KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/123456789/1

Browse

Search Results

Now showing 1 - 6 of 6

Some of the metrics are blocked by your
consent settings
In vitro measurement of myocardial impedivity anisotropy with a miniature rectangular tube
(2003-04-01)
Tsai, Jang Zern
;
Will, James A.
;
Vorperian, Vicken R.
;
Hubbard-Van Stelle, Scott
;
Cao, Hong
Due to rapid change of fiber orientation, it is difficult to measure myocardial impedivity separately in a longitudinal or transverse fiber direction without mutual influence in the two directions. Previously published values of the longitudinal and the transverse myocardial impedivity were derived indirectly from measurements that mixed the impedivity in all directions. Those values are questionable because the derivations were based on a simplified uniform myocardial fiber model. In this paper, a miniature rectangular tube was devised to facilitate direct measurement of myocardial impedivity in a uniform fiber direction. The average transverse-to-longitudinal ratio of the measured in vitro swine myocardial impedivity was about 1.66 from 1 Hz to 1 kHz and dropped to 1.25 at 1 MHz. The result is important for accurate modeling of the electrical property of myocardium in biomedical research of radio-frequency cardiac catheter ablation.
Some of the metrics are blocked by your
consent settings
In-vivo measurement of swine myocardial resistivity
(2002-04-30)
Tsai, Jang Zern
;
Will, James A.
;
Stelle, Scott Hubbard Van
;
Cao, Hong
;
Tungjitkusolmun, Supan
We used a four-terminal plunge probe to measure myocardial resistivity in two directions at three sites from the epicardial surface of eight open-chest pigs in-vivo at eight frequencies ranging from 1Hz to 1 MHz. We calibrated the plunge probe to minimize the error due to stray capacitance between the measured subject and ground. We calibrated the probe in saline solutions contained in a metal cup situated near the heart that had an electrical connection to the pig's heart. The mean of the measured myocardial resistivity was 319 Ω cm at 1 Hz down to 166 Ωcm at 1 MHz. Statistical analysis showed the measured myocardial resistivity of two out of eight pigs was significantly different from that of other pigs. The myocardial resistivity measured with the resistivity probe oriented along and across the epicardial fiber direction was significantly different at only one out of the eight frequencies. There was no significant difference in the myocardial resistivity measured at different sites.
Some of the metrics are blocked by your
consent settings
Error analysis of tissue resistivity measurement
(2002-04-30)
Tsai, Jang Zern
;
Will, James A.
;
Stelle, Scott Hubbard Van
;
Cao, Hong
;
Tungjitkusolmun, Supan
We identified the error sources in a system for measuring tissue resistivity at eight frequencies from 1 Hz to 1 MHz using the four-terminal method. We expressed the measured resistivity with an analytical formula containing all error terms. We conducted practical error measurements with in-vivo and bench-top experiments. We averaged errors at all frequencies for all measurements. The standard deviations of error of the quantization error of the 8-bit digital oscilloscope with voltage averaging, the nonideality of the circuit, the in-vivo motion artifact and electrical interference combined to yield an error of ±1.19%. The dimension error in measuring the syringe tube for measuring the reference saline resistivity added ±1.32% error. The estimation of the working probe constant by interpolating a set of probe constants measured in reference saline solutions added ±0.48% error. The difference in the current magnitudes used during the probe calibration and that during the tissue resistivity measurement caused ±0.14% error. Variation of the electrode spacing, alignment, and electrode surface property due to the insertion of electrodes into the tissue caused ±0.61% error. We combined the above errors to yield an overall standard deviation error of the measured tissue resistivity of ±1.96%.
Some of the metrics are blocked by your
consent settings
Using electrical impedance to predict catheter-endocardial contact during RF cardiac ablation
(2002-02-26)
Cao, Hong
;
Tungjitkusolmun, Supan
;
Choy, Young Bin
;
Tsai, Jang Zern
;
Vorperian, Vicken R.
During radio-frequency (RF) cardiac catheter ablation, there is little information to estimate the contact between the catheter tip electrode and endocardium because only the metal electrode shows up under fluoroscopy. We present a method that utilizes the electrical impedance between the catheter electrode and the dispersive electrode to predict the catheter tip electrode insertion depth into the endocardium. Since the resistivity of blood differs from the resistivity of the endocardium, the impedance increases as the catheter tip lodges deeper in the endocardium. In vitro measurements yielded the impedance-depth relations at 1, 10, 100, and 500 kHz. We predict the depth by spline curve interpolation using the obtained calibration curve. This impedance method gives reasonably accurate predicted depth. We also evaluated alternative methods, such as impedance difference and impedance ratio.
Some of the metrics are blocked by your
consent settings
Modeling bipolar phase-shifted multielectrode catheter ablation
(2002-01-05)
Tungjitkusolmun, Supan
;
Haemmerich, Dieter
;
Cao, Hong
;
Tsai, Jang Zern
;
Choy, Young Bin
Atrial fibrillation (AFIB) is a common clinical problem affecting approximately 0.5-1% of the United States population. Radio-frequency (RF) multielectrode catheter (MEC) ablation has successes in curing AFIB. We utilized finite-element method analysis to determine the myocardial temperature distribution after 30 s, 80 °C temperature-controlled unipolar ablation using three 7F 12.5-mm electrodes with 2-mm interelectrode spacing MEC. Numerical results demonstrated that cold spots occurred at the edges of the middle electrode and hot spots at the side electrodes. We introduced the bipolar phase-shifted technique for RF energy delivery of MEC ablation. We determined the optimal phase-shift (φ) between the two sinusoidal voltage sources of a simplified two-dimensional finite-element model. At the optimal φ, we can achieve a temperature distribution that minimizes the difference between temperatures at electrode edges. We also studied the effects of myocardial electric conductivity (σ), thermal conductivity (κ), and the electrode spacing on the optimal φ. When we varied σ and κ from 50% to 150%, optimal φ ranged from 29.5° to 23.5°, and in the vicinity of 26.5°, respectively. The optimal φ for 3-mm spacing MEC was 30.5°. We show the design of a simplified bipolar phase-shifted MEC ablation system.
Some of the metrics are blocked by your
consent settings
Flow effect on lesion formation in RF cardiac catheter ablation
(2001-04-23)
Cao, Hong
;
Vorperian, Vicken R.
;
Tungjitkusolmun, Supan
;
Tsai, Jang Zern
;
Haemmerich, Dieter
This study investigated the flow effect on the lesion formation during radio-frequency cardiac catheter ablation in temperature-controlled mode. The blood flow in heart chambers carries heat away from the endocardium by convection. This cooling effect requires more power from the ablation generator and causes a larger lesion. We set up a flow system to simulate the flow inside the heart chamber. We performed in vitro ablation on bovine myocardium with three different flow rates (0 L/min, 1 L/rain and 3 L/min) and two target temperatures (60 °C and 80 °C). During ablation, we also recorded the temperatures inside the myocardium with a three-thermocouple temperature probe. The results show that lesion dimensions (maximum depth, maximum width and lesion volume) are larger in high flow rates (p < 0.01). Also, the temperature recordings show that the tissue temperature rises faster and reaches a higher temperature under higher flow rate.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results