Ultrasound image has already been proved to be a useful tool for non-invasive strain quantifications in soft tissue.
While clinical applications only include cardiac imaging, the development of techniques suitable for musculoskeletal
system is an active area of research. On this study, a technique for speckle tracking on ultrasound images
using non-rigid image registration is presented. This approach is based on a single 2D+t registration procedure,
in which the temporal changes on the B-mode speckle patterns are locally assessed. This allows estimating
strain from ultrasound image sequences of tissues under deformation while imposing temporal smoothness in
the deformation field, originating smooth strain curves. METHODS: The tracking algorithm was systematically
tested on synthetic images and gelatin phantoms, under sinusoidal deformations with amplitudes between 0.5%
and 4.0%, at frequencies between 0.25Hz and 2.0Hz. Preliminary tests were also performed on Achilles tendons
isolated from human cadavers. RESULTS: The strain was estimated with deviations of -0.011%±0.053% on the
synthetic images and agreements of ±0.28% on the phantoms. Some tests with real tendons show good tracking
results. However, significant variability between the trials still exists. CONCLUSIONS: The proposed image
registration methodology constitutes a robust tool for motion and deformation tracking in both simulated and
real phantom data. Strain estimation in both cases reveals that the proposed method is accurate and provides
good precision. Although the ex-vivo results are still preliminary, the potential of the proposed algorithm is
promising. This suggests that further improvements, together with systematic testing, can lead to in-vivo and
The goal of radiotherapy is to deliver maximal dose to the tumor and minimal dose to the surrounding tissue.
This requires accurate target definition. In sites were the tumor is difficult to see on the CT images, such as for
rectal cancer, PET-CT imaging can be used to better define the target. If the information from multiple PETCT
images with different tracers needs to be combined, a nonrigid registration is indispensable to compensate
for rectal tissue deformations. Such registration is complicated by the presence of different volumes of bowel
gas in the images to be registered. In this paper, we evaluate the performance of different nonrigid registration
approaches by looking at the overlap of manually delineated rectum contours after registration. Using a B-spline
transformation model, the results for two similarity measures, sum of squared differences and mutual information,
either calculated over the entire image or on a region of interest are compared. Finally, we also assess the effect
of the registration direction.
We show that the combination of MI with a region of interest is best able to cope with residual rectal contrast
and differences in bowel filling. We also show that for optimal performance the registration direction should be
chosen depending on the difference in bowel filling in the images to be registered.