Is kidney length a good predictor of kidney volume?

A Study of Normal Renal Dimensions at Ultrasonography and Their Influencing Factors in an Indian Population

Background: Kidney dimensions play one of the most vital roles in the diagnosis and identification of any renal disease. Renal dimensions are generally used in clinical practices to determine the size of the kidney as well as correlate with renal function to have a better understanding of acute and chronic renal diseases. This study aimed to find out the normal renal dimensions with the help of ultrasonography and their impact on the Indian population. Methods: Renal dimensions, which include parenchymatous thickness and length as well as the width of about 60 healthy adult Indian populations, were estimated with the help of sonography, and a detailed study has been performed on the difference observed based on age, sex, height, weight, body mass index, and body surface area. Results: There was no particular difference found on the basis of width and length between the left and right kidneys; however, the parenchymal thickness between the left and right has been shown to have a significant difference. The mean width, length, and parenchymal thickness were 4.6 ± 0.43, 9.64 ± 0.62, and 2.03 ± 0.1 cm, respectively. While doing estimation based on gender, it has been observed that there is a noticeable difference in width but no difference in height or parenchymal thickness. A significant diversity has been observed in patients in age groups above 49 compared to other age groups. A positive correlation with body weight, body height, and body mass index has also been observed in some cases. Conclusion: The given study has attempted to define the standard reference for renal dimension in the Indian census. The observations made in the given study demonstrated the possibility of renal dimensions being smaller in the Indian population in contrast to those of the Western population, which are much larger.

The old becomes new: advances in imaging techniques to assess nephron mass in children

Renal imaging is widely used in the assessment of surrogate markers of nephron mass correlated to renal function. Autopsy studies have tested the validity of various imaging modalities in accurately estimating "true" nephron mass. However, in vivo assessment of nephron mass has been largely limited to kidney volume determination by ultrasonography (US) in pediatric populations. Practical limitations and risks create challenges in incorporating more precise 3D volumetric imaging, like magnetic resonance imaging (MRI), and computed tomography (CT) technologies, compared to US for routine kidney volume assessment in children. Additionally, accounting for structural anomalies such as hydronephrosis when estimating renal parenchymal area in congenital anomalies of the kidney and urinary tract (CAKUT) is important, as it correlates with chronic kidney disease (CKD) progression. 3D imaging using CT and MRI has been shown to be superior to US, which has traditionally relied on 2D measurements to estimate kidney volume using the ellipsoid calculation. Recent innovations using 3D and contrast-enhanced US (CEUS) provide improved accuracy with low risk. Indexing kidney volume to body surface area in children is an important standard that may allow early detection of CKD progression in high-risk populations. This review highlights current understanding of various imaging modalities in assessing nephron mass, discusses applications and limitations, and describes recent advances in the field of imaging and kidney disease. Although renal imaging has been a long-standing, essential tool in assessing kidney disease, innovation and new applications of established technologies provide important tools in the study and management of kidney disease in children.

A Comparability of Renal Length and Volume Measurements in MRI and Ultrasound in Children

Introduction: Despite the significant increase in use of magnetic resonance imaging (MRI) in children, there is still a lack of normal reference values of renal size in this method and reference values are being interpolated from the ultrasound (US) studies. The study provides comparative analysis of agreement in renal length and volume measurements between MRI and ultrasound. Materials and Methods: Ninety-three children with a mean age of 8.0 ± 6.0 years, who had undergone both renal US and MRI exams, were included in the study. Participants were divided into three subgroups; each kidney was considered separately. Group 1 included 106 kidneys without any anomalies. Group 2 comprised 48 kidneys with a dilated collecting system. Group 3 included 32 kidneys with a duplicated collecting system. Measurements were taken in three dimensions, and renal volume was calculated from the ellipsoid formula. Results: We found no significant difference between US and MRI measurements in Group 1 and Group 2. In Group 3, the difference between measurements in both imaging methods was significant. The mean difference varied from 0.05% in Group 1, 2.95% in Group 2, to 4.99% in Group 3. Conclusion: The US and MRI are comparable methods in renal size measurements. The interpolation of sonographic renal length and volume reference values to the MRI in the pediatric population is justified, as there is a strong agreement between both methods. Both methods can be used interchangeably for following up of the renal size changes in the pediatric population.

