¹⁹F MRI Probes for Multimodal Imaging**

Abstract

Magnetic resonance imaging (MRI) is one of the most powerful imaging tools today, capable of displaying superior soft‐tissue contrast. This review discusses developments in the field of 19F MRI multimodal probes in combination with optical fluorescence imaging (OFI), 1H MRI, chemical exchange saturation transfer (CEST) MRI, ultrasonography (USG), X‐ray computed tomography (CT), single photon emission tomography (SPECT), positron emission tomography (PET), and photoacoustic imaging (PAI). In each case, multimodal 19F MRI probes compensate for the deficiency of individual techniques and offer improved sensitivity or accuracy of detection over unimodal counterparts. Strategies for designing 19F MRI multimodal probes are described with respect to their structure, physicochemical properties, biocompatibility, and the quality of images.

Design Principles of Responsive Relaxometric 19F Contrast Agents: Evaluation from the Point of View of Relaxation Theory and Experimental Data

“…For 19 F MRI, the most attractive contrast agents are low-molecular weight compounds whose metal ions change their oxidation state in a reducing or oxidizing environment. Consequently, these smart contrast agents can be used to track redox activity in living organisms using MRI. , For example, in the pair of Mn 2+ and Mn 3+ , the former oxidation state exerts much greater PRE effect than the latter. , As a result, the 19 F signal will change due to increased or decreased relaxation rates. In a similar way, other metal ion pairs can be utilized including Eu 2+/3+ , Mn 2+/3+ , Co 2+/3+ , Cu +/2+ , and Fe 2+/3+ .…”

“…Consequently, these smart contrast agents can be used to track redox activity in living organisms using MRI. 7 , 91 For example, in the pair of Mn 2+ and Mn 3+ , the former oxidation state exerts much greater PRE effect than the latter. 28 , 91 As a result, the 19 F signal will change due to increased or decreased relaxation rates.…”

“…An alternative way to improve the diagnostic value of MR images is the use of heteronuclear resonances such as 3 He, 13 C, 23 Na, 31 P, 129 Xe, and foremost 19 F. , The undoubted advantages of using 19 F are its 100% natural abundance and similar sensitivity to 1 H (83%) . Furthermore, it is possible to use existing clinical MR scanners for the 1 H and 19 F modalities after slight hardware modifications (i.e., tuning at 282 MHz for 19 F instead of 300 MHz for 1 H). − Because fluorine is not present in soft tissues, 19 F MRI is essentially a background-free technique since only fluorine atoms introduced with the contrast agent are visible. Typically, the 19 F MR image is superimposed with the 1 H anatomical images for precise localization of the injected fluorinated tracer. , …”

Ratiometric pH-Responsive 19F Magnetic Resonance Imaging Contrast Agents Based on Hydrazone Switches

“…MRI is a noninvasive diagnostic tool for soft tissues that uses the magnetic properties of the 1 H nucleus. It is one of the most widely used imaging procedures in medicine and offers excellent spatial resolution and unlimited penetration depth and provides knowledge that cannot be accessed by other means. , In order to improve the quality of the images, 19 F MRI has been extensively investigated as a complementary modality that allows so-called hot spot imaging. , Since 19 F atoms are not present in soft tissues, this modality allows for the accurate representation of the targeted organ without background signals; however, it requires the introduction of an appropriate contrast agent containing 19 F nuclei into the organism …”

“…10,11 In order to improve the quality of the images, 19 F MRI has been extensively investigated as a complementary modality that allows so-called hot spot imaging. 12,13 Since 19 F atoms are not present in soft tissues, this modality allows for the accurate representation of the targeted organ without background signals; however, it requires the introduction of an appropriate contrast agent containing 19 F nuclei into the organism. 14 Regarding the 19 F NMR or MRI as an aid in pH measurements, several molecular probes have been developed.…”