Development of novel quantitative medical imaging techniques for MPI and MRI (2016)

Tomographic imaging has become indispensable in the clinical routine. In a tomographic scan, images of the inner human body are produced without the need of dissecting the human skin. The common types of medical images are two-dimensional slices and entire three-dimensional volumes. To image dynamic processes such as organ function or perfusion, time series are produced at multiple spatial locations. To date, the most common medical imaging modalities are X-ray imaging, Computed Tomography (CT), Magnetic Resonance Imaging (MRI) or tracer-based imaging such as Positron-Emission Tomography (PET) or Single-Photon Emission Tomography (SPECT). Next to the common modalities, a novel medical imaging modality called Magnetic Particle Imaging (MPI) has been introduced, and its position between the established modalities still needs to be defined. \nIn general, cardiovascular applications impose specific challenges on medical imaging. Imaging speed is required to compensate for respiratory and cardiac motions, and to capture rapid uptake rates of contrast agents in the heart tissue. At the same time, high spatial resolution is demanded to accurately assess cardiac anatomy. In this work, we focus on two main cardiovascular applications: cardiac perfusion imaging and cardiac function imaging. \nEach imaging modality stands out with particular advantages and drawbacks for cardiovascular imaging. Magnetic Resonance Imaging (MRI), for example, has its main advantage in the use of non-ionizing radiation and its superb soft-tissue contrast and is hence suitable for cardiac function assessment. However, due to non-linearity of the MR signal with the contrast concentration, an application such as cardiac perfusion imaging is challenging and requires complex mathematical and practical treatment to measure the arterial input function. A more adequate tool for application on perfusion imaging would be Magnetic Particle Imaging (MPI) since its signal is linear with the contrast concentration over a wide range of concentration. Yet, a drawback of MPI is that no anatomic information is inside the MPI images since it is a purely tracer-based imaging method such as PET or SPECT. Therefore, image registration is required to fuse anatomic reference scans with MRI or CT with obtained MPI images in order to locate cardiac tissues. \nMagnetic Particle Imaging (MPI) renders for the application on cardiac perfusion imaging, due to its high spatial and temporal resolution and the linearity of the signal with the contrast concentration. Nevertheless, spatial coverage of MPI is currently limited to small volumes, thus there is a need for extended spatial coverage to assess human tissue structures maintaining high temporal resolution. In this work, methods are explored to extend spatial coverage with the aim to improve image registration of MPI images with anatomic reference scans from MRI or CT. \nMagnetic Resonance Imaging (MRI) is a suitable tool for cardiac function assessment. Cardiac cine imaging is the standard method to acquire heart motion during the entire cardiac cycle. Though, practical challenges still remain in the clinical application of cardiac cine MRI. The common way to obtain cine images is a stack of slices in short axis and long axis orientation, each acquired during 10-12 separate breath-holds. This is a time-consuming task and can be a tedious procedure especially for elder or illed patients in a clinical scenario. Additionally, due to possible patient movements between the breath-holds, slices at different locations can be miss-aligned leading to decreased accuracy in the assessment of cardiac function. \nWe introduce and implement in this work a novel method for cardiac cine MRI called VF 3D-BRISA (“Very Fast 3D Breath-hold ISotropic Imaging using Spatio-temporal Acceleration”) allowing high image acceleration rates of over 30 and implement it on a real 3T MRI system. The high image acceleration is appreciated to perform non-angulated isotropic 3D cine imaging in a single breath-hold, overcoming the challenges of multi-slice 2D cine imaging. \nFor the objective of this thesis, 2D and 3D experiments are conducted to assess optimal imaging parameters for VF 3D-BRISA. Furthermore, we conduct an in-vivo validation study of VF 3D-BRISA to demonstrate that cardiac function can be assessed with the same accuracy as with a reference method of 2D multi-slice cine imaging.