(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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