Efficient high-frequency body coil for high-field MRI.

The use of body coils is favored for homogeneous excitation, and such coils are often paired with surface coils or arrays for sensitive reception in many MRI applications. While the body coil's physical size and resultant electrical length make this circuit difficult to design for any field strength, recent efforts to build efficient body coils for applications at 3T and above have been especially challenging. To meet this challenge, we developed an efficient new transverse electromagnetic (TEM) body coil and demonstrated its use in human studies at field strengths up to 4 T. Head, body, and breast images were acquired within peak power constraints of <8 kW. Bench studies indicate that these body coils are feasible to 8 T. RF shimming was used to remove a high-field-related cardiac imaging artifact in these preliminary studies. P41RR13230     

Endothelial and smooth muscle properties of coronary and mesenteric resistance arteries in spontaneously hypertensive rats compared to WKY rats

Summary— To investigate if the functional alterations observed in resistance arteries of spontaneously hypertensive rats (SHRs) were also present at the coronary level, in vitro experiments were performed in mesenteric resistance arteries (MRA) and in right (RIC) and left interventricular coronary (LIC) arteries taken from 15–25-week-old SHR and age-matched Wistar Kyoto rats WKYs. Using a passive extension protocol, internal diameters corresponding to 100 mmHg intraluminal pressure (D₁₀₀) were determined and vessels were set up to a normalized internal diameter (0.9 D₁₀₀). SHR mesenteric resistance arteries had a significantly smaller diameter compared to WKY arteries, whereas both types of SHR coronary arteries had a greater diameter compared to those of WKY rats. In arteries in the absence of contracting agonist, nitro-L-arginine (NOLA, 100 μM) induced a progressive rise in basal tone, which could be reversed by subsequent addition of L-arginine (100 μM) but not D-arginine (100 μM). When expressed as percent of maximal contractions induced by agonists (noradrenaline, NA [10 μM] in MRA; serotonin, 5-HT [10 μM], in RIC and LIC), these contractions were significantly stronger in WKY compared to SHR coronary and mesenteric resistance arteries. In NA-precontracted MRA and 5HT-precontracted coronary arteries in the presence of indomethacin (10 μM), the magnitude of acetylcholine-induced maximal relaxations (expressed as percent of maximal contractions induced by agonists) was greater in WKY compared to SHR arteries. After a 30-min incubation period, NOLA (100 μM) completely inhibited relaxations induced by acetylcholine (0.01–10 μM) in all types of precontracted arteries. Subsequent additions of sodium nitroprusside, (SNP, 10 μM) induced complete relaxations in all preparations. These results show that a basal release of NO or NO-like compound by endothelial cells is present in isolated mesenteric resistance and coronary arteries of WKY rats and SHRs. The contribution of endothelium-derived relaxing factor-nitric oxide (EDRF-NO) to arterial tone was lower in MRA compared to coronary arteries in both strains and in SHR compared to WKY arteries. In the SHR preparations, the impaired relaxation induced by acetylcholine appeared to be due to a functional alteration of the endothelium in the presence of normal reactivity of the smooth muscle cells.     

Monitoring health care system performance in Iowa.

Monitoring the performance of the health care delivery system is a public health function that becomes more important as organized delivery systems begin to take control over larger portions of the medical care market. The study reported here illustrates how standard medical care epidemiology can be applied to analysis of health care system performance to aid governmental efforts to monitor new developments in the medical care market. In order to evaluate the efficiency of hospital care delivered in Iowa, age- and sex-adjusted population admission rates for five common procedures were generated for all 99 counties. The five common procedures were defined as follows: hernia, tonsillectomy, cesarean section, hysterectomy, and cholecystectomy. In addition, variations in 11 ambulatory care-sensitive condition rates were analyzed. Residents of at least 15 counties were at significantly greater than average risk of receiving each of the common procedures (chi 2 test, P < 0.05). Counties that had a high rate for one procedure tended to have a high rate for at least one other procedure. Several counties had more than twice the mean rate. Even a 10% reduction, when added across all five common procedures. amounts to well over 2,000 hospitalizations avoided. It is assumed that reductions would be concentrated in high-rate counties. If a 50% reduction could be achieved in only part of the ambulatory care-sensitive procedures, more than 10,000 hospital admissions could be avoided.     

Involvement of platelet activating factor and thromboxane A2 in the renal response to unilateral ureteral obstruction

Platelet activating factor (PAF) and thromboxane A2 (TxA2) are two vasoactive mediators which can decrease renal blood flow. Both are synthesized by various intrarenal cell types or by macrophages which may infiltrate the kidney during unilateral ureteral obstruction (UUO). In several experimental systems, PAF receptor activation is accompanied by TxA2 release; pharmacological modification of TxA2 synthesis or receptor activation modulates the response to PAF. The involvement of PAF in UUO has not been studied previously, and the role of TxA2 has not been clearly defined by previous investigations. The hemodynamic response to acute UUO is characterized by decreases in renal blood flow (RBF) and glomerular filtration rate and an acute increase in ureteral pressure. In the present experiments, the involvement of either PAF or TxA2 in the acute response to UUO was studied by determining if blockade of either the TxA2 or PAF receptor would affect the renal hemodynamic response to UUO. In addition, the effect of blockade of the TxA2 receptor on the renal response to PAF was determined. Our results indicate that only a small portion of the renal response to PAF is mediated by TxA2, and that neither PAF nor TxA2 can be implicated in the acute hemodynamic response to UUO. TxA2 or PAF involvement in the chronic response to UUO still remains to be determined.     

Penile blood flow changes in the flaccid and erect state in potent young men measured by duplex scanning

We studied penile blood flow changes with duplex ultrasound scanning in 8 potent young men during the flaccid state and during the erect state induced by visual sexual stimulation. Measured parameters obtained from the cavernous arteries were arterial diameter, peak blood flow velocity and blood flow acceleration. The mean arterial diameter change was 72% associated with average blood flow velocity and acceleration changes of approximately 200%. Actual values for blood flow velocity and acceleration were considerably higher when compared to papaverine-induced values measured in psychogenically impotent men. Visual sexually stimulated penile arterial changes are not analogous to papaverine-induced arterial changes and these differences raise questions about the appropriateness of using psychogenically impotent men as controls for measurement of penile arterial function with duplex scanning.