Gadolinium Deposition in the Brain in a Large Animal Model: Comparison of Linear and Macrocyclic Gadolinium-Based Contrast Agents

Deposition of Gadolinium in the Central and Peripheral Nervous Systems and Its Effects on Sensory, Cognitive, and Athletic Implications after Multiple Injections of Gadolinium-Based Contrast Agents in Rats

BACKGROUND AND PURPOSE

After repeat administration of gadolinium-based contrast agents (GBCAs), the association between gadolinium retention in the central and peripheral nervous systems and the main manifestations of myelopathy and progressive neurologic symptoms remains unclear. We investigated the effects of the repeat administration of GBCAs on gadolinium retention in the central and peripheral nervous systems and the sensory, cognitive, and athletic implications.

MATERIALS AND METHODS

Forty-eight male Wistar rats (6 weeks of age) were randomly divided into 4 experimental groups (12 rats in each group): the gadodiamide group (linear and nonionic GBCAs), the gadopentetate dimeglumine group (linear and ionic GBCAs), the gadoterate meglumine group (macrocyclic and ionic GBCAs), and the control group (0.9% saline solution). The brains of the rats were scanned using 9.4T MRI. Sensory behavioral tests were performed to assess the effect of GBCAs on pain sensitivity function. Gadolinium deposition in the brain, spinal cord, and peripheral nerves was determined by inductively coupled plasma mass-spectrometry. Transmission electron microscopy was used to observe the microscopic distribution of gadolinium after deposition in the spinal cord. The histopathologic features in the spinal cord were analyzed by H&E staining, Nissl staining, glial fibrillary acidic protein staining, and neuron-specific enolase staining after administration of GBCAs.

RESULTS

All GBCAs resulted in gadolinium deposition in the central and peripheral nerve tissues, with the highest deposition in the sciatic nerve tissue (mean, 62.86 [SD, 12.56] nmol/g). Decreased muscle power, impairment of spatial cognitive function power, and pain hypersensitivity to thermal and mechanical stimuli were observed after exposure to gadodiamide. At the spinal cord, transmission electron microscopy found that the region of gadolinium depositions had a spheric structure similar to "sea urchins" and was mainly located near the vascular basement membrane.

CONCLUSIONS

Multiple injections of GBCAs caused gadolinium deposition in the brain, spinal cord, and peripheral nerves, especially in the spinal cords of the gadodiamide group. Gadodiamide led to pain hypersensitivity and decreased muscle power and cognitive ability. For the patients who are hypersensitive to pain and need multiple MRI examinations, we recommend using macrocyclic GBCAs and the lowest dose possible.

Elemental Bioimaging of Sheep Bone and Articular Cartilage After Single Application of Gadolinium-Based Contrast Agents

BACKGROUND

Gadolinium-based contrast agents (GBCAs) are applied to enhance magnetic resonance imaging. Gadolinium (Gd), a rare earth metal, is used in a chelated form when administered as GBCA to patients. There is an ongoing scientific debate about the clinical significance of Gd retention in tissues after administration of GBCAs. It is known that bone serves as Gd reservoir, but only sparse information on localization of Gd in bone is available.

PURPOSE

The aim of this study was to compare Gd tissue concentration and spatial distribution in femoral epiphysis and diaphysis 10 weeks after single-dose injection of linear and macrocyclic GBCAs in a large animal model.

MATERIALS AND METHODS

In this prospective animal study, Swiss-Alpine sheep (n = 36; age range, 4-10 years) received a single injection (0.1 mmol/kg) of macrocyclic (gadobutrol, gadoteridol, and gadoterate meglumine), linear (gadodiamide and gadobenate dimeglumine) GBCAs, or saline. Ten weeks after injection, sheep were killed, and femur heads and shafts were harvested. Gadolinium spatial distribution was determined in 1 sample of each treatment group by laser ablation-inductively coupled plasma-mass spectrometry. All bone specimens were analyzed histopathologically.

RESULTS

Injection of GBCAs in female Swiss-Alpine sheep (n = 36) resulted in Gd localization at the endosteal and periosteal surface and in a subset of GBCAs additionally at the cement lines and the bone cartilage junction. No histopathological alterations were observed in the investigated tissue specimens.

CONCLUSIONS

Ten weeks after single injection of a clinically relevant dose in adult sheep, both linear species of GBCA resulted in considerably higher accumulation than macrocyclic GBCAs. Gadolinium deposits were restricted to distinct bone and cartilage compartments, such as in bone linings, cement lines, and bone cartilage junctions. Tissue histology remained unaffected.

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.

Effects of Gadolinium Retention in the Brains of Type 2 Diabetic Rats after Repeated Administration of Gadolinium-Based MRI Contrast Agents on Neurobiology and NLRP3 Inflammasome Activation

BACKGROUND

The neurotoxic potential of gadolinium (Gd)-based contrast agents (GBCAs) retention in the brains of patients with type 2 diabetes mellitus (T2DM) is unclear.

PURPOSE

To determine the deposition and clearance of GBCAs in T2DM rats and the mechanism by which Gd enhances nucleotide-binding oligomerization domain-3 (NLRP3) inflammasome activation.

STUDY TYPE

Cross-sectional, prospective.

ANIMAL MODEL

104 T2DM male Wistar rats.

FIELD STRENGTH/SEQUENCE

9.4-T, T1-weighted fast spin echo sequence.

ASSESSMENT

T2DM (male Wistar rats, n = 52) and control group (healthy, male Wistar rats, n = 52) rats received saline, gadodiamide, Gd-diethylenetriaminepentaacetic acid, and gadoterate meglumine for four consecutive days per week for 7 weeks. The distribution and clearance of Gd in the certain brain were assessed by MRI (T1 signal intensity and relaxation rate R1, on the last day of each week), inductively coupled plasma mass-spectroscopy, ultraperformance liquid chromatography mass spectrometry, and transmission electron microscopy. Behavioral tests, histopathological features, and the effects of GBCAs on neuroinflammation were also analyzed.

STATISTICAL TESTS

One-way analysis of variance, bonferroni method, and unpaired t-test. A P-value <0.05 was considered statistically significant.

RESULTS

The movement distance and appearance time in the open field test of the T2DM rats in the gadodiamide group were significantly shorter than in the other groups. Furthermore, the expression of NLRP3, Pro-Caspase-1, interleukin-1β (IL-1β), and apoptosis-associated speck-like protein containing a CARD protein in neurons was significantly higher in the gadodiamide group than in the saline group, as shown by Western blot. Gadodiamide also induced differentiation of microglia into M1 type, decreased the neuronal mitochondrial membrane potential, and significantly increased neuronal apoptosis from flow cytometry.

DATA CONCLUSION

T2DM may affect both the deposition and clearance of GBCAs in the brain. Informed by the T2DM model, gadodiamide could mediate the neuroinflammatory response by NLRP3 inflammasome activation.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 1.

Ten years of gadolinium retention and deposition: ESMRMB-GREC looks backward and forward

In 2014, for the first time, visible hyperintensities on unenhanced T1-weighted images in the nucleus dentatus and globus pallidus of the brain were associated with previous Gadolinium-based contrast agent (GBCA) injections and gadolinium deposition in patients with normal renal function. This led to a frenzy of retrospective studies with varying methodologies that the European Society of Magnetic Resonance in Medicine and Biology Gadolinium Research and Educational Committee (ESMRMB-GREC) summarised in 2019. Now, after 10 years, the members of the ESMRMB-GREC look backward and forward and review the current state of knowledge of gadolinium retention and deposition. CLINICAL RELEVANCE STATEMENT: Gadolinium deposition is associated with the use of linear GBCA but no clinical symptoms have been associated with gadolinium deposition. KEY POINTS : • Traces of Gadolinium-based contrast agent-derived gadolinium can be retained in multiple organs for a prolonged time. • Gadolinium deposition is associated with the use of linear Gadolinium-based contrast agents. • No clinical symptoms have been associated with gadolinium deposition.

Artificial Intelligence to Reduce or Eliminate the Need for Gadolinium-Based Contrast Agents in Brain and Cardiac MRI: A Literature Review

ABSTRACT

Brain and cardiac MRIs are fundamental noninvasive imaging tools, which can provide important clinical information and can be performed without or with gadolinium-based contrast agents (GBCAs), depending on the clinical indication. It is currently a topic of debate whether it would be feasible to extract information such as standard gadolinium-enhanced MRI while injecting either less or no GBCAs. Artificial intelligence (AI) is a great source of innovation in medical imaging and has been explored as a method to synthesize virtual contrast MR images, potentially yielding similar diagnostic performance without the need to administer GBCAs. If possible, there would be significant benefits, including reduction of costs, acquisition time, and environmental impact with respect to conventional contrast-enhanced MRI examinations. Given its promise, we believe additional research is needed to increase the evidence to make these AI solutions feasible, reliable, and robust enough to be integrated into the clinical framework. Here, we review recent AI studies aimed at reducing or replacing gadolinium in brain and cardiac imaging while maintaining diagnostic image quality.

