flip angle

flip an·gle

in a magnetic resonance imaging pulse sequence, the deviation toward transverse plane of the average axis of the protons induced by radiofrequency signals; low angles are used in rapid or bright blood imaging sequences.

flip angle

An MRI term for the angle to which the net magnetisation is rotated or tipped relative to the main magnetic field direction by applying a radiofrequency excitation pulse at the Larmor frequency. The flip angle is used to define the angle of excitation for a field echo pulse sequence.

flip an·gle

(flip ang'gĕl)
In a magnetic resonance imaging sequence, the rotation of the average axis of the protons induced by radiofrequency signals; low angles are used in rapid-imaging sequences and to show a signal from flowing blood.
References in periodicals archive ?
The protocol included: T2-weighted HASTE (Half-Fourier acquisition single-shot turbo spin-echo) (TR/TE, 1200/94; flip angle, 150[degrees]), T1-weighted FLASH (fast low angle shot magnetic resonance imaging) (TR/TE, 169/4.76; flip angle, 70[degrees]) and T2-weighted TruFISP (true fast imaging with steady-state precession) (TR/TE, 3.75/1.8; flip angle, 50[degrees]) with slice thickness 4 mm, FOV 320-400 mm, and acquisition matrix 256-448 mm in three planes.
The image sequence included the following: (1) a sagittal and axial PD-weighted turbo spin-echo sequence with fat suppression, a flip angle of 90[degrees], a repetition time of 3000 ms, an echo time of 41 ms, a field of view (FOV) of 170 mm, 20 slices, a 480 x 640-pixel matrix, and a slice thickness of 3 mm; (2) a coronal PD-weighted sequence with fat suppression, a flip angle of 150[degrees], a repetition time of 3500 ms, an echo time of 41 ms, a FOV of 170 mm, 20 slices, a 217 x 320-pixel matrix, and a slice thickness of 3 mm; and (3) a sagittal T1-weighted turbo spin-echo with a repetition time of 579 ms, an echo time of 11 ms, a flip angle of 90[degrees], a FOV of 170 mm, 20 slices, a 480 x 640-pixel matrix, and a slice thickness of 3 mm.
Previous studies have used a variable flip angle (VFA) approach [18] to acquire volume T1 maps within a clinically acceptable time.
The parameters used for the patients were as follows: Turbospin echo T2 weighted sequences (T2 w) (TR: 3000, TE:74, flip angle: 150), spin echo T1 w sequence (TR:473, TE:7.7, flip angle: 90) on the axial plane, turbospin echo fat-saturated T2 w sequence (TR: 3300, TE:74, flip angle: 150) on the coronal plane, and turbospin echo T2 w sequence (TR: 6030, TE:103, flip angle: 150) on the sagittal plane.
3D-Proton Density-Non-Fat Suppressed-SPACE (Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) sequence (flip angle = 120[degrees]; repetition time (TR) = 1,000 msec; echo time (TE) = 46 msec; bandwidth = 460 Hz/pixel; Field of View (FOV) = 160 mm x 160 mm; matrix size = 320 x 300 pixels; voxel size = 0.5 x 0.5 x 0.5 mm (3) ) and
Increased flip angle is recommended in the evaluation of the biliary tree using liver-specific gadolinium-enhanced MRC.
Four acquisitions were obtained in a chronological order with a field of view (FOV) of 22 x 22 x 6 cm (AP x RL x FH): precontrast [T.sub.1]-weighted fast field echo (FFE) acquisition using a flip angle of 5[degrees] ("FA5" acquisition) in 1 minute 22 seconds; [T.sub.2]-weighted imaging ("T2W" acquisition) in 50 seconds; B1 mapping measurement acquisition ("B1MAP" acquisition) in 1 minute 23 seconds; and DCE acquisition using a flip angle of 15[degrees] ("FA15" acquisition) in 6 minutes 47 seconds with 65 dynamic scans.
The T1-weighted images were acquired as a 3D volume (256 x 256 x 174) using a spoiled gradient echo sequence with TR/TI/TE = 10400/4500/300 ms, flip angle = 15[degrees], and voxel size = 0.9375 x 0.9375 x 1 [mm.sup.3].
The imaging parameters for the 3D TOF-MRA scan were as follows: TR/TE = 23/3.5 ms; flip angle = 20.0[degrees]; FOV = 200 x 200 mm; matrix size = 488 x 249; SENSE factor = 2.5; slice thickness = 1.0 mm; and NEX = 1.
The 3D TOF MRA protocol utilizes TONE (tilted optimized nonsaturating excitation) to reduce saturation effects [7]; the mean flip angle was 25[degrees].
BMAT of the L3 and femoral necks on T1-weighted MRI (TR/TE, 150ms/4.4ms, flip angle, 70[degrees]) was segmented at the Image Analysis Laboratory by trained, quality-controlled, and cross-validated technicians using image analysis software (SliceOmatic, Tomovision Inc., Montreal, Canada).
It is apparent that the flip angle, important as it is, it does not directly show deviation from uniformity.