Voxel-Based Similarity Measures for Medical Image Registration in Radiological Diagnosis and Image Guided Surgery

Registration of images is a key technique for numerous medical applications from diagnosis to image guided therapy. In the present paper we focus on gray-value based registration methods. Of special interest is the so-called similarity measure which must be optimized. It is the intention of the paper to emphasize the fact that a successful registration requires a similarity measure that is carefully chosen with respect to the underlying medical application. Two single-modality examples are presented in the paper, i.e. the diagnostic tool of digital subtraction angiography and an intervention guidance under X-ray fluoroscopic control. We discuss new similarity measures, i.e. the class of one-dimensional hi stogram based measures and the pattern intensity, designed for these applications and compare them with frequently used measures like the cross-correlation function , cross-structure function and deterministic sign change criterion. It is demonstrated that the results obtained with the new measures are superior to the results obtained with the latter mentioned ones

Towards Picogram Detection of Superparamagnetic Iron-Oxide Particles Using a Gradiometric Receive Coil

Superparamagnetic iron-oxide nanoparticles can be used in a variety of medical applications like vascular or targeted imaging. Magnetic particle imaging (MPI) is a promising tomographic imaging technique that allows visualizing the 3D nanoparticle distribution concentration in a non-invasive manner. The two main strengths of MPI are high temporal resolution and high sensitivity. While the first has been proven in the assessment of dynamic processes like cardiac imaging, it is unknown how far the detection limit of MPI can be lowered. Within this work, we will present a highly sensitive gradiometric receive-coil unit combined with a noise-matching network tailored for the measurement of mice. The setup is capable of detecting 5 ng of iron in vitro at 2.14 sec acquisition time. In terms of iron concentration we are able to detect 156 {\mu}g/L marking the lowest value that has been reported for an MPI scanner so far. In vivo MPI mouse images of a 512 ng bolus at 21.5 ms acquisition time allow for capturing the flow of an intravenously injected tracer through the heart of a mouse. Since it has been rather difficult to compare detection limits across MPI publications we propose guidelines improving the comparability of future MPI studies.Comment: 15 Pages, 7 Figures, V2: Changed the initials of Author Kannan M Krishnan, added two citations, corrected typo

Optimized Compression of MPI System Matrices Using a Symmetry-Preserving Secondary Orthogonal Transform

In this paper, we study the compression of the magnetic particle imaging system matrix for imaging setups in which field free point is moved along a Lissajous trajectory. We show that a large number of zeros in the simulated transformed system matrix is obtained when orthogonal transforms applied to the spatial domain have only symmetric and antisymmetric basis functions. For measured system matrices, this property only holds approximately, because of noise induced by the scanner hardware. The required symmetry properties are naturally fulfilled by some standard orthogonal transforms such as the type-two discrete cosine transform and the discrete Chebychev transform. However, these transforms are not yet optimal for compressing system matrices, and we propose a new method to obtain better transforms that retain the required symmetry properties

A Trajectory Study for Obtaining MPI System Matrices in a Compressed-Sensing Framework

In this paper, we study the efficiency of five different field free point trajectories in two-dimensional magnetic particle imaging for the compressed-sensing based reconstruction of partially measured system matrices. To show the suitability of the trajectories, different trajectories with identical repetition times were simulated using on the same scanner setup. We show that for all trajectories, the compressed-sensing based reconstruction approach for the system matrix is possible and promising for real-world scenarios. Also we validate the already known fact that the Lissajous trajectory is appropriate for the compressed sensing approach. However, there are still other trajectory choices which show similar and even better performance in the compressed-sensing based reconstruction

From Magnetic Nanoparticle Spectroscopy to Imaging Methodology

This first issue of the second volume of the novel International Journal on Magnetic Particle Imaging (IJMPI) mainly focuses on two topics, magnetic nanoparticle spectroscopy and magnetic imaging methodology. A high potential of improvement of magnetic particle imaging (MPI) with respect to its sensitivity is seen in the optimization of tailored nanoparticles. However, even commercial particle systems available today are not fully understood. Therefore, spectroscopic approaches to characterize the particles are in the center of interest of many research groups. The second focus of this issue is on imaging methodology. This splits up into instrumentation, where efficient coil concepts for focus-field based measurements are demonstrated, and reconstruction mathematics, where sparse sensing concepts are applied to MPI image calculation.