Evaluation of two diuresis renography decision support systems to determine the need for furosemide in patients with suspected obstruction

Abstract

Objective: The purpose of this study was to compare the decisions regarding the need for furosemide made by two independent renal decision support systems, RENEX and CAR-TAN, with the need for furosemide determined in clinical practice and by expert reviewers using the baseline plus furosemide protocol.

Subjects and methods: RENEX and CARTAN are independent decision support systems that reach their conclusions without operator input. RENEX is a knowledge-based system and CARTAN is a statistical decision support system. Both were trained using the same pilot group of 31 adult patients (61 kidneys) referred for suspected obstruction. Subsequently, both systems were prospectively applied to 102 patients (200 kidneys) of whom 70 received furosemide; decisions regarding the need for furosemide were compared with the clinical decisions and the decisions of three experts who independently scored each kidney on the need for furosemide. Differences were resolved by consensus.

Results: RENEX agreed with the clinical and experts' decisions to give furosemide in 97% (68/70) and 98% (65/66) of patients, respectively, whereas CARTAN agreed in 90% (63/70) and 89% (59/66), respectively, p < 0.03. In contrast, CARTAN agreed with the experts' decision to withhold furosemide in 78% of kidneys (87/111), whereas RENEX agreed in only 69% of kidneys (77/111), p = 0.008.

Conclusion: Use of RENEX or CARTAN as decision support tools in the baseline plus furosemide protocol has the potential to help the radiologist avoid unnecessary imaging and reduce the technologist, computer, camera, and physician time required to perform the procedure.

Fig. 1. Knowledge library was generated for each parameter to convert any given parameter value into certainty factor

A, Graph shows parameter knowledge library to convert any time to half maximum count value for left kidney (whole-kidney region of interest [ROI]) to certainty factor value. Boundary values (see Subjects and Methods section for more detail) were 8, 11, 13, 15, and 20 minutes, respectively. B, Graph shows parameter knowledge library to convert any 20 minute to maximum count ratio for left kidney (cortical ROI) to certainty factor value. Boundary values were 0.17, 0.27, 0.32, 0.43, and 0.92, respectively.

Fig. 2. 50-year-old woman referred for mercaptoacetyltriglycine (MAG3) scanning because of suspected obstruction

A, QuantEM (developed at Emory University, licensed to GE Healthcare) review of baseline scan shows no infiltration. MAG3 clearance is reduced. Right kidney shows prompt uptake and excretion and is not obstructed. Left kidney shows reduction in relative function (18%). There was uniform uptake in left kidney with slow washout, but, importantly, there was no retention of tracer in collecting system. Clinically, study was interpreted as not obstructed and furosemide was not administered. RENEX, CARTAN, and experts agreed with this decision. Tmax = time to maximum counts, T_1/2 = half-time, 20 min/max = 20-minute-to-maximum-count ratio, k = kilo. B, Expanded QuantEM review display shows patient values for MAG3 clearance; residual urine volume; percent relative uptake; and time to maximum counts (Tmax), 20-minute-to-maximum-count ratio (20/max), half-time (T_1/2), and postvoid to maximum (postvoid/max) ratios for whole-kidney and cortical regions of interest as well as normal ranges for each of these values. Expanded review page also shows enlarged parenchymal image obtained at 2–3 minutes, enlarged display of 19- to 20-minute image, and quality control images showing preinjection and postinjection syringe counts and time of bolus arrival in kidneys. Postvoid to maximum count ratio of left kidney is slightly elevated at 23%, but this ratio tells clinician that almost 80% of maximal activity has washed out of left kidney by conclusion of study. Such high washout percentage is strong evidence against obstruction.

Fig. 3. 40-year-old man referred for mercaptoacetyltriglycine (MAG3) scanning because of suspected obstruction

A, QuantEM (developed at Emory University, licensed to GE Healthcare) review of baseline scan shows no infiltration. Camera-based MAG3 clearance is normal. Left kidney shows rapid uptake and washout of tracer in sequential 2-minute images (center). Relative uptake of left kidney is 56%, whole-kidney half-time (T_1/2) is 10.8 minutes, and postvoid to maximum count ratio (postvoid/max) is normal (B) excluding obstruction. Relative function of right kidney was 46%, and right kidney showed dilatation of renal pelvis, which can be appreciated on 2-minute image as well as on enlarged 2- to 3-minute image (B). T_1/2 for whole-kidney region of interest (ROI) was prolonged at 20.3 minutes and 20-minute-to-maximum-count ratio (20/max) was elevated at 0.58. However, visually pelvis empties after voiding and postvoid/max was 0.20 (B). Although postvoid/max count ratio is slightly elevated (0.16 is the upper limit of normal [15]), experts’ and clinical decisions were that furosemide was not indicated. CARTAN agreed with experts, but RENEX concluded that furosemide was needed to exclude obstruction of right kidney (see Discussion). Tmax = time to maximum count ratio, 20/max = 20-minute-to-maximum-count ratio, k = kilo. B, Expanded QuantEM review display shows patient values for MAG3 clearance; residual urine volume; percent relative uptake; and time to maximum (Tmax), 20-minute-to-maximum-count ratio (20/max), half-time (T_1/2), and postvoid to maximum count (postvoid/max) ratios for whole-kidney and cortical ROIs as well as normal ranges for each of these values. Expanded review page also shows enlarged parenchymal image obtained at 2–3 minutes, enlarged display of 19- to 20-minute image, and quality control images showing preinjection and postinjection syringe counts and time of bolus arrival in kidneys. In particular, enlarged 2- to 3-minute image shows dilated renal pelvis, and postvoid/max ratio for right kidney is slightly elevated.