Techniques, pitfalls and artifacts in magnetic resonance imaging.

To facilitate the proper interpretation of MR images, it is necessary for the radiologist to be alert to the many potential sources of image artifacts.

Dynamic fluctuations in blood and spleen radioactivity: splenic contraction and relation to clinical radionuclide volume calculations.

Alterations in the blood radioactivity affect ventricular volume calculations using count-based radionuclide ventriculography. To study this phenomenon, the effect of time, posture and supine exercise on blood radioactivity, red blood cell count and splenic radioactivity was evaluated. The red blood cell count, and blood, splanchnic and splenic radioactivity remained stable in five patients studied at rest in the supine position. On standing, blood radioactivity increased 10 +/- 3% (standard error of the mean), and abdominal radioactivity decreased 14.5 +/- 6.5% (both p less than 0.05). In 10 patients, splenic radioactivity decreased after supine exercise by 49 +/- 7%, while blood radioactivity increased 10.5 +/- 1.5% and red blood cell count increased 7.5 +/- 1.5% (all p less than 0.001). Splenic radioactivity increased gradually after exercise and decreased after a second exercise period. In the exercising patients, blood radioactivity increased by 14.5% and correlated with an increase in the red blood cell count (r = 0.57, p = 0.01, 19 samples from 10 patients). Reduction in splenic radioactivity also correlated with the increase in red blood cell count (r = -0.51, p = 0.025). The data demonstrate splenic shrinkage in human beings and an inverse relation between changes in splenic and blood radioactivity. These dynamic fluctuations emphasize the need for simultaneous blood sampling for accurate calculation of left ventricular volume and high-light the importance of regional volume shifts during exercise.

Comparison of radionuclide and contrast ventriculography for detection and quantitation of regions of myocardial ischemia in dogs.

Radionuclide and contrast ventriculography were evaluated for their ability to estimate myocardial ischemia. In 14 closed-chest, sedated dogs, a small and larger region of ischemia were produced by inflating balloon occluders on the left anterior descending coronary artery. The systemic arterial pressure, atrial-paced heart rate, global ejection fraction by radionuclide and contrast ventriculography, regional wall-motion abnormalities (as the percentage of abnormally contracting segments), and regional myocardial blood flow (using the microsphere technique) were measured during an initial control period, two separate ischemic periods, and a final control period. The regional ischemic weights based on myocardial blood flow ranged from 0 to 38.5 g and were grouped as zero, small (range 0 to less than 10 g, mean 3.40 g), and large regions of ischemia (greater than 10 g, mean 24.8 g). Regional wall-motion abnormalities were sensitive qualitative indicators of ischemia. Receiver operating characteristic analysis showed that both ventriculographic methods were highly sensitive, specific, and accurate for detecting regional ischemia. Contrast ventriculography was slightly superior for detecting small regions less than 4 g, but the methods were equal for regions greater than 4 g. The arterial pressure and heart rate were unchanged during ischemia. For small regions of ischemia, the global ejection fraction did not fall using either the contrast or radionuclide technique, but it fell significantly when large regions were produced. There was a quantitative relationship between the percentage of abnormally contracting segments and the grams of myocardial ischemia (for radionuclide ventriculography, r = 0.65, P = 0.003, and for contrast ventriculography, r = 0.75, P less than 0.001), but for many small regions of ischemia, wall-motion changes were greater than anticipated, suggesting hypofunction of the continguous normal tissue. This study demonstrated that both radionuclide and contrast ventriculography were quite sensitive and specific for detecting measured amounts of regional ischemia. The functional changes resulting from ischemia are quantitatively related to the extent of regional ischemia, small areas resulting in regional wall motion abnormalities, and large areas producing both reduced global ejection fraction and wall motion changes.

The paediatrician's responsibility for the prevention of coronary heart disease.

A strong case exists in favour of encouraging children not to smoke, to be reasonably physically active and to eat in moderation to avoid obesity. The principal role of the paediatrician is in the education of health personnel who are in a position to influence children and their families to adopt these measures. Paediatricians will also be involved with children at special risk of ischaemic heart disease. They have a responsibility to promote reasearch to determine the efficacy of these measures in the prevention of coronary heart disease.