Gadolinium-based contrast agents suppress adipocyte differentiation in 3T3-L1 cells

Gadolinium-based contrast agents (GBCAs) are widely used in magnetic resonance imaging (MRI) to improve the sensitivity and enhance diagnostic performance. GBCAs are mostly eliminated from the body through the kidney after administration; however small amounts of gadolinium are retained in the brain and other tissues. Although there is increasing concern about the adverse health effects of gadolinium, the cellular effects of GBCAs remains poorly understood. Here, we elucidated the potential cytotoxicity of the GBCAs Omniscan and Gadovist in 12 different cell lines, especially 3T3-L1 adipocyte cell line. Omniscan and Gadovist treatments significantly increased intracellular gadolinium levels in 3T3-L1 cells in a time- and dose-dependent manner. Additionally, Omniscan and Gadovist treatments downregulated the expression of adipocyte differentiation markers, including peroxisome proliferator-activated receptor γ (PPARG), adiponectin (ADIPOQ), and fatty acid-binding protein (FABP4), in 3T3-L1 cells, especially during early differentiation (day 0-2). Moreover, histological analysis using Oil red O staining showed that gadolinium chloride (GdCl₃) treatment suppressed lipid droplet accumulation and the expression of adipocyte differentiation markers. Overall, the results showed that Omniscan and Gadovist treatment suppressed adipocyte differentiation in 3T3-L1 cells, contributing to the understanding of the potential toxic effects of GBCA exposure.

Kinetically Inert Macrocyclic Europium(III) Receptors for Phosphate

The significant role that phosphate plays in environmental water pollution and biomedical conditions such as hyperphosphatemia highlights the need to develop robust receptors that can sequester the anion effectively and selectively from complex aqueous media. Toward that goal, four macrocyclic tris-bidentate 1,2-hydroxypyridonate (HOPO) europium(III) complexes containing either a cyclen, cyclam, TACN, or TACD ligand cap were synthesized and evaluated as phosphate receptors. The solubility of EuIII-TACD-HOPO in water was insufficient for luminescent studies. Whereas EuIII-cyclen-HOPO is eight coordinate with two inner-sphere water molecules, both EuIII-cyclam-HOPO and EuIII-TACN-HOPO are nine coordinate with three inner-sphere water molecules, suggesting that the two coordination states are very close in energy. As observed previously with linear analogues of tripodal HOPO complexes, there is no relationship between the number of inner-sphere water molecules and the affinity of the complex for phosphate. Whereas all three complexes do bind phosphate, EuIII-cyclen-HOPO has the highest affinity for phosphate with the anion displacing both of its inner-sphere water molecules. On the other hand, only one or two of the three inner-sphere water molecules of EuIII-TACN-HOPO and EuIII-cyclam-HOPO are displaced by phosphate, respectively. All three complexes are highly selective for phosphate over other anions, including arsenate. All three complexes are highly stable. EuIII-cyclen-HOPO and, to a lesser extent, EuIII-TACN-HOPO are more kinetically inert than the linear EuIII-Ser-HOPO. EuIII-cyclam-HOPO, on the other hand, is not. This study highlights the significant effect that minor changes in the ligand cap can have on both the ligand exchange rate and affinity for phosphate of tripodal 1,2-dihydroxypyridinonate complexes.

Elemental bioimaging and transcriptomics reveal unchanged gene expression in mouse cerebellum following a single injection of Gadolinium-based contrast agents

Gadolinium (Gd) deposition in the brain, first and foremost in the dentate nucleus in the cerebellum, following contrast enhanced MRI, rose awareness of potential adverse effects of gadolinium-based contrast agent (GBCA) administration. According to previous in vitro experiments, a conceivable side-effect of Gd deposition could be an alteration of gene expression. In the current study, we aimed to investigate the influence of GBCA administration on gene expression in the cerebellum of mice using a combination of elemental bioimaging and transcriptomics. In this prospective animal study, three groups of eight mice each were intravenously injected with either linear GBCA gadodiamide, macrocyclic GBCA gadoterate (1 mmol GBCA/kg body weight) or saline (NaCl 0.9%). Animals were euthanized four weeks after injection. Subsequently, Gd quantification via laser ablation-ICP-MS and whole genome gene expression analysis of the cerebellum were performed. Four weeks after single application of GBCAs to 24-31 days old female mice, traces of Gd were detectable in the cerebellum for both, the linear and macrocyclic group. Subsequent transcriptome analysis by RNA sequencing using principal component analysis did not reveal treatment-related clustering. Also differential expression analysis did not reveal any significantly differentially expressed genes between treatments.

[Li-Fraumeni syndrome]

BACKGROUND

The autosomal dominant inherited Li-Fraumeni syndrome (LFS) increases the lifetime risk of developing a malignancy to almost 100%. Although breast cancer, central nervous system (CNS) tumors and sarcomas are particularly common, tumors can ultimately occur almost anywhere in the body. As causal therapy is not available, the primary focus for improving the prognosis is early cancer detection. To this end, current cancer surveillance recommendations include a series of examinations including regular imaging beginning at birth.

CHALLENGES IN IMAGING IN LFS

Due to the wide range of tumor entities that can occur in individuals affected by LFS, a sensitive detection requires imaging of various tissue contrasts; however, because life-long screening is potentially initiated at a young age, this requirement for comprehensiveness must be balanced against the presumed high psychological burden associated with frequent or invasive examinations. As radiation exposure may lead to an increased (secondary) tumor risk, computed tomography (CT) and X‑ray examinations should be avoided as far as possible.

CURRENT STATUS AND PERSPECTIVES

Because annual whole-body magnetic resonance imaging (MRI) has no radiation exposure and yet a high sensitivity for many tumors, it forms the basis of the recommended imaging; however, due to the rarity of the syndrome, expertise is sometimes lacking and whole-body MRI examinations are performed heterogeneously and sometimes with limited diagnostic quality. Optimization and standardization of MRI protocols should therefore be pursued. In addition, the need for an intravenously administered contrast agent has not been conclusively clarified despite its high relevance.

Different Impact of Gadopentetate and Gadobutrol on Inflammation-Promoted Retention and Toxicity of Gadolinium Within the Mouse Brain

OBJECTIVES

Using a murine model of multiple sclerosis, we previously showed that repeated administration of gadopentetate dimeglumine led to retention of gadolinium (Gd) within cerebellar structures and that this process was enhanced with inflammation. This study aimed to compare the kinetics and retention profiles of Gd in inflamed and healthy brains after application of the macrocyclic Gd-based contrast agent (GBCA) gadobutrol or the linear GBCA gadopentetate. Moreover, potential Gd-induced neurotoxicity was investigated in living hippocampal slices ex vivo.

MATERIALS AND METHODS

Mice at peak of experimental autoimmune encephalomyelitis (EAE; n = 29) and healthy control mice (HC; n = 24) were exposed to a cumulative dose of 20 mmol/kg bodyweight of either gadopentetate dimeglumine or gadobutrol (8 injections of 2.5 mmol/kg over 10 days). Magnetic resonance imaging (7 T) was performed at baseline as well as at day 1, 10, and 40 post final injection (pfi) of GBCAs. Mice were sacrificed after magnetic resonance imaging and brain and blood Gd content was assessed by laser ablation-inductively coupled plasma (ICP)-mass spectrometry (MS) and ICP-MS, respectively. In addition, using chronic organotypic hippocampal slice cultures, Gd-induced neurotoxicity was addressed in living brain tissue ex vivo, both under control or inflammatory (tumor necrosis factor α [TNF-α] at 50 ng/μL) conditions.

RESULTS

Neuroinflammation promoted a significant decrease in T1 relaxation times after multiple injections of both GBCAs as shown by quantitative T1 mapping of EAE brains compared with HC. This corresponded to higher Gd retention within the EAE brains at 1, 10, and 40 days pfi as determined by laser ablation-ICP-MS. In inflamed cerebellum, in particular in the deep cerebellar nuclei (CN), elevated Gd retention was observed until day 40 after last gadopentetate application (CN: EAE vs HC, 55.06 ± 0.16 μM vs 30.44 ± 4.43 μM). In contrast, gadobutrol application led to a rather diffuse Gd content in the inflamed brains, which strongly diminished until day 40 (CN: EAE vs HC, 0.38 ± 0.08 μM vs 0.17 ± 0.03 μM). The analysis of cytotoxic effects of both GBCAs using living brain tissue revealed an elevated cell death rate after incubation with gadopentetate but not gadobutrol at 50 mM. The cytotoxic effect due to gadopentetate increased in the presence of the inflammatory mediator TNF-α (with vs without TNF-α, 3.15% ± 1.18% vs 2.17% ± 1.14%; P = 0.0345).

CONCLUSIONS

In the EAE model, neuroinflammation promoted increased Gd retention in the brain for both GBCAs. Whereas in the inflamed brains, efficient clearance of macrocyclic gadobutrol during the investigated time period was observed, the Gd retention after application of linear gadopentetate persisted over the entire observational period. Gadopentetate but not gadubutrol appeared to be neurotoxic in an ex vivo paradigm of neuronal inflammation.

