Dynamic imaging with lanthanide chelates in normal brain: contrast due to magnetic susceptibility effects

Using a one-dimensional rapid imaging technique, we have found that injection of lanthanide chelates such as Gd(DTPA)2- leads to a significant decrease (50%) in rat brain signal intensity at 1.45 T using T2-weighted pulse sequences; however, no effect of comparable size is observed with T1-weighted pulse sequences. The transient effect and its kinetics were followed with a temporal resolution of between 1 and 8 s. Experiments with different lanthanide chelates show that the observed decrease in signal intensity correlates with the magnetic moment of each agent but not with their longitudinal relaxivity. Three-dimensional chemical-shift resolved experiments demonstrate significant line broadening in brain during infusion with Dy(DTPA)2-. Our results show that the cause of this effect is the difference in susceptibility between the capillaries, containing the contrast agent, and the surrounding tissue. As a result of these susceptibility differences, field gradients are produced in the tissue and diffusion of water through these gradients leads to a loss of spin phase coherence and thus a decrease in signal intensity. We propose this as a new type of contrast agent mechanism in NMR. The effect and its kinetics are likely to be related to important physiological parameters such as cerebral blood volume and cerebral blood flow, and do not depend on a breakdown of the blood-brain barrier as do conventional contrast agent techniques.     

A SURVEY OF CONCURRENT DRUG THERAPY AMONG DAY UNIT PATIENTS

SUMMARY In order to assess the reliability of drug information supplied by day-stay cases, 85 consecutive patients were interviewed. A comparison of the interview answers with the details previously volunteered during the admission procedure showed an increase of 80% in the information given by the patient. While the detailed interviewing technique is time-consuming and may not be infallible, this substantial increase in information highlights problems in the current routine.     

In vivo X-ray fluorescence of lead in bone using K X-ray excitation with 109Cd sources: radiation dosimetry studies.

Independent experiments have been performed at two centers, to evaluate the dosimetric properties of their respective 109Cd K X-ray fluorescence (XRF) bone lead measurement systems. Measurements were made of the dose to several points on the skin on the lower leg, at the surface of the tibia, in the red marrow tibia cavity, at the midcalf, and in the abdominal region occupied by the conceptus. Overall agreement between the two data sets was found. Similarities and differences are discussed. The effective dose values for an in vivo measurement of tibia lead concentration in 1-, 5-, and 10-year-old and adult subjects were calculated from one data set to be 1100, 420, 190, and 34/38 (male/female) nSv, respectively, for an in vivo median precision (one standard deviation) of 4.9 micrograms Pb (g bone mineral)-1 for a 30-min adult measurement.     

Indomethacin therapy and fetal urine production in twins with polyhydramnios.

Indomethacin has been used in twins with polyhydramnios to decrease amniotic fluid volume. Under therapy, a marked reduction of both fetuses' urine production has been demonstrated within 24 hours concomitant with maternal symptomatic relief. Discontinuation of therapy was associated with a rapid increase in fetal urine production. The clinical observation indicates that the benefit of indomethacin in prolonging such pregnancies is most probably the result of relief of polyhydramnios through decreased fetal urine production.