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Preliminary clinical results with low flip angle spin-echo MR imaging of the head and neck
R Chisin1, R B Buxton, M W Ragozzino
1Department of Radiology, Massachusetts General Hospital, Boston 02114.
Abstract:
A new approach for producing primarily T2- and proton-density-weighted MR images in less time than the conventional long TR, long TE imaging is to reduce the TR of a double spin-echo pulse sequence and to also reduce the RF excitation flip angle to minimize the resulting T1 sensitivity. In preliminary studies with a human volunteer and five patients with various diseases of the head and neck, conventional long TR, long TE and short TR, short TE images were compared with short TR, long TE images with reduced flip angles (45 degrees, 30 degrees), which required only 40% of the imaging time of the long TR images. The latter images showed a similar contrast pattern to the conventional T2-weighted image, and contrast-to-noise measurements indicated an increase in contrast between the lesion and nearby tissue when the flip angle was reduced. Furthermore, the maximum contrast/noise per unit imaging time on the short TR, long TE image was comparable to that on the long TR, long TE image. Optimization of the flip angle with short TR allows a substantial reduction in imaging time but with a reduction in multislice capability. This technique will be most useful in areas of complex anatomy where two or more orthogonal imaging planes are required, such as the head and neck.
Insights
This study introduces a faster magnetic resonance imaging (MRI) method using reduced flip angles to produce T2-weighted images. This technique significantly cuts imaging time while maintaining diagnostic image quality for head and neck scans.
Area of Science:
- Medical Imaging
- Radiology
- Magnetic Resonance Imaging (MRI)
Background:
- Conventional MRI sequences for T2- and proton-density-weighted imaging require long repetition times (TR) and echo times (TE).
- This extended imaging duration can be a limitation, particularly in complex anatomical regions or for patients requiring multiple imaging planes.
Purpose of the Study:
- To develop and evaluate a novel, time-efficient MRI approach for generating T2- and proton-density-weighted images.
- To assess the feasibility of reducing imaging time by modifying pulse sequence parameters.
Main Methods:
- A modified double spin-echo pulse sequence was employed, reducing the repetition time (TR) and RF excitation flip angle.
- Images acquired with short TR and reduced flip angles (45°, 30°) were compared to conventional long TR, long TE sequences.
- Contrast-to-noise ratio (CNR) was measured to assess image quality.
Main Results:
- The novel technique achieved comparable contrast patterns to conventional T2-weighted images.
- Reduced flip angles increased the contrast between lesions and surrounding tissues.
- Imaging time was reduced by approximately 60% (requiring only 40% of the time).
- Maximum contrast-to-noise per unit imaging time was comparable to conventional methods.
Conclusions:
- Optimizing flip angles with a short TR in spin-echo sequences allows for substantial MRI scan time reduction.
- This accelerated imaging technique is particularly beneficial for complex anatomical areas like the head and neck, where multiple orthogonal planes are often needed.