Chang CC et al, 2012: In Vitro Study of the Revised Ultrasound Based Real-Time Tracking of Renal Stones for Shock Wave Lithotripsy: Part 1
Chang CC, Pu YR, Manousakas I, Liang SM, Yu FM, Tong YC, Lin SH.
Dept. of Urology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
PURPOSE: Extracorporeal Shock Wave Lithotripsy has been popular since 1980s. Of all the conventional lithotriptors, only 30% to 50% of shock waves are focused on stones. We developed an ultrasound based real-time stone tracking system (1st version) to improve accuracy and treatment efficiency. Yet, some problems remained. We have now revised the existing system and tested its reliability and performance.
MATERIALS & METHODS: We revised the system by adding more algorithms to reduce misidentification of renal stones (2nd version). We verified the advanced system with two tests. In each test, non-tracking and tracking with the 1st and 2nd versions were conducted by using thirteen stone trajectories.
1. Coincidence Test: Evaluating the accuracy of targeting the stone within the effective focal area.
2. Stone Fragmentation Efficiency Test: Clarifying the decrease in number of shocks for stone fragmentation.
RESULT: In the Coincidence Test, the results (Mean±S.D.) of the non-tracking, 1st, and 2nd version of tracking systems are 68.8±18.8%, 89.9±5.2% and 94.3±4.5%, respectively. Statistically, the 2nd version is significantly better than the 1st version (p=1.5×10-4). In the Stone Fragmentation Efficiency Test, the results (Mean±S.D.) of the non-tracking, 1st and 2nd version are 49.5±14.2%, 85.1±4.5% and 89.5±4.2%, respectively. Statistically, the 2nd version is significantly better than the 1st version as well (p=1.9×10-8).
CONCLUSIONS: The results show that the revised tracking system is better than the 1st one. It not only improves the efficiency of treatment, decreases the misidentification of stones, but also has the ability to shorten the treatment time.
J Urol. 2012 Nov 27. doi:pii: S0022-5347(12)05620-0. 10.1016/j.juro.2012.11.111. [Epub ahead of print]
PMID: 23201381[PubMed - as supplied by publisher]
I like this paper because it offers a technique to improve ESWL but… The group has essentially published 3 papers concerning ultrasound guided targeting within 11 years.
(1. Chang CC, Liang SM, Pu YR et al: In vitro study of ultrasound based real-time tracking of renal stones for shock wave lithotripsy: part 1. J Urol 2001; 166: 28.
2. Chang CC, Manousakas I, Pu YR et al: In vitro study of ultrasound based real-time tracking for renal stones in shock wave lithotripsy: Part II - A simulated animal experiment. J Urol 2002; 167: 2594.
3. Chen CJ, Hsu HC, Chung WS et al: Clinical experience with ultrasound-based real-time tracking lithotripsy in the single renal stone treatment. J Endourol 2009; 23: 1811). and others have done similar studies (Orkisz, M., Farchtchian, T., Saighi, D. et al: Image based renal stone tracking to improve efficacy in extracorporeal lithotripsy. J Urol, 160: 1237, 1998)
A major problem of continuous ultrasound targeting is the three-dimensional movement of the kidney while ultrasound offers only a two-dimensional imaging. The authors use a trick in their experiments to overcome this problem but I have some doubts if this works in real life.
Fig.2a in the 2001 publication and the fig. 4a in the current publication illustrate stone trajectories without real-time tracking “to demonstrate how much a stone can deviate from the focal area during treatment.” To me both recordings seem to show examples of badly centered stone positioning in relation to the focal area of the lithotripter. By a simple change in the position the hit rate could be improved. I tried to illustrate that in the subsequent figure without using the author’s original figures.
In their first publication in 2001 the authors stressed that "it is important that a skillful and experienced physician should localize the stone." and they changed their setting: "At the end of this study we decided to adjust the stone position by moving the table rather than moving the generator."
In their 2009 publication on first clinical results on 1332 patients they stressed again that "it is important to have a skillful and experienced physician localizing the stone." We know from several reports that a devoted user will improve the results of EWSL simply by taking extra care to achieve good results. There are no other publications on the lithotripter used except the author's 2009 publication.
The interested reader could broaden his view on the problem of ultrasound focusing by having a second look at the reviewers choice of the 2nd Quarter 2012 No.33: Quantitative Assessment of Shockwave Lithotripsy Accuracy and the Effect of Respiratory Motion by Sorensen MD, Bailey MR, Shah AR, Hsi RS, Paun M, Harper JD. J Endourol. 2012, 26(8): 1070-1074.