PubMed Health⌕ Search

Biomedical subjects

H Bogren

Publications and source records attributed to H Bogren.

14 recordsLinked to original sources
PubMed1992

Factors influencing the accuracy and precision of velocity-encoded phase imaging.

Velocity-encoded phase contrast imaging is being used increasingly in clinical imaging for quantization of blood flow. In this study, the accuracy and precision of ascending aorta flow measurements were found to depend on several subtle aspects of the scan prescription and image analysis. While the usual scan parameters such as TR, TE, and flip angle gave incremental changes in the flow measurements, four additional factors that had a much greater effect on the measurements were identified. These factors were (1) the zero velocity (background) pixel value, (2) the size and shape of the vessel region of interest, (3) the maximum velocity encoded in diastole, and (4) the temporal resolution. Statistical analysis was done on a total of 48 scans on nine normal subjects to confirm the significance of the measured differences using the various choices for each of these factors. These factors must be considered if accurate and precise measurements of blood flow are desired. Estimates of accuracy and precision suggest that quantitative flow measurements from velocity-encoded MR imaging can be clinically useful.

Aorta↗
PubMed1991

Optimized pulse sequences for magnetic resonance measurement of aortic cross sectional areas.

This study was done to improve the ability of magnetic resonance (MR) imaging to provide clear cross-sectional images of the ascending and descending aorta in diastole. The study was motivated by interest in measuring the regional compliance of the ascending aorta, which requires determination of the change in cross sectional area of the vessel between systole and diastole. In diastolic images, residual signal from slow flowing blood and flow artifact consistently obscured the inner boundary of the aortic wall and precluded tracing and measurement of the cross sectional area. We concluded that cross sectional area measurement of the ascending aorta was impossible on our system using standard spin echo sequences. To improve wall delineation in diastolic images, SAT pulses were optimized with respect to pulse timing, slice thickness, and gap. Optimized SAT pulses greatly improved the delineation of the vessel wall by removing unwanted signal from flowing spins. Measurement precision was vastly improved by running two scans with and without flow compensation, and correlating visually and numerically the area measurements from each. We established that each image should be measured by two independent observers and traced three times by each. Using these procedures, diastolic cross-sectional areas of the mid-ascending aorta could be measured with a precision of 2.5%, and the change of cross-sectional area between systole and diastole could be measured with a precision of 10.8%. These measurements were precise enough to detect CAD patients with low aortic compliance from the age-matched controls previously reported in one study. The test based on cross sectional area measurement, with a false positive detection rate of 5%, had a false negative rate of 58%. Compliance measurements by MR at 1.5 T could become clinically useful if normal and abnormal populations are sufficiently separated.

Aorta↗
PubMed1990

Aortic compliance in hypercholesterolemic Watanabe rabbits compared to normal New Zealand controls.

This study was designed to test the hypothesis that severe atherosclerosis changes aortic compliance. Compliance of a vessel is defined as change in volume per unit change in pressure and is a measure of the stiffness or distensibility of the vascular wall. Part of the energy delivered by the left ventricle in systole is used to propel the blood forward into the aorta and part of it to distend the aorta and major vessels. During diastole, the arterial walls recoil and provide energy for propulsion of blood, thereby making blood flow continuous. It is known that Watanabe hereditary hyperlipidemic rabbits develop severe atherosclerosis beginning at 6 months of age. Compliance of the ascending thoracic aorta was studied angiographically in eight Watanabe hereditary hyperlipidemic rabbits of ages greater than 6 months and six normal lipidemic New Zealand white rabbits of ages greater than 6 months, used as controls. The normal New Zealand white rabbits had an average blood cholesterol of 27.4 mg/dL, SD = 13.8, and a regional compliance in the ascending aorta of 0.004 mL/mm Hg, SD = 0.002, compared to the Watanabe hereditary hyperlipidemic rabbits with a cholesterol of 583.1 mg/dL, SD = 162.7, and a compliance of 0.0022 mL/mm Hg, SD = 0.0015. These are significant differences (p less than .05). In addition, the histopathology of the aorta of the Watanabe hyperlipidemic rabbit compared to that of the controls showed a significant decrease in the number of medial lamellar elastin units, an indicator of the decreased elasticity of the blood vessel wall.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Watanabe hyperlipidemic rabbit as a model of aortic degeneration of the medial lamellar elastin unit.

At age 3 years, WHHL rabbits are near the end of their lifespan, frequently dying from the progression of their hyperlipidemic disease from events such as myocardial infarction. Out of a colony of 20 three-year-old WHHL rabbits raised as part of a NIH breeding project, 2 rabbits actually died of a ruptured thoracic aortic aneurysm. The need for a model to study abdominal aortic aneurysm formation led us to explore further the abdominal aortic pathology in aged WHHL rabbits. Six rabbit abdominal aortas from 3-year-old WHHL rabbits were preserved in formalin, sectioned, and stained for elastin. These were compared to the same sections of six normolipidemic age matched New Zealand white (NZW) rabbits. There was significant (P less than or equal to .001) destruction of the medial lamellar elastin unit in the aorta of the WHHL rabbits compared with the control NZW rabbits. Severe cholesterol deposits appeared to destroy the medial lamellae from the inside out. No definite aneurysm formation was seen in the abdominal aorta despite the significant changes in the medial lamellar elastin units. Thus, this model could be used to study the elastin degeneration of the media, but not necessarily abdominal aortic aneurysm formation.

Animals↗