Reconstruction of an input function from a dynamic PET water image using multiple tissue curves.

Area of Science:

• Nuclear Medicine
• Radiochemistry
• Medical Imaging

Background:

• Cerebral blood flow (CBF) quantification is crucial for understanding brain physiology and pathology.
• Current Positron Emission Tomography (PET) methods for CBF assessment, using tracers like Oxygen-15 (15O), typically require invasive arterial blood sampling to determine the arterial input function (AIF).
• The need for a non-invasive alternative to arterial blood sampling in PET-based CBF studies is significant.

Purpose of the Study:

• To develop and validate a novel, completely non-invasive technique for reconstructing an image-derived input function (IDIF) from dynamic 15O-PET images.
• To enable accurate CBF quantification without the need for invasive arterial blood sampling.

Main Methods:

• A new formula was developed to express the input function using tissue time-activity curves and a rate constant parameter.
• Rate constants were estimated by minimizing differences between reproduced inputs derived from multiple tissue curves extracted from dynamic 15O-PET images.
• The mean of these estimated inputs was used as the IDIF, and the method was validated in 29 human subjects against the conventional arterial blood sampling method, alongside simulation studies.

Main Results:

• The reconstructed IDIFs closely matched measured arterial input functions in human subjects.
• CBF values calculated using the IDIF method showed a strong correlation (r=0.97) and minimal difference (<8%) compared to the arterial blood sampling method.
• Simulation studies indicated potential parameter-related errors below 10% and suggested an optimal number of around 500 tissue curves for robust input function reconstruction.

Conclusions:

• Image-derived input functions (IDIFs) can be successfully reconstructed directly from tissue curves in dynamic 15O-PET imaging.
• This non-invasive technique offers a viable alternative to arterial blood sampling for CBF quantification.
• The developed method holds promise for simplifying and improving the accessibility of CBF assessments in various patho-physiological studies.