The "BPET prototype" is a small aperture PET scanner. The BPET prototype will be used with patients, which have just finished their regularly scheduled PET examination on a clinical whole body PET system. The radioactive tracer used for this procedure will still be active. This remaining acitivity will be used for an image acquisition with the BPET prototype without the need for an additional radioactive tracer dose.

The control intervention is be a brain PET scan as part of standard clinical routine. It will be done immediately before the scan on the BPET prototype.

Inclusion Criteria:

• Capable of giving Informed Consent as documented by signature (Appendix Informed Consent Form)
• ability to sit still in the head-only PET scanner for 15 minutes
• Are scheduled to receive a regular brain PET scan as part of clinical routine.
• Male and Female patients 18 years to 80 years of age

Exclusion Criteria:

• Contraindications to PET examination,
• Patient height smaller than 160 cm or taller than 200 cm,
• Patient weight more than 120 kg,
• Patient cannot sit upright for at least 15 minutes,
• Metal implants in the head,
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, severe dementia, etc. of the participant,
• Participation in another study with investigational drug/device within the 30 days preceding and during the present study,
• Previous enrolment into the current study,
• Enrolment of the investigator, his/her family members, employees and other dependent persons.