Basics of the magnetic resonance phenomenon.

Magnetic Resonance is increasing its importance as a diagnostic mean. For an effective and accurate MRI practice, new fundamental principles, which are at the basis of this phenomenon, must be acquired. In this chapter an extremely simplified overview of the physical basics of MRI is introduced, to help the readers understand the principles underlying this complex technique. Basic physics, T1 and T2 relaxation times, spin echo sequences, which can be acquired with the now available units, and tissue characteristics are illustrated. For those who are interested in a further and more detailed reading in this field, a bibliography is also quoted.

Intraarterial portography with gadopentetate dimeglumine: improved liver-to-lesion contrast in MR imaging.

Magnetic resonance imaging during arterial portography (MRAP) was performed by the authors in a selected group of 12 patients with hepatic lesions. A low dose of gadopentetate dimeglumine (4 mL of a 0.5-mol/L solution, corresponding to a dose of 0.05-0.07 mmol/kg) was injected into the superior mesenteric artery during acquisition of breath-holding gradient-echo or rapid acquisition spin-echo images. Images were always acquired during the first passage of gadopentetate dimeglumine through the liver parenchyma. An increase in liver-to-lesion contrast was obtained with MRAP imaging (contrast-to-noise ratio = 8 +/- 1.8 vs 19 +/- 2.7). Signal intensity enhancement of the liver was high (signal-to-noise ratio = 9.48 +/- 2.42), while the lesion presented no significant enhancement (signal-to-noise ratio = 0.55 +/- 0.22). Lobar portal vein thrombosis was detected in one patient owing to lack of enhancement of the left lobe of the liver. No side effects related to administration of iodinated and paramagnetic contrast agents were observed. This new technique provides specific enhancement of liver parenchyma with improved liver-to-lesion contrast.

Comparison of Gd-BOPTA with Gd-DTPA in MR imaging of rat liver.

A new lipophilic compound, gadolinium benzyloxypropionictetraacetate (BOPTA), with a high rate of biliary excretion was assessed as a magnetic resonance (MR) hepatospecific contrast-enhancing agent and compared with Gd-DTPA (diethylenetriaminepentaacetic acid) in MR imaging of normal rats. T1-weighted spin-echo images obtained before and after administration of each contrast agent at doses of 0.25, 0.5, and 1.0 mmol/kg showed greater enhancement of the liver with Gd-BOPTA than with Gd-DTPA, with the advantage more evident at lower doses. Images obtained with an inversion recovery sequence at the null value of rat liver parenchyma after injection of 0.1- and 0.5-mmol/kg doses of the contrast agent provided better evidence of the greater and longer-lasting hepatic enhancement due to Gd-BOPTA when compared with that of Gd-DTPA. Gd-BOPTA is a potentially good contrast agent for obtaining prolonged enhancement of the liver, permitting studies during the long time needed to acquire conventional T1-weighted images.

Space Station atmospheric monitoring systems.

A technology assessment study on atmospheric monitoring systems was performed by Battelle Columbus Division for the National Aeronautics and Space Administration's John F. Kennedy Space Center under Contract No. NAS 10-11033. In this assessment, the objective was to identify, analyze, and recommend systems to sample and measure Space Station atmospheric contaminants and identify where additional research and technology advancements were required. To achieve this objective, it was necessary to define atmospheric monitoring requirements and to assess the state of the art and advanced technology and systems for technical and operational compatibility with monitoring goals. Three technical tasks were defined to support these needs: Definition of Monitoring Requirements, Assessment of Sampling and Analytical Technology, and Technology Screening and Recommendations. Based on the analysis, the principal candidates recommended for development at the Space Station's initial operational capability were: (1) long-path Fourier transform infrared for rapid detection of high-risk contamination incidences, and (2) gas chromatography/mass spectrometry utilizing mass selective detection (or ion-trap) technologies for detailed monitoring of extended crew exposure to low level (ppbv) contamination. The development of a gas chromatography/mass spectrometry/matrix isolation-Fourier transform infrared system was recommended as part of the long range program of upgrading Space Station trace-contaminant monitoring needs.