The Qualifier None is identified by letter "Z" and occupies the 6th position in the ICD10-PCS procedure code structure.
Below a selection of ICD 10 PCS codes related to CG121Z
Planar Nucl Med Imag of Thyroid Gland using Oth Radionuclide
Planar Nucl Med Imag of Thyroid Gland using Iodine 131
Planar Nucl Med Imag of Thyroid Gland using Technetium 99m
Planar Nucl Med Imag of Thyroid Gland using Iodine 123