# Impact of image reconstruction on cerebral blood flow measured with 15O-water positron emission tomography

## TL;DR

This study shows that cerebral blood flow measurements using 15O-water PET depend on image reconstruction methods and spatial resolution, especially in grey and white matter.

## Contribution

The study reveals that regional cerebral blood flow values are reconstruction-dependent due to partial volume effects, while whole brain values are not.

## Key findings

- Whole brain CBF showed little dependence on reconstruction methods.
- Grey matter CBF negatively correlated with spatial resolution (r = -0.96).
- White matter CBF positively correlated with spatial resolution (r = 0.93).

## Abstract

15O-water positron emission tomography (PET) is considered the gold standard method for non-invasive measurement of cerebral blood flow (CBF). However, previously published average CBF values in healthy subjects have varied greatly and the cause of these variations remains unclear. This study investigates how image reconstruction methods and spatial resolution affect CBF measurements with 15O-water PET.

Eight healthy subjects each underwent dynamic 15O-water PET scans with continuous arterial blood sampling. Images were reconstructed using two different algorithms; ordered subset expectation maximisation and block sequential regularised expectation maximalisation with varying reconstruction parameters. CBF was estimated for the whole brain, grey matter, and central white matter. Reconstruction-specific effective spatial resolution was estimated using phantom measurements and simulations.

The mean whole brain CBF was 0.48 mL/cm3/min and showed little dependence on the image reconstruction method. Grey matter CBF varied between 0.52 and 0.57 mL/cm3/min, and central white matter CBF between 0.20 and 0.28 mL/cm3/min. Regional CBF showed great dependence on effective spatial resolution with a negative correlation between grey matter CBF and resolution (r = -0.96) and a positive correlation between central white matter and resolution (r = 0.93).

This study concludes that grey matter and central white matter CBF, but not whole brain CBF measured with quantitative 15O-water PET is reconstruction method dependent, mainly due to varying spatial resolution with consequent partial volume effects. Variations in published CBF values cannot be explained solely by reconstruction methods or spatial resolution.

The online version contains supplementary material available at 10.1186/s40658-025-00760-5.