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High Precision Medical Imaging

Structural and Functional neuro MRI (Natalia Petridou)

Functional MRI at ultra-high resolution is a unique avenue to non-invasively measure brain function at the spatial scale at which the brain is organized. 7 tesla MRI offers the option to achieve this dimension because of the high signal- and contrast-to-noise. This advantage is capitalized with the development of imaging techniques to allow ultra-high resolution functional imaging within clinically feasible scan times, and ultra-high resolution structural imaging with endogenous enhancement of tissue features that mark the cortical micro-architecture. These imaging techniques involve MR signal reception/transmission technology for accelerated ultra-high resolution (f)MRI (Italiaander (MR Coils), Voogt, Goselink, Arteaga de Castro), and data acquisition and analysis methods for BOLD-based functional (Hendriks, Gaglianese), T2*/T1 based structural (Visser (Philips), Zwanenburg), and neuro-metabolic spectroscopic (Arteaga de Castro) data. The information obtained is used to develop neuro-hemodynamic models that account for the cortical micro-architecture, in order to map fMRI signals to specific groups of neurons (Gaglianese, Siero (thesis 2013)). It is also used to map the functional-and-structural organization within brain regions (for example within visual cortex) (Dumoulin, Fracasso, Gaglianese, Batson, Harvey) and across brain networks (Caballero (BCBL Spain), Raemaekers, Mandl) in volunteers and patients. 

  

MRI – Advanced MRI Technology – Cerebro Vascular Disease (Jaco Zwanenburg)

In the field of cerebrovascular diseases, the increased resolutions of conventional MRI techniques at 7T allow to study: microinfarcts and microbleeds in vivo (Suzanne van Veluw, Brain), small anatomical structures like enlarged perivascular spaces in the white matter (Willem Bouvy), the walls of the carotid arteries (Wouter Koning), and even intracranial vessel walls (Jeroen Siero, Anja van der Kolk, Anita Harteveld). A less conventional technique, called T1rho mapping, is a quantitative technique based on endogenous contrast. Without the use of contrast agents, it allows to assess the amount of collagen in the myocardium of patients with various forms of cardiac fibrosis. T1rho mapping is currently being validated in patients, in comparison to state of the art contrast enhanced techniques (Joep van Oorschot). To better understand the role of cerebral small vessel disease in elderly patients with neurodegenerative diseases, new techniques are being developed to study cardiac related pulsations in the microcirculation (perfusion) of the brain (Lennart Geurts), to assess blood-brain-barrier dysfunction by quantitative T1- and T2-mapping of cerebrospinal fluid (Jolanda Spijkerman), to quantify the amount and composition of perivascular fluid (Martijn Froeling, Spijkerman) and to measure the brain tissue volume pulsation during the cardiac cycle, which is driving the transport of perivascular fluids through the brain (Ayodeji Adams).

MRI – Advanced MRI Technology – Metabolism (Dennis Klomp)

MRI is unique in its capability to measure, in a non-destructive and non-invasive manner, both morphology, function and metabolism.  Having access to ultra-high field strengths provides more spatial resolution in morphological images and higher sensitivity and specificity in metabolic images. This can be applied in brain, as well as in other organs. This research line requires the design and implementation of new pulses and pulse sequences (Wijnen, Kemp, vd Velde, Luttje, Kalleveen), radiofrequency (Italiaander) and gradient coils, as well as interactive methods to stabilize the magnetic field in real time (Boer).

Quantitative and advanced MR techniques (PI: Hans Hoogduin)

 

An important feature of medical imaging is the development and introduction of more quantitative imaging biomarkers.  Both magnetic resonance imaging and spectroscopy offer the option to derive new, quantitative functional and metabolic information based of the intrinsic physico-chemical properties of tissue, e.g. totally non-disruptive, non-contrast enhanced. Examples of these techniques are qT1 mapping (Daniel Polders (thesis 2012)), CEST, pH mapping(Vitaliy Khlebnikov), CVR mapping (Alex Bhogal), DTI/DWI (Daniel Polders, AIO Schakel), R2* mapping (Alexander Raaijmakers). Making use of increased signal to noise and contrast that ultra-high field MRI offers new technology solutions that are being developed to optimize the extraction of these new biomarkers in volunteers and patients. These technologies focus on spatially selective excitation (Alessandro Sbrizzi, Ronald Mooiweer),  transmit homogenization (Alessandro Sbrizzi), Real time SAR evaluation Giel (Mens (Philips), Mat Restivo) and the development of a parallel transmit system (Giel Mens (Philips), Alexander Raaijmakers).

Advanced MRI Technology – Electro Magnetics  (PI: Nico van den Berg)

As the RF operating frequency of MRI increases with field strength, ultra high field MRI breaches a fundamental electromagnetic barrier. The RF wavelength in tissue becomes shorter than anatomical dimensions resulting in interference problems and increased levels of RF tissue heating.  To overcome these challenges new phased antenna arrays are developed for 7T body (Raaijmakers) and 7T H&N imaging (Bluemink). These arrays can address in combination with intelligent RF pulse design (Sbrizzi) disturbing destructive RF magnetic interferences. In parallel, new tools to manage and monitor RF tissue heating for individual patient cases are developed (Restivo, Sbrizzi, Raaijmakers). An important aspect is understanding of thermo-regulatory response of the human body on intense RF exposure (Simonis).

Although MRI is primarily a magnetic imaging modality, electric tissue properties are also encrypted into the MR signal. Recent electromagnetic insights have lead to development of reconstruction techniques (e.g MR Electrical Property Tomography) that can image electric properties of tissue based on MRI. This has created a new category of electrical endogenous biomarkers that, depending on the operation frequency,  probe different electrical tissue properties finding aplications in oncology (Van Lier)  or neuroscience (Mandija).

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