Transtemporal Ultrasound Application Potentially Elevates Brain Temperature: Results of an Anthropomorphic Skull Model

Abstract

Purpose: Transtemporal sonothrombolysis is a tool for a more effective treatment in acute stroke patients. However, some reports revealed side effects, which might be potentially connected to temperature elevation. To gain better insight into cerebral temperature changes during transtemporal sonication, diagnostic and therapeutic ultrasound (US) applications were evaluated using an anthropomorphic skull model.

Materials and Methods: The impact of diagnostic (PW-Doppler, 1.8-MHz, 0.11 W/cm², TIC 1.2) and therapeutic (1-MHz and 3-MHz, 0.07 – 0.71 W/cm², continuous and pulsed mode) US application on temperature changes was evaluated at the level of muscle/temporal bone (TB), TB/brain, brain and at the middle cerebral artery (MCA) using 4 miniature thermocouples along the US beam. Sonication lasted 120 minutes.

Results: Diagnostic ultrasound revealed a maximum temperature increase of 1.45°/0.60°/0.39°/0.41°C (muscle/TB, TB/brain, brain, MCA) after 120 minutes. Therapeutic-1-MHz ultrasound raised temperature by 4.33°/2.02°/1.05 °C/0.81°C (pulsed 1:20) and by 10.38°/4.95°/2.43°/2.08°C (pulsed 1:5) over 120 minutes. Therapeutic-3-MHz US raised temperature by 4.89°/2.56°/1.24/1.25°C (pulsed 1:20) and by 14.77°/6.59°/3.56°/2.86°C (pulsed 1:5) over 120 minutes, respectively. Continuous application of therapeutic US (1-MHz and 3-MHz) led to a temperature increase of 13.86°/3.63°/1.66°/1.48°C and 17.09°/4.28°/1.38/0.99°C within 3 minutes.

Conclusion: Diagnostic PW-Doppler showed only a moderate temperature increase and can be considered as safe. Therapeutic sonication is very powerful in delivering energy so that even pulsed application modes resulted in significant and potentially harmful temperature increases.

Zusammenfassung

Ziel: Transtemporale Sonothrombolyse ist eine nicht invasive Technik zur effizienteren Behandlung bei Patienten mit ischämischen Insult. Allerdings gab es Berichte über Nebenwirkungen, welche möglicherweise in Zusammenhang mit zerebraler Temperaturerhöhung stehen könnten. Um einen besseren Einblick in Temperaturveränderungen bei transtemporaler Beschallung zu bekommen, wurden diagnostischer und therapeutischer Ultraschall (US) anhand eines anthropomorphen Schädelmodells untersucht.

Material und Methoden: Der Einfluss von diagnostischem (PW-Doppler, 1,8 MHz, 0,11 W/cm², TIC 1,2) und therapeutischen (1 MHz und 3 MHz, 0,07 – 0,71 W/cm², kontinuierlicher und gepulster Modus) US wurde entlang der transtemporalen Schallachse mittels 4 Miniatur-Thermoelementen (Muskulatur/Temporalknochen [TK], TK/Gehirn, im Gehirn und an der Arteria cerebri media [MCA]) über 120 Minuten (min) untersucht.

Ergebnisse: Diagnostischer US ergab einen maximalen Temperaturanstieg von 1,45°/0,60°/0,39°/0,41°C (Muskulatur/TK, TK/Gehirn, Gehirn, MCA). Therapeutischer 1MHz-US zeigte eine maximale Temperaturerhöhung von 4,33°/2,02°/1,05 °C/0,81°C (gepulst 1:20) und von 10,38°/4,95°/2,43°/2,08°C (gepulst 1:5). Therapeutischer 3MHz-US ergab einen Anstieg von 4,89°/2,56°/1,24/1,25°C (gepulst 1:20) und von 14,77°/6,59°/3,56°/2,86°C (gepulst 1:5). Kontinuierliche Applikation von therapeutischem US (1 MHz und 3 MHz) zeigte einen Temperaturanstieg von 13,86°/3,63°/1,66°/1,48°C bzw. 17,09°/4,28°/1,38/0,99 °C bereits nach 3 min.

Schlussfolgerung: Diagnostischer PW-Doppler ergab lediglich einen moderaten Temperaturanstieg und kann als sicher eingeschätzt werden. Bei Beschallung mit therapeutischen Schallköpfen wird viel Energie transportiert und in Wärme umgesetzt, sodass es auch im gepulsten Modus zu signifikanten und potenziell gefährlichen Temperaturanstiegen kommt.

Key words

side effects - brain - skull - ultrasound - temperature

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