In a related field, autism research, new findings show a brain-scanning measurement of “grey matter (GM) volumetric data, to assess whether individual ADHD adolescents can be accurately differentiated from healthy controls based on objective, brain structure measures…”
from Autism Speaks, http://asdresearchinitiative.wordpress.com/2013/05/24/grey-matter-adhd-autism/
While this study is looking for biological measurements to identify people with autism spectrum disorders AND ADHD, it explains that the screening mechanism is a good way to detect ADHD. Rather than compare brain waves (see my blog post here), it looks at actual structures of different parts of the brain.
Many doctors and psychologists say that there are usually enough (subjective) behavioral reports from parents and teachers to determine if a person suffers from ADHD. However, these objective biometric tests may be useful in deciding on medication/s, which could be enormously helpful.