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

CT surveillance for type 1 autoimmune pancreatitis: cumulative radiation dose and diagnostic performance for disease relapse

OBJECTIVES

Long-term follow-up is essential for type 1 autoimmune pancreatitis (AIP) patients due to high relapse rates. The cumulative radiation dose from repeated CT scans during follow-up should not be ignored. We aim to investigate the cumulative radiation dose in AIP patients undergoing CT surveillance and the diagnostic performance of CT in detecting disease relapse. The diagnostic performance of MRI from a secondary cohort during the same period was also investigated.

METHODS

This retrospective single-institutional study included 247 type 1 AIP patients with one or more follow-up CT scans, and 120 patients with MR follow-ups. Four metrics were utilized to report the radiation dose, including the volume computed tomography dose index, the dose length product, size-specific dose estimate and effective dose. The diagnostic performance for AIP relapse was assessed, taking the final clinical diagnosis in retrospect as the reference standard.

RESULTS

With a median 2.3-year follow-up period, AIP patients followed up with CT exhibited a median cumulative radiation dose of 37.5 mSv. 11.3% of patients have accumulated doses exceeding 100 mSv. For the 169 patients followed over a year, 30.8% sustained an average annual radiation dose surpassing 20 mSv. The sensitivity/specificity/accuracy of CT for detecting abdominal organ relapse was 64.1%/99.6%/97.0%. For AIP patients followed up with MRI, the sensitivity for detecting disease relapse was 90.5%.

CONCLUSION

Considering the accumulation of radiation dose in AIP patients and the insufficient sensitivity in detecting disease relapse with CT, safer and more sensitive imaging follow-up strategies should be explored.

KEY POINTS

Question CT, as the primary imaging modality for autoimmune pancreatitis (AIP) follow-up, raises concerns regarding radiation exposure and lacks reported diagnostic performance in detecting AIP relapse. Findings CT in AIP follow-up causes significant cumulative radiation exposure and exhibits insufficient sensitivity in relapse detection. Clinical relevance Type 1 AIP necessitates long-term imaging follow-up, yet current guidelines lack consensus regarding the prioritization of CT or MRI for such follow-up. CT is widely used but has radiation concerns and limited sensitivity, calling for safer, efficient strategies.

Diagnostic performance of abbreviated non-contrast MRI for liver metastases in patients with newly diagnosed breast cancer

PURPOSE

To compare the diagnostic performance of non-contrast abbreviated liver MRI (abMRI) and standard MRI (sMRI) with gadoxetic acid enhancement in the detection of liver metastasis during the initial workup for patients with breast cancer.

METHODS

Of 7621 patients diagnosed with breast cancer who underwent abdominopelvic CT for their initial staging, 222 underwent sMRI between January 2016 and June 2019 to evaluate and/or characterize CT-indeterminate liver lesions. The abMRI protocol included diffusion-weighted images, apparent diffusion coefficient maps, and T2-weighted fat-suppression images, while the reference standard was histopathology or composite imaging follow-up. Two radiologists utilized a five-point scale to determine the probability of malignancy for each lesion. The per-patient diagnostic parameters were compared using generalized estimating equation and chi-square test.

RESULTS

A total of 222 female patients (age, 49.8 ± 10.4 years) including 17 with metastases (7.7 %) were included in the present analysis. When defining scores ≥4 as metastasis, there were no significant differences in the per-patient sensitivities (82.4 % vs. 82.4 %; p > 0.99), specificities (97.6 % vs. 98.1 %; p = 0.61), positive predictive values (73.7 % vs. 77.8 %; p = 0.63), negative predictive values (98.5 % vs. 98.5 %; p = 0.99), or accuracies (96.4 % vs. 96.9 %; p = 0.99) between the abMRI and sMRI groups, respectively. Additionally, there were no significant differences in the subgroups of patients with subcentimetre and stage II or higher disease.

CONCLUSION

During the patients' initial workup, the diagnostic performance of non-contrast abMRI was comparable to that of sMRI with gadoxetic acid for CT-indeterminate liver lesions.

Enhanced detection of glioblastoma vasculature with superparamagnetic iron oxide nanoparticles and MRI

Detecting glioblastoma infiltration in the brain is challenging due to limited MRI contrast beyond the enhancing tumour core. This study aims to investigate the potential of superparamagnetic iron oxide nanoparticles (SPIONs) as contrast agents for improved detection of diffuse brain cancer. We examine the distribution and pharmacokinetics of SPIONs in glioblastoma models with intact and disrupted blood-brain barriers. Using MRI, we imaged RN1-luc and U87MG mice injected with Gadovist and SPIONs, observing differences in blood-brain barrier permeability. Peripheral imaging showed strong uptake of nanoparticles in the liver and spleen, while vascular and renal signals were transient. Susceptibility gradient mapping enabled positive nanoparticle contrast within tumours and provided additional information on tumour angiogenesis. This approach offers a novel method for detecting diffuse brain cancer. Our findings demonstrate that SPIONs enhance glioblastoma detection beyond conventional MRI, providing insights into tumour angiogenesis and opening new avenues for early diagnosis and targeted treatment strategies.

