Hyperpolarized ¹³C MR angiography using trueFISP

Abstract

A13 C-enriched water-soluble compound (bis-1,1-(hydroxymethyl)-1-13 C-cyclopropane-D 8 ), with a 13 C-concentration of approximately 200 mM, was hyperpolarized to ϳ15% using dynamic nuclear polarization, and then used as a contrast medium (CM) for contrast-enhanced magnetic resonance angiography (CE-MRA). The long relaxation times (in vitro: T 1 Ϸ 82 s, T 2 Ϸ 18 s; in vivo: T 1 Ϸ 38 s, T 2 Ϸ 1.3 s) are ideal for steady-state free precession (SSFP) imaging with a true fast imaging and steady precession (trueFISP) pulse sequence. It was shown both theoretically and experimentally that the optimal flip angle was 180°. CE-MRA was performed in four anesthetized live rats after intravenous injection of 3 ml CM. The angiograms covered the thoracic/abdominal region in two of the animals, and the head-neck region in the other two. Fifteen consecutive images were acquired in each experiment, with a flip-back pulse at the end of each image acquisition. In the angiograms, the vena cava (SNR Ϸ 240), aorta, renal arteries, carotid arteries (SNR Ϸ 75), jugular veins, and several other vessels were visible. The SNR in the cardiac region was 500. Magnetization was preserved from one image acquisition to the next using the flipback technique (SNR cardiac The most widespread technique for MR angiography (MRA) today utilizes an intravenous injection of a T 1 -shortening contrast medium (CM) in combination with T 1 -weighted pulse sequences (1,2). This contrast-enhanced (CE) MRA technique has substantially shorter imaging times than time-of-flight and phase-contrast methods, and is relatively insensitive to variations in blood flow velocity. Consequently, CE-MRA has increased the clinical impact of MRA. An interesting possibility for further elevation of the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in CE-MRA would be to use a hyperpolarized (HP) CM.It has been demonstrated that certain noble gases ( 3 He and 129 Xe) can be hyperpolarized to a much higher level (Ͼ10%) than that of thermal polarization of 1 H at clinical magnetic fields (ϳ0.0005%). This high degree of polarization compensates for the low spin density of the gases in vivo, and they (mostly 3 He) have been used to image airways and lungs (3-5). HP 3 He and 129 Xe have also been proposed for use in vascular imaging. Helium has low solubility in blood, but it can be delivered to the vascular system using encapsulation techniques (6 -9). Xenon, on the other hand, is directly soluble in blood, and inhalation of the gas is one way to administer HP xenon to the human vascular system (10 -12). Xenon can also be dissolved in a biocompatible carrier (13-16), to be delivered through intravenous injection. However, even if the hyperpolarized gases could be efficiently administered to the blood, the inherently low concentration of a gas makes 3 He and 129 Xe unsuitable as a CM for CE-MRA.A high vascular concentration of a hyperpolarized CM can be obtained if 13 C, as part of a water-soluble molecule, is polarized instead of 129 Xe and 3 He. We have previously...

Renal MR angiography and perfusion in the pig using hyperpolarized water

“…The produced volume of 15 mL exceeds the previously demonstrated volumes of ~4 mL produced on the HyperSense (25), and the SPINlab and fluid path technology facilitates sterile samples for clinical applications (10). Good agreement was found between the calculated hyperpolarized water perfusion and both the reported Gd-based perfusion values in healthy porcine models (30) and with our Gd-based perfusion measurements (average of 450 mL/100 mL/min).…”

“…By rapid dissolution in a hot medium, the hyperpolarized nuclei can be brought to liquid state and injected into the patient before the polarization is lost due to longitudinal relaxation (7). Alternatively, metabolically inert 13 C-labeled molecules can be used for angiographic imaging (9)(10)(11), as demonstrated in rodent and porcine models, and for perfusion of rodent organs (12)(13)(14)(15) or of tumor models (16,17). 13 C or 15 N labelled molecules for angiography and perfusion imaging exploits the long T 1 for selected 13 C and 15 N molecules and the low signal background (18).…”

Hyperpolarized 13C MR Angiography

“…When the substance is injected in a carotid artery, only arteries branching from that specific carotid artery as well as the corresponding veins are highlighted. [21]. This means that the signal decay should be caused mainly by dilution in the vasculature and extravasation of the agent to the surrounding tissue, and to a smaller extent by relaxation processes.…”

“…The bSSFP imaging technique has been demonstrated to be a rapid, high-SNR technique for angiography and spectroscopic applications using hyperpolarized substances ( Figure 2) [21,22,24,25]. The gradient echo (GRE) technique has been used extensively for single resonance HP lung imaging [26][27][28], but less for HP-angiography using 13 C-labeled substances.…”

“…The gradient echo (GRE) technique has been used extensively for single resonance HP lung imaging [26][27][28], but less for HP-angiography using 13 C-labeled substances. A theoretical basis and in vitro measurement comparison between bSSFP and GRE for the HP angiography application was performed by Svensson et al [21], but in vivo comparisons between the combinations of the two imaging techniques (bSSFP and GRE) and the two injection techniques (i.v. and i.a.)…”