Cumulative administrations of gadolinium-based contrast agents: risks of accumulation and toxicity of linear vs macrocyclic agents

Hepatobiliary phase MRI-guided radiofrequency ablation of small hepatocellular carcinomas invisible on precontrast MRI

PURPOSE

In cirrhotic livers reliable visualization and exact localization of small hepatocellular carcinoma (HCC) can be challenging without adequate contrast enhancement. To investigate the feasibility, technical success rate, and safety of hepatobiliary phase MRI-guided percutaneous radiofrequency ablation (RFA) of small HCCs invisible on precontrast MRI.

METHODS

53 patients (17f, 63.6 ± 16.7 years), with small HCC that were not visible in non-contrast MRI underwent MRI guided RFA. Feasibility was assessed by analyzing proper identification of the target tumor, tumor delineation during MRI-guided needle positioning and number of needle adjustments required for accurate placement. Technical success was defined as complete ablation with a safety margin of 5 mm. Safety was assessed from reports of procedure-related complications.

RESULTS

In all 53 cases, target tumors were not visible in non-contrast MRI but in the hepatobiliary phase. In 5 cases, planning imaging showed new tumors, which were either treated in the same session (n = 4) or altered the therapeutic approach (n = 1). Mean tumor diameter was 9.7 ± 1.9 mm and the number of needle adjustments was 5 ± 3. Post-ablation imaging showed a technical success rate of 98 % (51 cases, 55 tumors). No major complications occurred. Follow-up imaging (26.2 ± 22.4 month) showed no local tumor progression or recurrence.

CONCLUSIONS

Use of the hepatobiliary phase for MRI-guided ablation of otherwise MR-occult tumors is a feasible approach for an effective and safe treatment of small HCC nodules.

Electrochemical Filtration of Gadolinium from Patient Urine after Magnetic Resonance Imaging

The widespread use of gadolinium-based contrast agents for magnetic resonance imaging (MRI) in recent decades has led to a growing demand for Gd and raised environmental concerns due to their direct discharge into wastewater systems. In response, we developed an electrochemical filtration method to recover Gd from patient urine following contrast-enhanced MRI. This method involves modifying a conventional vacuum filtration apparatus by introducing electrodes into the filter membrane, creating a strong electric field of ∼5 kV/m and a steep three-zone pH gradient within the filter membrane. These electric and pH fields facilitate the dissociation of Gd-based contrast agents, releasing GdIII ions, electrophoretic separation of GdIII and its ligand, and eventually precipitation and trapping of GdIII as GdPO4 and Gd(OH)3 on the filter membrane. Using gadopentetate dimeglumine (GdDTPA) as a model Gd-based contrast agent, we achieved a Gd trapping efficiency of ∼70% for artificial and real urine samples. For macrocyclic Gd-based contrast agents such as gadoterate meglumine (GdDOTA), the Gd trapping efficiency decreased to 25.4% due to the slow dissociation kinetics of macrocyclic contrast agents. However, the trapping efficiency can be improved to ∼40% by allowing the macrocyclic contrast agent to predissociate in an acidic environment before electrochemical filtration. The Gd trapped on the filter membrane can be recovered by thermal treatment in a muffle furnace. After thermal treatment, the reclaimed Gd from the real urine sample was primarily identified as GdPO4. This electrochemical filtration design offers a straightforward and practical approach to recovering Gd from contrast-enhanced MRI scans, addressing the increasing demand for Gd and helping alleviate concerns about Gd contamination in surface water.

MR Imaging of Pediatric Neuroblastoma: Is Gadolinium Enhancement Necessary for Evaluation of Image-Defined-Risk Factors?

Background: Pre-treatment stratification and outcomes of neuroblastoma patients often depend on the assessment of image-defined risk factors (IDRFs) on MR Imaging, usually using Gadolinium-contrast materials which are cautioned in pediatrics. We aimed to address whether gadolinium contrast-enhanced sequences are necessary to identify the presence/absence of IDRFs. Methods: Patients with neuroblastoma with MR imaging were retrospectively identified from 2005 to 2021. Ninety confirmed IDRFs were evaluated in 23 patients. Corresponding MR studies were anonymized, randomized, and independently evaluated by 3 fellowship-trained pediatric radiologists. Each radiologist assessed the studies twice. At the first reading, all enhanced sequences were omitted, while in the second reading, the full study with enhanced sequences were included. Consensus reading was obtained among readers. Inter- and intra-rater agreements using Kappa statistics (κ) as well as the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of non-enhanced MR in assessing IDRFs with respect to enhanced MR were calculated. Results: There were substantial (ĸ: 0.64-0.73) intra-reader agreements, and moderate to substantial (ĸ: 0.57-0.62) inter-reader agreements among radiologists in identifying IDRFs using non-enhanced MR. Non-enhanced MR had a sensitivity of 87.8% (95% CI [79-94]), specificity of 93% (89-96), PPV of 82.3 (73-89), NPV of 95.4 (92-98), and accuracy of 91.6 (88-94) in identifying IDRFs. However, 5/23 patients (21.7%) had a change in staging with the inclusion of contrast sequences. Conclusion: Although contrast sequences have a role in IDRF assessment, the majority can be adequately assessed on MR without gadolinium-contrast enhancement. Validation in a larger cohort is an important next step.

Safety, Tolerability, and Pharmacokinetics of a Novel Macrocyclic Gadolinium-Based Contrast Agent, HNP-2006, in Healthy Subjects

OBJECTIVES

Gadolinium-based contrast agents (GBCAs) are indispensable in contrast-enhanced magnetic resonance imaging. A higher risk of gadolinium deposition in linear GBCAs required the introduction of macrocyclic GBCAs with a stable molecular structure. We conducted the first-in-human study to evaluate the safety, tolerability, and pharmacokinetics (PKs) of HNP-2006, a novel macrocyclic GBCA, in healthy male subjects.

MATERIALS AND METHODS

A randomized, placebo-controlled, double-blind, single-ascending dose study was conducted. Subjects received either a single intravenous bolus injection of HNP-2006 or its matching placebo with a treatment-to-placebo ratio of 6:2 at the dose level of 0.02, 0.05, 0.1, 0.2, and 0.3 mmol/kg. Safety was assessed through routine clinical assessments. Blood sampling and urine collection were performed up to 72 hours postdose for PK assessments. Noncompartmental methods were used to calculate PK parameters, and a population PK model was constructed.

