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Automated Identification of Minimal Myocardial Motion for Improved Image Quality on MR Angiography at 3 T

¹ Department of Radiology, Johns Hopkins University Medical School, JHOC 4223, 601 N Caroline St., Baltimore, MD 21287. Address correspondence to M. Stuber.
² Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD.
³ Department of Cardiovascular Medicine, Cleveland Clinic Foundation, Cleveland, OH.
⁴ Philips Medical Systems, Cleveland, OH.
⁵ Department of Medicine, Johns Hopkins University Medical School, Baltimore, MD.

View larger version (54K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1 —Screen shot shows FREEZE software tool. Rectangle on axial image shows user-defined region of interest (ROI) in which motion is analyzed. FREEZE operates on user-friendly interface in which user can zoom in or out and pan and level image; user can also select different time frames and pick most suitable frame for ROI selection. After ROI selection, algorithm starts automatically and result (software-prescribed trigger delay = Tdsf) is sent directly to scanner. Another option is that user can select restricted time window (on displacement vs time plot [small window]) for which period of minimal motion should be analyzed by algorithm.

View larger version (41K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A —Navigator-gated and navigator-corrected 3D high-resolution segmented k-space imaging of phantom (1.5 T, TR/TE = 7.0/2.4, =35°, resolution=0.7x1x3 mm, 10 k-space lines per cardiac cycle, acquisition time window [Tacq] = 70 milliseconds, field of view = 280 x 350 mm, 160 x 240 matrix). Static image of phantom. Arrow points to plastic tube, with internal diameter of 1.8 mm, that is attached to water bottle. B0 = external magnetic field.

View larger version (41K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B —Navigator-gated and navigator-corrected 3D high-resolution segmented k-space imaging of phantom (1.5 T, TR/TE = 7.0/2.4, =35°, resolution=0.7x1x3 mm, 10 k-space lines per cardiac cycle, acquisition time window [Tacq] = 70 milliseconds, field of view = 280 x 350 mm, 160 x 240 matrix). Image of phantom obtained at maximum velocity (10.2 cm/s). Vessel diameter is measured approximately 2.7 mm.

View larger version (36K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C —Navigator-gated and navigator-corrected 3D high-resolution segmented k-space imaging of phantom (1.5 T, TR/TE = 7.0/2.4, =35°, resolution=0.7x1x3 mm, 10 k-space lines per cardiac cycle, acquisition time window [Tacq] = 70 milliseconds, field of view = 280 x 350 mm, 160 x 240 matrix). Image of phantom at trigger delay (493 milliseconds) identified using FREEZE. Vessel diameter is measured approximately 1.8 mm. Diameter in contiguous segments was quantified perpendicular and parallel to direction of motion. Measurements between I and II and between III and IV, respectively, were performed.

View larger version (8K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A —Graphs show diameter (A) and sharpness (B) values of plastic tube obtained at different instances of sinusoidal motion of phantom. No significant diameter change was measured in segment that is oriented parallel to motion direction (dashed line). However, diameter changes considerably in segment oriented perpendicular to motion direction (solid line). Arrow identifies diameter value in image obtained using trigger delay found by FREEZE software tool.

View larger version (9K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B —Graphs show diameter (A) and sharpness (B) values of plastic tube obtained at different instances of sinusoidal motion of phantom. There is no significant change in sharpness in segment oriented parallel to motion direction (dashed line). However, sharpness changes substantially in segment that is oriented perpendicular to motion direction (solid line). Arrow identifies sharpness value in image obtained using trigger delay found by FREEZE.

View larger version (165K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A —Volume-targeted navigator-gated and navigator-corrected double oblique 3D segmented k-space gradient-echo images obtained in three subjects (3 T, TR/TE = 4.3/1.47, =20°, resolution=0.7x1x3 mm, field of view = 360 x 270 mm, 512 x 268 matrix, 16 radiofrequency excitations per R-R interval, acquisition time window [Tacq] = 69 milliseconds, bandwidth = 362 Hz/pixel, scan duration = 145-259 seconds depending on navigator efficiency and heart rate, 10 slices [acquired], 20 slices [reconstructed using zero filling], fat saturation, adiabatic T2 prepulse [TE = 50 milliseconds]). Axial views of left anterior descending coronary artery in 31-year-old healthy man acquired at trigger delay of 579 milliseconds using visual assessment method (A) and at trigger delay of 675 milliseconds using FREEZE software tool (B). Conspicuity of vessel (arrows) differs between B and A.

View larger version (161K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B —Volume-targeted navigator-gated and navigator-corrected double oblique 3D segmented k-space gradient-echo images obtained in three subjects (3 T, TR/TE = 4.3/1.47, =20°, resolution=0.7x1x3 mm, field of view = 360 x 270 mm, 512 x 268 matrix, 16 radiofrequency excitations per R-R interval, acquisition time window [Tacq] = 69 milliseconds, bandwidth = 362 Hz/pixel, scan duration = 145-259 seconds depending on navigator efficiency and heart rate, 10 slices [acquired], 20 slices [reconstructed using zero filling], fat saturation, adiabatic T2 prepulse [TE = 50 milliseconds]). Axial views of left anterior descending coronary artery in 31-year-old healthy man acquired at trigger delay of 579 milliseconds using visual assessment method (A) and at trigger delay of 675 milliseconds using FREEZE software tool (B). Conspicuity of vessel (arrows) differs between B and A.

