Background and Purpose-Endovascular treatment of cerebral aneurysms, a minimally invasive alternative to surgery, is too often followed by recanalization and recurrences. The purpose of this work was to assess if in situ beta radiation can inhibit recanalization after coil embolization. Methods-Radioactive platinum coils ( 32 P-coils) were produced by ion implantation of 32 P. A single-coil arterial occlusion model was used to compare angiographic and pathological results at 1 to 12 weeks after nonradioactive and 32 P-coil embolization of maxillary, cervical, and vertebral arteries in 26 dogs. Coils of varying activities were used and results compared to define the minimal activity required to inhibit recanalization. Similar experiments were performed in 16 porcine maxillary and lingual and 8 rabbit axillary arteries. Results of 32 P-coil embolization of bifurcation aneurysms were then compared with embolization with nonradioactive coils in 12 dogs at 3 months. Results-Nonradioactive coil embolization of canine arteries led to occlusion at 1 week, followed by recanalization at 2 weeks, which persisted at 3 months in all cases. 32 P-coils, ion-implanted with activities above 0.13 Ci/cm, led to persistent occlusion at 3 months in 80% of arteries.32 P-coils ion-implanted with the same activity inhibited recanalization in porcine and rabbit arteries. Bifurcation aneurysms treated with 32 P-coils had better angiographic results at 3 months (Pϭ0.006) than aneurysms treated with nonradioactive coils. Arteries occluded were filled with fibrous tissue at 3 months. Aneurysms embolized with 32 P-coils showed more complete neointimal coverage of the neck, without recanalization, as compared with aneurysms treated with nonradioactive coils. Conclusion-In

The near field dose distribution of a realistic vascular stent impregnated with radioactive 32P is calculated employing the dose-point-kernel (DPK) method in a homogeneous and uniform medium. The cylindrical wire mesh geometry for the Palmaz-Schatz [Palmaz-Schatz is a tradename of Cordis (a Johnson & Johnson company)] stent is incorporated in the model calculation, and the dose distribution generated by the beta particles emitted from the decayed radioactive 32P is computed at distances ranging from 0.1 to 2 mm exterior to the stent surface. Dose measurements were obtained using radiochromic film dosimetry media on an actual Palmaz-Schatz half-stent impregnated with 32P using ion implantation, and compared to the DPK model predictions. The close agreement between the model calculation and the film dosimetry data confirms the validity of the model which can be adapted to a variety of different stent designs.

Up to five arrays of soft-x-ray detectors are used with the Fourier-Bessel harmonic reconstruction method to generate 2D images of sawtooth collapses during Ohmic plasma discharges on the Tokamak de Varennes. For low-harmonic reconstructions (M< 2), a quasi-interchange behavior (Wesson model) is observed during the sawtooth crash, but a reconnectionlike behavior (Kadomtsev model) is recovered using higher harmonics {M>L 3) on the same data. This indicates that the Kadomtsev model is a better description for the sawtooth collapse, although the collapse time remains shorter than predicted.PACS numbers: 52.55. Fa, 52.30.Jb, 52.35.Py, 52.70.La Sawtooth oscillations' are internal disruptive instabilities observed on most tokamaks. This periodic phenomenon is observed on many plasma diagnostics and each cycle consists of a slow^ increase in the central temperature and density followed by a sudden collapse. As an explanation, Kadomtsev proposed the total reconnection model, ^ where an m = l mode disappears nonlinearly through resistive reconnection at the q = 1 surface, resulting in a flattening of the temperature, density, and current profile, and a release of energy. Detailed investigations using nonlinear two-dimensional codes ^"^ have shown that this model is consistent with MHD theory, and is able to explain several experimental observations on small tokamaks. ^"^ Recently though, this model has been called into question in the light of new experimental results obtained on large tokamaks.^'^ The total reconnection model would fail to explain the fast sawtooth crash, and to a lesser extent, the lack of large precursors and the presence of large slowly decaying successor oscillations. A number of recent works have attempted to explain these new observations, *^"^^ but most of the attention has been focused on the quasi-interchange (Wesson) model'^ since soft-x-ray-emission reconstructions on the Joint European Torus (JET) seem to agree with topological predictions of the sawtooth collapse phase. ^''^ In this model, a flattened q profile leads to an unstable m = l mode, which drives a cold bubble toward the center of the plasma, expelling the initial hot core through an interchange mechanism. Qualitative diff*erences between the total reconnection model and the quasi-interchange model should make clear experimental identification possible through tomographic imaging of soft-x-ray emission during the sawtooth collapse. In the total reconnection model, the hot core of the q < 1 region moves almost rigidly to one side, whereas in the quasiinterchange model, the initial hot core becomes a crescent when the cold bubble penetrates the center region due to convective flow, ^ ^ Despite such contrasting topological diff*erences, experimental identification is not straightforward since spatial inversion techniques must be used to unfold line-integrated data obtained with discrete detectors. On tokamaks, several limitations on viewing angles and the number of detectors favor the Fourier-harmonic-reconstruction technique, whic...