JNM: Florbetapir F18 performs well as Alzheimers biomarker

Images of both brain FDG-PET (top row) and brain AVID-45 (amyloid imaging agent, bottom row) PET scans, with the FDG-PET coming from two different points in progression of disease ... from mild cognitive impairment to full-blown Alzheimer’s disease four years later. Source: Kelsey Mason, research associate, Cheri Geist, research associate, and Daniel Silverman, MD, Neuronuclear Imaging Center at University of California, Los Angeles

Florbetapir F18 is an effective biomarker for Alzheimer’s disease (AD) pathology and has a wide effective dose range and high test—retest reliability, according to a study published in the March 1 issue of the Journal of Nuclear Medicine.

“Although there has been longstanding work on the development and evaluation of biomarkers that identify the consequences of AD pathology, such as MRI-defined regional brain atrophy and cerebral spinal fluid measures of B-amyloid and t-proteins, the ability to directly measure a disease-defining pathology using molecular imaging has only recently become possible,” wrote Abhinay D. Joshi, MS, of Avid Radiopharmaceuticals in Philadelphia, and colleagues.

The authors explained that initial studies used ¹¹C-Pittsburgh compound B to demonstrate the feasibility of this approach, but the 20 minute half-life of the compound limits its use. Florbetapir F18 (¹⁸F-AV-45) is an ¹⁸F amyloid PET ligand with a number of benefits. It has rapid brain uptake and rapid washout from gray tissues not containing amyloid, a short imaging time and good separation between the amyloid retention and background signal.

Joshi et al designed their study to examine the appropriate radiotracer dose for optimal image quality and test—retest reliability of amyloid PET with florbetapir F18. Visual ratings of PET image quality and tracer retention were examined in nine patients with AD and 11 younger healthy controls who received both low and standard doses of florbetapir F18. A separate set of subjects was used to assess test—retest reliability.

Results showed there were no significant differences between the 111-MBq (3-mCi) and 370-MBq (10-mCi) dose of florbetapir F18 in the visual rating of standardized uptake value ratios (SUVr).

“At both dose levels, visual ratings of amyloid burden identified 100 percent of AD subjects as AB-positive and 100 percent of [younger healthy controls] as AB-negative,” wrote the authors.

Mean intrasubject test—retest variability for cortical average SUVrs was 2.4 percent for AD subjects and 1.5 percent for controls and the overall SUVr test—retest correlation coefficient was 0.99.

“Both the dose-ranging study and the test–retest study indicate that florbetapir F18 is a robust imaging tool well suited for use as a biomarker for AD pathology in standard community PET facilities,” summed Joshi et al.