Gadolinium Retention as a Safety Signal: Experience of a Manufacturer

MRI Gadolinium-Based Contrast Media: Meeting Radiological, Clinical, and Environmental Needs

Gadolinium-based contrast agents (GBCAs) are routinely used in magnetic resonance imaging (MRI). They are essential for choosing the most appropriate medical or surgical strategy for patients with serious pathologies, particularly in oncologic, inflammatory, and cardiovascular diseases. However, GBCAs have been associated with an increased risk of nephrogenic systemic fibrosis in patients with renal failure, as well as the possibility of deposition in the brain, bones, and other organs, even in patients with normal renal function. Research is underway to reduce the quantity of gadolinium injected, without compromising image quality and diagnosis. The next generation of GBCAs will enable a reduction in the gadolinium dose administered. Gadopiclenol is the first of this new generation of GBCAs, with high relaxivity, thus having the potential to reduce the gadolinium dose while maintaining good in vivo stability due to its macrocyclic structure. High-stability and high-relaxivity GBCAs will be one of the solutions for reducing the dose of gadolinium to be administered in clinical practice, while the development of new technologies, including optimization of MRI acquisitions, new contrast mechanisms, and artificial intelligence may help reduce the need for GBCAs. Future solutions may involve a combination of next-generation GBCAs and image-processing techniques to optimize diagnosis and treatment planning while minimizing exposure to gadolinium. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 3.

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.

A Comprehensive Overview of the Efficacy and Safety of Gadopiclenol: A New Contrast Agent for MRI of the CNS and Body

ABSTRACT

This review describes the pharmacokinetics, efficacy, and safety of gadopiclenol, a new macrocyclic gadolinium-based contrast agent (GBCA) recently approved by the Food and Drug Administration at the dose of 0.05 mmol/kg. Gadopiclenol is a high relaxivity contrast agent that shares similar pharmacokinetic characteristics with other macrocyclic GBCAs, including a predominant renal excretion. In pediatric patients aged 2-17 years, the pharmacokinetic parameters (assessed through a population pharmacokinetics model) were comparable to those observed in adults, indicating no need for age-based dose adjustment. For contrast-enhanced magnetic resonance imaging (MRI) of the central nervous system (CNS) and body indications, gadopiclenol at 0.05 mmol/kg was shown to be noninferior to gadobutrol at 0.1 mmol/kg in terms of 3 lesion visualization parameters (ie, lesion border delineation, internal morphology, and contrast enhancement). Moreover, for contrast-enhanced MRI of the CNS, compared with gadobenate dimeglumine at 0.1 mmol/kg, gadopiclenol exhibited superior contrast-to-noise ratio at 0.1 mmol/kg and comparable contrast-to-noise ratio at 0.05 mmol/kg. A pooled safety analysis of 1047 participants showed a favorable safety profile for gadopiclenol. Comparative studies showed that the incidence and nature of adverse drug reactions with gadopiclenol were comparable to those observed with other GBCAs. Importantly, no significant safety concerns were identified in pediatric and elderly patients, as well as in patients with renal impairment. Overall, these findings support the clinical utility and safety of gadopiclenol for MRI in adult and pediatric patients aged 2 years and older in CNS and body indications.

Review of the Efficacy and Safety of Gadopiclenol: A Newly Emerging Gadolinium-Based Contrast Agent

Gadolinium-based contrast agents (GBCAs) are one of the most commonly used agents in magnetic resonance imaging. Gadopiclenol is a new GBCA aimed at providing improved diagnostic efficacy with a favorable safety profile. The proposed advantages are due to its specific pharmacological properties, one of which is high relaxivity values. The aim of this review is to assess the efficacy, diagnostic accuracy, and safety of gadopiclenol in comparison to other currently used gadolinium-based contrast agents. PubMed and other database systems were used to identify relevant studies. The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines were followed, resulting in 10 articles that were included in the review. The outcomes were reviewed according to several factors regarding efficacy and accuracy in terms of qualitative and quantitative descriptors relative to properties of enhancement provided by the contrast agent. In terms of safety profile, a number of outcomes were assessed such as the occurrence of serious adverse effects, severe kidney injury, and organ-based contrast retention. Gadopiclenol was found to provide outcomes comparable to other commonly used GBCAs at lower doses with further favorable results at higher doses while maintaining an acceptable safety profile. However, it was found to have high rates of retention within the liver and can cause nonsignificant QT prolongation in healthy individuals, which arguably creates the need for further research regarding more long-term implications of these possible adverse effects.

