Method for measuring tracer uptake in brain tissue using PET image analysis

The invention consists of a method for analyzing brain images acquired using Positron Emission Tomography (PET). The PET acquisition procedure required for the invention involves acquiring a first static brain PET scan of short duration, between 1 and 8 minutes after administration of the tracer, and a second static brain PET scan approximately 50-70 minutes after administration.

How does it work?

The method is applicable to brain PET scans acquired with non-receptor tracers in general, also known as “flow tracers,” in particular fluorinated tracers selective for amyloid protein.

The first scan is performed by positioning the patient in the scanner before injecting the tracer. A scan lasting 0-10 minutes is then performed starting from the complete injection of the tracer (called early). The patient is then removed from the scanner and taken to a suitable waiting room nearby. Approximately 50-70 minutes after the injection (the exact time depends on the tracer), the patient is placed back in the scanner for a second scan (called late) lasting approximately 20 minutes (the duration also depends on the tracer).

The analysis method (b) comprises the following steps:

1) have two static brain PET images acquired on an individual between 0 and 10 minutes and approximately 50 minutes after administration of a non-receptor tracer;

2) spatially normalize the first and second images (typically, the early image is used as the “moving image” and the late image as the “fixed image”);

3) Preselect a region of interest (brain ROI) that includes the brain parenchyma and excludes the theca, ventricles, cerebellum, and brainstem.

4) select a region corresponding to the 85th percentile of intensities (ROI 1) in the first (early) PET image;

5) select a region corresponding to the 95th percentile of intensities (ROI 2) in the second (delayed) PET image;

6) calculate the average of the counts <I_roi1> e <I_roi2> respectively in ROI 1 and ROI 2on late scanning;

7) calculate the ratio of average intensities according to the equation TDr = <I_roi1> / <I_roi2>

Applications

Clinical evaluation of brain PET with tracer.

Advantages

• More accurate and stable measurements over time;
• independence from segmentation issues and choice of Region of Interest.