Infographics / Nuclear Medicine

SPECT reconstruction: FBP vs iterative, filters & resolution

The same set of 2D projection views acquired at many angles around the patient can be reconstructed two ways. Filtered back projection applies a ramp filter and smears each projection back across the matrix: it is fast but amplifies noise and produces streak or star artefacts, with only approximate attenuation correction. Iterative reconstruction (OSEM) loops through estimate, forward-project, compare and update, modelling collimator response, Poisson noise and a CT attenuation map each iteration, giving fewer artefacts and lower noise; it is now the standard method. Either route yields a 3D voxel volume that can be resliced in any plane.

SPECT reconstruction: filtered back projection versus iterative reconstruction The same set of 2D projection views acquired at many angles around the patient can be reconstructed two ways. Filtered back projection applies a ramp filter and smears each projection back across the matrix: it is fast but amplifies noise and produces streak or star artefacts, with only approximate attenuation correction. Iterative reconstruction (OSEM) loops through estimate, forward-project, compare and update, modelling collimator response, Poisson noise and a CT attenuation map each iteration, giving fewer artefacts and lower noise; it is now the standard method. Either route yields a 3D voxel volume that can be resliced in any plane. Projection views at many angles 2D line-integral images, 180–360° Filtered back projection (FBP) ramp filter + smear back • Fast, historically common • Ramp filter amplifies noise • Prone to streak / star artefacts • Attenuation correction approximate Iterative reconstruction (OSEM) estimate forward project compare update iterate until predicted ≈ measured • Models collimator response + Poisson noise • Attenuation μ-map (CT) each iteration I = I₀ e⁻ᵘˣ along each path • Fewer artefacts, lower noise • Now standard for SPECT 3D voxel volume — reslice in any plane axial, coronal, sagittal or oblique
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