Breast cancer is the most commonly diagnosed cancer in females worldwide,rncontributing around 11.7 % (~2.3 million people) of new cancer cases in 2020 only,rnwith a death rate of 6.9%. Early diagnosis and check-up are essential for effectiverntreatment and reduction of incidences and mortality rates. Different modalities exist torndiagnose breast cancers. Positron emission tomography (PET) is the one imaging toolrnin nuclear medicine providing physiological information about the breast byrnquantifying the metabolic activities of the cells in the breast tissues. Both whole-bodyrn(WB) PET scanners and organ-specific PET scanners are available in the market. Butrncurrent trends show that there is a complete shift towards dedicated, organ specificrnPETs. One of those is Positron Emission Mammography (PEM), believed to be betterrnthan mammography and other imaging modalities to detect small breast lesions.rnSemiconductor-based PEM detectors are simulated with good spatial resolution but arernexpensive. Scintillator-based PET and PEM detectors can provide quit good sensitivityrnand are cost effective. On the contrary, these detectors cannot detect small breast lesionsrndue to their poor spatial resolution. This requires development of detectors that givernrise to better spatial resolution. In the current thesis work, a high-performance PEMrnscanner is simulated using TOC (Transparent Optical Ceramic) scintillators of 1 x 1 xrn10mmrn3 rncrystals with the aim to improve the spatial resolution, sensitivity as well asrnscattering fraction. Those TOC scintillators are LHO: cerium doped lutetium hafnatern(Lurn2rn Hfrn2rn Orn7rn: Ce), BHO: cerium doped barium hafnate (BaHfOrn3rn: Ce) and SHO: ceriumrndoped strontium hafnate (SrHforn3rn: Ce). The design was based on the GATE (Geant4rnApplication for Emission Tomography) simulation software. Its performance wasrntested and evaluated by following the NEMA (National Electrical ManufacturersrnAssociation) NU 4-2008 standards. The complete scanner has 39 heads and 10 x 30 xrn59 modules in the detector. Based on the type of scintillator used, the designed scannerrnprovided a spatial resolution between 1.0 and 1.1 mm FWHM (Full Width at HalfrnMaximum) in the axial direction, 7.24% to 9.11% system sensitivity and 11.01% torn11.19% scatter fraction. The design offered good uniformity as well as image quality.rnThe computed spatial resolution, sensitivity and scatter fraction values are superior tornthose already reported in the literature.