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Biomedical subjects

P C Li

Publications and source records attributed to P C Li.

6 recordsLinked to original sources
PubMed1992

Synthetic aperture imaging using a Lagrange based filtering technique.

Synthetic aperture imaging using a catheter based, circular phased array providing high resolution, dynamic focusing has been explored. Due to the high input impedance and low signal-to-noise ratio (SNR) of a classic single element synthetic aperture system, multi-element synthetic aperture processing has been proposed with SNR improvement of about 8 dB for a 33 element aperture. Reconstruction in this case uses an optimal filtering approach based on minimizing the mean square error between filter output and desired beam pattern. This approach, however, does not directly control both mainlobe beamwidth and sidelobe levels. To overcome this problem, a Lagrange based filter design technique has been developed that not only satisfies the minimum energy criterion, but also constrains sidelobe levels under a certain threshold. The new technique provides better spatial and contrast resolution. Both the mathematical formulation and simulation results are presented.

Algorithms↗
PubMed1991

Effects of increased heart rate and sympathetic tone on intraventricular electrogram morphology.

Electrogram pattern recognition by way of morphologic analysis has been proposed as a technique that may improve discrimination of ventricular tachycardia from sinus rhythm by antitachycardia devices. The potential impact that increases in heart rate and sympathetic tone could have on such techniques, however, has not been previously determined. A comparative study was undertaken to quantify possible changes in ventricular electrogram morphology using correlation waveform, area of difference, and amplitude analyses in 6 patients during atrial overdrive pacing at cycle lengths of 600 and 400 ms (group A), in 13 patients during infusions of physiologic doses of epinephrine (group B), and in 20 patients undergoing infusions of isoproterenol (group C). Four patients were in both groups A and B. A bipolar intraventricular template of cardiac depolarization during sinus rhythm at rest was compared with depolarization during subsequent passages of sinus rhythm at rest and subsequently increased heart rate. In 36 of 39 patients, waveform configuration as assessed by correlation waveform analysis remained relatively stable during atrial overdrive pacing, epinephrine infusion, and isoproterenol infusion when compared with sinus rhythm at rest. The correlation value did not fall below 0.950 in any patient. Area of difference values for the same 36 patients changed by an average of 6 and 37% during atrial overdrive pacing at cycle lengths of 600 and 400 ms intervals, respectively, by 3% during epinephrine infusion, and by 17% during isoproterenol infusion. In these same patients, there was an average change in electrogram amplitude of -1% during atrial overdrive pacing at 600 ms, 26% during pacing at 400 ms, -1% during epinephrine infusion, and 12% during isoproterenol infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

[Relation between malondialdehyde generation by platelets and plasma thromboxane B2 and diagnostic classification by syndrome differentiation of traditional Chinese medicine in stroke during acute stage].

The malondialdehyde generation by platelets and TXB2 in poor platelet plasma were examined in 36 patients with stroke during acute stage. By CT examination 19 cases were diagnosed hemorrhagic, 17 cases ischemic; while by syndrome differentiation of TCM 16 cases belonged to Zhongzangfu(middle internal organs), 20 cases Zhongjingluo (middle channels). Results showed that the malondialdehyde generation by platelets was reduced, TXB2 in poor platelet plasma increased in patients, compared with those in the healthy controls. This finding was common in stroke during acute stage and was not related to diagnostic classes by either CT examination or syndrome differentiation of TCM. This study indicates that maintenance of normal platelet function may have significant implication in the prevention and treatment of cerebrovascular disease.

Adult↗