RESULTS

Overall, 40 subjects completed the study. Fourteen subjects reported 22 treatment-emergent adverse events (TEAEs). The severity of all TEAEs was mild, and the HNP-2006 dose was associated with the incidence of TEAEs. The most common TEAEs included nausea and dizziness, which occurred within an hour of administration. HNP-2006 was rapidly eliminated by urinary excretion with a half-life of 1.8-2.0 hours and showed a dose-proportional PK. A 2-compartment model had the best fit with the population PK analysis.

CONCLUSIONS

A single intravenous dose of HNP-2006 was well-tolerated and safe up to 0.30 mmol/kg. HNP-2006 was rapidly excreted in urine and exhibited dose-independent PK profiles.

Preclinical Safety Assessment of Gadopiclenol: A High-Relaxivity Macrocyclic Gadolinium-Based MRI Contrast Agent

OBJECTIVE

Gadopiclenol is a new high-relaxivity macrocyclic gadolinium-based contrast agent for magnetic resonance imaging of the central nervous system and other body regions. The product has been approved by US Food and Drug Administration and is currently being evaluated by European Medicines Agency. For risk assessment of the single diagnostic use in humans, the safety profile of gadopiclenol was evaluated with a series of preclinical studies.

MATERIALS AND METHODS

With exception of dose-ranging studies, all safety pharmacology and toxicology studies were performed in compliance with Good Laboratory Practice principles. Safety pharmacology studies were conducted to assess potential effects on cardiovascular (in vitro and in dogs), respiratory (in rats and guinea pigs), neurological (in rats), and renal endpoints (in rats). Toxicology studies were also performed to investigate acute toxicity (in rats and mice), extended single-dose (in rats and dogs) and repeated-dose toxicity (in rats and dogs), reproductive (in rats), developmental (in rats and rabbits) and juvenile toxicity (in rats), as well as genotoxicity (in vitro and in rats), local tolerance (in rabbits), potential immediate hypersensitivity (in guinea pigs), and potential tissue retention of gadolinium (in rats).

RESULTS

Safety pharmacology studies conducted at high intravenous (IV) doses showed a satisfactory tolerance of gadopiclenol in the main body systems. After either single or repeated IV dosing (14 and 28 days) in rats and dogs, gadopiclenol was well tolerated even at high doses. The no-observed-adverse-effect level values (ie, the highest experimental dose without adverse effects) representing between 8 times in rats and 44 times in dogs (based on the exposure), the exposure achieved in humans at the intended diagnostic dose, provide a high safety margin. No or only minor and reversible effects on body weight, food consumption, clinical signs, clinical pathology parameters, or histology were observed at the highest doses. The main histological finding consists in renal tubular vacuolations (exacerbated after repeated exposure), which supports a well-known finding for this class of compounds that has no physiological consequence on kidney function. Reproductive toxicity studies showed no evidence of effects on reproductive performance, fertility, perinatal and postnatal development in rats, or reproductive development in rats or rabbits. The safety profile of gadopiclenol in juvenile rats was satisfactory like in adults. Gadopiclenol was not genotoxic in vitro in the Ames test, a mouse lymphoma assay, and a rat in vivo micronucleus test. There were no signs of local intolerance at the injection site after IV and intra-arterial administration in rabbits. However, because of minor signs of intolerance after perivenous administration, misadministration must be avoided. Gadopiclenol exhibited no signs of potential to induce immediate hypersensitivity in guinea pigs.

CONCLUSIONS

High safety margins were observed between the single diagnostic dose of 0.05 mmol/kg in humans and the doses showing effects in animal studies. Gadopiclenol is, therefore, well tolerated in various species (mice, rats, dogs, rabbits, and guinea pigs). All observed preclinical data support the clinical approval.

Mn-Based MRI Contrast Agents: An Overview

MRI contrast agents are required in the clinic to detect some pathologies, such as cancers. Nevertheless, at the moment, only small extracellular and non-specific gadolinium complexes are available for clinicians. Moreover, safety issues have recently emerged concerning the use of gadolinium complexes; hence, alternatives are urgently needed. Manganese-based MRI contrast agents could be one of these alternatives and increasing numbers of studies are available in the literature. This review aims at synthesizing all the research, from small Mn complexes to nanoparticular agents, including theranostic agents, to highlight all the efforts already made by the scientific community to obtain highly efficient agents but also evidence of the weaknesses of the developed systems.

Long-term safety of MRI-guided administration of AAV2-GDNF and gadoteridol in the putamen of individuals with Parkinson's disease

Direct putaminal infusion of adeno-associated virus vector (serotype 2) (AAV2) containing the human glial cell line-derived neurotrophic factor (GDNF) transgene was studied in a phase I clinical trial of participants with advanced Parkinson's disease (PD). Convection-enhanced delivery of AAV2-GDNF with a surrogate imaging tracer (gadoteridol) was used to track infusate distribution during real-time intraoperative magnetic resonance imaging (iMRI). Pre-, intra-, and serial postoperative (up to 5 years after infusion) MRI were analyzed in 13 participants with PD treated with bilateral putaminal co-infusions (52 infusions in total) of AAV2-GDNF and gadoteridol (infusion volume, 450 mL per putamen). Real-time iMRI confirmed infusion cannula placement, anatomic quantification of volumetric perfusion within the putamen, and direct visualization of off-target leakage or cannula reflux (which permitted corresponding infusion rate/cannula adjustments). Serial post-treatment MRI assessment (n = 13) demonstrated no evidence of cerebral parenchyma toxicity in the corresponding regions of AAV2-GDNF and gadoteridol co-infusion or surrounding regions over long-term follow-up. Direct confirmation of key intraoperative safety and efficacy parameters underscores the safety and tissue targeting value of real-time imaging with co-infused gadoteridol and putative therapeutic agents (i.e., AAV2-GDNF). This delivery-imaging platform enhances safety, permits delivery personalization, improves therapeutic distribution, and facilitates assessment of efficacy and dosing effect.

