Radioisotopic evaluation of renal transplants

Diagnosis of renal allograft rejection and acute tubular necrosis by 99mTc-mononuclear leukocyte imaging

One hundred kidney transplant recipients were evaluated on the first and fifth days after transplantation by Tc-99m mononuclear cell scintigraphy. We have developed a quantitative method to diagnose rejection and acute tubular necrosis (ATN) by comparing regions of interest drawn on allograft scintigraphs at different times after endovenous administration of the labeled cells. We suggest that the use of Tc-99m-WBC may be useful for the early diagnosis of rejection and the differential diagnosis of ATN.

Preliminary results of [99mTc]OKT3 scintigraphy to evaluate acute rejection in renal transplants

Allograft rejection can be classified as humoral or cellular mechanisms. Accurate diagnosis of acute rejection remains a formidable challenge in renal transplantation. The need to avoid unnecessary immunosuppressive therapy to treat this complication has led to a continued search for improved diagnostic methods to evaluate and identify postoperative episodes. Here we evaluated the use of [(99m)Tc]OKT3 scintigraphy to diagnose acute rejection in renal transplants. Among 22 patients undergoing renal transplant, we observed an increased [(99m)Tc]OKT3 kidney uptake with the passage of time in patients with rejecting allografts. These findings agreed with those of biopsies. We suggest the [(99m)Tc]OKT3 scans may be useful for the monitoring of renal transplants to detect acute rejection.

Renography within 1 hour of renal transplantation: technical feasibility and clinical utility

OBJECTIVE

Renographies obtained within 1 h of renal transplantation were studied prospectively to evaluate their technical feasibility and potential clinical impact on successful treatment of immediate posttransplantation complications such as arterial or venous thrombosis, which require prompt diagnosis and management.

SUBJECTS AND METHODS

During December 1996 to December 1998, 127 renal transplants were performed. Ninety-four patients had complete renographic studies within 1 h of surgery. It was not possible to perform renography on 26 patients who were not sent to the Department of Nuclear Medicine within 1 h of transplant and 7 other patients who could not undergo a complete renogram because of their postoperative condition.

RESULTS

There was no complication attributed to transporting patients to the Department of Nuclear Medicine for these studies so soon after surgery. Of the 94 renographies obtained immediately following transplant surgery 46 were abnormal. However, when compared with the usual policy of obtaining baseline renograms between 12 and 72 h after surgery, treatment was changed for only 2 patients. Radionuclide renography within 1 h of transplant surgery was technically feasible.

CONCLUSION

Based on the results of this study the clinical utility of obtaining renography within 1 h posttransplant was minimal and hence we recommended that it should not be performed routinely but could be used on an individual basis when imminent intervention is highly likely.

Tc-99m MAG3 evaluation of recipients with dual adult cadaveric renal allografts. Simultaneous transplantation of both kidneys from marginal donors

PURPOSE

The application of Tc-99m mercaptoacetyl triglycine (MAG3) renal scintigraphy in patients who had simultaneous unilateral retroperitoneal transplant of both kidneys from marginal adult cadaveric donors is assessed.

METHODS

Eighteen patients who had this unusual form of kidney transplant were monitored and evaluated by Tc-99m MAG3 renal scintigraphy. More than 60 of the radioisotopic studies, including immediate postoperative and subsequent follow-up examinations, were performed among these patients.

RESULTS

In all the studies, the two transplanted kidneys were not equally well visualized by this scintigraphic procedure because of the inherent difference in their depth from the body surface, a feature of this particular surgical design. Despite this limitation, the efficacy of the scintigraphic procedure for such dual renal allografts appears to be similar to that established for kidney transplants performed in the conventional manner.

CONCLUSION

To use the scintigraphic procedure effectively, certain sensible and logical adjustments are needed for the comparative visual and semiquantitative assessments of the two kidneys in this special form of transplantation.

Quantitative scintigraphic parameters for the assessment of renal transplant patients

Radionuclide renal diagnostic studies play an important role in assessing renal allograft function especially in the early post transplant period. In the last two decades various quantitative parameters have been derived from the radionuclide renogram to facilitate and confirm the changes in perfusion and/or function of the kidney allograft. In this review article we discuss the quantitative parameters that have been used to assess graft condition with emphasis on the early post-operative period. These quantitative methods were divided into parameters used for assessing renal graft perfusion and parameters used for evaluating parenchymal function. The blood flow in renal transplants can be quantified by measuring (a) the rate of activity appearance in the kidney graft; (b) the ratio of the integral activity under the transplanted kidney and arterial curves e.g. Hilson's perfusion index and Kircher's kidney/aortic ratio; (c) calculating the renal vascular transit time by deconvolution analysis. The literature overview on these parameters showed us that they have some practical disadvantages of requiring high quality bolus injection and numerical variations related to changes in the site and size of regions of interest. In addition, the perfusion parameter values suffer from significant overlap when various graft pathologies coexist. Quantitative evaluation of the graft parenchymal extraction and excretion was assessed by parameters derived from 123I/131I-OIH, 99mTc-DTPA or 99mTc-MAG3 renograms. We review in this article a number of parenchymal parameters which include (1) plasma clearance methods like glomerular filtration rate (GFR) and effective renal plasma flow (ERPF); (2) renal transit times such as parenchymal mean transit time, Tmax, T1/2; (3) parenchymal uptake and excretion indices as the accumulation index, graft uptake capacity at 2 and 10 min, excretion index and elimination index. These indices, however, are non-specific and far from defining a specific cause for graft parenchymal dysfunction. In conclusion, despite that the literature is replete with mathematical strategies for quantitating perfusion and parenchymal functions, none of these have enough diagnostic power for specific diagnosis of graft dysfunction. In addition, no universal agreement on the use of certain quantitation parameters in transplant patients has been reached.

Scintigraphic demonstration of postural induced drainage stasis in an en bloc renal allograft

Within 6 months after an en bloc transplantation of two kidneys from a cadaveric pediatric donor, the recipient was referred for further scintigraphic evaluation because of clinical suspicion of having a postural related function impairment of the grafted kidneys. Tc-99m MAG3 imaging, modified by varying the position of the patient during the procedure, resulted in detection of drainage stasis only with the patient standing. This drainage stasis had not been appreciated in the preceding routine examinations performed with the patient supine. Although the positional outflow stasis by itself may not be severe enough to cause alarming dysfunction of the grafted kidneys, it could conceivably be a significant contributing factor.

Renal nuclear medicine

The measurement of renal function has been a major field of interest in nuclear medicine. Many studies in the literature are still dedicated to this subject, with the aim of replacing the traditional urinary clearance methods with simpler and easier techniques. Simplified plasma clearance methods appear of sufficient accuracy to estimate global kidney function, except in very low function in which urinary clearance is still indicated. Gamma-camera methods have also been developed that, although of a lesser accuracy than the in vitro techniques, offer the important advantage of allowing renal imaging with the estimation of separate kidney function. Because of the intimate link between kidney function and structure, the diagnosis of nephrourological diseases has represented an important goal of nuclear medicine research. The functional information attainable with radionuclides is a valuable complement to the morphological information of imaging techniques such as x-ray computed tomography, ultrasonography, and magnetic resonance imaging. Recent contributions of nuclear medicine to the progress of clinical nephrology include the evaluation of renal function and the diagnostic work-up of renovascular hypertension, obstructive nephropathy, urinary tract infection, and renal transplantation.