Tissue damage from ultrasonic, pneumatic, and combination lithotripsy.

PURPOSE: To conduct a comparative evaluation of ultrasonic, pneumatic, and dual ultrasonic (DUS) lithotripsy to predict the safety of probes on urinary tract tissue. MATERIALS AND METHODS: The Swiss Lithoclast Ultra (ultrasonic-only [US] and ultrasonic-pneumatic combination [US+P]) and the Gyrus ACMI Cyberwand (DUS) were evaluated. Fresh porcine ureter, bladder, and renal pelvis tissues were used with a hands-free setup to vertically apply 0, 400, or 700 g of force with each probe for a duration of 3 seconds, 5 seconds, or 3 minutes (or until perforation occurred). Data collection included whether perforation occurred and time to perforation. Histological analysis of nonperforated samples was used to compare the anatomical depth to which damage occurred. RESULTS: The total percentage of trials resulting in perforation for all tissue types, contact durations, and forces was found to be 8.5% (10/117) for US, 13.7% (16/117) for US+P, and 26.4% (31/117) for DUS. No perforations occurred with light contact (0 g) of probe force, regardless of tissue type, lithotripsy mode, or contact duration. Overall, the renal pelvis was most resistant to perforation (p=0.0004), while no difference was found between the bladder and ureter tissue (p=0.32). Force beyond 400 g and contact greater than 5 seconds increased risk for damage. CONCLUSIONS: Mode of lithotripsy, tissue type, probe force, and probe-tissue contact duration all significantly impacted the extent of damage and likelihood for perforation to occur. All devices and tissue types provided a reasonable margin of safety for probe-tissue contact times of 3 and 5 seconds with no more than 400 g of force.

Computational modeling of pedunculopontine nucleus deep brain stimulation.

OBJECTIVE: Deep brain stimulation (DBS) near the pedunculopontine nucleus (PPN) has been posited to improve medication-intractable gait and balance problems in patients with Parkinson's disease. However, clinical studies evaluating this DBS target have not demonstrated consistent therapeutic effects, with several studies reporting the emergence of paresthesia and oculomotor side effects. The spatial and pathway-specific extent to which brainstem regions are modulated during PPN-DBS is not well understood. APPROACH: Here, we describe two computational models that estimate the direct effects of DBS in the PPN region for human and translational non-human primate (NHP) studies. The three-dimensional models were constructed from segmented histological images from each species, multi-compartment neuron models and inhomogeneous finite element models of the voltage distribution in the brainstem during DBS. MAIN RESULTS: The computational models predicted that: (1) the majority of PPN neurons are activated with -3 V monopolar cathodic stimulation; (2) surgical targeting errors of as little as 1 mm in both species decrement activation selectivity; (3) specifically, monopolar stimulation in caudal, medial, or anterior PPN activates a significant proportion of the superior cerebellar peduncle (up to 60% in the human model and 90% in the NHP model at -3 V); (4) monopolar stimulation in rostral, lateral or anterior PPN activates a large percentage of medial lemniscus fibers (up to 33% in the human model and 40% in the NHP model at -3 V) and (5) the current clinical cylindrical electrode design is suboptimal for isolating the modulatory effects to PPN neurons. SIGNIFICANCE: We show that a DBS lead design with radially-segmented electrodes may yield improved functional outcome for PPN-DBS.