Monitoring Locally Induced Hyperthermia with Magnetic Resonance Imaging

__Abstract__ Magnetic resonance thermometry is a relatively new and unique technology for non-invasive monitoring of (local) therapeutic temperature changes that is not yet in common use. Temperature measurements using magnetic resonance heat thermometry can be performed in several ways. Four common methods are described. Spin-lattice (T1) relaxation thermometry seems robust and viable, but relatively inaccurate. Diffusion thermometry is slightly more accurate at the cost of increased scan time. Chemical shift thermometry is most accurate but inherently slow and therefore impracticable. Its derivative, phase shift thermometry seems most promising for monitoring mild temperature changes. Phase shift imaging is, however, difficult to implement due to motion artifacts and susceptibility effects. Apparently two fields for use of MR thermometry in practical therapeutic applications emerge: high temperature gradients for thermoablation that need not be quantified exactly, and low temperature gradients for heat related biological effects that must be controlled precisely

Implementation and validation of ASL perfusion measurements for population imaging

Purpose: Pseudocontinuous arterial spin labeling (pCASL) allows for noninvasive measurement of regional cerebral blood flow (CBF), which has the potential to serve as biomarker for neurodegenerative and cardiovascular diseases. This work aimed to implement and validate pCASL on the dedicated MRI system within the population-based Rotterdam Study, which was installed in 2005 and for which software and hardware configurations have remained fixed. Methods: Imaging was performed on two 1.5T MRI systems (General Electric); (I) the Rotterdam Study system, and (II) a hospital-based system with a product pCASL sequence. An in-house implementation of pCASL was created on scanner I. A flow phantom and three healthy volunteers (<27 years) were scanned on both systems for validation purposes. The data of the first 30 participants (86 ± 4 years) of the Rotterdam Study undergoing pCASL scans on scanner I only were analyzed with and without partial volume correction for gray matter. Results: The validation study showed a difference in blood flow velocity, sensitivity, and spatial coefficient of variation of the perfusion-weighted signal between the two scanners, which was accounted for during post-processing. Gray matter CBF for the Rotterdam Study participants was 52.4 ± 8.2 ml/100 g/min, uncorrected for partial volume effects of gray matter. In this elderly cohort, partial volume correction for gray matter had a variable effect on measured CBF in a range of cortical and sub-cortical regions of interest. Conclusion: Regional CBF measurements are now included to investigate novel biomarkers in the Rotterdam Study. This work highlights that when it is not feasible to purchase a novel ASL sequence, an in-house implementation is valuable

Accuracy and repeatability of QRAPMASTER and MRF-vFA

Our purpose is to evaluate bias and repeatability of the quantitative MRI sequences QRAPMASTER, based on steady-state imaging, and variable Flip Angle MRF (MRF-VFA), based on the transient response. Both techniques are assessed with a standardiz