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.

Evaluatıon of Pituıtary/Cranial imagıng results of central puberty precocıous cases

Background

The activation of the gonadotropin-releasing hormone (GnRH) pulse generator before the age of 8 years in girls and 9 years in boys results in central precocious puberty (CPP). Previous studies have shown that the height of the pituitary gland in the CPP cases is higher than in the normal children.

Aim

In this study, ıt was aimed to evaluate the pituitary gland volüme by MRI in CPP children, and explore the intracranial lesions among children with CPP.

Patients and Methods

The study was performed with 50 children (41 girls, 9 boys) who had been diagnosed with CPP. Pituitary MRI was performed in every child after the diagnosis of CPP. Pituitary gland volüme in CPP children was compared with age/sex-matched control subjects. In addition, if available, cranial MRI of patients were evaluated for the presence of additional intracranial abnormalities or space-occupying lesions.

Results

The mean chronological age at diagnosis was 7.1 ± 1.0 (2.4-7.9) years in girls and 7.4 ± 1.7 (3.7-8.8) years in boys. CNS imaging showed pathological findings in 17% (7/41) of the girl cases and 55.5% (5/9) of the boy cases. Pituitary volumes of girls aged 6.0-7.9 years and boys aged 8.0-8.9 years were found to be increased compared to the control group.

Conclusion

In this study, we found that CNS imaging showed pathological findings in 17% of the girl cases, and 55.5% of the boy cases. Pituitary volumes of girls aged 6.0-7.9 years and boys aged 8.0-8.9 years were found to be increased compared to the control group.

Incidental pineal gland cyst in girls with early onset of puberty

Background

The causes of an early onset of puberty are still not clearly defined and may vary from subject to subject. In girls, even if 90% of early puberty is idiopathic, magnetic resonance imaging (MRI) of the brain is performed to exclude secondary causes of precocious puberty, in particular pathological lesions as hypothalamic tumours (hamartoma). In some cases, other intracranial lesions are considered as incidental findings. Aim of the study is evaluating the prevalence of abnormal intracranial lesions detected by brain magnetic resonance imaging MRI with particular focus on the prevalence of pineal gland cysts in the diagnostic work-up of girls with central precocious puberty (CPP) as onset before 8 years and central early puberty (CEP) as onset before 10 years.

Material and methods

MRI data of girls referred from January 2010 to December 2015 to the Pediatric Endocrinology Unit of University of Pavia for early onset of breast development were collected.

Results

We collected 123 MRI data of girls referred to the Pediatric Endocrinology Unit of University of Pavia for early onset of breast development in the study period. Out of them, 25 (20.3%) had cerebral abnormalities and 15 (12.2%) had pineal gland cysts. No significant differences were noted in auxological, ultrasound and hormonal parameters at diagnosis among girls with or without pineal cysts. Patients have been observed for at least three years after the discontinuation of therapy. None of our patients had an unfavorable evolution.

Conclusions

Although pineal cysts seem to be not involved in the onset of puberty, the relevance of the finding remains controversial. Our study wants to provide further insight into the incidence of pineal cysts in pubertal advances. Of note, pineal cysts are often asymptomatic and do not evolve over time.

Gadolinium Retention in the Brain of Mother and Pup Mouse: Effect of Pregnancy and Repeated Administration of Gadolinium‐Based Contrast Agents

Background

The association of repeated administration of gadolinium‐based contrast agents (GBCAs) with the gadolinium (Gd) retention in the brains of mother and fetus remains unclear.

Purpose

To investigate the effects of pregnancy and repeated administration of GBCAs on Gd retention in the brains of mother and pup mice.

Study type

Cross‐sectional cohort toxicity study.

Animal Model

From gestational days 16–19, pregnant (n = 48) BALB/c mice.

Field Strength

A 9.4 T and fast spin echo sequence.

Assessment

Half of the mother mice (n = 24) were killed at postnatal day 1 (P1) for inductively coupled plasma mass spectrometry (ICP‐MS) and transmission electron microscopy (TEM). Besides the ICP‐MS and TEM, four pups were randomly selected from each mother and killed at P1 for ultraperformance liquid chromatography mass spectrometry (UPLC‐MS) and Nissl staining.

Statistical Tests

One‐way analysis of variance and unpaired t‐test.

Results

In the group of gadodiamide, retention of Gd in the brains of pregnant mice was significantly lower than that of nonpregnant mice in the area of the deep cerebellar nuclei (DCN) (10.35 ± 2.16 nmol/g vs. 18.74 ± 3.65 nmol/g). Retention of Gd in the DCN of pups whose mothers were administered gadoterate meglumine was significantly lower than that of pups whose mothers were administered gadodiamide (0.21 ± 0.09 nmol/g vs. 6.15 ± 3.21 nmol/g) at P1. In mice treated with gadodiamide, most of the retained Gd in the brain tissue was insoluble (19.5% ± 9.5% of the recovered amount corresponded to the intact complex in the DCN).

Data Conclusion

In different brain areas of the mother and pup mice, the retention of Gd after gadoterate meglumine administration was lower than that of gadodiamide and gadopentetate dimeglumine administration, and almost all the detected Gd in pups' brains was intact soluble GBCAs.

Evidence Level

1

Technical Efficacy

Stage 2

Combined speciation analysis and elemental bioimaging provides new insight into gadolinium retention in kidney

This study uses a leaching approach in combination with elemental bioimaging and speciation analysis to obtain insight into the gadolinium species present in the kidney of rats that were treated with either a linear or a macrocyclic gadolinium-based contrast agent. Fresh frozen thin sections of the harvested kidneys were immersed halfway into water to wash out hydrophilic species and subsequently analyzed by laser ablation-inductively coupled plasma-mass spectrometry. The water-extracted gadolinium species were analyzed by means of hydrophilic interaction liquid chromatography-inductively coupled plasma-mass spectrometry. Information on the water-soluble species could not only be obtained from the full kidney, but also be traced back to its localization in the tissue. On longitudinal kidney sections treated with gadobutrol, it was found that water-insoluble, permanent Gd depositions were mainly located in the renal cortex, while water-soluble species were found in the medulla, which contains the intact contrast agent up to one year after injection. Moreover, kidney samples from gadodiamide-treated rats showed more water-insoluble Gd deposition in both cortex and medulla, while the concentration of intact contrast agent in the water-soluble fraction was below the limit of detection after twelve months. In conclusion, this rapid approach allowed the spatially resolved differentiation between water-soluble and insoluble gadolinium deposition and is therefore capable of generating new insight into the retention and transportation behavior of gadolinium.

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.

Can Deep Learning Replace Gadolinium in Neuro-Oncology?: A Reader Study

MATERIALS AND METHODS

This monocentric retrospective study leveraged 200 multiparametric brain MRIs acquired between November 2019 and February 2020 at Gustave Roussy Cancer Campus (Villejuif, France). A total of 145 patients were included: 107 formed the training sample (55 ± 14 years, 58 women) and 38 the separate test sample (62 ± 12 years, 22 women). Patients had glioma, brain metastases, meningioma, or no enhancing lesion. T1, T2-FLAIR, diffusion-weighted imaging, low-dose, and standard-dose postcontrast T1 sequences were acquired. A deep network was trained to process the precontrast and low-dose sequences to predict "virtual" surrogate images for contrast-enhanced T1. Once trained, the deep learning method was evaluated on the test sample. The discrepancies between the predicted virtual images and the standard-dose MRIs were qualitatively and quantitatively evaluated using both automated voxel-wise metrics and a reader study, where 2 radiologists graded image qualities and marked all visible enhancing lesions.

RESULTS

The automated analysis of the test brain MRIs computed a structural similarity index of 87.1% ± 4.8% between the predicted virtual sequences and the reference contrast-enhanced T1 MRIs, a peak signal-to-noise ratio of 31.6 ± 2.0 dB, and an area under the curve of 96.4% ± 3.1%. At Youden's operating point, the voxel-wise sensitivity (SE) and specificity were 96.4% and 94.8%, respectively. The reader study found that virtual images were preferred to standard-dose MRI in terms of image quality (P = 0.008). A total of 91 reference lesions were identified in the 38 test T1 sequences enhanced with full dose of contrast agent. On average across readers, the brain lesion SE of the virtual images was 83% for lesions larger than 10 mm (n = 42), and the associated false detection rate was 0.08 lesion/patient. The corresponding positive predictive value of detected lesions was 92%, and the F1 score was 88%. Lesion detection performance, however, dropped when smaller lesions were included: average SE was 67% for lesions larger than 5 mm (n = 74), and 56% with all lesions included regardless of their size. The false detection rate remained below 0.50 lesion/patient in all cases, and the positive predictive value remained above 73%. The composite F1 score was 63% at worst.

