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Sensitivity EncodingInfoSheet: - Sequences - 
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(SENSE) A MRI technique for relevant scan time reduction. The spatial information related to the coils of a receiver array are utilized for reducing conventional Fourier encoding. In principle, SENSE can be applied to any imaging sequence and k-space trajectories. However, it is particularly feasible for Cartesian sampling schemes. In 2D Fourier imaging with common Cartesian sampling of k-space sensitivity encoding by means of a receiver array enables to reduce the number of Fourier encoding steps.
SENSE reconstruction without artifacts relies on accurate knowledge of the individual coil sensitivities. For sensitivity assessment, low-resolution, fully Fourier-encoded reference images are required, obtained with each array element and with a body coil.
The major negative point of parallel imaging techniques is that they diminish SNR in proportion to the numbers of reduction factors. R is the factor by which the number of k-space samples is reduced. In standard Fourier imaging reducing the sampling density results in the reduction of the FOV, causing aliasing. In fact, SENSE reconstruction in the Cartesian case is efficiently performed by first creating one such aliased image for each array element using discrete Fourier transformation (DFT).
The next step then is to create a full-FOV image from the set of intermediate images. To achieve this one must undo the signal superposition underlying the fold-over effect. That is, for each pixel in the reduced FOV the signal contributions from a number of positions in the full FOV need to be separated. These positions form a Cartesian grid corresponding to the size of the reduced FOV.
The advantages are especially true for contrast-enhanced MR imaging such as dynamic liver MRI (liver imaging) , 3 dimensional magnetic resonance angiography (3D MRA), and magnetic resonance cholangiopancreaticography (MRCP).
The excellent scan speed of SENSE allows for acquisition of two separate sets of hepatic MR images within the time regarded as the hepatic arterial-phase (double arterial-phase technique) as well as that of multidetector CT.
SENSE can also increase the time efficiency of spatial signal encoding in 3D MRA. With SENSE, even ultrafast (sub second) 4D MRA can be realized.
For MRCP acquisition, high-resolution 3D MRCP images can be constantly provided by SENSE. This is because SENSE resolves the presence of the severe motion artifacts due to longer acquisition time. Longer acquisition time, which results in diminishing image quality, is the greatest problem for 3D MRCP imaging.
In addition, SENSE reduces the train of gradient echoes in combination with a faster k-space traversal per unit time, thereby dramatically improving the image quality of single shot echo planar imaging (i.e. T2 weighted, diffusion weighted imaging).
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Sequential Line Imaging
 
MR imaging techniques in which the image is built up from successive lines through the object. In various schemes, the lines are isolated by oscillating magnetic field gradients or selective excitation, and then the NMR signals from the selected line are encoded for position by detecting the FID or spin echo in the presence of a magnetic field gradient along the line; the Fourier transformation of the detected signal then yields the distribution of emitted NMR signal along the line.
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Sinc InterpolationMRI Resource Directory:
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A method of interpolating image data by zero filling the high spatial-frequency components of the raw data so that after Fourier transformation the image matrix size has been increased. This method can significantly improve the image display.
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Spatial Frequency
 
Measure of resolution (lp/mm or lp/cm).
A dimension of the Fourier transformation space (k-space representation of an image), having units of inverse distance. Higher values of spatial frequencies correspond to finer detail in the image.
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Spin Warp Imaging
 
A form of Fourier transformation imaging in which phase encoding gradient pulses are applied for a constant duration but with varying amplitude. The spin warp method, as other Fourier imaging techniques, is relatively tolerant of inhomogeneities in the magnetic fields.
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