Figure 1.
Schematic of the computational domain used for simulations.
(A) 2-D axisymmetric view along the longitudinal direction and dimensions of vessel-injection catheter-conductance catheter configuration. (B) 3-D computational domain illustrating in vitro conductance catheter measurements. DL, DIC, and DCC respectively denote the vessel lumen diameter, injection catheter diameter, and conductance catheter diameter. In the present simulations, the injection and conductance catheter diameter were assumed to be 2 mm (corresponding to 6 Fr. guide-catheter) and 0.9 mm, respectively (corresponding to 0.035” guide-wire). LE, LD, and LDT respectively denote the excitation electrode distance (set as 4 mm), detection electrode distance (set as 1 mm), and distance of detection electrode from the injection catheter tip. Note that the excitation electrode spacing was set as 20 mm for the larger vessel sizes considered (i.e., 7 and 10 mm).
Table 1.
Flow Conditions and Physical Parameters used in Simulations.
Figure 2.
Temporal evolution of (A) saline fraction field, (B) average saline fraction over the cross-section at detection electrodes center, and (C) corresponding voltage detection for the 7 mm diameter vessel (i.e., DL = 7 mm) at flow rate ratio of 3 (i.e., = 3).
Red and blue colors denote pure blood and saline, respectively. Saline was assumed to be injected at t = 0 s. The voltage detection position (i.e., center of detection electrodes) is 20 mm from the injection catheter tip. Four black dashed lines in (A) denote the positions of excitation (outer pair) and detection (inner pair) electrodes.
Figure 3.
Streamlines and blood fraction contours (left panels) and pressure contours (right panels) at the flow rate ratio of (A) 2, (B) 3, and (C) 5.
The vessel lumen diameter DL is 7 mm.
Figure 4.
Percent error in predicted diameter for three different ratios of saline injection rate to blood flow rate (i.e., = 2, 3, and 5) along the various axial positions of conductance catheter relative to injection catheter for a variety of lumen diameters (A) DL = 4 mm, (B) DL = 7 mm, and (C) DL = 10 mm with a commonly used injection catheter size (i.e., DIC = 6 Fr.).
Circle, rectangle, and triangle symbols denote the ratio of 2, 3, and 5, respectively. The detection electrodes distance relative to injection tip indicates the distance of detection electrodes center from the distal end of injection catheter.
Figure 5.
Effect of combinations of saline injection and blood flow rate on conductance measurement at a given flow rate ratio.
(A) Streamlines and blood fraction contours in the 7 mm diameter vessel at the flow rate ratio of 3 for three different combinations of saline injection and blood flow rates (i.e., QS = 3 ml/s and QB = 1 ml/s, QS = 6 ml/s and QB = 2 ml/s, and QS = 9 ml/s and QB = 3 ml/s). (B) Percent error in diameter corresponding to the three different flow rate conditions. Circle, rectangle, and triangle symbols denote the flow condition of QS = 3 ml/s and QB = 1 ml/s, QS = 6 ml/s and QB = 2 ml/s, and QS = 9 ml/s and QB = 3 ml/s, respectively.
Figure 6.
Comparison of the percent error in diameter calculated by simulations and conductance measurements of phantoms at four different ratios of injection rate to baseline flow rate (i.e., = 2, 2.5, 3.3, and 5) for two different sizes (A) DL = 7 mm and (B) DL = 10 mm.
Lines and symbols represent simulations and measurements, respectively. Circle and solid, rectangle and dashed, triangle and dashed-dot, and gradient and dashed dot-dot denote the flow rate ratio of 2, 2.5, 3.3, and 5, respectively. Half normal saline was used as a baseline flow medium. Each conductance measurement was made in three (n = 3) phantoms for each diameter. The largest error was found to be 4 and 3.2% for 7 and 10 mm diameter phantom, respectively.