Exploring EPR Parameters of 187Re Complexes for Designing New MRI Probes: From the Gas Phase to Solution and a Model Protein Environment

Breast cancer is one of the major types of cancer around the world, and early diagnosis is essential for successful treatment. New contrast agents (CAs), with reduced toxicology, are needed to improve diagnosis. One of the most promising Magnetic Resonance Imaging (MRI) CA is based on rhenium conjugated with a benzothiazole derivate (ReABT). In this sense, DFT has been used to evaluate the best methodology for calculating the hyperfine coupling constant (Aiso) of ReABT. Then, a thermodynamic analysis was performed to confirm the stability of the complex. Furthermore, a docking study of ReABT at the enzyme PI3K active site and Aiso calculations of ReABT in the enzyme environment were carried out. The best methodology for the Aiso calculation of ReABT was using the M06L functional, SARC-ZORA-TZVP (for Re) and TZVP (for all other atoms) basis set, relativistic Hamiltonian, and the CPCM solvation model with water as the solvent which confirm that the relativistic effects are important for calculating the Aiso values. In addition, thermodynamic analysis indicates that ReABT presents a higher stability and a lower toxicity than Gd-based CAs. The docking studies point out that ReABT interacts with amino acids residues of alanine, aspartate, and lysine from the PI3K active site. Considering the enzyme environment, Aiso values decrease significantly. These findings indicate that the CA candidate ReABT could be a good candidate for a new contrast agent.

Preclinical Profile of Gadoquatrane: A Novel Tetrameric, Macrocyclic High Relaxivity Gadolinium-Based Contrast Agent

OBJECTIVES

The aim of this report was to characterize the key physicochemical, pharmacokinetic (PK), and magnetic resonance imaging (MRI) properties of gadoquatrane (BAY 1747846), a newly designed tetrameric, macrocyclic, extracellular gadolinium-based contrast agent (GBCA) with high relaxivity and stability.

MATERIALS AND METHODS

The r1-relaxivities of the tetrameric gadoquatrane at 1.41 and 3.0 T were determined in human plasma and the nuclear magnetic relaxation dispersion profiles in water and plasma. The complex stability was analyzed in human serum over 21 days at pH 7.4 at 37°C and was compared with the linear GBCA gadodiamide and the macrocyclic GBCA (mGBCA) gadobutrol. In addition, zinc transmetallation assay was performed to investigate the kinetic inertness. Protein binding and the blood-to-plasma ratio were determined in vitro using rat and human plasma. The PK profile was evaluated in rats (up to 7 days postinjection). Magnetic resonance imaging properties were investigated using a glioblastoma (GS9L) rat model.

RESULTS

The new chemical entity gadoquatrane is a macrocyclic tetrameric Gd complex with one inner sphere water molecule per Gd ( q = 1). Gadoquatrane showed high solubility in buffer (1.43 mol Gd/L, 10 mM Tris-HCl, pH 7.4), high hydrophilicity (logP -4.32 in 1-butanol/water), and negligible protein binding. The r1-relaxivity of gadoquatrane in human plasma per Gd of 11.8 mM -1 ·s -1 (corresponding to 47.2 mM -1 ·s -1 per molecule at 1.41 T at 37°C, pH 7.4) was more than 2-fold (8-fold per molecule) higher compared with established mGBCAs. Nuclear magnetic relaxation dispersion profiles confirmed the more than 2-fold higher r1-relaxivity in human plasma for the clinically relevant magnetic field strengths from 0.47 to 3.0 T. The complex stability of gadoquatrane at physiological conditions was very high. The observed Gd release after 21 days at 37°C in human serum was below the lower limit of quantification. Gadoquatrane showed no Gd 3+ release in the presence of zinc in the transmetallation assay. The PK profile (plasma elimination, biodistribution, recovery) was comparable to that of gadobutrol. In MRI, the quantitative evaluation of the tumor-to-brain contrast in the rat glioblastoma model showed significantly improved contrast enhancement using gadoquatrane compared with gadobutrol at the same Gd dose administered (0.1 mmol Gd/kg body weight). In comparison to gadoterate meglumine, similar contrast enhancement was reached with gadoquatrane with 75% less Gd dose. In terms of the molecule dose, this was reduced by 90% when compared with gadoterate meglumine. Because of its tetrameric structure and hence lower number of molecules per volume, all prepared formulations of gadoquatrane were iso-osmolar to blood.

CONCLUSIONS

The tetrameric gadoquatrane is a novel, highly effective mGBCA for use in MRI. Gadoquatrane provides favorable physicochemical properties (high relaxivity and stability, negligible protein binding) while showing essentially the same PK profile (fast extracellular distribution, fast elimination via the kidneys in an unchanged form) to established mGBCAs on the market. Overall, gadoquatrane is an excellent candidate for further clinical development.

Long-term Gadolinium Retention in the Healthy Rat Brain: Comparison between Gadopiclenol, Gadobutrol, and Gadodiamide

Background Safety concerns caused by gadolinium retention call for the development of high-relaxivity gadolinium-based contrast agents (GBCAs) allowing minimal dosing. Purpose To investigate brain gadolinium retention in healthy rats after exposure to gadopiclenol (Elucirem, Guerbet; macrocyclic GBCA) compared with gadobutrol (Gadovist or Gadavist, Bayer; macrocyclic GBCA) and gadodiamide (Omniscan, GE Healthcare; linear GBCA) over 1 year. Materials and Methods In this study conducted between May 2018 and April 2020, 9-week-old healthy Sprague Dawley rats received five injections of either gadopiclenol, gadobutrol, or gadodiamide (2.4 mmol of gadolinium per kilogram of body weight for each), or saline (control animals) over a period of 5 weeks. Rats were randomly assigned to different groups (six female and six male rats per group). MRI examinations were performed before euthanasia at 1, 3, 5, or 12 months after the last injection. Brains were sampled to determine the total gadolinium content via inductively coupled plasma mass spectrometry (ICP-MS), to characterize gadolinium species with size exclusion chromatography (SEC)-ICP-MS, and to perform elemental mapping with laser ablation (LA)-ICP-MS. Mann-Whitney tests were performed on pairwise comparisons of the same time points. Results For both macrocyclic agents, no T1 signal hyperintensities were observed in the cerebellum, and approximately 80% of gadolinium washout was found between 1 month (gadobutrol, 0.30 nmol/g; gadopiclenol, 0.37 nmol/g) and 12 months (gadobutrol, 0.062 nmol/g; gadopiclenol, 0.078 nmol/g). After 12 months, only low-molecular-weight gadolinium species were detected in the soluble fraction. Gadodiamide led to significantly higher gadolinium concentrations after 1 month in the cerebellum (gadodiamide, 2.65 nmol/g; P < .001 vs both macrocyclics) combined with only 15% washout after 12 months (gadodiamide, 2.25 nmol/g) and with gadolinium detected bound to macromolecules. Elemental bioimaging enabled visualization of gadolinium deposition patterns colocalized with iron. Conclusion Gadopiclenol and gadobutrol demonstrated similar in vivo distribution and washout of gadolinium in the healthy rat brain, markedly differing from gadodiamide up to 12 months after the last injection. © RSNA, 2022 Online supplemental material is available for this article.

