Peter van de Haar

Validation of 3D multimodality roadmapping in interventional neuroradiology

Three-dimensional multimodality roadmapping is entering clinical routine utilization for neuro-vascular treatment. Its purpose is to navigate intra-arterial and intra-venous endovascular devices through complex vascular anatomy by fusing pre-operative computed tomography (CT) or magnetic resonance (MR) with the live fluoroscopy image. The fused image presents the real-time position of the intra-vascular devices together with the patients 3D vascular morphology and its soft-tissue context. This paper investigates the effectiveness, accuracy, robustness and computation times of the described methods in order to assess their suitability for the intended clinical purpose: accurate interventional navigation. The mutual information-based 3D-3D registration proved to be of sub-voxel accuracy and yielded an average registration error of 0.515 mm and the live machine-based 2D-3D registration delivered an average error of less than 0.2 mm. The capture range of the image-based 3D-3D registration was investigated to characterize its robustness, and yielded an extent of 35 mm and 25° for >80% of the datasets for registration of 3D rotational angiography (3DRA) with CT, and 15 mm and 20° for >80% of the datasets for registration of 3DRA with MR data. The image-based 3D-3D registration could be computed within 8 s, while applying the machine-based 2D-3D registration only took 1.5 µs, which makes them very suitable for interventional use.

Diamond project: Video-on-demand system, and trials

The DIAMOND project (Domestic IBC Applications for Multimedia on Demand; IBC = Integrated Broadband Communications), sponsored by the EC (RACE R2105), had the objective of exploring and demonstrating the technical feasibility of providing Video On Demand (VOD) to the home, with an acceptable quality of service at an acceptable cost level. Within Philips, a Video Server (VS) and Set Top Box (STB) were developed, while Octacon developed a Service Gateway (SGW). The system was tested on both a public switched network using ADSL (Helsinki, Finland) and on a CATV network (Sligo, Ireland); both trials were of a small scale and free of charge. The purpose of this paper is to present an overview of the overall system as developed for the DIAMOND trials, together with user evaluation results from the Helsinki trial.

FBP and BPF reconstruction methods for circular X-ray tomography with off-center detector

PURPOSE Circular scanning with an off-center planar detector is an acquisition scheme that allows to save detector area while keeping a large field of view (FOV). Several filtered back-projection (FBP) algorithms have been proposed earlier. The purpose of this work is to present two newly developed back-projection filtration (BPF) variants and evaluate the image quality of these methods compared to the existing state-of-the-art FBP methods. METHODS The first new BPF algorithm applies redundancy weighting of overlapping opposite projections before differentiation in a single projection. The second one uses the Katsevich-type differentiation involving two neighboring projections followed by redundancy weighting and back-projection. An averaging scheme is presented to mitigate streak artifacts inherent to circular BPF algorithms along the Hilbert filter lines in the off-center transaxial slices of the reconstructions. The image quality is assessed visually on reconstructed slices of simulated and clinical data. Quantitative evaluation studies are performed with the Forbild head phantom by calculating root-mean-squared-deviations (RMSDs) to the voxelized phantom for different detector overlap settings and by investigating the noise resolution trade-off with a wire phantom in the full detector and off-center scenario. RESULTS The noise-resolution behavior of all off-center reconstruction methods corresponds to their full detector performance with the best resolution for the FDK based methods with the given imaging geometry. With respect to RMSD and visual inspection, the proposed BPF with Katsevich-type differentiation outperforms all other methods for the smallest chosen detector overlap of about 15 mm. The best FBP method is the algorithm that is also based on the Katsevich-type differentiation and subsequent redundancy weighting. For wider overlap of about 40-50 mm, these two algorithms produce similar results outperforming the other three methods. The clinical case with a detector overlap of about 17 mm confirms these results. CONCLUSIONS The BPF-type reconstructions with Katsevich differentiation are widely independent of the size of the detector overlap and give the best results with respect to RMSD and visual inspection for minimal detector overlap. The increased homogeneity will improve correct assessment of lesions in the entire field of view.

Lag correction for flat-panel cone-beam CT in SPECT/CT

MR spectroscopy (MRS) is an analytic technique widely used in chemistry for analyzing the structure of compounds and the composition of mixtures of compounds. Compounds are identified by their unique spectra, based on chemical shifts and coupling constants. MRS allows the noninvasive measurement of selected biologic compounds in vivo. Major technical advances have occurred in MRS over the last several decades, including superconducting magnets and Fourier transform for signal processing. Feasibility was first demonstrated in humans in the mid1980s, and much experience with MRS has accumulated in both research and clinical applications. Nearly all MRI scanners have the capability of performing MRS, and MRS techniques continue to improve even after 2 decades of development. Despite this considerable research effort and the unique biochemical information provided, only limited integration of MRS into clinical practice has occurred, for multiple reasons including nonstandardization of acquisition and analysis protocols, limited vendor support, difficult interpretation, limited perceived added value above conventional MRI, and lack of reimbursement. However, in vivo MRS is increasingly being used in clinical practice, particularly for neurologic disorders. Proton spectroscopy of the human brain is most widely used, but other organ systems such as breast and prostate, and other nuclei including 31P and 13C, have been studied. In the brain, compounds of key importance measured by MRS include N-acetyl aspartate (located predominantly in neurons), choline, myoinositol (located primarily in glial cells), creatine, lactate, glutamate, and glutamine. This book was written by leading MRS experts, and it is an invaluable guide for anyone interested in in vivo MRS, including radiologists, nuclear physicians, neurologists, neurosurgeons, oncologists, and medical researchers. It gives the reader a solid basis for understanding both the techniques and the applications of clinical MRS. The book is organized into 14 chapters. Chapter 1 introduces in vivo MRS, and chapter 2 discusses pulse sequences and protocol design. Chapter 3 addresses spectral analysis methods, quantitation, and common artifacts, and chapter 4 handles normal regional variations, particularly brain development and aging. The rest of the chapters discuss MRS findings in brain tumors; in stroke and hypoxic–ischemic encephalopathy; in infectious, inflammatory and demyelinating lesions; in epilepsy; in neurodegenerative diseases; in traumatic brain injury; in cerebral metabolic disorders; in prostate cancer; in breast cancer; and in musculoskeletal diseases. Each chapter begins with key points and ends with recommendations and a conclusion. References are updated and useful. The aim of this book is to serve as a practical reference work that covers all aspects of in vivo human spectroscopy for clinical purposes. The book explains physical principles and provides a comprehensive and perceptive review of clinical applications. Also discussed are the limitations of MRS, such as its low spatial resolution when compared with MRI, common artifacts, and diagnostic pitfalls. More widespread adoption of MRS into the clinic will lead to better diagnoses and improved outcomes for individual patients. There are 140 figures, which are clear and have detailed legends, and 7 tables that are helpful for readers. The index is convenient and useful. I highly recommend this book to trainees and practitioners in medical physics, radiology, nuclear medicine, oncology, neurology, and cardiology.