Ultraschall in Med 2012; 33(7): E313-E320
DOI: 10.1055/s-0032-1312924
Original Article
© Georg Thieme Verlag KG Stuttgart · New York

Thermal Effects of Diagnostic Ultrasound in an Anthropomorphic Skull Model

Thermische Effekte diagnostischen Ultraschalls in einem anthropomorphen Schädelmodell
E. Vyskocil
1  Department of Internal Medicine II, Medical University Vienna
,
S. Pfaffenberger
2  Department of Internal Medicine II, Cardiology, Medical University Vienna
,
C. Kollmann
3  Center for Biomedical Engineering & Physics, Medical University Vienna
,
A. Gleiss
4  Center for Medical Statistics, Informatics, and Intelligent Systems, Medical University Vienna
,
G. Nawratil
5  Institute of Discrete Mathematics and Geometry, Vienna University of Technology
,
S. Kastl
1  Department of Internal Medicine II, Medical University Vienna
,
E. Unger
3  Center for Biomedical Engineering & Physics, Medical University Vienna
,
K. Aumayr
6  Department of Pathology, Medical University of Vienna
,
O. Schuhfried
7  Department of Physical Medicine and Rehabilitation, Medical University Vienna
,
K. Huber
8  3rd Medical Department for Cardiology and Emergency Medicine, Wilhelminenhospital
,
J. Wojta
1  Department of Internal Medicine II, Medical University Vienna
,
M. Gottsauner-Wolf
1  Department of Internal Medicine II, Medical University Vienna
› Author Affiliations
Further Information

Publication History

07 November 2011

27 April 2012

Publication Date:
28 June 2012 (eFirst)

Abstract

Purpose: Exposure to diagnostic ultrasound (US) can significantly heat biological tissue although conventional routine examinations are regarded as safe. The risk of unwanted thermal effects increases with a high absorption coefficient and extended insonation time. Certain applications of transcranial diagnostic US (TC-US) require prolonged exposure. An anthropomorphic skull model (ASM) was developed to evaluate thermal effects induced by TC-US of different modalities. The objective was to determine whether prolonged continuous TC-US application results in potentially harmful temperature increases.

Materials and Methods: The ASM consists of a human skull with tissue mimicking material and exhibits acoustic and anatomical characteristics of the human skull and brain. Experiments are performed with a diagnostic US device testing four different US modalities: Duplex PW (pulsed wave) Doppler, PW Doppler, color flow Doppler and B-mode. Temperature changes are recorded during 180 minutes of insonation.

Results: All measurements revealed significant temperature increases during insonation independent of the US modality. The maximum temperature elevation of + 5.25° C (p < 0.001) was observed on the surface of the skull exposed to duplex PW Doppler. At the bone-brain border a maximum temperature increae of + 2.01 °C (p < 0.001) was noted. Temperature increases within the brain were < 1.23 °C (p = 0.001). The highest values were registered using the duplex PW Doppler modality.

Conclusion: TC-US induces significant local heating effects in an ASM. An application duration that extends routine clinical periods causes potentially harmful heating especially in tissue close to bone. TC-US elevates the temperature in the brain mimicking tissue but is not capable of producing harmful temperature increases during routine examinations. However, the risk of thermal injury in brain tissue increases significantly after an exposure time of > 2 hours.

Zusammenfassung

Ziel: Thermische Effekte stellen ein potenzielles Risiko bei der Verwendung von prolongierter Ultraschall(US)-Anwendung dar. Ein entscheidender Faktor ist die Expositionszeit, welche die Gefahr von thermischen Schäden am Gehirn, aber auch an den dem Schallkopf näherliegenden Geweben erhöht. Anhand 1eines anthropomorphen Schädelmodells wurde die Temperaturentwicklung über eine Applikationsdauer über 180 min analysiert.

Material und Methoden: Es wurden 4 unterschiedliche diagnostische US-Modalitäten getestet: Duplex-PW-Doppler, PW-Doppler, Color-Flow-Doppler und B-Mode. Gemessen wird die Temperaturveränderung während einer Expositionszeit von 180 min an unterschiedlichen Messpunkten entlang des Schallverlaufs mittels Thermosensoren.

Ergebnisse: Unabhängig von der Modalität zeigten sich signifikante Temperaturanstiege in allen Messlokalisationen. Der höchste Anstieg von + 5,25 °C (< 0,001) wurde zwischen Muskel und Schädelknochen gemessen. Im Bereich zwischen Knochen und Gehirn betrug die maximale Temperaturanstieg + 2,01 °C (p < 0,001). In tiefer liegenden Hirngewebsschichten fand sich kein potenziell schädigender Temperaturanstieg (< 1,23°C; p < 0,001).

Schlussfolgerung: Transkranieller diagnostischer US erzeugt signifikante Temperaturanstiege entlang des Schallverlaufes. Eine prolongierte Anwendungsdauer verursacht potenziell schädliche thermische Effekte in knochennahen Geweben. Auch die Temperatur in gehirnäquivalentem Gewebe wird signifikant erhöht. Es entstehen jedoch keine thermischen Schäden innerhalb einer Applikationszeit von 2 h.