Beyond perfusion imaging: the growing clinical role of myocardial blood flow quantification by SPECT

Although perfusion imaging is effective for evaluating relative myocardial blood flow (MBF) distribution, it has a well-known limitation in single photon emission computed tomography (SPECT): it often underestimates ischemia, particularly in patients with three-vessel coronary artery disease or left main trunk disease. In such cases, global reductions in MBF may not create significant perfusion defects, complicating the accurate detection of ischemia. In contrast, positron emission tomography (PET) has long offered absolute MBF quantification through dynamic imaging, allowing for a more precise assessment of coronary artery disease and microvascular dysfunction. By integrating absolute MBF quantification with perfusion imaging, PET has significantly improved diagnostic accuracy in ischemia evaluation. Relative to PET, traditional SPECT has struggled to achieve comparable MBF quantification due to its lower sensitivity and spatial resolution. However, recent advancements in semiconductor-based detector technology have enabled SPECT to approximate PET's quantification accuracy. Emerging studies indicate that modern SPECT systems can now deliver absolute MBF values with enhanced reliability, opening new possibilities for clinical application. Despite PET's superior quantification capability, its availability remains confined to specialized facilities, limiting its broader clinical use. In this context, the implementation of SPECT to quantify MBF presents a promising avenue for expanding access to more accurate ischemia assessment. Enhancing the diagnostic precision of SPECT could improve patient stratification and treatment planning, particularly in environments where PET is not readily available. This review summarizes recent advancements in MBF quantification using SPECT, discusses its clinical implications, and explores the prospects for its integration into routine cardiovascular imaging.