• Ulrich Raff, Michael Hutchinson, Gonzalo M Rojas, and Isidro Huete.
• Department of Physics, University of Santiago de Chile, Santiago. uraff@usach.cl
• Acad Radiol. 2006 Jun 1; 13 (6): 721-7.

Rationale And ObjectivesSegmented inversion recovery (IR) ratio imaging (SIRRIM) has been established as a sensitive tool to assess neurodegeneration of the substantia nigra pars compacta (SN(C)) in patients with idiopathic Parkinson disease (IPD). The obtained results suggest the possibility of magnetic resonance imaging (MRI) as a biological marker for IPD. The strength and a parsimonious analysis of the technique are discussed to assess the potential of using MRI as a biological marker for IPD and improve the differential diagnosis of sporadic Parkinson disease. Our hypothesis states that the magnetic resonance SIRRIM technique allows direct visualization and quantitation of neural cell loss in the SN(C) and therefore could become a reliable biological marker for Parkinson disease. To achieve this goal, some key aspects of data acquisition and data analysis need to be addressed. The clinical impact of the SIRRIM technique could be considerable, considering that it might become a viable surrogate to other techniques.Patients And MethodsTwelve patients with IPD and 12 age-matched control subjects were imaged by using the SIRRIM technique based on two IR imaging sequences that were designed to suppress white and gray matter to assess loss of neural cells in situ by means of a ratio image (white matter suppressed image to gray matter suppressed image). The radiological index was correlated with the Unified Parkinson Disease Rating Scale (UPDRS) for patients with IPD.ResultsAll patients with IPD were identified correctly, and full dichotomization between healthy volunteers and patients was obtained with our database. Our SIRRIM technique shows that it can be used to rule out Parkinson disease from essential tremor and other forms of Parkinsonism, such as progressive supranuclear palsy and multisystem atrophy. In addition, it is sensitive enough to identify patients with early-stage IPD.ConclusionThe hypothesis of using SIRRIM as a biological marker to assess IPD is supported by excellent correlation with clinical UPDRS scoring and has proved useful for the evaluation and quantitation of neurodegeneration with our SIRRIM technique, showing, in addition, that the differential diagnosis of IPD can be improved. Technical aspects of acquisition and data processing that need to be addressed can be overcome. It ultimately confirms that our objectives can be achieved and allows us to expect assessment of the progressive development of neurodegeneration in longitudinal studies and the putative neuroprotective approaches taken during the evolution of the disease.

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