CONCLUSIONS

The proposed deep learning method for virtual contrast-enhanced T1 brain MRI prediction showed very high quantitative performance when evaluated with standard voxel-wise metrics. The reader study demonstrated that, for lesions larger than 10 mm, good detection performance could be maintained despite a 4-fold division in contrast agent usage, unveiling a promising avenue for reducing the gadolinium exposure of returning patients. Small lesions proved, however, difficult to handle for the deep network, showing that full-dose injections remain essential for accurate first-line diagnosis in neuro-oncology.

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.

Gadolinium: pharmacokinetics and toxicity in humans and laboratory animals following contrast agent administration

Gadolinium-based contrast agents (GBCAs) have transformed magnetic resonance imaging (MRI) by facilitating the use of contrast-enhanced MRI to allow vital clinical diagnosis in a plethora of disease that would otherwise remain undetected. Although over 500 million doses have been administered worldwide, scientific research has documented the retention of gadolinium in tissues, long after exposure, and the discovery of a GBCA-associated disease termed nephrogenic systemic fibrosis, found in patients with impaired renal function. An understanding of the pharmacokinetics in humans and animals alike are pivotal to the understanding of the distribution and excretion of gadolinium and GBCAs, and ultimately their potential retention. This has been well studied in humans and more so in animals, and recently there has been a particular focus on potential toxicities associated with multiple GBCA administration. The purpose of this review is to highlight what is currently known in the literature regarding the pharmacokinetics of gadolinium in humans and animals, and any toxicity associated with GBCA use.

Laser Ablation ICP-MS Analysis of Chemically Different Regions of Rat Prostate Gland with Implanted Cancer Cells

The comparison of tissues analyzed by LA-ICP-MS is challenging in many aspects, both medical and mathematical. The concept of distinguishing regions of interest (ROIs) was proposed in the literature, allowing for data reduction and targeted comparative analysis. ROIs can be drawn before any analysis, by indicating the anatomical parts of tissue, or after the first step of analysis, by using elemental distribution maps and characteristic regions of enrichment in selected elements. A simple method for identifying different regions, without the manual extraction of image fragments, is highly needed in biological experiments, where large groups of individuals (with samples taken from each of them) is very common. In the present study, two ROIs were distinguished: (1) tissue-rich in fat (and tissue-poor in water); and (2) tissue-rich in water (and tissue-poor in fat). ROIs were extracted mathematically, using an algorithm based on the relationship between 13C and 23Na signal intensities. A cut-off point was indicated in the point of the simultaneous decrease in 13C and increase in 23Na signal intensity. Separate analyses of chemically different ROIs allow for targeted comparison, which is a great advantage of laser ablation over liquid introductions to ICP-MS. In the present experiment, tissues were provided from animals with implanted prostate cancer cells as well as supplemented with mineral compounds particularly important both for prostate gland functions (Zn and Se) and neoplastic processes (Ca, Fe, and Cu). One of the goals was to try to determine whether dietary supplementation qualitatively and quantitatively affects the mineral composition of the prostate gland.

Gadolinium deposition in the brain is related to various contrast agents: a matched case-control study

AIM

To assess the relationship between gadolinium deposition in the brain and various gadolinium-based contrast agents (GBCAs) and to explore confounding variables.

METHODS

The study group included 87 patients with multiple enhanced brain magnetic resonance imaging (MRI) examinations of which 48 patients were in the linear GBCA group (33 patients in gadopentetate dimeglumine group and 15 patients in gadobenate dimeglumine group) and 39 patients in the macrocyclic GBCA group (22 patients in gadobutrol group and 17 patients in gadoterate meglumine group). The control group included 87 normal participants who were matched regarding age, sex, MRI machine and imaging sequences to the study cohort. T1 signal intensity (SI) ratios of the dentate nucleus to the pons (DN/pons) and of the globus pallidus to the frontal white matter (GP/FWM) in both groups were calculated and compared. The relationships between SI ratios and confounding variables were analysed.

RESULTS

Significant differences were detected between two linear GBCA groups and control groups in T1 SI ratios of the DN/pons and GP/FWM (all p<0.001). There were no differences for two the macrocyclic GBCA groups compared with matching control groups (all p>0.05). T1 SI ratios of the linear GBCA group were significantly higher than those of the macrocyclic GBCA group (p<0.001). In the linear GBCA group, the T1 SI ratios of the DN/pons correlated moderately positively with the number of GBCA administrations (r=0.643, p<0.001), and MRI machine and sequence used.

CONCLUSIONS

Increased T1 SI could be observed after repeated administrations of linear GBCA. T1 SI of the DN correlated with the number of linear GBCA administrations, and detection might be affected by MRI machine and sequence.

Pediatric Congenital Lung Malformations: Imaging Guidelines and Recommendations

Congenital lung malformations are a spectrum of developmental anomalies comprised of malformations of the lung parenchyma, airways, and vasculature. Imaging assessment plays a pivotal role in the initial diagnosis, management, and follow-up evaluation of congenital lung malformations in the pediatric population. However, there is currently a lack of practical imaging guidelines and recommendations for the diagnostic imaging assessment of congenital lung malformations in infants and children. This article reviews the current evidence regarding the imaging evaluation of congenital lung malformations and provides up-to-date imaging recommendations for pediatric congenital lung malformations.

Updated International Tuberous Sclerosis Complex Diagnostic Criteria and Surveillance and Management Recommendations

BACKGROUND

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disease affecting multiple body systems with wide variability in presentation. In 2013, Pediatric Neurology published articles outlining updated diagnostic criteria and recommendations for surveillance and management of disease manifestations. Advances in knowledge and approvals of new therapies necessitated a revision of those criteria and recommendations.

METHODS

Chairs and working group cochairs from the 2012 International TSC Consensus Group were invited to meet face-to-face over two days at the 2018 World TSC Conference on July 25 and 26 in Dallas, TX, USA. Before the meeting, working group cochairs worked with group members via e-mail and telephone to (1) review TSC literature since the 2013 publication, (2) confirm or amend prior recommendations, and (3) provide new recommendations as required.

RESULTS

Only two changes were made to clinical diagnostic criteria reported in 2013: "multiple cortical tubers and/or radial migration lines" replaced the more general term "cortical dysplasias," and sclerotic bone lesions were reinstated as a minor criterion. Genetic diagnostic criteria were reaffirmed, including highlighting recent findings that some individuals with TSC are genetically mosaic for variants in TSC1 or TSC2. Changes to surveillance and management criteria largely reflected increased emphasis on early screening for electroencephalographic abnormalities, enhanced surveillance and management of TSC-associated neuropsychiatric disorders, and new medication approvals.

CONCLUSIONS

Updated TSC diagnostic criteria and surveillance and management recommendations presented here should provide an improved framework for optimal care of those living with TSC and their families.

Gadolinium is not necessary for surveillance MR imaging in children with chiasmatic-hypothalamic low-grade glioma

BACKGROUND

Patients with chiasmatic-hypothalamic low-grade glioma (CHLGG) have frequent MRIs with gadolinium-based contrast agents (GBCA) for disease monitoring. Cumulative gadolinium deposition in the brains of children is a potential concern. The purpose of this study is to evaluate whether MRI with GBCA is necessary for determining radiographic tumor progression in children with CHLGG.

METHODS

Children who were treated for progressive CHLGG from 2005 to 2019 at Texas Children's Cancer Center were identified. Pre- and post-contrast MRI sequences were separately reviewed by one neuroradiologist who was blinded to the clinical course. Three dimensional measurements and tumor characteristics were evaluated. Radiographic progression was defined as a 25% increase in size (product of two largest dimensions) compared with baseline or best response after initiation of therapy.

RESULTS

A total of 28 patients with progressive CHLGG were identified with a total of 683 MRIs with GBCA reviewed (mean 24 MRIs/patient; range, 11-43 MRIs). Radiographic progression was observed 92 times, 91 (99%) on noncontrast and 90 (98%) on contrast imaging. Sixty-seven progressions necessitating management changes were identified in all (100%) noncontrast sequences and 66 (99%) contrast sequences. Tumor growth > 2 mm in any dimension was identified in 184/187 (98%) noncontrast and 181/187 (97%) with contrast imaging. Metastatic tumors were better visualized on contrast imaging in 4/7 (57%).

CONCLUSION

MRI without GBCA effectively identifies patients with progressive disease. When imaging children with CHLGG, eliminating GBCA should be considered unless monitoring patients with metastatic disease.

