At the recent Charing Cross International Symposium, London, UK, Dr Reto Bale, Interdisciplinary Stereotactic Intervention and Planning Laboratory (SIP-Lab) Innsbruck, Austria, discussed the advantages of combining various pre- and intraoperative imaging modalities while minimising radiation exposure.
In a presentation entitled 'Image fusion and 3D navigation in interventional radiology', Bale explained that image fusion allows for pre-operative image data to be collected, fused, and then integrated into therapy. This allows for morphological information (eg. computerised tomography [CT], magnetic resonance imaging [MRI], 2-dimensional [2D]/three-dimensional [3D] ultrasound [US], 2D/3D angiography, and 2D/3D fluoroscopy) and functional information (eg. positron emission tomography [PET], SPECT, and Doppler-US) to be combined and incorporated into one data set.
When referring to endovascular procedures, Bale asked the question 'What do we want?' He then identified the top five requirements, which included:
High-resolution imaging with good soft-tissue contrast
Visualisation from any desired angle
Real-time visualisation of the instrument with respect to the fused image modalities (e.g. road mapping)
Minimise radiation exposition and nephrotoxic contrast media
Adaptable visualisation (always use the optimal modality/information at the right time)
Modern flat-panel detector based 3D rotational angiography systems provide 'CT-like' reconstructed cross-sections and 3D vessel reconstructions. According to Bale, 3D road-mapping is a multi-modality visualisation technique that involves real-time fusion of 2D fluoroscopy with 3D angiography and creates a dynamic roadmap with real-time registration, e.g. Allura Xper FD20. This ability allows freedom to change angulation and rotation of C-arc, field of view, and source to image distance. In addition the intraoperative 2D/3D fluoroscopy based images may be superimposed to pre-operative acquired morphological or functional image data.
Finally, Bale discussed electromagnetic 3D navigation. The guidewire has sensor coils at the tip. Magnetic fields are generated and the Faraday Effect induces a small passive current in the sensor coil. The software can determine location and orientation of the sensor. This navigation technique allows for real-time localization of the catheter position on cross sections and 3D reconstructions without any radiation, and also allows for multimodal datasets to be integrated. Initial phantom and animal experiments performed at the National Institute of Health (NIH) in Bethesda and at the SIP-Lab Innsbruck showed sufficient accuracy.
To conclude, Bale explained, "Image fusion enhances the information of single modalities, and fused image data may be used for diagnosis, planning and 3D-navigation. Multimodal 3D-navigation systems with real-time image updating will be integrated in the interventional suite of the future."
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