One aspect of the invention relates to novel complexes of technetium (Tc) with various heteroaromatic ligands, e.g., pyridyl and imidazolyl ligands, and their use in radiopharmaceuticals for a variety of clinical diagnostic and therapeutic applications. Another aspect of the invention relates to novel pyridyl ligands that form a portion of the aforementioned complexes. Methods for the preparation of the technetium complexes are also described. Another aspect of the invention relates to novel pyridyl ligands based on derivatized lysine, alanine and bis-amino acids for conjugation to small peptides by solid phase synthetic methods. Additionally, the invention relates to methods for imaging regions of a mammal using the complexes of the invention.