Laboratory evaluation of a next generation transversal ultrasound system
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Laboratory Evaluation of a Next Generation Transversal Ultrasound System. Mark E. Schafer, Ph.D. President and Principal Scientist, Sonic Tech, Inc . Chief Technology Officer and VP, R&D, Sound Surgical Technologies, LLC.

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Laboratory Evaluation of a Next Generation Transversal Ultrasound System

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Laboratory Evaluation of a Next Generation Transversal Ultrasound System

Mark E. Schafer, Ph.D.

President and Principal Scientist, Sonic Tech, Inc.

Chief Technology Officer and VP, R&D,

Sound Surgical Technologies, LLC

I am a consultant to several phaco companies, and have received research funding for this work

Contact email: [email protected]


Purpose & Outline

Purpose:

  • To provide baseline comparative data for different phaco devices, specifically for a newly introduced transversal system – AMO Whitestar Signature with Ellips FX

  • Testing focused on Clinically Relevant settings

    Outline:

  • Measurement results using several previously studied approaches:

    • Needle Shaft Temperature Rise (non-frictional)

    • Cutting Effectiveness into artificial lens material

    • Acoustic Output

  • Compare results with another non-longitudinal phaco device – Infiniti Torsional Ozil

  • Discussion and Conclusion


Standard “Longitudinal” phaco is an in/out motion

“Torsional” or “T-phaco” uses a twisting motion of the tip rather than a longitudinal motion (only one of the two modes can operate at a time, therefore the need to switch back and forth)

“Transverse” or “Ellips” uses a combination of side to side and in/out simultaneously; may be used with either straight or bent tips

What are the technologies/modes?


Thermal Measurements: Materials & Methods

  • Full computer control and acquisition of thermal images for analysis

  • Irrigation and aspiration flows balanced to mimic closed system in eye: Fluid rate precisely measured at 30ml/min, at temperature of 22±0.5°C

  • Systems run for 5 second foot pedal time; results scaled to 0.5 or 1 sec

  • High resolution thermal imaging (FLIR) camera records thermal image of hub, needle, and tip

  • An open fluid chamber allows the entire length of the needle to be examined

  • Cup designed so that fluid would only touch tip, to allow aspiration, but not interfere with thermal imaging

  • Inner cutaway cup maintained fluid at desired level; outer cup held overflow

  • Hub, shaft, and tip tracked and separately recorded


  • Thermal Testing: Results

    • Thermal imaging showed distributed heat sources for transversal mode included both the hub region and the shaft

    • In longitudinal mode, the heat source was predominantly in the hub transition region

    • Hyperpulse (WhiteStar) modes reduced the thermal rise

    • Analysis was scaled to the one second on-time point, as shown in the graph by the vertical line

    • Multiple experiments were conducted under the same conditions and the results averaged


    Thermal Testing: Results

    • The one-second temperature rise for Elllips at typical clinical settings of 25-50% amplitude, in a WhiteStar 6-12 mode, ranged from 2.1 to 3.5°C

    • In Longitudinal mode, for the same WS mode, the temperature rise was lower, on the order of 0.5 to 1.0°C

    • The difference is due to the location of the heat source

    • Note that this does not account for friction between the shaft and the sleeve, which would be significantly higher in longitudinal mode than in transversal or torsional


    Measuring Cutting: Materials & Methods

    • Custom cutting force system

    • Full computer control of motor and high resolution acquisition of position and force data for analysis

    • Simulated lens target material

  • Constant force (60g weight), measure displacement as a function of time

    • Fluid rates maintained at 30cc/min

    • 10 second experiment; initial 2 seconds to establish position baseline; systems then run for 8 second foot pedal time

    • Systems operated over a range of clinically relevant/recommended settings


    Cutting Effectiveness: Results

    • Multiple test runs conducted for each measured condition

    • Penetration measured and analyzed to find a cutting rate in terms of millimeters per second

    • Ellips cutting rates varied from 0.35mm/sec at 25% setting to 1.7mm/sec at the 50% setting


    Acoustic Output: Materials & Methods

    • Acoustic measurement system captures both the low frequency (handpiece drive) energy as well as the cavitational energy

    • Rotational fixture allows mapping the distribution of energy, which relates to the motional direction of the tip

    • Data can correlate to cutting efficiency depending upon cavitation readings


    Acoustic Output: Results

    • Drive energy levels match theory for longitudinal; for transversal, less acoustic energy is generated because of the acoustic dipole pattern, as confirmed by angular data

    • Difference between theory and measurement represents low frequency ultrasonic energy converted into Cavitation

    • In Transveral mode, Cavitation is generated in region around the tip including the sides, rather than just at the front, as is the case for Longitudinal

    • The front panel setting which denotes the start of Cavitation action matches the setting which demonstrates increased cutting effectiveness


    Comparison to Torsional

    • Transversal mode produces less internal heating, with improved cutting performance, in comparison with Torsional, at clinically relevant/recommended amplitude settings

    • This is due in part because Transversal motion preserves some longitudinal component

    • Transversal mode can also be used with straight tips, which permits more choices for the surgeon; bent tips would be expected to have slightly better cutting performance, and higher acoustic output, without significantly higher thermal rise


    Discussion / Conclusion

    • This study provided an initial investigation into this new phaco modality, which was only introduced into the market this year

    • Additional work will be required to examine all the interdependent configuration possibilities, such as drive setting/mode and tip size and configuration

    • Preliminary data suggest that Transversal mode demonstrates superior characteristics in terms of the balance of safety and efficacy, relative to other non-longitudinal modalities

      • Ultimate goal is to provide users with a consistent set of metrics by which to compare different systems, permitting a better understanding of energy input and clinical outcome


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