Research Opportunities in the Medical Imaging Group
We are always looking for new students with
knowledge and interest in one or more of the following areas: C/C++
programming and algorithm design, signal processing, computer
graphics, image processing, ultrasound.
The list below gives an overview of some of our current
- 3D freehand elastography. Some tumours can be felt as a
lump beneath the skin, because of the difference between
the elastic modulus in the tumour and that of the surrounding tissue. In
elastography the goal is to map the elastic modulus at a fine
resolution and thus enable the detection of tumours that are too
small or deep to feel. The medical imaging group have recently demonstrated
the first ever 3D elastogram based on freehand 3D ultrasound. A
paper has been submitted to MICCAI04 reporting this result.
- Combining freehand 3D ultrasound with volumetric probes.
There are currently two ways to acquire 3D ultrasound data:
volumetric probe and freehand. In a volumetric probe either a 2D
array of transducer elements, or some sort of mechanical scanning
arrangement is used to sweep the ultrasound beam over the volume of
interest. In a freehand system the clinician sweeps the 2D probe
over the volume and the probe trajectory is measured to permit
subsequent 3D visualisation and measurement. The volumetric probe
is good for small volumes. The freehand system is good for larger
volumes, when specialist probes are required, and when registration
of the data to an external coordinate system is required
(eg. radiotherapy planning). In the medical imaging group, we
intend to combine both approaches by building a freehand system
around a volumetric probe. This system will offer data of
good homogeneity and local resolution, yet permit the scanning
and measurement of structures that cannot fit into a single sweep of
- Freehand 3D ultrasound without an external position
sensor. Freehand 3D ultrasound involves tracking the trajectory of
the ultrasound probe as the clinician performs the scan so that the
2D ultrasound slices can be subsequently reconstructed in 3D by
computer. Such systems are inconvenient to use in a clinical
environment because of the need to have a position sensing system
with a fixed datum (eg. magnetic transmitter or camera unit)
external to the ultrasound probe. There are currently two
image-based algorithms for performing freehand 3D ultrasound without
any sensor at all; one developed by Siemens, and the other by
ourselves. However, these techniques are of limited accuracy and
prone to drift. We are currently developing combinations of other
sensors, such as optical fibre tapes that can sense their own
curvature and MEMS accelerometers and gyros to combine with the
image-based algorithms. The result will be a system that is both
accurate and easy to use. For the MEMS work we are collaborating
with Dr Ashwin Seshia from the micromechanics research centre.
- Realtime radio frequency (RF) 3D ultrasound. Most
freehand 3D ultrasound systems work by combining conventional 2D
scan slices. Through a unique collaboration with Dynamic Imaging
Ltd, the medical imaging group have built a system in which the RF
data from the ultrasound machine is recorded live at 66.7 MHz. This
enables 3D information to be computed directly from the raw data,
without the loss of phase and dynamic range caused by conventional
2D pre-processing. The realtime RF system is a key first step to
enable us to make progress on the two projects listed below.
- Determining material properties using ultrasound.
Ultrasound images are formed using information from backscattered
sound. Information about deep structures is therefore liable to be
corrupted by the material properties of the superficial tissue
through which the ultrasound beam has to pass during the imaging
process. To overcome this limitation we will use high
frequency short-range scans to determine the speed of sound and
attenuation characteristics of the superficial tissue. This
information can then be used to correct any distortion in the deeper
scans. Data from each depth is used to correct the next level down.
We therefore call the approach "Progressive establishment of tissue
properties at depth".
- Increasing ultrasound resolution by deconvolution.
Traditionally, ultrasound imaging has always been limited by an
inability to resolve scatterers closer together than the wavelength
of the sound used. The rate of attenuation of sound in the body is
proportional to its frequency. This means that high frequency
ultrasound (with a short wavelength and good resolution), has
limited penetration range. We are studying techniques based on
combining multiple scans to overcome this limitation. Some of this
work is being performed in collaboration with Dr Nick Kingsbury and
James Ng from the Signal Processing Laboratory.