In Moscow, Russia, Dr. Ivan Maksimovich has been experimenting with the transcatheter revascularization of the brains of dementia patients.

Using local anesthesia, he catheterizes a patient's femoral artery.  Then he sends a small laser device to the patient's cerebral arteries via the catheter. When the laser is inside the cerebral arteries, the laser delivers light energy to these arteries.

Here are Dr. Maksimovich's clinical trials:

https://file.scirp.org/pdf/JBBS20120100008_20001073.pdf

https://www.scirp.org/pdf/WJNS20120400002_96618626.pdf

It seems that Dr. Maksimovich is performing Peripheral Laser Atherectomy on cerebral arteries, and that he has had success in helping dementia patients.

Dr. Maksimovich has been working with this technique for about 10 years. Is there any doctor or scientist in the United States who is working with this technique? This sounds very interesting.

I have not been able to locate yet a similar approach being taken in the United States.  There have been several studies and trials some in the United States (some ongoing) using photobiomodulation to treat Alzheimer's disease.  Some of the most promising results came from this study.  

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5568598/

The following provides an explanation as to why this form of therapy may help in the treatment of Alzheimer's disease (and likely other forms of dementia):

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6664299/