Estimation of nephron number in living humans by combining unenhanced computed tomography with biopsy-based stereology

Methods for estimating nephron number in a clinical setting may be useful for predicting renal outcomes. This study aimed to establish such a method using unenhanced computed tomography (CT) and biopsy-based stereology. Patients or living kidney donors simultaneously subjected to enhanced and unenhanced CT examinations were randomly assigned to development and validation groups. The enhanced CT-measured arterial phase and the venous phase images of kidneys were regarded as the true values for cortical volume and parenchymal volume, respectively. Linear multiple regression analysis was used to create models for estimating cortical volume using explanatory variables including unenhanced CT-measured parenchymal volume. Nephron number was determined as the product of cortical volume and the glomerular density in biopsies of donors. Five equations for estimating cortical volume were created and verified. In donors, estimated nephron number by unenhanced CT was consistent with that by enhanced CT, with minimal errors in all models (636–655 ± 210–219 vs. 648 ± 224 × 10³/kidney). Clinical characteristics combined with parenchymal volume did not improve the equation over parenchymal volume alone. These results support the feasibility of estimating nephron number by a combination of unenhanced CT and biopsy-based stereology, with a possible application for renal disease patients who are often not suitable for contrast media.

A useful method for assessing differences of compensatory hypertrophy in the contralateral kidney before and after radical nephrectomy in patients with renal cell carcinoma: ellipsoid formula on computed tomography

OBJECTIVE

To investigate the usefulness of the ellipsoid formula for assessing compensatory hypertrophy of the contralateral kidney on pre-operative and post-operative CT in renal cell carcinoma (RCC) patients.

METHODS

We retrospectively identified 389 patients who had radical nephrectomy for RCC between 2011  and 2015. Contrast-enhanced CT was performed within 3 months pre-operative and at 1 year post-operative. The kidney volumes were calculated from CT using the ellipsoid formula. We subdivided patients into three groups based on tumour size (I: ≤4 cm, II: 4-7 cm, III: >7 cm). Volumetric renal parameters were compared and multivariate analyses were performed to determine predictors associated with pre-operative  and post-operative compensatory hypertrophy.

RESULTS

Kidney volume calculation using the ellipsoid  method took a median of 51 s. Group III had a significantly larger median pre-operative contralateral renal volume than Groups I and II (I:  140.4, II: 141.6, III: 166.7 ml, p < 0.05). However, the median ratio of post-operative contralateral renal volume change was significantly higher in Groups I and II than Group III (I: 0.36, II: 0.23, III: 0.12, p < 0.001). On multivariate analysis, tumour size revealed the strongest positive association with pre-operative contralateral kidney volume (partial regression coefficient: β = 30.8, >7 cm) and ratio of post-operative contralateral kidney volume change (β  = 0.214, I vs III; β = 0.168, II vs III).

CONCLUSION

Kidney volume calculation for assessing pre- and post-operative compensatory hypertrophy of the contralateral kidney in RCC patients can be easily and rapidly performed from CT images using the ellipsoid formula. Advances in knowledge: The ellipsoid formula allows reliable method for assessing pre-operative and post-operative compensatory hypertrophy of the contralateral kidney in RCC.

An equation to estimate the renal cortex volume in chronic kidney disease patients

BACKGROUND

The renal cortex volume is associated with the kidney function and chronic kidney disease (CKD) risk factors, and it may also be a prognostic factor. We aimed to create an equation to estimate the renal cortex volume of CKD patients in day-to-day clinical practice.

METHODS

The subjects included 116 ethnic Japanese CKD patients who were ≥ 18 years of age. The renal size (length, width and thickness) was measured by ultrasound. The body height, weight, year of age, sex, birth weight, gestational age, diabetes status, hypertension status, family history of CKD and dialysis and estimated glomerular filtration rate (eGFR) were collected as expected dependent variables. We made models for the equation regarding the renal cortex volume measured by non-contrast magnetic resonance imaging as a true renal cortex volume. Stepwise multiple linear regression analyses were performed with the log-transformation of dependent and independent variables. The accuracy of the models was compared using the leave one out cross-validation method.

