This paper reviews the technological advancements, clinical impact, and future directions of SPECT and SPECT/CT imaging. The focus is on signal amplifier devices, detector materials, camera head and collimator designs, image reconstruction techniques, and quantitative methods. Bulky photomultiplier tubes (PMTs) are being replaced by position-sensitive PMTs (PSPMTs), avalanche photodiodes (APDs), and silicon PMTs to achieve higher detection efficiency and improved energy and spatial resolution. New SPECT cameras designed for cardiac imaging use specialized collimators with conventional sodium iodide detectors (NaI(Tl)) or L-shaped camera heads with semiconductor detector materials like CdZnTe (CZT). These improvements include shorter scanning times, improved image quality, enhanced patient comfort, reduced claustrophobic effects, and decreased overall size. Software techniques, such as reconstruction algorithms, data correction methods, and quantitative methods, have also been developed to exploit the high photon-counting properties of new hardware technologies. The paper includes clinical examples in oncology, neurology, cardiology, musculoskeletal, and infectious diseases to demonstrate the impact of these advancements on clinical practice.This paper reviews the technological advancements, clinical impact, and future directions of SPECT and SPECT/CT imaging. The focus is on signal amplifier devices, detector materials, camera head and collimator designs, image reconstruction techniques, and quantitative methods. Bulky photomultiplier tubes (PMTs) are being replaced by position-sensitive PMTs (PSPMTs), avalanche photodiodes (APDs), and silicon PMTs to achieve higher detection efficiency and improved energy and spatial resolution. New SPECT cameras designed for cardiac imaging use specialized collimators with conventional sodium iodide detectors (NaI(Tl)) or L-shaped camera heads with semiconductor detector materials like CdZnTe (CZT). These improvements include shorter scanning times, improved image quality, enhanced patient comfort, reduced claustrophobic effects, and decreased overall size. Software techniques, such as reconstruction algorithms, data correction methods, and quantitative methods, have also been developed to exploit the high photon-counting properties of new hardware technologies. The paper includes clinical examples in oncology, neurology, cardiology, musculoskeletal, and infectious diseases to demonstrate the impact of these advancements on clinical practice.