Aim
The reproducibility of differential renal function (DRF) estimates on 99mTc-mercaptoacetyltriglycine (99m Tc-MAG3) is good in the majority of children. There is however a small but important group with poor reproducibility which, if not recognized, could affect clinical decision making. Some factors, such as age and glomerular filtration rate (GFR), have been implicated as causes for poor reproducibility. The aim of this study is to formally investigate image characteristics associated with the reproducibility of DRF measurements.
Patients and methods
The image characteristics and reproducibility of the DRF estimates of the 127 patients in cohort 1 was used to identify the characteristics associated with reproducibility. The associations between these image characteristics and reproducibility were then tested in a second cohort of 227 patients. The DRF measurements were calculated using two internationally accepted methods for calculating DRF, the HERMES area under the curve (HAUC) method and the HERMES Rutland Patlak (HRP) method. The images were visually inspected to categorise the categorical variables and processed to obtain the values of the continuous variables. The variables investigated included two nonimaging variables, age (in months) and GFR which included measured or estimated GFR values. The association between each variable and the reproducibility of DRF measurement for both the HAUC and the HRP methods was tested with univariate linear regression. The results of the univariate linear regression were used to plan the multiple linear regression combinations. All possible combinations were tested with multiple linear regression.
Results
The goodness-to-fit for the multiple regression models were much higher for all the combinations analysed in cohort 1 than in cohort 2. In cohort 1 the R2 -values ranged from 0.3510 to 0.4906 for log MAXMINHAUC and 0.3284 to 0.4500 for log MAXMINHRP. In cohort 2, they ranged from 0.1675 to 0.2163 for log MAXMINHAUC, and 0.1706 to 0.2191 for log MAXMINHRP. The combinations with the highest R2 -value for multiple linear regression analyses were similar in cohort 1 and 2. The only individual variable which was significant in all the multiple linear regression combinations for cohort 1 and 2 for both log MAXMINHAUC and log MAXMINHRP was LEFT KIDNEY TO BACKGROUND RATIO. RIGHT KIDNEY TO BACKGROUND RATIO, RIGHT RENAL MARGINS WELL DEFINED, RIGHT RENAL MARGINS POORLY VISUALISED and TIME VISUALISATION RIGHT CALYCES were significant in most of the combinations analysed. A high kidney to background ratio, RIGHT RENAL MARGINS WELL DEFINED and higher AGE predicted a good reproducibility. A low kidney to background ratio and later TIME VISUALISATION RIGHT CALYCES predicted poor reproducibility. The variables LEFT RENAL AREA, LEFT BACKGROUND AREA, BOTH RENAL MARGINS SMOOTH and RIGHT RENAL MARGINS IRREGULAR were not-significant in any combinations analysed cohort 1 and 2 for both log MAXMINHAUC and log MAXMINHRP. The remaining variables inconsistently predicted reproducibility in log MAXMINHAUC and log MAXMINHRP for both cohort 1 and 2.
Conclusion:
The only variables which consistently predicted good and poor reproducibility for the measurement of DRF on 99mTc-MAG3 renograms performed according to the EANM guidelines for both log MAXMINHAUC and log MAXMINHRP were AGE, LEFT KIDNEY TO BACKGROUND RATIO, RIGHT KIDNEY TO BACKGROUND RATIO, RIGHT RENAL MARGINS WELL DEFINED and TIME VISUALISATION RIGHT CALYCES. Consideration should be given to incorporating the kidney to background ratio into the renal processing screen display as a valuable quality control step. The DRF values should be interpreted with caution if the kidney to background ratio is < 2.0.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/31657 |
| Date | 22 April 2020 |
| Creators | Brink, Anita |
| Contributors | Levin, Mike, Mann, Michael |
| Publisher | Faculty of Health Sciences, Division of Nuclear Medicine |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, Doctoral, PhD |
| Format | application/pdf |
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