Noninvasive evaluation of a novel swine model of renal artery stenosis

Intrarenal hemodynamics and excretory function distal to renal artery stenosis are difficult to quantify noninvasively. In this study, a swine model of chronic unilateral renal artery stenosis, achieved by implantation of an intravascular device that leads to a gradual and progressive luminal area narrowing, was developed and evaluated. Bilateral cortical and medullary volumes, blood flows, and segmental tubular dynamics were assessed in the intact kidneys of seven pigs using electron-beam computerized tomography before and 1 mo after implantation of the device. Within 1 mo, a 66% angiographic stenosis was significantly correlated with a 25% increase in BP. The volume and blood flow were markedly lower in the stenotic compared with the contralateral kidney and cortex, while the medulla exhibited minimal changes. In the stenotic kidney, intratubular contrast content has decreased in all nephron segments, especially in the distal tubule, where it correlated with an increase in serum creatinine and stenosis severity. In the contralateral kidney, dilution of proximal tubular fluid correlated with the increase in BP, likely due to pressure-natriuresis. In conclusion, the swine model closely resembles human renovascular hypertension. In the stenotic kidney, the hemodynamic impairment of the cortex is dissociated from the relatively preserved renal medulla, and the earliest effect on excretory function is observed in the distal nephron, where the fall in the amount of fluid reaching that segment is directly proportional to the renal arterial compromise. Electron-beam computerized tomography shows promise to noninvasively quantify, follow-up, and study changes in concurrent, in vivo intrarenal hemodynamics and segmental tubular function in renovascular hypertension.

Localization and characterization of renal calcitonin receptors by in vitro autoradiography

Calcitonin receptor binding sites were identified in renal cortex and medulla using the radioligand 125I-salmon calcitonin. Microscopic localization of these receptors revealed binding over medullary and cortical thick ascending limb of the loop of Henle and in distal convoluted tubule. A number of receptor positive cells in the inner medulla were also identified. Characterization of the binding demonstrated a single class of high-affinity binding sites in both the medulla and the cortex with affinity constants of 0.74 +/- 0.09 x 10(9) M-1 and 0.32 +/- 0.05 x 10(9) M-1, respectively, and receptor concentrations of 205 +/- 45 fmol/mg protein and 453 +/- 54 fmol/mg protein, respectively. Competition for 125I-salmon calcitonin binding by a wide range of calcitonin analogs revealed a close correspondence between the reported biological potencies and activities in the current system. The localization of binding sites within the nephron corresponds to the reported localization of calcitonin-stimulated adenylate cyclase activity and suggests that the receptor mediated actions of calcitonin in the kidney utilize cyclic AMP as a second messenger. In addition, the microscopic identification of specific calcitonin receptors helps the delineation of direct actions of this hormone from those which are indirect.

Comparison of Mathematic Models for Assessment of Glomerular Filtration Rate with Electron-Beam CT in Pigs

PURPOSE

To prospectively compare in pigs three mathematic models for assessment of glomerular filtration rate (GFR) on electron-beam (EB) computed tomographic (CT) images, with concurrent inulin clearance serving as the reference standard.

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. Inulin clearance was measured in nine pigs (18 kidneys) and compared with single-kidney GFR assessed from renal time-attenuation curves (TACs) obtained with EB CT before and after infusion of the vasodilator acetylcholine. CT-derived GFR was calculated with the original and modified Patlak methods and with previously validated extended gamma variate modeling of first-pass cortical TACs. Statistical analysis was performed to assess correlation between CT methods and inulin clearance for estimation of GFR with least-squares regression analysis and Bland-Altman graphical representation. Comparisons within groups were performed with a paired t test.

RESULTS

GFR assessed with the original Patlak method indicated poor correlation with inulin clearance, whereas GFR assessed with the modified Patlak method (P < .001, r = 0.75) and with gamma variate modeling (P < .001, r = 0.79) correlated significantly with inulin clearance and indicated an increase in response to acetylcholine.

