|Year : 2019 | Volume
| Issue : 4 | Page : 259-263
Comparison of automatic depth correction versus manual depth correction in the calculation of glomerular filtration rate in gates renal processing of diethylenetriaminepentaacetic acid renogram in prospective renal donors
Ranadheer Mantri1, Priyanka Kosana1, Ramya Priya Rallapeta1, Ravi Parthasaradhi1, Sailaja Aka1, Tekchand Kalawat1, Siva Kumar Vishnubotla2
1 Department of Nuclear Medicine, Sri Venkateswara Institute of Medical Sciences, Tirupati, Andhra Pradesh, India
2 Department of Nephrology, Sri Venkateswara Institute of Medical Sciences, Tirupati, Andhra Pradesh, India
|Date of Submission||25-May-2019|
|Date of Acceptance||18-Nov-2019|
|Date of Web Publication||31-Dec-2019|
Dr. Tekchand Kalawat
Department of Nuclear Medicine, Sri Venkateswara Institute of Medical Sciences, Tirupati, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Aim: The aim of the study was to compare the glomerular filtration rate (GFR) obtained by gates method of renal processing using automated system generated method (ASGM) of depth correction with manual depth correction method (MDCM), in prospective renal donors using 99m-Tc diethylenetriaminepentaacetic acid (DTPA) scintigraphy. Materials and Methods: Prospective interventional study involving 20 voluntary renal donors of age 26–65 years were included. 99m-Tc DTPA renograms were acquired by dynamic acquisition for 30 min. Presyringe and postsyringe counts, prevoid and postvoid images, and both sides of lateral images (for manual depth correction) were acquired. GFR was calculated by Gates renal processing with the depth correction both by ASGM and MDCM methods. Results: The mean depth of right and left kidneys calculated by MDCM and ASGM were 7.2 ± 1.1 and 6.4 ± 1.1 and 7.0 ± 1.2 and 6 ± 1.2, respectively. The mean total GFR calculated by Gate's Method using MDCM and ASGM was 96.2 ± 15.4 and 82.0 ± 11.5. There was a statistically significant difference in the depth correction of both kidneys and improvement in total GFR values by MDCM methods compared to the ASGM method. Conclusion: There was a significant difference in depth and GFR values, calculated from MDCM compared to ASGM. Hence, the MDCM is better in calculating GFR for renal donors, especially when using low-energy high-resolution collimators, as full-width half-maximum varies considerably for every centimeter of the distance of the source from the collimator.
Keywords: Depth correction, diethylenetriaminepentaacetic acid Renogram, glomerular filtration rate calculation
|How to cite this article:|
Mantri R, Kosana P, Rallapeta RP, Parthasaradhi R, Aka S, Kalawat T, Vishnubotla SK. Comparison of automatic depth correction versus manual depth correction in the calculation of glomerular filtration rate in gates renal processing of diethylenetriaminepentaacetic acid renogram in prospective renal donors. Indian J Transplant 2019;13:259-63
|How to cite this URL:|
Mantri R, Kosana P, Rallapeta RP, Parthasaradhi R, Aka S, Kalawat T, Vishnubotla SK. Comparison of automatic depth correction versus manual depth correction in the calculation of glomerular filtration rate in gates renal processing of diethylenetriaminepentaacetic acid renogram in prospective renal donors. Indian J Transplant [serial online] 2019 [cited 2020 Feb 26];13:259-63. Available from: http://www.ijtonline.in/text.asp?2019/13/4/259/274599
| Introduction|| |
Glomerular filtration rate (GFR) is defined as the volume of blood filtered from the glomerular capillaries into Bowman's capsule per unit time. GFR is an important indicator of kidney function. It is determined by calculating the volume (ml) of plasma that would be completely cleared of a substance per minute. Traditionally, agents such as inulin, urea, or creatinine were used.
Renal dynamic imaging with 99m-Tc diethylenetriaminepentaacetic acid (DTPA) is an ideal method for the determination of GFR, also known as the Gates method. In Gates method, GFR can be estimated from renal uptake of 99m-Tc DTPA by a computer-linked gamma camera, known as camera-based methods.,
DTPA is a chelating agent, introduced into renal nuclear medicine in 1970, as it is known that chelating agents used in toxic metal poisoning were eliminated by glomerular filtration without any metabolic alteration. Since then, radiolabelled DTPA (99mTc DTPA) was used in assessing GFR by camera-based methods in nuclear medicine.
