Title: Transvaginal Ultrasound Scanning – Hazard and Clinical Practice
Funder: Department of Health (England)

Abstract: Background Two of the main Research Recommendations in the AGNIR Report on the health effects of ultrasound (AGNIR, 2010) were that “It would be desirable to determine the variation in the number, mode, intensity and duration of ultrasound examinations in different populations during pregnancy” and “Improved methods for the prediction of temperature rise caused by ultrasound should be developed, to include particular models for exposure of safety critical anatomical sites.” Transvaginal scanning is used to image the early fetus during pregnancy, during egg collection for IVF treatment, and to diagnose postmenopausal bleeding. In 2010/11 there were 2.7 million obstetric ultrasound examinations in the NHS (dh_129328.xls from www.dh.gov.uk), with approximately 9% of these being transvaginal (precise numbers were not available). In addition, a large number of gynaecological ultrasound scans are performed transvaginally (again precise numbers not available). Based on results for neonatal transcranial imaging (DH RPR Project RRX113 - Shaw et al, 2011) temperature rises above 6°C may occur for up to 30% of equipment. For comparison, the World Federation for Ultrasound in Medicine and Biology (WFUMB, 1998) recommended that an in situ temperature rise of 4°C for more than 5 minutes should be considered hazardous. Aims The overall aims are to use validated, anatomically relevant phantoms to survey the temperature increase caused by transvaginal clinical ultrasound equipment, and to collect quantitative data on past and current scanning practice. This will address the lack of data concerning ultrasound-related hazard arising during transvaginal ultrasound examination, particularly of the first trimester fetus. Methods The project will be divided into four technical Work Packages (WPs) and one dissemination WP. WP1: perform a detailed analysis of past and current transvaginal scanning practice using data from an archive of recorded examinations at Hillingdon hospital (1989 to 2011); and by automated monitoring of examinations at Addenbrooke's hospital. WP2: develop anatomically relevant phantoms to measure the temperature rise close to the transducer. WP3: collect data on routine clinical practice in the UK and carry out an audit of scanners in routine clinical use to measure temperature rise using the anatomical reference models at output settings typically selected by the user. WP4: measure the temperature rise occurring during real scans on patients; develop and validate thermal sensors which can be attached to the face of the probe without reducing image quality. WP5: dissemination of the results and conclusions. Team NPL brings expertise in medical ultrasound metrology, modelling of ultrasound fields and devices, thermal phantom development and hazard assessment, and national/international standards. Addenbrooke’s Hospital brings expertise in Obstetrics and Fetal Medicine, in sonography, and in medical engineering. Important collaborators are: Gail ter Haar (chair of the BMUS Safety Group and head of Therapy Ultrasound at the Institute for Cancer Research). Fiona Bottomley (Lead Sonographer at The Hillingdon Hospital NHS Trust). Trish Chudleigh (Lead Sonographer at Addenbrooke's Hospital). Impact/Policy The project will address this lack of information concerning ultrasound-related hazard and will provide a rigorous, scientific base for future DH policy and for safety guidance on routine use and clinical trials. It will also establish a methodology which can be adapted to provide similar guidance for other critical applications in the future. The issue of heating is directly relevant to the EC Medical Device Directive and there will be a clear need to follow-up the technical work of this project by establishing definitive supporting safety standards. Two members of the project team are very active in the preparation of international safety standards and so are ideally placed to ensure the UK obtains the widest benefits from the research results.


Research activity codes: 4.2 EVALUATION OF MARKERS AND TECHNOLOGIES
Health categories: REPRODUCTIVE HEALTH AND CHILDBIRTH