Non-invasive measurement of gastric accommodation in humans.

Gastric accommodation describes the reduction in gastric tone and increase in compliance that follows ingestion of a meal and involves at least two responses: "receptive relaxation" which allows the stomach to accept a volume load without a significant rise in gastric pressure and "adaptive relaxation" which modulates gastric tone in response to the specific properties of the meal ingested. However, there are considerable technical difficulties in measuring the accommodation process. The current standard barostat studies, and other methods such as conventional and three dimensional ultrasound, or single photon emission computed tomography have significant disadvantages. Preliminary findings from the development and validation of a new magnetic resonance imaging technique that addresses many of the deficiencies of previous methods are presented.

Anaplastic astrocytoma and glioblastoma: pion irradiation with the dynamic conformation technique at the Swiss Institute for Nuclear Research (SIN).

Clinical phase I/II studies have been performed at the Swiss Institute for Nuclear Research (SIN) since February 1982. Fifty-two out of 249 patients accepted for pion treatment by the end of 1986 were treated for malignant glioma with high dose pion irradiation. A substantial influence of their radioresistance was expected from increased radiation quality due to the contribution of high LET particles from pion capture, and by the possibility of target volume shaping and dose distribution related to the dynamic spot-scan conformation technique. The patients' treatment followed a dose escalation program with total doses from 2720-3420 cGy, fraction sizes from 170 to 205 cGy (90% isodose, minimum target dose), and treatment times from 4 to 5 weeks. 12/52 patients received an accelerated treatment with 3280 cGy in 14-22 days. 49/52 patients are eligible: 3 with astrocytoma of clinical aggressive behaviour, 14 with anaplastic astrocytoma (median age 42 years), and 32 patients with glioblastoma (median age 52 years). 8/49 patients had total/subtotal tumour resection, 19 patients a stereotactic biopsy. The patients were divided into three groups according to total dose, and a fourth group which received the accelerated treatment. There was no statistically significant difference in the median survival rate between the four groups, which was 13 months for the non-glioblastoma patients and 9 months for the glioblastoma patients. No radiation necrosis and no demyelination was found in 17 patients (6 recraniotomies, 11 autopsies). In 10/17 patients, clearly identifiable tumour cells were not demonstrated. NMR findings showed the tumour-surrounding oedema mostly stimulated by tumour necrosis and tumour progression. From these findings, further dose escalation programs, together with a shaping of the target volume close to the tumour, are not contraindicated.

Quantitative flow measurements on phantoms and on blood vessels with MR.

A broad spectrum of MR methods has been published in the last few years for the visualization and the quantification of flow in human blood vessels. We describe the results of an extended study to measure the flow quantitatively using the MR phase modulation method. A gradient echo sequence which allows short repetition times was synchronized with the ECG. The instantaneous velocity profiles and the integrated flow rate can be determined throughout the cardiac cycle in up to 45 consecutive time intervals. The instantaneous velocity distributions can be displayed as 2D profiles over the lumen of the blood vessel. The technique has been successfully evaluated with a set of phantom experiments. Following this, quantifications of the blood flow rates in vivo were performed on the abdominal aortas of healthy volunteers. The MR flow results were compared to those obtained with conventional Doppler ultrasound examinations. The results of both methods are in good quantitative agreement.

Localized double-quantum filter and correlation spectroscopy experiments.

Problems with in vivo proton spectroscopy include strong water and lipid signals, and the very complicated structures of the spectra. Multiple-quantum experiments can be designed to overcome these difficulties. Using a volume selective refocusing technique, one can demonstrate how multiple-quantum experiments can be performed in a spatially localized manner. Rather than trying to integrate a localization procedure into a particular spectroscopy experiment itself, the approach here is to leave the basic experiment intact and to add a volume selective "block" to the end of the sequence. This "block" must, of course, preserve the integrity of the particular experiment. The volume selective refocusing method, presented here, does just this for a wide variety of proton NMR experiments. The advantage of this approach is that the analysis of the particular experiment is not changed. This is very important considering the complexity involved. Using this procedure, two very elementary multiple-quantum experiments have been performed on a 1.5-T whole-body scanner. These experiments are a localized double-quantum filter experiment (for water suppression) and a localized two-dimensional correlation spectroscopy experiment.

MR imaging of large nonferromagnetic metallic implants at 1.5 T.

To evaluate the feasibility of magnetic resonance (MR) imaging in patients with nonferromagnetic metallic implants, we imaged implants in vitro and in 15 patients. Image artifacts both in vitro and in vivo occurred only locally and consisted of image distortions, areas of total signal loss, and lines of high signal intensity. The artifacts were most prominent in areas where the implants exhibited edges or points, but overall image quality was good except for regions lying very close to the implants. The implants themselves appeared as structures without signal in all patients. We conclude that in patients with femoral head prostheses or osteosynthetic plates that are nonferromagnetic MR may be preferable to CT, where beam hardening artifacts usually degrade image quality severely in the entire field of view.

The thermodynamic behaviour of labial gingiva in patients with destructive periodontal disease.

The temperature changes of the labial gingiva and mucosa of the maxillary incisor regions were investigated using computer-assisted thermography. 9 patients with destructive periodontal disease (7 female and 2 male, aged between 12 and 33 years, undergoing periodontal treatment for periods varying from 6 months to 12 years) and 10 volunteers with clinically normal periodontia (6 female and 4 male, aged between 19 and 26 years) took part in this study. The gingivae and mucosae were initially cooled using a homogeneous flow of air (15 l/min at 15 degrees C) for 3 min. 20 s after the cooling phase, temperature increases of these soft tissues were sequentially recorded using 48 thermograms per person. This procedure was repeated 4 times for each person examined. The weighted mean of the time constants of the tissue re-warming curves was significantly higher (p less than 0.025) for the periodontitis group (152 +/- 6 s) compared to the clinically healthy group (110 +/- 9 s). The different thermodynamic behaviour between the 2 groups studied indicated differences in the blood-flow and/or its regulation.