Research Papers

Influence of Needle Insertion Speed on Backflow for Convection-Enhanced Delivery

[+] Author and Article Information
Fernando Casanova

 Escuela de Ingenieria Mecanica, Universidad del Valle, Carrera 13 No. 100-00, Cali, Colombia; Department of Mechanical and Aerospace Engineering, University of Florida, Florida 32611bando1271@yahoo.es

Paul R. Carney

 Department of Pediatrics, Neurology, Neuroscience, and J. Crayton Pruitt Family Department of Biomedical Engineering, Wilder Center of Excellence for Epilepsy Research, University of Florida, 1600 SW Archer Road,Gainesville, Florida 32610carnepr@peds.ufl.edu

Malisa Sarntinoranont

 Department of Mechanical and Aerospace Engineering, 212 MAE A 212, Gainesville, Florida 32611msarnt@ufl.edu

J Biomech Eng 134(4), 041006 (Apr 26, 2012) (8 pages) doi:10.1115/1.4006404 History: Received November 28, 2011; Revised February 29, 2012; Posted March 21, 2012; Published April 26, 2012; Online April 26, 2012

Fluid flow back along the outer surface of a needle (backflow) can be a significant problem during the direct infusion of drugs into brain tissues for procedures such as convection-enhanced delivery (CED). This study evaluates the effects of needle insertion speed (0.2 and 1.8 mm/s) as well as needle diameter and flow rate on the extent of backflow and local damage to surrounding tissues. Infusion experiments were conducted on a transparent tissue phantom, 0.6% (w/v) agarose hydrogel, to visualize backflow. Needle insertion experiments were also performed to evaluate local damage at the needle tip and to back out the prestress in the surrounding media for speed conditions where localized damage was not excessive. Prestress values were then used in an analytical model of backflow. At the higher insertion speed (1.8 mm/s), local insertion damage was found to be reduced and backflow was decreased. The compressive prestress at the needle-tissue interface was estimated to be approximately constant (0.812 kPa), and backflow distances were similar regardless of needle gauge (22, 26, and 32 gauge). The analytical model underestimated backflow distances at low infusion flow rates and overestimated backflow at higher flow rates. At the lower insertion speed (0.2 mm/s), significant backflow was measured. This corresponded to an observed accumulation of material at the needle tip which produced a gap between the needle and the surrounding media. Local tissue damage was also evaluated in excised rat brain tissues, and insertion tests show similar rate-dependent accumulation of tissue at the needle tip at the lower insertion speed. These results indicate that local tissue damage and backflow may be avoided by using an appropriate insertion speed.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Material displaced due to cannula retraction (a: needle radius; ρ: position of the free surface after needle retraction)

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Figure 2

Mass conservation for cannula infusion with backflow. Radial symmetry was assumed. Q = total flow rate, Qs=flow through the spherical surface, Qc=flow through the cylindrical surface, a=cannula outer radius, r=radial coordinate, z=longitudinal coordinate, and Z=backflow distance.

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Figure 3

Backflow distances measured at varying flow rates, needle diameters, and insertion speeds (22G = 22 gauge needle; 32G = 32 gauge needle; slow: insertion speed of 0.2 mm/s; fast: insertion speed of 1.8 mm/s; bars indicate standard deviation)

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Figure 4

Tracer distributions in hydrogel for a needle inserted at (a) 1.8 mm/s and (b) 0.2 mm/s. Both figures show tracer infusions with a flow rate of 0.5 μ/min. Z is the reported backflow distance and e is the perpendicular tracer penetration distance in hydrogels (0.7176 mm needle diameter).

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Figure 5

Accumulation of hydrogel at the needle tip during: (a) insertion at 0.2 mm/s, (b) stop, (c) retraction, and (d) detachment (needle diameter = 0.7176 mm)

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Figure 6

Insertion of the needle at 1.8 mm/s: (a) insertion and (b) retraction (diameter of the needle = 0.7176 mm)

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Figure 7

Needle tip accumulation of hydrogel after passing through a hydrogel slice at (a) and (b) 0.2 mm/s and (c) 1.8 mm/s (diameter of the needle = 0.7176 mm)

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Figure 8

Needle tip accumulation of tissue after passi through a rat brain tissue sample at (a) 0.2 mm/s and (b) 1.8 mm/s (diameter of the needle = 0.7176 mm)

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Figure 9

Hole in the hydrogel left by the needle after retraction: (a) needle inserted at high speed (the circle outlines the hole); (b) and (c) needle inserted at low speed. The dark region surrounding the needle is the tracer. The needle was placed on hydrogel surface to provide a length scale (diameter of the needle = 0.7176 mm).

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Figure 10

Hydrogel prestress for varying needle gauges. Prestress was calculated from hole diameters after fast insertion, see Table 1.

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Figure 11

Predicted and experimental backflow distances for (a) 32 gauge and (b) 22 gauge needles



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