Pyruvate is included in the energy production of the heart muscle and is metabolized into lactate, alanine, and CO 2 in equilibrium with HCO 3 ؊ . The aim of this study was to evaluate the feasibility of using 13 C hyperpolarization enhanced MRI to monitor pyruvate metabolism in the heart during an ischemic episode. The left circumflex artery of pigs (4 months, male, 29 -34 kg) was occluded for 15 or 45 min followed by 2 hr of reperfusion. Pigs were examined by 13 C chemical shift imaging following intravenous injection of 1-13 C pyruvate. 13 C chemical shift MR imaging was used in order to visualize the local concentrations of the metabolites. After a 15-min occlusion (no infarct) the bicarbonate signal level in the affected area was reduced (25-44%) compared with the normal myocardium. Alanine signal level was normal. After a 45-min occlusion (infarction) the bicarbonate signal was almost absent (0.2-11%) and the alanine signal was reduced (27-51%). Due to image-folding artifacts the data obtained for lactate were inconclusive. These studies demonstrate that cardiac metabolic imaging with hyperpolarized 1-13 C-pyruvate is feasible. The changes in concentrations of the metabolites within a minute after injection can be detected and metabolic maps constructed. Magn Reson Med 59:1005-1013, 2008.

The evolution of magnetic resonance imaging (MRI) has been astounding since the early 1980s, and a broad range of applications has emerged. To date, clinical imaging of nuclei other than protons has been precluded for reasons of sensitivity. However, with the recent development of hyperpolarization techniques, the signal from a given number of nuclei can be increased as much as 100 000 times, sufficient to enable imaging of non-proton nuclei.Technically, imaging of hyperpolarized nuclei offers several unique properties, such as complete lack of background signal and possibility for local and permanent destruction of the signal by means of radio frequency (RF) pulses. These properties allow for improved as well as new techniques within several application areas. Diagnostically, the injected compounds can visualize information about flow, perfusion, excretory function, and metabolic status. In this review article, we explain the concept of hyperpolarization and the techniques to hyperpolarize 13 C. An overview of results obtained within angiography, perfusion, and catheter tracking is given, together with a discussion of the particular advantages and limitations. Finally, possible future directions of hyperpolarized 13 C MRI are pointed out.

A new diagnostic application of a water-soluble contrast medium (CM) based on the hyperpolarization of a 13 C substance is introduced. The degree of polarization achieved is >30%, which is about a factor of 10 5 higher than the thermal equilibrium polarization level at 1.5 T. Imaging of hyperpolarized (HP) CM during a cardiac interventional MRI procedure was studied. Catheters were positioned in the left and right coronary arteries of pigs. A coil tuned to 13 C was used for nonproton imaging. The HP-13 C CM (ϳ5 ml, 0.5 M, ϳ30% polarization) was injected during projection imaging using a fully balanced steady-state free precession (SSFP) pulse sequence with and without cardiac gating. The contrast agent-filled catheter was clearly visible during the procedure. The coronary arteries were well depicted and the signal-to-noise ratios (SNRs) were in the range of 10 -40. The use of HP- Magnetic resonance imaging (MRI)-guided vascular interventional procedures have several potential advantages compared to X-ray guided procedures (1-5). The patient and the interventionalist are not exposed to ionizing radiation, and the patient can avoid adverse reactions due to an iodinated contrast medium (CM) and its potential nephrotoxic effects.Coronary angiography is one of many interventional procedures that potentially could benefit from the advantages offered by MRI. In proton-based real-time MRI, coronary angiography with intraarterial injections of a conventional gadolinium-type CM is problematic. The Gdbased CM used can to be diluted to obtain optimal relaxation times to enhance signal from the blood in the vessels, but the CM will rapidly redistribute and accumulate in the surrounding tissue during the procedure and thus gradually decrease the contrast effect. A 2D projection technique is efficient for quickly localizing the coronaries without prior knowledge of their exact positions. However, in proton imaging, large signal from background tissue is present in the 2D projection, and the coronary arteries will only be a small fraction of the tissue. Saturation techniques and imaging based on inversion nulling of tissue have been suggested (2,3,5), but these methods reduce the possibility of imaging in real time. Another complicating factor is that the CM loads in the tissue as a function of time after the injection. Consequently, the optimum inversion time for nulling the tissue will change during the procedure.One way to improve the contrast-to-noise ratio (CNR) in projection imaging is to inject a CM that can be imaged at a resonance frequency other than that of protons. Before any contrast is injected, the signal from all tissue is virtually zero on the 13 C resonance frequency. Recently, MRI using hyperpolarized(HP) 13 C was introduced for MR angiography (MRA) in rats (6,7). In these studies it was calculated that the obtainable signal-to-noise ratio (SNR) in the injection solution could be higher by a factor of Ͼ100 than that obtained in a standard 3T proton image. If such high signals can be obtained from the CM solut...

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