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Biomedical subjects

J M Jin

Publications and source records attributed to J M Jin.

9 recordsLinked to original sources
PubMed2003

A temperature-based feedback control system for electromagnetic phased-array hyperthermia: theory and simulation.

A hybrid proportional-integral-in-time and cost-minimizing-in-space feedback control system for electromagnetic, deep regional hyperthermia is proposed. The unique features of this controller are that (1) it uses temperature, not specific absorption rate, as the criterion for selecting the relative phases and amplitudes with which to drive the electromagnetic phased-array used for hyperthermia and (2) it requires on-line computations that are all deterministic in duration. The former feature, in addition to optimizing the treatment directly on the basis of a clinically relevant quantity, also allows the controller to sense and react to time- and temperature-dependent changes in local blood perfusion rates and other factors that can significantly impact the temperature distribution quality of the delivered treatment. The latter feature makes it feasible to implement the scheme on-line in a real-time feedback control loop. This is in sharp contrast to other temperature optimization techniques proposed in the literature that generally involve an iterative approximation that cannot be guaranteed to terminate in a fixed amount of computational time. An example of its application is presented to illustrate the properties and demonstrate the capability of the controller to sense and compensate for local, time-dependent changes in blood perfusion rates.

Body Temperature↗
PubMed2000

Computation of the signal-to-noise ratio of high-frequency magnetic resonance imagers.

A method of computing the signal-to-noise ratio (SNR) in high-frequency magnetic resonance (MR) imaging systems is presented. The method uses a numerical solution to Maxwell's equations which can capture all relevant electrodynamic effects at high B0-field strengths. Using this method, the intrinsic SNR of both volume and surface coils loaded with the human head is calculated as a function of frequency. It is shown that although the available SNR from any point scales favorably with frequency, phase inhomogeneity over the volume of the head may pose a challenge to achieving improved SNR with traditional imaging techniques at high B0-field strengths.

Biomedical Engineering↗
PubMed1999

Fast frequency-sweep analysis of RF coils for MRI.

A fast frequency-sweep technique is developed for the analysis of radio-frequency coils for magnetic resonance imaging. This technique applies the method of asymptotic waveform evaluation to the moment method solution of the integral equation for the original physical problem. Numerical examples show that the proposed technique can speed up the analysis by more than an order of magnitude.

Equipment Design↗
PubMed1998

Numerical simulation of SAR and B1-field inhomogeneity of shielded RF coils loaded with the human head.

The finite-difference time-domain (FDTD) method is combined with the method of moments (MoM) to compute the electromagnetic fields of shielded radio-frequency (RF) coils loaded with an anatomically accurate model of a human head for high-frequency magnetic resonance imaging (MRI) applications. The combined method can predict both the specific energy absorption rate (SAR) and the magnetic field (known as the B1 field) excited by any RF coils. Results for SAR and B1 field distribution, excited by shielded and end-capped birdcage coils, are calculated at 64, 128, 171, and 256 MHz. The results show that the value of SAR increases when the frequency of the B1 field increases and the B1 field exhibits a strong inhomogeneity at high frequencies.

Algorithms↗
PubMed1996

Computation of electromagnetic fields for high-frequency magnetic resonance imaging applications.

A numerical method is presented to compute electromagnetic fields inside a 2 mm high resolution, anatomically detailed model of a human head for high-frequency magnetic resonance imaging (MRI) applications. The method uses the biconjugate gradient algorithm in combination with the fast Fourier transform to solve a matrix equation resulting from the discretization of an integrodifferential equation representing the original physical problem. Given the current distribution in an MRI coil, the method can compute both the electric field (thus the specific energy absorption rate (SAR)) and the magnetic field, also known as the B1 field. Results for the SAR and B1 field distribution, excited by a linear and a quadrature birdcage coil, are calculated and presented at 64 MHz, 128 MHz and 256 MHz, corresponding to the operating frequencies of the 1.5 T, 3 T and 6 T MRI systems. It is shown that compared with that at 64 MHz, the SAR at 128 MHz is increased by a factor over 5 and the SAR at 256 MHz is increased by a factor over 10, assuming the same current strength in the coil. Furthermore, compared with the linear excitation, the average SAR for the quadrature excitation is reduced by a factor over 2 and the maximum SAR is reduced by a factor over 3. It is also shown that the B1 field at high frequencies exhibits a strong inhomogeneity, which is attributed to dielectric resonance.

