The xenon washout technique and the renal blood flow response to vasoactive agents or alterations in sodium intake were used to characterize the effect of aging on the renal vasculature in 207 normal human subjects ranging in age from 17 to 76 years. A highly significant, progressive reduction in the mean blood flow, the rapid-component flow rate, and the percent of flow into the rapid-flow (cortical) compartment accompanied advancing age. Because 133 Xe measures flow per unit tissue mass, the results indicated a larger reduction in flow than in mass--the anticipated finding if flow reduction is primary in the genesis of atrophy. Age also reduced the vasodilation consequent to administration of acetylcholine or a sodium load; this finding is consistent with a fixed lesion of the vessels. Responses to angiotensin were not modified by age. Thus, offsetting factors of increased ratio of wall to lumen thickness and smooth muscle atrophy are precisely matched. The findings in this study agree with earlier hypotheses based on morphology that suggest a primary vascular process in the development of age-related renal changes.

A B S T R A C T The adrenal glomerulosa cell and the renal vasculature respond to similar arterial angiotensin II (A II) levels. We have assessed the effect of decreased sodium intake on their responses to A II in man. Studies were performed in 42 normal subjects in balance on a daily intake of 100 meq potassium and either 200 or 10 meq sodium/day. Renal blood flow was measured with AXe and arterial A II, renin and aldosterone concentrations by radioimmunoassay. A II was infused intravenously (1, 3, or 10 ng/kg/min) for 40-60 min; 14 subjects received graded doses. The A II level increased linearly with dose and plateaued within 3 min; blood pressure and renal vascular resistance showed a similar time-course. Aldosterone rose within 10 and plateaued within 20 min. Dose-response relationships were established between the rate of A II infusion and the adrenal, the renal vascular, and -pressor responses. Sodium restriction reduced the pressor (P <0.01) and the renal vascular response (P < 0.01), but potentiated the adrenal response to A II (P < 0.01). An excellent correlation was found between the plasma A II and aldosterone levels, but the slope of their regression relationship on a high (y = 0.13x + 6) and low salt intake (y = 0.32x + 14) differed significantly (P < 0.0005).Thus, sodium intake reciprocally influences vascular and adrenal responses to A II: salt restriction blunts the vascular response and potentiates the adrenal's, a physiologically important influence in view of aldosterone's role in sodium conservation.

Although CT fluoroscopy is a useful targeting technique, significant radiation exposures may result. Therefore, radiologists need to be aware of different methods of CT fluoroscopic guidance and the factors that contribute to radiation exposure.

MR imaging-guided percutaneous cryotherapy of liver tumors is feasible and safe. MR imaging can be used to estimate cryotherapy effects and guide therapy intraprocedurally.

High exposures to patients and personnel may occur during CT fluoroscopy-guided interventions. Radiation exposure to patients and personnel may be reduced by modifying CT scanning techniques and by limiting fluoroscopic time. In addition, scatter exposure to personnel may be substantially reduced by placing a lead drape adjacent to the scanning plane.

Very good correlation between ERCP and MRCP findings was demonstrated. Both modalities failed to depict pathologic conditions depicted by the alternative method. MRCP may obviate ERCP, particularly in patients who cannot undergo ERCP or in whom ERCP has been unsuccessful.

A nationwide survey was undertaken to determine the rate of complications due to coronary arteriography during 1970-71. The responses from 173 hospitals-including a total of 46,904 coronary arteriograms-were analyzed in relationship to the technique employed and to the number of examinations performed at each hospital during the two-year period. The overall mortality rate was 0.45% (brachial 0.13%, femoral 0.78%). The mortality rate in institutions performing fewer than 200 examinations per two years was eight times higher than in institutions performing more than 800 examinations per two years. Similarly, the incidence of myocardial infarction and cerebral embolism was significantly higher when a smaller number of examinations was performed. The incidence of major complications-including death, myocardial infarction, and cerebral embolism-was higher in examinations using the femoral approach than the brachial approach. The incidence of arterial thrombosis and contrast agent reactions was higher for the brachial approach. Factors which may help to explain these differences are considered and discussed. Additional Indexing Words: Myocardial infarction Thrombosis PseudoaneurysmVentricular fibrillation Embolism Contrast agent reactions T HE COMPLICATION RATES of coronary arteriography reported in the literature vary widely.'-'8 Yet it is essential that accurate data be available if an intelligent and informed appraisal of risk vs yield is to be made prior to arteriography. For this reason, a nationwide survey was undertaken to gather information on arteriographic complications from hospitals of varying size and with varying frequencies of arteriographic examinations. Materials and MethodsA questionnaire ( fig. 1) was mailed to the director of the coronary arteriography laboratory at each of the 373 institutions with an open heart surgical team listed in the AMA Directory of Medical Schools and Affiliated Hospitals. There were 173 responses. The data were tabulated for each question according to the technique (brachial, femoral, and total) and to the number of cases performed in each institution. Written statements From the

Polak JF, Jolesz FA, Adams DF. Magnetic resonance imaging of skeletal muscle: prolongation of T1 and T2 subsequent to denervation. Invest Radio1 1988;23365-369. The changes seen in the T1 and T2 relaxation times, water content and size of the extracellular fluid spaces of rat muscle samples following 15 days of denervation were studied by in vitro proton NMR spectrometry (10 MHz). Two different skeletal muscle groups (gastrocnemius and soleus) were studied. Denervation led to longer T1 values: 548 f 61 msec vs. 486 f 16 msec (P< .05) for the gastrocnemius and 581 f 27 msec vs. 521 f 25 msec (P < .05)for the soleus. Similar increases in T2 were measured. The sizes of the extracellular fluid spaces of denervated muscle were s i g n 5 cantly larger despite a minor increase in total water content. Overall, the relaxation times of skeletal muscle correlated better with the size of the extracellular fluid space than with the totnl water content.