Technical Note: A custom-designed flexible MR coil array for spine radiotherapy treatment planning

PURPOSE

To assess the performance and optimize the MR image quality when using a custom-built flexible radiofrequency (RF) spine coil array fitted between the immobilization device and the patient for spine radiotherapy treatment planning.

METHODS

A 32 channel flexible custom-designed receive-only coil array has been developed for spine radiotherapy simulation for a 3 T Philips MR scanner. Coil signal-to-noise performance and interactions with standard vendor hardware were assessed. In four volunteers, immobilization molds were created with a dummy version of the array within the mold, and subjects were scanned using the custom array in the mold. Phantoms and normal volunteers were scanned with both the custom spine coil array and the vendor's FDA-approved in-table posterior coil array to compare performance.

RESULTS

The superior-inferior field of view for the custom spine array was ~30 cm encompassing at least 10 vertebrae. A noise correlation matrix showed at least 25 dB isolation between all coil elements. Signal-to-noise ratio (SNR) calculated on a phantom scan at the depth of the spinal cord was a factor of 3 higher with the form-fit spine array as compared to the vendor's posterior coil array. The body coil B₁ transmit map was equivalent with and without the spine array in place demonstrating that the elements are decoupled from the body coil. Volunteer imaging showed improved SNR as compared to the vendor's posterior coil array. The custom array permitted a high degree of acceleration making possible the acquisition of isotropic high-resolution 1.1 × 1.1 × 1.1 mm³ three-dimensional data set over a 30-cm section of the spine in less than 5 min.

CONCLUSION

The custom-designed form-fitting flexible spine coil array provided enhanced SNR and increased acceleration compared to the vendor's posterior array. Future studies will assess MR-based spinal cord imaging with the custom coil in comparison to CT myelogram.

Preclinical safety assessment of contrast media: predictive value

The purpose of preclinical tests is to identify the potential benefits and risks of new diagnostic or therapeutic products. Regarding iodinated contrast media (CM), LD50 tests were used extensively in the past. However, from both scientific and ethical perspectives, it is today highly relevant to question the use of LD50 tests. Due to species differences and the very high volume of CM needed to kill half of the animals, such tests are not sensitive enough to differentiate between modern nonionic CM. Further, they are not very predictive in terms of human tolerability. In other tests with more relevant end-points than death, overall tolerance to the new dimeric compound iodixanol (Visipaque), representing the latest step in the development of CM, has been shown to be higher than to the nonionic monomers. Clinical experience has shown that the physiological parameters often stay closer to baseline after Visipaque than after administration of conventional CM.