Dementia is the progressive decline and loss of cognitive functions such as orientation, memory, perception, attention, and judgement that cause worsening in daily activities. There are many reasons causing dementia, but the most common one is Alzheimer's disease. The clinical diagnosis of dementia can be challenging especially in the early stages of disease. Early and accurate diagnosis of the disease has great importance because treatment is more effective when the medication is started before the irreversible brain damage. Although there are tests for exclusion of certain causes of dementia, results can rarely lead to definitive diagnosis. For this reason, imaging tools are playing an increasingly important role in the workup of dementia patients. Imaging can be performed by various methods such as structural-anatomical, cerebral blood flow, cerebral glucose metabolism, neurochemical, or molecular imaging. In chronological order, computed tomography (CT), magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), and positron emission tomography (PET) are the commonly used imaging techniques in dementia diagnosis. In many neurodegenerative disorders, significant brain function alterations can be detected by SPECT or PET even when structural images with CT or MRI reveal no specific abnormalities. By the development of new tracers, PET is becoming a commonly used imaging tool in the diagnosis and differential diagnosis of dementia. PET imaging can be performed by using tracers indicating cerebral glucose metabolism, neuropathology (amyloid p plaques, neurofibrillary tangles), and neurotransmitter activity (cholinergic, serotoninergic, dopaminergic). Brain 2-[fluorine-18]fluoro-2-deoxy-d-glucose (F-18) FDG PET is a minimally invasive diagnostic imaging procedure used to evaluate cerebral glucose metabolism which provides an index of local synaptic activity and the dominant biochemical maintenance processes in dementia. Cerebral glucose hypometabolism on FDG-PET is a downstream marker of neuronal injury and neurodegeneration. Except cerebral glucose metabolism, pathological protein deposits such amyloid and tau, neurotransmitter activity alterations and existing neuroinflammation can also be detected by various PET tracers. The use of nuclear medicine techniques alone or combined with MRI can lead to accurate diagnosis of various subtypes of dementia especially with overlapping clinical symptoms. Early and accurate diagnosis can also facilitate early and effective treatment options which prevent high treatment costs of advanced disease. In conclusion, by the development of new PET tracers, nuclear medicine imaging will continue to play an important role in dementia both now and in the future. Keywords: Dementia, nuclear medicine, diagnostic tools, PET/CT Demans; oryantasyon, hafiza, algilama, dikkat, yargilama, gercegi degerlendirme gibi kognitif fonksiyonlarin gunluk yasam aktivitesini bozacak oranda ve ilerleyici kaybi olarak tanimlanabilir. Demansin pek cok nedeni olmakla birlikte en sik nedeni Alzheimer hastaligidir. Demans sendromlarinin tanisi, ozellikle de hastaligin erken doneminde klinisyenler acisindan oldukca zordur. Hastaligin erken ve dogru tanisi, kullanilan tedavilerin erken donemde yani kalici beyin hasari olusmadan baslanmasi durumunda daha etkili olmasi nedeniyle buyuk onem tasimaktadir. Bilissel disfonksiyonlarin tanisinda belli basli nedenleri dislamada kullanilan testler olsa da, sonuclari nadiren kesin bir taniya yonlendirebilmektedir. Bu nedenle goruntuleme yontemleri demans hastalarinin tani/ayirici tanisinda giderek daha buyuk bir role sahip olmaktadir. Demansta goruntuleme; yapisal/anatomik degisiklikler, serebral kan akimi, glukoz metabolizmasi, norokimyasal yolaklar ve molekuler goruntuleme esaslari uzerinden yapilabilmektedir. Kronolojik siraya bakildiginda bilgisayarli tomografi (BT), ardindan manyetik rezonans goruntuleme (MRG), tek foton emisyon bilgisayarli tomografi (SPECT) ve pozitron emisyon tomografi (PET) demansta kullanilan goruntuleme yontemleridir. Pek cok norodejeneratif hastalikta, BT veya MRG gibi yapisal goruntuleme teknikleri ile henuz spesifik bulgular saptanmaz iken PET veya SPECT gibi nukleer tip yontemleri ile onemli beyin fonksiyon degisiklikleri saptanabilmektedir. Farkli ajanlarin gelistirilmesi ile de demans tani/ayirici tanisinda PET kullanimi giderek yayginlasmaktadir. PET goruntuleme; glukoz metabolizmasi, noropatoloji (amiloid birikimi, norofibriler yumaklar), noroenflamasyon (lokal glial cevap/mikroglial aktivasyon), norotransmitter (kolinerjik, serotonerjik, dopaminerjik) yolaklar uzerinden yapilabilmektedir. Klinikte en yaygin kullanilan goruntuleme yontemi olan 2-(fluorine-18) florodeoksiglukoz (F-18 FDG) PET, serebral glukoz metabolizmasi uzerinden lokal sinaptik aktivite ve dominant biyokimyasal islevin degerlendirilebildigi minimal invaziv tanisal bir goruntuleme yontemidir ve serebral glukoz metabolizmasinin olcumune olanak saglar. F-18 FDG PET ile saptanan serebral glukoz hipometabolizmasi noronal hasar ve norodejenerasyonun bir gostergesidir. FDG disinda norodejeneratif demans tiplerinde izlenen amiloid ve tau gibi patolojik protein birikimleri, degisim gosteren norotransmitter duzeyleri ve var olan noroenflamasyon da cok cesitli ajanlar kullanilarak PET ile gosterilebilmektedir. Demans patogenezinin farkli yolaklarini gosterebilen nukleer tip yontemlerinin tek basina veya MRG ile kombine olarak kullanilmasi, klinik olarak cakisan demans nedenlerinin buyuk bir tanisal dogruluk ile ayrimina olanak vermektedir. Erken ve dogru tani, erken ve efektif tedaviye olanak saglayacak, ileri demans tablosunun getirdigi maddi ve manevi yikimlarin onune gececektir. Demans tanisinda yeni gelistirilen goruntuleme ajanlari ile nukleer tip gelecekte de bu alandaki rolunu giderek pekistirecektir. Anahtar Kelimeler: Demans, nukleer tip, tanisal yontemler, PET/BT