In dynamic magnetic resonance imaging (MRI) studies, the motion kinetics or the contrast variability are often hard to predict, hampering an appropriate choice of the image update rate or the temporal resolution. A constant azimuthal profile spacing (111.246 degrees), based on the Golden Ratio, is investigated as optimal for image reconstruction from an arbitrary number of profiles in radial MRI. The profile order is evaluated and compared with a uniform profile distribution in terms of signal-to-noise ratio (SNR) and artifact level. The favorable characteristics of such a profile order are exemplified in two applications on healthy volunteers. First, an advanced sliding window reconstruction scheme is applied to dynamic cardiac imaging, with a reconstruction window that can be flexibly adjusted according to the extent of cardiac motion that is acceptable. Second, a contrast-enhancing k-space filter is presented that permits reconstructing an arbitrary number of images at arbitrary time points from one raw data set. The filter was utilized to depict the T1-relaxation in the brain after a single inversion prepulse. While a uniform profile distribution with a constant angle increment is optimal for a fixed and predetermined number of profiles, a profile distribution based on the Golden Ratio proved to be an appropriate solution for an arbitrary number of profiles.

To date, the rehabilitation of deaf patients with a multichannel cochlear implant has been established as a worldwide accepted method. In case of normal temporal bone anatomy the surgical procedure is standardized and offers few problems. Due to restrictive preoperative patient selection, the incidence of postoperative complications is rather low and is usually flap related.'-5 The percentage of so-called "major complications" which require surgical revision is estimated as low as 7.4%.3 To reduce the surgical risk a sufficient amount of experience in regard to the special type of implant is required. The flap design should be thoroughly planned, the posterior tympanotomy carefully performed and the electrode array gently inserted after an adequate cochleostomy. The importance of a reliable device fixation is emphasized in order to prevent migration.3,6

Purpose: To demonstrate a rapid MR technique that combines imaging and R2* mapping based on a single radial multi-gradient-echo (rMGE) data set. The technique provides a fast method for online monitoring of the administration of (super-)paramagnetic contrast agents as well as image-guided drug delivery. Materials and Methods:Data are acquired using an rMGE sequence, resulting in interleaved undersampled radial kspaces representing different echo times (TEs). These data sets are reconstructed separately, yielding a series of images with different TEs used for pixelwise R2* mapping. A fast numerical algorithm implemented on a real-time reconstruction platform provides online estimation of the relaxation rate R2*. Simultaneously the images are summed for the computation of a high-resolution image.Results: Convenient high-resolution R2* maps of phantoms and the liver of a healthy volunteer were obtained. In addition to stable intrinsic baseline maps, the proposed technique provides particularly accurate results for the high relaxation rates observed during the presence of (super-)paramagnetic contrast agents. Assuming that the change in R2* is proportional to the concentration of the agent, the technique offers a rough estimate for dynamic dosage. Conclusion:The simultaneous online display of morphological and parametric information permits convenient, quantitative surveillance of contrast-agent administration.

Osteoidosteomas are common bone tumours in childhood. Frequently they occur in the long bones of the lower extremities, less frequent in the humeri, phalanxes or the axial skeleton. The tumour is benign and noninfiltrative. Metastases do not occur. Typical complaints are nightly pain attacks, which are relieved by nonsteroidal antiinflammatory drugs. On X-ray, the classic finding is a small radiolucent area surrounded by sclerotic bone in the cortex. Surgical excision is often recommended, providing the possibility for a histological diagnosis. Therapeutic alternatives are percutaneous coagulation of the nidus by alcohol or laser, thermo-coagulation or high-frequency radioablation. Spontaneous remissions are well documented. Therefore the decision to wait and see and to treat with antiinflammatory medication is a considerable therapeutic option. We present two patient with an ostoidosteoma in the proximal femur. One of them underwent an unsuccessful trial for surgical extirpation and histological examination but afterwards developed a severe hip contraction with scoliosis. In the case of the other patient a primary operation was abandoned. Pain was completely controlled upon treatment with nonsteroidal antiinflammatory drugs in both patients. The contractions also disappeared completely upon physiotherapy. Serial MRI showed a significant regression of the inflammatory reaction in one case and the disappearance of the tumour in the other one. In conclusion, pharmacomedical therapy can be recommended, if the diagnosis is doubtlessly and a close follow up is established. The risk of anaesthesia and surgical treatment should be weighted against the risk of nonsteroidal antiinflammatory drug treatment.

The steady-state free precessing (SSFP) sequences, widely used in MRI today, acquire data only during a short fraction of the repetition time (TR). Thus, they exhibit a poor scan efficiency. In this paper, a novel approach to extending the acquisition window for a given TR without considerably modifying the basic sequence is explored for radial SSFP sequences. The additional data are primarily employed to increase the signal-to-noise ratio, rather than to improve the temporal resolution of the imaging. The approach is analyzed regarding its effect on the image SNR (signal to noise ratio) and the reconstruction algorithm. Results are presented for phantom experiments and cardiac functions studies. The gain in SNR is most notable in rapid imaging, since SNR enhancement for a constant repetition time may be used to compensate for the increase in noise resulting from angular undersampling.

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