CONCLUSION

CT-derived estimates of GFR can be significantly improved by modifications in image analysis methods (eg, use of a cortical region of interest).

Cortical Perfusion and Tubular Function as Evaluated by Magnetic Resonance Imaging Correlates with Annual Loss in Renal Function in Moderate Chronic Kidney Disease

BACKGROUND

Chronic hypoxia is a well-recognized factor in the pathogenesis of chronic kidney disease (CKD). Loss of microcirculation is thought to lead to enhanced renal hypoxia, which in turn results in the development of fibrosis, a hallmark of progressive CKD. To evaluate the role of functional magnetic resonance imaging (MRI), we performed perfusion, oxygenation, and diffusion MRI measurements in individuals with diabetes and stage 3 CKD.

METHODS

Fifty-four subjects (41 individuals with diabetes and stage 3 CKD and 13 healthy controls) participated in this study. Data with blood oxygenation level dependent (BOLD), arterial spin labeling perfusion and diffusion MRI were acquired using a 3T scanner.

RESULTS

Renal cortical perfusion was reduced in CKD compared to the controls (109.54 ± 25.38 vs. 203.17 ± 27.47 mL/min/100 g; p < 0.001). Cortical apparent diffusion coefficient showed no significant reduction in CKD compared to controls (1,596.10 ± 196.64 vs. 1,668.72 ± 77.29 × 10-6 mm2/s; p = 0.45) but was significantly associated with perfusion. Cortical R2* values were modestly increased in CKD (20.76 ± 4.08 vs. 18.74 ± 2.37 s-1; p = 0.12). Within the CKD group, R2*_Medulla and R2*_Kidney were moderately and negatively associated with estimated glomerular filtration rate. There was a significant association between cortical perfusion and medullary response to furosemide with annual loss of renal function, used as an estimate of CKD progression.

CONCLUSIONS

Subjects with a moderate degree of CKD had significantly lower renal perfusion. Diffusion and BOLD MRI showed more modest differences between the groups. Individuals with progressive CKD had lower perfusion and response to furosemide.

99mTc renal tubular function agents: current status

Orthoiodohippuric (OIH) acid labeled with 131I is a widely used renal radiopharmaceutical agent and has been the standard radiopharmaceutical agent for the measurement of effective renal plasma flow (EPRF). Limitations to the routine clinical use of 131I OIH are related to the suboptimal imaging properties of the 131I radionuclide and its relatively high radiation dose. 123I has been substituted for 131I; however, its high cost and short shelf-life have limited its widespread use. Recent work has centered on the development of a new 99mTc renal tubular function agent, which would use the optimal radionuclidic properties and availability of 99mTc and combine the clinical information provided by OIH. The search for a suitable 99mTc renal tubular function agent has focused on the diamide dithiolate (N2S2), the paraaminohippuric iminodiacetic acid (PAHIDA), and the triamide mercaptide (N3S) donor ligand systems. To date, the most promising 99mTc tubular function agent is the N3S complex: 99mTc mercaptoacetyltriglycine (99mTc MAG3). Studies in animal models in diuresis, dehydration, acid or base imbalance, ischemia, and renal artery stenosis demonstrate that 99mTc MAG3 behaves similarly to 131I OIH. A simple kit formulation is available that yields the 99mTc MAG3 complex in high radiochemical purity. Studies in normal subjects and patients indicate that 99mTc MAG3 is an excellent 99mTc renal tubular agent, but its plasma clearance is only 50% to 60% that of OIH. In an effort to develop an improved 99mTc renal tubular function agent, changes have been made in the core N3S donor ligand system, but to date no agent has been synthesized that is clinically superior to 99mTc MAG3.

Prevention of renal tubule re-absorption of radiometal (indium-111) labelled Fab fragment of a monoclonal antibody in mice by systemic administration of lysine

Systemic administration of lysine to mice injected with indium-111-labelled Fab fragment of a monoclonal antibody has been shown to reduce renal uptake/retention of the radiometal. This treatment should be applicable to clinical immunoscintigraphy and radioimmunotherapy with radiometal-labelled antibody fragments.