Efficacy and Safety of Gadopiclenol for Contrast-Enhanced MRI of the Central Nervous System: The PICTURE Randomized Clinical Trial

OBJECTIVES

Developing new high relaxivity gadolinium-based contrast agents (GBCAs) for magnetic resonance imaging (MRI) allowing dose reduction while maintaining similar diagnostic efficacy is needed, especially in the context of gadolinium retention in tissues. This study aimed to demonstrate that contrast-enhanced MRI of the central nervous system (CNS) with gadopiclenol at 0.05 mmol/kg is not inferior to gadobutrol at 0.1 mmol/kg, and superior to unenhanced MRI.

MATERIALS AND METHODS

PICTURE is an international, randomized, double-blinded, controlled, cross-over, phase III study, conducted between June 2019 and September 2020. Adult patients with CNS lesions were randomized to undergo 2 MRIs (interval, 2-14 days) with gadopiclenol (0.05 mmol/kg) then gadobutrol (0.1 mmol/kg) or vice versa. The primary criterion was lesion visualization based on 3 parameters (border delineation, internal morphology, and contrast enhancement), assessed by 3 off-site blinded readers. Key secondary outcomes included lesion-to-background ratio, enhancement percentage, contrast-to-noise ratio, overall diagnostic preference, and adverse events.

RESULTS

Of the 256 randomized patients, 250 received at least 1 GBCA administration (mean [SD] age, 57.2 [13.8] years; 53.6% women). The statistical noninferiority of gadopiclenol (0.05 mmol/kg) to gadobutrol (0.1 mmol/kg) was achieved for all parameters and all readers (n = 236, lower limit 95% confidence interval of the difference ≥-0.06, above the noninferiority margin [-0.35], P < 0.0001), as well as its statistical superiority over unenhanced images (n = 239, lower limit 95% confidence interval of the difference ≥1.29, P < 0.0001).Enhancement percentage and lesion-to-background ratio were higher with gadopiclenol for all readers ( P < 0.0001), and contrast-to-noise ratio was higher for 2 readers ( P = 0.02 and P < 0.0001). Three blinded readers preferred images with gadopiclenol for 44.8%, 54.4%, and 57.3% of evaluations, reported no preference for 40.7%, 21.6%, and 23.2%, and preferred images with gadobutrol for 14.5%, 24.1%, and 19.5% ( P < 0.001).Adverse events reported after MRI were similar for gadopiclenol (14.6% of patients) and gadobutrol (17.6%). Adverse events considered related to gadopiclenol (4.9%) and gadobutrol (6.9%) were mainly injection site reactions, and none was serious.

CONCLUSIONS

Gadopiclenol at 0.05 mmol/kg is not inferior to gadobutrol at 0.1 mmol/kg for MRI of the CNS, confirming that gadopiclenol can be used at half the gadolinium dose used for other GBCAs to achieve similar clinical efficacy.

Imaging peripheral lymphatic dysfunction in chronic conditions

The lymphatics play important roles in chronic diseases/conditions that comprise the bulk of healthcare worldwide. Yet the ability to routinely image and diagnose lymphatic dysfunction, using commonly available clinical imaging modalities, has been lacking and as a result, the development of effective treatment strategies suffers. Nearly two decades ago, investigational near-infrared fluorescence lymphatic imaging and ICG lymphography were developed as routine diagnostic for clinically evaluating, quantifying, and treating lymphatic dysfunction in cancer-related and primary lymphedema, chronic venous disease, and more recently, autoimmune and neurodegenerative disorders. In this review, we provide an overview of what these non-invasive technologies have taught us about lymphatic (dys) function and anatomy in human studies and in corollary animal studies of human disease. We summarize by commenting on new impactful clinical frontiers in lymphatic science that remain to be facilitated by imaging.

