2010 - A Study on Errors of Magnetic Resonance Flow Measurement by Slice Misalignment in Ascending Aorta

2010. 11. 7. 16:48James/Papers


A Study on Errors of Magnetic Resonance Flow Measurement by Slice Misalignment in Ascending Aorta

 

Ho NamKoong, Young-Dae Choi, Heung-Sun Im

 

MRI Center, Department of Radiology, Seoul National University Hospital, Seoul, Korea

 

I. Objectives: An image plane for MR flow measurement is placed perpendicular to the vessel of interest to avoid errors of measurement. There have been not only few studies but also reports in phantom studies about those errors. We investigated those errors of flow measurement by slice misalignment to ascending Aorta in patients clinically. 

 

II. Methods: Twenty three patients (7 women; 16 men; mean age, 55.6±19 years) were examined on 1.5T MRI (Magnetom Sonata, Siemens, Germany) from November to December 2009. Scan parameters were as follows: Phase Contrast FLASH 2D with retrospective electrocardiographic gating, TR/TE= 41/3.2ms, flip angle=30 degree, field of view=300mm, spatial resolution (1.3x 1.2 x 5mm3). Velocity encoding and calculated phases were 150cm/s and 20 phases. Different angles (0, 10, 20, and 30 degree) of slice inclination were tilted to the ascending aorta in each patient. We measured average velocity (Avg. V), net forward volume (Net FV), net forward volume / body surface area (Net FV/BSA), and average area (Avg. A) in all patients with Argus program. The percent error (%) for all measurements was calculated as ((with inclination – without inclination / without inclination) x 100) and compared with the mathematically calculated error in the equation (Fcalculated = Ftrue x cosθ, θ is the angle of slice misalignment, Ftrue is the value without inclination). A paired t-test was used to compare flow measurements by without vs. with inclination.

 

III. Results: In the patients clinically, the percent errors (%) of Avg. V in 10, 20,and 30 degree of inclination were higher than mathematically calculated values as 7.77±10.44, -12.78±11.78, and -21.05±13.74 (p<0.001) vs. -1.6, -6.1, and -13.4 respectively. However, it has shown lower errors than mathematically calculated values in Net FV and Net FV/BSA (p<0.0005) except the values of Net FV in 10 degree of inclination.

 

IV. Conclusions: The percent error of Net FV and Net FV/BSA were relatively small with < 10% errors within 30 degree of slice inclination. It is because the Avg. A was increased by slice inclination and also has reference to a flow equation (flow = average velocity x cross-sectional area). However that of Avg. V is over than 10% errors in 20 and 30 degree of inclination. Slice misalignment should be positioned within 10 degree of inclination in order to keep less than 5% errors.

* This paper was presented and published at the 2010 16th  Internatioanl Society of Radiographers and Radiological
Technologists World Congress in Gold Coast, Australia.

* Presentation Slides:

Presentation.pdf