A sequence of gamma camera images that follow the passage of a radiotracer through the kidneys constitutes a renogram. Radionuclide renography using 99m-Tc DTPA was performed by injecting it intravenously as a bolus injection, with the patient's abdomen region positioned under the camera. The following data acquisition images were displayed on the screen. Time-activity curves were derived by drawing regions of interest around the kidneys, bladder, and appropriate blood background area. 99m-Tc DTPA is diffusible and it rapidly enters the extravascular space following the injection., Therefore, the curve derived from a kidney region of interest (i.e., the raw renogram) contains a “background” contribution from uptake in tissues over and underlying the kidney that should be removed prior to the estimation of GFR.,
GFR is automatically calculated by the software in a commercially available computer according to the Gates algorithm automated system generated method (ASGM). Gates method includes parameters such as kidney depth from the surface of the skin, height, and weight of the patient. The accuracy of a camera-based method depends on the accuracy of estimated renal depth. Kidney depth may not be the same for all the patients, so kidney depth can also be calculated manually from the lateral images. GFR values calculated using Gates method with incorporation of manually calculated depth was considered as manual depth correction method.
The purpose of this study was to show the difference in GFR values obtained using the ASGM and MDCM.
| Materials and Methods|| |
Selection of patients
This was a prospective study performed in prospective renal donors who were referred from the Department of Nephrology for the evaluation of GFR in the Department of Nuclear Medicine, Sri Venkateswara Institute of Medical Sciences, Tirupati, during January 2016–June 2017. In all the renal donors, a renogram was performed following standard operating procedure guidelines prescribed by European Association of Nuclear Medicine (EANM) and Society of Nuclear Medicine (SNM). Written informed consent was obtained from all the renal donors.
The patient consent has been taken for participation in the study and for publication of clinical details and images. Patients understand that the names, initials would not be published, and all standard protocols will be followed to conceal their identity. The study has been approved by Institutional ethics committee of ECR/488/Inst/AP/2013/RR-16.
The continuous dynamic acquisition was performed using Siemens Symbia-e NaI (Tl) Dual Head Gamma camera for 30 min after the injection of 110–185 MBq (3–5 mCi) of 99m-Tc-labeled DTPA intravenously. The patient was advised not to move during the scan.
Full syringe counts were acquired initially for 10 s in 256 × 256 matrix. The scan was acquired by the activation of a posterior detector having low-energy-high resolution collimator with the patient positioned in the supine position and arms elevated over the head. Following an intravenous bolus injection of 110–185 MBq of 99m-Tc DTPA, the dynamic image acquisition was done using 64 × 64 matrix size at the rate of 2 s/frame for 1 min followed by 15 s/frame for 29 min to evaluate parenchymal radiotracer uptake and clearance. Prevoid and postvoid images were acquired with 128 × 128 matrix size for 60 s and empty syringe counts with 256 × 256 matrix size for 10 s. A 1-min static image of 99m-TcDTPA injection site was acquired on the computer to identify any infiltration of tracer (invalidate the GFR). For the manual depth correction, lateral images of the patient were acquired.
After all the data acquisition, the regions of interest for both kidneys and backgrounds were drawn manually. The GFR was calculated automatically by the Gates method (ASGM) between 2 and 3 min of the uptake phase of the renogram curve. GFR was calculated by system-generated kidney depth by entering the donor's height and weight and the final report is recorded. Kidney depth of the donors was also calculated manually from the lateral image, and this value was incorporated in the Gates method manually, and again, GFR was calculated (MDCM), and the results were compared statistically using the paired t-test.
The formula for Gates method GFR (3)
Kidney depth (measured in cm) is determined by the formula
Rt k cts = Right kidney counts
bkg = background counts
e−μx= kidney depth correction value;
μ = 0.153 (linear attenuation coefficient of 99m-Tc in soft tissue)
depth of the right kidney (×R) = ([wt/ht] × 13.3) +0.7
depth of the left kidney (×L) = ([wt/ht] × 1 3.2) +0.7
ht – height (measured in cm), wt – weight (measured in kg) of the patient.
