The use of iodinated contrast media in patients with end-stage renal disease

Noninvasive assessment of renal dynamics and pH in a unilateral ureter obstruction model using DCE MR‐CEST urography

PURPOSE

To assess the potential of DCE MR CEST urography for assessing renal function in mice with unilateral ureter obstruction (UUO) by simultaneous pH and renal uptake/clearance measurements following injection of iopamidol.

METHODS

The right ureter of nine mice was obstructed via suture ligation. The animals were imaged at day 1, 2, and 3 post-obstruction on an 11.7T MRI scanner. Ninety-six sets of saturated CEST images at 4.3 and 5.5 ppm were collected. Renal pH values were obtained by calculating the signal ratio for these two frequencies and using a pH calibration curve. Renal time activity curves were measured as a percentage change in the post-injection CEST signal at 4.3 ppm relative to the average pre-injection signal.

RESULTS

For the healthy mice, the time activity curves of both kidneys were nearly identical and displayed rapid excretion of contrast. For the UUO mice, the dynamic CEST curves for the obstructed kidneys displayed prolonged time to peak (TTP) values and delayed contrast excretion compared with the contralateral (CL) kidneys. Renal pH maps of the healthy animals showed similar acidic values for both kidneys (pH 6.65 ± 0.04 vs 6.67 ± 0.02), whereas in the obstructed kidneys there was a significant increase in pH values compared with the CL kidneys (pH 6.67 ± 0.08 vs 6.79 ± 0.11 in CL and UUO kidneys, respectively).

CONCLUSION

Our findings indicate that DCE-MR-CEST urography can detect changes in renal uptake/excretion and pH homeostasis and distinguish between obstructed and unobstructed kidney as early as 1 day after UUO.

CONTRAST INDUCED ACUTE KIDNEY INJURY IS NOT A SITUATION TO BE AFRAID OF

Acute kidney injury (AKI), formerly called acute renal failure (ARF), is clinically manifested as a reversible acute increase in nitrogen waste products, as measured by blood urea nitrogen (BUN) and serum creatinine levels. Contrast induced acute kidney injury (CIAKI) is a potentially fatal complication of angiographic procedures caused by the use of contrast media (CM). It is the third most prevalent cause of hospital acquired acute renal damage, accounting for around up to 30% of cases. Contrast induced nephropathy (CIN) is defined as a greater than 25% or 0.5 mg/dl (44 μmol/l) increase in serum creatinine (Scr) from baseline within 3 days. More sensitive indicators of renal damage are sought, hence numerous tubular injury biomarkers are being studied. Multiple risk factors may lead to the development of CIN; these risk factors are classified as patient-related and procedure-related. Treatment of CIN Is primarily symptomatic and consist firstly of careful fluid and electrolyte management, although dialysis may be necessary in some cases. With available treatment options, prevention is the cornerstone of management.

Clinical pearls in hospital nephrology

Hospitalized patients who have established kidney disease and those who have acute kidney injury in the hospital, along with patients with electrolyte disturbances tend to be some of the most complex to care for. Through working closely in nephrology consultation in the hospital with patients and providers, in both private and academic settings, we have come to encounter certain common presentations and recurrent themes that are worthy of emphasis, and of which a good understanding can translate into improved patient care. For the provider who works closely with such patients, many of these aspects are important to recognize and understand. In this review, we present 10 questions that address some of the highly relevant aspects of nephrology for the provider in the hospital. Through a MEDLINE database search, we reviewed the most pertinent studies as we then go through the explanation of management decisions in an evidence-based methodology with an up-to-date approach based on the current literature on the subject.

Dual assessment of kidney perfusion and pH by exploiting a dynamic CEST-MRI approach in an acute kidney ischemia-reperfusion injury murine model

Several factors can lead to acute kidney injury, but damage following ischemia and reperfusion injuries is the main risk factor and usually develops into chronic disease. MRI has often been proposed as a method with which to assess renal function. It does so by measuring the renal perfusion of an injected Gd-based contrast agent. The use of pH-responsive agents as part of the CEST (chemical exchange saturation transfer)-MRI technique has recently shown that pH homeostasis is also an important indicator of kidney functionality. However, there is still a need for methods that can provide more than one type of information following the injection of a single contrast agent for the characterization of renal function. Herein we propose, for the first time, dynamic CEST acquisition following iopamidol injection to quantify renal function by assessing both perfusion and pH homeostasis. The aim of this study is to assess renal functionality in a murine unilateral ischemia-reperfusion injury model at two time points (3 and 7 days) after acute kidney injury. The renal-perfusion estimates measured with iopamidol were compared with those obtained with a gadolinium-based agent, via a dynamic contrast enhanced (DCE)-MRI approach, to validate the proposed method. Compared with the contralateral kidneys, the clamped ones showed a significant decrease in renal perfusion, as measured using the DCE-MRI approach, which is consistent with reduced filtration capability. Dynamic CEST-MRI findings provided similar results, indicating that the clamped kidneys displayed significantly reduced renal filtration that persisted up to 7 days after the damage. In addition, CEST-MRI pH imaging showed that the clamped kidneys displayed significantly increased pH values, reflecting the disturbance to pH homeostasis. Our results demonstrate that a single CEST-MRI contrast agent can provide multiple types of information related to renal function and can discern healthy kidneys from pathological ones by combining perfusion measurements with renal pH mapping.

Contrast-associated acute kidney injury: does it really exist, and if so, what to do about it?

For decades, when contrast agents are administrated, physicians have been concerned because of the risk of inducing acute kidney injury (AKI). Recent literature questions the existence of AKI induced by contrast, but animal studies clearly showed harmful effects. The occurrence of contrast-associated AKI was likely overestimated in the past because of confounders for AKI. Several strategies have been investigated to reduce contrast-associated AKI but even for the most important one, hydration, there are conflicting data. Even if the occurrence rate of contrast-associated AKI is low, AKI is related to worse outcomes. Therefore, besides limiting contrast agent usage, general AKI preventive measurements should be applied in at-risk patients.