MRI detection of brain gadolinium retention in multiple sclerosis: Magnetization transfer vs. T1-weighted imaging

BACKGROUND AND PURPOSE

Evidence of brain gadolinium retention has affected gadolinium-based contrast agent usage. It is, however, unclear to what extent macrocyclic agents are retained and whether their in vivo detection may necessitate nonconventional MRI. Magnetization transfer (MT) could prove suitable to detect gadolinium-related signal changes since dechelated gadolinium ions bind to macromolecules. Therefore, this study aimed to investigate associations of prior gadolinium administrations with MT and T1 signal abnormalities.

METHODS

A cohort of 23 persons with multiple sclerosis (MS) (18 females, 5 males, 57 ± 8.0 years) with multiple past gadolinium administrations (median 6, range 3-12) and 23 age- and sex-matched healthy controls underwent 1.5 Tesla MRI with MT, T1-weighted 2-dimensional spin echo, and T1-weighted 3-dimensional gradient echo. The signal intensity index was assessed by MRI in gadolinium retention predilection sites.

RESULTS

There were dose-dependent associations of the globus pallidus signal on gradient echo (r = .55, p < .001) and spin echo (r = .38, p = .013) T1-weighted imaging, but not on MT. Relative to controls, MS patients had higher signal intensity index in the dentate nucleus on T1-weighted gradient echo (1.037 ± 0.040 vs. 1.016 ± 0.023, p = .04) with a similar trend in the globus pallidus on T1-weighted spin echo (1.091 ± 0.034 vs. 1.076 ± 0.014, p = .06). MT detected no group differences.

CONCLUSIONS

Conventional T1-weighted imaging provided dose-dependent associations with gadolinium administrations in MS, while these could not be detected with 2-dimensional MT. Future studies could explore newer MT techniques like 3D and inhomogenous MT. Notably, these associations were identified with conventional MRI even though most patients had not received gadolinium administrations in the preceding 9 years, suggestive of long-term retention.

A Neutral and Stable Macrocyclic Mn(II) Complex for MRI Tumor Visualization

A stable and inert amphiphilic Mn(II) complex based on a bisamide derivative of 1,4-DO2A (DO2A=tetraazacyclododecane-1,4-diacetic acid) was synthesized and its ¹ H NMR relaxometric behavior was investigated as a function of the magnetic field strength, pH and temperature. The interaction with human serum albumin (HSA) was also studied via relaxometry showing a good relaxivity enhancement at low field (at 1T and 298 K the relaxivity increases from 4.5 mM^-1  s^-1 of the Mn(II)-complex to 14.0 mM^-1  s^-1 of the complex-HSA supramolecular adduct). In vivo biodistribution and MRI studies highlighted a rapid and mixed renal/liver elimination without spleen accumulation from healthy mice and good contrast enhancing properties in a breast tumor murine model. A comparison with a clinically approved Gd(III) agent (GdBOPTA, Multihance®) underlined that the proposed Mn(II) contrast agent gave comparable tumor contrast enhancement up to 3 hours post-injection.

Use of Real-Life Safety Data From International Pharmacovigilance Databases to Assess the Importance of Symptoms Associated With Gadolinium Exposure

OBJECTIVE

Recent scientific publications have reported cases of patients who complained from a variety of symptoms after they received a gadolinium-based contrast agent (GBCA). The aim of this study was to appreciate the importance of these clinical manifestations in the overall population by assessing the weight of "symptoms associated with gadolinium exposure" (SAGE) among the bulk of safety experiences reported to major health authorities.

MATERIALS AND METHODS

Symptoms associated with gadolinium exposure were identified from a review of the scientific literature, and the corresponding preferred terms were searched in each system organ class (SOC) category recorded in the European and North American pharmacovigilance databases EudraVigilance (EV) and FDA Adverse Event Reporting System (FAERS), respectively. The numbers of SAGE per preferred term, and cumulatively per SOC, were recorded and their weights in the overall spectrum of adverse events (AEs) were determined for each GBCA.

