MRI pulse sequences
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At the time the article was created J. Ray Ballinger had no recorded disclosures.View J. Ray Ballinger's current disclosures
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An MRI pulse sequence is a programmed set of changing magnetic gradients. Each sequence will have a number of parameters, and multiple sequences grouped together into an MRI protocol.
A pulse sequence is generally defined by multiple parameters, including:
- time to echo (TE)
- time to repetition (TR)
- flip angle
- field of view and matrix size
- inversion pulse(s)
- spoiler gradient(s) (crusher gradients)
- echo train length (ETL)
- the spatial acquisition of k-space
- 3D acquisition vs. 2D acquisition vs. multiple overlapping slab acquisition
- post contrast imaging with gadolinium contrast agents
- diffusion weighting (b values)
Different combinations of these parameters affect tissue contrast and spatial resolution.
Parameters are discussed more fully in a separate article: MRI parameters.
MRI sequences can be grouped in a number of ways. Probably most accurately they are grouped according to the type of sequence (e.g. spin echo, or inversion recovery etc..) however for non radiologists another way of grouping sequences is by general image weighting (e.g. T1 or T2) and additional features (e.g. fat suppressed or gadolinium enhanced). This simplified approach is described in a separate article: MRI sequences (basic).
Pulse sequences can be broadly grouped as follows:
- spin echo sequences
- inversion recovery sequences
- gradient echo sequences
- diffusion weighted sequences
- saturation recovery sequences
- echo-planar pulse sequences
- spiral pulse sequences
Multiple sequences are usually needed to adequately evaluate a tissue, and the combination of sequences is referred to as a MRI protocol. The radiologist tailors the pulse sequences to try to best answer the clinical question posed by referring physician.
Protocols are discussed more fully in a separate article: MRI protocols.