Journal Club: Performance of a static-anode/flat-panel x-ray fluoroscopy system in a diagnostic strength magnetic field: A truly hybrid x-ray/MR imaging system

In the world of hybrid and integrated imaging systems, you can't get much more incompatible than MR and X-ray, at least until now. I'd been hearing about work on such an x-ray/MR hybrid system for a few years now, and now there's a paper by Fahrig et al in this month's Medical Physics (R. Fahrig, Z. Wen, A. Ganguly, G. DeCrescenzo, J. A. Rowlands, G. M. Stevens, R. F. Saunders, and N. J. Pelc, "Performance of a static-anode/flat-panel x-ray fluoroscopy system in a diagnostic strength magnetic field: A truly hybrid x-ray/MR imaging system", Med Phys 32, 1775-1784 (2005)) describing the performance characteristics of a flat panel fluoroscopy and open MRI blended together.

Talk about bleeding edge imaging. Not something that would have been possible just a few short years ago before flat panel image receptors were available. With MR, you get great soft tissue contrast, but you can't see solid objects like bone, implants or wires. With fluoroscopy, you have decent resolution, good visibility of bone, implants, and wires/catheters, but soft tissue contrast isn't so great.

Not entirely sure what kind of clinical demand there is for something like this, but from the quick glance I gave at the paper, there have been a number of clinical procedures performed on it already. I look forward to digging into this paper and finding out more about the system.

Abstract:

Minimally invasive procedures are increasing in variety and frequency, facilitated by advances in imaging technology. Our hybrid imaging system (GE Apollo™ flat panel, custom Brand x-ray static anode x-ray tube, GE Lunar high-frequency power supply and 0.5 T Signa SP™) provides both x-ray and MR imaging capability to guide complex procedures without requiring motion of the patient between two distant gantries. The performance of the x-ray tube in this closely integrated system was evaluated by modeling and measuring both the response of the filament to an externally applied field and the behavior of the electron beam for field strengths and geometries of interest. The performance of the detector was assessed by measuring the slanted-edge modulation transfer function (MTF) and when placed at zero field and at 0.5 T. Measured resonant frequencies of filaments can be approximated using a modified vibrating beam model, and were at frequencies well below the 25 kHz frequency of our generator for our filament geometry. The amplitude of vibration was not sufficient to cause shorting of the filament during operation within the magnetic field. A simple model of electrons in uniform electric and magnetic fields can be used to estimate the deflection of the electron beam on the anode for the fields of interest between 0.2 and 0.5 T. The MTF measured at the detector and the DQE showed no significant difference inside and outside of the magnetic field. With the proper modifications, an x-ray system can be fully integrated with a MR system, with minimal loss of image quality. Any x-ray tube can be assessed for compatibility when placed at a particular location within the field using the models. We have also concluded that a-Si electronics are robust against magnetic fields. Detailed knowledge of the x-ray system installation is required to provide estimates of system operation. ©2005 American Association of Physicists in Medicine