Glomerular and tubular function in glycogen storage disease

Urinary protein and calcium excretion were assessed in 77 patients with the hepatic glycogen storage diseases (GSD): 30 with GSD-I (median age 12.4 years, range 3.2-32.9 years), 25 with GSD-III (median age 10.5 years, range 4.2-31.3 years) and 22 with GSD-IX (median age 11.8 years, range 1.2-35.4 years). Inulin (Cinulin) and para-aminohippuric acid (CPAH) clearances were also measured in 33 of these patients. Those with GSD-I had significantly greater albumin (F = 15.07, P < 0.001), retinol-binding protein (RBP) (F = 14.66, P < 0.001), N-acetyl-beta-D-glucosaminidase (NAG) (F = 9.41, P < 0.001) and calcium (F = 7.41, P = 0.001) excretion than those with GSD-III and GSD-IX. GSD-I patients (n = 18) also had significantly higher Cinulin (F = 5.57, P = 0.009), but CPAH did not differ (F = 0.77, NS). Renal function was normal in GSD-III and GSD-IX patients. In GSD-I, Cinulin (r = -0.51, P = 0.03) and NAG excretion (r = -0.40, P = 0.03) were inversely correlated with age, whereas albumin excretion was positively correlated with age (r = +0.41, P = 0.03). RBP and calcium excretion were generally high throughout all age groups. Hyperfiltration in GSD-I is associated with renal tubular proteinuria that occurs before the onset of significant albuminuria. Deficiency of glucose-6-phosphatase within the proximal renal tubule may primarily cause tubular dysfunction, glomerular hyperfiltration being a secondary phenomenon.

The development of x-ray imaging to study renal function

The well-established role of the kidney in control of blood volume and ultimately arterial blood pressure has been underscored by the demonstration of alterations in renal hemodynamics and function recognized as responsible for these and other regulatory mechanisms. Nevertheless, the spatial complexity of intrarenal structure and function has made evident the need to study these separately in different regions of the intact kidney. Because of the introduction of x-rays, assessment of renal function has indeed been one of their attractive applications. However, despite the appeal of their noninvasiveness, several limitations confounded the different x-ray techniques used, most of which remained unresolved until the development of computed tomography. Furthermore, the development of fast imaging, which allows repetitive analysis of the same region of interest during the transit of contrast medium, holds a great potential to estimate intrarenal distribution of blood flow and the dynamic characteristics of tubular fluid flow in individual nephron segments. This latter assessment requires the administration of filterable x-ray contrast medium, which is cleared from the plasma almost exclusively by glomerular filtration, and the generation of contrast dilution curves. A historical review of the development and progress of the various x-ray techniques used will help understand the past and present of x-ray imaging, and will make it easier to envision the importance of their future roles in the study of renal physiology and pathophysiology.

Decreased renal uptake of (99m)Tc-DMSA in patients with tubular proteinuria

Although technetium-99m-dimercaptosuccinic acid ((99m)Tc-DMSA) renal scans are widely used to evaluate renal tubular mass function, the mechanism by which renal uptake of DMSA occurs is still the subject of debate. Patients with various proximal tubular disorders show markedly decreased renal DMSA uptake, even when there is normal creatinine clearance. We measured the renal uptake of (99m)Tc-DMSA 3 h after its injection in 13 patients with Dent disease or Lowe syndrome, both of which are typical proximal tubular disorders with defective megalin and cubilin-mediated endocytosis. Serial images of three patients were also obtained at 0.5, 1, 2 and 3 h post-injection. The correlations between renal uptake of (99m)Tc-DMSA and creatinine clearance and the degrees of acidemia and tubular proteinuria were then evaluated. The renal uptake of (99m)Tc-DMSA was markedly decreased in all patients, and the decreased uptake was detected in all serial images. In contrast, bladder radioactivity was higher than normal in all of the serial images when compared to renal radioactivity. Additionally, the uptake of (99m)Tc-DMSA was inversely proportional to the amount of urine beta(2)-microglobulin. These results strongly suggest that DMSA is filtered in the glomeruli and subsequently undergoes megalin- and cubilin-mediated endocytosis in the proximal tubules.

