The equations related to a recently published method to measure both the micellar average radius (R-mic) and aggregation number (N-ag) using a single technique, positron annihilation lifetime spectroscopy (PALS), are extended and applied to a 0.25 M sodium dodecylsulfate (SDS) aqueous solution in the presence of large amounts of NaCl (0.6 M) as a function of temperature (T). The analysis of the PALS spectra confirms that the triplet state of positronium, o-Ps, originally formed in the aqueous subphase (o-Ps(aq)) becomes trapped inside the organic core of the micelles (o-Ps(org)). The equations take into account the variety of o-Ps(org) lifetimes promoted when introducing a Ps oxidizer (duroquinone) into the solution, which distributes into the micelles according to Poisson's law. The variation with T of R-mic derived from PALS agrees well with two sets of values previously published, showing an important decrease upon heating, from about 5.8 nm at 305 K down to 2.3 nm at 343 K. By contrast, although all three sets of data agree on the concomitant decrease in N-ag with T, toward values denoting a nearly spherical shape of the micelles at high T, large differences are found at the lowest T studied, the PALS data giving much higher values than those previously published. However, our data show good agreement with the variation of N-ag with T, calculated from the measured R-mic and the volume of the SDS molecules on the assumption that the micelles display a prolate ellipsoid shape.