Increasingly, a large number of neuroimaging techniques are being developed and used for research, with some ultimately entering clinical practice (Scheltens et al., 2002; O'Brien, 2007). For most clinicians working with dementia patients, it can be very hard to keep abreast of developments in the field. For example, when does a potentially exciting new technique for diagnosis or monitoring disease progression become sufficiently validated to be accepted by the scientific community? When does such a validated method for research then become justified for use in routine clinical practice? Closely linked to this, when does one have sufficient evidence that a diagnostic tool changes practice to engage with discussions with those commissioning or paying for health services to make a strong business case for funding for the method to be made available? It is also often far from clear, when faced with a patient with cognitive difficulties, exactly what scan should be requested, at what point and why. If one scan is uninformative or equivocal then what should be the next steps? Are there factors that limit sensitivity of a given technique, such as age? Is it worth suggesting another form of brain imaging to find further information, should one wait and monitor the patient clinically over time, or even repeat the same scan to look at progression? These are challenging but important questions which are all addressed in this supplement. Different papers look critically at what imaging methods are currently available – or may very soon become available – in the clinic, what they can show in particular circumstances, how they should be interpreted and how and when such scans should be requested.

Neuroimaging has become part of the required investigations when assessing a patient with dementia. In this brief paper, we summarize the role of computed tomography (CT) in the routine work-up in dementia and provide some information about the role of the CT scan in the field of dementia research.

Although CT is far less sensitive than magnetic resonance imaging (MRI) in detecting changes associated with cognitive impairment, it may still have a role in this regard. This role is mainly that of detecting secondary, sometimes treatable causes of cognitive impairment, such as intracranial masses. In this sense, CT should be seen as a first-line tool. Possible advantages of CT are lower cost; shorter acquisition time, making it more adaptable to patients with poor compliance; and the possibility that it can be performed in patients with metal devices, such as a pacemaker.

The role of CT in the field of dementia research is very restricted in comparison to that of MRI, and is limited to the structural assessment of vascular lesions, and to a lesser extent, to that of degenerative changes, particularly when using specific slicing.

Clinical neuroimaging is increasingly being used in the diagnosis of neurodegenerative diseases and has become one of the most important paraclinical tools in the diagnosis of dementia. According to current guidelines, neuroimaging, preferably magnetic resonance imaging (MRI), should be performed at least once during the diagnostic work-up of patients with suspected or definite dementia. MRI is helpful in identifying or excluding potentially treatable causes of dementia; however, these account only for a small proportion of dementias. In addition, MRI is able to support the clinical diagnosis in a memory clinic setting by identifying certain patterns of atrophy and vascular damage. Visual rating scales are well-established methods in the clinical routine for the assessment and quantification of regional/global cortical atrophy, hippocampal atrophy and vascular damage. In addition, MRI is able to detect certain aspects of pathology associated with dementia, such as cerebral microbleeds which are related to cerebral amyloid angiopathy and Alzheimer pathology. This review paper aims to give an overview of the application of structural MRI in the diagnostic procedure for memory clinic patients in terms of excluding and supporting the diagnosis of various diseases associated with dementia.

Both perfusion SPECT and FDG-PET provide images that closely reflect neuronal activity. There is a characteristic regional impairment in Alzheimer's disease (AD) that involves mainly the temporo-parietal association cortices, mesial temporal structures and to a more variable degree also the frontal association cortex. This pattern of functional impairment can provide a biomarker for diagnosis of AD and other neurodegenerative dementias at the clinical stage of mild cognitive impairment, and for monitoring of progression. FDG-PET is quantitatively more accurate and thus better suited to multicenter studies than perfusion SPECT. Regional metabolic and blood flow changes are closely related to clinical symptoms, and most areas involved in these changes will also develop significant cortical atrophy. FDG-PET is complementary to amyloid PET, which targets a molecular marker that does not have a close relation to current symptoms. Current restrictions in the availability and cost of FDG-PET are being reduced, as oncological FDG-PET is being adopted as a standard clinical service in most countries. Limitations in the availability of trained staff should be overcome by training programs set up by professional organizations. Against the background of the development of new criteria for diagnosing AD before the onset of dementia, FDG-PET is expected to play an increasing role in diagnosing patients at an early stage of AD and in clinical trials of drugs aimed at preventing or delaying the onset of dementia.