Diagnosis of Caroli disease by computed tomography: report of two cases

Two patients are discussed in whom Caroli diseases was diagnosed with the aid of computed tomography (CT). One patient had the pure form of the disease, characterized primarily by saccular dilatation of the intrahepatic bile ducts and clinically manifesting as recurrent cholangitis. The second patient had a form ccharacterized primarily by hepatic fibrosis and clinically manifesting as portal hypertension. These are the first patients studied with CT to be reported to the authors' knowledge; CT is recommended as the optimal noninvasive method to evaluate such patients.

Molecular imaging of the kidneys

Radionuclide imaging of the kidneys with gamma cameras involves the use of labeled molecules seeking functionally critical molecular mechanisms to detect the pathophysiology of the diseased kidneys and achieve an early, sensitive, and accurate diagnosis. The most recent imaging technology, positron emission tomography, permits quantitative imaging of the kidney at a spatial resolution appropriate for the organ. H(2)(15)O, (82)RbCl, and [(64)Cu] ETS are the most important radiopharmaceuticals for measuring renal blood flow. The renin angiotensin system is the most important regulator of renal blood flow; this role is being interrogated by detecting angiotensin receptor subtype angiotensin subtype 1 receptor by the use of in vivo positron emission tomography. Membrane organic anion transporters are important for the function of the tubular epithelium; therefore, Tc99m MAG3 as well as some novel radiopharmaceuticals, such as copper-64 labeled mono oxo-tetraazamacrocyclic ligands, have been used for molecular renal imaging. In addition, other radioligands that interact with the organic cation transporters or peptide transporters have been developed. Focusing on early detection of kidney injury at the molecular level is an evolving field of great significance. Potential imaging targets are the kidney injury molecule 1, which is highly expressed in kidney injury and renal cancer but not in normal kidneys. Although pelvic clearance, in addition to parenchymal transport, is an important measure in obstructive nephropathy, techniques that focus on up-regulated molecules in response to tissue stress resulting from obstruction will be of great implication. Monocyte chemoattractant protein-1 is a well-suited molecule here. The greatest advances in molecular imaging of the kidneys have been recently achieved in detecting renal cancer. In addition to the ubiquitous [(18)F] fluorodeoxyglucose, other radioligands, such as [(11)C] acetate and anti-1-amino-3-[18F]fluorocyclobutane-1-carboxylic acid, have emerged. Radioimmunoimaging with [(124)I] G250 could lead to radioimmunotherapy for renal cancer. Considering the increasing age of general population, the incidence of kidney diseases, such as atherosclerosis, diabetic nephropathy, and cancer, is expected to increase. Successful management of these diseases offers an opportunity and a challenge for development of novel molecular imaging technologies.

Weight-gain induced changes in renal perfusion assessed by contrast-enhanced ultrasound precede increases in urinary protein excretion suggestive of glomerular and tubular injury and normalize after weight-loss in dogs