RESULTS

The estimated volume of the renal cortex (cm³) = 0.012 × renal length (cm)^0.92 × width (cm)^0.53 × body weight (kg)^0.40 × body height (cm)^0.67 × eGFR (ml/min/1.73 m²)^0.22 × 1.12 if diabetes. The adjusted R ² value and the accuracy within 30 and 50% were 0.73, 0.94 and 0.99, respectively.

CONCLUSIONS

This study provided a new method for estimating the renal cortex volume in day-to-day clinical practice.

The evaluation and comparison of kidney length obtained from axial cuts in spiral CT scan with its true length

Background:

Increased size of kidney is the main symptom of pyelonephritis and renal ischemia in children. Ultrasound and computed tomography (CT) scan methods are the imaging methods for evaluating the urogenital system. The aim of this study is to compare the kidney length obtained from spiral CT scan with the true length obtained from multi-slice CT.

Materials and Methods:

From 100 patients 200 kidneys were examined in Alzahra Hospital in 2012. Multi-slice CT was used to obtain coronal and sagittal cuts to find the length of kidneys.

Results:

The mean values of true size of axial sections of the right and left kidneys were 108.37 ± 12.3 mm and 109.74 ± 13.6 mm, respectively. The mean difference of axial sections’ lengths in the right and left kidneys was 1.37 ± 1.22 mm. The mean values of length in the spiral CT scan of the right and left kidneys were 98.61 ± 15.8 mm and 103.11 ± 15.9 mm, respectively. The difference in the estimated size by multi-slice CT scan in oblique and axial images was significant (9.77 ± 1.19 mm and 6.63 ± 0.8 mm for the right and left kidneys, respectively (P < 0.001).

Conclusion:

The average size of both kidneys determined in axial images was smaller than the actual size. The estimation of kidney size in axial images is not reliable, and to obtain the actual size, it is required to have the coronal and sagittal cuts with proper quality, which could be achieved by multi-slice method.

Correlation between CT-based measured renal volumes and nuclear-renography-based split renal function in living kidney donors. Clinical diagnostic utility and practice patterns

INTRODUCTION

Living donor evaluation involves imaging to determine the choice of kidney for nephrectomy. Our aim was to study the diagnostic accuracy and correlation between CT-based volume measurements and split renal function (SRF) as measured by nuclear renography in potential living donors and its impact on kidney selection decision.

METHODS

We analyzed 190 CT-based volume measurements in healthy donors, of which 65 donors had a radionuclide study performed to determine SRF.

RESULTS

There were no differences in demographics, anthropometric measurements, total volumes, eGFR, creatinine clearances between those who required a nuclear scan and those who did not. There was a significant correlation between CT-volume-measurement-based SRF and nuclear-scan-based SRF (Pearson coefficient r 0.59; p < 0.001). Furthermore, selective nuclear-based SRF allowed careful selection of donor nephrectomy, leaving the donor with the higher functioning kidney in most cases. There was also a significantly higher number of right-sided nephrectomies selected after nuclear-based SRF studies.

CONCLUSION

CT-based volume measurements in living donor imaging have sufficient correlation with nuclear-based SRF. Selective use of nuclear-scan-based SRF allows careful selection for donor nephrectomy.

Effect of the duration of bladder overdistention on renal function and morphology in rats

