1. Henderson JM, Moslim MA, Knox MK, Cowan NC
An Ellipsoid Model of the Kidney Calculated from Multidetector Computed Tomography Predicts Differential Function in Living Related Donors
Abstract ID:
Henderson JM, Moslim MA, Knox MK, Cowan NC
Introduction
Computed tomography and nuclear medicine studies are routinely used for the assessment of renal anatomy and function respectively. Assessment of renal volume and attenuation on CT for diseased kidneys has been shown to allow accurate calculation of differential renal function. We considered whether a simple ellipsoid approximation of renal volume, calculated from 3-axis renal measurements would predict differential renal function in healthy kidneys.
Height (H) maximum diameter of long-axis of the kidney in the sagittal plane
Depth (D) maximum antero-posterior diameter at 90 degrees to long-axis of kidney in sagittal plane
Width (W) maximum diameter medial to lateral in the coronal plane at 90 degrees to long-axis of the kidney
An ellipsoid model of the kidney was applied and the volume of each kidney calculated using the formula;
Renal volume= 4/3 x π x ½ H x ½ D x ½ W
The volume of each left and right kidney were summated to give total renal volume. Each renal volume was divided by total renal volume x 100 to give percentage renal volume.
Statistical Analysis
All statistical analysis was carried out using Graphpad Prism version 5.00 for Windows (GraphPad Software, San Diego, USA). The agreement between renal volume and DMSA derived differential renal function was compared using the Bland-Altman analysis1. Interobserver variability was tested with the Pearson correlation coefficient and statistical significance taken as p<0.05.
Methods
Potential living related donors (LRD) were evaluated with triple-bolus multidetector computed tomography (TB-MDCT) and technetium-99m dimercaptosuccinic acid renography (Tc-99m DMSA).
CT Acquisition
MDCT imaging was performed with a Lightspeed 8-section CT unit (General Electric Medical Systems, USA). Patients were given ml of tap water to drink 30 minutes before examination with intravenous furosemide (5 mg) administered immediately before the unenhanced CT acquisition.
tube voltage, 120 kVp;
reference mAs, 250 mAs;
table speed, mm/rotation; pitch, 1.675;
imaging field of view, 500 mm;
display field of view, 320 mm; matrix, 512x512.
Results
50 patients were evaluated with triple bolus CT and DMSA. The Bland-Altman analysis shows a bias of 0.3 with standard deviation 4.25 (figure 2).
Inter-observer Variability
Pearson r-value
0.76
95% confidence interval
0.62 to 0.86
P-value (two tailed)
P <0.0001
Figure 3: Inter-observer variability for renal volume derived DRF .
CT were acquired in the unenhanced and enhanced phases. A triple-bolus contrast administration protocol was used to enable simultaneous acquisition of arterial, nephrographic and excretory phases. Forty millilitres of non-ionic contrast medium (Iopamidol 300, 300 mg/ml) was administered intravenously via a cannula placed in the antecubital fossa at a rate of 2 ml/s. After 630 s, another30 ml of contrast medium was given at 4 ml/s. Finally, 80 ml of contrast medium at 4 ml/s was given at 730 s. Imaging commenced at 750 s after the initial contrast medium bolus. Images were reconstructed at 1.25 mm section thickness with mm overlap. Three dimensional reconstruction was undertaken and images analysed in the sagittal and axial planes.
Evaluation
Images were independently assessed by two observers, both blinded to patient demographics and result of DMSA renography. The measurements taken for the renal volume were;
Figure 1 : 3-dimensional reconstruction of triple-bolus CT image
Conclusions
An ellipsoid approximation of renal volume calculated from renal measurements correlates closely with differential renal function obtained from radionuclide studies.
This method is simple and reproducible between observers.
Obtaining both anatomical and functional information from a single study saves time and resources whilst exposing the patient to less radiation
Figure 2 : Bland-Altman analysis of DMSA derived DRF vs, renal volume derived DRF (95% confidence intervals shown by dotted line)
Bland JM, Altman DG (1986) Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 327: