Using in vivo magnetic resonance microscopy, registered 1H and hyperpolarized 3He images of the rat lung were obtained with a resolution of 0.098 × 0.098 × 0.469 mm (4.5 × 10–3 mm3). The requisite stability and SNR was achieved through an integration of scan‐synchronous ventilation, dual‐frequency RF coils, anisotropic projection encoding, and variable RF excitation. The total acquisition time was 21 min for the 3He images and 64 min for the 1H image. Airways down to the 6th and 7th orders are clearly visible. Magn Reson Med 45:365–370, 2001. © 2001 Wiley‐Liss, Inc.

The authors describe an automated technique of magnetic resonance (MR) image synthesis. Given a specific pulse sequence, MR signals are acquired for several pulse delay and/or repetition times and used to compute images of intrinsic parameters T1, T2, and N(H). Both the computed images and operator-specified pulse delay and repetition times are then used to "synthesize" a new image based on equations descriptive of MR signal behavior and comparable to that acquired by using the operator-specified parameters in an actual MR study. Instrumentation enabling rapid operator-interactive generation of synthesized images is described and initial results presented, allowing for dependence of the signal on T2 in spin echo images. Extension to full T1, T2, and N(H) dependence for arbitrary pulse sequences is described. Major advantages of this technique include retrospective optimization of contrast between arbitrary materials, rapid and systematic image analysis, and reduced scanning time; potential limitations include accuracy, noise, motion artifacts, and multicomponent behavior.

A simple method was devised to reduce ringing and blurring artifacts caused by discontinuous T2 weighting of k-space data in fast spin-echo magnetic resonance (MR) imaging. The method demodulates the weighting function along the phase-encoding direction by using multiple T2 values derived from a set of non-phase-encoded echoes obtained from an extra excitation. The performance of this method was evaluated by computer simulations and experiments, which confirmed its capability of effectively reducing or, in some cases, even completely removing the ringing and blurring artifacts. The results also show that the proposed method produces better results than other artifact reduction methods. The method is particularly useful at high magnetic field strengths (7.1-9.4 T) and with strong gradients (> 20 G/cm) used in MR microscopy, in which the apparent T2 values are short for most tissues. The authors expect that the proposed method will find useful applications in various fast spin-echo pulse sequences.

This work describes our first efforts to implement SWIFT (SWeep Imaging with Fourier Transformation) in continuous mode for imaging and spectroscopy. We connected a standard quadrature hybrid with a quad coil and acquired NMR signal during continuous radiofrequency excitation. We utilized a chirped radiofrequency pulse to minimize the instantaneous radiofrequency field during excitation of the spin system for the target flip angle and bandwidth. Due to the complete absence of “dead time”, continuous SWIFT has the potential to extend applications of MRI and spectroscopy in studies of spin systems having extremely fast relaxation or broad chemical shift distributions beyond the range of existing MRI sequences.