Supplemental Screening With MRI in Women With Dense Breasts: The European Perspective

Breast cancer is the most prevalent cancer in women in Europe, and while all European countries have some form of screening for breast cancer, disparities in organization and implementation exist. Breast density is a well-established risk factor for breast cancer; however, most countries in Europe do not have recommendations in place for notification of breast density or additional supplementary imaging for women with dense breasts. Various supplemental screening modalities have been investigated in Europe, and when comparing modalities, MRI has been shown to be superior in cancer detection rate and in detecting small invasive disease that may impact long-term survival, as demonstrated in the Dense Tissue and Early Breast Neoplasm Screening (DENSE) trial in the Netherlands. Based on convincing evidence, the European Society of Breast Imaging issued recommendations that women with category D density undergo breast MRI from ages 50 to 70 years at least every 4 years and preferably every 2 to 3 years. However, currently no countries in Europe routinely offer women with BI-RADS category D density breasts MRI as supplemental imaging. The reasons for lack of implementation of MRI screening are multifactorial. Concerns regarding increased recalls have been cited, as have cost and lack of resources. However, studies have demonstrated breast MRI in women with BI-RADS category D density breasts to be cost-effective compared with the current breast cancer screening standard of biannual mammography. Furthermore, abbreviated MRI protocols could facilitate more widespread use of affordable MRI screening. Women's perception on breast density notification and supplemental imaging is key to successful implementation.

Preoperative prediction of diffuse glioma type and grade in adults: a gadolinium-free MRI-based decision tree

OBJECTIVES

To develop a gadolinium-free MRI-based diagnosis prediction decision tree (DPDT) for adult-type diffuse gliomas and to assess the added value of gadolinium-based contrast agent (GBCA) enhanced images.

MATERIALS AND METHODS

This study included preoperative grade 2-4 adult-type diffuse gliomas (World Health Organization 2021) scanned between 2010 and 2021. The DPDT, incorporating eleven GBCA-free MRI features, was developed using 18% of the dataset based on consensus readings. Diagnosis predictions involved grade (grade 2 vs. grade 3/4) and molecular status (isocitrate dehydrogenase (IDH) and 1p/19q). GBCA-free diagnosis was predicted using DPDT, while GBCA-enhanced diagnosis included post-contrast images. The accuracy of these predictions was assessed by three raters with varying experience levels in neuroradiology using the test dataset. Agreement analyses were applied to evaluate the prediction performance/reproducibility.

RESULTS

The test dataset included 303 patients (age (SD): 56.7 (14.2) years, female/male: 114/189, low-grade/high-grade: 54/249, IDH-mutant/wildtype: 82/221, 1p/19q-codeleted/intact: 34/269). Per-rater GBCA-free predictions achieved ≥ 0.85 (95%-CI: 0.80-0.88) accuracy for grade and ≥ 0.75 (95%-CI: 0.70-0.80) for molecular status, while GBCA-enhanced predictions reached ≥ 0.87 (95%-CI: 0.82-0.90) and ≥ 0.77 (95%-CI: 0.71-0.81), respectively. No accuracy difference was observed between GBCA-free and GBCA-enhanced predictions. Group inter-rater agreement was moderate for GBCA-free (0.56 (95%-CI: 0.46-0.66)) and substantial for GBCA-enhanced grade prediction (0.68 (95%-CI: 0.58-0.78), p = 0.008), while substantial for both GBCA-free (0.75 (95%-CI: 0.69-0.80) and GBCA-enhanced (0.77 (95%-CI: 0.71-0.82), p = 0.51) molecular status predictions.

CONCLUSION

The proposed GBCA-free diagnosis prediction decision tree performed well, with GBCA-enhanced images adding little to the preoperative diagnostic accuracy of adult-type diffuse gliomas.

KEY POINTS

Question Given health and environmental concerns, is there a gadolinium-free imaging protocol to preoperatively evaluate gliomas comparable to the gadolinium-enhanced standard practice? Findings The proposed gadolinium-free diagnosis prediction decision tree for adult-type diffuse gliomas performed well, and gadolinium-enhanced MRI demonstrated only limited improvement in diagnostic accuracy. Clinical relevance Even inexperienced raters effectively classified adult-type diffuse gliomas using the gadolinium-free diagnosis prediction decision tree, which, until further validation, can be used alongside gadolinium-enhanced images to respect standard practice, despite this study showing that gadolinium-enhanced images hardly improved diagnostic accuracy.

