Real‐time interactive MRI on a conventional scanner

Kerr, Adam B.; Pauly, John M.; Hu, B. L.; Li, King C.; Hardy, Christopher J.; Meyer, Ciraig H.; Macovski, Albert; Nishimura, Dwight G.

doi:10.1002/mrm.1910380303

Cited by 229 publications

(180 citation statements)

References 41 publications

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“…The key to our method is to begin the iteration at each pixel with an initial guess that is closer to the true value by exploiting correlations within neighboring pixels. We assume that the field map is spatially smooth (17,18) and use a region growing algorithm guided by a low-resolution reconstruction. We will refer to the field map estimation method proposed by Reeder (7) as the "pixel independent method" and to our new scheme as the "region growing method," described below with reference to Figs.…”

Section: Methodsmentioning

confidence: 99%

Field map estimation with a region growing scheme for iterative 3‐point water‐fat decomposition

Reeder

Shimakawa

et al. 2005

Magnetic Resonance in Med

203

327

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Robust fat suppression techniques are required for many clinical applications. Multi-echo water-fat separation methods are relatively insensitive to B 0 field inhomogeneity compared to the fat saturation method. Estimation of this field inhomogeneity, or field map, is an essential and important step, which is well known to have ambiguity. For an iterative water-fat decomposition method recently proposed, ambiguities still exist, but are more complex in nature. They were studied by analytical expressions and simulations. To avoid convergence to incorrect field map solutions, an initial guess closer to the true field map is necessary. This can be achieved using a region growing process, which correlates the estimation among neighboring pixels. Further improvement in stability is achieved using a low-resolution reconstruction to guide the selection of the starting pixels for the region growing. The proposed method was implemented and shown to significantly improve the algorithm's immunity to field inhomogeneity. Magn Reson Med 54: 1032-1039, 2005.

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Section: Methodsmentioning

confidence: 99%

Field map estimation with a region growing scheme for iterative 3‐point water‐fat decomposition

Reeder

Shimakawa

et al. 2005

Magnetic Resonance in Med

203

327

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“…All experiments were performed on a 1.5T GE SIGNA CV/i scanner (gradient amplitude ϭ 40 mT/m, slew rate ϭ 150 T/m/s) with a BiT3 interface to a Sun Ultra 60 (360 MHz). The associated acquisition and control software was an adapted version of the Stanford real-time system (18).…”

Section: Methodsmentioning

confidence: 99%

“…To conform to gradient duty cycle limits, a TR of 40 ms was used. While the temporal resolutions in Table 1 indicate the time for complete inner-spiral image updates, a sliding window reconstruction (18,19) provided partial updates every TR. Due to the short TR, a low flip angle of 30°was necessary to provide an adequate SNR.…”

Section: Methodsmentioning

confidence: 99%

Variable‐density adaptive imaging for high‐resolution coronary artery MRI

Sussman¹,

Stainsby²,

Robert³

et al. 2002

Magnetic Resonance in Med

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Variable-density (VD) spiral k-space acquisitions are used to acquire high-resolution (0.78 mm), motion-compensated images of the coronary arteries. Unlike conventional methods, information for motion compensation is obtained directly from the coronary anatomy itself. Specifically, periods of minimal coronary distortion are identified by applying the correlation coefficient template matching algorithm to real-time images generated from the inner, high-density portions of the VD spirals. Combining the data associated with these images together, high-resolution, motion-compensated coronary images are generated. Because coronary motion is visualized directly, the need for cardiac-triggering, breath-holding, and navigator echoes is eliminated. The motion compensation capability of the technique is determined by the inner-spiral spatial and temporal resolution. Results indicate that the best performance is achieved using inner-spiral images with high spatial resolution (1.6 -2.9 mm), even though temporal resolution (four to six independent frames per second) suffers as a result. Image quality within the template region in healthy volunteers was found to be comparable to that achieved with cardiac-triggered breath-hold scans, although Key words: variable-density; template matching; coronary artery; motion compensation; real-time Diagnostic-quality MR coronary images must possess submillimeter spatial resolution. While the theoretical limits of MR do not preclude the attainment of such resolutions, respiratory-(1) and cardiac-(2) induced displacement and distortion (3) of the arteries can significantly degrade image quality. To counteract these effects, motion compensation schemes have been developed (4,5). With the evolution toward higher-resolution imaging, however, a number of concerns are arising with respect to their accuracy. Most of these approaches use indirect measures such as the position of bellows placed over the chest, ECG waveforms, and diaphragm position determined by navigator echoes to infer coronary motion. Recent studies have indicated that while indirect measures may correlate with coronary displacement, they do not give a precise characterization of the actual motion (1,6,7). Additionally, indirect measures generally do not give any indication of the degree of distortion associated with the coronary motion (3). Furthermore, arrhythmias and/or difficulties in breathholding, commonly found in patients with coronary disease, give rise to added difficulties in the application of these techniques (8).A technique that makes use of direct visualization of the coronary anatomy for motion compensation was developed recently by Hardy et al. (9). In this "adaptive averaging" technique, a series of interleaved high-resolution echo-planar images are acquired. From each of the individual interleaves, aliased "subimages" are formed. Since these subimages are generated from every interleaf, they provide real-time visualization of the coronary anatomy. Each subimage is used to evaluate the motion present during the...

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“…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.…”

mentioning

confidence: 99%

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

Makki

Graves

Lomas

2002

Magnetic Resonance Imaging

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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...

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Real‐time interactive MRI on a conventional scanner

Cited by 229 publications

References 41 publications

Field map estimation with a region growing scheme for iterative 3‐point water‐fat decomposition

Field map estimation with a region growing scheme for iterative 3‐point water‐fat decomposition

Variable‐density adaptive imaging for high‐resolution coronary artery MRI

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

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