Biomedical subjects

M Gies

Publications and source records attributed to M Gies.

3 recordsLinked to original sources

PubMed2006

Absorption characteristics of EC-MPS--an enteric-coated formulation of mycophenolic sodium.

UNLABELLED: Enteric-coated mycophenolate sodium is an advanced formulation delivering mycophenolic acid (MPA), designed to improve MPA-related upper gastrointestinal adverse events by delaying MPA release until the small intestine. OBJECTIVE: Two studies were undertaken to identify the absolute bioavailability and dose-proportionality of enteric-coated mycophenolate sodium in stable renal transplant patients receiving cyclosporine. METHODS: Study 1: The mean MPA AUC(0-t) was shown to be greater after MPA infusion than after oral enteric-coated mycophenolate sodium (42.1 vs. 28.9 microg x h/ml). Mean absolute bioavailability was 0.71 +/- 0.21 (SD). Study 2: The AUC(0-t) and C(max) for MPA were proportional to the dose of enteric-coated mycophenolate sodium, similarly mean AUC(0-infinity) and C(max) for MPA glucuronide were proportional to dose administered. RESULTS AND CONCLUSIONS: In patients receiving cyclosporine the absolute bioavailability of MPA provided by enteric-coated mycophenolate sodium is equivalent to that provided by mycophenolate mofetil when administered in combination with cyclosporine, and exhibits dose-proportionality. Enteric-coated mycophenolate sodium was well tolerated from 180 - 2,160 mg with no serious adverse events reported.

Administration, Oral↗

PubMed1999

Dose reduction in CT by on-line tube current control: principles and validation on phantoms and cadavers.

We investigated approaches to reducing the dose in CT without impairing image quality. Dose can be reduced for non-circular object cross-sections without a significant increase in noise if X-ray tube current is reduced at angular tube positions where the X-ray attenuation by the patients is small. We investigated different schemes of current modulation during tube rotation by simulation and phantom measurements. Both pre-programmed sinusoidal modulation functions and attenuation-based on-line control of the tube current were evaluated. All relevant scan parameters were varied, including constraints such as the maximum modulation amplitude. A circular, an elliptical and two oval water phantoms were used. Results were validated on six cadavers. Dose reduction of 10-45% was obtained both in simulations and in measurements for the different non-circular phantom geometries and current modulation algorithms without an increase in pixel noise values. On-line attenuation-based control yielded higher reductions than modulation by a sinusoidal curve. The maximal dose reduction predicted any simulations could not be achieved due to limits in the modulation amplitude. In cadaver studies, a reduction of typically 20-40% was achieved for the body and about 10% for the head. Variations of our technique are possible; a slight increase in nominal tube current for high-attenuation projections combined with attenuation-based current modulation still yields significant dose reduction, but also a reduction in the structured noise that may obscure diagnostic details. We conclude that a significant reduction in dose can be achieved by tube current modulation without compromising image quality. Attenuation-based on-line control and a modulation amplitude of at least 90% should be employed.

Cadaver↗

PubMed1999

Dose reduction in CT by anatomically adapted tube current modulation. I. Simulation studies.

Tube current modulation governed by x-ray attenuation during CT (computed tomography) acquisition can lead to noise reduction which in turn can be used to achieve patient dose reduction without loss in image quality. The potential of this technique was investigated in simulation studies calculating both noise amplitude levels and noise distribution in CT images. The dependence of noise on the inodulation function, amplitude of modulation, shape and size of the object, and possible phase shift between attenuation and modulation function were examined. Both sinusoidal and attenuation-based control functions were used to modulate tube current. Noise reduction was calculated for both ideal systems and for real systems with limited modulation amplitude. Dose reductions up to 50% can be achieved depending on the phantom geometry and tube current modulation function. Attenuation-based tube current modulation yields substantially higher reduction than fixed-shape modulation functions. Optimal results are obtained when the current is modulated as a function of the square root of attenuation. A modulation amplitude of at least 90% should be available to exploit the potential of these techniques.

Air Pollutants, Radioactive↗