Surveillance for hepatocellular carcinoma: current status and future perspectives for improvement

INTRODUCTION

Hepatocellular carcinoma (HCC) is a globally relevant medical problem. Fortunately, risk factors for this tumor have been identified, and surveillance protocols developed. Patients with liver cirrhosis have the highest risk of developing HCC and have historically been included in surveillance programs. Special categories have also emerged in recent years, especially patients with eradicated HCV infection or nonalcoholic fatty liver disease. Novel serum biomarkers and magnetic resonance imaging protocols are currently being proposed to refine existing surveillance protocols.

AREAS COVERED

We discuss the rationale of surveillance programs for HCC and report the most recent recommendations from international guidelines about this topic. Gray areas, such as nonalcoholic fatty liver disease and the role of intrahepatic cholangiocellular carcinoma, are also discussed.

EXPERT OPINION

Surveillance is recognized as a tool to favor early diagnosis of HCC, access to curative treatment, and increase survival, even if the supporting evidence is mainly based on observational studies. As new randomized clinical trials are difficult to propose, future challenges will include optimizing implementation in the primary care setting and a more personalized approach, balancing the opportunities and risks of overdiagnosis of novel techniques and biomarkers.

Assessment of genetic damage induced by gadolinium-based radiocontrast agents

BACKGROUND

Today, although gadolinium based contrast agents have been frequently used in the field of medicine, there is limited data available whether gadolinium based agents affect the genome.

AIM

The present study aimed to investigate the genotoxic and cytotoxic potentials of gadoteric acid and gadoversetamide used as gadolinium-based contrast agents for magnetic resonance (MR) imaging.

MATERIAL AND METHODS

The cytokinesis-block micronucleus assay was applied to human peripheral blood lymphocytes to assess the genotoxicity measured as micronucleus (MN), nucleoplasmic bridge (NPBs) and nuclear bud (NBUDs) frequencies. Furthermore, cytokinesis-block proliferation index (CBPI) was calculated to determine cytostasis. Lymphocytes were treated with gadoteric acid at concentrations of 1.0, 2.5, 5.0, and 25 mM and with gadoversetamide at concentrations of 0.25, 1.0, 2.5, and 5.0 mM for 48 h.

RESULTS

Gadoteric acid did not cause significant increase in MN, NBPs and NBUDs frequencies and CBPI values at any concentration. Gadoversetamide induced significantly increase MN formation at concentration of 2.5 mM, NBP formation at concentrations of 1.0 and 2.5 mM, and NBUD formation at concentrations of 0.25, 1.0 and 2.5 mM. Additionally, gadoversetamide exposure resulted in statistically significant decrease in CBPI values compared to the control at concentrations of 2.5 and 5.0 mM. In addition, CBPI levels in response to concentrations of gadoversetamide was negatively and significantly associated with concentration.

CONCLUSION

These findings show that gadoteric acid does not have genotoxic or cytotoxic potential, while gadoversetamide might have both genotoxic and cytotoxic potential on human peripheral blood lymphocytes. As a comparison, gadoversetamide was found more genotoxic and cytotoxic.

Survey of centers performing cardiovascular magnetic resonance in pediatric and congenital heart disease: a report of the Society for Cardiovascular Magnetic Resonance

BACKGROUND

There are few data on practice patterns and trends for cardiovascular magnetic resonance (CMR) in pediatric and congenital heart disease. The Society for Cardiovascular Magnetic Resonance (SCMR) sought to address this deficiency by performing an international survey of CMR centers.

METHODS

Surveys consisting of 31 (2014) and 33 (2018) items were designed to collect data on the use of CMR for the evaluation of pediatric and congenital heart disease patients. They were sent to all SCMR members in 2014 and 2018. One response per center was collected.

RESULTS

There were 93 centers that responded in 2014 and 83 in 2018. The results that follow show data from 2014 and 2018 separated by a dash. The median annual number of pediatric/congenital CMR cases per center was 183-209. The median number of scanners for CMR was 2-2 (range, 1-8) with 58-63% using only 1.5T scanners and 4-4% using only 3T scanners. The mean number of attending/staff reading CMRs was 3.7-2.6; among them, 52-61% were pediatric or adult cardiologists and 47-38% were pediatric or adult radiologists. The median annual case volume per attending was 54-86. The median number of technologists per center doing CMRs was 4-5. The median scanner time allocated for a non-sedated examination was 75-75 min (range, 45-120). Among the 21 centers responding to both surveys, the mean annual case volume increased from 320 in 2014 to 445 in 2018; 17 (81%) of the centers had an increase in annual case volume. For this subgroup, the median attending/staff per center was 4 in both 2014 and 2018. The median scanner time allotted per study was unchanged at 90 min. The mean time for an attending/staff physician to perform a typical CMR examination including reporting was 143-141 min.

CONCLUSION

These survey data provide a novel comprehensive view of CMR practice in pediatric and congenital heart disease. This information is useful for internal benchmarking, resource allocation, addressing practice variation, quality improvement initiatives, and identifying unmet needs.

Small Brain Lesion Enhancement and Gadolinium Deposition in the Rat Brain: Comparison Between Gadopiclenol and Gadobenate Dimeglumine

OBJECTIVES

The aim of the set of studies was to compare gadopiclenol, a new high relaxivity gadolinium (Gd)-based contrast agent (GBCA) to gadobenate dimeglumine in terms of small brain lesion enhancement and Gd retention, including T1 enhancement in the cerebellum.

