Probe-Specific Procedure to Estimate Sensitivity and Detection Limits for 19F Magnetic Resonance Imaging

Abstract

Due to low fluorine background signal in vivo, 19F is a good marker to study the fate of exogenous molecules by magnetic resonance imaging (MRI) using equilibrium nuclear spin polarization schemes. Since 19F MRI applications require high sensitivity, it can be important to assess experimental feasibility during the design stage already by estimating the minimum detectable fluorine concentration. Here we propose a simple method for the calibration of MRI hardware, providing sensitivity estimates for a given scanner and coil configuration. An experimental “calibration factor” to account for variations in coil configuration and hardware set-up is specified. Once it has been determined in a calibration experiment, the sensitivity of an experiment or, alternatively, the minimum number of required spins or the minimum marker concentration can be estimated without the need for a pilot experiment. The definition of this calibration factor is derived based on standard equations for the sensitivity in magnetic resonance, yet the method is not restricted by the limited validity of these equations, since additional instrument-dependent factors are implicitly included during calibration. The method is demonstrated using MR spectroscopy and imaging experiments with different 19F samples, both paramagnetically and susceptibility broadened, to approximate a range of realistic environments.

Enhanced Performance of Polymeric 19F MRI Contrast Agents through Incorporation of Highly Water-Soluble Monomer MSEA

“…The linear relationship between NMR/MRI intensity and the concentration of the fluorinated polymers is important for use of these molecules in quantitative 19 F MRI studies. In addition, if we propose a minimum detectable SNR as 3.5 as suggested in previous studies, , the detection limit for this PMSEA–PTFEA polymer is determined as ∼5 mg/mL by linear extrapolation of the relationship between SNR and polymer concentration. This is much lower than the detection limit (8.5 mg/mL) for the PPEGA–PTFEA polymer.…”

Enhanced Fluorine-19 MRI Sensitivity using a Cryogenic Radiofrequency Probe: Technical Developments and Ex Vivo Demonstration in a Mouse Model of Neuroinflammation

“…Here, pulse power was adjusted in order to avoid substantial signal loss at the dorsal part of the brain, which is observed when using a RARE sequence with excessive RF power. Predicting the sensitivity and detection limits of 19 F measurements for specific hardware setups 51 will help facilitate further 19 F - CRP studies with other fluorinated compounds.…”

Accelerated 19F·MRI Detection of Matrix Metalloproteinase-2/-9 through Responsive Deactivation of Paramagnetic Relaxation Enhancement

“…(2) A relatively high concentration of the probe molecule was required in order to perform the MR imaging experiment in the current and previous studies. The 19 F signal intensity [ 29 ] requires further improvement to be viable for in vivo applications. Generally, various successful efforts have been made to improve the signal intensity by increasing the 19 F spins per molecule unit [ 38 , 39 ], and these approaches need to be explored to make responsive PRE deactivation more biocompatible by reducing the required concentration of biosensor molecules.…”

“…Although significant progress has been made with nonspecific 19 F·MRI tracers for cell labelling, including clinical applications [ 27 , 28 ], the use of specifically targeted 19 F·MRI probes for molecular imaging, in particular for in vivo studies, is frustrated by inadequate 19 F·MRI signal intensity [ 29 ]. The MMP biosensor concept described above utilizes reduced transverse ( T 2 or T 2 ∗ ) relaxation; however, the longitudinal relaxation is also reduced, and long T 1 times diminish the amount of signal averaging that is feasible within the time span of typical in vivo MRI experiments.…”