Category: Clinical Stones: Ureteroscopy

MP24-6 - Is your finger on the pulse? A study of laser fiber to stone distance on fragmentation when altering pulse modulation or width

Sun, Sep 23
10:00 AM - 12:00 PM

Introduction & Objective :

New generation holmium lasers allow the surgeon to choose multiple parameters for lithotripsy, including variable pulse width and pulse modulation. The Moses technology is a pulse modulation that offers a “Contact” and “Distance” mode, optimized for operation at a laser fiber to stone distance of 0-1 mm, and 1-2 mm respectively. Pulse modes may have different effects on ablation based on the distance of the fiber tip to stone. In light of this, we assessed the effect of fiber to stone distance on stone crater volume testing a range of pulse parameters.

Methods :

Single pulse experiments were conducted using a flat plate BegoStone (15:3) model at 1.0J utilizing short pulse (SP), long pulse (LP), Moses Contact, and Moses Distance modes. Energy was delivered from a 120W Ho:YAG laser (Moses P120, Lumenis)) by a 230 µm core fiber (Moses 200 D/F/L, Lumenis,) placed with a 3D positioner at various distances (0, 0.5, 1.0, 2.0, and 3 mm) from the stone in a grid of locations. Five trials were performed for each experiment. The fiber was stripped and cleaved prior to each trial. The study outcome was the volume of the crater measured by reflectance microscopy. Volume was estimated using the following formula (𝑉𝑜𝑙𝑢𝑚𝑒 = (4/3∗𝑋⁄2∗𝑌⁄2∗𝑍∗π) ∗1/2). Two sample t-test was used to compare cohort means.

Results :

Figure 1 presents the mean crater volume for each pulse parameter at different fiber to stone distances. The volume of ablated material declined rapidly as the distance increased. Even at 0.5 mm, the ablation volume was significantly lower than at 0 mm distance. The ablation crater produced when using Moses Distance was significantly higher than other pulse modes at 1 mm fiber distance (p<0.05), and higher than SP and LP at 2 mm fiber distance (p<0.05).

Conclusions : Holmium laser lithotripsy ablation is significantly affected by fiber distance with the greatest ablation volume obtained with the fiber in contact with the stone. If ablation is performed in a “non-touch” manner, at 1-2 mm distance, Moses Distance mode produced the larger ablation crater at a single pulse energy of 1J. Future work is needed to understand the role of pulse modulation and the role of distance in optimizing a dusting technique for ureteroscopy.

Ali H. Aldoukhi

Research fellow
University of Michigan
Ann Arbor, Michigan

I'm a research fellow in the Urology department at the University of Michigan. In our lab we study factors affecting stone fragmentation during holmium laser lithtotripsy.

William W. Roberts

University of Michigan
Ann Arbor, Michigan

William W. Roberts, MD is Professor of Urology and Biomedical Engineering at the University of Michigan. He earned a B.S. in Physics from the Massachusetts Institute of Technology in 1992, an M.D. from the Johns Hopkins University School of Medicine in 1997, and completed his urology training at the Brady Urological Institute at Johns Hopkins. He joined the faculty of the University of Michigan in 2004 and is now Director of the Division of Endourology. His clinical practice is focused on minimally invasive surgery, endourology, and urinary stone disease.

Dr. Roberts is part of the multidisciplinary scientific team at the University of Michigan that developed histotripsy, a non-invasive, focused ultrasound technology that induces controlled cavitation to mechanically ablate targeted tissues within the body. He is the director of the Translational Histotripsy Laboratory and has led the research effort to apply histotripsy for treatment of urologic diseases in preclinical models.

Dr. Roberts has presented his work at international and national meetings and has authored over 100 peer-reviewed publications. His research contributions have been recognized in the form of multiple grants and awards from the National Institutes of Health, American Urological Association Foundation, Coulter Foundation, and Engineering and Urology Society. He was the 2014 recipient of the prestigious AUA Gold Cystoscope Award.

Timothy L. Hall

Associate Research Scientist
University of Michigan
Ann Arbor, Michigan

Khurshid R. Ghani

Associate Professor of Urology
University of Michigan
Ann Arbor, Michigan

Khurshid Ghani is an Associate Professor of Urology at the University of Michigan. His research interests include novel techniques of endoscopic and robotic surgery for renal stone disease, health services research and surgical quality improvement. In particular Dr Ghani has been focused on advancing a Dusting technique for endoscopic stone surgery and has extramural funding to study optimal laser settings for holmium laser lithotripsy. He is the Course Director of the Developments in Ureteroscopic Stone Treatment (D.U.S.T.) symposium. In addition, Dr Ghani serves as Co-Director of the Michigan Urological Surgery Improvement Collaborative, which is a consortium of 44 urology practices aiming to improve the quality of urological care in the state of Michigan.