Gadolinium Tissue Distribution in a Large-Animal Model after a Single Dose of Gadolinium-based Contrast Agents

Background There is an ongoing scientific debate about the degree and clinical importance of gadolinium deposition in the brain and other organs after administration of gadolinium-based contrast agents (GBCAs). While most published data focus on gadolinium deposition in the brain, other organs are rarely investigated. Purpose To compare gadolinium tissue concentrations in various organs 10 weeks after one injection (comparable to a clinically applied dose) of linear and macrocyclic GBCAs in a large-animal model. Materials and Methods In this prospective animal study conducted from March to May 2018, 36 female Swiss-Alpine sheep (age range, 4-10 years) received one injection (0.1 mmol/kg) of macrocyclic GBCAs (gadobutrol, gadoteridol, and gadoterate meglumine), linear GBCAs (gadodiamide and gadobenate dimeglumine), or saline. Ten weeks after injection, sheep were sacrificed and tissues were harvested. Gadolinium concentrations were quantified with inductively coupled plasma mass spectrometry (ICP-MS). Histologic staining was performed. Data were analyzed with nonparametric tests. Results At 10 weeks after injection, linear GBCAs resulted in highest mean gadolinium concentrations in the kidney (502 ng/g [95% CI: 270, 734]) and liver (445 ng/g [95% CI: 202, 687]), while low concentrations were found in the deep cerebellar nuclei (DCN) (30 ng/g [95% CI: 20, 41]). Tissue concentrations of linear GBCAs were three to 21 times higher compared with those of macrocyclic GBCAs. Administered macrocyclic GBCAs resulted in mean gadolinium concentrations of 86 ng/g (95% CI: 31, 141) (P = .08) in the kidney, 21 ng/g (95% CI: 4, 39) (P = .15) in liver tissue, and 10 ng/g (95% CI: 9, 12) (P > .99) in the DCN, which were not significantly elevated when compared with concentrations in control animals. No histopathologic alterations were observed irrespective of tissue concentrations within any examined organ. Conclusion Ten weeks after one injection of a clinically relevant dose of gadolinium-based contrast agents, the liver and kidney appeared to be reservoirs of gadolinium; however, despite gadolinium presence, no tissue injury was detected. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Clément in this issue.

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).

Repeat and single dose administration of gadodiamide to rats to investigate concentration and location of gadolinium and the cell ultrastructure

Gadolinium based contrast agents (GBCA) are used to image patients using magnetic resonance (MR) imaging. In recent years, there has been controversy around gadolinium retention after GBCA administration. We sought to evaluate the potential toxicity of gadolinium in the rat brain up to 1-year after repeated gadodiamide dosing and tissue retention kinetics after a single administration. Histopathological and ultrastructural transmission electron microscopy (TEM) analysis revealed no findings in rats administered a cumulative dose of 12 mmol/kg. TEM-energy dispersive X-ray spectroscopy (TEM-EDS) localization of gadolinium in the deep cerebellar nuclei showed ~ 100 nm electron-dense foci in the basal lamina of the vasculature. Laser ablation-ICP-MS (LA-ICP-MS) showed diffuse gadolinium throughout the brain but concentrated in perivascular foci of the DCN and globus pallidus with no observable tissue injury or ultrastructural changes. A single dose of gadodiamide (0.6 mmol/kg) resulted in rapid cerebrospinal fluid (CSF) and blood clearance. Twenty-weeks post administration gadolinium concentrations in brain regions was reduced by 16-72-fold and in the kidney (210-fold), testes (194-fold) skin (44-fold), liver (42-fold), femur (6-fold) and lung (64-fold). Our findings suggest that gadolinium does not lead to histopathological or ultrastructural changes in the brain and demonstrate in detail the kinetics of a human equivalent dose over time in a pre-clinical model.

Comparison of Human Tissue Gadolinium Retention and Elimination between Gadoteridol and Gadobenate

Background Linear gadolinium-based contrast agents (GBCAs) are known to be retained at higher levels of gadolinium than macro-cyclic GBCAs. However, very little is known regarding their relative elimination rates and retained fraction of injected gadolinium. Purpose To quantify and compare gadolinium retention and elimination rates in human brain tissue, skin, and bone obtained from cadavers exposed to single-agent administration of either gadoteridol (macrocyclic GBCA) or gadobenate dimeglumine (linear GBCA). Materials and Methods Autopsy cases from August 2014 to July 2019 of patients exposed to a single type of GBCA, either gadoteridol or gadobenate dimeglumine, either single or multiple doses, were included. Gadolinium levels in the brain, skin, and bone were analyzed with inductively coupled plasma mass spectrometry. Linear regression was used to compare gadolinium retention between agents and estimate elimination rates of the retained gadolinium using the time between last injection and death. Results Twenty-eight cadavers with gadoteridol exposure and nine with gadobenate dimeglumine exposure were identified (22 men; age range, 19-83 years). The median gadolinium retention of gadobenate dimeglumine was 3.0-6.5 times higher than that of gadoteridol in the brain (P < .02), 4.4 times higher in bone (P = .002), and 2.9 times higher in skin (P = .05). Gadolinium retention in the globus pallidus (GP), dentate nucleus (DN), white matter (WM), bone, and skin decreased with time elapsed from last administration to death in both the gadobenate dimeglumine (GP: -3% per twofold increase in time, P = .69; DN: -2%, P = .83; WM: -20%, P = .01; bone: -22%, P = .07; skin: -47%, P < .001) and gadoteridol (GP: -17%, P = .11; DN: -16%, P = .15; WM: -30%, P < .001; bone: -11%, P = .16; skin: -24%, P = .01) groups (P values for elimination are compared with a null hypothesis of no elimination). Conclusion The linear agent gadobenate dimeglumine retains several-fold higher levels of gadolinium in the brain and bone compared with the macrocyclic agent gadoteridol. Nonzero elimination of retained gadolinium was detected in the white matter and skin for both agents. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Tweedle in this issue.

Gadolinium Clearance in the First 5 Weeks After Repeated Intravenous Administration of Gadoteridol, Gadoterate Meglumine, and Gadobutrol to rats

Background

Studies of gadolinium (Gd) clearance from animals in the first weeks after administration of gadolinium‐based contrast agents (GBCAs) have previously looked at solitary timepoints only. However, this does not give information on differences between GBCAs and between organs in terms of Gd elimination kinetics.

Purpose

To compare Gd levels in rat cerebellum, cerebrum, skin, and blood at 1, 2, 3, and 5 weeks after repeated administration of macrocyclic GBCAs.

Study Type

Prospective.

Animal Model

One hundred eighty male Sprague–Dawley rats randomized to three groups (n = 60/group), received intravenous administrations of gadoteridol, gadoterate meglumine, or gadobutrol (0.6 mmol/kg for each) four times/week for 5 consecutive weeks. Rats were sacrificed after washout periods of 1, 2, 3, or 5 weeks.

Field Strength/Sequence

Not applicable.

Assessment

Cerebellum, cerebrum, skin, and blood were harvested for Gd determination by inductively coupled plasma‐mass spectrometry (15 animals/group/all timepoints).

Statistical Tests

Anova and Dunnett's test (data with homogeneous variances and normal distribution). Kruskal–Wallis and Wilcoxon's rank sum tests (data showing nonhomogeneous variances or a non‐normal distribution, significance levels: P < 0.05, P < 0.01, and P < 0.001).

Results

Gd levels in cerebellum, cerebrum, and skin were significantly lower after gadoteridol than after gadoterate and gadobutrol at all timepoints. Mean cerebellum Gd concentrations after gadoteridol, gadoterate, and gadobutrol decreased from 0.693, 0.878, and 1.011 nmol Gd/g at 1 week to 0.144, 0.282, and 0.297 nmol Gd/g at 5 weeks after injection. Similar findings were noted for cerebrum and skin. Conversely, significantly higher Gd levels were noted in blood after gadoteridol compared to gadobutrol at 1, 2, and 3 weeks and compared to gadoterate at all timepoints.

Data Conclusion

Gadoteridol is eliminated more rapidly from rat cerebellum, cerebrum, and skin compared to gadoterate and gadobutrol in the first 5 weeks after administration, resulting in lower levels of retained Gd in these tissues.

Evidence Level

1

Technical Efficacy

Stage 5

Is Small Fiber Neuropathy Induced by Gadolinium-Based Contrast Agents?

OBJECTIVES

In recent years, complaints of patients about burning pain in arms and legs after the injection of gadolinium-based contrast agents (GBCAs) have been reported. In the current study, we investigated changes of small fibers in the epidermis as a potential cause of the patient complaints in a mouse model.

METHODS

Six groups of 8 mice were intravenously injected with either a macrocyclic GBCA (gadoteridol, gadoterate meglumine, gadobutrol), a linear GBCA (gadodiamide or gadobenate dimeglumine) (1 mmol/kg body weight), or saline (NaCl 0.9%). Four weeks after injection, animals were euthanized, and footpads were assessed using immunofluorescence staining. Intraepidermal nerve fiber density (IENFD) was calculated, and the median number of terminal axonal swellings (TASs) per IENFD was determined.

RESULTS

Nonparametric Wilcoxon signed-rank test revealed significantly lower IENFDs for all GBCAs compared with the control group (P < 0.0001) with the linear GBCAs showing significantly lower IENFDs than the macrocyclic GBCAs (P < 0.0001). The linear GBCAs presented significantly more TAS per IENFD than the control group (P < 0.0001), whereas no significant increase of TAS per IENFD compared with the control group was found for macrocyclic GBCAs (P < 0.237).

INTERPRETATION

It is unclear whether or at what dosage the decrease of IENFDs and the increase of TAS per IENFD found in the current animal model will appear in humans and if it translates into clinical symptoms. However, given the highly significant findings of the current study, more research in this field is required.