View larger version (161K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C —Volume-targeted navigator-gated and navigator-corrected double oblique 3D segmented k-space gradient-echo images obtained in three subjects (3 T, TR/TE = 4.3/1.47, =20°, resolution=0.7x1x3 mm, field of view = 360 x 270 mm, 512 x 268 matrix, 16 radiofrequency excitations per R-R interval, acquisition time window [Tacq] = 69 milliseconds, bandwidth = 362 Hz/pixel, scan duration = 145-259 seconds depending on navigator efficiency and heart rate, 10 slices [acquired], 20 slices [reconstructed using zero filling], fat saturation, adiabatic T2 prepulse [TE = 50 milliseconds]). Oblique sagittal views of right coronary artery (RCA) in 29-year-old healthy man acquired at trigger delay of 614 milliseconds obtained by visual assessment method (C) and at trigger delay of 561 milliseconds obtained by FREEZE (D). Length of visible vessel (arrows) is increased in image acquired with FREEZE.

View larger version (164K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4D —Volume-targeted navigator-gated and navigator-corrected double oblique 3D segmented k-space gradient-echo images obtained in three subjects (3 T, TR/TE = 4.3/1.47, =20°, resolution=0.7x1x3 mm, field of view = 360 x 270 mm, 512 x 268 matrix, 16 radiofrequency excitations per R-R interval, acquisition time window [Tacq] = 69 milliseconds, bandwidth = 362 Hz/pixel, scan duration = 145-259 seconds depending on navigator efficiency and heart rate, 10 slices [acquired], 20 slices [reconstructed using zero filling], fat saturation, adiabatic T2 prepulse [TE = 50 milliseconds]). Oblique sagittal views of right coronary artery (RCA) in 29-year-old healthy man acquired at trigger delay of 614 milliseconds obtained by visual assessment method (C) and at trigger delay of 561 milliseconds obtained by FREEZE (D). Length of visible vessel (arrows) is increased in image acquired with FREEZE.

View larger version (185K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4E —Volume-targeted navigator-gated and navigator-corrected double oblique 3D segmented k-space gradient-echo images obtained in three subjects (3 T, TR/TE = 4.3/1.47, =20°, resolution=0.7x1x3 mm, field of view = 360 x 270 mm, 512 x 268 matrix, 16 radiofrequency excitations per R-R interval, acquisition time window [Tacq] = 69 milliseconds, bandwidth = 362 Hz/pixel, scan duration = 145-259 seconds depending on navigator efficiency and heart rate, 10 slices [acquired], 20 slices [reconstructed using zero filling], fat saturation, adiabatic T2 prepulse [TE = 50 milliseconds]). Oblique sagittal views of RCA in 33-year-old healthy man acquired at trigger delay of 674 milliseconds obtained by visual assessment method (E) and at trigger delay of 193 milliseconds obtained by FREEZE (F).

View larger version (173K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4F —Volume-targeted navigator-gated and navigator-corrected double oblique 3D segmented k-space gradient-echo images obtained in three subjects (3 T, TR/TE = 4.3/1.47, =20°, resolution=0.7x1x3 mm, field of view = 360 x 270 mm, 512 x 268 matrix, 16 radiofrequency excitations per R-R interval, acquisition time window [Tacq] = 69 milliseconds, bandwidth = 362 Hz/pixel, scan duration = 145-259 seconds depending on navigator efficiency and heart rate, 10 slices [acquired], 20 slices [reconstructed using zero filling], fat saturation, adiabatic T2 prepulse [TE = 50 milliseconds]). Oblique sagittal views of RCA in 33-year-old healthy man acquired at trigger delay of 674 milliseconds obtained by visual assessment method (E) and at trigger delay of 193 milliseconds obtained by FREEZE (F).

View larger version (8K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5 —Graph shows trigger delays found using FREEZE and using visual assessment. In two subjects, volume-targeted navigator-gated and navigator-corrected double oblique 3D segmented k-space gradient-echo imaging was performed (3 T, TR/TE = 4.3/1.47, = 20°, resolution = 0.7 x 1 x 3 mm, field of view = 360 x 270 mm, 512 x 268 matrix, 16 radiofrequency excitations per R-R interval, acquisition time window [Tacq] = 69 milliseconds, bandwidth = 362 Hz/pixel, scan duration = 145-259 seconds depending on navigator efficiency and heart rate, 10 slices [acquired], 20 slices [reconstructed using zero filling], fat saturation, adiabatic T2 prepulse [TE = 50 milliseconds]). FREEZE found end-systolic trigger delay (arrows), whereas visual inspection led to diastolic acquisition interval in same subjects.

View larger version (199K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6 —Navigator-gated and navigator-corrected double oblique 3D segmented k-space gradient-echo imaging sequence (3 T, TR/TE = 7.5/2.3, =20°, resolution=0.35x0.35x1.5 mm, field of view=270x216 mm, 800x610 matrix, scan duration = 906 seconds, 12 radiofrequency excitations per R-R interval, acquisition time window [Tacq] = 90 milliseconds, 10 slices [acquired], 20 slices [reconstructed], fat saturation). High-resolution scan of 23-year-old healthy man acquired at trigger delay of 591 milliseconds using FREEZE software tool shows highly visible interface in region of coronary arteries (small-diameter branches [A]) as well as pericardium and lung-liver interface (B). Together with ability to reveal small-diameter branching vessels, this suggests excellent suppression of both intrinsic and extrinsic myocardial motion.

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