MATERIALS AND METHODS

In a first study, T1 enhancement at 0.1 mmol/kg body weight (bw) of gadopiclenol or gadobenate dimeglumine was evaluated in a small brain lesions rat model at 2.35 T. The 2 GBCAs were injected in an alternated and cross-over manner separated by an interval of 4.4 ± 1.0 hours (minimum, 3.5 hours; maximum, 6.1 hours; n = 6). In a second study, the passage of the GBCAs into cerebrospinal fluid (CSF) was evaluated by measuring the fourth ventricle T1 enhancement in healthy rats at 4.7 T over 23 minutes after a single intravenous (IV) injection of 1.2 mmol/kg bw of gadopiclenol or gadobenate dimeglumine (n = 6/group). In a third study, Gd retention at 1 month was evaluated in healthy rats who had received 20 IV injections of 1 of the 2 GBCAs (0.6 mmol/kg bw) or a similar volume of saline (n = 10/group) over 5 weeks. T1 enhancement of the deep cerebellar nuclei (DCN) was assessed by T1-weighted magnetic resonance imaging at 2.35 T, performed before the injection and thereafter once a week up to 1 month after the last injection. Elemental Gd levels in central nervous system structures, in muscle and in plasma were determined by inductively coupled plasma mass spectrometry (ICP-MS) 1 month after the last injection.

RESULTS

The first study in a small brain lesion rat model showed a ≈2-fold higher number of enhanced voxels in lesions with gadopiclenol compared with gadobenate dimeglumine. T1 enhancement of the fourth ventricle was observed in the first minutes after a single IV injection of gadopiclenol or gadobenate dimeglumine (study 2), resulting, in the case of gadopiclenol, in transient enhancement during the injection period of the repeated administrations study (study 3). In terms of Gd retention, T1 enhancement of the DCN was noted in the gadobenate dimeglumine group during the month after the injection period. No such enhancement of the DCN was observed in the gadopiclenol group. Gadolinium concentrations 1 month after the injection period in the gadopiclenol group were slightly increased in plasma and lower by a factor of 2 to 3 in the CNS structures and muscles, compared with gadobenate dimeglumine.

CONCLUSIONS

In the small brain lesion rat model, gadopiclenol provides significantly higher enhancement of brain lesions compared with gadobentate dimeglumine at the same dose. After repeated IV injections, as expected for a macrocyclic GBCA, Gd retention is minimalized in the case of gadopiclenol compared with gadobenate dimeglumine, resulting in no T1 hypersignal in the DCN.

Iron Rims in Patients With Multiple Sclerosis as Neurodegenerative Marker? A 7-Tesla Magnetic Resonance Study

Introduction: Multiple sclerosis (MS) is a demyelinating and neurodegenerative disease of the central nervous system, characterized by inflammatory-driven demyelination. Symptoms in MS manifest as both physical and neuropsychological deficits. With time, inflammation is accompanied by neurodegeneration, indicated by brain volume loss on an MRI. Here, we combined clinical, imaging, and serum biomarkers in patients with iron rim lesions (IRLs), which lead to severe tissue destruction and thus contribute to the accumulation of clinical disability.

Objectives: Subcortical atrophy and ventricular enlargement using an automatic segmentation pipeline for 7 Tesla (T) MRI, serum neurofilament light chain (sNfL) levels, and neuropsychological performance in patients with MS with IRLs and non-IRLs were assessed.

Methods: In total 29 patients with MS [15 women, 24 relapsing-remitting multiple sclerosis (RRMS), and five secondary-progressive multiple sclerosis (SPMS)] aged 38 (22–69) years with an Expanded Disability Status Score of 2 (0–8) and a disease duration of 11 (5–40) years underwent neurological and neuropsychological examinations. Volumes of lesions, subcortical structures, and lateral ventricles on 7-T MRI (SWI, FLAIR, and MP2RAGE, 3D Segmentation Software) and sNfL concentrations using the Simoa SR-X Analyzer in IRL and non-IRL patients were assessed.

Results: (1) Iron rim lesions patients had a higher FLAIR lesion count (p = 0.047). Patients with higher MP2Rage lesion volume exhibited more IRLs (p <0.014) and showed poorer performance in the information processing speed tested within 1 year using the Symbol Digit Modalities Test (SDMT) (p <0.047). (2) Within 3 years, patients showed atrophy of the thalamus (p = 0.021) and putamen (p = 0.043) and enlargement of the lateral ventricles (p = 0.012). At baseline and after 3 years, thalamic volumes were lower in IRLs than in non-IRL patients (p = 0.045). (3) At baseline, IRL patients had higher sNfL concentrations (p = 0.028). Higher sNfL concentrations were associated with poorer SDMT (p = 0.004), regardless of IRL presence. (4) IRL and non-IRL patients showed no significant difference in the neuropsychological performance within 1 year.

Conclusions: Compared with non-IRL patients, IRL patients had higher FLAIR lesion counts, smaller thalamic volumes, and higher sNfL concentrations. Our pilot study combines IRL and sNfL, two biomarkers considered indicative for neurodegenerative processes. Our preliminary data underscore the reported destructive nature of IRLs.

Long-term evolution of multiple sclerosis iron rim lesions in 7 T MRI

Recent data suggest that multiple sclerosis white matter lesions surrounded by a rim of iron containing microglia, termed iron rim lesions, signify patients with more severe disease course and a propensity to develop progressive multiple sclerosis. So far, however, little is known regarding the dynamics of iron rim lesions over long-time follow-up. In a prospective longitudinal cohort study in 33 patients (17 females; 30 relapsing-remitting, three secondary progressive multiple sclerosis; median age 36.6 years (18.6-62.6), we characterized the evolution of iron rim lesions by MRI at 7 T with annual scanning. The longest follow-up was 7 years in a subgroup of eight patients. Median and mean observation period were 1 (0-7) and 2.9 (±2.6) years, respectively. Images were acquired using a fluid-attenuated inversion recovery sequence fused with iron-sensitive MRI phase data, termed FLAIR-SWI, as well as a magnetization prepared two rapid acquisition gradient echoes, termed MP2RAGE. Volumes and T1 relaxation times of lesions with and without iron rims were assessed by manual segmentation. The pathological substrates of periplaque signal changes outside the iron rims were corroborated by targeted histological analysis on 17 post-mortem cases (10 females; two relapsing-remitting, 13 secondary progressive and two primary progressive multiple sclerosis; median age 66 years (34-88), four of them with available post-mortem 7 T MRI data. We observed 16 nascent iron rim lesions, which mainly formed in relapsing-remitting multiple sclerosis. Iron rim lesion fraction was significantly higher in relapsing-remitting than progressive disease (17.8 versus 7.2%; P < 0.001). In secondary progressive multiple sclerosis only, iron rim lesions showed significantly different volume dynamics (P < 0.034) compared with non-rim lesions, which significantly shrank with time in both relapsing-remitting (P < 0.001) and secondary progressive multiple sclerosis (P < 0.004). The iron rims themselves gradually diminished with time (P < 0.008). Compared with relapsing-remitting multiple sclerosis, iron rim lesions in secondary progressive multiple sclerosis were significantly more destructive than non-iron rim lesions (P < 0.001), reflected by prolonged lesional T1 relaxation times and by progressively increasing changes ascribed to secondary axonal degeneration in the periplaque white matter. Our study for the first time shows that chronic active lesions in multiple sclerosis patients evolve over many years after their initial formation. The dynamics of iron rim lesions thus provide one explanation for progressive brain damage and disability accrual in patients. Their systematic recording might become useful as a tool for predicting disease progression and monitoring treatment in progressive multiple sclerosis.

