Imaging Patients with Kidney Failure.

The approach to imaging a patient with kidney failure continues to evolve. Overstatement of the risk of iodinated contrast material-induced (ie, contrast-induced) acute kidney injury and new guidelines for administration of gadolinium-based contrast media affect screening and the choice of contrast material. Treatment of kidney failure requires dialysis or a kidney transplant. Pretransplant imaging includes assessment for the feasibility of performing a transplant and evaluation for underlying malignancy and peripheral vascular disease. Patients with kidney failure are at high risk for renal cell carcinoma. Subtypes that occur exclusively or more commonly in patients with kidney failure, such as acquired cystic kidney disease, renal cell carcinoma, and clear cell papillary renal cell carcinoma, have specific clinical-pathologic characteristics, with indolent behavior. Performing US for dialysis planning increases the success of placement of an arteriovenous fistula, while postoperative US evaluation is essential in assessment of access dysfunction. Systemic manifestations in patients with kidney failure are multifactorial and may relate to the underlying cause of renal failure or may be secondary to treatment effects. Disturbances in mineral and bone metabolism and soft-tissue and vascular calcifications are seen in patients with chronic kidney disease and mineral bone disorder. Neurologic and cardiothoracic complications are also common. The authors provide a comprehensive overview of imaging considerations for patients with kidney failure, including the appropriate use of CT, MRI, and US with their respective contrast agents; the use of imaging in transplant workup and dialysis assessment; and the common renal and extrarenal manifestations of kidney failure. ©RSNA, 2023 Quiz questions for this article are available in the supplemental material.

Intermodality feature fusion combining unenhanced computed tomography and ferumoxytol-enhanced magnetic resonance angiography for patient-specific vascular mapping in renal impairment.

OBJECTIVE: The purpose of this study was to establish the feasibility of fusing complementary, high-contrast features from unenhanced computed tomography (CT) and ferumoxytol-enhanced magnetic resonance angiography (FE-MRA) for preprocedural vascular mapping in patients with renal impairment. METHODS: In this Institutional Review Board-approved and Health Insurance Portability and Accountability Act-compliant study, 15 consecutive patients underwent both FE-MRA and unenhanced CT scanning, and the complementary high-contrast features from both modalities were fused to form an integrated, multifeature image. Source images from CT and MRA were segmented and registered. To validate the accuracy, precision, and concordance of fused images to source images, unambiguous landmarks, such as wires from implantable medical devices or indwelling catheters, were marked on three-dimensional (3D) models of the respective modalities, followed by rigid co-registration, interactive fusion, and fine adjustment. We then compared the positional offsets using pacing wires or catheters in the source FE-MRA (defined as points of interest [POIs]) and fused images (n = 5 patients, n = 247 points). Points within 3D image space were referenced to the respective modalities: x (right-left), y (anterior-posterior), and z (cranial-caudal). The respective 3D orthogonal reference axes from both image sets were aligned, such that with perfect registration, a given point would have the same (x, y, z) component values in both sets. The 3D offsets (Δx mm, Δy mm, Δz mm) for each of the corresponding POIs represent nonconcordance between the source FE-MRA and fused images. The offsets were compared using concordance correlation coefficients. Interobserver agreement was assessed using intraclass correlation coefficients and Bland-Altman analyses. RESULTS: Thirteen patients (aged 76 ± 12 years; seven female) with aortic valve stenosis and chronic kidney disease and two patients with thoracoabdominal vascular aneurysms and chronic kidney disease underwent FE-MRA for preprocedural vascular assessment, and unenhanced CT examinations were available in all patients. No ferumoxytol-related adverse events occurred. There were 247 matched POIs evaluated on the source FE-MRA and fused images. In patients with implantable medical devices, the mean offsets in spatial position were 0.31 ± 0.51 mm (ρ = 0.99; Cb = 1; 95% confidence interval [CI], 0.99-0.99) for Δx, 0.27 ± 0.69 mm (ρ = 0.99; Cb = 0.99; 95% CI, 0.99-0.99) for Δy, and 0.20 ± 0.59 mm (ρ = 1; Cb = 1; 95% CI, 0.99-1.00) for Δz. Interobserver agreement was excellent (intraclass correlation coefficient, >0.99). The mean difference in offset between readers was 1.5 mm. CONCLUSIONS: Accurate 3D feature fusion is feasible, combining luminal information from FE-MRA with vessel wall information on unenhanced CT. This framework holds promise for combining the complementary strengths of magnetic resonance imaging and CT to generate information-rich, multifeature composite vascular images while avoiding the respective risks and limitations of both modalities.

Biological effects of MRI contrast agents: gadolinium retention, potential mechanisms and a role for phosphorus.

No discussion of challenges for chemistry in molecular imaging would be complete without addressing the elephant in the room-which is that the purest of chemical compounds needs to interact with a biological system in a manner that does not perturb normal biology while still providing efficacious feedback to assist in diagnosis of disease. In the past decade, magnetic resonance imaging (MRI) agents long considered inert have produced adverse effects in certain patient populations under certain treatment regimens. More recently, inert blood pool agents have been found to deposit in the brain. Release of free metal is often suspected as the culprit but that hypothesis has yet to be validated. In addition, even innocuous agents can cause painful side effects during injection in some patients. In this brief review, we summarize known biological effects for gadolinium- and iron-based MRI contrast agents, and discuss some of the potential mechanisms for the observed biological effects, including the potential role of phosphorus imbalance, related to kidney disease or cancer, in destabilizing gadolinium-based chelates and precipitating free gadolinium.This article is part of the themed issue 'Challenges for chemistry in molecular imaging'.