Biomedical subjects

Per Thunberg

Publications and source records attributed to Per Thunberg.

5 recordsLinked to original sources

PubMed2005

Comparison of different methods for combining phase-contrast images obtained with multiple coils.

The ability to determine coil sensitivities implies that a method optimized in terms of maximized signal-to-noise ratio (SNR) can be applied to the combination of multiple coil images. An optimization of SNR subsequently results in a minimized variance in quantitative velocity measurements using phase-contrast imaging. When coil sensitivities are unknown, the weighted mean method, utilizing the square of the signal magnitude as weights, is suitable for combination of multiple phase images. In this study, the optimized method using estimated coil sensitivities was compared to the weighted mean method both theoretically and experimentally. It is shown that absence of noise correlation between the different coil images implies no difference between the methods regarding the variance of the phase. In the practical situation, noise correlation does exist, implying an opportunity for further reduction of phase variance using the optimized method. In vitro and in vivo studies showed, however, no significant difference between the two methods studied.

Aorta↗

PubMed2004

Comparison between angiographic right coronary artery motion and echocardiographic tricuspid annulus motion.

OBJECTIVE: To compare echocardiographic M-mode measurements of tricuspid annulus motion (TAM) with angiographic M-mode measurements of right coronary artery motion (RAM). DESIGN: Twenty-four patients were included and examined by echocardiography before the angiographic examination. The amplitudes and the velocities of TAM and the atrial contribution to the total amplitude of TAM were measured. The obtained values were compared with angiographic M-mode measurements of RAM at a proximal and a distal site of the second segment of the right coronary artery. RESULTS: There was no significant difference between several of the echocardiographic M-mode measurements of TAM and the angiographic M-mode measurements of RAM. However, the agreement was rather poor for some variables. CONCLUSION: Different parameters obtained from echocardiographic TAM are not interchangeable with values from angiographic RAM. If measurements of RAM are to be used in the assessment of right ventricular (RV) function further studies are needed to examine the correlation and agreement between RAM and different methods of measuring RV function, i.e. radionuclide angiography or magnetic resonance imaging.

Adult↗

PubMed2003

Accuracy and reproducibility in phase contrast imaging using SENSE.

The purpose of this study was to evaluate the accuracy and reproducibility of phase contrast imaging using the sensitivity encoding (SENSE) method at different reduction factors. Analytical expressions were derived that state how reproducibility is influenced for velocity and flow measurements. Computer simulations, and in vitro and in vivo studies were performed in order to validate these expressions and to assess how accuracy is affected when different reduction factors are applied. It was shown that reproducibility depends on the reduction and geometry factors. Since the geometry factor varies spatially, so does the reproducibility for phase contrast imaging. In areas with high geometry factors, the standard deviation (SD) may become so large that aliasing occurs. The accuracy of phase contrast imaging is not influenced directly when SENSE is used, but may be indirectly influenced due to high SDs of the measured phase that may subsequently cause aliasing. The current results show that it is possible to achieve accurate flow measurements even at high reduction factors. By taking the geometry factor into account, it may be possible to find areas where phase contrast imaging is accurate even at high reduction factors.

Blood Flow Velocity↗

PubMed2003

Assessment of left ventricular function from M-mode measurement of circumflex artery motion recorded by coronary angiography.

OBJECTIVE: To evaluate the usefulness of M-mode measurement of circumflex artery motion (CAM) for assessment of left ventricular (LV) function. DESIGN: Seventy-two patients referred for coronary angiography and LV angiography were included. Ejection fraction (EF) was calculated from LV angiography and systolic and diastolic parameters of CAM were measured by M-mode from coronary angiography. Twenty-three patients, examined by echocardiography of mitral annulus motion (MAM) within 24 h before the angiographic examination, formed a subgroup for comparison between angiographic M-mode of CAM and echocardiographic M-mode of MAM. RESULTS: In addition to previous reported CAM amplitude and longitudinal fractional shortening (FSL) the maximal systolic velocity of CAM can be reliably recorded by M-mode. The diastolic indices, atrial contribution to the total amplitude and maximal early and late diastolic velocities, are also well monitored by M-mode of CAM in comparison with echocardiographic MAM. CONCLUSION: LV systolic and diastolic function can be assessed by M-mode of CAM.

Adult↗

PubMed2002

Correction for displacement artifacts in 3D phase contrast imaging.

PURPOSE: To correct for displacement artifacts in 3D phase contrast imaging. MATERIALS AND METHODS: A 3D phase contrast pulse sequence was modified so that displacements of velocity measurements were restricted to one direction. By applying a postprocessing method, displaced measurements could be traced back to their accurate positions. Flow studies were performed using a phantom that generated flow through a stenosis, directed oblique relative to the phase and frequency encoding directions. Velocity profiles and streamline visualization were used to compare displaced and corrected velocity data to a reference. RESULTS: Velocity profiles obtained from the original measurement showed skewed profiles due to the displacement artifact, both at close proximity to the orifice as well as further downstream. After correction, concordance with the reference improved considerably. CONCLUSION: The displacement artifact, which restricts the accuracy of phase contrast measurements, can be corrected for using the proposed method. Correction of the phase contrast velocity data may improve the accuracy of subsequent flow analysis and visualization.

Artifacts↗