Fig. 4

a Calibration profiles obtained in the well counter for 300-μl pure ¹⁸F (red squares) and ⁶⁸Ga (blue circles) samples with different activity values using the full energy window (W_200–2000). Each dataset was fitted to a straight line with y-intercept forced to be 0 obtaining the calibration factors ε_F = 0.335 cps Bq⁻¹ and ε_Ga = 0.371 cps Bq⁻¹ at this volume. b Variation of calibration factors with the sample volume for ¹⁸F (ε_F) and ⁶⁸Ga (ε_Ga)