Pre-examinations Improve Automated Metastases Detection on Cranial MRI

MATERIALS AND METHODS

Our local ethics committee approved this retrospective monocenter study.First, a dual-time approach was assessed, for which the CNN was provided sequences of the MRI that initially depicted new MM (diagnosis MRI) as well as of a prediagnosis MRI: inclusion of only contrast-enhanced T1-weighted images (CNNdual_ce) was compared with inclusion of also the native T1-weighted images, T2-weighted images, and FLAIR sequences of both time points (CNNdual_all).Second, results were compared with the corresponding single time approaches, in which the CNN was provided exclusively the respective sequences of the diagnosis MRI.Casewise diagnostic performance parameters were calculated from 5-fold cross-validation.

RESULTS

In total, 94 cases with 494 MMs were included. Overall, the highest diagnostic performance was achieved by inclusion of only the contrast-enhanced T1-weighted images of the diagnosis and of a prediagnosis MRI (CNNdual_ce, sensitivity = 73%, PPV = 25%, F1-score = 36%). Using exclusively contrast-enhanced T1-weighted images as input resulted in significantly less false-positives (FPs) compared with inclusion of further sequences beyond contrast-enhanced T1-weighted images (FPs = 5/7 for CNNdual_ce/CNNdual_all, P < 1e-5). Comparison of contrast-enhanced dual and mono time approaches revealed that exclusion of prediagnosis MRI significantly increased FPs (FPs = 5/10 for CNNdual_ce/CNNce, P < 1e-9).Approaches with only native sequences were clearly inferior to CNNs that were provided contrast-enhanced sequences.

CONCLUSIONS

Automated MM detection on contrast-enhanced T1-weighted images performed with high sensitivity. Frequent FPs due to artifacts and vessels were significantly reduced by additional inclusion of prediagnosis MRI, but not by inclusion of further sequences beyond contrast-enhanced T1-weighted images. Future studies might investigate different change detection architectures for computer-aided detection.

No Changes in T1 Relaxometry After a Mean of 11 Administrations of Gadobutrol

OBJECTIVES

Quantitative T1 relaxometry is the benchmark in imaging potential gadolinium deposition and known to be superior to semiquantitative signal intensity ratio analyses. However, T1 relaxometry studies are rare, commonly limited to a few target structures, and reported results are inconsistent.We systematically investigated quantitative T1 relaxation times (qT1) of a variety of brain nuclei after serial application of gadobutrol.

MATERIALS AND METHODS

Retrospectively, qT1 measurements were performed in a patient cohort with a mean number of 11 gadobutrol applications (n = 46) and compared with a control group with no prior gadolinium-based contrast agent administration (n = 48). The following target structures were evaluated: dentate nucleus, globus pallidus, thalamus, hippocampus, putamen, caudate, amygdala, and different white matter areas. Subsequently, multivariate regression analysis with adjustment for age, presence of brain metastases and previous cerebral radiotherapy was performed.

RESULTS

No assessed site revealed a significant correlation between qT1 and number of gadobutrol administrations in multivariate regression analysis. However, a significant negative correlation between qT1 and age was found for the globus pallidus as well as anterior and lateral thalamus (P < 0.05 each).

CONCLUSIONS

No T1 relaxation time shortening due to gadobutrol injection was found in any of the assessed brain structures after serial administration of 11 doses of gadobutrol.

Impact of Kidney Function on CNS Gadolinium Deposition in Patients Receiving Repeated Doses of Gadobutrol

BACKGROUND AND PURPOSE

Studies associate repeat gadolinium-based contrast agent administration with T1 shortening in the dentate nucleus and globus pallidus, indicating CNS gadolinium deposition, most strongly with linear agents but also reportedly with macrocyclics. Renal impairment effects on long-term CNS gadolinium deposition remain underexplored. We investigated the relationship between signal intensity changes and renal function in patients who received ≥10 administrations of the macrocyclic agent gadobutrol.

MATERIALS AND METHODS

Patients who underwent ≥10 brain MR imaging examinations with administration of intravenous gadobutrol between February 1, 2014, and January 1, 2018, were included in this retrospective study. Dentate nucleus-to-pons and globus pallidus-to-thalamus signal intensity ratios were calculated, and correlations were calculated between the estimated glomerular filtration rate (minimum and mean) and the percentage change in signal intensity ratios from the first to last scan. Partial correlations were calculated to control for potential confounders.

RESULTS

One hundred thirty-one patients (73 women; mean age at last scan, 55.9 years) showed a mean percentage change of the dentate nucleus-to-pons of 0.31%, a mean percentage change of the globus pallidus-to-thalamus of 0.15%, a mean minimum estimated glomerular filtration rate of 69.65 (range, 10.16-132.26), and a mean average estimated glomerular filtration rate at 89.48 (range, 38.24-145.93). No significant association was found between the estimated glomerular filtration rate and percentage change of the dentate nucleus-to-pons (minimum estimated glomerular filtration rate, r = -0.09, P = .28; average estimated glomerular filtration rate, r = -0.09, P = .30,) or percentage change of the globus pallidus-to-thalamus (r = 0.07, P = .43; r = 0.07, P = .40). When we controlled for age, sex, number of scans, and total dose, there were no significant associations between the estimated glomerular filtration rate and the percentage change of the dentate nucleus-to-pons (r = 0.16, P = .07; r = 0.15, P = .08) or percentage change of the globus pallidus-to-thalamus (r = -0.14, P = .12; r = -0.15, P = .09).

CONCLUSIONS

In patients receiving an average of 12 intravenous gadobutrol administrations, no correlation was found between renal function and signal intensity ratio changes, even in those with mild or moderate renal impairment.

The value of qualitative muscle MRI in the diagnostic procedures of myopathies: a biopsy-controlled study in 191 patients

Background and aims

The role of muscle magnetic resonance imaging (MRI) in the diagnostic procedures of myopathies is still controversially discussed. The current study was designed to analyze the status of qualitative muscle MRI, electromyography (EMG), and muscle biopsy in different cases of clinically suspected myopathy.

Methods

A total of 191 patients (male: n = 112, female: n = 79) with suspected myopathy who all received muscle MRI, EMG, and muscle biopsy for diagnostic reasons were studied, with the same location of biopsy and muscle MRI (either upper or lower extremities or paravertebral muscles). Muscle MRIs were analyzed using standard rating protocols by two different raters independently.

Results

Diagnostic findings according to biopsy results and genetic testing were as follow: non-inflammatory myopathy: n = 65, inflammatory myopathy (myositis): n = 51, neurogenic: n = 18, unspecific: n = 23, and normal: n = 34. The majority of patients showed myopathic changes in the EMG. Edema, atrophy, muscle fatty replacement, and contrast medium enhancement (CM uptake) in MRI were observed across all final diagnostic groups. Only 30% of patients from the myositis group (n = 15) showed CM uptake.

Discussion and conclusion

The study provides guidance in the definition of the impact of muscle MRI in suspected myopathy: despite being an important diagnostic tool, qualitative MRI findings could not distinguish different types of neuromuscular diagnostic groups in comparison with the gold standard histopathologic diagnosis and/or genetic testing. The results suggest that neither muscle edema nor gadolinium enhancement are able to secure a diagnosis of myositis. The current results do not support qualitative MRI as aiding in the diagnostic distinction of various myopathies. Quantitative muscle MRI is, however, useful in the diagnostic procedure of a suspected neuromuscular disease, especially with regard to assessing progression of a chronic myopathy by quantification of the degree of atrophy and fatty replacement and in exploring patterns of muscle group involvements in certain genetic myopathies.

Alternatives to Gadolinium-Based Contrast Agents

Gadolinium-based contrast agents have been used in hundreds of millions of patients in the past 30 years, with an exemplary safety record. However, assumptions made at their inception have been recently challenged, rekindling innovation efforts. This critical review outlines the motivations, technical obstacles, problems, and the most recent published progress toward the creation of alternatives to the existing gadolinium-based contrast agent.

Deposition patterns of iatrogenic lanthanum and gadolinium in the human body depend on delivered chemical binding forms

BACKGROUND

Recently, gadolinium from linear GBCAs has been reported to deposit in various regions of the body. Besides gadolinium, other lanthanides are used in medical care. In the current study, we investigated deposition of lanthanum in two patients who received lanthanum carbonate as a phosphate binder due to chronic kidney injury and compared it to additionally found Gd deposition.

METHODS

Tissue specimens of two patients with long-term application of lanthanum carbonate as well as possible GBCA application were investigated. Spatial distribution of gadolinium and lanthanum was determined by quantitative laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging of tissue sections. The deposition of gadolinium and lanthanum in different organs was compared, and the ratio of Gd concentration to La concentration (Gd-to-La-ratio) was investigated on an individual pixel base within the images.

