Elastography is a non-invasive medical imaging modality that is used as a diagnostic
tool for the early detection of several pathological changes in soft tissues. Elastography
techniques provide the local strain distributions experienced by soft tissues due to
compression. The resulting strain images are called “elastograms”. In elastography, the
local tissue strains are usually estimated as the gradient of local tissue displacement. The
local tissue displacements are estimated from the time delays between gated pre- and
post-compression echo signals. The quality of the resulting elastograms is highly
dependent on the accuracy of these local displacement estimates. While several time
delay estimation (TDE) techniques have been proposed for elastography applications,
there is a lack of systematic study that statistically compares the performance of these
techniques. This information could prove to be of great importance to improve currently
employed elastographic clinical methods.
This study investigates the performance of selected time delay estimators for
elastography applications. Time delay estimators based on Generalized Cross
Correlation (GCC), Sum of Squared Differences (SSD) and Sum of Absolute Differences (SAD) are proposed and implemented. Within the class of GCC algorithms,
we further consider: an FFT-based cross correlation algorithm (GCC-FFT), a hybrid
time-domain and frequency domain cross correlation algorithm with prior estimates
(GCC-PE) and an algorithm based on the use of fractional Fourier transform to compute
the cross correlation (GCC -FRFT) . Image quality factors of the elastograms obtained
using the different TDE techniques are analyzed and the results are compared using
standard statistical tools.
The results of this research suggests that correlation based techniques outperform
SSD and SAD techniques in terms of SNRe, CNRe, dynamic range and robustness. The
sensitivity of GCC-FFT and SSD were statistically similar and statistically higher than
those of all other methods. Within the class of GCC methods, there is no statistically
significant difference between SNRe of GCC-FFT, GCC-PE and GCC –FRFT for most
of the strain values considered in this study. However, in terms of CNRe, GCC-FFT and
GCC-FRFT were significantly better than other TDE algorithms. Based on these results,
it is concluded that correlation-based algorithms are the most effective in obtaining high
quality elastograms.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-08-8445 |
| Date | 2010 August 1900 |
| Creators | Sambasubramanian, Srinath |
| Contributors | Righetti, Raffaella |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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