Superparamagnetic iron oxide-enhanced MRI-guided stereotactic ablative radiation therapy for liver metastasis

Background

MRI-guided radiation therapy can image a target and irradiate it at the same time. Superparamagnetic iron oxide (SPIO) is a liver-specific contrast agent that can selectively visualize liver tumors, even if plain MRI does not depict them. The purpose of this study was to present a proof of concept of SPIO-enhanced MRI-guided radiation therapy for liver tumor.

Case presentation

MRI-guided stereotactic ablative radiation therapy (SABR) was planned for a patient with impaired renal function who developed liver metastases after nephroureterectomy for ureteral cancer. Because liver metastasis was not visualized on plain MRI, SPIO-enhanced MRI was performed at 0.35 T using true fast imaging with steady-state free precession (true FISP) pulse sequence and SABR was performed. Liver metastasis was clearly visualized by SPIO-enhanced MRI, and MRI-guided SABR was performed without adverse events.

Conclusion

Even if liver metastasis is not visualized by plain MRI, liver metastasis can be clearly depicted by administering SPIO, and MRI-guided radiation therapy can be performed.

Clinical Efficacy of Reduced Dose Gadobutrol Versus Standard Dose Gadoterate for Contrast-Enhanced MRI of the CNS: An International Multicenter Prospective Crossover Trial (LEADER-75)

Background: Gadobutrol and gadoterate are widely used macrocyclic gadolinium-based contrast agents. Given gadobutrol's higher T1 relaxivity, reduced gadobutrol dose should achieve essentially equivalent diagnostic efficacy as standard gadoterate dose. Objective: To demonstrate that efficacy of 25%-reduced dose of gadobutrol (rd-gadobutrol) is non-inferior to 100%-standard-dose of gadoterate (sd-gadoterate) for contrast-enhanced MRI of the CNS. Methods: In this international, prospective, multicenter, open-label, cross-over trial (LEADER-75), adult patients with known or suspected CNS pathology underwent contrast-enhanced brain MRI with sd-gadoterate (0.1 mmol/kg); if an enhancing lesion was identified, a second MRI with rd-gadobutrol (0.075 mmol/kg) was performed within 15 days. Three radiologists independently reviewed images to score three primary efficacy measures (subjective lesion enhancement, lesion border delineation, lesion internal morphology); primary non-inferiority analysis used readers' mean scores. Non-inferiority of rd-gadobutrol to sd-gadoterate for primary efficacy measures was defined as difference in score between rd-gadobutrol and unenhanced images achieving at least 80% of difference in score between sd-gadoterate and unenhanced images. Post-hoc analysis was performed to directly compare contrast-enhanced images for equivalence. Secondary efficacy variables included number of lesions detected, reader confidence, diagnostic performance for malignancy, and reader preference in side-by-side comparison. Results: The efficacy analysis included 141 patients (78 men, 63 women; mean age, 58.5±13.5 years). Improvement of rd-gadobutrol over unenhanced images was non-inferior to improvement of sd-gadoterate over unenhanced images using 20% non-inferiority margin for all three primary efficacy measures using mean readings (p≤.025). In post-hoc analysis, mean reading for the three primary efficacy measures differed by less than 1% between rd-gadobutrol and sd-gadoterate, supporting equivalence of all measures using a narrow ±5% margin (p≤.025). Total lesions detected by mean reading was 301 for rd-gadobutrol versus 291 for sd-gadoterate. Mean confidence was 3.3±0.6 for rd-gadobutrol versus 3.3±0.6 for sd-gadoterate. Sensitivity (58.7%), specificity (91.8%), and accuracy (70.2%) for malignancy from majority reading were identical for rd-gadobutrol and sd-gadoterate. Reader preference was not different (95% CI [-0.10, 0.11]). Conclusion: A 25%-reduced dose of gadobutrol is non-inferior to sd-gadoterate for contrast-enhanced brain MRI. Clinical Impact: Use of rd-gadobutrol should be considered for brain MRI, particularly in patients undergoing multiple contrast-enhanced examinations.

Measuring Perfusion: Intravoxel Incoherent Motion MR Imaging

The signal acquired in vivo using a diffusion-weighted MR imaging (DWI) sequence is influenced by blood motion in the tissue. This means that perfusion information from a DWI sequence can be obtained in addition to thermal diffusion, if the appropriate sequence parameters and postprocessing methods are applied. This is commonly regrouped under the denomination intravoxel incoherent motion (IVIM) perfusion MR imaging. Of relevance, the perfusion information acquired with IVIM is essentially local, quantitative and acquired without intravenous injection of contrast media. The aim of this work is to review the IVIM method and its clinical applications.

PVP-coated Gd-grafted nanodiamonds as a novel and potentially safer contrast agent for in vivo MRI

PURPOSE

Testing the potential use of saline suspension of polyvinylpyrrolidone (PVP)-coated gadolinium(Gd)-grafted detonation nanodiamonds (DND) as a novel contrast agent in MRI.

METHODS

Stable saline suspensions of highly purified de-agglomerated Gd-grafted DND particles coated by a PVP protective shell were prepared. T₁ and T₂ proton relaxivities of the suspensions with varying gadolinium concentration were measured at 8 Tesla. A series of ex vivo (phantom) and in vivo dynamic scans were obtained in 3 Tesla MRI using PVP-coated Gd-grafted DND and gadoterate meglumin in equal concentrations of gadolinium, and then T₁ -weighted hyperintensity was compared.

