Cone-beam reconstruction (CBR) is growing in importance, but current computer systems are slower than desirable for clinical use. We have built a high-speed system for high-quality, 3-D imaging. We partitioned the problem into input, filtering, backprojection, postprocessing, and output components. We mapped most of the components to standard RACE++ processing nodes. The backprojection component is very compute-intensive; we mapped it to a fieldprogrammable gate array (FPGA)-based adjunct processor. We built a prototype FPGA card, optimized for flexibility, and implemented the backprojection in that FPGA. This strategy allows for redesigning the backprojection function when necessary, and keeps the other details of the CBR algorithm in easily programmable processors. We present a system that performs Feldkamp CBR of 300 projections into a 512 3 cubical image in 38.7 seconds. The system is designed to be scalable, so that Feldkamp CBR of 21.4 seconds can be performed with two adjunct processors, and Feldkamp CBR of other regions of interest or dimensions could be performed in proportionately shorter times. Further optimization and faster-processing parts will also contribute to continual speed improvements. This system is flexible and can be extended to perform other imaging functions, such as real-time planar angiography, with the same hardware.
Adjunct processors have traditionally been used for certain tasks in medical imaging systems. Often based on application-specific integrated circuits (ASICs), these processors formed X-ray image-processing pipelines or constituted the backprojectors in computed tomography (CT) systems. We examine appropriate functions to perform with adjunct processing and draw some conclusions about system design trade-offs. These trade-offs have traditionally focused on the required performance and flexibility of individual system components, with increasing emphasis on timeto-market impact. Typically, front-end processing close to the sensor has the most intensive processing requirements. However, the performance capabilities of each level are dynamic and the system architect must keep abreast of the current capabilities of all options to remain competitive. Designers are searching for the most efficient implementation of their particular system requirements. We cite algorithm characteristics that point to effective solutions by adjunct processors. We have developed a field-programmable gate array (FPGA) adjunct-processor solution for a Cone-Beam Reconstruction (CBR) algorithm that offers significant performance improvements over a general-purpose processor implementation. The same hardware could efficiently perform other image processing functions such as twodimensional (2D) convolution. The potential performance, price, operating power, and flexibility advantages of an FPGA adjunct processor over an ASIC, DSP or general-purpose processing solutions are compelling.
Digital vascular computer systems are used for radiology and fluoroscopy (RJF), angiography, and cardiac applications. In the United States alone, about 26 million procedures ofthese types are performed annually: about 8 1% R/F, I 1% cardiac, and 8% angiography'. Digital vascular systems have a very wide range ofperformance requirements, especially in terms of data rates.In addition, new features are added over time as they are shown to be clinically efficacious. Application-specific processing modes such as roadmapping, peak opacification, and bolus chasing are particular to some vascular systems23. New algorithms continue to be developed and proven, such as Cox and deJager's precise registration methods for masks and live images in digital subtraction angiography4. A computer architecture must have high scalability and reconfigurability to meet the needs ofthis modality. Ideally, the architecture could also serve as the basis for a nonvascular R/F system.
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