Misregistration artifacts in image-derived arterial input function in non-echo-planar imaging-based dynamic contrast-enhanced MRI.

PURPOSE: To characterize misregistration artifact in arterial input function (AIF) pixels in dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) using a two-dimensional non-echo-planar imaging (EPI)-based gradient-recalled echo (GRE) sequence. MATERIALS AND METHODS: Dynamic gadopentetate-enhanced MRI was acquired in the rat using a semikeyhole acquisition scheme. The AIF was obtained from abdominal aorta pixels. Different sliding-window reconstruction techniques were applied to determine which lines in a series of the semikeyhole acquisition were associated with the misregistration artifacts. RESULTS: The misregistration along the phase-encoding direction arose when k-space lines were acquired during the rise-time of the aortic gadolinium concentration. The maximum blood concentration of gadolinium estimated from the phase shift calculation agreed with that estimated from dosage. CONCLUSION: AIF misregistration results from a phase shift due to increasing gadolinium concentration in the aorta, and may need to be considered in small animal DCE-MRI studies with a high rate of rise in the AIF in high-field MR applications.

Effective blood signal suppression using double inversion-recovery and slice reordering for multislice fast spin-echo MRI and its application in simultaneous proton density and T2 weighted imaging.

PURPOSE: To design a multislice double inversion-recovery fast spin-echo (FSE) sequence, with k-space reordered by inversion time at slice position (KRISP) technique, to produce black-blood vessel wall magnetic resonance imaging (MRI). MATERIALS AND METHODS: In this sequence, central k-space sampling for each slice is required at inversion time (TI) of the blood signal. To fill the entire k-space, the peripheral lines are obtained less or greater the TI and using a rotating slice order. Blood flow signal suppression was first evaluated using a phantom. Simulation studies were used to investigate FSE image quality. The final sequence was then applied to the rabbit abdominal aorta MRI at 4.7 T. RESULTS: In the flow phantom study, artifacts from slow-flowing water were substantially reduced by the KRISP technique; residual water spins were dephased by the strong phase-encoding gradient required for peripheral k-space. These dephased spins flowed into the slice plane where the center of k-space was being acquired at the TI of the flowing water signal. Multislice black-blood MR images were successfully obtained in the rabbit abdomen using the sequence with the k-trajectory optimized by the simulation study. CONCLUSION: The KRISP technique was effective both in multislice double inversion-recovery FSE and in blood signal suppression.

Averaging keyhole pulse sequence with presaturation pulses and EXORCYCLE phase cycling for dynamic contrast-enhanced MRI.

The purpose of this study was to design a keyhole pulse sequence for quantitative 2D dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) based on a spoiled gradient echo T1-weighted acquisition. Saturation recovery was applied to achieve a linear correlation between signal intensity and contrast agent concentration in an arterial input function (AIF) while simultaneously removing time-of-flight effect. To remove ghosting artifacts arising from incomplete presaturation, EXORCYCLE phase cycling with averaging was applied to the pulse sequence. RF spoiling by radiofrequency switching with the synthesizer can be combined with EXORCYCLE phase cycling. Images affected by the large difference in signal intensity before and after contrast agent administration with the keyhole technique were improved by interleaving of peripheral lines of k-space with groups of central lines. Both peripheral and central lines were renewed during the dynamic scan. AIFs were obtained from the rat abdominal aorta with this keyhole sequence.