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Real-Time Interactive Duplex MR Measurements

Application in Neurovascular Imaging

Stephan G. Wetzel1, Vivian S. Lee1, Andrew G. S. Tan1, Oliver Heid2, Soonmee Cha1, Glyn Johnson1 and Neil M. Rofsky1,3

1 Department of Radiology, New York University Medical Center, 530 First Ave., HCC Basement-MRI, New York, NY 10016.
2 Siemens Medical Engineering, MRI Division, Karl-Schall-Str., 91052 Erlangen, Germany.
3 Present address: Magnetic Resonance Imaging, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave., Boston, MA 02215.



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  		Fig. 1. —Line drawing shows real-time duplex flow-evaluation sequence, consisting of two-dimensional spatial radiofrequency (RF) excitation pulse, followed by bipolar flow-encoding and echoplanar readout gradient pulses. Note that during selective RF pulse, slice and phase-encoding gradients are applied to select column that subsequently can be encoded with few phase-encoding steps and without aliasing. AQ = Acquisition, GR = readout gradient, Gp = phase-encoding gradient, Gs = slice select gradient.

 


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  		Fig. 2A. —Normal duplex MR study of carotid arteries in 36-year-old healthy male volunteer. MR image as displayed online by real-time duplex MR imaging (encoding velocity, 100 cm/sec) shows measurement of common carotid artery. At top, magnitude image is displayed. Four white circles indicate region of interest containing four voxels placed over left common carotid artery. Time—velocity plot at bottom reveals flow that is directed caudocranially below baseline. Baseline tick interval is 1 sec; gap on baseline indicates current point of measurement. Distance from baseline to systolic peak represents peak systolic velocity, depending on velocity encoding. Using encoding velocity of 100 cm/sec, we measured 5.9 cm with an electronic caliper (vertical line) that represents peak systolic velocity of 73.75 cm/sec. Note sharp systolic upstroke (straight arrow) and downstroke (curved arrow), characteristic of normal common carotid artery flow.

 


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  		Fig. 2B. —Normal duplex MR study of carotid arteries in 36-year-old healthy male volunteer. MR image shows measurement of right-sided internal carotid artery, for which vessel is shifted by input device under region of interest as marked by four white circles in center of image. Time—velocity plot shows less acute downstroke and persistent end-diastolic flow. Peak systolic velocity is slightly lower, with 4.1 cm (vertical line) representing 51.25 cm/sec.

 


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  		Fig. 3. —Graph shows correlation of Doppler sonography with duplex MR imaging (large [UNK] = common carotid artery; small [UNK] = internal carotid artery; solid line = regression line, with y = 0.59x + 20.2; r = 0.83) and phase-contrast MR imaging (large {diamond} = common carotid artery; small {diamond} = internal carotid artery; dashed line represents regression line with y = 0.58x + 14.6; r = 0.75) for measurements in carotid arteries. Note that velocities as determined by sonography (x-axis) are on average higher compared with both MR imaging methods (y-axis) and that conventional phase—contrast measurements are, on average, higher than duplex MR measurements.

 


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  		Fig. 4. —Normal duplex MR imaging of superior sagittal sinus in 34-year-old healthy female volunteer. Real-time duplex MR image (encoding velocity, 100 cm/sec) shows measurement of superior sagittal sinus (region of interest indicated by four white circles) during normal breathing. Note slow pulsatile flow with peak systolic velocity of 36.25 cm/sec. Craniocaudally directed flow is displayed above baseline.

 

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