Modeling dynamic radial contrast enhanced MRI with linear time invariant systems for motion correction in quantitative assessment of kidney function.

Early identification of kidney function deterioration is essential to determine which newborn patients with congenital kidney disease should be considered for surgical intervention as opposed to observation. Kidney function can be measured by fitting a tracer kinetic (TK) model onto a series of Dynamic Contrast Enhanced (DCE) MR images and estimating the filtration rate parameter from the model. Unfortunately, breathing and large bulk motion events due to patient movement in the scanner create outliers and misalignments that introduce large errors in the TK model parameter estimates even when using a motion-robust dynamic radial VIBE sequence for DCE-MR imaging. The misalignments between the series of volumes are difficult to correct using standard registration due to 1) the large differences in geometry and contrast between volumes of the dynamic sequence and 2) the requirement of fast dynamic imaging to achieve high temporal resolution and motion deteriorates image quality. These difficulties reduce the accuracy and stability of registration over the dynamic sequence. An alternative registration approach is to generate noise and motion free templates of the original data from the TK model and use them to register each volume to its contrast-matched template. However, the TK models used to characterize DCE-MRI are tissue specific, non-linear and sensitive to the same motion and sampling artifacts that hinder registration in the first place. Hence, these can only be applied to register accurately pre-segmented regions of interest, such as kidneys, and might converge to local minima under the presence of large artifacts. Here we introduce a novel linear time invariant (LTI) model to characterize DCE-MR data for different tissue types within a volume. We approximate the LTI model as a sparse sum of first order LTI functions to introduce robustness to motion and sampling artifacts. Hence, this model is well suited for registration of the entire field of view of DCE-MR data with artifacts and outliers. We incorporate this LTI model into a registration framework and evaluate it on both synthetic data and data from 20 children. For each subject, we reconstructed the sequence of DCE-MR images, detected corrupted volumes acquired during motion, aligned the sequence of volumes and recovered the corrupted volumes using the LTI model. The results show that our approach correctly aligned the volumes, provided the most stable registration in time and improved the tracer kinetic model fit.

Has the robot caught up? National trends in utilization, perioperative outcomes, and cost for open, laparoscopic, and robotic pediatric pyeloplasty in the United States from 2003 to 2015.

INTRODUCTION: Since 2010, there have been few new data comparing perioperative outcomes and cost between open (OP) and robotic pyeloplasty (RP). In a post-adoption era, the value of RP may be converging with that of OP. OBJECTIVE: To 1) characterize national trends in pyeloplasty utilization through 2015, 2) compare adjusted outcomes and median costs between OP and RP, and 3) determine the primary cost drivers for each procedure. STUDY DESIGN: We performed a retrospective cohort study using the Premier database, which provides a nationally representative sample of U.S. hospitalizations between 2003 and 2015. ICD9 codes and itemized billing were used to abstract our cohorts. Trends in utilization and cost were calculated and then stratified by age. We used propensity scores to weight our cohorts and then applied regression models to measure differences in the probability of prolonged operative time (pOT), prolonged length of stay (pLOS), complications, and cost. RESULTS: During the study period 11,899 pyeloplasties were performed: 75% open, 10% laparoscopic, and 15% robotic. The total number of pyeloplasty cases decreased by 7% annually; OP decreased by a rate of 10% while RP grew by 29% annually. In 2015, RP accounted for 40% of cases. The largest growth in RPs was among children and adolescents. The average annual rate of change in cost for RP and OP was near stagnant: -0.5% for open and -0.2% for robotic. The summary table provides results from our regression analyses. RP conferred an increased likelihood of pOT, but a reduced likelihood of pLOS. The odds of complications were equivalent. RP was associated with a significantly higher median cost, but the absolute difference per case was $1060. DISCUSSION: Despite advantages in room and board costs for RP, we found that the cost of equipment and OR time continue to make it more expensive. Although the absolute difference may be nominal, we likely underestimate the true cost because we did not capture amortization, hidden or down-stream costs. In addition, we did not measure patient satisfaction and pain control, which may provide the non-monetary data needed for comparative value. CONCLUSION: Despite an overall decline in pyeloplasties, RP utilization continues to increase. There has been little change in cost over time, and RP remains more expensive because of equipment and OR costs. The robotic approach confers a reduced likelihood of pLOS, but an increased likelihood of pOT. Complication rates are low and similar in each cohort.

