Multiobjective Optimization for Reconfigurable Implementation of Medical Image Registration

In real-time signal processing, a single application often has multiple computationally intensive kernels that can benefit from acceleration using custom or reconfigurable hardware platforms, such as field-programmable gate arrays (FPGAs). For adaptive utilization of resources at run time, FPGAs with capabilities for dynamic reconfiguration are emerging. In this context, it is useful for designers to derive sets of efficient configurations that trade off application performance with fabric resources. Such sets can be maintained at run time so that the best available design tradeoff is used. Finding a single, optimized configuration is difficult, and generating a family of optimized configurations suitable for different run-time scenarios is even more challenging. We present a novel multiobjective wordlength optimization strategy developed through FPGA-based implementation of a representative computationally intensive image processing application: medical image registration. Tradeoffs between FPGA resources and implementation accuracy are explored, and Pareto-optimized wordlength configurations are systematically identified. We also compare search methods for finding Pareto-optimized design configurations and demonstrate the applicability of search based on evolutionary techniques for identifying superior multiobjective tradeoff curves. We demonstrate feasibility of this approach in the context of FPGA-based medical image registration; however, it may be adapted to a wide range of signal processing applications

HIGH-PERFORMANCE 3D IMAGE PROCESSING ARCHITECTURES FOR IMAGE-GUIDED INTERVENTIONS

Minimally invasive image-guided interventions (IGIs) are time and cost efficient, minimize unintended damage to healthy tissues, and lead to faster patient recovery. Advanced three-dimensional (3D) image processing is a critical need for navigation during IGIs. However, achieving on-demand performance, as required by IGIs, for these image processing operations using software-only implementations is challenging because of the sheer size of the 3D images, and memory and compute intensive nature of the operations. This dissertation, therefore, is geared toward developing high-performance 3D image processing architectures, which will enable improved intraprocedural visualization and navigation capabilities during IGIs. In this dissertation we present an architecture for real-time implementation of 3D filtering operations that are commonly employed for preprocessing of medical images. This architecture is approximately two orders of magnitude faster thancorresponding software implementations and is capable of processing 3D medical images at their acquisition speeds. Combining complementary information through registration between pre- and intraprocedural images is a fundamental need in the IGI workflow. Intensity-base

Image registration accuracy with low-dose CT: How low can we go

ABSTRACT Image-guided interventions are known to lead to improved outcomes and significantly faster patient recovery as compared with conventional open, invasive procedures. Common intraoperative imaging techniques such as endoscopy and fluoroscopy are two-dimensional (2D), and provide a 2D representation of the 3D anatomy. Use of recently emerged multislice computed tomography (CT) can facilitate 3D visualization of anatomy during an intervention. The speed and dimensionality of these CT scanners make their use in image-guided interventions technically feasible. For clinical acceptance, however, the net radiation dose to the patient and the interventionist must be minimized. This article suggests a strategy to reduce radiation dose and describes an evaluation scheme to identify the optimal dose which does not sacrifice the specificity of the image-guided procedure. Our work indicates at least a tenfold reduction in radiation dose

Multiobjective Optimization of FPGA-Based Medical Image Registration

With a multitude of technological innovations, one emerging trend in image processing, and medical image processing, in particular, is custom hardware implementation of computationally intensive algorithms in the quest to achieve real-time performance. For reasons of area-efficiency and performance, these implementations often employ limited-precision datapaths. Identifying effective wordlengths for these datapaths while accounting for tradeoffs between design complexity and accuracy is a critical and time consuming aspect of this design process. Having access to optimized tradeoff curves can equip designers to adapt their designs to different performance requirements and target specific devices while reducing design time. This paper presents a multiobjective optimization strategy developed in the context of fieldprogrammable gate array–based implementation of medical image registration. Within this framework, we compare several search methods and demonstrate the applicability of an evolutionary algorithm–based search for efficiently identifying superior multiobjective tradeoff curves. This strategy can easily be adapted to a wide range of signal processing applications, including areas of image and video processing beyond the medical domain

Incorporation of Preprocedural PET into CT-Guided Radiofrequency Ablation of Hepatic Metastases: a Nonrigid Image Registration Validation Study

This study evaluates the accuracy of augmenting initial intraprocedural computed tomography (CT) during radiofrequency ablation (RFA) of hepatic metastases with preprocedural positron emission tomography (PET) through a hardware-accelerated implementation of an automatic nonrigid PET–CT registration algorithm. The feasibility of augmenting intraprocedural CT with preprocedural PET to improve localization of CT-invisible but PET-positive tumors with images from actual RFA was explored. Preprocedural PET and intraprocedural CT images from 18 cases of hepatic RFA were included. All PET images in the study originated from a hybrid PET/CT scanner, and PET–CT registration was performed in two ways: (1) direct registration of preprocedural PET with intraprocedural CT and (2) indirect registration of preprocedural CT (i.e., the CT of hybrid PET/CT scan) with intraprocedural CT. A hardware-accelerated registration took approximately 2 min. Calculated registration errors were 7.0 and 8.4 mm for the direct and indirect methods, respectively. Overall, the direct registration was found to be statistically not distinct from that performed by a group of clinical experts. The accuracy, execution speed, and compactness of our implementation of nonrigid image registration suggest that existing PET can be overlaid on intraprocedural CT, promising a novel, technically feasible, and clinically viable approach for PET augmentation of CT guidance of RFA