Magnetic resonance imaging of the coronary arteries is a particularly difficult task because of the small size of the vessels and the motion of the heart during the cardiac and respiratory cycles. The authors developed a non-breath-hold three-dimensional (3D) technique to accomplish this goal. Imaging was performed with voxel sizes of 1.50-4.50 mm3. This allows for excellent multiplanar reconstruction to view the coronary arteries from any angle. The short echo time usually makes blood isointense with surrounding tissue since inflow enhancement is weak with a thick-slab 3D method. This problem is overcome by applying fat saturation and magnetization transfer contrast techniques to suppress the signals of fat and myocardium surrounding the coronary arteries. Respiratory motion artifacts are reduced by taking four acquisitions and averaging the data. The authors acquired the first 3-10 cm of both the left and right coronary arteries in most cases in 7-10 minutes with single slab coverage. Acquisition of multiple slabs should further increase the length of coverage of the coronary arteries. Further improvements will occur when respiratory gating is used.

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Systems physiology, studied by biomedical engineers, is an analytical way to approach the homeostatic foundations of basic physiology. In many systems physiology courses, students attend lectures and are given homework and reading assignments to complete outside of class. The effectiveness of this traditional approach was compared with an approach in which a wireless classroom communication system was used to provide instant feedback on in-class learning activities and reading assignment quizzes. Homework was eliminated in this approach. The feedback system used stimulated 100% participation in class and facilitated rapid formative assessment. The results of this study indicate that learning of systems physiology concepts including physiology is at least, as if not more, effective when in-class quizzes and activities with instant feedback are used in place of traditional learning activities including homework. When results of this study are interpreted in light of possible effects of the September 11, 2001 terrorist attacks on student learning in the test group, it appears that the modified instruction may be more effective than the traditional instruction.

Magnetic resonance imaging (MRI) sequences are characterized by both radio frequency (RF) pulses and time-varying gradient magnetic fields. The RF pulses manipulate the alignment of the resonant nuclei and thereby generate a measurable signal. The gradient fields spatially encode the signals so that those arising from one location in an excited slice of tissue may be distinguished from those arising in another location. These signals are collected and mapped into an array called k-space that represents the spatial frequency content of the imaged object. Spatial frequencies indicate how rapidly an image feature changes over a given distance. It is the action of the gradient fields that determines where in the k-space array each data point is located, with the order in which k-space points are acquired being described by the k-space trajectory. How signals are mapped into k-space determines much of the spatial, temporal, and contrast resolution of the resulting images and scan duration. The objective of this article is to provide an understanding of k-space as is needed to better understand basic research in MRI and to make well-informed decisions about clinical protocols. Four major classes of trajectories-echo planar imaging (EPI), standard (non-EPI) rectilinear, radial, and spiral-are explained. Parallel imaging techniques SMASH (simultaneous acquisition of spatial harmonics) and SENSE (sensitivity encoding) are also described.

Magnetic resonance angiography has matured to the point where clinically useful images can be acquired in half an hour or less. In this paper, the role of 3D imaging techniques is primarily considered. Specifically, the optimal imaging parameters, sequences, and reconstruction techniques are evaluated for moving spins. A variant of FISP known as ROAST with low flip angles, short repeat times, and a thick slab has been found to yield the best 3D survey scan of the cranial vessels with roughly 1 X 1 X 1-mm3 resolution in each of the processed images (slices). For the faster flowing carotids, a sagittal scout with as short a TE as possible is required to avoid spin dephasing. Localization is accomplished in both cases by acquiring thin slab 3D, thin partition, larger flip angle, longer repeat time FLASH sequences. Different choices of dephase/rephase sequences and directions are also reviewed. These choices are discussed from a practical and theoretical perspective. In particular, improvements in contrast and resolution are evaluated using half-Fourier, 512 acquisition, small fields of view and constrained reconstruction for both rephased gradient echo sequences and dephased thin slice long TR spin-echo sequences. A resolution of 0.5-0.75 mm is recommended to obtain sufficient image quality for consistent clinical interpretation of stenoses and vessel abnormalities.