Multi-planar dynamic contrast-enhanced ultrasound assessment of blood flow in a rabbit model of testicular torsion.

To assess correlation between multi-planar, dynamic contrast-enhanced ultrasound (US) blood flow measurements and radiolabeled microsphere blood flow measurements, five groups of six rabbits underwent unilateral testicular torsion of 0°, 180°, 360°, 540° or 720°. Five US measurements per testis (three transverse/two longitudinal) were obtained pre-operatively and immediately and 4 and 8 h post-operatively using linear transducers (7-4 MHz/center frequency 4.5 MHz/10 rabbits; 9-3 MHz/center frequency 5.5 MHz/20 rabbits). Björck's linear least-squares method fit the rise phase of mean pixel intensity over a 7-s period for each time curve. Slope of fit and intervention/control US pixel intensity ratios were calculated. Means of transverse, longitudinal and combined transverse/longitudinal US ratios as a function of torsion degree were compared with radiolabeled microsphere ratios using Pearson's correlation coefficient, ρ. There was high correlation between the two sets of ratios (ρ ≥ 0.88, p ≤ 0.05), except for the transverse US ratio in the immediate post-operative period (ρ = 0.79, p = 0.11). These results hold promise for future clinical applications.

Economic and radiation costs of initial imaging approaches after a child's first febrile urinary tract infection.

BACKGROUND. The traditional initial imaging approach following pediatric urinary tract infection is the "bottom-up" approach (cystogram and renal ultrasound). Recently, the "top-down" approach (nuclear renal scan followed by cystogram for abnormal scans only) has gained increasing attention. The relative cost and radiation doses of these are unknown METHODS. The authors used a decision model to evaluate these imaging approaches. Cost and effective radiation dose estimates, including sensitivity analyses, were based on one-time imaging only. RESULTS. Comparing hypothetical cohorts of 100 000 children, the top-down imaging approach cost $82.9 million versus $59.2 million for the bottom-up approach. Per-capita effective radiation dose was 0.72 mSv for top-down compared with 0.06 mSv for bottom-up. CONCLUSIONS. Routine use of nuclear renal scans in children following initial urinary tract infection diagnosis would result in increased imaging costs and radiation doses as compared to initial cystogram and ultrasound. Further data are required to clarify the long-term clinical implications of this increase.

Costs and consequences of universal sibling screening for vesicoureteral reflux: decision analysis.

OBJECTIVE: Our objective was to evaluate screening for vesicoureteral reflux (VUR) among siblings of patients with VUR, in terms of cost, radiation exposure, and number of febrile urinary tract infections (fUTIs) averted. METHODS: We constructed a Markov model to evaluate 2 competing management options, that is, universal screening (cystographic evaluation of all siblings without symptoms) and usual care (cystographic evaluation of siblings only after fUTIs). Published data were used to inform all model inputs. Costs were estimated by using a societal perspective. RESULTS: Universal screening yielded 2980 fUTIs, whereas usual care yielded 6330. Therefore, universal screening for VUR in a cohort of 100,000 siblings 1 year of age without symptoms resulted in the prevention of 1 initial fUTI per 3360 siblings, at an excess cost of $55,600 per averted fUTI, in comparison with usual care. These estimates were heavily dependent on screening age and the effectiveness of antibiotic prophylaxis; prevention of a single fUTI would require screening of 166 siblings 5 years of age and 694 siblings 10 years of age. Similarly, if prophylaxis was ineffective in preventing fUTIs, then up to 10,000 siblings would need to be screened for prevention of a single fUTI. CONCLUSIONS: Prevention of a single fUTI would require screening of 30 to 430 siblings 1 year of age without symptoms, at an estimated excess cost of $56,000 to $820,000 per averted fUTI. These estimates are heavily dependent on screening age and the effectiveness of antibiotic prophylaxis.