International Journal of Psychiatry in Clinical Practice
ISSN: 1365-1501 (Print) 1471-1788 (Online) Journal homepage: http://www.tandfonline.com/loi/ijpc20
Topics in contemporary psychiatric practice: Neuroimaging Gin S Malhi, Mantosh Dewan To cite this article: Gin S Malhi, Mantosh Dewan (2001) Topics in contemporary psychiatric practice: Neuroimaging, International Journal of Psychiatry in Clinical Practice, 5:1, 77-78 To link to this article: http://dx.doi.org/10.1080/136515001300225259
Published online: 12 Jul 2009.
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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijpc20 Download by: [Universite Laval]
Date: 05 November 2015, At: 16:41
Ó
2001 Martin Dunitz Ltd
International Journal of Psychiatry in Clinical Practice 2001 Volume 5 Pages 77 ± 78
77
Topics in contemporary psychiatric practice Neuroimaging GIN S MALHI1 and MANTOSH DEWAN2 1
Lecturer and Consultant Psychiatrist, Mood Disorders Unit, The School of Psychiatry, UNSW, Sydney, Australia and 2 Professor and Chairman, Department of Psychiatry and Behavioural Sciences, Upstate Medical University, SUNY, 750 East Adams Street, Syracuse, NY, USA
Downloaded by [Universite Laval] at 16:41 05 November 2015
Correspondence Address Gin S Malhi, Mood Disorders Unit, School of Psychiatry, UNSW, Prince of Wales Hospital, Randwick, Sydney, NSW 2031, Australia. E-mail: [email protected]
Not long ago, imaging the living brain relied on imagination alone. It was simply not possible. Encased in bone and bathed in fluids and tissue, the brain seemed beyond direct investigation . However, over the past couple of decades rapid advances in physics and computing have made modern neuroimagin g an affordable and accessible reality. For today’s physicians , imaging the brain is a `routine investigation ’ that has considerabl e clinical utility. This in itself is a monumental achievemen t and one that is perhaps often taken for granted. Recently further advances in brain imaging technology have led to the development of functional imaging techniques that permit examination of the brain `in action’. As yet, the majority of these functional technologies are used primarily for the purposes of research. However, it is likely that in the very near future, many will find clinical use and it is important therefore that doctors in general and psychiatrist s in particular have a reasonable understanding of brain neuroimagi ng. One such application, already being realised to some extent in a few centres around the world, is the differentiatio n of Alzheimer’ s disease, with its typical parieto-temporal pattern, from other pathology. Broadly speaking, brain-imagin g technologies (see Table 1) can be divided into those that examine structure and those that examine function. Alternatively they can be described in terms of the quantities they measure. For instance, computed tomography (CT) and magnetic resonance imaging (MRI) determine physical quantities, namely, electron and proton density whereas positron emission tomography (PET) and single photon emission computed tomography (SPECT) determine metabolic quantities. However, the complexitie s of these sophisticated techniques do not lend themselves to easy classifica tion. For example, MRI, which is also known as nuclear magnetic resonance (NMR) imaging, forms the basis of both magnetic resonance spectroscopy (MRS), which is used to study chemical composition, and functional MRI
(fMRI) which detects stimulus-rela ted changes in blood flow. Strictly speaking MRS is neither structural, nor functional. Indeed, MRS does not even produce `images’, yielding instead metabolite spectra reflecting tissue composition of the chosen region. A common factor, amongst these newer technologies , is their reliance on computer processing and multiple sophisticated analyses. With many of the imaging techniques the images can be manipulated and modified to highlight certain aspects or features. However, because of this interpretation is a little more difficult . A good example of such a problem is the oft-reported functional finding of a region of `activity’. Functional activity is usually defined relative to the surroundin g areas or the average of a particular region or the whole brain. In itself it is likely to be the result of increased synaptic activity, however, this ’activity’ could be either excitatory or inhibitory. It could also be the consequence of underactivity in surrounding regions. Hence detecting and defining changes is difficult and then meaningfull y interpreting them perhaps even more so. This then is the dilemma that we face. Neuroimagin g is intrinsicall y exciting as it allows visualisatio n of the brain. It allows quantitative measuremen t and provides a generally safe and reliable method of investigation . For deriving structural information, neuroimagin g has proven to be very useful and in a variety of forms it is now an indispensabl e tool. However, functionall y it is relatively blunt and clinically difficult to interpret with confidence. Therefore it is important to be aware of the technological limitations of various neuroimagi ng techniques and be able to critically evaluate new findings. To this end the references in this article provide an overview of the techniques and their limitations. Many of the articles are reviews that are both clinically and methodologica lly instructive and have been chosen because together they deal with the majority of neuroimagi ng technologies.
