Rowland Frederick Saunders

A truly hybrid interventional MR/X-ray system: feasibility demonstration.

A system enabling both x‐ray fluoroscopy and MRI in a single exam, without requiring patient repositioning, would be a powerful tool for image‐guided interventions. We studied the technical issues related to acquisition of x‐ray images inside an open MRI system (GE Signa SP). The system includes a flat‐panel x‐ray detector (GE Medical Systems) placed under the patient bed, a fixed‐anode x‐ray tube overhead with the anode‐cathode axis aligned with the main magnetic field and a high‐frequency x‐ray generator (Lunar Corp.). New challenges investigated related to: 1) deflection and defocusing of the electron beam of the x‐ray tube; 2) proper functioning of the flat panel; 3) effects on B0 field homogeneity; and 4) additional RF noise in the MR images. We have acquired high‐quality x‐ray and MR images without repositioning the object using our hybrid system, which demonstrates the feasibility of this new configuration. Further work is required to ensure that the highest possible image quality is achieved with both MR and x‐ray modalities. J. Magn. Reson. Imaging 2001;13:294–300.

Truly hybrid interventional MR/x-ray system: Investigation of in vivo applications

RATIONALE AND OBJECTIVES The purpose of this study was to provide in vivo demonstrations of the functionality of a truly hybrid interventional x-ray/magnetic resonance (MR) system. MATERIALS AND METHODS A digital flat-panel x-ray system (1,024(2) array of 200 microm pixels, 30 frames per second) was integrated into an interventional 0.5-T magnet. The hybrid system is capable of MR and x-ray imaging of the same field of view without patient movement. Two intravascular procedures were performed in a 22-kg porcine model: placement of a transjugular intrahepatic portosystemic shunt (TIPS) (x-ray-guided catheterization of the hepatic vein, MR fluoroscopy-guided portal puncture, and x-ray-guided stent placement) and mock chemoembolization (x-ray-guided subselective catheterization of a renal artery branch and MR evaluation of perfused volume). RESULTS The resolution and frame rate of the x-ray fluoroscopy images were sufficient to visualize and place devices, including nitinol guidewires (0.016-0.035-inch diameter) and stents and a 2.3-F catheter. Fifth-order branches of the renal artery could be seen. The quality of both real-time (3.5 frames per second) and standard MR images was not affected by the x-ray system. During MR-guided TIPS placement, the trocar and the portal vein could be easily visualized, allowing successful puncture from hepatic to portal vein. CONCLUSION Switching back and forth between x-ray and MR imaging modalities without requiring movement of the patient was demonstrated. The integrated nature of the system could be especially beneficial when x-ray and MR image guidance are used iteratively.

Alignment of a volumetric tomography system

A test-bed system has been developed for imaging phantoms with tomosynthesis and volumetric computed tomography. This system incorporates an amorphous silicon flat panel detector on a movable gantry and a computer-controlled rotational positioning stage. In this paper, an analysis of the sensitivity of reconstructed images to geometrical misalignment is presented. Application of this method to circular digital tomosynthesis is examined, with spatial resolution in the focal plane as the criterion for evaluating the effect of misalignment. A software-based method is presented for correcting data for imperfect system alignment prior to image reconstruction. Experimental results yield reconstructed images with spatial resolution approaching the theoretical limit based on detector pixel size and accounting for data interpolation.

Method for combining ultrasound vector data from multiple firings to improve image quality

An ultrasound imaging system is provided with a vector compounder and a vector splicer for respectively compounding and splicing vector data from multiple firings along a scan line to improve image quality. The compounder consists of an accumulator which sums the vector data of at least two vector data sets and then scales the summed vector data by a scaling factor. Preferably, the scaling factor equals 1/n, where n is the number of vector data sets being summed. The splicer splices compounded vector data to form a single output vector data set in accordance with a weighting function that splices vector data from a first compounded vector data set for a firing having a first range of maximum focus and vector data from a second compounded vector data set for a firing having a second range of maximum focus with a transition region therebetween. The vector data from the first and second compounded vector data sets are combined in the transition region using a piecewise linear weighting function. The piecewise linear weighting function uses a first set of weighting factors which increase linearly in magnitude from a number less than 1.0 to 1.0 and a second set of weighting factors which decrease linearly in magnitude from 1.0 to a number less than 1.0, the weighting factors of the first and second sets forming pairs of weighting factors having magnitudes the sum of which equals 1.0.