PET (positron emission tomography) scans can help detect plaques in the brain (amyloid lesions) which are associated with Alzheimer’s disease, researchers reported in Archives of Neurology.

The authors explain, as background information, that researchers are trying to understand AD more deeply, as well as other forms of dementia. In doing so, the usage of PET scans has been explored.

PET scans use nuclear medicine imaging (radiation) to create 3-dimensional color images of how things function inside the human body. The device detects pairs of gamma rays which are emitted indirectly by a positron-emitting radionuclide (tracer) – this is placed in the body on a biologically active molecule. Computers reconstruct the images.

Before performing a PET scan, a radioactive substance is produced in a machine (cyclotron); it is then tagged to a natural chemical, which is known as a radiotracer, or simply a tracer. The radiotracer is then inserted into the body.

Various teams of scientists are examining how effective various types of tracers are in identifying brain findings linked to Alzheimer’s.

First Study – Dr. David A. Wolk and team set out to see how good 18-labeled flutemetamol (a tracer) might be for brain imaging. They carried out PET scans on seven participants. They were all given a dose of 18-labeled flutemetamol.

All participants had already undergone a biopsy for normal pressure hydrocephalus, a progressive condition that is often hard to distinguish from Alzheimer’s.

They identified PET scan evidence of amyloid lesions which corresponded with laboratory analyses of the biopsied tissue.

Second Study – Dr. Adam S. Fleisher and team used the tracer florbetapir F 18 for their PET scans on 68 participants with probable AD, as well as 60 people with mild cognitive impairment, and another 82 healthy volunteers (controls).

They found variations in the brain uptake of florbetapir F 18 between the three groups, and in the identification of amyloid plaque. The authors added that the differences could be wide enough to help tell the difference between the conditions, and between unimpaired and impaired brains.

The authors wrote:

“With the potential emergence of disease-specific interventions for AD,” state Wolk et al, “biomarkers that provide molecular specificity will likely become of greater importance in the differential diagnosis of cognitive impairment in older adults.” Indeed, Fleisher et al write, “Amyloid imaging offers great promise to facilitate the evaluation of patients in a clinical setting.”

William J. Jagust wrote that the detection of amyloid lesions is “a topic of active investigation.”

He added:

“Most clinical imaging methods rely on interpretation, not quantitation,” he states. “Nevertheless, quantitation of these scans has considerable value because it provides a reliable measure that can be compared across laboratories on either a continuous or dichotomous level.”

“Using Positron Emission Tomography and Florbetapir F 18 to Image Cortical Amyloid in Patients With Mild Cognitive Impairment or Dementia Due to Alzheimer Disease”
Adam S. Fleisher, MD; Kewei Chen, PhD; Xiaofen Liu, MS; Auttawut Roontiva, MS; Pradeep Thiyyagura, MS; Napatkamon Ayutyanont, PhD; Abhinay D. Joshi, MS; Christopher M. Clark, MD; Mark A. Mintun, MD; Michael J. Pontecorvo, PhD; P. Murali Doraiswamy, MBBS, FRCP; Keith A. Johnson, MD; Daniel M. Skovronsky, MD, PhD; Eric M. Reiman, MD
Arch Neurol. Published online July 11, 2011. doi:10.1001/archneurol.2011.150

Written by Christian Nordqvist