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ref: -0 tags: Na Ji 2p two photon fluorescent imaging pulse splitting damage bleaching date: 05-31-2019 19:55 gmt revision:5 [4] [3] [2] [1] [0] [head]

PMID-18204458 High-speed, low-photodamage nonlinear imaging using passive pulse splitters

  • Core idea: take a single pulse and spread it out to N=2 kN= 2^k pulses using reflections and delay lines.
  • Assume two optical processes, signal SI αS \propto I^{\alpha} and photobleaching/damage DI βD \propto I^{\beta} , β>α>1\beta \gt \alpha \gt 1
  • Then an NN pulse splitter requires N 11/αN^{1-1/\alpha} greater average power but reduces the damage by N 1β/α.N^{1-\beta/\alpha}.
  • At constant signal, the same NN pulse splitter requires N\sqrt{N} more power, consistent with two photon excitation (proportional to the square of the intensity: N pulses of N/N\sqrt{N}/N intensity, 1/N per pulse fluorescence, Σ1\Sigma \rightarrow 1 overall fluorescence.)
  • This allows for shorter dwell times, higher power at the sample, lower damage, slower photobleaching, and better SNR for fluorescently labeled slices.
  • Examine the list of references too, e.g. "Multiphoton multifocal microscopy exploiting a diffractive optical element" (2003)

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ref: -0 tags: tissue probe neural insertion force damage wound speed date: 06-02-2018 00:03 gmt revision:0 [head]

PMID-21896383 Effect of Insertion Speed on Tissue Response and Insertion Mechanics of a Chronically Implanted Silicon-Based Neural Probe

  • Two speeds, 10um/sec and 100um/sec, monitored out to 6 weeks.
  • Once the probes were fully advanced into the brain, we observed a decline in the compression force over time.
    • However, the compression force never decreased to zero.
    • This may indicate that chronically implanted probes experience a constant compression force when inserted in the brain, which may push the probe out of the brain over time if there is nothing to keep it in a fixed position.
      • Yet ... the Utah probe seems fine, up to many months in humans.
    • This may be a drawback for flexible probes [24], [25]. The approach to reduce tissue damage by reducing micromotion by not tethering the probe to the skull can also have this disadvantage [26]. Furthermore, the upward movement may lead to the inability of the contacts to record signals from the same neurons over long periods of time.
  • We did not observe a difference in initial insertion force, amount of dimpling, or the rest force after a 3-min rest period, but the force at the end of the insertion was significantly higher when inserting at 100 μm/s compared to 10 μm/s.
  • No significant difference in histological response observed between the two speeds.

{1406}
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ref: -0 tags: insertion speed needle neural electrodes force damage injury cassanova date: 06-01-2018 23:51 gmt revision:0 [head]

Effect of Needle Insertion Speed on Tissue Injury, Stress, and Backflow Distribution for Convection-Enhanced Delivery in the Rat Brain

  • Tissue damage, evaluated as the size of the hole left by the needle after retraction, bleeding, and tissue fracturing, was found to increase for increasing insertion speeds and was higher within white matter regions.
    • A statistically significant difference in hole areas with respect to insertion speed was found.
  • While there are no previous needle insertion speed studies with which to directly compare, previous electrode insertion studies have noted greater brain surface dimpling and insertion forces with increasing insertion speed [43–45]. These higher deformation and force measures may indicate greater brain tissue damage which is in agreement with the present study.
  • There are also studies which have found that fast insertion of sharp tip electrodes produced less blood vessel rupture and bleeding [28,29].
    • These differences in rate dependent damage may be due to differences in tip geometry (diameter and tip) or tissue region, since these electrode studies focus mainly on the cortex [28,29].
    • In the present study, hole measurements were small in the cortex, and no substantial bleeding was observed in the cortex except when it was produced during dura mater removal.
    • Any hemorrhage was observed primarily in white matter regions of the external capsule and the CPu.

{1405}
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ref: -0 tags: insertion speed neural electrodes force damage date: 06-01-2018 23:38 gmt revision:2 [1] [0] [head]

In vivo evaluation of needle force and friction stress during insertion at varying insertion speed into the brain

  • Targeted at CED procedures, but probably applicable elsewhere.
  • Used a blunted 32ga CA glue filled hypodermic needle.
  • Sprague-dawley rats.
  • Increased insertion speed corresponds with increased force, unlike cardiac tissue.
  • Greatuer surface dimpling before failure results in larger regions of deformed tissue and more energy storage before needle penetration.
  • In this study (blunt needle) dimpling increased with insertion speed, indicating that more energy was transferred over a larger region and increasing the potential for injury.
  • However, friction stresses likely decrease with insertion speed since larger tissue holes were measured with increasing insertion speeds indicating lower frictional stresses.
    • Rapid deformation results in greater pressurization of fluid filled spaces if fluid does not have time to redistribute, making the tissue effectively stiffer. This may occur in compacted tissues below or surrounding the needle and result in increasing needle forces with increasing needle speed.