RESULTS

The analysis of the selected AEs revealed a significantly higher SAGE weight for gadobenate dimeglumine (EV: 25.83%, FAERS: 32.24%) than for gadoteridol (EV: 15.51%; FAERS: 21.13%) and significantly lower SAGE weights for gadobutrol (EV: 7.75%; FAERS: 13.31%) and gadoterate meglumine (EV: 8.66%; FAERS: 12.99%). A similar ranking was found for most of the SOCs except for "nervous system disorders," probably owing to a limitation in the methods of data selection. Furthermore, this analysis showed a greater percentage of reports mentioning a decrease in the quality of life of the patients when they were exposed to gadobenate dimeglumine or gadoteridol than to gadobutrol or gadoterate meglumine.

CONCLUSION

This study showed that SAGE represent a significant percentage of the bulk of AEs reported to the health authorities for each GBCA. It provided real-life arguments suggesting that SAGE may be more prevalent with linear than macrocyclic GBCAs and that gadoteridol may present a higher SAGE risk than the other macrocyclic contrast agents.

Pharmacokinetics, Safety, and Efficacy of Gadopiclenol in Pediatric Patients Aged 2 to 17 Years

OBJECTIVES

The aim of this study was to evaluate the pharmacokinetic (PK) profile, safety, and efficacy of gadopiclenol, a new high-relaxivity gadolinium-based contrast agent, in children aged 2 to 17 years.

MATERIALS AND METHODS

Children scheduled to undergo contrast-enhanced magnetic resonance imaging of the central nervous system (CNS cohort) or other organs (body cohort) were included sequentially into 3 age groups (12-17, 7-11, and 2-6 years). Gadopiclenol was administered at the dose of 0.05 mmol/kg. A sparse sampling approach was applied, with 4 blood samples per child collected up to 8 hours postinjection. Population PK modeling was used for the analysis, including the CNS cohort and adult subjects from a previous study. Adverse events were recorded, and efficacy was assessed for all children.

RESULTS

Eighty children were included, 60 in the CNS cohort and 20 in the body cohort. The 2-compartment model with linear elimination from the central compartment developed in adults was also suitable for children. Pharmacokinetic parameters were very similar between adults and children. Terminal elimination half-life was 1.82 hours for adults and 1.77 to 1.29 hours for age groups 12-17 to 2-6 years. The median clearance ranged from 0.08 L/h/kg in adults and 12-17 years to 0.12 L/h/kg in 2-6 years. The median central and peripheral volumes of distribution were 0.11 to 0.12 L/kg and 0.06 L/kg, respectively, for both adults and children. Simulations of plasma concentrations showed minor differences, and median area under the curve was 590 mg·h/L for adults and 582 to 403 mg·h/L for children. Two patients (2.5%) experienced nonserious adverse events considered related to gadopiclenol: a mild QT interval prolongation and a moderate maculopapular rash. Despite the limited number of patients, this study showed that gadopiclenol improved lesion detection, visualization, and diagnostic confidence.

CONCLUSIONS

The PK profile of gadopiclenol in children aged 2 to 17 years was similar to that observed in adults. Thus, there is no indication for age-based dose adaptation, and comparable plasma gadopiclenol concentrations are predicted to be achieved with body weight-based dosing in this population. Gadopiclenol at 0.05 mmol/kg seems to have a good safety profile in these patients and could improve lesion detection and visualization, therefore providing better diagnostic confidence.

Comprehensive Speciation Analysis of Residual Gadolinium in Deep Cerebellar Nuclei in Rats Repeatedly Administered With Gadoterate Meglumine or Gadodiamide

PURPOSE

Several preclinical studies have reported the presence of gadolinium (Gd) in different chemical forms in the brain, depending on the class (macrocyclic versus linear) of Gd-based contrast agent (GBCA) administered. The aim of this study was to identify, with a special focus on insoluble species, the speciation of Gd retained in the deep cerebellar nuclei (DCN) of rats administered repeatedly with gadoterate or gadodiamide 4 months after the last injection.