Early detection of obesity-related glomerulopathy in humans is challenging as it might not be detected by routine biomarkers of kidney function. This study's aim was to use novel kidney biomarkers and contrast-enhanced ultrasound (CEUS) to evaluate the effect of obesity development and weight-loss on kidney function, perfusion, and injury in dogs. Sixteen healthy lean adult beagles were assigned randomly but age-matched to a control group (CG) (n = 8) fed to maintain a lean body weight (BW) for 83 weeks; or to a weight-change group (WCG) (n = 8) fed the same diet to induce obesity (week 0-47), to maintain stable obese weight (week 47-56) and to lose BW (week 56-83). At 8 time points, values of systolic blood pressure (sBP); serum creatinine (sCr); blood urea nitrogen (BUN); serum cystatin C (sCysC); urine protein-to-creatinine ratio (UPC); and urinary biomarkers of glomerular and tubular injury were measured. Glomerular filtration rate (GFR) and renal perfusion using CEUS were assayed (except for week 68). For CEUS, intensity- and time-related parameters representing blood volume and velocity were derived from imaging data, respectively. At 12-22% weight-gain, cortical time-to-peak, representing blood velocity, was shorter in the WCG vs. the CG. After 37% weight-gain, sCysC, UPC, glomerular and tubular biomarkers of injury, urinary immunoglobulin G and urinary neutrophil gelatinase-associated lipocalin, respectively, were higher in the WCG. sBP, sCr, BUN and GFR were not significantly different. After 23% weight-loss, all alterations were attenuated. Early weight-gain in dogs induced renal perfusion changes measured with CEUS, without hyperfiltration, preceding increased urinary protein excretion with potential glomerular and tubular injury. The combined use of routine biomarkers of kidney function, CEUS and site-specific urinary biomarkers might be valuable in assessing kidney health of individuals at risk for obesity-related glomerulopathy in a non-invasive manner.

High-resolution ultrasonography in the differential diagnosis of cystic diseases of the kidney in infancy and childhood: preliminary experience

Autosomal recessive polycystic kidney disease, autosomal dominant polycystic disease, and glomerulocystic disease may all appear in the perinatal period as bilaterally enlarged echogenic kidneys. Current ultrasonographic equipment can better demonstrate the underlying pathologic state and assist in the differentiation of these conditions. The primary abnormality in autosomal recessive polycystic kidney disease is at the level of the collecting ducts, which are dilated and saccular. The nephrons remain normal. These dilated ectatic tubules are seen in their usual distribution as a radial array, with major ducts being perpendicular to the renal capsule, in both the renal cortex and the medulla. The peripheral renal cortex does not normally contain collecting ducts and remains unaffected in patients with mild disease. Autosomal dominant polycystic disease is characterized by cystic changes involving both the nephron and the collecting ducts. The nephron may become cystic at any point. Multiple discrete cysts of varying sizes are seen in both the renal cortex and the medulla in the severely affected infant. Subcapsular cysts are seen regularly. Glomerulocystic disease is an unusual sporadic condition characterized by the cystic dilation of the space of Bowman and the proximal convoluted tubule. On ultrasonographic examination tiny, isolated cysts, usually smaller than those occurring in autosomal dominant polycystic kidney disease, are seen in the echogenic renal cortex and may extend to the periphery of the kidney. No cysts are seen in the renal medulla. Correlation between pathologic findings and sonographic images is of value in correctly diagnosing these conditions.

Noninvasive quantitative magnetization transfer MRI reveals tubulointerstitial fibrosis in murine kidney

Excessive tissue scarring, or fibrosis, is a critical contributor to end stage renal disease, but current clinical tests are not sufficient for assessing renal fibrosis. Quantitative magnetization transfer (qMT) MRI provides indirect information about the macromolecular composition of tissues. We evaluated measurements of the pool size ratio (PSR, the ratio of immobilized macromolecular to free water protons) obtained by qMT as a biomarker of tubulointerstitial fibrosis in a well-established murine model with progressive renal disease. MR images were acquired from 16-week-old fibrotic hHB-EGF^Tg/Tg mice and normal wild-type (WT) mice (N = 12) at 7 T. QMT parameters were derived using a two-pool five-parameter fitting model. A normal range of PSR values in the cortex and outer stripe of outer medulla (CR + OSOM) was determined by averaging across voxels within WT kidneys (mean ± 2SD). Regions in diseased mice whose PSR values exceeded the normal range above a threshold value (tPSR) were identified and measured. The spatial distribution of fibrosis was confirmed using picrosirius red stains. Compared with normal WT mice, scattered clusters of high PSR regions were observed in the OSOM of hHB-EGF^Tg/Tg mouse kidneys. Moderate increases in mean PSR (mPSR) of CR + OSOM regions were observed across fibrotic kidneys. The abnormally high PSR regions (% area) detected by the tPSR were significantly increased in hHB-EGF^Tg/Tg mice, and were highly correlated with regions of fibrosis detected by histological fibrosis indices measured from picrosirius red staining. Renal tubulointerstitial fibrosis in OSOM can thus be assessed by qMT MRI using an appropriate analysis of PSR. This technique may be used as an imaging biomarker for chronic kidney diseases.