RESULTS

Deposition of Gd and La was found in all investigated tissues of both patients. Gd and La exhibited high spatial correlation for all samples, with the main deposition being located in the middle coat (tunica media) of blood vessels. The Gd-to-La-ratio was similar in the tissues investigated (between 8 ± 4 (mean ± standard deviation) and 10 ± 2), except for the thyroid vasculature and surrounding tissue (90 ± 17) as well as the cerebellum (270 ± 18). Here, the ratio was significantly increased towards higher Gd concentration.

CONCLUSION

The results of this study demonstrate long-term deposition of La and comparable localization of additionally found Gd in various tissues of the body. La deposition was relatively low, considering the total administered amount of lanthanum carbonate of up to 11.5 kg, indicating a low absorption and/or high excretion of lanthanum. However, the total amount of deposited La is significant and raises questions about possible adverse side effects. The ratio-approach allows for the usage of the additionally generated Gd data, without detailed knowledge about possible GBCA applications. The significantly decreased Gd-to-La-ratio in the brain might be explained by the lanthanum being released and taken up as free La³⁺ ion in the stomach that impedes a crossing of the blood-brain-barrier while the intravenously injected GBCAs might dechelate first when they have already crossed the blood-brain-barrier.

Microdistribution of Magnetic Resonance Imaging Contrast Agents in Atherosclerotic Plaques Determined by LA-ICP-MS and SR-μXRF Imaging

Purpose

Contrast-enhanced magnetic resonance imaging (MRI) has the potential to replace angiographic evaluation of atherosclerosis. While studies have investigated contrast agent (CA) uptake in atherosclerotic plaques, exact CA spatial distribution on a microscale is elusive. The purpose of this study was to investigate the microdistribution of gadolinium (Gd)- and iron (Fe) oxide-based CA in atherosclerotic plaques of New Zealand White rabbits.

Procedures

The study was performed as a post hoc analysis of archived tissue specimens obtained in a previous in vivo MRI study conducted to investigate signal changes induced by very small superparamagnetic iron oxide nanoparticles (VSOP) and Gd-BOPTA. For analytical discrimination from endogenous Fe, VSOP were doped with europium (Eu) resulting in Eu-VSOP. Formalin-fixed arterial specimens were cut into 5-μm serial sections and analyzed by immunohistochemistry (IHC: Movat’s pentachrome, von Kossa, and Alcian blue (pH 1.0) staining, anti-smooth muscle cell actin (anti-SMA), and anti-rabbit macrophage (anti-RAM-11) immunostaining) and elemental microscopy with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and synchrotron radiation μX-ray fluorescence (SR-μXRF) spectroscopy. Elemental distribution maps of Fe, Eu, Gd, sulfur (S), phosphorus (P), and calcium (Ca) were investigated.

Results

IHC characterized atherosclerotic plaque pathomorphology. Elemental microscopy showed S distribution to match the anatomy of arterial vessel wall layers, while P distribution corresponded well with cellular areas. LA-ICP-MS revealed Gd and Fe with a limit of detection of ~ 0.1 nmol/g and ~ 100 nmol/g, respectively. Eu-positive signal identified VSOP presence in the vessel wall and allowed the comparison of Eu-VSOP and endogenous Fe distribution in tissue sections. Extracellular matrix material correlated with Eu signal intensity, Fe concentration, and maximum Gd concentration. Eu-VSOP were confined to endothelium in early lesions but accumulated in cellular areas in advanced plaques. Gd distribution was homogeneous in healthy arteries but inhomogeneous in early and advanced plaques. SR-μXRF scans at 0.5 μm resolution revealed Gd hotspots with increased P and Ca concentrations at the intimomedial interface, and a size distribution ranging from a few micrometers to submicrometers.

Conclusions

Eu-VSOP and Gd have distinct spatial distributions in atherosclerotic plaques. While Eu-VSOP distribution is more cell-associated and might be used to monitor atherosclerotic plaque progression, Gd distribution indicates arterial calcification and might help in characterizing plaque vulnerability.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-020-01563-z.

Long-Term Evaluation of Gadolinium Retention in Rat Brain After Single Injection of a Clinically Relevant Dose of Gadolinium-Based Contrast Agents

PURPOSE

The aim of this study was to investigate the presence and chemical forms of residual gadolinium (Gd) in rat brain after a single dose of Gd-based contrast agent.

METHODS

Four groups of healthy rats (2 sacrifice time-points, n = 10/group, 80 rats in total) were randomized to receive a single intravenous injection of 1 of the 3 Gd-based contrast agents (GBCAs) (gadoterate meglumine, gadobenate dimeglumine, or gadodiamide) or the same volume of 0.9% saline solution. The injected concentration was 0.6 mmol/kg, corresponding to a concentration of 0.1 mmol/kg in humans after body surface normalization between rats and humans (according to the US Food and Drug Administration recommendations). Animals were sacrificed at 2 washout times: 1 (M1) and 5 (M5) months after the injection. Total Gd concentrations were determined in cerebellum by inductively coupled plasma mass spectrometry. Gadolinium speciation was analyzed by size-exclusion chromatography coupled to inductively coupled plasma mass spectrometry after extraction from cerebellum.

RESULTS

A single injection of a clinically relevant dose of GBCA resulted in the detectable presence of Gd in the cerebellum 1 and 5 months after injection. The cerebellar total Gd concentrations after administration of the least stable GBCA (gadodiamide) were significantly higher at both time-points (M1: 0.280 ± 0.060 nmol/g; M5: 0.193 ± 0.023 nmol/g) than those observed for macrocyclic gadoterate (M1: 0.019 ± 0.004 nmol/g, M5: 0.004 ± 0.002 nmol/g; P < 0.0001). Gadolinium concentrations after injection of gadobenate were significantly lower at both time-points (M1: 0.093 ± 0.020 nmol/g; M5: 0.067 ± 0.013 nmol/g; P < 0.05) than the Gd concentration measured after injection of gadodiamide. At the 5-month time-point, the Gd concentration in the gadoterate group was also significantly lower than the Gd concentration in the gadobenate group (P < 0.05). Gadolinium speciation analysis of the water-soluble fraction showed that, after injection of the macrocyclic gadoterate, Gd was still detected only in its intact, chelated form 5 months after injection. In contrast, after a single dose of linear GBCAs (gadobenate and gadodiamide), 2 different forms were detected: intact GBCA and Gd bound to soluble macromolecules (above 80 kDa). Elimination of the intact GBCA form was also observed between the first and fifth month, whereas the amount of Gd present in the macromolecular fraction remained constant 5 months after injection.

CONCLUSIONS

A single injection of a clinically relevant dose of GBCA is sufficient to investigate long-term Gd retention in the cerebellar parenchyma. Administration of linear GBCAs (gadodiamide and gadobenate) resulted in higher residual Gd concentrations than administration of the macrocyclic gadoterate. Speciation analysis of the water-soluble fraction of cerebellum confirmed washout of intact GBCA over time. The quantity of Gd bound to macromolecules, observed only with linear GBCAs, remained constant 5 months after injection and is likely to represent a permanent deposition.

Anterior pituitary gland T1 signal intensity is influenced by time delay after injection of gadodiamide

To test the hypothesis of washout from the anterior pituitary (AP) gland after serial injections of gadodiamide. We included 59 patients with history of at least 5 injections of gadodiamide. Values of mean signal intensity of the AP and of the central pons were measured on unenhanced sagittal T1-weighted images. AP-to-pons signal intensity ratios were calculated dividing the values of the AP by those of the pons. The measurements were performed using MR images acquired at four different time points including baseline (prior to any gadodiamide injection), minimum post-injection time delay, maximum post-injection time delay, and last available MR scans. Normalized ratios (i.e. ratios divided total volume of injected gadodiamide) were also calculated. To assess the difference between ratios, non-parametric Wilcoxon signed-rank test was applied. The correlations were tested with non-parametric Spearman correlation coefficient. A p-value < 0.05 was considered as statistically significant. A statistically significant increase of AP signal intensity was found by comparing the baseline scans with both the minimum time delay (p = 0.003) and maximum time delay scans (p = 0.005). We found significant higher normalized ratios for minimum post-injection time delay with respect to maximum post-injection time delay (p < 0.001). The normalized ratios demonstrated a statistically significant negative correlation with the post-injection time delay (r = − 0.31; p = 0.006). The findings of this study suggest that washout phenomena of retained/deposited gadolinium from the AP are influenced by the total injected volume and post-injection time delay.

Clinical Value of Noncontrast-Enhanced Radial Quiescent-Interval Slice-Selective (QISS) Magnetic Resonance Angiography for the Diagnosis of Acute Pulmonary Embolism Compared to Contrast-Enhanced Computed Tomography and Cartesian Balanced Steady-State Free Precession

BACKGROUND

Free-breathing noncontrast-enhanced (non-CE) magnetic resonance angiography (MRA) techniques are of considerable interest for the diagnosis of acute pulmonary embolism (APE), due to the possibility for repeated examinations, avoidance of side effects from iodine-based contrast agents, and the absence of ionizing radiation exposure as compared to CE-computed tomographic angiography (CTA).

