{"entity":{"id":"quantitative-spect","kind":"technology","name":"Quantitative SPECT","aka":["qSPECT","SPECT/CT quantification"],"tldr":"Modern gamma-camera scans can now be turned into maps of exactly how much radioactivity (in becquerels) sits in each part of the body, not just a picture, which is what lets doctors calculate a real radiation dose to a tumour or organ.","summary":"Conventional SPECT reconstructs relative counts per pixel; quantitative SPECT (qSPECT) converts those counts into absolute activity concentration, expressed in becquerels per millilitre (Bq/mL), by combining CT-based attenuation correction, scatter correction and collimator/detector resolution-recovery within an iterative reconstruction (typically ordered-subset expectation maximisation) and then applying a system-specific calibration factor. Attenuation correction requires a co-registered CT-derived attenuation map covering the full photon path length; scatter correction commonly uses dual- or triple-energy-window methods, with the choice of scatter-correction weighting shown to materially affect quantitative accuracy (activity underestimation of roughly 8-22% has been reported when using default rather than object-optimised scatter weighting). Cross-calibration between the gamma camera and an independent, traceable radionuclide (dose) calibrator, verified with a uniform cylindrical phantom, is required before patient images can be trusted quantitatively.\n\nThe 2022 EANM practice guideline for quantitative SPECT/CT recommends accuracy targets of 5-10% for diagnostic and about 5% for therapeutic radionuclides, and specifies phantom-based validation of recovery coefficients for small-volume accuracy (partial-volume effects remain the dominant source of negative bias for small lesions even with full correction). With these corrections in place, reconstructed qSPECT images at 24-iteration-equivalent settings can achieve activity-concentration accuracy within about 10% of true values for spheres down to roughly 11-12 mL. Quantitative SPECT is the imaging foundation for post-therapy dosimetry of 177Lu-, 90Y- and other radionuclide therapies and for deriving SUV-like metrics from SPECT rather than PET.","asOf":"2026-09-22","links":[{"label":"EANM practice guideline for quantitative SPECT-CT (EJNMMI 2022)","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC9931838/"},{"label":"Optimisation of SPECT/CT imaging protocols for quantitative accuracy (EJNMMI Physics 2021)","url":"https://ejnmmiphys.springeropen.com/articles/10.1186/s40658-021-00405-3"},{"label":"Physical quantities useful for quality control of quantitative SPECT/CT (Nuclear Medicine Review 2021)","url":"https://journals.viamedica.pl/nuclear_medicine_review/article/download/NMR.2021.0020/63672"}],"tags":["dosimetry","imaging physics","SPECT"],"related":["spect-ct","monte-carlo-dosimetry","spect-dosimetry-workflow","radioligand-dosimetry","lu-177","y-90"],"indications":[],"sections":[],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":["spect-ct"],"notes":[],"principle":"Raw SPECT counts are corrected, within the image reconstruction, for photon attenuation using a co-registered CT map, for scattered photons using multiple energy windows, and for the camera's own blurring; the corrected counts are then converted to absolute activity concentration (becquerels per millilitre) using a calibration factor measured against a traceable radionuclide calibrator and a phantom of known activity.","strengths":[],"limitations":[],"since":"CT-based attenuation correction on hybrid SPECT/CT from the early 2000s; formal EANM quantitative SPECT/CT guideline 2022"},"route":"/technologies/quantitative-spect/","neighbours":{"technology":[{"id":"monte-carlo-dosimetry","kind":"technology","name":"Monte Carlo dosimetry","route":"/technologies/monte-carlo-dosimetry/"},{"id":"radioligand-dosimetry","kind":"technology","name":"Radioligand dosimetry","route":"/technologies/radioligand-dosimetry/"},{"id":"spect-dosimetry-workflow","kind":"technology","name":"SPECT dosimetry workflow for radionuclide therapy","route":"/technologies/spect-dosimetry-workflow/"},{"id":"spect-ct","kind":"technology","name":"SPECT/CT","route":"/technologies/spect-ct/"}],"isotope":[{"id":"lu-177","kind":"isotope","name":"Lutetium-177","route":"/isotopes/lu-177/"},{"id":"y-90","kind":"isotope","name":"Yttrium-90","route":"/isotopes/y-90/"}]}}