Biomedical subjects

Xiaokui Li

Publications and source records attributed to Xiaokui Li.

22 records · Page 2Linked to original sources

PubMed2002

Strain rate imaging: an in vitro "validation" study using a physiologic balloon model mimicking the left ventricle.

BACKGROUND: Strain rate imaging (SRI) can be implemented from digital ultrasound loops of tissue Doppler imaging (TDI) data and is performed as an autocorrelation solution of the distance between intramyocardial targets. As such, it should have better resolution along longer distances of wall segments that are imaged at the length of individual ultrasound scan lines. METHODS: We used a new left ventricular double-balloon phantom with a tissue-mimicking gel between the walls. Mounted in a water bath and connected to a pulsatile flow pump at four-stroke volume (30-50 ml/beat), the high frame rate, digital, multiple two-dimensional/tissue/TDI loops of balloon wall motion were recorded using a GE VingMed system FiVe (3.5 MHz phased array transducer), with the model scanned longitudinally from the apex. The strain rate (SR) values were measured at the apex and the lateral wall using an offline measurement program, and mean SR values for every 100 msec were calculated by averaging three determinations at each point. The excursions of the apex and lateral wall also were measured directly by high speed digital video imaging, and consecutive velocity profiles were calculated every 100 msec. A total of 40 data points for four-stroke volumes were analyzed. RESULTS: While our balloon model had enough gel targets between the walls to produce a good mimic of myocardial speckle with walls that thickened and thinned, samples immediately across the apex and apex SR values (Hz) varied substantially. In contrast, systematic signals could be obtained from lines imaged >15 degrees from the true apex and crossing a longer length of myocardium. At the lateral wall, there was a close correlation between the video velocities and SR values, as well as a close overlap of the phasic patterns. CONCLUSIONS: SRI produces more reliable data from wall segments parallel to scan lines.

Blood Flow Velocity↗

PubMed2002

New technology and methodologies for intraoperative, perioperative, and intraprocedural monitoring of surgical and catheter interventions for congenital heart disease.

We review the new technology and methods available for support of intraoperative and intraprocedural imaging in the catheterization laboratory for surgical and interventional catheterization procedures in the treatment of congenital heart disease. The methods reviewed include miniaturized probes and new ways of using them perioperatively for cardiac imaging from transesophageal, substernal, and intracardiac imaging locations. The smaller and more versatile the probes, the better adapted they will be in providing methods to improve the outcomes in babies born with serious forms of congenital heart disease.

Cardiac Surgical Procedures↗

PubMed2002

Quantification of instantaneous flow rate and dynamically changing effective orifice area using a geometry independent three-dimensional digital color Doppler method: An in vitro study mimicking mitral regurgitation.

OBJECTIVE: Our study was intended to test the accuracy of a 3-dimensional (3D) digital color Doppler flow convergence (FC) method for assessing the effective orifice area (EOA) in a new dynamic orifice model mimicking a variety of mitral regurgitation. BACKGROUND: FC surface area methods for detecting EOA have been reported to be useful for quantifying the severity of valvular regurgitation. With our new 3D digital direct FC method, all raw velocity data are available and variable Nyquist limits can be selected for computation of direct FC surface area for computing instantaneous flow rate and temporal change of EOA. METHODS: A 7.0-MHz multiplane transesophageal probe from an ultrasound system (ATL HDI 5000) was linked and controlled by a computer workstation to provide 3D images. Three differently shaped latex orifices (zigzag, arc, and straight slit, each with cutting-edge length of 1 cm) were used to mimic the dynamic orifice of mitral regurgitation. 3D FC surface computation was performed on parallel slices through the 3D data set at aliasing velocities (14-48 cm/s) selected to maximize the regularity and minimize lateral dropout of the visualized 3D FC at 5 points per cardiac cycle. Using continuous wave velocity for each, 3D-calculated EOA was compared with EOA determined by using continuous wave Doppler and the flow rate from a reference ultrasonic flow meter. Simultaneous digital video images were also recorded to define the actual orifice size for 9 stroke volumes (15-55 mL/beat with maximum flow rates 45-182 mL/s). RESULTS: Over the 9 pulsatile flow states and 3 orifices, 3D FC EOAs (0.05-0.63 cm(2)) from different phases of the cardiac cycle in each pump setting correlated well with reference EOA (r = 0.89-0.92, SEE = 0.027-0.055cm(2)) and they also correlated well with digital video images of the actual orifice peak (r = 0.97-0.98, SEE = 0.016-0.019 cm(2)), although they were consistently smaller, as expected by the contraction coefficient. CONCLUSION: The digital 3D FC method can accurately predict flow rate, and, thus, EOA (in conjunction with continuous wave Doppler), because it allows direct FC surface measurement despite temporal variability of FC shape.

Blood Flow Velocity↗

PubMed2002

No ischemic preconditioning in heterozygous connexin43-deficient mice.

Protein kinase Cepsilon (PKCepsilon) plays a central role in ischemic preconditioning (IP) in mice and rabbits, and activated PKCepsilon colocalizes with and phosphorylates connexin43 (Cx43) in rats and humans. Whether or not Cx43 contributes to the mechanism(s) of IP in vivo is yet unknown. Therefore, wild-type (n = 8) and heterozygous Cx43-deficient mice (n = 8) were subjected to 30 min occlusion and 120 min reperfusion of the left anterior descending coronary artery. IP was induced by one cycle of 5 min occlusion and 10 min reperfusion (n = 8/8 mice) before the sustained occlusion. Infarct size was reduced by IP in wild-type mice [11.3 +/- 3.4% vs. 23.7 +/- 7.2% of the left ventricle (LV), P < 0.05] but not in Cx43-deficient mice (26.0 +/- 6.0% vs. 25.1 +/- 3.8% of LV). Also, three cycles of 5 min occlusion and 10 min reperfusion (n = 5) did not induce protection in Cx43-deficient mice (27.6 +/- 5.5 % of LV). Thus Cx43 contributes to the protection of IP in mice in vivo.

Animals↗