Design of a RF-resonant set improving locally the B1+ efficiency. Applications for clinical MRI in andrology and urology.

Modern diagnostic imaging methods for andrology and urology fall behind other well-developed applications such as cardiology or neurology. Particularly, MRI despite its superior soft tissue contrast is hardly used for MR-imaging of the penis, primarily due to the lack of the corresponding receive or transmit coils. In order to fix this, a new radio frequency resonator, based on the birdcage operating principles has been designed, simulated, fabricated, tested and compared experimentally to existing RF coils. In order to provide high transmit efficiency and high sensitivity, while maintaining the coil safety, the resonator spatially separates alternating magnetic and electric fields. The transmitted magnetic field (B1+) is concentrated in the centre of the imaging volume, while the electric field remains on its edge and does not lead to tissue heating. The resonator design was optimised for human MRI in 1.5 T scanners. Both simulations and experiment showed the resonator to provide around 100-fold specific absorption rate reduction, around 10-fold improvement of the transmit efficiency and more than 10-fold enhancement of the signal to noise ratio (SNR) in a phantom compared to the body coil, around 2-fold SNR enhancement in a phantom compared to the commercial flexible 4-element coil, and up to 1.5-fold enhancement compared to the same coil in-vivo.

Stereotactic Cryodestruction of Gliomas.

Surgical resection of gliomas affecting functionally important brain structures is associated with high risk of permanent postoperative neurological deficit and deterioration of the patient's quality of life. The availability of modern neuroimaging and neuronavigation permits the application of minimally invasive stereotactic cryodestruction of the tumor in such cases. The authors used this treatment in 88 patients with supratentorial gliomas of various WHO histopathological grades not suitable for microsurgical resection. Postoperative mortality (1.1%) and rate of surgical complications (11.4%) were comparable to reported results of stereotactic brain tumor biopsy, whereas the rate of neurological morbidity (42%) was comparable to outcome after resection of gliomas within eloquent brain areas. The majority of complications were temporary, and permanent deterioration of neurological function was noted in 8% of cases only. The median survival after treatment in patients with glioblastoma and anaplastic astrocytoma was 12.4 and 46.9 months, respectively, and was not reached in cases of diffuse astrocytoma, which compared favorably both with historical controls and literature data. Therefore, it seems reasonable to consider stereotactic cryodestruction in multimodality management strategies of "unresectable" intracranial gliomas, and further studies directed at evaluation of its efficacy are definitely needed.