RESULTS

The proton relaxivities of PVP-coated Gd-grafted DND were found to be r₁ = 15.9 ± 0.8 s^-1 mM^-1 and r₂ = 262 ± 15 s^-1 mM^-1 , respectively, which are somewhat less than those for uncoated Gd-grafted DND but still high enough. Ex vivo MRI evaluation of PVP-coated Gd-grafted DND results with a dose-dependent T₁ -weighted hyperintensity with a significant advantage over the same for gadoterate meglumin. The same was found when the 2 contrast agents were tested in vivo.

CONCLUSION

The novel MRI contrast agent - saline suspensions of PVP-coated Gd-grafted DND - provides significantly higher signal intensities than the common tracer gadoterate meglumin, therefore increasing its potential for a safer use in clinics.

Signal Intensity Evaluation in the Dentate Nucleus and Subcortical Gray Matter : Effect of Several Administrations of Gadoterate Meglumine in Multiple Sclerosis

PURPOSE

Several studies reported gadolinium deposition in the dentate nuclei (DN) and the globus pallidus (GP) that was associated to linear GBCA administrations rather than macrocyclic. It is therefore imperative to evaluate and assess the safety of cumulative administration of gadoterate meglumine (macrocyclic). Thus, T1-weighted images (T1WI) of multiple sclerosis (MS) patients longitudinally followed for 4 years were retrospectively analyzed.

METHODS

In this study 44 patients, 10 with clinically isolated syndrome (CIS), 24 relapsing-remitting MS (RRMS) and 10 primary-progressive MS (PPMS) were examined every 6 months (first four scans) and then with a 1-year interval (last two scans). Image processing consisted in reorienting unenhanced T1WI to standard space, followed by B1 inhomogeneity correction. A patient-specific template was then generated to normalize T1WI signal intensity (SI) and segment the DN and subcortical GM structures. All structures were then transformed to each patient space in order to measure the SI in each region. The cerebellar peduncles (CP) and semi-oval (SO) white matter were then manually delineated and used as reference to calculate SI ratios in the DN and subcortical GM structures. A linear mixed-effect model was finally applied to longitudinally analyze SI variations.

RESULTS

The SI measurements performed in all structures showed no significant increases with the cumulative GBCA administration.

CONCLUSION

This study showed no significant SI increases within the DN and subcortical GM structures of longitudinally followed MS patients even with the cumulative administration of the macrocyclic GBCA gadoterate meglumine.

A gadofullerene based liver-specific MRI contrast agent for an early diagnosis of orthotopic hepatocellular carcinoma

Hepatocellular carcinoma has become one of the most prevalent cancers, with a high mortality rate. Accurate diagnosis at an earlier stage is regarded as an effective measure to reduce the disease-related mortality of liver cancer. Magnetic resonance imaging (MRI) as a non-invasive checking mode has become a powerful tool in medical diagnosis. However, MRI contrast agents for liver-specific imaging either have some side effects or the imaging effect is not ideal. Thus, development of more efficient and security MRI contrast agents for the early diagnosis of hepatocellular carcinoma is urgent. Herein, a kind of water-soluble gadofullerene nanoparticle (GFNP) with high efficiency and security has been successfully used to achieve in situ liver cancer imaging. By comparing GFNPs with different functional groups, Gd@C82 modified by a hydroxyl group (GF-OH) presents the highest contrast efficiency both in vitro and in vivo. Notably, the smallest tumor with a diameter of only 0.5 mm could be clearly observed by GF-OH using MRI. Moreover, the imaging window of GF-OH is more than 3-6 hours. In addition, GF-OH can be mostly excreted from the living body and causes no serious toxicity. These results demonstrate that GF-OH is a safe, efficient MRI contrast agent for the diagnosis of early orthotopic hepatocellular carcinoma.

Gadolinium-based contrast agents: What we learned from acute adverse events, nephrogenic systemic fibrosis and brain retention

BACKGROUND

 Radiologists have been administering gadolinium-based contrast agents (GBCA) in magnetic resonance imaging for several decades, so that there is abundant experience with these agents regarding allergic-like reactions, nephrogenic systemic fibrosis (NSF) and gadolinium retention in the brain.

METHODS

 This review is based on a selective literature search and reflects the current state of research on acute adverse effects of GBCA, NSF and brain retention of gadolinium.

RESULTS

 Due to the frequent use of GBCA, data on adverse effects of these compounds are available in large collectives. Allergic-like reactions occurred rarely, whereas severe acute reactions were very rarely observed. Systemic changes in NSF also occur very rarely, although measures to avoid NSF resulted in a significantly reduced incidence of NSF. Due to gadolinium retention in the body after administration of linear MR contrast agents, only macrocyclic preparations are currently used with few exceptions. Clear clinical correlates of gadolinium retention in the brain could not be identified so far. Although the clinical added value of GBCA is undisputed, individual risks associated with the injection of GBCA should be identified and the use of non-contrast enhanced MR techniques should be considered. Alternative contrast agents such as iron oxide nanoparticles are not clinically approved, but are currently undergoing clinical trials.

CONCLUSION

 GBCA have a very good risk profile with a low rate of adverse effects or systemic manifestations such as NSF. Gadolinium retention in the brain can be minimized by the use of macrocyclic GBCA, although clear clinical correlates due to gadolinium retention in the brain following administration of linear GBCA could not be identified yet.

KEY POINTS

· Acute adverse effects are predominantly mild/moderate, rarely severe reactions occur.. · International guidelines resulted in significant reduction of nephrogenic systemic fibrosis.. · Application of macrocyclic contrast agents minimizes gadolinium retention in the brain..

CITATION FORMAT

· Bäuerle T, Saake M, Uder M. Gadolinium-based contrast agents: What we learned from acute adverse events, nephrogenic systemic fibrosis and brain retention. Fortschr Röntgenstr 2021; 193: 1010 - 1018.