PURPOSE

To analyze the clinical performance of free-breathing and electrocardiogram (ECG)-gated radial quiescent-interval slice-selective (QISS)-MRA compared to CE-CTA and to Cartesian balanced steady-state free precession (bSSFP)-MRA.

STUDY TYPE

Prospective.

SUBJECTS

Thirty patients with confirmed APE and 30 healthy volunteers (HVs).

FIELD STRENGTH/SEQUENCE

Radial QISS- and bSSFP-MRA at 1.5T.

ASSESSMENT

Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were computed to compare the pulmonary imaging quality between MRA methods. The pulmonary arterial tree was divided into 25 branches and an ordinal scoring system was used to assess the image quality of each pulmonary branch. The clinical performance of the two MRA techniques in accurately assessing APE was evaluated with respect to CE-CTA as the clinical reference standard.

STATISTICAL TESTS

Wilcoxon signed-rank and Spearman's correlation tests were performed. Sensitivity and specificity of the MRA techniques were determined using CE-CTA as the clinical reference standard.

RESULTS

Thrombus-mimicking artifacts appeared more frequently in lobar and peripheral arteries of patients with Cartesian bSSFP than with radial QISS-MRA (pulmonary trunk: 12.2% vs. 14.0%, P = 0.64; lobar arteries: 35.6% vs. 22.0%, P = 0.005, peripheral arteries: 74.4% vs. 49.0%, P < 0.001). The relative increases in SNR and of CNR provided by radial QISS-MRA with respect to Cartesian bSSFP-MRA were 30-35% (P-values of SNR/CNR, HVs: 0.09/0.09, patients: 0.03/0.02). The image quality of pulmonary arterial branches was considered good to excellent in 77.2% of patients with radial QISS-MRA and in 43.2% with Cartesian bSSFP-MRA (P < 0.0001). The clinical performance of radial QISS-MRA was higher than Cartesian bSSFP-MRA for grading embolism, with a total sensitivity of 86.0% vs. 80.6% and a specificity of 93.3% vs. 84.0%, respectively.

DATA CONCLUSION

Radial QISS-MRA is a reliable and safe non-CE angiographic technique with promising clinical potential compared to Cartesian bSSFP-MRA and as an alternative technique to CE-CTA for the diagnosis of APE.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 3.

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.

Gadolinium deposition in the brain of dogs after multiple intravenous administrations of linear gadolinium based contrast agents

Objective

To determine the effect of a linear gadolinium-based contrast agent (GBCA) on the signal intensity (SI) of the deep cerebellar nuclei (DCN) in a retrospective clinical study on dogs after multiple magnetic resonance (MR) examinations with intravenous injections of gadodiamide and LA-ICP-MS analysis of a canine cerebellum after gadodiamide administration.

Animals

15 client-owned dogs of different breeds and additionally 1 research beagle dog cadaver.

Procedures

In the retrospective study part, 15 dogs who underwent multiple consecutive MR imaging examinations with intravenous injection of linear GBCA gadodiamide were analyzed. SI ratio differences on unenhanced T1-weighted MR images before and after gadodiamide injections was calculated by subtracting SI ratios between DCN and pons of the first examination from the ratio of the last examination. Additionally, 1 research beagle dog cadaver was used for LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry) analysis of gadolinium in the cerebellum as an add-on to another animal study. Descriptive and non-parametrical statistical analysis was performed and a p-value of < 0.05 was considered significant.

Results

No statistically significant differences of SI ratios, between DCN and pons, were detectable based on unenhanced T1-weighted MR images. LA-ICP-MS analyses showed between 1.5 to 2.5 μg gadolinium/g tissue in the cerebellum of the examined dog, 35 months after the last of 3 MRI examination with gadodiamide (two examinations at a dose of 1 x 0.1mmol/kg, last examination at a dose of 3 x 0.05mmol/kg).

Conclusion and clinical relevance

Although the retrospective MRI study did not indicate any visible effect of SI increase after multiple gadodiamide exposures, further studies based on LA-ICP-MS showed that the optical threshold was not reached for a potential visible effect. Gadolinium was detectable at a level of 1.5 to 2.5 μg gadolinium/g tissue by using LA-ICP-MS in the cerebellum 35 months after last MRI examination. The general importance of gadolinium retention of subvisible contents requires further investigation.

Texture signatures of native myocardial T1 as novel imaging markers for identification of hypertrophic cardiomyopathy patients without scar

BACKGROUND

In patients with suspected or known hypertrophic cardiomyopathy (HCM), late gadolinium enhancement (LGE) provides diagnostic and prognostic value. However, contraindications and long-term retention of gadolinium have raised concern about repeated gadolinium administration in this population. Alternatively, native T₁ -mapping enables identification of focal fibrosis, the substrate of LGE. However HCM-specific heterogeneous fibrosis distribution leads to subtle T₁ -maps changes that are difficult to identify.

PURPOSE

To apply radiomic texture analysis on native T₁ -maps to identify patients with a low likelihood of LGE(+), thereby reducing the number of patients exposed to gadolinium administration.

STUDY TYPE

Retrospective interpretation of prospectively acquired data.

SUBJECTS

In all, 188 (54.7 ± 14.4 years, 71% men) with suspected or known HCM.

FIELD STRENGTH/SEQUENCE

A 1.5T scanner; slice-interleaved native T₁ -mapping (STONE) sequence and 3D LGE after administration of 0.1 mmol/kg of gadobenate dimeglumine.

ASSESSMENT

Left ventricular LGE images were location-matched with native T₁ -maps using anatomical landmarks. Using a split-sample validation approach, patients were randomly divided 3:1 (training/internal validation vs. test cohorts). To balance the data during training, 50% of LGE(-) slices were discarded.

STATISTICAL TESTS

Four sets of texture descriptors were applied to the training dataset for capture of spatially dependent and independent pixel statistics. Five texture features were sequentially selected with the best discriminatory capacity between LGE(+) and LGE(-) T₁ -maps and tested using a decision tree ensemble (DTE) classifier.

RESULTS

The selected texture features discriminated between LGE(+) and LGE(-) T₁ -maps with a c-statistic of 0.75 (95% confidence interval [CI]: 0.70-0.80) using 10-fold cross-validation during internal validation in the training dataset and 0.74 (95% CI: 0.65-0.83) in the independent test dataset. The DTE classifier provided adequate labeling of all (100%) LGE(+) patients and 37% of LGE(-) patients during testing.

DATA CONCLUSION

Radiomic analysis of native T₁ -images can identify ~1/3 of LGE(-) patients for whom gadolinium administration can be safely avoided.

LEVEL OF EVIDENCE

2 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020. J. Magn. Reson. Imaging 2020;52:906-919.

Pathological and Incidental Findings in 403 Taiwanese Girls With Central Precocious Puberty at Initial Diagnosis

Background: Whether girls with central precocious puberty (CPP) should undergo routine brain magnetic resonance imaging (MRI) to identify potential intracranial pathologies is controversial. Aims: To evaluate the brain MRI results of girls with CPP and identify the clinical and endocrine predictors of brain abnormalities. Methods: This retrospective study obtained data from pediatric endocrine clinics at Chang Gung Children's Hospital. From 1997 and 2017, 403 girls were consecutively diagnosed with CPP. After the exclusion of patients with a history of central nervous system (CNS) insults or associated neuropsychiatric symptom or signs, we studied the prevalence of brain abnormalities in 251 girls with CPP who received detailed MRI examinations of the hypothalamus and pituitary area. We also recorded the demographic data of the participants, including the onset of puberty; initial pubertal status; height; weight; uterus and ovary sizes; and basal luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol levels, and the response to GnRH stimulation test. Results: Among the 251 girls with CPP, we observed no brain alterations in 190 (75.70%), abnormalities in the hypothalamic-pituitary (H-P) area in 54 (21.51%), and abnormalities in the non-H-P area in 7 (2.79%). Among the 54 patients that had H-P lesions, we noted pathological findings related to CPP (hypothalamic hamartoma) in only one (0.4%) girl aged below 6 years old. We also identified incidental findings in the other girls with H-P lesions, including non-functioning pituitary microadenomas (12.35%), pituitary pars intermedia cysts (4.38%), Rathke's pouch cysts (1.99%), pituitary hypoplasia (1.59%), and pineal gland cysts (0.8%). The patients that had non-H-P lesions were found to have arachnoid cysts (1.59%), Chiari I malformation (0.4%), prepontine nodule (0.4%), and choroidal fissure cyst (0.4%). Of all the patients with brain lesions, 45 (73.77%) underwent regular MRI follow-up. While none of the H-P and non-H-P lesions showed progression, 19.67% of these regressed during the follow-up. None of the participants exhibited other hormonal abnormalities or underwent surgery. Conclusion: The prevalence of true pathological brain lesions related to CPP in girls without prior symptoms or signs of CNS lesions was low (0.4%). None of the girls with intracranial lesions required further intervention besides the GnRH agonist treatment. These data question the routine use of brain MRI in all girls with CPP, especially in those who are healthy without neurologic symptoms.