Preliminary Research Of Virtual Touch Tissue Quantification In Diagnosis Of Chronic Allograft Nephropathy

Background and objectiveThe ideal treatment of chronic renal failure (CRF) is kidney transplantation. Presently, with the great improvement of the tissue matching technology and the transplantation operations as well as the wide use of the immunosuppressive drugs, the incidence of peri-operative complications and acute rejection has been significantly reduced. The short-term survival rate of the transplanted kidney has been greatly increased. However, the half-life of the transplanted kidney is still about11to12years. The long-term survival rate of the transplanted kidney has still not been greatly improved, and it has become one of the important public health problems in the world. Chronic allograft nephropathy (CAN) is the main reason for the dysfunction of the transplanted kidney. CAN occurs a few months after kidney transplant. The clinical manifestation is renal dysfunction, with or without hypertension and/or proteinuria, with the acute rejection and chronic renal damage being excluded, such as glomerulonephritis recurrence, obstruction or reflux, renal vascular stenosis, acute CSA/FK506poisoning. This kind of graft dysfunction was called chronic rejection earlier, but in terms of the disease related to both immune and non-immune factors, it is more appropriate to use the term "chronic allograft nephropathy". Histopathological changes include glomerulo sclerosis, tubular atrophy and interstitial fibrosis, vascular intimal hyperplasia and so on. Allograft biopsy has been considered as the gold standard for the diagnosis of CAN, however, Its clinical popularity was limited by the expensive cost, the dangers of the biopsy and postoperative bleeding and pain. In addition, the pathological results usually come out about one week after the allograft biopsy, which delays the treatment proposal.Virtual touch tissue quantification (VTQ) is a non-invasive and quantitative assessment of tissue elasticity. By this imaging technique, the elasticity and compliance of interested tissue would be assessed quantificationally. The VTQ values of renal allograft were measured in this study, in order to reflect the elastic compliance of the cortex of transplanted kidney. Comparison and statistical analysis of the measured values between different groups (group one in which renal transplant recipients with normal renal function and group two in which with chronic allograft nephropathy) have been carried out to investigate the elastic differences between normal group and chronic allograft nephropathy group after renal transplantation, and to provide a new guidance and direction for the clinical prevention and treatment of CAN.Materials and methodsPatients dataTwenty-eight patients, with renal biopsy or clinically diagnosed of chronic allograft nephropathy in Qilu hospital of Shandong University from September2010to December2012, were included as the CAN group, including24males and4females, aging at20to62years, with mean age of (36.32±10.67) years. Thirty-three cases of renal transplant patients with normal renal function were included as the control group, including19males and14females, aging at20to69years, with mean age of (41.48±10.83) years.1. Ultrasound Examination Siemens Acuson S2000color Doppler ultrasonograph with the VTQ quantitative analysis software was used.4-C1convex array probe with frequency of3.0to4.5MHz was chosen, setting depth of8.0cm and the sampling frame size of1.0×0.5cm2. First, patients underwent routine ultrasound examination to make a routine diagnosis. Then the same position which we sampled for at least five times with VTQ exam, taking the average values as the final results.2. Statistical analysisAll the data were evaluated using SPSS16.0software. Measurement data were reported as mean±SD (standard deviation). Intra-group differences used non-parametric tests, and inter-group comparison used independent samples t-est, correlation analysis of the SWV mean and renal transplantation function used Spearman’s rank-correlation test. The Receiver Operator Characteristic (ROC) curve was established by the two groups’data. When the sum of sensitivity and specificity tended to a maximum, the corresponding to the value of the parameter was the truncated value, with P<0.05considered to be statistical significant.Results1. The mean Shear Wave Velocities (SWV) of renal cortex in the normal group and the CAN group were (2.71±0.23)m/s and (3.03±0.23)m/s respectively. The renal parenchyma SWV of the CAN group was greater than the normal group. So was the SWV of renal medulla. The difference was statistically significant between the two groups (P<0.05). But there was no statistical significance between the SWVs of renal sinus in two groups.2. There was significant correlation between the GFR and the SWVs of renal cortex in two groups (r=-0.369, P=0.003), the GFR smaller, the SWV greater. But there was no correlation between the GFR and the SWVs of renal medulla and sinus.3. The ROC curve showed that cutoff value of VTQ was2.83m/s, and the sensitivity, specificity, positive predictive value, negative predictive value, the diagnostic accuracy of CAN were92.9%,66.7%,70.3%,91.7%,78.7%, and0.85, respectively. The area under the curve was0.85.ConclusionThe VTQ technique can quantitatively assess elastic changes of the renal parenchyma of the transplanted kidney, and advantages in presenting kidney dysfunction was showed. The stiffness measured is stable and repeatable, which can be used to the early diagnosis of patients with CAN. The VTQ would show great importance in delaying or stopping the progress of CAN.