Biomedical subjects

Georg Hansson

Publications and source records attributed to Georg Hansson.

5 recordsLinked to original sources

PubMed2005

13C imaging-a new diagnostic platform.

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 nonproton 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 13C. 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 13C MRI are pointed out.

Angiography↗

PubMed2005

3He MRI-based assessment of posture-dependent regional ventilation gradients in rats.

A recently developed method for quantitative assessment of regional lung ventilation was employed for the study of posture-dependent ventilation differences in rats. The measurement employed hyperpolarized (3)He MRI to detect the build-up of the signal intensity after increasing numbers of (3)He breaths, which allowed for computation of a regional ventilation parameter. A group of six anesthetized rats was studied in both supine and prone postures. Three-dimensional maps of the ventilation parameter were obtained with high spatial resolution (voxel volume approximately 2 mm(3)). Vertical (dorsal-ventral) gradients of the ventilation index, defined as the regional ventilation normalized by the average ventilation within the whole lung, were investigated. Variations in the regional distribution of the ventilation parameter, as well as of the ventilation index, could be detected, depending on the posture of the rats. In supine posture, ventilation was elevated in the dependent parts of the lungs, with a linear gradient of the ventilation index of -0.11 +/- 0.03 cm(-1). In prone posture, the distribution of ventilation was more uniform, with a significantly (P < 0.001) smaller gradient of the ventilation index of -0.01 +/- 0.02 cm(-1). It is concluded that the (3)He MRI-based method can detect and quantify regional ventilation gradients in animals as small as the rat and that these gradients depend on prone or supine posture of the animal.

Administration, Inhalation↗

PubMed2003

Increase in signal-to-noise ratio of > 10,000 times in liquid-state NMR.

A method for obtaining strongly polarized nuclear spins in solution has been developed. The method uses low temperature, high magnetic field, and dynamic nuclear polarization (DNP) to strongly polarize nuclear spins in the solid state. The solid sample is subsequently dissolved rapidly in a suitable solvent to create a solution of molecules with hyperpolarized nuclear spins. The polarization is performed in a DNP polarizer, consisting of a super-conducting magnet (3.35 T) and a liquid-helium cooled sample space. The sample is irradiated with microwaves at approximately 94 GHz. Subsequent to polarization, the sample is dissolved by an injection system inside the DNP magnet. The dissolution process effectively preserves the nuclear polarization. The resulting hyperpolarized liquid sample can be transferred to a high-resolution NMR spectrometer, where an enhanced NMR signal can be acquired, or it may be used as an agent for in vivo imaging or spectroscopy. In this article we describe the use of the method on aqueous solutions of [13C]urea. Polarizations of 37% for 13C and 7.8% for 15N, respectively, were obtained after the dissolution. These polarizations correspond to an enhancement of 44,400 for 13C and 23,500 for 15N, respectively, compared with thermal equilibrium at 9.4 T and room temperature. The method can be used generally for signal enhancement and reduction of measurement time in liquid-state NMR and opens up for a variety of in vitro and in vivo applications of DNP-enhanced NMR.

Magnetic Resonance Spectroscopy↗

PubMed2002

Quantitative measurement of regional lung ventilation using 3He MRI.

A new strategy for a quantitative measurement of regional pulmonary ventilation using hyperpolarized helium-3 (3He) MRI has been developed. The method employs the build-up of the signal intensity after a variable number of (3)He breaths. A mathematical model of the signal dynamics is presented, from which the local ventilation, defined as the fraction of gas exchanged per breath within a given volume, is calculated. The model was used to create ventilation maps of coronal slices of guinea pig lungs. Ventilation values very close to 1 were found in the trachea and the major airways. In the lung parenchyma, regions adjacent to the hilum showed values of 0.6-0.8, whereas 0.2-0.4 was measured in peripheral regions. Monte Carlo simulations were used to investigate the accuracy of the method and its limitations. The simulations revealed that, at presently attainable signal-to-noise ratios, the ventilation parameter can be determined with a relative uncertainty of <5% over a wide range of values.

Animals↗

PubMed2002

13C-angiography.

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Animals↗