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 C7551Z
Nonimag Nucl Med Prob Head & Neck Lymph w Oth Radionuclide
Nonimag Nucl Med Prob Head & Neck Lymph w Technetium 99m