat exchange surface, or the heat exchange surface (224, 226) includes corrugations, undulations, fins, or one or more ridges. a) the heat exchange surface (224, 226) is located on at least a portion of an inner surface of the cannula or on at least a portion of an outer surface of an outer conductor of the coaxial cable; and b) the distance between the heat exchange surface (224, 226) and the longitudinal axis of the probe body varies around the circumference of the heat exchange surface, or the heat exchange surface (224, 226) includes corrugations, undulations, fins, or one or more ridges.