Long-term effects of linear versus macrocyclic GBCAs on gene expression in the central nervous system of mice

BACKGROUND

We examined chronic gadolinium retention impact on gene expression in the mouse central nervous system (CNS) after injection of linear or macrocyclic gadolinium-based contrast agents (GBCAs).

METHODS

From 05/2022 to 07/2023, 36 female mice underwent weekly intraperitoneal injections of gadodiamide (2.5 mmol/kg, linear), gadobutrol (2.5 mmol/kg, macrocyclic), or saline. Mice were sacrificed on day 29 or 391 after a 1-year washout. Assessments included magnetic resonance imaging (MRI), mechanical hyperalgesia tests, and inductively coupled plasma mass spectrometry to measure gadolinium levels. Ribonucleic acid (RNA) sequencing and bioinformatic analyses identified differentially expressed genes (DEGs), with validation by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot (WB).

RESULTS

Post-gadodiamide, MRI showed increased signal intensity in the deep cerebellar nuclei (pre, 0.997 ± 0.006 versus post, 1.086 ± 0.013, p < 0.001). Mechanical hyperalgesia tests indicated transient sensory changes. After 1-year, gadolinium retention was noted in the brain (5.92 ± 0.32 nmol/kg) and spinal cord (1.23 ± 0.66 nmol/kg) with gadodiamide, compared to saline controls (0.06 ± 0.02 nmol/kg in brains and 0.28 ± 0.06 nmol/kg in spinal cords). RNA sequencing identified 17 shared DEGs between brain and spinal cord in the gadodiamide group on day 391, with altered Hmgb2 and Sgk1 expression confirmed by qRT-PCR and WB. Reactome pathway analysis showed enrichment in neuroinflammation pathways. No DEGs were detected in brains on day 29.

CONCLUSION

Chronic gadolinium deposition from repeated linear GBCA but not macrocyclic administration causes significant gene expression alterations in the mouse CNS, particularly affecting neuroinflammation pathways.

RELEVANCE STATEMENT

This study examined the long-term impact of chronic gadolinium retention on gene expression in the mouse CNS, uncovering significant changes associated with neuroinflammation pathways after repeated administration of linear GBCA, but not with macrocyclic GBCA. These findings highlight the importance of further research on the long-term safety of linear GBCA in medical imaging.

KEY POINTS

Chronic gadolinium retention alters gene expression in the mouse central nervous system. Significant neuroinflammatory pathway changes were observed after linear gadodiamide exposure. MRI showed increased signal intensity in deep cerebellar nuclei after gadodiamide injection.

Nanoparticle Contrast Agents for Photon-Counting Computed Tomography: Recent Developments and Future Opportunities

The clinical availability of photon-counting computed tomography (PCCT) has ushered in a new era of CT imaging. Spectral imaging coupled with superior contrast resolution, and ultrahigh spatial resolution (200 μm) offered by PCCT has the potential to revolutionize value-driven imaging. The potential of multicolor PCCT has generated excitement, and renewed interest, in novel contrast agent development for comprehensive disease interrogation, prediction and monitoring of treatment outcomes. Nanoparticles provide a versatile and powerful platform for the development of next generation contrast agents for spectral PCCT. In this article, we review recent developments and use of nanoparticle contrast agents for PCCT. We also discuss future research and translational opportunities for nanoparticle-based CT contrast agents enabled by the advent of PCCT and describe key considerations for their clinical translation.

Reliability of Central Vein Sign Imaging With 3T FLAIR* in a Multicenter Study

BACKGROUND AND PURPOSE

The central vein sign (CVS) is a diagnostic imaging biomarker for multiple sclerosis (MS). FLAIR* is a combined MRI contrast that provides high conspicuity for CVS at 3 Tesla (3T), enabling its sensitive and accurate detection in clinical settings. This study evaluated whether CVS conspicuity of 3T FLAIR* is reliable across imaging sites and MRI vendors and whether gadolinium (Gd) contrast increases CVS conspicuity.

METHODS

A cross-sectional, multicenter study recruited adults referred for possible diagnosis of MS at 10 sites. FLAIR* contrast was generated using high-resolution T2*-weighted (acquired pre- and post-injection of Gd) and T2-weighted fluid-attenuated inversion recovery (T2-FLAIR) brain images at 3T from two MRI vendors. Lesions and veins were segmented to compute lesion-to-vein contrast-to-noise ratio (CNRlesion-to-vein), a quantitative measure of CVS conspicuity. CNRlesion-to-vein measures for pre- and post-Gd FLAIR* were compared across sites and vendors.

