Detection of Acute Tubular Necrosis Using Blood Oxygenation Level-Dependent (BOLD) MRI

Background/Aims: To date, there is no imaging technique to assess tubular function in vivo. Blood oxygen level-dependent magnetic resonance imaging (BOLD MRI) measures tissue oxygenation based on the transverse relaxation rate (R2*). The present study investigates whether BOLD MRI can assess tubular function using a tubule-specific pharmacological maneuver. Methods: Cross sectional study with 28 participants including 9 subjects with ATN-induced acute kidney injury (AKI), 9 healthy controls, and 10 subjects with nephron sparing tumor resection (NSS) with clamping of the renal artery serving as a model of ischemia/reperfusion (I/R)-induced subclinical ATN (median clamping time 15 min, no significant decrease of eGFR, p=0.14). BOLD MRI was performed before and 5, 7, and 10 min after intravenous administration of 40 mg furosemide. Results: Urinary neutrophil gelatinase-associated lipocalin was significantly higher in ATN-induced AKI and NSS subjects than in healthy controls (p=0.03 and p=0.01, respectively). Before administration of furosemide, absolute medullary R2*, cortical R2*, and medullary/cortical R2* ratio did not significantly differ between ATN-induced AKI vs. healthy controls and between NSS-I/R vs. contralateral healthy kidneys (p>0.05 each). Furosemide led to a significant decrease in the medullary and cortical R2* of healthy subjects and NSS contralateral kidneys (p<0.05 each), whereas there was no significant change of R2* in ATN-induced AKI and the NSS-I/R kidneys (p>0.05 each). Conclusion: BOLD-MRI is able to detect even mild tubular injury but necessitates a tubule-specific pharmacological maneuver, e.g. blocking the Na+-K+-2Cl- transporter by furosemide

Transient stent placement versus tubeless procedure after ureteroscopy retrograde surgery stone extraction (Fast Track Stent study 2)

$\bf Objectives$ To determine whether in pre-stented patients undergoing ureteroscopic stone removal (ureteroscopy retrograde surgery) a tubeless procedure provides a better outcome compared with short-term (6 h) ureteral stenting using an external ureteral catheter. $\bf Methods$ In this single academic center study (Fast Track Stent study 2), carried out between May 2016 and April 2018, 121 patients with renal or ureteral calculi were initially treated with double-J insertion. Before secondary ureteroscopy retrograde surgery, patients were prospectively randomized into two groups: tubeless versus ureteral catheter insertion for 6 h after ureteroscopy retrograde surgery. Exclusion criteria were acute urinary tract infection, solitary kidney or stone diameter >25 mm. Study end-points were stent-related symptoms assessed by a validated questionnaire (ureteral stent symptom questionnaire), administered both before and 4 weeks after surgery. Numerical ureteral stent symptom questionnaire scores were compared using the Mann–Whitney-U-test. The level of significance was defined as $\it P$ < 0.05. $\bf Results$ Ureteroscopy retrograde surgery procedures carried out by 13 surgeons resulted in >90% stone removal in all patients ($\it n$ = 121), with a mean operation time of 19.9 versus 18.0 min for ureteral catheter versus tubeless, respectively ($\it P$ = 0.37). Patient groups did not differ significantly in their ureteral stent symptom questionnaire scores (urinary index $\it P$ = 0.24; pain index $\it P$ = 0.35). Patients showed a significant preference for tubeless procedure over ureteral catheter reinsertion (Question GQ $\it P$ < 0.0001). The reintervention rate was 13.3% for the tubeless procedure ($\it n$ = 8) and 1.6% for the ureteral catheter group ($\it n$ = 1), respectively ($\it P$ = 0.034). $\bf Conclusions$ Short-term ureteral catheter and no stent insertion after ureteroscopy retrograde surgery stone extraction in pre-stented patients result in comparable quality of life. However, the reintervention rate is higher for tubeless procedures

Detection of acute tubular necrosis using blood oxygenation level-dependent (BOLD) MRI

$\it Background/Aims:$ To date, there is no imaging technique to assess tubular function in vivo. Blood oxygen level-dependent magnetic resonance imaging (BOLD MRI) measures tissue oxygenation based on the transverse relaxation rate (R2*). The present study investigates whether BOLD MRI can assess tubular function using a tubule-specific pharmacological maneuver. $\it Methods:$ Cross sectional study with 28 participants including 9 subjects with ATNinduced acute kidney injury (AKI), 9 healthy controls, and 10 subjects with nephron sparing tumor resection (NSS) with clamping of the renal artery serving as a model of ischemia/reperfusion (I/R)-induced subclinical ATN (median clamping time 15 min, no significant decrease of eGFR, p=0.14). BOLD MRI was performed before and 5, 7, and 10 min after intravenous administration of 40 mg furosemide. $\it Results:$ Urinary neutrophil gelatinaseassociated lipocalin was significantly higher in ATN-induced AKI and NSS subjects than in healthy controls (p=0.03 and p=0.01, respectively). Before administration of furosemide, absolute medullary R2*, cortical R2*, and medullary/cortical R2* ratio did not significantly differ between ATN-induced AKI vs. healthy controls and between NSS-I/R vs. contralateral healthy kidneys (p>0.05 each). Furosemide led to a significant decrease in the medullary and cortical R2* of healthy subjects and NSS contralateral kidneys (p0.05 each). $\it Conclusion:$ BOLD-MRI is able to detect even mild tubular injury but necessitates a tubulespecific pharmacological maneuver, e.g. blocking the Na$^{+}$-K$^{+}$-2Cl- transporter by furosemide