Over the past ten years, dopaminergic imaging has become increasingly part of the assessment and diagnosis of dementia. There are numerous PET and SPECT ligands available that target different steps in the process of neurotransmission. Abnormalities in dopaminergic imaging measures are consistent features of dementia with Lewy bodies (DLB) and other parkinsonian syndromes, and can be used to facilitate diagnosis, particularly in distinguishing between DLB and Alzheimer's disease. This review summarizes present knowledge in this area and the implications for current and future clinical practice.

Molecular neuroimaging techniques such as PET are proving valuable in the early and differential diagnosis of Alzheimer's disease (AD). With the advent of new therapeutic strategies aimed at reducing β-amyloid (Aβ) burden in the brain to potentially prevent or delay functional and irreversible cognitive loss, there is increased interest in developing agents that allow assessment of Aβ burden in vivo.

Amyloid imaging with PET has proven useful in the discrimination of dementias, showing significantly higher Aβ burden in the gray matter of AD patients when compared with healthy controls or patients with frontotemporal dementia. ApoE ɛ4 carriers, independent of diagnosis or disease severity, present with higher Aβ burden than non-ɛ4 carriers. Amyloid imaging matches histopathological reports in aging and dementia, reflecting the true regional density of Aβ plaques in cortical areas. It also appears to be more sensitive than FDG-PET for the diagnosis of AD.

In healthy older people there is an increasing prevalence of amyloid positive scans with age, rising from 20% in the seventh decade to 60% in the ninth decade. Of people with mild cognitive impairment (MCI), 40–60% present with detectable cortical Aβ deposition. In both groups, Aβ deposition is associated with a higher risk for cognitive decline and dementia due to AD. These observations suggest that Aβ deposition is not part of normal aging, supporting the hypothesis that it occurs well before the onset of symptoms and is likely to represent preclinical AD in asymptomatic persons and prodromal AD in MCI. Further longitudinal observations, coupled with different disease-specific tracers and biomarkers, are required to confirm this hypothesis and further elucidate the precise role of Aβ deposition in the course of AD.

Relatively new developments in MRI, such as functional MRI (fMRI), magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) are rapidly developing into imaging modalities that will become clinically available in the near future. They have in common that their signal is somewhat easier to interpret than structural MRI: fMRI mirrors excess cerebral blood flow, in many cases representing brain activity, MRS gives the average volume concentrations of specific chemical compounds, and DTI reflects “directedness” of micro-anatomical structures, of particular use in white matter where fiber bundle disruption can be detected with great sensitivity. While structural changes in MRI have been disappointing in giving a diagnosis of sufficient sensitivity and specificity, these newer methods hold out hope for elucidating pathological changes and differentiating patient groups more rigorously. This paper summarizes promising research results that will yet have to be translated into real life clinical studies in larger groups of patients (e.g. memory clinic patients). Where available, we have tried to summarize results comparing different types of dementia.

Over the past five to ten years, neuroimaging capability for neurodegenerative diseases has made remarkable progress. However, debate remains as to the true clinical utility of these advanced and costly investigations. Not only is the place of these tests in diagnostic algorithms unclear, but the access to them varies both within and between countries. We sought to gather informed opinion from recognized leaders in the field who can combine both an academic and a clinical perspective on the use of neuroimaging in their own countries. Opinion is presented from Scotland, Argentina, the Czech Republic, France, the USA and Australia. The emerging consensus was one of ongoing caution. While in most countries there was a sense that the use of more advanced imaging techniques was growing, their hour has not yet cometh. However, these techniques, rather than falling from the Ivory Tower, should descend slowly step by step onto fertile and receptive clinics from where better clinical guidelines will emerge.