The aim of this study was to investigate the influence of the duration of bladder overdistention (DOBO) on kidney structure and function in rats. Bladder overdistention was induced in male Sprague-Dawley rats by an infusion of saline. Forty rats were divided into five groups: DOBO 1, 2, 4 or 8 h groups and the control. Renal function was evaluated using serum creatinine (SCr) and blood urea nitrogen (BUN). Apoptotic indices and morphologic changes of the kidney were detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) staining and transmission electron microscopy (TEM). Compared with the control, rats undergoing 2, 4 or 8 h of overdistention showed significant, time-dependent increases in SCr (12.375 vs. 23.125, 34.375 and 51.500 μmol/l, respectively), BUN (6.980 vs. 18.689, 25.184 and 32.079 mmol/l, respectively), renal size (1.041 vs. 1.472, 1.484 and 1.634 cm³, respectively) and renal pelvis separation (0.000 vs. 0.223, 0.320, 0.308 and 0.277 cm, respectively; P<0.01). In the rats, 2, 4 and 8 h of overdistention elicited time-dependent increases in the blood flow rate in the main renal artery (MRA; 44.827 vs. 49.082, 59.688 and 67.123 cm³/sec, control vs. DOBO 2, 4 and 8 h), the interlobar renal artery (IRA; 32.095 vs. 39.16 and 51.745 cm³/sec, control vs. DOBO 4 and 8 h) and the segmental renal artery (SRA; 21.171 vs. 24.355 and 25.358 cm³/sec, control vs. DOBO 4 and 8 h; P<0.01). TUNEL results showed that prolonged overdistention increased the apoptotic index of renal cells significantly (1.15, 1.77, 3.40, 5.34 and 13.91% for control and DOBO 1, 2, 4 and 8 h, respectively; P<0.01) and TEM indicated that prolonged overdistention resulted in ultrastructural injuries of increased severity. DOBO plays a significant role in the functional and structural impairment of the rat kidney. With increasing duration, the hemodynamic changes, cell apoptosis and ultrastructural injuries of the kidney are more evident, all of which may contribute to the increasingly serious impairment of renal function and morphology.

Ultrasonographic renal sizes, cortical thickness and volume in Nigerian children with acute falciparum malaria

BACKGROUND

Utility of sonographic assessments of renal changes during malaria illness are rarely reported in African children in spite of the high burden of malarial-related kidney damage.

METHODS

In this case-control study, renal sizes, cortical thickness and volume of the kidneys of 131 healthy children and 170 with acute falciparum malaria comprising 85 uncomplicated malaria (UM) and 85 complicated malaria (CM) cases, measured within 24 hours of presenting in the hospital were compared.

RESULTS

The mean age of children with UM, CM and control groups was 49.7 ± 26.2 months, 50.7 ± 29.3 months and 73.4 ± 25.5 months, respectively (p < 0.001). The mean right kidney length of CM group was higher than control by 0.41cm (95% CI = 0.16, 0.65; p < 0.001) and UM by 0.32 cm (95% CI = 0.02, 0.62; p = 0.030). Similarly, mean left kidney length of CM was higher than control and UM by 0.34 cm (95% CI = 0.09, 0.60; p = 0.005) and 0.41cm (95% CI = 0.09, 0.72; p = 0.006), respectively. Estimated mean renal volume of the CM group was significantly higher than control group by 7.82 cm(3) for right and by 5.79 cm(3) for left kidneys respectively; in the UM group by 9.31cm(3) for right and 8.87 cm(3) for left kidneys respectively.

CONCLUSION

There was a marginal increase in renal size of children with Plasmodium falciparum infection, which worsened with increasing severity of malaria morbidity. Ultrasonography provides important information for detecting renal changes in children with acute malaria.

Estimation of feline renal volume using computed tomography and ultrasound

Renal volume estimation is an important parameter for clinical evaluation of kidneys and research applications. A time efficient, repeatable, and accurate method for volume estimation is required. The purpose of this study was to describe the accuracy of ultrasound and computed tomography (CT) for estimating feline renal volume. Standardized ultrasound and CT scans were acquired for kidneys of 12 cadaver cats, in situ. Ultrasound and CT multiplanar reconstructions were used to record renal length measurements that were then used to calculate volume using the prolate ellipsoid formula for volume estimation. In addition, CT studies were reconstructed at 1 mm, 5 mm, and 1 cm, and transferred to a workstation where the renal volume was calculated using the voxel count method (hand drawn regions of interest). The reference standard kidney volume was then determined ex vivo using water displacement with the Archimedes' principle. Ultrasound measurement of renal length accounted for approximately 87% of the variability in renal volume for the study population. The prolate ellipsoid formula exhibited proportional bias and underestimated renal volume by a median of 18.9%. Computed tomography volume estimates using the voxel count method with hand-traced regions of interest provided the most accurate results, with increasing accuracy for smaller voxel sizes in grossly normal kidneys (-10.1 to 0.6%). Findings from this study supported the use of CT and the voxel count method for estimating feline renal volume in future clinical and research studies.

Noninvasive and direct measures of kidney size in kidney donors

BACKGROUND

Kidney size is important for clinical assessment of kidney disease. This study was performed to determine the usefulness of radiologic methods for predicting direct measurements of kidney size.

