In several applications, MRI is used to monitor the time behavior of the signal in an organ of interest; e.g., signal evolution because of physiological motion, activation, or contrast-agent accumulation. Dynamic applications involve acquiring data in a k‐t space, which contains both temporal and spatial information. It is shown here that in some dynamic applications, the t axis of k‐t space is not densely filled with information. A method is introduced that can transfer information from the k axes to the t axis, allowing a denser, smaller k‐t space to be acquired, and leading to significant reductions in the acquisition time of the temporal frames. Results are presented for cardiac-triggered imaging and functional MRI (fMRI), and are compared with data obtained in a conventional way. The temporal resolution was increased by nearly a factor of two in the cardiac-triggered study, and by as much as a factor of eight in the fMRI study. This increase allowed the acquisition of fMRI activation maps, even when the acquisition time for a single full time frame was actually longer than the paradigm cycle period itself. The new method can be used to significantly reduce the acquisition time of the individual temporal frames in certain dynamic studies. This can be used, for example, to increase the temporal or spatial resolution, increase the spatial coverage, decrease the total imaging time, or alter sequence parameters e.g., repetition time (TR) and echo time (TE) and thereby alter contrast. Magn Reson Med 42:813‐828, 1999. r 1999 Wiley

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Unaliasing by fourier-encoding the overlaps using the temporal dimension (UNFOLD), applied to cardiac imaging and fMRI.

In five healthy subjects and 18 patients, cine magnetic resonance (MR) imaging of the heart was performed with a true fast imaging with steady-state precession (FISP) sequence. Results were compared both quantitatively and qualitatively with those at cine fast low-angle shot (FLASH) MR imaging. The blood-myocardial contrast-to-noise ratio (CNR) was 2.0 times higher and the normalized (for measurement time and pixel size) blood-myocardial CNR was 4.0 times higher for true FISP compared with FLASH MR imaging. Qualitative scores for image quality were significantly higher with true FISP MR imaging. Segmented cine true FISP MR imaging generated high-contrast MR images of the heart in healthy subjects and in patients with heart disease and produced image quality superior to that with cine FLASH MR imaging.

Cine MR angiography of the heart with segmented true fast imaging with steady-state precession.

In clinical magnetic resonance (MR) imaging, the diagnostic quality of examinations is often degraded by streaklike flow artifacts that obscure anatomic details and reduce contrast. In addition, vascular structures are often not depicted clearly because the desired flow voids are obliterated by spurious intraluminal signals. On the basis of analysis of the physical mechanism of flow artifact formation, the authors developed a new technique for suppressing these artifacts. This applies interleaved, spectrally shaped radio frequency pulses to selectively saturate spins located in regions outside the image volume. In phantom, volunteer, and clinical imaging studies, the technique has proved to be effective by yielding a striking reduction in flow artifacts and markedly improving the reliability with which arterial and venous structures are imaged. The method has few drawbacks: It is applicable to most MR pulse sequences and, in principle, can be implemented on most imagers. It is particularly helpful for high-resolution surface coil studies of the neck, mediastinal imaging, gated cardiac imaging, and for detecting thrombus and other intravascular lesions such as dissections.

Spatial presaturation: a method for suppressing flow artifacts and improving depiction of vascular anatomy in MR imaging.

NMR relaxation of protons in tissues and other macromolecular water solutions.

In this study, magnetic resonance imaging was compared with histology to evaluate the usefulness of magnetic resonance imaging to distinguish malignant from benign cardiac and paracardiac masses in 55 patients. Tumor location, tissue composition, and pericardial or pleural effusion all were identified as key predictors of lesion type. Observers were accurate in the prediction of lesion type (area under curve 0.88 and 0.92), and there was good interobserver variability (Cohen's κ = 0.64).

Usefulness of magnetic resonance imaging of cardiac and paracardiac masses.

Nuclear magnetic resonance (NMR) images of live rats with sterile and pyogenic abscesses, hematomas, and various implanted and spontaneous neoplasms demonstrated good contrast differentiation between pathologic and surrounding normal tissues. This differentiation was maximal when both the T1 and T2 tissue relaxation times were used as criteria. Neoplasms have a broad range of T1 and T2 values and may be confused with abscesses or hematomas. Tissue rate constants (1/T1 and 1/T2) are mainly dependent on total water content, the exception being fat, which has a 1/T2 value much shorter than that expected on the basis of water content alone.

Nuclear magnetic resonance imaging of the abnormal live rat and correlations with tissue characteristics

Given a suitable trigger signal, cardiac synchronized magnetic resonance (MR) imaging is simple to implement; however, single section techniques are not efficacious, especially when the heart rate sets the repetition interval. We demonstrate multi-section, double, and single-echo imaging, any of which rapidly covers the cardiac volume; 3-D modes capable of achieving very thin sections; and cycled multi-section imaging capable of efficaciously providing dynamic data on heart motion. These modes form a complementary, powerful set of options for clinical work.

Magnetic resonance imaging strategies for heart studies.

To overcome the limitations of magnetic resonance (MR) cardiac imaging using nongated data acquisition, three methods for acquiring a gating signal, which could be applied in the presence of a magnetic field, were tested: an air-filled plethysmograph, a laser-Doppler capillary perfusion flowmeter, and an electrocardiographic gating device. The gating signal was used for timing of MR imaging sequences (IS). Application of each gating method yielded significant improvements in structural MR image resolution of the beating heart, although with both plethysmography and laser-Doppler velocimetry it was difficult to obtain cardiac images from the early portion of the cardiac cycle due to an intrinsic delay between the ECG R wave and peripheral detection of the gating signal. Variations in the temporal relationship between the R wave and plethysmographic and laser-Doppler signals produced inconsistencies in the timing of IS. Since the ECG signal is virtually free of these problems, the preferable gating technique is IS synchronization with an electrocardiogram. The gated images acquired with this method provide sharp definition of internal cardiac morphology and can be temporarily referenced to end diastole and end systole or intermediate points.

Cardiac Imaging Using Gated Magnetic Resonance

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Nuclear magnetic resonance imaging of the abnormal live rat and correlations with tissue characteristics

Magnetic resonance imaging strategies for heart studies.

Cardiac Imaging Using Gated Magnetic Resonance