METHODS

Three groups (N = 6/group) of healthy female Sprague-Dawley rats (SPF/OFA rats; Charles River, L'Arbresle, France) received a cumulated dose of 50 mmol/kg (4 daily intravenous administrations of 2.5 mmol/kg, for 5 weeks, corresponding to 80-fold the usual clinical dose if adjusted for man) of gadoterate meglumine (macrocyclic) or gadodiamide (linear) or isotonic saline for the control group (4 daily intravenous administrations of 5 mL/kg, for 5 weeks). The animals were sacrificed 4 months after the last injection. Deep cerebellar nuclei were dissected and stored at -80°C before sample preparation. To provide enough tissue for sample preparation and further analysis using multiple techniques, DCN from each group of 6 rats were pooled. Gadolinium species were extracted in 2 consecutive steps with water and urea solution. The total Gd concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). Soluble Gd species were analyzed by size-exclusion chromatography coupled to ICP-MS. The insoluble Gd species were analyzed by single-particle (SP) ICP-MS, nanoscale secondary ion mass spectroscopy (NanoSIMS), and scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDX) for elemental detection.

RESULTS

The Gd concentrations in pooled DCN from animals treated with gadoterate or gadodiamide were 0.25 and 24.3 nmol/g, respectively. For gadoterate, the highest amount of Gd was found in the water-soluble fractions. It was present exclusively as low-molecular-weight compounds, most likely as the intact GBCA form. In the case of gadodiamide, the water-soluble fraction of DCN was composed of high-molecular-weight Gd species of approximately 440 kDa and contained only a tiny amount (less than 1%) of intact gadodiamide. Furthermore, the column recovery calculated for this fraction was incomplete, which suggested presence of labile complexes of dissociated Gd3+ with endogenous molecules. The highest amount of Gd was detected in the insoluble residue, which was demonstrated, by SP-ICP-MS, to be a particulate form of Gd. Two imaging techniques (NanoSIMS and STEM-EDX) allowed further characterization of these insoluble Gd species. Amorphous, spheroid structures of approximately 100-200 nm of sea urchin-like shape were detected. Furthermore, Gd was consistently colocalized with calcium, oxygen, and phosphorous, strongly suggesting the presence of structures composed of mixed Gd/Ca phosphates. No or occasional colocalization with iron and sulfur was observed.

CONCLUSION

A dedicated analytical workflow produced original data on the speciation of Gd in DCN of rats repeatedly injected with GBCAs. The addition, in comparison with previous studies of Gd speciation in brain, of SP element detection and imaging techniques allowed a comprehensive speciation analysis approach. Whereas for gadoterate the main fraction of retained Gd was present as intact GBCA form in the soluble fractions, for linear gadodiamide, less than 10% of Gd could be solubilized and characterized using size-exclusion chromatography coupled to ICP-MS. The main Gd species detected in the soluble fractions were macromolecules of 440 kDa. One of them was speculated to be a Gd complex with iron-binding protein (ferritin). However, the major fraction of residual Gd was present as insoluble particulate species, very likely composed of mixed Gd/Ca phosphates. This comprehensive Gd speciation study provided important evidence for the dechelation of linear GBCAs and offered a deeper insight into the mechanisms of Gd deposition in the brain.

Speciation Analysis of Gadolinium in the Water-Insoluble Rat Brain Fraction After Administration of Gadolinium-Based Contrast Agents

PURPOSE

To date, the analysis of gadolinium (Gd) speciation in the brain of animals administered with macrocyclic and linear Gd-based contrast agents (GBCAs) has been limited to Gd soluble in mild buffers. Under such conditions, less than 30% of the brain tissue was solubilized and the extraction recoveries of GBCAs into the aqueous phase were poor, especially in the case of the linear GBCAs. The aim of this study was to find the conditions to solubilize the brain tissue (quasi-)completely while preserving the Gd species present. The subsequent analysis using size exclusion chromatography-inductively coupled plasma-mass spectrometry (SEC-ICP-MS) was intended to shed the light on the speciation of the additionally recovered Gd.

