Magnetic resonance imaging-controlled laser-induced interstitial thermotherapy.

RATIONALE AND OBJECTIVES: Laser-induced interstitial thermotherapy (LITT) may become an attractive modality for minimally invasive tumor therapy. Magnetic resonance imaging (MRI) could be used to assist this procedure. METHODS: A T1-weighted turbo fast low-angle shot (FLASH) sequence for on-line monitoring of the laser-influenced region (liver, muscle) was investigated. Sequence parameters were optimized for maximal image contrast. Magnetic resonance imaging-controlled LITT was performed in vitro, in vivo (rabbits), and in 8 human investigations (6 patients). Special laser applicators were used to establish a uniform laser light distribution. RESULTS: With the MRI sequence used, the LITT region is visualized as a bright area outlined by a dark border. This dark border corresponds to an isotherm of 45 +/- 2 degrees C depending on the sequence parameters used. CONCLUSION: With the T1-weighted turbo-FLASH sequence, MRI can be used for on-line monitoring of interstitial laser-induced thermotherapy in moving organs.

Detection and localization of perfluorodecalin in the human eye by fluorine 19 magnetic resonance.

Perfluorocarbons are applied as heavy liquids during vitreoretinal surgery. They are removed again intraoperatively because of possible harmful long-term effects. Following vitreoretinal surgery, residual perfluorodecalin (PFD) was detected in four eyes and localized in two others by fluorine 19 magnetic resonance (19F-MR). In vitro analysis of 19F-MR spectra shows that chemical shift artifacts can be avoided much better with PFD than with perfluorotributylamine and perfluoroctane. Therefore, PFD localization by 19F-MR imaging is superior to that of perfluorotributylamine and perfluoroctane. This examination can be performed on currently employed magnetic resonance imaging systems equipped with a fluorine channel. In the event of significant inadvertent residual quantities of PFD and obscured media, 19F-MR may specifically detect and localize PFD.

Human eye: visualization of perfluorodecalin with F-19 MR imaging.

Perfluorodecalin (PFD) was demonstrated in a human eye with fluorine-19 magnetic resonance (MR) imaging by employing a standard two-dimensional fast low-angle shot (FLASH) sequence. The presence and intraocular distribution of PFD were revealed despite the posterior eye segment being obscured by a narrow pupil, multiple small intraocular gas bubbles, and an intraocular hemorrhage. This examination can be performed with standard sequences on MR imaging systems equipped with a fluorine channel.

Electron microscopic and 31-P NMR studies of ischemic injured rat livers during preservation and reflow.

Ischemic injury induced during preservation and reperfusion contributes to post-operative failure in liver transplantation. Hepatic injury and recovery from preservation was studied in an isolated rat liver model reperfused with oxygenated erythrocytes. In order to correlate morphological and functional findings, 31-P nuclear magnetic resonance spectroscopy and electron microscopy were used to investigate metabolic and ultrastructural changes during 6 hours of reperfusion. Following cold preservation, EM's showed a primary sinusoidal cell injury, whereas the hepatocytes were well maintained. During reperfusion, hepatocytes displayed further damage. The simultaneous presence of vacuolarly degenerated mitochondria and mitochondria of increased activity was noted. 31-P NMP spectra demonstrated initially a partial ATP-recovery. The maximum level of 60% of the control ATP-value could not be further increased. EM and 31-P NMR indicate that the progressive injury to the liver is due to microcirculatory malfunction induced by an endothelial cell damage, followed by injured hepatocytes themselves, and the consequent intracellular energy crisis that is produced.

Liver tumors: follow-up with P-31 MR spectroscopy after local chemotherapy and chemoembolization.

The authors examined and quantified the changes observed in the phosphorus-31 magnetic resonance (MR) spectra of liver tumors after chemotherapy and chemoembolization to investigate the suitability of P-31 MR spectroscopy for follow-up. A 1.5-T unit was used before and at specific times during therapy to obtain spectra of liver tumors in 10 patients with liver metastases from colorectal carcinoma and two patients with hepatocellular carcinoma. A marked increase in inorganic phosphate and a decrease in the alpha- and beta-nucleotide phosphate portions of the spectra were observed during the first few hours after local chemotherapy or chemoembolization. Later, the phosphomonoester signals increased markedly and the phosphodiester signals decreased slightly. The effects of successful chemoembolization or local chemotherapy become apparent in the P-31 MR spectrum during the first few hours after the start of therapy. The results demonstrate that P-31 MR spectroscopy is a suitable method for follow-up. However, long-term studies are needed to determine whether it also yields prognostic information.

Effect of pentoxiphylline on the recovery of the preserved rat liver: 31P NMR and ultrastructural studies.

