Identifying acoustic scattering sources in normal renal parenchyma in vivo by varying arterial and ureteral pressures.

Ultrasonic backscatter properties of normal dog kidney parenchyma are examined in vivo to determine sources of acoustic scattering. We systematically varied the renal perfusion and ureteral pressures to obtain detailed information about scattering sources that could not be seen under in vitro conditions. These data suggest that in normal parenchyma the principal sources of backscatter are Bowman's capsule at low frequencies (2.5-5.0 MHz) and glomerular arterioles at high frequencies (5.0-15.0 MHz). We found that the integrated backscatter coefficient (IBC) in normally perfused kidney cortex is approximately half that measured in the ischemic organ at all frequencies. Ischemia was found to reduce scatterer size estimates (D) by 10% at low frequencies and increase D54% at high frequencies. Acute obstruction of the kidney, under diuresis, produced an 11% increase in D at low frequencies, and no significant change in D at high frequencies. These variations in backscatter measurements are explained in terms of changes in the microscopic anatomy of the kidney.