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Chapter 16

Neuropsychiatry Disorders

Jean-Paul Soucy, Denis Lacroix and Catherine Kissel Introduction

Nuclear medicine has a lengthy and distinguished reputation in the fields of neurology and psychiatry as a powerful research and clinical tool. Noninvasive in vivo demonstration of brain lesions was initially performed more than forty years ago with agents which accumulated nonspecifically. Since then we have witnessed an important evolution in the techniques used for the diagnosis of neuropsychiatric disorders. The "traditional" brain scan, based on agents sensitive to blood-brain barrier (BBB) disruption (Fig. 1), has been replaced by anatomically superior approaches such as x-ray transmission computed tomography (CT) and magnetic resonance imaging (MRI) for the study of most focal lesions.

More recently, the demonstration by nuclear medicine techniques of disturbances in regional perfusion patterns, energy consumption and neurotransmission in the brains of psychiatric patients has made a major contribution to the recognition that mental diseases (including drug addictions) are organically-based metabolic alterations, in every way comparable to diseases found in other systems. Presently, the most frequently performed clinical nuclear medicine test in neuropsychiatric disorders is SPECT evaluation of cerebral perfusion. These perfusion maps provide a snapshot of "brain activity" and are altered in a variety of neurological and psychiatric conditions even when anatomic imaging is normal.

Until recently in vivo study of neurotransmission was only possible with positron emission tomography (PET), but new SPECT agents have made this much more widely available. PET itself is undergoing a major increase in availability through technological developments that are making it a far less complicated and costly technique. Neurology and psychiatry can only benefit from this transformation.

Regional Cerebral Perfusion

Non-invasive measurements of regional cerebral blood flow (rCBF) were initially performed with freely diffusible tracers such as xenon-133 (imaged in planar or SPECT mode) or 15O-water and 11C-butanol (imaged with PET). Unfortunately, those techniques had limited availability due to complexity and the high cost of the required equipment. The development of iodine-123-labelled compounds (123I-IMP, 123I -HIPDM) which have a blood-flow related distribution in the brain afforded an easy means of evaluating rCBF, not through absolute quantification but through the description of its relative distribution. Subsequent development in the field of radiochemistry led to the synthesis of the currently used radiopharmaceuticals, 99mTc-HMPAO (Hexa Methyl Propylene Amine Oxime, Ceretec®) and 99mTc-ECD

Nuclear Medicine, edited by William D. Leslie and I. David Greenberg. ©2003 Landes Bioscience.

Figure 1. Disrupted blood-brain barrier (BBB). Two metastases (left posterior frontal, A, and right temporal, B) from a lung carcinoma: the tumors are devoid of normal astrocytes and therefore of an intact blood-brain barrier. This allows passage of 99mTc-glucoheptonate, normally excluded from the cerebral parenchyma, into the lesions.

Figure 1. Disrupted blood-brain barrier (BBB). Two metastases (left posterior frontal, A, and right temporal, B) from a lung carcinoma: the tumors are devoid of normal astrocytes and therefore of an intact blood-brain barrier. This allows passage of 99mTc-glucoheptonate, normally excluded from the cerebral parenchyma, into the lesions.

(Ethylene Cysteinate Dimer, Neurolite®). The following discussion will focus on these two agents.

Principles of rCBF Imaging

99mTc-HMPAO and 99mTc-ECD (Fig. 2) the two most commonly used agents for imaging rCBF, are injected into a peripheral vein which allows uniform mixing

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