Absolute quantitation of brain 1H nuclear magnetic resonance spectra. Comparison of different approaches.

RATIONALE AND OBJECTIVES: Three different calibration techniques of 1H localized nuclear magnetic resonance (NMR) spectra were applied to a group of healthy volunteers. Absolute concentrations of the metabolites and their standard deviations were compared, and the clinical feasibility of these calibration technique is discussed. METHODS: Eighteen healthy volunteers were included in the study. Both water and creatine were used as internal standard, and a pertinent solution of metabolites was used as an external standard. The T2 relaxation times of the brain metabolites were evaluated in each examination. RESULTS AND CONCLUSIONS: The concentrations obtained using water as an internal standard and using an external standard are very similar, and the first of these methods show smaller standard deviations. The authors' results show that the use of creatine as an internal standard may induce systematic errors in absolute calibration because of the uncertainty on the true creatine concentration.

In vivo localized 1H NMR spectroscopy: an experimental characterization of the PRESS technique.

The aim of this study was the experimental characterization of the PRESS technique for image-guided in vivo 1H NMR spectroscopy, as implemented on a commercially available 1.5 T NMR whole-body system. Three characterization parameters were defined and evaluated in test object measurements: selection efficiency, suppression efficiency and contamination. The characterization parameters were evaluated in different experimental conditions. The profile of signal intensity across the volume of interest (VOI) was investigated. Our results show that the characterization parameters are slightly affected by the echo time, while they are not affected by changes in the repetition time. When the VOI is co-extensive with the inner cube of the test object the suppression efficiency is good but the selection efficiency is not very high. Contamination is affected by the synthesizer frequency offset, while the selection efficiency is quite stable. Contamination effects become significant in case of 90 degrees pulse maladjustment.

[The dose and quality program in mammography (DQM). Results of the study carried out in 20 Fruili-Venezia Giulia centers]. / Programma dose e qualità nella mammografia (DQM). Risultati dell'indagine svolta in 20 centri del Friuli-Venezia Giulia.

Recently, 20 breast centers in Friuli Venezia Giulia have been investigated for the mammography optimization program known as DQM (Dose and Quality in Mammography). This was the second trial, the first one dating 1987-1988 and including only 10 centers. The chosen parameters were evaluated by means of a performance phantom containing 15 details, a Victoreen 660 ionizing camera, a star pattern and several plexiglass phantoms of different thickness. Statistical-methodological data were collected by means of a questionnaire. The results of the trial were communicated to each center as well as directions for future improvements. All centers were found to use mammographic equipment with a molybdenum anode and the film-screen combination; 18 center use grids daily, while 11 can perform direct radiographic magnification. Only 40% of the examined centers use a dedicated daylight printer. The overall quality of the radiographic image was seen to be acceptable, as 8 or more details of 15 hidden in the phantom were visualized, in 16 of 20 centers. The mean glandular dose was below the minimum threshold in all centers: in 45% of cases it was below 1.5 mGy. The setting of the automatic exposition control system was found to be poor, especially that of the adjustment related to breast thickness. Acceptability thresholds were met only by 31% of the examined centers (density variations < 20%). Notwithstanding the identification of areas where improvements can be made also from a methodological point of view, we can conclude that the quality provided by regional breast centers is definitely adequate. Good image quality and acceptable doses were observed in 80% of the centers. The results are significant and encouraging when compared with those from the first DQM trial carried out in our region, which confirms the value of periodical quality programs.

Fatty infiltration of the liver. Quantification by 1H localized magnetic resonance spectroscopy and comparison with computed tomography.

RATIONALE AND OBJECTIVES: The authors evaluated the degree of fatty infiltration of the liver in subjects with diffuse liver steatosis using image-guided 1H localized MR spectroscopy and correlated the magnetic resonance (MR)-determined fat fraction with the computed tomography (CT) liver/spleen density ratio and histologic evaluation. METHODS: MR measurements were performed at 1.5 T by applying a double-spin-echo localization sequence. Twenty-six patients underwent MR and CT examinations and ultrasound (US)-guided biopsy. Additionally, three healthy volunteers underwent MR examination. Steatosis severity was estimated using 1) the ratio between fat and total MR signal areas; 2) the ratio between liver and spleen CT number; and 3) histologic score. RESULTS: The linear correlation between MR fat/fat-plus-water signal ratio and CT liver/spleen density values ratio is statistically significant. Both techniques correlate well with histologic score. No significant correlation exists between water or fat T2 values and the severity of steatosis. CONCLUSIONS: 1H MR spectroscopy allows a noninvasive estimate of the hepatic fat content.

Quantitative 31P MRS of the normal adult human brain. Assessment of interindividual differences and ageing effects.

The characteristics of the 31P MR spectra from a large central volume in the brain of 47 healthy adults (aged 25-85 years) were assessed. Spectral parameters were estimated by means of a time-domain fitting technique. Statistical uncertainties of the estimates were determined by means of the Cramer-Rao theory and minimized by introducing a priori knowledge into the fitting procedure. Age-dependency of the spectral parameters was assessed by means of linear regression. Significant differences between individuals were established for some parameters. A significant age-dependency (p < or = 0.001) of ca 20% over the age range considered was found for the intensity of the phosphocreatine resonance line.