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Twenty-one patients with intraocular disease were studied by magnetic resonance (MR) imaging and computed tomography (CT). In 13 cases, malignant uveal melanoma was considered the likely diagnosis. Both imaging methods were accurate in determining the location and size of uveal melanomas. MR imaging was superior for the assessment of possible associated retinal detachment, for assessment of vitreous change, and for differentiating uveal melanoma from choroidal hemangioma and choroidal detachment. A case of retinal gliosis could not be differentiated from uveal melanoma by either technique. Uveal melanomas appeared as hyperintense lesions on T1-weighted images and as hypointense lesions on T2-weighted images. High signal intensity of the vitreous was observed in patients with vitritis and in those who were thought to have protein leaking into the vitreous as a result of impairment of the retinal-blood barrier.

Fast large-angle spin echo (FLASE) is a common pulse sequence designed for quantitative imaging of trabecular bone (TB) microarchitecture. However, imperfections in the nonselective phase-reversal pulse render it prone to stimulated echo artifacts. The problem is further exacerbated at isotropic resolution. Here, a substantially improved RF-spoiled FLASE sequence (sp-FLASE) is described and its performance is illustrated with data at 1.5T and 3T. Additional enhancements include navigator echoes for translational motion sensing applied in a slice parallel to the imaging slab. Whereas recent work suggests the use of fully-balanced FLASE (b-FLASE) to be advantageous from a signal-to-noise ratio (SNR) point of view, evidence is provided here that the greater robustness of sp- Key words: FLASE; trabecular bone; micro-MRI; spin-echo; microarchitectureMost osteoporotic fractures occur at anatomic sites that contain a significant portion of trabecular bone (TB). Key among these skeletal locations are the vertebrae and the ends of the long bones near the joints where stresses are multidirectional (distal and proximal femur, distal radius and ulna). Even though osteoporosis is always associated with a loss of bone mass, there has been increasing evidence of the role of structure as independent predictors of the mechanical competence of TB (1). This situation has spurred the development of noninvasive imaging techniques for regional quantification of TB architecture (2). MRI has been shown to be particularly useful and both spin-echo (SE) and gradient-echo-(GRE) type pulse sequences are currently in use for this task (3).Gradient-echo based steady-state free precession (SSFP) techniques, although used widely for TB imaging (4), suffer from signal loss and artifactual broadening of trabeculae due to susceptibility-induced gradient fields at the bone/bone marrow interface (5). The more recently implemented balanced SSFP (b-SSFP) is also sensitive to offresonance effects (6,7). Although b-SSFP has been shown to produce images with spin-echo type qualities at short repetition times (on the order of 10 ms) (7), this sequence has comparatively low signal-to-noise ratio (SNR) efficiency at the target resolution (ϳ150 m) due to the necessarily high receiver bandwidth. Indeed, with TR ϭ 10 ms, readout time per repetition cannot be much longer than 5 ms (considering the excitation pulse, phase encode, and rewinder gradients), compared with a fast large-angle spin-echo (FLASE) readout time of 18 ms per repetition (TR ϭ 80 ms). These constraints result in an approximate SNR penalty factor of ͱ3 for b-SSFP that must be considered when comparing the relative efficiency of the two types of pulse sequences.* Of course, some of the signal loss is recovered in b-SSFP by the refocused transverse magnetization carried over from one repetition to the next. However, since the steady-state signal level is heavily T 2 -dependent, the relative performance of b-SSFP and FLASE is not straightforward to predict from simulation due to the complex rel...

The effects of section separation on image contrast and calculated T1 relaxation times were investigated in healthy volunteers and a phantom using an early commercial version magnetic resonance imaging system. The effects are explained qualitatively on the basis of side lobes of excitation occurring outside the selected section resulting in reduction of the time permitted for T1 relaxation. The options for dealing with imperfect section selection, including separation of the sections (i.e., leaving gaps) and nonsequential excitation, are illustrated and the trade-offs involved in each explained.

The authors present a method for obtaining magnetic resonance (MR) images of intra- and extracranial vessels from thin contiguous transaxial sections. A section-selective gradient refocusing pulse sequence with a short repetition time caused flow-related enhancement from spins that flowed perpendicular to the transaxial sections. The signal was further enhanced by means of flow compensation gradients to rephase any phase shifts resulting from moving spins in the presence of the imaging gradients. Coronal and sagittal sections, reformatted from multiple transaxial sections, are shown to have excellent vessel contrast without the use of contrast material. These images were obtained in 12 minutes of acquisition time from as many as 60 sections of 3-mm thickness. Such a technique shows significant promise for MR angiography.