METHODS

Four groups of healthy female Sprague Dawley rats (SPF/OFA rats; Charles River, L'Arbresle, France) received randomly 5 intravenous injections (1 injection per week during 5 consecutive weeks) of either gadoterate meglumine, gadobenate dimeglumine, gadodiamide (cumulated dose of 12 mmol/kg), or no injection (control group). The animals were sacrifice 1 week (W1) after the last injection. Brain tissues were solubilized with urea solution, whereas tissues extracted with water served as controls. Total Gd concentrations were determined in the original brain tissue and its soluble and insoluble fractions by inductively coupled plasma-mass spectrometry (ICP-MS) to calculate the Gd accumulation and extraction efficiency. Size exclusion chromatography coupled to ICP-MS was used to monitor the speciation of Gd in the soluble fractions. The stability of GBCAs in the optimum conditions was monitored by spiking the brain samples from the untreated animals. The column recoveries were precisely determined in the purpose of the discrimination of weakly and strongly bound Gd complexes. The identity of the eluted species was explored by the evaluation of the molecular size and retention time matching with Gd chelates and ferritin standard. The speciation analyses were carried out for 2 different brain structures, cortex and cerebellum.

RESULTS

The combination of water and urea extractions (sequential extraction) managed to solubilize efficiently the brain tissue (97% ± 1%) while preserving the stability of the initially injected form of GBCA. For macrocyclic gadoterate, 97% ± 1% and 102% ± 3% of Gd initially present in the cortex and cerebellum were extracted to the soluble fraction. For gadobenate, similar amounts of Gd (49% ± 1% and 46% ± 4%) were recovered from cortex and cerebellum. For gadodiamide, 48% ± 2% of Gd was extracted from cortex and 34% ± 1% from cerebellum. These extraction efficiencies were higher than reported elsewhere. The SEC-ICP-MS and the column recovery determination proved that Gd present at low nmol/g levels in brain tissue was exclusively in the intact GBCA form in all the fractions of brain from the animals treated with gadoterate. For the linear GBCAs (gadobenate and gadodiamide), 3 Gd species of different hydrodynamic volumes were detected in the urea-soluble fraction: (1) larger than 660 kDa, (2) approximately 440 kDa, and (3) intact GBCAs. The species of 440 kDa corresponded, on the basis of the elution volume, to a Gd3+ complex with ferritin. Gd3+ was also demonstrated by SEC-ICP-MS to react with the ferritin standard in 100 mM ammonium acetate (pH 7.4). In contrast to macrocyclic gadoterate, for linear GBCAs, the column recovery was largely incomplete, suggesting the presence of free, hydrolyzed, or weakly bound Gd3+ with endogenous ligands.

CONCLUSIONS

The sequential extraction of rat brain tissue with water and urea solution resulted in quasi-complete solubilization of the tissue and a considerable increase in the recoveries of Gd species in comparison with previous reports. The macrocyclic gadoterate was demonstrated to remain intact in the brain 1 week after administration to rats. The linear GBCAs gadobenate and gadodiamide underwent ligand exchange reactions resulting in the presence of a series of Gd3+ complexes of different strength with endogenous ligands. Ferritin was identified as one of the macromolecules reacting with Gd3+. For the linear GBCAs, 3% of the insoluble brain tissue was found to contain more than 50% of Gd in unidentified form(s).

What's Hot in Breast MRI

Several articles in the literature have demonstrated a promising role for breast MRI techniques that are more economic in total exam time than others when used as supplement to mammography for detection and diagnosis of breast cancer. There are many technical factors that must be considered in the shortened breast MRI protocols to cut down time of standard ones, including using optimal fat suppression, gadolinium-chelates intravascular contrast administrations for dynamic imaging with post processing subtractions and maximum intensity projections (MIP) high spatial and temporal resolution among others. Multiparametric breast MRI that includes both gadolinium-dependent, i.e., dynamic contrast-enhanced (DCE-MRI) and gadolinium-free techniques, i.e., diffusion-weighted/diffusion-tensor magnetic resonance imaging (DWI/DTI) are shown by several investigators that can provide extremely high sensitivity and specificity for detection of breast cancer. This article provides an overview of the proven indications for breast MRI including breast cancer screening for higher than average risk, determining chemotherapy induced tumor response, detecting residual tumor after incomplete surgical excision, detecting occult cancer in patients presenting with axillary node metastasis, detecting residual tumor after incomplete breast cancer surgical excision, detecting cancer when results of conventional imaging are equivocal, as well patients suspicious of having breast implant rupture. Despite having the highest sensitivity for breast cancer detection, there are pitfalls, however, secondary to false positive and false negative contrast enhancement and contrast-free MRI techniques. Awareness of the strengths and limitations of different approaches to obtain state of the art MR images of the breast will facilitate the work-up of patients with suspicious breast lesions.

