Magnetic resonance measurement of velocity and flow: technique, validation, and cardiovascular applications.

A broad spectrum of MR methods has been published in the last few years for the visualization and the quantification of flow in human blood vessels. We describe the results of an extended study to measure the flow quantitatively using the MR phase modulation method. A gradient echo sequence which allows short repetition times was synchronized with the ECG. The instantaneous velocity profiles and the integrated flow rate can be determined throughout the cardiac cycle in up to 45 consecutive time intervals. The instantaneous velocity distributions can be displayed as 2D profiles over the lumen of the blood vessel. The technique has been successfully evaluated with a set of phantom experiments. Following this, quantifications of the blood flow rates in vivo were performed on the abdominal aortas of healthy volunteers. The MR flow results were compared to those obtained with conventional Doppler ultrasound examinations. The results of both methods are in good quantitative agreement. © 1988 Academic Press, Inc.

Quantitative flow measurements on phantoms and on blood vessels with MR.

Methods for measurement of blood flow with MR were devised many years ago but have been used for diagnosis in only the past few years. The two methods of measurement that have been used most extensively are based on the principles of time of flight and phase shift. A number of factors can influence the accuracy of MR measurements of blood flow. In vitro studies using flow phantoms have verified the accuracy of the phase-shift technique for measuring flow velocities exceeding 5 m/sec, which for practical purposes, encompasses the peak flow encountered in cardiovascular disorders. The flow measurements have been used to quantify valvular heart disease, congenital heart disease, pulmonary arterial disease, thoracic aortic disease, and peripheral vascular disease.

MR measurement of blood flow in the cardiovascular system.

Arterial spin labeling (ASL) perfusion measurements may have many applications outside the brain. In the abdomen, severe image artifacts can arise from motions between acquisitions of multiple signal averages in ASL, even with single-shot image acquisition. Background suppression and respiratory motion synchronization techniques can be used to ameliorate these artifacts. Two separate in vivo studies of renal perfusion imaging using pulsed continuous ASL (pCASL) were performed. The first study assessed various combinations of background suppression and breathing strategies. The second investigated the retrospective sorting of images acquired during free breathing based on respiratory position. Quantitative assessments of the test-retest repeatability of perfusion measurements and the image quality scored by two radiologists were made. Image quality was most significantly improved by using background suppression schemes and controlled breathing when compared to other combinations without background suppression or with free breathing, assessed by test-retests (5% level, F-test), and by radiologists' scores (5% level, Mann-Whitney U-test). Under free breathing, retrospectively sorting images based on respiratory position showed significant improvement. Both radiologists found 100% of the images had preferable image sharpness after sorting. High-quality renal perfusion measurements with reduced respiratory motion artifacts have been demonstrated using ASL when appropriate background suppression and breathing strategies are applied.

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Strategies for reducing respiratory motion artifacts in renal perfusion imaging with arterial spin labeling.

The nature of flow in the systemic venous pathway measured by magnetic resonance blood tagging in patients having the fontan operation

An innovative magnetic resonance imaging technique was applied to the measurement of blood flow in the abdominal aorta. The technique combines selective excitation and visualization from an orthogonal view. The distance that fluid has moved is directly visualized. The blood flow velocity at every 50 msec throughout the cardiac cycle was measured in a short time (about 4 minutes) using electrocardiographic gating and repeated excitations in each cycle. Measurements were compared with those obtained by Doppler ultrasound (US) as a reference. The pulsatile change of flow velocity in the cycle correlated well with the Doppler US recording. Two flow velocity indexes, peak flow velocity and the velocity integral, also showed good correlation (r = .98 for both). This method is applicable for clinical use and is useful for measurement of high flow rates, as found in arteries.

Measurement of aortic blood flow with MR imaging: comparative study with Doppler US.

A new method for the measurement of blood flow using magnetic resonance imaging has been developed. The flow velocities are calculated from the distances that the fluid has moved. The distances are directly visualized by a new pulse sequence. In a phantom study, the measured flow rates showed very good correlation with actual flow rates of up to 20 l/min (3 m/sec). In a volunteer study, pulsatile flow velocities of a large artery were measured with electrocardiographic gating. The flow pattern of a cardiac cycle at the abdominal aorta is similar to that revealed by other methods of measurement, such as Doppler ultrasound. This method allows reasonably accurate quantitative analysis of blood flow in the large arteries.

S Hashimoto

Papers

Measurement of aortic blood flow with MR imaging: comparative study with Doppler US.

Visualization of moving fluid: quantitative analysis of blood flow velocity using MR imaging.