Figure 1.
Coronal section of the rat brain schematically showing the needle track (in red) passing through the cortex and the external capsule and targeting the caudate putamen (CPu).
Slice picture adapted from [41].
Figure 2.
Schematic of the experimental set up used for needle insertion and CED.
Figure 3.
Schematic showing the relation between holes left in tissue after needle retraction and pre-stresses at needle-tissue interface when the needle is in tissue.
The hole of diameter ρ can be expanded to the diameter of the needle (a) which introduces compressive pre-stress (σrr).
Figure 4.
Brain tissue slice showing (A) EBA distribution and (B) corresponding tissue concentration map.
The concentration map of Evans blue is in units of mg/mm3. The needle was inserted at a speed of 0.2 mm/s and CED was at a flow rate of 1 µL/min.
Figure 5.
EBA backflow distribution along the needle track.
For backflow calculations, distance along the needle track from the brain surface to the top most backflow region (d) was measured. Image is of an excised 100 µm brain slice.
Figure 6.
Insertion speed dependence of infusion pressure for CED at 2 µL/min; A) typical pressure profiles during infusion; B) average peak, steady state pressure, and second peak () for varying needle insertion speeds.
(Bars indicate ±1 standard deviation; n = 8).
Figure 7.
Different types of tissue damage left after needle retraction.
A) approximately circular hole surrounded by infused EBA; B) hole as a slender opening/crack; and C) red blood cell accumulation where it was difficult to measure the hole opening. All images are for fixed, 100 µm thick brain tissue slices.
Figure 8.
Tissue penetration damage along the length of the needle track.
Areas of holes left after needle retraction are plotted as a function of insertion depth for varying fixation time points (10 and 25 minutes) and insertion speeds: A) 0.2 mm/s; B) 2.0 mm/s; and C) 10 mm/s. D) Aspect ratio of holes for an insertion speed of 0.2 mm/s and fixation after 10 min. Each data point corresponds to the average of 4 hole measurements. Bars represent ±1 standard deviation.
Figure 9.
Variation of hole measurements.
A) histogram showing non-Gaussian distribution of the hole areas for 10 mm/s needle insertion speed and fixation after 10 min (combined data from 4 needle tracks, 161 total hole measurements); B) average hole areas for the three insertion speeds and the two fixation time points evaluated for depths greater than 1.4 mm. Each bar corresponds to the average of n = 144 hole measurements. Significant difference with 10 mm/s is noted by *; C) analysis of variance to evaluate the influence of insertion speeds (0.2, 2, and 10 mm/s) and the influence of fixation time point (10 and 25 min). p-value is plotted for varying insertion depths; D) average area of holes for main tissue regions along the needle track. Each average value was significantly different from each other. Each bar corresponds to the average of n = 336, n = 48, and n = 504 measurements for cortex, external capsule (ec) and caudate putamen (CPu) regions, respectively. For cortex, points between 1.4 and 2.7 mm depth were considered. For external capsule, points at depth 2.8 mm and 2.9 mm were considered. For caudate putamen, points at depth higher than 2.9 mm were considered. Bars represent ±1 standard deviation.
Table 1.
Needle insertion and CED results for the evaluated needle insertion speeds.
Figure 10.
Needle tissue damage at the hole surface.
A) cell separation and bleeding in the external capsule for insertion at 10 mm/s, and B) torn fibrous tissue (arrow) in the CPu for insertion at 0.2 mm/s. Both images are for 50 um thick fixed brain tissue slices with no staining.
Figure 11.
Needle tissue damage observed with H&E staining.
A) external capsule region showing deformation and compaction of surrounding tissue. In the enclosed area (dotted lines), layers of cells conform around the hole (needle insertion at 0.2 mm/s); B) CPu region showing extensive bleeding and tissue fracture at some distance away from of the hole (insertion at 10 mm/s).
Figure 12.
Pre-stress along the needle track for the needle inserted at: A) 0.2 mm/s, B) 2 mm/s, and C) 10 mm/s.
(Bars represent the calculated standard deviation, n = 4.) D) Average pre-stress values for cortex, external capsule, and CPu regions. Significant difference is noted by *, p-value<0.05. Each bar corresponds to the average of n = 144 pre-stress values.
Figure 13.
CED backflow in the rat brain.
Images show distributions along the needle track after infusion of 4 µL of EBA at 0.5 µL/min. Infusion needles were inserted at varying speeds: A) 0.2 mm/s, B) 2 mm/s, and C) 10 mm/s. Rat brain slices are 100 µm thick slices and unfixed (ec: external capsule, CPu: caudate putamen, Lss: lateral stripe of the striatum, cc: corpus callosum).
Figure 14.
CED backflow following infusion of 4 µL of EBA.
A) percentage of the EBA infusate outside the target CPu. Significant difference is noted by *, p-value<0.05 only for 10 mm/s insertion speed. For other flow rates, only the difference between 0.2 mm/s and 10 mm/s was significant. B) Backflow distances. Bars indicate ±1 standard deviation; n = 5 for each test group.