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

139 living kidney donors were enrolled.

INDEX TEST

Body mass index, body surface area, and total-body water were estimated from body height and weight. Kidney lengths were estimated using ultrasound sonography (US) and computed tomography (CT), and kidney volumes were estimated from CT scans using the ellipsoid and voxel-count methods.

REFERENCE TEST

Kidney length and weight were measured directly after donor nephrectomy.

RESULTS

Mean measured kidney length and weight were 11.5 ± 0.9 cm and 188.5 ± 33.5 g, respectively. All body indexes correlated with measured size of the left kidney; the highest correlation was between body weight and measured kidney weight (γ = 0.54; P < 0.001). The difference between measured and estimated lengths was greater for US than for CT (-1.1 ± 0.9 cm for US [P < 0.001] vs -0.7 ± 0.7 cm for CT [P < 0.001]). Bland-Altman analysis showed that limits of agreement between CT estimates and measured kidney length (-0.62 to 2.75 cm) were narrower than those between US estimates and measured kidney length (-0.78 to 2.15 cm). Correlation coefficients between radiologic estimates and measured kidney weight were 0.41 and 0.49 for US and CT estimates of kidney length and 0.72 and 0.79 for volume estimates using the ellipsoid and voxel-count methods, respectively (all P < 0.01).

LIMITATIONS

No direct measurement of kidney volume.

CONCLUSIONS

CT estimation of kidney length is more accurate than US estimation, and CT estimation of kidney volume using the voxel-count method is most useful to predict kidney weight.

Normal kidney size and its influencing factors - a 64-slice MDCT study of 1.040 asymptomatic patients

BACKGROUND

Normal ultrasound values for pole-to-pole kidney length (LPP) are well established for children, but very little is known about normal kidney size and its influencing factors in adults. The objectives of this study were thus to establish normal CT values for kidney dimensions from a group of unselected patients, identify potential influencing factors, and to estimate their significance.

METHODS

In multiphase thin-slice MDCTs of 2.068 kidneys in 1.040 adults, the kidney length pole to pole (LPP), parenchymal (PW) and cortical width (CW), position and rotation status of the kidneys, number of renal arteries, pyelon width and possible influencing factors that can be visualized, were recorded from a volume data set. For length measurements, axes were adjusted individually in double oblique planes using a 3D-software. Analyses of distribution, T-tests, ANOVA, correlation and multivariate regression analyses were performed.

RESULTS

LPP was 108.5 +/- 12.2 mm for the right, and 111.3 +/- 12.6 mm for the left kidney (p < 0.0001 each). PW on the right side was 15.4 +/- 2.8 mm, slightly less than 15.9 +/- 2.7 mm on the left side (p < 0.0001), the CW was the same (6.6 +/- 1.9 mm). The most significant independent predictors for LPP, CW, and PW were body size, BMI, age, and gender (p < 0.001 each). In men, the LPP increases up to the fifth decade of life (p < 0.01). It is also influenced by the position of the kidneys, stenoses and number of renal arteries (SRA/NRA), infarctions suffered, parapelvic cysts, and absence of the contralateral kidney; CW is influenced by age, position, parapelvic cysts, NRA and SRA, and the PW is influenced in addition by rotation status (p < 0.05 each). Depending on the most important factors, gender-specific normal values were indicated for these dimensions, the length and width in cross section, width of the renal pelvis, and parenchyma-renal pyelon ratio.

CONCLUSIONS

Due to the complex influences on kidney size, assessment should be made individually. The most important influencing factors are BMI, height, gender, age, position of the kidneys, stenoses and number of renal arteries.

Three-dimensional ultrasonography can detect the modulation of kidney volume in two-kidney, one-clip hypertensive rats

