Effects of the method of drawing regions of interest on the differential diagnosis of extrapyramidal syndromes using 123I-iodolisuride SPET

SPECT imaging evaluation in movement disorders: far beyond visual assessment

Single photon emission computed tomography (SPECT) imaging with (123)I-FP-CIT is of great value in differentiating patients suffering from Parkinson's disease (PD) from those suffering from essential tremor (ET). Moreover, SPECT with (123)I-IBZM can differentiate PD from Parkinson's "plus" syndromes. Diagnosis is still mainly based on experienced observers' visual assessment of the resulting images while many quantitative methods have been developed in order to assist diagnosis since the early days of neuroimaging. The aim of this work is to attempt to categorize, briefly present and comment on a number of semi-quantification methods used in nuclear medicine neuroimaging. Various arithmetic indices have been introduced with region of interest (ROI) manual drawing methods giving their place to automated procedures, while advancing computer technology has allowed automated image registration, fusion and segmentation to bring quantification closer to the final diagnosis based on the whole of the patient's examinations results, clinical condition and response to therapy. The search for absolute quantification has passed through neuroreceptor quantification models, which are invasive methods that involve tracer kinetic modelling and arterial blood sampling, a practice that is not commonly used in a clinical environment. On the other hand, semi-quantification methods relying on computers and dedicated software try to elicit numerical information out of SPECT images. The application of semi-quantification methods aims at separating the different patient categories solving the main problem of finding the uptake in the structures of interest. The semi-quantification methods which were studied fall roughly into three categories, which are described as classic methods, advanced automated methods and pixel-based statistical analysis methods. All these methods can be further divided into various subcategories. The plethora of the existing semi-quantitative methods reinforces the feeling that visual assessment is still the base of image interpretation and that the unambiguous numerical results that will allow the absolute differentiation between the known diseases have not been standardized yet. Switching to a commonly agreed-ideally PC-based-automated software that may take raw or mildly processed data (checked for consistency and maybe corrected for attenuation and/or scatter and septal penetration) as input, work with basic operator's inference and produce validated numerical results that will support the diagnosis is in our view the aim towards which efforts should be directed. After all, semi-quantification can improve sensitivity, strengthen diagnosis, aid patient's follow-up and assess the response to therapy. Objective diagnosis, altered diagnosis in marginal cases and a common approach to multicentre trials are other benefits and future applications of semi-quantification.

Quantitative analysis of striatal dopamine D2 receptors with 123 I-iodolisuride SPECT in degenerative extrapyramidal diseases

123I-Iodolisuride has high specific affinity for binding on dopamine D2 receptors in the striatum and has been used in a few single photon emission computed tomography (SPECT) studies of extrapyramidal disorders. The diagnosis of Parkinson's disease (PD) is very difficult in the first 5 years of evolution, with 15-25% false positive diagnoses. The aim of this study was therefore to determine the value of iodolisuride SPECT in discriminating Parkinson's from the most frequent Parkinson-plus syndromes (PPS). Seventeen patients with an extrapyramidal syndrome had a SPECT examination 1 h after injection of 180-185 MBq of 123I-iodolisuride. They were followed under dopaminergic treatment for at least 2 years. After 2 years, they were separated in two groups according to specific clinical criteria and sensitivity to dopaminergic treatment: nine patients had PD (age = 59.8+/-8.8 years; Hoehn and Yahr = 1.8+/-0.7; evolution = 4.3+/-3 years) and eight had PPS (age = 71.6+/-7.3 years; Hoehn and Yahr = 2.9+/-2.0; evolution = 4.1+/-1.5 years). The binding potential of iodolisuride in the striatum was assessed by considering the striatum (S)/occipital lobe (O) ratio at the pseudo-equilibrium 1 h after injection. The S/O ratio was statistically different between PD and PPS (1.97+/-0.3 vs. 1.65+/-0.2 (P<0.02)). Iodolisuride SPECT could differentiate both groups with a sensitivity of 88.8% and a specificity of 75%. Iodolisuride is a good specific D2 receptor ligand for SPECT and complements specific clinical criteria for the diagnosis of Parkinson's disease and differentiation between different extrapyramidal disorders.

Development of Tc-99m labeled tropanes: TRODAT-1, as a dopamine transporter imaging agent

Advances in the technetium chemistry have significantly enhanced the development of Tc-99m radiopharmaceuticals for clinical use. Efforts in designing novel Tc-99m labeled receptor or site-specific imaging agents using [Tc(v)O](+3)N(2)S(2) core have produced useful imaging agents for single photo emission computed tomography (SPECT). The success in developing Tc-99m TRODAT-1 for CNS dopamine transporters (DAT) serves as the first example of Tc-99m site-specific imaging of human brain. New innovative Tc-99m labeled site-specific agents are particularly suitable to develop simple and useful routine diagnostic procedures.

Imaging of the dopaminergic system in parkinsonism with SPET

Parkinsonism is a feature of various neurodegenerative diseases. Since it is well known that the dopaminergic system plays a major role in parkinsonism, numerous reports have focused on the assessment of the dopaminergic system in vivo. While the use of positron emission tomography (PET) for routine application is still hampered by its limited availability, single photon emission tomography (SPET) has been shown to deliver comparable results to PET in clinical settings. In recent years SPET investigations of the dopamine transporter and of the dopamine D2-like receptors have provided valuable information about the pre- and postsynaptic dopaminergic system in parkinsonism. This article briefly reviews the literature dealing with SPET imaging in parkinsonism and specifically addresses the ligands used, the methodology applied, and the current major clinical applications.