A mini-review of X-ray photodynamic therapy (XPDT) nonoagent constituents' safety and relevant design considerations

Conventional photodynamic therapy (PDT) has proved effective in the management of primary tumors and individual metastases. However, most cancer mortality arises from wide-spread multiple metastases. The latter has thus become the principal target in oncology, and X-ray induced photodynamic therapy (XPDT or PDTX) offers a great solution for adapting the PDT principle to deep tumors and scattered metastases. Developing agents capable of being excited by X-rays and emitting visible light to excite photosensitizers is based on challenging physical and chemical technologies, but there are fundamental biological limitations that are to be accounted for as well. In the present review, we have established eight major groups of safety determinants of NPs encompassing 22 parameters of clinical applicability of XPDT nanoparticulate formulations. Most, if not all, of these parameters can be accounted for and optimized during the design and development of novel XPDT nanoparticles.

Retention of Gadolinium in Brain Parenchyma: Pathways for Speciation, Access, and Distribution. A Critical Review

The unexpected appearance of T₁ hyperintensities, mostly in the dentate nucleus and the globus pallidus, during nonenhanced MRI was reported in 2014. This effect is associated with prior repeated administrations of gadolinium (Gd)‐based contrast agents (GBCAs) in patients with a functional blood–brain barrier (BBB). It is widely assumed that GBCAs do not cross the intact BBB, but the observation of these hypersignals raises questions regarding this assumption. This review critically discusses the mechanisms of Gd accumulation in the brain with regard to access pathways, Gd species, tissue distribution, and subcellular location. We propose the hypothesis that there is early access of Gd species to cerebrospinal fluid, followed by passive diffusion into the brain parenchyma close to the cerebral ventricles. When accessing areas rich in endogenous metals or phosphorus, the less kinetically stable GBCAs would dissociate, and Gd would bind to endogenous macromolecules, and/or precipitate within the brain tissue. It is also proposed that Gd species enter the brain parenchyma along penetrating cortical arteries in periarterial pial‐glial basement membranes and leave the brain along intramural peri‐arterial drainage (IPAD) pathways. Lastly, Gd/GBCAs may access the brain parenchyma directly from the blood through the BBB in the walls of capillaries. It is crucial to distinguish between the physiological distribution and drainage pathways for GBCAs and the possible dissociation of less thermodynamically/kinetically stable GBCAs that lead to long‐term Gd deposition in the brain.

Level of Evidence

5.

Technical Efficacy Stage

3.

Impact of the Kaiser score on clinical decision-making in BI-RADS 4 mammographic calcifications examined with breast MRI

OBJECTIVES

To investigate whether the application of the Kaiser score for breast magnetic resonance imaging (MRI) might downgrade breast lesions that present as mammographic calcifications and avoid unnecessary breast biopsies METHODS: This IRB-approved, retrospective, cross-sectional, single-center study included 167 consecutive patients with suspicious mammographic calcifications and histopathologically verified results. These patients underwent a pre-interventional breast MRI exam for further diagnostic assessment before vacuum-assisted stereotactic-guided biopsy (95 malignant and 72 benign lesions). Two breast radiologists with different levels of experience independently read all examinations using the Kaiser score, a machine learning-derived clinical decision-making tool that provides probabilities of malignancy by a formalized combination of diagnostic criteria. Diagnostic performance was assessed by receiver operating characteristics (ROC) analysis and inter-reader agreement by the calculation of Cohen's kappa coefficients.

RESULTS

Application of the Kaiser score revealed a large area under the ROC curve (0.859-0.889). Rule-out criteria, with high sensitivity, were applied to mass and non-mass lesions alike. The rate of potentially avoidable breast biopsies ranged between 58.3 and 65.3%, with the lowest rate observed with the least experienced reader.

CONCLUSIONS

Applying the Kaiser score to breast MRI allows stratifying the risk of breast cancer in lesions that present as suspicious calcifications on mammography and may thus avoid unnecessary breast biopsies.

KEY POINTS

• The Kaiser score is a helpful clinical decision tool for distinguishing malignant from benign breast lesions that present as calcifications on mammography. • Application of the Kaiser score may obviate 58.3-65.3% of unnecessary stereotactic biopsies of suspicious calcifications. • High Kaiser scores predict breast cancer with high specificity, aiding clinical decision-making with regard to re-biopsy in case of negative results.

A Bioinspired Nanoprobe with Multilevel Responsive T1 -Weighted MR Signal-Amplification Illuminates Ultrasmall Metastases

Metastasis remains the major cause of death in cancer patients. Thus, there is a need to sensitively detect tumor metastasis, especially ultrasmall metastasis, for early diagnosis and precise treatment of cancer. Herein, an ultrasensitive T₁ -weighted magnetic resonance imaging (MRI) contrast agent, UMFNP-CREKA is reported. By conjugating the ultrasmall manganese ferrite nanoparticles (UMFNPs) with a tumor-targeting penta-peptide CREKA (Cys-Arg-Glu-Lys-Ala), ultrasmall breast cancer metastases are accurately detected. With a behavior similar to neutrophils' immunosurveillance process for eliminating foreign pathogens, UMFNP-CREKA exhibits a chemotactic "targeting-activation" capacity. UMFNP-CREKA is recruited to the margin of tumor metastases by the binding of CREKA with fibrin-fibronectin complexes, which are abundant around tumors, and then release of manganese ions (Mn²⁺ ) to the metastasis in response to pathological parameters (mild acidity and elevated H₂ O₂ ). The localized release of Mn²⁺ and its interaction with proteins affects a marked amplification of T₁ -weighted magnetic resonance (MR) signals. In vivo T₁ -weighted MRI experiments reveal that UMFNP-CREKA can detect metastases at an unprecedented minimum detection limit of 0.39 mm, which has significantly extended the detection limit of previously reported MRI probe.

Metal-Based Complexes as Pharmaceuticals for Molecular Imaging of the Liver

This article reviews the use of metal complexes as contrast agents (CA) and radiopharmaceuticals for the anatomical and functional imaging of the liver. The main focus was on two established imaging modalities: magnetic resonance imaging (MRI) and nuclear medicine, the latter including scintigraphy and positron emission tomography (PET). The review provides an overview on approved pharmaceuticals like Gd-based CA and ^99mTc-based radiometal complexes, and also on novel agents such as ⁶⁸Ga-based PET tracers. Metal complexes are presented by their imaging modality, with subsections focusing on their structure and mode of action. Uptake mechanisms, metabolism, and specificity are presented, in context with advantages and limitations of the diagnostic application and taking into account the respective imaging technique.