As volume changes are a typical finding in the two-kidney, one-clip hypertensive rat model (2K1C), it is of interest to investigate within what time frame these volume changes occur and their relation to hypertension. Kidney volume changes in Wistar rats were measured by three-dimensional (3D) ultrasonography (USG). Clipped induced stenosis was applied to the left renal artery in 11-wk-old animals (n = 8), using age-matched nonclipped rats as controls (n = 7). Ultrasonographic recordings were made before clipping and, thereafter, weekly with corresponding systolic blood pressure and body weight measurements. The nonclipped kidney showed increased volume at week 2, 5 and 7. Three wk after clipping, clipped kidneys were smaller than the nonclipped kidneys (0.47 +/- 0.11 mL versus 1.28 +/- 0.07 mL). No difference was found between the left and right kidney in the control group at any week. Blood pressure was significantly higher in the 2K1C hypertensive group 4 weeks after clipping (201 +/- 16 versus 139 +/- 4 mm Hg) with stable blood pressure thereafter. Three-dimensional USG showed that clipping caused a decrease in kidney volume from week 3 in the clipped kidney and a volume increase in the nonclipped kidney at week 2. A significant increase in blood pressure appeared after week 4.

Kidney dimensions at sonography are correlated with glomerular filtration rate in renal transplant recipients and in kidney donors

The gold standard to assess renal function is the measurement of glomerular filtration rate (GFR). For practical reasons, renal function is often evaluated from serum creatinine (S Cr) or cystatin C (S Cys), and GFR is predicted from SCr. Ultrasound scanning of the kidneys is used only to evaluate renal morphology. The aim of this study was to evaluate the relationship between sonographic renal dimensions and GFR in renal transplant recipients and in kidney donors. GFR (urinary clearance of (99m)Tc-DTPA), S Cr, and S Cys were measured in 33 donors (28 females [F], 5 males [M]; SCr, 0.81-1.90 mg/dL) and 30 recipients (8 F, 22 M; SCr, 0.96-2.42 mg/dL). GFR was also predicted using the Cockcroft and Gault (CG) formula and with the simplified Modification of Diet in Renal Disease (MDRD) formula. Length, width, and depth of kidneys and renal sinus were measured using renal sonography. Among sonographic measurements, kidney length showed the best correlation with GFR. A closer correlation with GFR was found in donors (r = 0.639; P < .00007) than in recipients (r = 0.511; P < .005). In either case, the correlation of kidney length with GFR was greater than that of S Cr or S Cys, and similar to that of CG or MDRD GFR. Accuracy of kidney length as an indicator of GFR impairment was not statistically different from laboratory tests. Only in donors did CG show better accuracy. In conclusion, renal dimensions at sonography closely correlated with GFR. Thus, renal sonography can give information also on the function of the renal graft and of the remaining kidney of living donors.

Normal values for renal length and volume as measured by magnetic resonance imaging

The objective of this magnetic resonance imaging (MRI) study was to (1) test the validity of the ellipsoid formula for estimating kidney volume using ex vivo and in vivo models and (2) establish a normal range of values for kidney length and volume in patients with no known history of renal disease. The volumes of five excised porcine kidneys were measured by (1) disc-summation method, (2) ellipsoid formula, and (3) water displacement method. In a retrospective, consecutive group of clinically referred patients (n = 150; 300 kidneys), individual kidney volume and length were calculated by the disc-summation method and by multiplanar reformation of MRI data, respectively. For comparison, kidney volumes also were calculated using the ellipsoid formula in all patients. Renal volume that was obtained by MRI using the disc-summation method was within 5% of the volume that was determined by the water displacement method, independent of the spatial resolution of the MRI technique used. Data from both the in vivo and the ex vivo models revealed that the ellipsoid formula that commonly is used in ultrasonography underestimates renal volume by 17 to 29% compared with the disc-summation method (P < 0.05). As measured by MRI (mean +/- SD), kidney lengths were 12.4 +/- 0.9 cm for men and 11.6 +/- 1.1 cm for women, and kidney volumes were 202 +/- 36 ml for men and 154 +/- 33 ml for women. The results from the ex vivo MRI study show that the kidney volume that was obtained using the disc-summation method is within 5% of the true kidney volume as measured by the water displacement method. The ellipsoid formula consistently and significantly underestimates the true kidney volume. The length and the volume of kidneys that are obtained by MRI in patients with no known history of intrinsic renal disease are greater than the commonly quoted reference values that are obtained by ultrasonography.