78
GS Malhi and M Dewan
Table 1 Overview of Neuroimaging Techniques
Neuroimaging Technique
Description
Skull Radiography Computerized Tomography (CT)
Uses X-rays to visualise bone pathology and trauma. Dependent upon attenuation of X-rays as they pass through tissues of varying density. Results in computer-generated radiodensity maps in which dense matter, such as bone, appears white and less dense matter appears black. Application of a strong magnetic field and radiofrequency pulses produce magnetic resonance signals from which MR images can be computer-generated. The technique can be modified to provide functional information (fMRI) in addition to structural information. This relies on nuclear magnetic resonance principles (like MRI and fMRI). It provides chemical spectra of certain metabolites in specified regions of the brain. A radioactively labelled compound is administered and its gamma photon emissions are then tracked. Data thus derived is used to create images of the brain. This relies on short-acting radioactive isotopes, which eventually lead to greater resolution images than SPECT. However, it is much more expensive than SPECT as it requires an on-site cyclotron to generate the isotopes. A non-invasive technique that characterises per millisecond brain electrophysiology by analysing cerebral biomagnetic fields.
Downloaded by [Universite Laval] at 16:41 05 November 2015
Magnetic Resonance Imaging (MRI) & Functional MRI (fMRI) Magnetic Resonance Spectroscopy (MRS) Single Photon Emission Computed Tomography (SPECT) Positron Emission Tomography (PET)
Magnetic Encephalography (MEG)
RECOMMENDED LITERATURE REVIEWS 1. Steffens DC, Krishnan RR (1998) Structural neuroimagin g and mood disorders . Recent findings, implications for classificatio ns, and future directions. Biol Psychiatry 43: 705 ± 12. This review has a clear description of the clinical correlates of neuroimaging changes in mood disorders and puts forward criteria for specifying subtypes. 2. Kegeles LS, Humaran TJ, Mann JJ (1998) In vivo neurochemis try of the brain in schizophreni a as revealed by magnetic resonance spectroscopy . Biological Psychiatry 44: 382 ± 98. An excellent review that summarises recent spectroscopy studies in schizophrenia and provides a brief explanation of the technical basis of MRS and its potential future applications. 3. Dougherty D, Rauch SL (1997) Neuroimagi ng and neurobiologi cal models of depression . Harvard Rev Psychiatry 5: 138 ± 59. A comprehensive overview that integrates the significant findings from studies on structural and functional neuroimaging in depression. 4. Chakos MH, Esposito S, Charles C, Lieberman JA (1998) Clinical applications of neuroimagin g in psychiatry. Magn Reson Imag Clin North Am 6: 155 ± 64. A comprehensive review of neuroimaging in epilepsy, dementia, psychiatric and developmental disorders. 5. Dolan RJ, Friston KJ (1997) Functional imaging and neuropsychi atry. Psychol Med 27: 1241 ± 46. An informative review that discusses the conceptual issues and paradigms of functional neuroimaging. 6. Drevets WC (1998) Functional neuroimagi ng studies of depression : the anatomy of melancholia . Annu Rev Med 49: 341 ± 61. A thorough overview that shows that major depression is associated with reversible, mood state dependent, neurophysiological abnormalities in some structures, and irreversible, trait-like abnormalities in others. The article also discusses pertinent technical issues in relation to data interpretation. 7. Buchsbaum MS, Hazlett EA (1998) Positron emission tomography studies of abnormal glucose metabolism in schizophreni a. Schizophr Bull 24: 343 ± 64. Well written review, that brings together a vast literature and provides an insightful perspective on the difficulties of functional imaging.
