Assessment of renal function in patients with unilateral ureteral obstruction using whole-organ perfusion imaging with 320-detector row computed tomography

Abstract

Background: Obstructed nephropathy is a common complication of several disease processes. Accurate evaluation of the functional status of the obstructed kidney is important to achieve a good outcome. The purpose of this study was to investigate renal cortical and medullary perfusion changes associated with unilateral ureteral obstruction (UUO) using whole-organ perfusion imaging with 320-detector row computed tomography (CT).

Methodology/principle findings: Sixty-four patients with UUO underwent whole-organ CT perfusion imaging. Patients were divided into 3 groups, mild, moderate, and severe, based on hydronephrosis severity. Twenty sex- and age-matched patients without renal disease, who referred to abdominal CT, were chosen as control subjects. Mean cortical and medullary perfusion parameters of obstructed and contralateral kidneys were compared, and mean perfusion ratios between obstructed and contralateral kidneys were calculated and compared. Mean cortical or medullary blood flow (BF) and blood volume (BV) of the obstructed kidneys in the moderate UUO and BF, BV, and clearance (CL) in the severe UUO were significantly lower than those of the contralateral kidneys (p < 0.05). The mean cortical or medullary BF of the obstructed kidney in the moderate UUO, and BF, BV, and CL in the severe UUO were significantly lower than those of the kidneys in control subjects (p < 0.05). Mean cortical or medullary BF of the non-obstructed kidneys in the severe UUO were statistically greater than that of normal kidneys in control subjects (p < 0.05). An inverse correlation was observed between cortical and medullary perfusion ratios and grades of hydronephosis (p < 0.01).

Conclusions/significance: Perfusion measurements of the whole kidney can be obtained with 320-detector row CT, and estimated perfusion ratios have potential for quantitatively evaluating UUO renal injury grades.

Fig 1. Time–density curves (TDCs) of renal cortex (a) and medulla (b) from the single input maximum slope and Patlak graph from the Patlak plot (c).

TDC indicates the enhancement characteristics of the aorta and renal cortex or medulla during the first pass. BF can be determined from the maximum gradient of renal cortical or medullary TDC divided by the peak enhancement of the aorta. The Patlak plot is a graphical analysis method, which quantifies the passage of contrast from the intravascular space into the extravascular space. BV and CL can be obtained from the Patlak equation. TDC curve: SP: start phase; EP: end phase. Patlak graph: SP: start phase; FE: flow end; EP line: early perfusion regression line (green line); CL line: clearance regression line (purple line). BF, blood flow; BV, blood volume; CL, clearance.

Fig 2. Examples for regions of interest (ROIs) measurements.

ROIs of renal cortex (a, b) and medulla (c, d) were defined manually in the coronal plane.

Fig 3. BF, BV and CL maps from control subjects and the three groups of UUO.

The perfusions of both kidneys were uniform in control subjects and renal cortex showed an intact red ring. For UUO patients, BF, BV and CL maps showed dilation of collecting system in the obstructed kidney (arrow) and normal contralateral kidney. The renal cortex from obstructed kidney was less continuous and local yellow or blue areas were observed in the perfusion maps. BF, blood flow; BV, blood volume; CL, clearance.