Ultrasound measured renal length versus low dose CT volume in predicting single kidney glomerular filtration rate

Ultrasound measured renal length and CT measured renal volume are potential surrogate markers for single kidney glomerular filtration rate (SKGFR). The aims of this study are to determine: (1) the repeatability of ultrasound measured length and low radiation dose spiral CT measured volume; (2) the relationship between renal length and volume; and (3) whether length and/or volume is a predictor of SKGFR. 69 patients with suspected renal artery stenosis underwent ultrasound renal length measurement, CT evaluation of renal volume and assessment of SKGFR. 40 patients had ultrasound measurement of length and CT evaluation of volume performed twice on two separate visits. 25 patients also had ultrasound measured renal parenchymal thickness and area. The region of interest was drawn around the kidneys and a threshold set to subtract renal peripelvic fat and renal pelvis. The volume from each slice was summed to obtain the total volume for each kidney. The limits of agreement for ultrasound measured renal length were -1.6 cm to 1.52 cm and that for CT renal volume were -33 ml to 32 ml. There was significant correlation between ultrasound measured length and CT volume (r=0.74, p<0.01). Volume was a better predictor of SKGFR (r(2)=0.57) than length (r(2)=0.48). The combined parameters of ultrasound measured length, area and parenchymal thickness were a better predictor of volume (r(2)=0.81) and SKGFR (r(2)=0.58) than ultrasound measured length on its own. The low dose CT technique was reasonably reproducible and renal volume measurements correlate better with SKGFR than length. Ultrasound predictions of renal volume and SKGFR can be improved by incorporating cross-sectional area and parenchymal thickness. Further investigation is required to refine our low dose CT technique.

Volume estimation of small phantoms and rat kidneys using three-dimensional ultrasonography and a position sensor

To evaluate the accuracy of small volume estimation, both in vivo and in vitro, measurements with a three-dimensional (3D) ultrasound (US) system were carried out. A position sensor was used and the transmitting frequency was 10 MHz. Balloons with known volumes were scanned while rat kidneys were scanned in vivo and in vitro. The Archimedes' principle was used to estimate the true volume. For balloons, the 3D US system gave very good agreement with true volumes in the volume range 0.1 to 10.0 mL (r = 0.999, n = 45, mean difference +/- 2SD = 0.245 +/- 0.370 mL). For rat kidneys in vivo (volume range 0.6 to 2.7 mL) the method was less accurate (r = 0.800, n = 10, mean difference +/- 2SD = -0.288 +/- 0.676 mL). For rat kidneys in vitro (volume range 0.3 to 2.7 mL) the results showed good agreement (r = 0.981, n = 23, mean difference +/- 2SD = 0.039 +/- 0.254 mL). For balloons, kidneys in vivo and in vitro, the mean percentage error was 9.3 +/- 4.8%, -17.1 +/- 17.4%, and 4.6 +/- 11.5%, respectively. This method can estimate the volume of small phantoms and rat kidneys and opens new possibilities for volume measurements of small objects and the study of organ function in small animals. (E-mail ).

Kidney ultrasound and Doppler ultrasound findings during and after acute urinary retention

OBJECTIVE

To evaluate changes in kidney ultrasound and Doppler ultrasound images during and subsequent to acute urinary retention (AUR).

METHODS

Twenty-five men with a mean age of 69 years suffering AUR for a mean of 31 h were studied by measuring serum creatinine, creatinine clearance and renal ultrasound. Renal Doppler ultrasound was applied in 19 of these cases and all patients were followed for 6 months after acute retention was relieved.

RESULTS

During AUR hydronephrosis was noted in three patients; this disappeared during follow-up. During the acute period, after 1 month and after 6 months the average resistive indexes (RI) were 0.71, 0.70 and 0.69, respectively. The changes were not statistically significant. During follow-up, the proportion of patients with normal RI increased from 42 to 64%. Median serum creatinine was normal during retention and follow-up. Median creatinine clearance was reduced during retention and became normal during follow-up (P < 0.05). No correlation was found between RI and serum creatinine at any time-point, nor was any correlation noted between RI and creatinine clearance during retention or at the 1-month follow-up; at 6 months, however, there was a significant inverse correlation between them (P = 0.01).

CONCLUSION

AUR caused elevation of RI, which may be interpreted as diminished renal blood flow. Although in the majority of patients it recovered after treatment, elevated RI was still found in one third of the patients, possibly due to previous chronic bladder outlet obstruction. Our findings stress the importance of both fast release of AUR and effective treatment of its cause.