You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Small Molecule Radiopharmaceuticals – A Review of Current Approaches 
Chapter Title:  Applications of BLA 
1. Abstract of Cited Paper (BIB001):  Dopamine D2 receptor homodimers might be of particular importance in the pathophysiology of schizophrenia and, thus, serve as promising target proteins for the discovery of atypical antipsychotics. A highly attractive approach to investigate and control GPCR dimerization may be provided by the exploration and characterization of bivalent ligands, which can act as molecular probes simultaneously binding two adjacent binding sites of a dimer. The synthesis of bivalent dopamine D2 receptor ligands of type 1 is presented, incorporating the privileged structure of 1,4-disubstituted aromatic piperidines/piperazines (1,4-DAPs) and triazolyl-linked spacer elements. Radioligand binding studies provided diagnostic insights when Hill slopes close to two for bivalent ligands with particular spacer lengths and a comparative analysis with respective monovalent control ligands and unsymmetrically substituted analogues indicated a bivalent binding mode with a simultaneous occupancy of two neighboring binding sites. 
2. Abstract of Cited Paper (BIB002):  G-protein-coupled receptors (GPCRs) represent the largest family of membrane proteins involved in cellular signal transduction and are activated by various different ligand types including photons, peptides, proteins, but also small molecules like biogenic amines. Therefore, GPCRs are involved in diverse physiological processes and provide valuable drug targets for numerous diseases. Emerging body of evidence suggests that GPCRs exist as monomers or cross-react forming dimers and higher-ordered oligomers. In this Perspective we will review current biochemical and biophysical techniques to visualize GPCR dimerization, functional consequences of homo- and heterodimers, and approaches of medicinal chemists to target these receptor complexes with homo- and heterobivalent ligands.

Literature Review:
A BL functions best when multiple binding pockets are present in the target. Depending on the pharmacophores, a BL can target one or multiple biomarkers. Tumor targeting can benefit from the high binding avidity and selectivity of BL. Furthermore, hetero-BL can result in more specificity as it targets different receptors simultaneously. Receptor-based imaging, especially for neuroreceptors, can also benefit from the bivalent approach. Many receptors/ neuroreceptors belong to G-protein coupled receptor (GPCR) family BIB001 . After the reports about the existence of GPCRs as oligomers and higher-orders started pouring (11), BLs were successfully developed and validated against them. The approach has been of high relevance in the design and development of second generation antipsychotics BIB002 BIB003 . A BL can target both homo-and hetero-dimeric receptor systems depending on the pharmacophores. Another target for BLs is β-amyloid plaques because of the presence of multiple binding sites (14) .