ISSN: 1365-1501 (Print) 1471-1788 (Online) Journal homepage: http://www.tandfonline.com/loi/ijpc20
Topics in contemporary psychiatric practice: Neuroimaging Gin S Malhi, Mantosh Dewan To cite this article: Gin S Malhi, Mantosh Dewan (2001) Topics in contemporary psychiatric practice: Neuroimaging, International Journal of Psychiatry in Clinical Practice, 5:1, 77-78 To link to this article: http://dx.doi.org/10.1080/136515001300225259
Published online: 12 Jul 2009.
Submit your article to this journal
Article views: 6
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijpc20 Download by: [Universite Laval]
Date: 05 November 2015, At: 16:41
Ó
2001 Martin Dunitz Ltd
International Journal of Psychiatry in Clinical Practice 2001 Volume 5 Pages 77 ± 78
77
Topics in contemporary psychiatric practice Neuroimaging GIN S MALHI1 and MANTOSH DEWAN2 1
Lecturer and Consultant Psychiatrist, Mood Disorders Unit, The School of Psychiatry, UNSW, Sydney, Australia and 2 Professor and Chairman, Department of Psychiatry and Behavioural Sciences, Upstate Medical University, SUNY, 750 East Adams Street, Syracuse, NY, USA
Downloaded by [Universite Laval] at 16:41 05 November 2015
Correspondence Address Gin S Malhi, Mood Disorders Unit, School of Psychiatry, UNSW, Prince of Wales Hospital, Randwick, Sydney, NSW 2031, Australia. E-mail: [email protected]
Not long ago, imaging the living brain relied on imagination alone. It was simply not possible. Encased in bone and bathed in fluids and tissue, the brain seemed beyond direct investigation . However, over the past couple of decades rapid advances in physics and computing have made modern neuroimagin g an affordable and accessible reality. For today’s physicians , imaging the brain is a `routine investigation ’ that has considerabl e clinical utility. This in itself is a monumental achievemen t and one that is perhaps often taken for granted. Recently further advances in brain imaging technology have led to the development of functional imaging techniques that permit examination of the brain `in action’. As yet, the majority of these functional technologies are used primarily for the purposes of research. However, it is likely that in the very near future, many will find clinical use and it is important therefore that doctors in general and psychiatrist s in particular have a reasonable understanding of brain neuroimagi ng. One such application, already being realised to some extent in a few centres around the world, is the differentiatio n of Alzheimer’ s disease, with its typical parieto-temporal pattern, from other pathology. Broadly speaking, brain-imagin g technologies (see Table 1) can be divided into those that examine structure and those that examine function. Alternatively they can be described in terms of the quantities they measure. For instance, computed tomography (CT) and magnetic resonance imaging (MRI) determine physical quantities, namely, electron and proton density whereas positron emission tomography (PET) and single photon emission computed tomography (SPECT) determine metabolic quantities. However, the complexitie s of these sophisticated techniques do not lend themselves to easy classifica tion. For example, MRI, which is also known as nuclear magnetic resonance (NMR) imaging, forms the basis of both magnetic resonance spectroscopy (MRS), which is used to study chemical composition, and functional MRI
(fMRI) which detects stimulus-rela ted changes in blood flow. Strictly speaking MRS is neither structural, nor functional. Indeed, MRS does not even produce `images’, yielding instead metabolite spectra reflecting tissue composition of the chosen region. A common factor, amongst these newer technologies , is their reliance on computer processing and multiple sophisticated analyses. With many of the imaging techniques the images can be manipulated and modified to highlight certain aspects or features. However, because of this interpretation is a little more difficult . A good example of such a problem is the oft-reported functional finding of a region of `activity’. Functional activity is usually defined relative to the surroundin g areas or the average of a particular region or the whole brain. In itself it is likely to be the result of increased synaptic activity, however, this ’activity’ could be either excitatory or inhibitory. It could also be the consequence of underactivity in surrounding regions. Hence detecting and defining changes is difficult and then meaningfull y interpreting them perhaps even more so. This then is the dilemma that we face. Neuroimagin g is intrinsicall y exciting as it allows visualisatio n of the brain. It allows quantitative measuremen t and provides a generally safe and reliable method of investigation . For deriving structural information, neuroimagin g has proven to be very useful and in a variety of forms it is now an indispensabl e tool. However, functionall y it is relatively blunt and clinically difficult to interpret with confidence. Therefore it is important to be aware of the technological limitations of various neuroimagi ng techniques and be able to critically evaluate new findings. To this end the references in this article provide an overview of the techniques and their limitations. Many of the articles are reviews that are both clinically and methodologica lly instructive and have been chosen because together they deal with the majority of neuroimagi ng technologies.
