The present invention provides a catheter apparatus for temperature measurement of vascular tissue, comprising a flexible body, at least one resiliently biased projection depended from the body, a sensor carried by the projection and an electrical carrier for transmitting data from the sensor to a remote device, wherein the projection, in a deployed configuration, adopts an arcuate shape along at least part of its length, wherein the gradient of the arcuate portion of the projection, with respect to the longitudinal axis of the catheter, increases as a function of distance along the projection from the end attached to the catheter body.