Correlations between physiological parameters related with kidney function and minute-by-minute urine output.

AIM: Recently, devices capable of measuring minute-by-minute urine output (UOm) have become available. It is not known how UOm correlates with physiological parameters in normal conditions and in disease states characterized by vascular dysfunction. This paper analyzes correlations between UOm and physiological parameters related to kidney perfusion to provide some insight about UOm pathophysiological interpretation and its relationship with renal blood flow. METHODS: We studied 14 male pigs were anesthetized, tracheostomized, and mechanically ventilated. Mean systemic blood pressure (PART ), mean pulmonary artery blood pressure (PPA ), carotid artery blood flow (QCA ), as well as total (QREN ), cortical (QCOR ) and medullary (QMED ) renal blood flows, and the renal resistive index (RRI) were measured or calculated. Animals received an intravenous dose of live E. coli for the induction of sepsis (septic group), or an equivalent amount of normal saline (nonseptic group). Three groups were studied: nonseptic (n = 6) and septic (n = 4), both receiving for resuscitation NaCl 0.9% at 4 mL/kg per h; and septic (n = 4), receiving for resuscitation NaCl 0.9% at 17 mL/kg per h. Animals were monitored for 5 h after the induction of sepsis. RESULTS: In septic animals, UOm was strongly positively correlated with QREN (Kendall's τ = 0.770, P < 0.05), QCOR (τ = -0.566, P < 0.05) and QMED (τ = 0.632, P < 0.05); and negatively correlated with PPA (τ = -0.524, P < 0.05) and RRI (τ = -0.672, P < 0.05). Control animals exhibited weaker correlations. CONCLUSION: UOm is a good physiological surrogate marker of total and regional renal blood flows and vascular resistance, particularly under septic conditions, probably reflecting glomerulo-tubular dysfunction in sepsis.

Iterative reconstruction for pet scanners with continuous scintillators.

Several technical developments have led to a comeback of the continuous scintillators in positron emission tomography (PET). Important differences exist between the resurgent continuous scintillators and the prevailing pixelated devices, which can translate into certain advantages of the former over the latter. However, if the peculiarities of the continuous scintillators are not considered in the iterative reconstruction in which the measured data is converted to images, these advantages will not be fully exploited. In this paper, we review which those peculiarities are and how they have been considered in the literature of PET reconstruction. In light of this review, we propose a new method to compute one of the key elements of the iterative schemes, the system matrix. Specifically, we substitute the traditional Gaussian approach to the so-called uncertainty term by a more general Monte Carlo estimation, and account for the effect of the optical photons, which cannot be neglected in continuous-scintillators devices. Finally, we gather in a single scheme all the elements of the iterative reconstruction that have been individually reformulated, in this or previous works, for continuous scintillators, providing the first reconstruction framework fully adapted to this type of detectors. The preliminary images obtained for a commercially available PET scanner show the benefits of adjusting the reconstruction to the nature of the scintillators.