Biomedical subjects

F R Korosec

Publications and source records attributed to F R Korosec.

3 recordsLinked to original sources

PubMed1992

ECG-optimized phase contrast line-scanned MR angiography.

We describe a rapid phase contrast line scan MR angiographic imaging technique. A projection angiogram is obtained by sequentially imaging a series of thin slices oriented perpendicular to the primary flow direction. Bipolar gradient subtraction is employed to suppress signal from static tissues, which in turn allows elimination of phase encoding in the depth dimension. The sequence is cardiac gated to improve image quality and to allow observation of hemodynamics. To further improve image quality, the amplitude of the bipolar gradient is altered throughout the cardiac cycle to provide maximum vessel signal at all cardiac phases. The ECG-gated phase contrast line scan sequence has been used to image regions where cardiac pulsatility and respiratory motion compromise the quality of images obtained using standard spin warp angiographic methods.

Blood Flow Velocity↗

PubMed1992

A data adaptive reprojection technique for MR angiography.

Inability to detect vessel overlap and vascular loops can compromise the interpretation of magnetic resonance angiograms. A data-adaptive ray tracing (DART) technique was developed to produce the appropriate variations in signal intensity at points of vessel overlap in order to simulate the standard angiographic representation of vessels. In this technique a threshold is utilized to identify vessels in the image slices composing a 3D angiographic data set. A mask, which defines regions slightly larger than the vessel boundaries, is obtained by blurring the vessel information surviving the initial threshold. This mask is converted to binary form prior to multiplication by the original angiographic data set. Following application of an additional threshold to the masked data, line integrals through the regions defined by the mask are performed to obtain an angiographic signal proportional to the integrated vessel signal as in conventional angiography. This integrated reprojection is then uniquely combined with a maximum intensity pixel (MIP) reprojection to produce the final DART image. The application of the DART technique to 2D time-of-flight and 3D phase-contrast angiograms successfully enabled the identification of over-lapping vessels and vascular loops. DART was also found to produce less vessel narrowing than the MIP technique.

Algorithms↗

PubMed1992

Peripheral MR angiography with variable velocity encoding. Work in progress.

An electrocardiographically triggered two-dimensional phase-contrast (PC) magnetic resonance angiographic pulse sequence was developed in which velocity encoding (VENC) was varied throughout an acquisition in response to changes in blood velocity during the cardiac cycle. This was done to better capture signal in the peripheral vasculature, where pulsatile flow degrades images. After reconstruction, a matched filter addition technique was applied to the cardiac phase images to obtain a single high-quality static image. Images were obtained of six healthy volunteers--with and without varying VENC--and contrast-to-noise ratio (C/N) calculations were performed for the added images. Varying VENC significantly improved vascular signal from small and large vessels (P less than .02), but it was most helpful for small vessels, for which the C/N increased by as much as 260% (average increase, 149%). These preliminary findings suggest that variable VENC can enhance the signal from the small and large peripheral blood vessels in cardiac-gated PC acquisitions.

Angiography↗