Measurement of exchangeable sodium: 22Na or 24Na?

A case is made for the use of 22Na in low activities in preference to 24Na for routine diagnostic estimation of exchangeable sodium, and is based chiefly on considerations of availability, cost and radiation dosimetry. A method in which only 37 kBq (1 microCi) 22Na is administered orally is shown to be sufficiently accurate and to possess distinct advantages in terms of cost and convenience with a committed radiation dose no greater than that for a measurement using 24Na.