Presented by: Jeffrey Johnson MD
Weill Cornell Medicine

Introduction

There is limited data on ablation effects of thulium fiber laser (TFL) settings with varying stone composition. Little is known surrounding the photothermal effects of TFL lithotripsy regarding the chemical and structural changes with charring. We aim to identify ablation settings that predict optimal ablation efficiency across stone types and to better understand the photothermal effects of TFL lithotripsy.

Materials

Human specimens of calcium oxalate monohydrate (COM), calcium oxalate dihydrate (COD), uric acid (UA), struvite, cystine, carbonate apatite (CA) and brushite stones were ablated using 13 pre-specified settings with the Coloplast© TFL Drive. Pre- and post-ablation mass, ablation time, and total energy were recorded. Gross ablative effects were recorded during every 1-minute interval with photographs and gross description. Samples were analyzed with Fourier-transform infrared (FTIR) spectroscopy and electron microscopy (EM) to assess post-ablative effects.

Results

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Across all settings and stone types, 0.05J x 1000Hz was the most efficient ablation setting. When selected for more clinically relevant laser settings (i.e. 10-20W), 0.2J x 100Hz short pulse (SP) proved the most efficient ablation setting for COD, cystine, and struvite stones, 0.4J x 40Hz SP for COM, 0.3J x 60Hz SP for UA and CA, and 0.5J x 30Hz SP for brushite. Pulse duration impacted ablation effectiveness greatly with 6/8 (75.0%) of inadequate ablations occurring in medium or long pulse settings. The average percent of mass lost after ablation was 56.9%; cystine stones averaged the highest percent mass lost at 70.8%. Charring was observed in 39.5% specimens, most often in UA, cystine, and brushite stones across all laser settings. EM of char demonstrated a porous melting effect different to that of brittle fracture. FTIR spectroscopy of brushite char demonstrated a chemical composition change to amorphous calcium phosphate.

 

Conclusion

We describe the optimal ablation settings of TFL lithotripsy by stone composition. For patients with unknown stone composition, lasers can be pre-set to target common stone types. We recommend using short pulse for TFL lithotripsy.

Funding

Coloplast

Lead Authors

Ojas Shah, MD
Columbia University Irving Medical Center

Co-Authors

Miyad Movassaghi, MD
Columbia University Irving Medical Center

David Han, MD, MS
Columbia University Irving Medical Center

Srinath-Reddi Pingle, MD
Columbia University Irving Medical Center

Justin Lee, MD
Columbia University Irving Medical Center

James Williams, PHD
Indiana University School of Medicine

Michael Schulster, MD
Columbia University Irving Medical Center

Prakash Gorroochurn, PHD
Columbia University Department of Biostatistics

Yinming Shao, PHD
Columbia University Physics Department

Dmitri Basov, PHD
Columbia University Physics Department