31653 Project course in Biomedical Engineering

Acoustical calibration unit for Spatial Compound scanning in surgery:

A research project is currently taking place at Gentofte Hospital, in which an artery is scanned with ultrasound during surgery (in vivo), removed from the patient and subsequently scanned again (in vitro). The aim of the project is to investigate the changes in acoustic properties of the tissue, due to change from living state at 37°C to dead state at 20°C.

The ultrasound scanner used (HDI 5000), is a quite complicated piece of equipment, and it is used by others between the two sets of scannings. Because we are interested in differences between the two sets of scannings, it is very important that the scanner works exactly the same way during the two scanning sessions.

Thus, in this project, a small phantom (a box with given acoustic properties) must be designed, into which the transducer can easily be inserted and an image recorded. This will make it possible to make a reference image after each scanning session.

This project has several phases:

1. Medical diagnostic ultrasound is studied, the transducer and scanning geometry is studied.
2. It is discussed what the most ideal image would be. Some simulations with Field II might be nescessary. Ways to make the phantom with rubber and different tissue mimicking materials are discussed. Pros and cons are considered.
3. A design is agreed upon. Drawings are made to scale in Matlab. A small report is written. This report is commented by the advisor and ATL.
4. The phantom is build by our instrument maker based on the drawings. Report writing.
5. The phantom is tested. Report writing.

Details:

The transducer has a length of 4 cm and 256 elements. It uses the scan angles -12°, -8°, -4°, 0°, 4°, 8°, 12°. All numbers are approximative. The center frequency of the emitted pulse is 7.5 MHz. When ultrasound travels in living tissue, it is attenuated with approximately 1 dB/cm/MHz. The transducer is fixed by two rods of approximately 2 cm in diameter, as shown on the photo below.