| Results|| |
In this study, the right and left kidney mean depth calculated by MDCM and ASGM was 7.2 ± 1.1 and 6.4 ± 1.1 and 7.0 ± 1.2 and 6 ± 1.2, respectively. As shown in [Figure 1] and [Figure 2]. There was a statistically significant difference in depth values with P < 0.05. Manual depth was calculated from acquired lateral images as shown in the [Figure 3] and [Figure 4]. The right and left kidney mean GFR calculated by MDCM and ASGM was 48.8 ± 7.5 and 42.2 ± 5.9 and 47.4 ± 9.6 and 39.8 ± 7.55, respectively [Table 1]. There was a statistically significant difference in the mean GFR values of both kidneys with P < 0.05. The mean total GFR calculated by MDCM and ASGM was 96.2 ± 15.4 and 82.0 ± 11.5, respectively. There was a statistically significant difference in mean total GFR values with P < 0.05. In this study, the MDCM has an additional role in calculating GFR values and became a valuable tool in providing corrected values with scientific validity to help the clinicians in their decision-making with regard to the procedure of donor selection.
|Figure 1:99m-Tc diethylenetriaminepentaacetic acid renogram of a 45-year-old female renal donor with obtained glomerular filtration rate values by automated system generated depth correction method|
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|Figure 2:99m-Tc diethylenetriaminepentaacetic acid renogram of a 45-year-old female (the same patient) renal donor with obtained glomerular filtration rate values by the manual depth correction method|
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|Figure 3: Manually calculated depth of the right kidney from the right lateral image. (Note: Depth was calculated from the mid-pole of the kidney to surface of the skin)|
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|Figure 4: Manually calculated depth of the left kidney from the left lateral image. (Note: Depth was calculated from the mid-pole of the kidney to the surface of the skin)|
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|Table 1: Comparison of automatic depth correction versus manual depth correction in the calculation of GFR in Gates method|
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| Discussion|| |
GFR refers to the amount of ultrafiltrate generated by kidneys per unit time, which is an important indicator of kidney function. Accurate estimation of GFR is important in renal donors to consider suitable for renal donation or not. Camera-based methods were one of the important modality in the estimation of GFR. Among them, the Gates method using 99m-Tc DTPA was one of the ideal methods for GFR determination. However, the accuracy of the Gates method was affected by many factors; among them, renal depth was an important one. The renal depth helps in determining the attenuation coefficient used to calculate kidney function from scintigraphic scans. Renal depth is much more significant when using low-energy high-resolution collimators, as the full-width half-maximum varies considerably with a distance of the source to the collimator compared to low-energy all-purpose collimator.
This was a single-center prospective study done in 20 renal donors of age range 26–65 years who were referred for the estimation of GFR. Six of twenty donors were male and 14/20 were female. In all the renal donors, GFR was calculated by the Gates method. In this study, two methods of depth correction were used, i.e., the automated system generated kidney depth (ASGM) and manually corrected kidney depth (MDCM) from the lateral images (mid of the kidney to the surface of the body). In this study, the right kidney mean depth calculated by MDCM and ASGM was 7.2 ± 1.1 and 6.4 ± 1.1 and left kidney mean depth was 7.0 ± 1.2 and 6 ± 1.2, respectively. There was a statistically significant difference in depth values calculated by MDCM compared to ASGM with P < 0.05. Similarly, the right kidney mean GFR calculated by MDCM and ASGM was 48.8 ± 7.5 and 42.2 ± 5.9 and left kidney mean GFR was 47.4 ± 9.6 and 39.8 ± 7.55, respectively. There was a statistically significant difference in mean GFR values of both the kidneys with P < 0.05. The mean total GFR calculated by MDCM and ASGM was 96.2 ± 15.4 and 82.0 ± 11.5, respectively. There was a statistically significant difference in mean total GFR values with P < 0.05.
Renal depth deviation can cause GFR error., To overcome this, various new formulae were proposed in the previous studies for depth correction.,, Ma et al., in their study, have shown that a 1 cm error in true kidney depth may cause an 18% difference in GFR in adults. In our study for 1 cm error in kidney depth there was 13% difference in GFR. While evaluating the prospective renal donors, it is important to use both the methods, especially when there is a low GFR on ASGM. Our study has proved that MDCM gains over ASGM by rendering optimal GFR values and making donors suitable for renal donation by apt correction of falsely low GFR values obtained by ASGM.
This was single-center study. The study population was small.
The study needs to be extended by including more number of renal donors.
| Conclusion|| |
There was a significant difference in depth and GFR values, calculated from the MDCM compared to the ASGM. Few of the donors became suitable for renal donation (optimal GFR values) whose GFR was underestimated by ASGM. Hence, the MDCM is better in calculating GFR for renal donors, especially when using low-energy high-resolution collimators, as full-width half-maximum varies considerably for every centimeter of the distance of the source from the collimator.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]