Biomedical subjects

Andreas Anayiotos

Publications and source records attributed to Andreas Anayiotos.

4 recordsLinked to original sources

PubMed2005

Extension of rapid phase-contrast magnetic resonance imaging using BRISK in multidirectional flow.

We developed BRISK-CON-VPS, a rapid phase-contrast cine approach that is a hybrid of the BRISK-VPS (Block Regional Interpolation Scheme for k-space) and conventional (CONV-VPS) scanning employing k-space views per segment (VPS). BRISK-CON-VPS allows data acquisition approximately four times faster than CONV-VPS imaging and has the advantage compared to BRISK-VPS that it can potentially be incorporated into real-time applications. In BRISK-CON-VPS contiguous regions of k-space are sampled using a views per segment factor that is varied as a function of distance from the k-space center. Computational fluid dynamics (CFD) data were used to simulate CONV-VPS, BRISK-VPS, and BRISK-CON-VPS. BRISK-CON-VPS was simulated by incrementing the VPS progressively with increasing distance from the k-space origin while BRISK-VPS was simulated using a uniform VPS applied to the sparse sampling scheme. Simulations showed that up to a base VPS of 5, both BRISK-CON-VPS and BRISK-VPS retained excellent axial-velocity accuracy. Secondary in-plane velocity flow fields were well represented with BRISK-CON-VPS and BRISK-VPS up to a base VPS of 3. CONV-VPS, BRISK-CON-VPS, and BRISK-VPS were applied in vivo and shown to provide comparable quantitative flow data. BRISK-CON-VPS accomplishes breath-hold acquisitions as efficiently as BRISK-VPS, but without requiring data interpolation or under-sampling k-space.

Animals↗

PubMed2004

The challenges of imaging based computational fluid dynamics.

Image based Computational Fluid Dynamics (CFD) simulation of the cardiovascular system is increasingly becoming important and its application in everyday medical practice can already be envisaged. The goal of this workshop is to address all the factors involved in the development of a computational framework/software for modelling and analyses of the cardiovascular system and provide examples. The development of such framework, requires integration, management and interpretation of data from several technology areas such as a) feature detection and extraction of arterial geometry from imaging data, b) adaptive grid generation techniques for 3-D asymmetric geometries c) hemodynamic modelling, disparate length-scale model, and fluid-tissue interaction with high-performance computing, d) CFD data validation, e) feature extraction/detection and visualisation algorithms, f) graphical user interface to allow remote visualisation of post processed data. These computational tools are employed to study flow in specific problem sites in the vascular tree such as the carotid, femoral, coronary and abdominal arteries. Such studies provide understanding of the factors involved in the initialisation and evolution of arterial disease due to altered flow conditions (as a result of plaque formation) such as flow separation and reversal, and low and oscillatory wall shear stress. It is also used to study the effect of various clinical procedures such as the implantation of stents, vascular grafts, vascular prostheses and artificial valve implants on local and global hemodynamics. This workshop will address a new emerging paradigm in clinical practice known as predictive medicine for effective surgical planning and post surgical rehabilitation. The workshop will also address the difficulties in the implementation of some of the technology areas in this application with examples of carotid, femoral, and abdominal artery simulations.

Algorithms↗

PubMed2002

Effect of contrast agent viscosity and injection flow velocity on bolus injection pressures for peripheral venous injection in first-pass myocardial perfusion studies.

Myocardial perfusion imaging using Gd contrast agents is typically performed with bolus injections of the contrast agent using a power injector to provide for consistent and sufficiently rapid injection rates for all patients. For protocols in which a peripheral venous injection is called for (e.g. antecubital vein) injection catheters of 18 ga are used where vessel geometry permits. In some patients, particularly women with smaller veins, 20 and 22 ga catheters are used. The effect of catheter size and pressure tubing length can result in high injection pressures that occasionally cause leakage or connector failure. The viscosity of the contrast agent also impacts injection pressure. In this study, a simulation of the injection pathway was constructed with time resolved pressures measured at two points in the pathway. Pressure drops were calculated for a typical MR perfusion injection protocol.

Catheterization, Peripheral↗

PubMed2002

Comparative MRI compatibility of 316 L stainless steel alloy and nickel-titanium alloy stents.

The initial success of coronary stenting is leading to a proliferation in peripheral stenting. A significant portion of the stents used in a clinical setting are made of 316 low carbon stainless steel (SS). Other alloys that have been used for stent manufacture include tantalum, MP35N, and nickel-titanium (NiTi). The ferromagnetic properties of SS cause the production of artifacts in magnetic resonance imaging (MRI). The NiTi alloys, in addition to being known for their shape memory or superelastic properties, have been shown to exhibit reduced interference in MRI. Thus, the objective of this study was to determine the comparative MRI compatibility of SS and NiTi stents. Both gradient echo and spin-echo images were obtained at 1.5 and 4.1 T field strengths. The imaging of stents of identical geometry but differing compositions permitted the quantification of artifacts produced due to device composition by normalizing the radio frequency shielding effects. These images were analyzed for magnitude and spatial extent of signal loss within the lumen and outside the stent. B1 mapping was used to quantify the attenuation throughout the image. The SS stent caused significant signal loss and did not allow for visibility of the lumen. However, the NiTi stent caused only minor artifacting and even allowed for visualization of the signal from within the lumen. In addition, adjustments to the flip angle of standard imaging protocols were shown to improve the quality of signal from within the lumen.

Alloys↗