Neuraceq images should be interpreted only by readers who successfully complete Electronic Media- or In-Person Training provided by the manufacturer [seeWarnings and Precautions (5.1)]. The objective of Neuraceq image interpretation is to estimate β-amyloid neuritic plaque density in brain gray matter, not to make a clinical diagnosis. Image interpretation is performed independently of a patient’s clinical features and relies upon the recognition of image features in certain brain regions.

Image Display   
PET images should be displayed in the transaxial orientation using gray scale or inverse gray scale. The sagittal and coronal planes may be used for additional orientation purposes. CT or MR images may be helpful for anatomic reference purposes. However, visual assessment should be performed using the axial planes according to the recommended reading methodology.

Image Interpretation   
Interpretation of the images is made by visually comparing the activity in cortical gray matter with activity in adjacent white matter. Regions displayed in the PET images which ‘anatomically’ correspond to white matter structures (e.g., the cerebellar white matter or the splenium) should be identified to help the readers orient themselves. Images should be viewed and assessed in a systematic manner, starting with the cerebellum and scrolling up through the lateral temporal and frontal lobes, the posterior cingulate cortex/precuneus, and the parietal lobes. For a gray matter cortical region to be assessed as showing ‘tracer uptake’, the majority of slices from the respective region must be affected.

For each patient, the PET image assessment is categorized as either “β-amyloid-positive” or “β-amyloid-negative”. This determination is based on the assessment of tracer uptake in the gray matter of the following four brain regions: the temporal lobes, the frontal lobes, the posterior cingulate cortex/precuneus, and the parietal lobes; according to the following ‘rules for assessment’ [see Warnings and Precautions (5.1.)]:

  
• β-amyloid negative \- tracer uptake (i.e., signal intensity) in gray matter is lower than in white matter in all four brain regions (no β- amyloid deposition)

• β-amyloid positive \- smaller area(s) of tracer uptake equal to or higher than that present in white matter extending beyond the white matter rim to the outer cortical margin involving the majority of the slices within at least one of the four brain regions (“moderate” β-amyloid deposition), or a large confluent area of tracer uptake equal to or higher than that present in white matter extending beyond the white matter rim to the outer cortical margin and involving the entire region including the majority of slices within at least one of the four brain regions (“pronounced” β-amyloid deposition). There is no known clinical or histopathologic correlation distinguishing “moderate” from “pronounced”   
β-amyloid deposition.

Examples of positive and negative scans for each of the four brain regions are illustrated in Figure 1.

Figure 1 Axial view of negative (top row) and positive (bottom row) Neuraceq PET scans

Cerebellum: A contrast between the white matter (arrows) and gray matter is seen in both negative and positive scans. Extracerebral tracer uptake in scalp and in the posterior sagittal sinus (arrowhead) can be seen. Lateral temporal lobes: Spiculated or “mountainous” appearance of the white matter (arrows) is seen in the negative scan, and radioactive signal does not reach the outer rim of the brain (dashed line) due to lower tracer uptake in the gray matter. The positive scan shows a “plumped”, smooth appearance of the outer border of the brain parenchyma (dashed line) due to tracer uptake in the gray matter. Frontal Lobes: Spiculated appearance of the white matter in the frontal lobes (arrows) is seen in the negative scan. The positive scan shows the tracer uptake in these regions has a “plumped”, smooth appearance due to the increased gray matter signal (dashed line). Posterior cingulate/precuneus: Adjacent and posterior to the splenium (arrow), these regions appear as a hypo-intense “hole” (circle) in the negative scan, whereas this hole is “filled-up” (circle) in the positive scan. Parietal lobes: In the negative scan, the midline between the parietal lobes can be easily identified (long arrow); white matter has a spiculated appearance (short arrow) with low signal near the outer rim of the brain (dashed line). In the positive scan, the midline between the parietal lobes is much thinner. The cortical areas are “filled-up” and are smooth in appearance as tracer uptake extends to the outer rim of the brain.

Some scans may be difficult to interpret due to image noise, atrophy with a thinned cortex, or image blur. If a co-registered computerized tomography (CT) image is available, the CT image may be used to clarify the relationship of the Neuraceq uptake and the gray matter anatomy.