Renal tubular dysgenesis: a description of early renal maldevelopment in siblings

A family is described in which three siblings, born after pregnancies complicated by oligohydramnios, developed renal abnormalities. In the first infant, of 38 weeks gestation, histologic changes were nearly identical to those found in renal tubular dysgenesis (RTD), a recently identified disorder characterized by the absence of recognizable renal proximal tubules. Additional findings include bilateral renal vein thrombosis and marked calvarial bone hypoplasia. The other two gestations were 20 and 22 weeks long. Renal histology in these cases showed nonspecific abnormalities with focal tubular dilatation, decreased tubule formation, and increased interstitial connective tissue. Clearly recognizable proximal tubules were present, though decreased in number. The latter two gestations described herein are the earliest examined in a family with RTD and the renal abnormalities may represent early changes seen in this disorder.

Causes of increased renal medullary echogenicity in Turkish children

The primary disorders of 50 children with increased renal medullary echogenicity on renal ultrasound were studied; 28 girls and 22 boys aged from 1 month to 16 years were classified into four groups based on underlying disease and ultrasound findings. Group 1 was composed of 17 patients with distal renal tubular acidosis (34%); intense echoes throughout the pyramid were predominant. Group 2 consisted of 14 patients with vitamin D toxicity (28%) and an intense echogenic rim around the pyramids. Group 3 included 10 patients with different types of tubulopathies. A slight hyperechogenic rim around the sides and tip of the medullary pyramids was detected. Group 4 was made up of 9 patients with rare underlying conditions. Abdominal X-rays detected medullary calcinosis in only 12 (24%) of the total 50 patients. Ultrasonography appears to be an important tool in the early diagnosis of increased renal medullary echogenicity and medullary nephrocalcinosis.

Comparison of Tc-99m DTPA and Tc-99m MAG3 Perfusion Time-Activity Curves in Patients With Renal Allograft Dysfunction

AIM

The perfusion time-activity curve on DTPA renal scintigraphy shows a peak and plateau pattern which is usually absent or less marked when using tubular agents such as MAG3. The exact mechanism that results in this difference between the two tracers is not well understood. A descending pattern on MAG3 has been proposed to be due to decreased extraction. In this study we compared the diagnostic utility of perfusion patterns obtained with DTPA and MAG3 among patients with renal allograft dysfunction.

MATERIALS AND METHODS

This study included 48 patients with renal allograft dysfunction and 18 recipients with normal graft function. Every recipient had renal scintigraphy with Tc-99m MAG3 and Tc-99m DTPA 1 day apart. The second phase of the perfusion curve after the initial rise was classified as ascending, flat, or descending. In patients with a descending curve on DTPA study, we calculated the ratio of counts at peak perfusion to that at plateau (P:PL). Impaired perfusion was based on a deterioration of the peak-to-plateau pattern on DTPA and the presence of a flat-descending curve on MAG3.

RESULTS

In patients with dysfunction, impaired perfusion was observed in 77% of DTPA and in 54% of MAG3 studies. A flat-descending curve on MAG3 was present in 44% of patients with normal graft function. By MAG3, 67% of acute rejection and 28% of chronic allograft nephropathy (CAN) cases showed deteriorated perfusion. The corresponding values for DTPA were 67% and 94%, respectively. A flat-ascending pattern on DTPA was more frequent in CAN than it was in acute rejection (33% and 17%, respectively).