Positron Emission Tomography-Magnetic Resonance Imaging Pharmacokinetics, In Vivo Biodistribution, and Whole-Body Elimination of Mn-PyC3A

OBJECTIVES

Mn-PyC3A is an experimental manganese (Mn)-based extracellular fluid magnetic resonance imaging (MRI) contrast agent that is being evaluated as a direct replacement for clinical gadolinium (Gd)-based contrast agents. The goals of this study were to use simultaneous positron emission tomography (PET)-MRI to (1) compare the whole-body pharmacokinetics, biodistribution, and elimination of Mn-PyC3A with the liver-specific contrast agent mangafodipir (Mn-DPDP), (2) determine the pharmacokinetics and fractional excretion of Mn-PyC3A in a rat model of renal impairment, and (3) compare whole-body elimination of Mn-PyC3A to gadoterate (Gd-DOTA) in a rat model of renal impairment.

METHODS

Mn-PyC3A and Mn-DPDP were radiolabeled with the positron emitting isotope Mn-52 via Mn2+ exchange with 52MnCl2. Dynamic simultaneous PET-MRI was used to measure whole-body pharmacokinetics and biodistribution of Mn-52 immediately and out to 7 days after an intravenous 0.2 mmol/kg dose of [52Mn]Mn-PyC3A to normal or to 5/6 nephrectomy rats or a 0.01 mmol/kg dose of [52Mn]Mn-DPDP to normal rats. The fractional excretion and 1- and 7-day biodistribution in rats after the injection of 2.0 mmol/kg [52Mn]Mn-PyC3A (n = 11 per time point) or 2.0 mmol/kg Gd-DOTA (n = 8 per time point) were quantified by gamma counting or Gd elemental analysis, respectively. Comparisons of Mn-PyC3A pharmacokinetics and in vivo biodistribution in normal and 5/6 nephrectomy rats and comparisons of ex vivo Mn versus Gd biodistribution data in 5/6 nephrectomy were made with an unpaired t test.

RESULTS

Dynamic PET-MRI data demonstrate that both [52Mn]Mn-PyC3A and [52Mn]Mn-DPDP were eliminated by mixed renal and hepatobiliary elimination but that a greater fraction of [52Mn]Mn-PyC3A was eliminated by renal filtration. Whole-body PET images show that Mn-52 from [52Mn]Mn-PyC3A was efficiently eliminated from the body, whereas Mn-52 from [52Mn]Mn-DPDP was retained throughout the body. The blood elimination half-life of [52Mn]Mn-PyC3A in normal and 5/6 nephrectomy rats was 13 ± 3.5 minutes and 23 ± 12 minutes, respectively (P = 0.083). Area under the curve between 0 and 60 minutes postinjection (AUC0-60) in the bladder of normal and 5/6 nephrectomy rats was 2600 ± 1700 %ID/cc*min and 750 ± 180 %ID/cc*min, respectively (P = 0.024), whereas AUC0-60 in the liver of normal and 5/6 nephrectomy rats was 33 ± 13 %ID/cc*min and 71 ± 16 %ID/cc*min, respectively (P = 0.011), indicating increased hepatobiliary elimination in 5/6 nephrectomy rats. The %IDs of Mn from [52Mn]Mn-PyC3A and Gd from Gd-DOTA recovered from 5/6 nephrectomy rats 1 day after injection were 2.0 ± 1.1 and 1.3 ± 0.34, respectively (P = 0.10) and 7 days after injection were 0.14 ± 0.11 and 0.41 ± 0.24, respectively (P = 0.0041).

