Transcranial Perfusion Sonography Using a Low Mechanical Index and Pulse Inversion Harmonic Imaging: Reliability, Inter-/Intraobserver Variability

Zusammenfassung

Ziel: Die transkranielle Perfusionssonografie (TPS) ist eine neue, nicht invasive Methode zur Darstellung der Hirnperfusion. Ziel war die Bewertung einer neuen TPS-Modalität, die einen niedrigen MI mit einer hohen (nahezu Echtzeit) Bildrate kombiniert und die Untersuchung deren Intra- und Interobserver-Variabilität. Material und Methoden: 10 gesunde Probanden erhielten 3-mal TPS mit einem niedrigen MI (1,0) und einer hohen Bildrate (8,3 Hz). Die Untersuchungen wurden von 2 Sonografeuren im Cross-over-Design durchgeführt: 1. 2-fache Messungen bei je 5 Probanden (Intraobserver-Testung); und 2. einfache Untersuchung der jeweils anderen 5 Probanden (Interobserver-Testung). Aus 8 etablierten Regions of Interest (ROI) wurden Zeitintensitätskurven (TIC) und deren Maximalintensität (PI), Zeit-bis-zur-PI (TTP), Fläche-unter-der-Kurve (AUC) und zerebrale Transitzeit (CTT) berechnet. Die Qualität der TIC wurde mithilfe des Determinationskoeffizienten abgebildet. TIC-Parameter wurden deskriptiv dargestellt. Intra- und Interobserver-Variabilität wurde nach Spearman untersucht. Ergebnisse: Die TIC-Qualität war sehr gut (r² = 0,92, 0,87 – 0,97). Die Intraobserver-Variabilität war bei dem erfahreneren Untersucher geringer (r = 0,70 vs. r = 0,29). Die Interobserver-Reliabilität lag bei r = 0,34 (p < 0,05) und war damit moderat. TTP (25,7 – 28,1 s; Mittel 26,8 s) und CTT (8,2 – 10,7 s; Mittel 9,9 s) waren die robustesten Parameter. Schlussfolgerung: TPS mit niedrigem MI erlaubt transkranielle Perfusionsuntersuchungen unter nahezu Echtzeitbedingungen. Dies ermöglicht eine bessere Kontrolle der Sondenposition. Solide Ultraschallerfahrung gewährt eine hohe Reliabilität dieser Technik und macht TPS zu einem interessanten Modus für Diagnostik und Follow-up von Perfusionsveränderungen z. B. bei Schlaganfällen oder anti-angiogenetischer Tumortherapie.

Abstract

Purpose: Transcranial perfusion sonography (TPS) is an emerging noninvasive bedside method for evaluating brain perfusion. The purpose was to assess the feasibility of a low MI/almost real-time frame rate approach and to test its intra-/interobserver variability. Materials and Methods: 10 healthy volunteers were investigated 3 times with TPS at a low MI (1.0) and a high frame rate (8.3 Hz). Investigations were performed by 2 sonographers in a cross-over design: 1.) twofold measurements each with 5 volunteers (intraobserver test), and 2.) single measurements of the other 5 volunteers (interobserver test). From 8 established regions of interest (ROI), time-intensity curves (TIC) with the following parameters were calculated: peak intensity (PI), time-to-PI (TTP), area-under-curve (AUC), and cerebral transit time (CTT). The TIC quality was described by the coefficient of determination. TIC parameters were presented descriptively. Intra- and interobserver variability was tested by Spearman’s correlation. Results: The overall quality of the TIC was very good (mean r² = 0.92, 0.87 – 0.97). TTP (25.7 – 28.1 sec; mean 26.8 sec) and CTT (8.2 – 10.7 sec; mean 9.9 sec) were the most robust parameters. The intraobserver variability was lower with the more experienced sonographer (r = 0.70 vs. r = 0.29). The interobserver reliability was r = 0.34 (p < 0.05). Conclusion: Low MI TPS allows for nearly real-time imaging facilitating probe control. Sound sonographer experience allows for a high reliability and makes TPS an interesting tool for the diagnosis and follow-up of perfusion changes, e. g. in stroke or anti-angiogenic brain tumor therapy.

Key words

harmonic imaging - brain perfusion - transcranial sonography - ultrasound contrast agents - microcirculation

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