# Quantitative SPECT

Source: https://nuclide.cc/technologies/quantitative-spect/  
Nuclide record `quantitative-spect` (Technology). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

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.

The 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.

## Fields

- Kind: Technology
- Last checked: 2026-09-22
- Also known as: qSPECT; SPECT/CT quantification
- Tags: dosimetry; imaging physics; SPECT
- 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.
- Since: CT-based attenuation correction on hybrid SPECT/CT from the early 2000s; formal EANM quantitative SPECT/CT guideline 2022

## Sources

- EANM practice guideline for quantitative SPECT-CT (EJNMMI 2022): https://pmc.ncbi.nlm.nih.gov/articles/PMC9931838/
- Optimisation of SPECT/CT imaging protocols for quantitative accuracy (EJNMMI Physics 2021): https://ejnmmiphys.springeropen.com/articles/10.1186/s40658-021-00405-3
- Physical quantities useful for quality control of quantitative SPECT/CT (Nuclear Medicine Review 2021): https://journals.viamedica.pl/nuclear_medicine_review/article/download/NMR.2021.0020/63672

## Connected records

- technologies: [Monte Carlo dosimetry](https://nuclide.cc/technologies/monte-carlo-dosimetry/), [Radioligand dosimetry](https://nuclide.cc/technologies/radioligand-dosimetry/), [SPECT dosimetry workflow for radionuclide therapy](https://nuclide.cc/technologies/spect-dosimetry-workflow/), [SPECT/CT](https://nuclide.cc/technologies/spect-ct/)
- isotopes: [Lutetium-177](https://nuclide.cc/isotopes/lu-177/), [Yttrium-90](https://nuclide.cc/isotopes/y-90/)

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