CONCLUSION

The sensitivity of DTPA perfusion pattern for diagnosing dysfunction was significantly greater than that for MAG3. Our results suggest that the major determinant of a curve pattern on DTPA or MAG3 study is the extraction relative to perfusion. Thus for patients with CAN, extraction is higher relative to perfusion, resulting in a lower P:PL ratio or an ascending curve on DTPA. Although the extraction of DTPA is less than that of MAG3, this level of extraction renders DTPA more sensitive to serial changes in renal function and pathophysiological mechanisms related to kidney function.

Non-invasive evaluation of bilateral renal regional blood flow and tubular dynamics during acute unilateral ureteral obstruction

BACKGROUND

Global renal haemodynamic responses to acute unilateral ureteral obstruction (AUUO) have been studied extensively in animals, yet little is known about the concurrent changes in haemodynamics and tubular fluid dynamics that occur within the distinct regions of the kidney during AUUO. The advent of electron beam computerized tomography (EBCT) now allows us to evaluate non-invasively intrarenal haemodynamics and tubular fluid dynamics in vivo.

METHODS

Using EBCT, we quantified total, cortical and medullary renal blood flow (RBF, C-RBF and M-RBF), and the concurrent intratubular fluid contrast concentration (ITCC) from contrast media dilution curves, prior to, and at 30 and 90 min after the onset of AUUO in five pigs.

RESULTS

At 30 min after AUUO, there was a small 17+/-7% fall in C-RBF that did not quite reach significance (P = 0.076), whereas RBF, M-RBF, glomerular filtration rate (GFR) and ITCC were preserved. At 90 min, both C-RBF and RBF had fallen by 54+/-8 and 45+/-5%, respectively (P<0.05). GFR also tended to decrease (by 49+/-8%, P<0.06), whereas there was preservation of M-RBF. ITCC increased in the proximal and distal tubules, and tended to increase in Henle's loop. In the contralateral kidney, AUUO did not alter the haemodynamics, but transiently decreased ITCC in all tubular segments.

CONCLUSION

EBCT allows evaluation of AUUO-induced changes in intrarenal haemodynamics and tubular fluid dynamics. AUUO decreased cortical, but not medullary perfusion of the ipsilateral kidney, and increased the ITCC in most tubular segments, suggesting increased tubular reabsorption that may have helped maintain GFR and tubular fluid flow.

Significance of early tubular extraction in the first minute of Tc-99m MAG3 renal transplant scintigraphy

Renal transplant perfusion curves obtained using Tc-99m MAG3 differ from those with Tc-99m DTPA. The perfusion curve can be divided into a first phase (up to the first-pass peak) and a second phase (the curve after the initial peak). The second phase of the MAG3 perfusion curve is usually ascending in contrast to the descending Tc-99m DTPA curve. This ascending MAG3 curve reflects early tubular extraction of MAG3. However, the second phase of the MAG3 curve is sometimes flat or descending. We hypothesized that a flat or descending curve reflects poor early tubular extraction and therefore graft dysfunction. Ninety-two studies of 59' renal transplant patients were retrospectively reviewed. The second phase of the perfusion curve was visually classified as ascending, flat, or descending. 77.2% of studies had ascending curves, 16.3% flat curves, and 6.5% descending curves. A descending curve had a positive predictive value (PPV) of 100% for medical graft dysfunction, while a flat curve had a PPV of 93.3%. A nonascending second phase curve was specific (96.4%) but not sensitive (33.9%) for graft dysfunction. Patients with acute tubular necrosis were not significantly more likely to have a nonascending curve than those with acute rejection. There was no significant difference in creatinine level between patients with medical graft dysfunction and ascending vs. nonascending curves. A nonascending second phase Tc-99m MAG3 perfusion curve is predictive for graft dysfunction. An ascending curve is nonspecific and can be seen in both normally and poorly functioning grafts.