CONCLUSIONS

Mn-PyC3A has different pharmacokinetics and is more efficiently eliminated than Mn-DPDP in normal rats. Mn-PyC3A is efficiently eliminated from both normal and 5/6 nephrectomy rats, with increased fractional hepatobiliary excretion from 5/6 nephrectomy rats. Mn-PyC3A is more completely eliminated than Gd-DOTA from 5/6 nephrectomy rats after 7 days.

Randomized study of the effect of gadopiclenol, a new gadolinium-based contrast agent, on the QTc interval in healthy subjects

AIMS

We investigated the effect of gadopiclenol, a new gadolinium-based contrast agent, on the QTc interval at clinical and supraclinical dose, considering the relative hyperosmolarity of this product.

METHODS

This was a single centre, randomized, double-blind, placebo- and positive-controlled, 4-way crossover study. Forty-eight healthy male and female subjects were included to receive single intravenous (i.v.) administrations of gadopiclenol at the clinical dose of 0.1 mmol kg^-1 , standard for current gadolinium-based contrast agents, the supraclinical dose of 0.3 mmol kg^-1 , placebo and a single oral dose of 400 mg moxifloxacin.

RESULTS

The largest time-matched placebo-corrected, mean change from-baseline in QTcF (ΔΔQTcF) was observed 3 hours after administration of 0.1 mmol kg^-1 gadopiclenol (2.39 ms, 90% confidence interval [CI]: 0.35, 4.43 ms) and 5 minutes after administration of 0.3 mmol kg^-1 (4.81 ms, 90%CI: 2.84, 6.78 ms). The upper limit of the 90% CI was under the threshold of 10 ms, demonstrating no significant effect of gadopiclenol on QTc interval. From 1.5 to 4 hours postdose moxifloxacin, the lower limit of the 90% CI of ΔΔQTcF exceeded 5 ms demonstrating assay sensitivity. Although there was a positive slope, the concentration-response analysis estimated that the values of ΔΔQTcF at the maximal concentration of gadopiclenol at 0.1 and 0.3 mmol kg^-1 were 0.41 and 2.23 ms, respectively, with the upper limit of the 90% CI not exceeding 10 ms. No serious or severe adverse events or treatment discontinuations due to adverse events were reported.

CONCLUSION

This thorough QT/QTc study demonstrated that gadopiclenol did not prolong the QT interval at clinical and supraclinical doses and was well tolerated in healthy volunteers. The positive slope of the QTc prolongation vs concentration relationship suggests that hyperosmolarity could be associated with QTc prolongation. However, the amplitude of this effects is unlikely to be associated with proarrhythmia.

Peptide-Based Soft Hydrogels Modified with Gadolinium Complexes as MRI Contrast Agents

Poly-aromatic peptide sequences are able to self-assemble into a variety of supramolecular aggregates such as fibers, hydrogels, and tree-like multi-branched nanostructures. Due to their biocompatible nature, these peptide nanostructures have been proposed for several applications in biology and nanomedicine (tissue engineering, drug delivery, bioimaging, and fabrication of biosensors). Here we report the synthesis, the structural characterization and the relaxometric behavior of two novel supramolecular diagnostic agents for magnetic resonance imaging (MRI) technique. These diagnostic agents are obtained for self-assembly of DTPA(Gd)-PEG8-(FY)3 or DOTA(Gd)-PEG8-(FY)3 peptide conjugates, in which the Gd-complexes are linked at the N-terminus of the PEG8-(FY)3 polymer peptide. This latter was previously found able to form self-supporting and stable soft hydrogels at a concentration of 1.0% wt. Analogously, also DTPA(Gd)-PEG8-(FY)3 and DOTA(Gd)-PEG8-(FY)3 exhibit the trend to gelificate at the same range of concentration. Moreover, the structural characterization points out that peptide (FY)3 moiety keeps its capability to arrange into β-sheet structures with an antiparallel orientation of the β-strands. The high relaxivity value of these nanostructures (~12 mM⁻¹·s⁻¹ at 20 MHz) and the very low in vitro cytotoxicity suggest their potential application as supramolecular diagnostic agents for MRI.