“Keyhole” method for accelerating imaging of contrast agent uptake

Abstract

Magnetic resonance (MR) imaging methods with good spatial and contrast resolution are often too slow to follow the uptake of contrast agents with the desired temporal resolution. Imaging can be accelerated by skipping the acquisition of data normally taken with strong phase-encoding gradients, restricting acquisition to weak-gradient data only. If the usual procedure of substituting zeroes for the missing data is followed, blurring results. Substituting instead reference data taken before or well after contrast agent injection reduces this problem. Volunteer and patient images obtained by using such reference data show that imaging can be usefully accelerated severalfold. Cortical and medullary regions of interest and whole kidney regions were studied, and both gradient- and spin-echo images are shown. The method is believed to be compatible with other acceleration methods such as half-Fourier reconstruction and reading of more than one line of k space per excitation.

Arterial input functions for dynamic susceptibility contrast MRI: Requirements and signal options

“…Temporal resolution is another important property that is used to resolve the peak of the AIF. Higher temporal resolution can be obtained in FLASH using keyhole acquisitions (45)(46)(47) or using EPI in general (48). With EPI, temporal resolution can be improved further using interlaced zipper acquisition and processing (37)(38)(39) in which additional neck slices are acquired at the same location at intermediate times during the multislice acquisition of brain slices.…”

x‐f choice: Reconstruction of undersampled dynamic MRI by data‐driven alias rejection applied to contrast‐enhanced angiography

“…With multiple receivers (the number of receiver coils is denoted as ), this aliased x-f space is viewed independently by each coil. In this case the signal can be described as C ϭs [ 1 ] or written explicitly as C i (x j ) (x j ,f j ) ϭ s i . Here s i is the aliased signal viewed by the i th coil, C i (x j ) is the sensitivity of the i th coil at spatial location x j , and (x j ,f j ) is the unknown signal from locations (x j ,f j ) in the nonaliased space.…”

“…This step can be used to improve the conditioning of Eq. [1] or indeed to reduce it enough in size so that an underdetermined problem becomes tractable. Information on signal contribution requires a model of the power distribution in x-f space with no aliasing, analogously to the training data in the k-t BLAST method.…”

“…Excluded j receive zero signal and all others receive the values from the solution of the reduced version of Eq. [1]. Using this reconstruction scheme will produce a result with varying problem sizes throughout x-f space, each of which is chosen to reflect the number of significantly contributing aliases present at that point.…”

Noquist: Reduced field‐of‐view imaging by direct Fourier inversion

“…Many other methods have been proposed to accelerate specific applications in MRI, including dynamic imaging problems. Keyhole imaging (8) exploits the observation that in many dynamic imaging problems, such as contrast uptake monitoring, intensity changes are often relatively uniform over large regions in the field of view (FOV), i.e., the dynamics are spatially band-limited. Methods such as the block regional interpolation scheme for k-space (BRISK) (9) and 3D time resolved imaging of contrast kinetics (TRICKS) (10) employ more elegant algorithms that have been built around this idea.…”