SPECT Alzheimer’s imaging gains more momentum

PET has dominated the amyloid imaging ring for several years now, but a preclinical study is showing some signs that SPECT could give PET a run for its money eventually, especially in translational research, according to a study published Dec. 4 in the Journal of Nuclear Medicine.

Bin Ji, PhD, from the Molecular Imaging Center at the National Institute of Radiological Sciences in Chiba, Japan, and colleagues evaluated I-125 DRM106 beta amyloid binding in transgenic mouse models and compared the results to imaging with I-125 IMPY, another investigative amyloid SPECT agent. Sensitivity of the former was then assessed using a different radiolabel, I-123, and I-123 DRM106 was then compared to the PET agent C-11 Pittsburgh compound B (PiB) and C-11 PBB3. Ex-vivo autoradiographic imaging analyses and in vivo molecular imaging were both performed to see how the SPECT agents measured up.

“Although inferior to PET in terms of sensitivity and quantitative performance, [SPECT] imaging has advantages of operating cost and already-installed rate in medical hospitals, making it more suitable for primary screening for prodromal Alzheimer's disease patients,” wrote the authors.

Results of the study showed that I-125 DRM106 had a higher sensitivity for amyloid imaging than IMPY, which appears to have a low signal-to-noise ratio for amyloid imaging and a metabolic instability that hampers its potential. There also was a strong correlation between I-123 DRM106 binding and amyloid deposition in C-11 PiB scans. DRM106 appears to bind preferentially to dense cored/neuritic plaques compared to PiB, which also binds to areas of diffuse plaques.

“This suggests that I-123/125 DRM106 is more suitable than C-11 PiB for translational research of the progression of amyloid pathology when using existing [amyloid precursor protein] transgenic mouse models, most of which express numerous dense-cored, but not Alzheimer's disease-like diffuse plaques,” the researchers wrote.

Unlike other potential amyloid agents that have shown non-specific binding, especially in white matter, and less-than-ideal washout, I-125 DRM106 in healthy brain tissues was reduced to less than 4 percent after 60 minutes.

“As a result, there was very low non-specific binding in white matter and other brain regions without amyloid pathology,” the authors concluded.

More research will need to be conducted to validate DRM106 SPECT amyloid imaging as a viable diagnostic test for Alzheimer’s pathology and progression.