2012 Proceedings - International Tissue Elasticity Conference

079 REAL–TIME STRAIN IMAGING OF THE PROSTATE USING THE ABLATHERM® HIFU DEVICE.
Lucie Brasset 1 , Remi Souchon 1 , Stefan Catheline 1 , Jean–Yves Chapelon 1 , Albert Gelet 2 ,
Olivier Rouviere 2 .
1 INSERM, Laboratory of Therapeutic Applications of Ultrasound (LabTAU), Lyon, FRANCE;
2 Hospices Civils de Lyon, Edouard Herriot Hospital, Department of Urology, Lyon, FRANCE.
Background: Transrectal high–intensity focused ultrasound (HIFU) has become a reasonable option for the
treatment of prostate cancer, with 5–year disease–free survival similar to that of radiotherapy. However,
future improvements are desirable in patient selection, localization of the tumor foci, assessment of the
volume treated and early detection of recurrence [1]. Previous studies demonstrated that strain imaging has
the potential to detect cancer foci [2] and HIFU lesions [3]. However, image quality in vivo was suboptimal
because acquisition frame rates were low and real time capabilities were missing.
Aims: Develop a fast, real time and stable strain imaging system that can be used during HIFU therapy of the
prostate. We hypothesized that high quality strain imaging of the prostate was feasible through the
combination of high acquisition frame rate and stable probe positioning (to minimize undesired motion),
directional compression (to ensure that the principal direction of displacements coincides with the direction of
propagation of the ultrasound beam) and real time feedback (allowing the visual assessment of consistency
between consecutive images and corrective action whenever image quality was deemed unsatisfactory).
Methods: Axial images of the prostate were acquired before and after HIFU treatment in five patients.
Strain imaging was performed using the transrectal imaging probe integrated in the Ablatherm® HIFU
device (Edap–TMS, Vaulx–en–Velin, France) and a Hawk 2102EXL scanner (B&K Medical, Herlev,
Denmark) equipped with a research interface. The transrectal probe was attached to a motorized table,
thus ensuring stability of the system, and covered with a balloon. The balloon was filled with a coupling
liquid to provide acoustic coupling. Prostate compression was performed by filling the balloon. Strain
images were calculated and displayed in real time using a time–domain cross–correlation algorithm [4]
running on an 8–core computer. The algorithm uses pre–calculated sums to speed–up the calculation [5].
Results: The strain imaging system was capable of imaging the prostate in real time, with a frame rate up
to 60 frames per second. Excellent correlation (>0.95) was obtained in most parts of the gland, except in
highly hypoechoic areas. The zonal anatomy of the prostate was clearly visible in the strain images in all
patients, with a soft peripheral zone and a stiff transition zone. These features were consistent with those
previously observed in vitro [2].
Conclusions: The system provided high–quality strain images of the prostate in all patients. Future work
is now needed to assess the performance of the system for cancer foci detection and for the assessment of
the treated volume.
Acknowledgements: The authors gratefully acknowledge EDAP–TMS for technical support.
References:
[1] Rouviere O et al.: Transrectal High–Intensity Focused Ultrasound Ablation of Prostate Cancer: Effective
Treatment Requiring Accurate Imaging. Eur J Radiology, 63, pp. 317–327 2007.
[2] Souchon R et al.: Human Prostate Elastography: In Vitro Study. Proc IEEE Ultrasonics Symp, pp. 1251–1253; 2003.
[3] Souchon R et al.: Visualisation of HIFU Lesions using Elastography of the Human Prostate In Vivo: Preliminary
Results. Ultrasound Med Bio, 29(7), pp. 1007–1015, 2003.
[4] Zahiri–Azar R and Salcudean SE: Motion Estimation in Ultrasound Images using Time Domain Cross Correlation
with Prior Estimates. IEEE Transactions on Biomedical Engineering, 53(10), pp. 1990–2000 2006.
[5] Luo J and Konofagou EE: A Fast Normalized Cross–Correlation Calculation Method for Motion Estimation. IEEE
Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 57(6), pp. 1347–1357, 2010.
Figure 1: The system provided high–quality strain images, as illustrated by these typical sonogram and strain images.
Displacement (upper right) and cross–correlation (lower right) images were displayed in real time and were used for
quality control, demonstrating consistent displacements and high (>0.95) correlation.
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