A real‐time reconstruction system for magnetic resonance imaging

Gmitro, Arthur F.; Ehsani, Ali Reza; Berchem, Guy; Snell, R.

doi:10.1002/mrm.1910350515

Cited by 24 publications

(13 citation statements)

References 11 publications

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“…e ϪTread/T2 [3] Equation 3 provides a closed-form solution which is instructive for determining the conditions under which driven equilibrium is useful. In general, driven equilibrium provides the greatest gain when T 2 is greater than T read and T 1 is greater than T rec .…”

Section: Driven Equilibriummentioning

confidence: 99%

Interactive fast spin‐echo imaging

et al. 2000

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It is shown that a spin-echo sequence may be used to acquire T 2 -weighted, high-resolution, high-SNR sections at quasi-realtime frame rates for interactive, diagnostic imaging. A singleshot fast spin-echo sequence was designed which employs driven equilibrium to realign transverse magnetization remaining at the final spin echo. Driven equilibrium is shown to improve T 2 contrast at a given TR, or conversely to reduce TR by approximately 1000 msec and thus increase temporal resolution while maintaining a given level of contrast. Wiener demodulation of k-space data prior to reconstruction is shown to reduce blurring caused by T 2 -decay while constraining noise often associated with other inverse filters. Images are continuously acquired, reconstructed, and displayed at rates of one image every one to two seconds, while section position and contrast may be altered interactively. MR fluoroscopy, used for interactive examination of dynamic processes, has typically been based on gradientecho (1), spiral (2), or EPI (3) sequences. While these sequences have been useful and often necessary for applications which require sub-second temporal resolution, such as cardiac imaging (4), they often do not produce the contrast, or have the signal-to-noise ratio (SNR) or resolution needed for diagnostic-quality images. Within this context of real-time interactive imaging, it would be desirable for some applications to have the benefits of spin-echo imaging, particularly reduced sensitivity to off-resonance, high-SNR, and T 2 -weighting.The half-Fourier acquisition single-shot turbo-spin-echo (HASTE) (or single-shot fast spin-echo (SSFSE)) sequence can acquire a single section with T 2 -weighted contrast in as little as 300 msec, providing an opportunity for spinecho-based real-time imaging. Half-Fourier acquisition (5) allows shorter effective TEs to be achieved than does the original rapid acquisition with relaxation enhancement (RARE) sequence (6), providing T 2 -weighted images of soft-tissue as well as fluid. The sequence is inherently very robust against motion and off-resonance, and the spinwarp k-space trajectory limits any aliasing to one spatial direction, thus allowing significant freedom to choose arbitrary orientations and spatial offsets. HASTE, in the conventional, non-real-time paradigm, has been successfully applied to abdominal (7), pelvic (7), cholangiopancreatographic (8), ankle (9), brain (10), small bowel (11), uterus (12), liver (13), fetal (14), urinary tract (15), and salivary gland (16) imaging.Two factors have limited the implementation of the HASTE sequence for real-time T 2 imaging. First, the period required for many materials to recover in order to achieve T 2 -weighting is long, limiting temporal resolution. Second, transverse magnetization decay during the long readout train limits spatial resolution. In this work we address these challenges by: 1) designing a pulse sequence using driven equilibrium (17) to enhance the signal from fluids and thus shorten the required recovery time, and 2) applyin...

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Section: Driven Equilibriummentioning

confidence: 99%

Interactive fast spin‐echo imaging

et al. 2000

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“…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)(2)(3)(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.…”

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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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“…Using a view-sharing reconstruction, a single measurement of a given view may be used in the formation of more than one image; views are acquired continuously, but only the most recent measurement for each view is used in reconstructing a given frame, thus allowing more frequent image updating than if waiting for an entire set of new views to be collected. Similar view-sharing reconstruction techniques have subsequently been implemented for radial (9), spiral (10), and echoplanar imaging (EPI) (11) acquisitions. Although the data acquisition rate in 2DFT gradient-echo imaging is typically lower than for these other pulse sequences, 2DFT gradient-recalled echo(GRE) offers a number of distinct advantages for fluoroscopic imaging.…”

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confidence: 99%

A flexible view ordering technique for high‐quality real‐time 2DFT MR fluoroscopy

et al. 1999

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A method to tailor the view order to the reconstruction cycle is introduced for real-time MRI. It is well known that view sharing and oversampling central k-space views can improve the temporal resolution of gradient-echo pulse sequences. By ordering phase-encodes to synchronize k-space acquisition with the reconstruction cycle, apparent temporal resolution can match the frame rate with as few as one-fourth of the phase-encodes sampled per reconstruction. Spatial resolution is maintained by periodically updating high spatial frequencies. In addition to apparent temporal resolution, three other criteria for real-time imaging are identified and evaluated: display latency, dispersion, and frame-to-frame consistency. Latency is minimized by ordering views in a reverse-centric manner within each reconstruction interval, sampling high-energy views immediately prior to beginning reconstruction. Dispersion is kept low and consistent by synchronizing acquisition and reconstruction, thus avoiding poorly timed reconstruction instances. The ability to provide MR images to the operator in real time is becoming critical to more and more applications such as contrast bolus triggering (1), interventional MR (2-4), and cardiac imaging (5-7). Real-time imaging requires continuous, efficient data acquisition as well as rapid, on-line reconstruction and display.MR ''fluoroscopy'' was first demonstrated using a fast two-dimensional Fourier transform (2DFT) gradient-echo sequence with sequential phase-encode sampling (8). Using a view-sharing reconstruction, a single measurement of a given view may be used in the formation of more than one image; views are acquired continuously, but only the most recent measurement for each view is used in reconstructing a given frame, thus allowing more frequent image updating than if waiting for an entire set of new views to be collected. Similar view-sharing reconstruction techniques have subsequently been implemented for radial (9), spiral (10), and echoplanar imaging (EPI) (11) acquisitions. Although the data acquisition rate in 2DFT gradient-echo imaging is typically lower than for these other pulse sequences, 2DFT gradient-recalled echo(GRE) offers a number of distinct advantages for fluoroscopic imaging. These include robustness against off-resonance effects, negligible T2* resolution limitations, anti-alias filtering in the frequency-encode direction, moderate gradient strength requirements, relatively easy implementation, straightforward image reconstruction, and arbitrary ordering of the phase encodings.Because low spatial frequency views provide gross positional and contrast information while high-frequency views provide edge and detail information, temporal resolution is determined not only by the frequency of reconstruction, but also by the frequency at which the central region of k-space is sampled. Considering this, it was proposed in ref. 8 that temporal resolution could be increased by sampling the central region of k-space more frequently than the remainder. Several investigators h...

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A real‐time reconstruction system for magnetic resonance imaging

Cited by 24 publications

References 11 publications

Interactive fast spin‐echo imaging

Interactive fast spin‐echo imaging

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

A flexible view ordering technique for high‐quality real‐time 2DFT MR fluoroscopy

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