nature.com/articles/s41598-...
Published: 13 September 2019
There is a very clear diagram Fig. 1 - describes the thyroid hormone network highlighting the biologically active triiodothyronine (T3).
It is worth scrolling down to Fig. 1 showing T4, T3, rT3, T2 and the role of DIO1, DIO2, DIO3 and also MCT8.