Hepatic failure often occurs following transplantation. This is primarily due to cold ischemia during preservation, warm ischemia during implantation, and finally reperfusion damage after transplantation and reflow. The possibility that this ischemia and reperfusion-induced damage can be reduced by preischemic application of a xanthine derivative (pentoxiphylline) was examined using 31P NMR spectroscopy and electron microscopy (EM) studies of bioenergetic and ultrastructural changes in oxygenated erythrocyte-perfused rat livers. EM illustrated that the hepatocytes and the mitochondria appeared to be relatively unaffected by cold preservation of the liver, whereas the endothelial cells lining the sinusoids became disrupted. After reperfusion, NMR spectroscopy showed a partial recovery of ATP levels, and EM indicated progressive mitochondrial injury. This progressive injury to the liver was probably due to endothelial cell damage which resulted in microcirculatory malfunction and free radical formation during reperfusion. Pentoxiphylline pretreated livers showed better preservation of the cell morphology and exhibited better ATP recovery than untreated livers. Pentoxiphylline is known to prevent the loss of precursors of ATP resynthesis by inhibiting AMP dephosphorylation during ischemia and improves the microcirculation via vasodilatory properties following ischemia. Thus, it is concluded that pentoxiphylline may ameliorate ischemia-induced cell damage during transplantation.

31P nuclear magnetic resonance spectroscopy, histology and cytokinetics of a xenografted hypopharynx carcinoma following treatment with cisplatin: comparison in three sublines with increasing resistance.

The changes in the phosphorus metabolism of a xenografted hypopharynx carcinoma (Hyp 1), sensitive to cisplatin (CDDP), were compared to those occurring in two sublines of the tumour, characterised by moderate or high resistance to CDDP (Hyp 1/H and Hyp 1/R) following, i.p. administration of 4, 8 or 12 mg CDDP/kg-1. The investigations were performed by in vivo 31P nuclear magnetic resonance (NMR) spectroscopy. Parallel to the NMR experiments, the cytokinetic and histological alterations in the tumours were studied under the same experimental conditions. No mentionable differences in the levels of the main phosphorus-containing metabolites could be detected between the three tumour lines before treatment. Following application of CDDP, the alterations in the NMR spectra were clearly related to the degree of tumour response. The most sensitive and earliest marker of tumour regression was a decrease in the phosphomonoester/phosphodiester ratio, parallelled by a gradual increase in the phosphocreatine/inorganic phosphorus quotient. In the resistant tumour lines Hyp 1/H and Hyp 1/R non-responding tumours showed alterations in the 31P NMR spectrum which were similar to those observed during uninfluenced tumour growth. Marked changes in the 31P NMR spectrum were always associated with severe cytotoxic lesions following therapy. The results suggest that the changes detected by 31P NMR spectroscopy following chemotherapy with CDDP are response-specific.

[The effect of nutritional status on the 31P MR spectrum of the normal liver]. / Einfluss der Ernährungslage auf das 31P-MR-Spektrum der gesunden Leber.

Previous investigations in animal and human liver spectroscopy revealed a strong effect of metabolic activity on the 31P-spectra of the liver. This study examined the influence of a standardised meal on the liver spectra of healthy volunteers. The measurements were performed at 1.5 T (Magnetom, Siemens). The results show that the metabolic condition has a strong effect on the 31P MR liver spectra. The changes are of the same order of magnitude as those described in spectra of focal or diffuse liver diseases. This indicates that identical metabolic conditions are necessary for measuring liver spectra of volunteers and patients, especially in follow-ups.

[Magnet resonance spectroscopy of tumor-bearing rat livers: magnetite particles as an aid in volume selection]. / Magnetresonanzspektroskopie der tumortragenden Rattenleber: Magnetitpartikel als Hilfe bei der Volumenselektion.

Magnetite, an RES-specific contrast medium, has been used in animal experiments and in a few patients for MRI of the liver. We examined the use of magnetite particles for 31P-MR spectroscopy using a phantom, and perfused tumour-bearing rat livers and liver tumours in living rats. As expected, there is homogeneous uptake of the magnetite in normal liver leading to extinction of the signal when one uses suitable spectroscopic parameters. Since the ferrite particles do not penetrate non-hepatic tissue, such as metastases, a signal remains uniquely from the tumour and this can be used, for instance, for following the effect of cytostatic therapy. The use of magnetite produces a selective effect and interference from normal liver is thereby avoided. Multiple lesions with irregular configuration can be examined simultaneously by this method. It remains to be seen how useful the application of magnetite will be for avoiding motion artifacts during spectroscopy.

[Effect of static magnetic fields on the acoustic action potential of the cochlea in guinea pigs]. / Einfluss statischer Magnetfelder auf das Summenaktionspotential der Cochlea des Meerschweinchens.

Several experiments carried out during the past years indicate that strong magnetic fields induce disturbed blood circulation in capillaries and arterioles. When exposed to a magnetic field, disturbed blood circulation was found in the capillaries in frog webs as well as changes in skin temperature in several kinds of species. In our experiments we assessed the influence of a 8.5 T static magnetic field on the function of the inner ear of guinea pigs by monitoring the cochlea action potential. When blood circulation is disturbed in this organ it shows a rapid decline in function. Even when exposed to the magnetic field for 3 h, we could find no change in the function of the inner ear of the guinea pigs.