Interactive body magnetic resonance fluoroscopy using modified single‐shot half‐Fourier rapid acquisition with relaxation enhancement (RARE) with multiparameter control

Abstract

Purpose: To develop a technique for interactive fluoroscopic abdominal magnetic resonance imaging (MRI) based on a single-shot half-Fourier rapid acquisition and relaxation-enhanced sequence. Materials and Methods:The sequence was modified by incorporating inner-volume excitation, driven-equilibrium signal enhancement, and reduced flip angle refocusing pulses. Contrast control was provided by integrating "onthe-fly" selection of phase encoding view order, fat suppression, and section thickness. The resulting sequence was evaluated with phantom experiments to quantify the signal-to-noise ratio (SNR) effects of the modifications and in healthy volunteers for imaging the bile ducts, stomach, and duodenum using water and gaseous contrast media. Results:Observed SNR relating to driven-equilibrium and flip angle scaling matched theoretical predictions. Volunteer examinations demonstrated the ability of the modified sequence to provide interactive, artifact-free imaging of the abdomen, including switching between conventional proton density-weighted, T2-weighted imaging and "hydrographic" projection imaging. Conclusion:Refinement of this technique may provide an abdomino-pelvic imaging capability similar in concept to real-time ultrasound, but with the advantages of MRI. MAGNETIC RESONANCE (MR) FLUOROSCOPIC techniques using gradient echo sequences and fast reconstruction methods were developed on dedicated research systems and first described over 10 years ago (1-4). At that time these techniques did not find useful clinical applications, and with the substantial hardware and software demands involved, typically using stand-alone reconstruction systems, there was little impetus to implement them on commercial systems.In the last few years higher performance of both gradient and image reconstruction subsystems has made it possible for "fluoroscopic" techniques to be implemented on commercial systems. These systems have found clinical application for interactive localization in cardiac imaging (5,6) and for monitoring the passage of intravenous contrast medium for first-pass contrastenhanced magnetic resonance angiography (MRA) (7), and are also being developed for interventional MR applications.In general these techniques have still not found a role in routine abdomen and pelvis imaging. Several reasons can be identified, including the use of predominantly gradient echo sequences that have a limited range of interactive contrast manipulation and suffer from image artifacts related to tissue motion-and susceptibility-induced distortions at gas-tissue interfaces. The lack of robust T2-weighted (T2w) imaging is particularly relevant for interventional work involving fluid collections such as abscesses, where transient gadolinium-based enhancement on T1-weighted (T1w) imaging may not provide adequate long-term demonstration of such collections to allow for drainage or aspiration. This has been partly addressed by recent versions of balanced gradient echo or "True-FISP" sequences (8). Perhaps most importantly, beyond interve...

Interactive two-dimensional fresh blood imaging: a feasibility study

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Targeted‐HASTE imaging with automated device tracking for MR‐guided needle interventions in closed‐bore MR systems

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Interactive magnetic resonance cholangiography (MRC) with adaptive averaging

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