Algorithms↗
PubMed1992

Beneficial effects of berberine on hemodynamics during acute ischemic left ventricular failure in dogs.

In 18 dogs ischemic left ventricular failure characterized by a 30 percent reduction in peak rate of rise of left ventricular pressure (+dp/dt) and elevation of left ventricular end-diastolic pressure (LVEDP) to 15 mmHg or more was produced by ligation of the proximal left anterior descending coronary artery followed by serial occlusions of the distal left circumflex coronary artery. In 10 days, administration of berberine in an intravenous bolus injection (1 mg/kg, within 3 minutes) followed by a constant infusion (0.2 mg/kg/min, 30 minutes) increased the cardiac output (CO) from 1.25 +/- 0.12 to 1.61 +/- 0.17 L/min (P < 0.05), and +dp/dt from 810 +/- 85 to 1021 +/- 130 mmHg/s (P < 0.01), and decreased LVEDP from 16.5 +/- 1.3 to 12.0 +/- 1.0 mmHg (P < 0.05), diastolic blood pressure from 94 +/- 6 to 84 +/- 5 mmHg (P < 0.01), systemic vascular resistance from 7303 +/- 278 to 5442 +/- 231 dynes.x/cm5 (P < 0.01), but did not affect the heart rate. Injection of 5% glucose with the same volume did not improve CO and dp/dt (P > 0.05) but increased the LVEDP from 17.1 +/- 1.4 to 17.8 +/- 1.6 mmHg (P < 0.01) in 8 dogs. The levels of plasma concentration of berberine was determined with high-performance liquid chromatography. The changes in plasma drug level were found parallel to hemodynamic effects of berberine. The results of this study showed that berberine was able to improve the impaired left ventricular function by its positive inotropic effect and mild systemic vasodilatation.

Animals↗
PubMed1992

[Effect of total saponins of Panax ginseng on hematopoietic progenitor cells in normal human and aplastic anemia patients].

Ginseng was said to be benefit for anemia in TCM. Proliferation effects of total saponins of panax ginseng (TSPG) on hematopoietic progenitor cell in normal individuals and 29 patients with aplastic anemia (AA) were observed by bone marrow culture of BFU-E, CFU-E, CFU-GM in vitro compared with methyltestosterone (MT). The results showed that TSPG might prompt proliferation of normal progenitor cells at the concentration of 20 micrograms/ml. The number of BFU-E, CFU-E and CFU-GM had increased by 37.8 +/- 2.9%, 31.4 +/- 2.9% and 33.3 +/- 4.0% over the controls respectively; furthermore TSPG was still useful to BFU-E, CFU-E growth without Epo in vitro, although the colony numbers were very lower. Otherwise MT was useless to CFU-GM. 14 of the 29 patients with AA who responded to MT showed sensitivity to TSPG in marrow culture (the rising rate of colony formation exceeded 30%), but immune-mediated AA (patient's PBMNC suppressed normal hematopoiesis) and stem cell-decreased AA (few of colony was formed) showed almost no expression for TSPG activity because of immunological suppression system and absence of progenitors.

Adolescent↗
PubMed1989

[Leukemic clonogenic assay and drug sensitivity test of homoharringtonine and cytarabine in acute myeloid leukemia].

Bone marrow cells from 33 patients with AML were cultured in vitro using PHA-LCM. The test consisted of two phases: an initial liquid phase and then a semi-liquid phase as described by Dicke et al. Drug sensitivity test for homoharringtonine (H) and cytarabine (A) were performed with clonogenic assay. All patients were treated with these drugs. The results showed that PHA-induced leukemic colonies (CFU-AML) varied from 0 to 812/2 x 10(5) cells (median 175). Three patterns of cell growth were recognized in analysis: high degree (7 patients) with more than 250 CFU-AML colonies, median degree (17 patients) with 50-250 and low, degree with 0 to 49 colonies (9 patients). Drug sensitivity was closely related to the cell growth patterns as evaluated with the clinical outcome. Patients with "high" growth pattern needed more sensitive drugs. When clonogenic assay showed "low" growth pattern, all patients responded to H and A very well regardless the degree of drug sensitivity. Most patients with M3 had high or median growth patterns and relatively low sensitivity to HA. Only one of the six patients with M3 got remission.

Alkaloids↗