Analiza artefactelor în rezonanță magnetică nucleară

Modern operative techniques and local therapies such as radiofrequency (RF) ablation are effective methods to treat liver metastases or primary hepatic malignancies. Therefore, the determination of liver lesion count, and the nature of the lesion are important.

At present, the most accurate noninvasive method for the assessment of liver lesion count is magnetic resonance imaging (MRI). The magnetization transfer (MT) technique in MRI was introduced in 1989 (Wolff and Balaban, 1989). The method is based on saturating macromolecular spins with a dedicated irradiation radiofrequency (RF) -pulse, and observing the effects of the subsequent exchange processes. The signal of tissues with a high macromolecular content is reduced on MT images in comparison to the standard images. MT based tissue contrast may even more effectively be generated with the spin lock (SL) technique which probes tissue relaxation processes at very low magnetic field strengths while maintaining the high signal-to-noise ratio provided by the polarizing magnetic system In a SL experiment, a preparation or locking pulse is applied before the signal collecting conventional imaging sequence. The multiple slice SL imaging technique was introduced in 1993. Contrast agents are widely used in routine clinical MR imaging.

Extracellular gadolinium chelates such as gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) or gadolinium tetraazacyclododecanetetraacetic acid (Gd-DOTA) constitute the major group of MR contrast agents used today. Because of their unspecific nature with rapid extracellular distribution, fast imaging techniques and knowledge about the different enhancement patterns of liver lesions are essential. More recently, research has focused on the development of tissue-specific MR contrast agents with a long imaging window due to their prolonged removal from the target-tissue. In this thesis, a resistive 0. 1T magnet and superconducting MR systems operating at 1. 0T and 1. 5T were used for evaluating patients with known or suspected focal liver lesions. The ability of the multiple slice SL technique in the generation of MT-like tissue contrast, and the potential of the multiple slice SL technique in the liver metastases.

Rezonanta magnetica nucleara (RMN) este o metoda de investigare de ultima ora pe plan mondial, considerata topul imagistic in diagnosticul clinic.

A fost introdusa si in tara noastra din 1991. La ora actuala, la noi, exista unitati de RMN, doar in marile orase. Facilitatile oferite de aceasta metoda imagistica va face ca si in tara noastra numarul unitatilor RMN sa creasca. Noutatea metodei obliga la o cat mai adecvata cunoastere a bazelor ei fizice, tehnice si metodologice. Numai cunoasterea aprofundata a performantelor tehnice deosebite ale RMN poate permite o eficienta maxima atat de importanta intr-un diagnostic clinic precis. RMN este recunoscuta ca o metoda neinvaziva datorita insusi principiului tehnicii sale. Spre deosebire de metodele bazate pe ...

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