Transcranial Sonography of the Substantia Nigra: Digital Image Analysis

BACKGROUND AND PURPOSE:Increased echogenicity of the substantia nigra is a typical transcranial sonography finding in Parkinson disease. Experimental software for digital analysis of the echogenic substantia nigra area has been developed. The aim of this study was to compare the evaluation of substantia nigra echogenicity by using digital analysis with a manual measurement in patients with Parkinson disease and healthy volunteers.MATERIALS AND METHODS:One hundred thirteen healthy volunteers were enrolled in the derivation cohort, and 50 healthy volunteers and 30 patients with Parkinson disease, in the validation cohort. The substantia nigra was imaged from the right and left temporal bone window by using transcranial sonography. All subjects were examined twice by using different sonographic machines by an experienced sonographer. DICOM images of the substantia nigra were encoded; then, digital analysis and manual measurement of the substantia nigra were performed. The 90th percentile of the derivation cohort values was used as a cut-point for the evaluation of the hyperechogenic substantia nigra in the validation cohort. The Spearman coefficient was used for assessment of the correlation between both measurements. The Cohen κ coefficient was used for the assessment of the correlation between both measurements and Parkinson disease diagnosis.RESULTS:The Spearman coefficient between measurements by using different machines was 0.686 for digital analysis and 0.721 for manual measurement (P < .0001). Hyperechogenic substantia nigra was detected in the same 26 (86.7%) patients with Parkinson disease by using both measurements. Cohen κ coefficients for digital analysis and manual measurement were 0.787 and 0.762, respectively (P < .0001).CONCLUSIONS:The present study showed comparable results when measuring the substantia nigra features conventionally and by using the developed software.

Parkinson disease (PD) is a progressive neurodegenerative disorder. Postmortem and neuroimaging studies showed that PD-associated neuronal dysfunction, cell loss, and α-synuclein pathology begin years before clinical symptoms appear and clinical diagnosis is possible.^1–4 This preclinical period may be the most promising time window for successful neuroprotective interventions in PD.⁵Increased echogenicity of the substantia nigra (SN) is a typical transcranial sonography (TCS) finding in patients with PD. Recent studies reported an enlarged hyperechogenic SN in approximately 90% of patients with PD, by using cutoff values between 0.20 and 0.25 cm², depending on the specific sonography system used.^6,7 In contrast, a hyperechogenic enlarged SN is detectable in only approximately 10% of healthy volunteers.⁸ Moreover, this feature is already present in prediagnostic disease stages and persists during the course of PD without significant changes.^9,10 Approximately 60% of healthy volunteers with hyperechogenic SN show a decrease in ¹⁸F-DOPA uptake in the striatum,⁸ and hyperechogenic SN is more frequently observed in subjects prone to develop extrapyramidal symptoms after neuroleptic therapy.¹¹However, the main limitation of TCS in the evaluation of SN hyperechogenicity is the dependence of image quality on both the sonographer''s experience and the quality of the bone window.^12–14 Digital analysis of TCS images of the SN could eliminate this limitation. We developed an experimental application B-mode Assist System with a graphic user interface in Matlab (MathWorks, Natick, Massachusetts), an integrated development environment with a plug-in Image Processing Toolbox, for digital analysis of SN echogenicity.^15,16The aim of the study was to compare the manual measurement of SN with digital analysis of SN echogenicity by using the developed software obtained by 2 different sonography machines in patients with PD and healthy volunteers.