78
GS Malhi and M Dewan
Table 1 Overview of Neuroimaging Techniques
Neuroimaging Technique
Description
Skull Radiography Computerized Tomography (CT)
Uses X-rays to visualise bone pathology and trauma. Dependent upon attenuation of X-rays as they pass through tissues of varying density. Results in computer-generated radiodensity maps in which dense matter, such as bone, appears white and less dense matter appears black. Application of a strong magnetic field and radiofrequency pulses produce magnetic resonance signals from which MR images can be computer-generated. The technique can be modified to provide functional information (fMRI) in addition to structural information. This relies on nuclear magnetic resonance principles (like MRI and fMRI). It provides chemical spectra of certain metabolites in specified regions of the brain. A radioactively labelled compound is administered and its gamma photon emissions are then tracked. Data thus derived is used to create images of the brain. This relies on short-acting radioactive isotopes, which eventually lead to greater resolution images than SPECT. However, it is much more expensive than SPECT as it requires an on-site cyclotron to generate the isotopes. A non-invasive technique that characterises per millisecond brain electrophysiology by analysing cerebral biomagnetic fields.
Downloaded by [Universite Laval] at 16:41 05 November 2015
Magnetic Resonance Imaging (MRI) & Functional MRI (fMRI) Magnetic Resonance Spectroscopy (MRS) Single Photon Emission Computed Tomography (SPECT) Positron Emission Tomography (PET)
Magnetic Encephalography (MEG)
RECOMMENDED LITERATURE REVIEWS 1. Steffens DC, Krishnan RR (1998) Structural neuroimagin g and mood disorders . Recent findings, implications for classificatio ns, and future directions. Biol Psychiatry 43: 705 ± 12. This review has a clear description of the clinical correlates of neuroimaging changes in mood disorders and puts forward criteria for specifying subtypes. 2. Kegeles LS, Humaran TJ, Mann JJ (1998) In vivo neurochemis try of the brain in schizophreni a as revealed by magnetic resonance spectroscopy . Biological Psychiatry 44: 382 ± 98. An excellent review that summarises recent spectroscopy studies in schizophrenia and provides a brief explanation of the technical basis of MRS and its potential future applications. 3. Dougherty D, Rauch SL (1997) Neuroimagi ng and neurobiologi cal models of depression . Harvard Rev Psychiatry 5: 138 ± 59. A comprehensive overview that integrates the significant findings from studies on structural and functional neuroimaging in depression. 4. Chakos MH, Esposito S, Charles C, Lieberman JA (1998) Clinical applications of neuroimagin g in psychiatry. Magn Reson Imag Clin North Am 6: 155 ± 64. A comprehensive review of neuroimaging in epilepsy, dementia, psychiatric and developmental disorders. 5. Dolan RJ, Friston KJ (1997) Functional imaging and neuropsychi atry. Psychol Med 27: 1241 ± 46. An informative review that discusses the conceptual issues and paradigms of functional neuroimaging. 6. Drevets WC (1998) Functional neuroimagi ng studies of depression : the anatomy of melancholia . Annu Rev Med 49: 341 ± 61. A thorough overview that shows that major depression is associated with reversible, mood state dependent, neurophysiological abnormalities in some structures, and irreversible, trait-like abnormalities in others. The article also discusses pertinent technical issues in relation to data interpretation. 7. Buchsbaum MS, Hazlett EA (1998) Positron emission tomography studies of abnormal glucose metabolism in schizophreni a. Schizophr Bull 24: 343 ± 64. Well written review, that brings together a vast literature and provides an insightful perspective on the difficulties of functional imaging.