RESULTS

Eighty-seven participants from nine sites were included in the analysis. There was no significant difference in mean CNRlesion-to-vein between sites for pre-Gd (p-value = 0.07) or post-Gd (p-value = 0.27) FLAIR*. There were also no significant differences between vendors for pre-Gd (p-value = 0.10) or post-Gd (p-value = 0.31) FLAIR*. Patient-level pairwise differences in CNRlesion-to-vein between pre-Gd and post-Gd FLAIR* revealed a significant increase for post-Gd FLAIR* (p-value < 0.001).

CONCLUSIONS

CVS conspicuity on 3T FLAIR* is consistent across imaging sites and MRI vendors. Moreover, Gd-based contrast agent significantly improved CVS conspicuity on 3T FLAIR*. These findings support the implementation of FLAIR* in clinical settings for MS.

ESR Essentials: gadolinium-wise MRI-practice recommendations by the European Society for Magnetic Resonance in Medicine and Biology

The Gadolinium Research and Education Committee (GREC) is a working group of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB), established in 2016. The aim of the committee is to monitor scientific evidence for a continuous quality and safety improvement of enhanced MRI using gadolinium-based contrast agents (GBCAs), and also assess potential alternatives. The scope of the present article is to describe the level of evidence concerning safety beyond the single patient (access to community and environmental impact), justification and optimization of the use of GBCAs beyond dosage (appropriateness and influence on clinical decision making), dose reduction with the use of AI (benefits and pitfalls), the advent of next-generation GBCAs (based on currently available data). CLINICAL RELEVANCE: GBCAs are extensively used in MRI and influence clinical decision-making. Their use to enhance the contrast-to-noise ratio is guided by recommendations from subspecialty societies. These guidelines advocate for GBCA use as an additional tool when necessary, ensuring they are administered at the lowest reasonable dose. KEY POINTS: The choice of GBCAs used in radiology should be based on MRI cost-effectiveness, MRI access to the patient community, and impact on the environment, (evidence level: low). GBCA optimization includes reducing GBCA volume burden and increasing appropriateness by including post-contrast enhancement in MRI protocols, depending on clinical indications, (evidence level: moderate). Next-generation GBCAs show higher kinetic stability and higher T1 relaxivity when compared with standard macrocyclic GBCAs allowing comparable diagnostic accuracy at lower doses, (evidence level: moderate).

Welding techniques and manganese concentrations in blood and brain: Results from the WELDFUMES study

This study used whole-brain mapping to investigate the effect of different welding processes on manganese (Mn) accumulation in the brain. Exposure measurements were performed at the welders' workplaces about 3 weeks before a magnetic resonance imaging (MRI) examination. The welders were categorized into three main groups based on welding method, and the T1-relaxation rate (R1) was measured using quantitative MRI (qMRI). Welders using shielded metal arc welding (SMAW) were found to have lower accumulations of total Mn in clusters encompassing white matter, thalamus, putamen, pallidum, and substantia nigra compared with welders using inert gas tungsten arc welding (GTAW) or continuous consumable electrode arc welding (CCEAW). A positive correlation was found between Mn in red blood cells (Mn-RBC) and R1 in a region encompassing pre-and post-central gyri. The results of this study show that the accumulation of free, bound, or compartmentalized Mn ions in the brain differed depending on the welding method used. These differences were predominately located in the basal ganglia but were also found in regions encompassing white matter. The level of Mn-RBC was correlated to the deposition of Mn in the left primary somatosensory and motor cortex and may therefore be linked to neurological and neurobehavioral symptoms.

Phenotyping of COPD with MRI in comparison to same-day CT in a multi-centre trial

OBJECTIVES

A prospective, multi-centre study to evaluate concordance of morphologic lung MRI and CT in chronic obstructive pulmonary disease (COPD) phenotyping for airway disease and emphysema.

METHODS

A total of 601 participants with COPD from 15 sites underwent same-day morpho-functional chest MRI and paired inspiratory-expiratory CT. Two readers systematically scored bronchial wall thickening, bronchiectasis, centrilobular nodules, air trapping and lung parenchyma defects in each lung lobe and determined COPD phenotype. A third reader acted as adjudicator to establish consensus. Inter-modality and inter-reader agreement were assessed using Cohen's kappa (im-κ and ir-κ).

RESULTS

The mean combined MRI score for bronchiectasis/bronchial wall thickening was 4.5/12 (CT scores, 2.2/12 for bronchiectasis and 6/12 for bronchial wall thickening; im-κ, 0.04-0.3). Expiratory right/left bronchial collapse was observed in 51 and 47/583 on MRI (62 and 57/599 on CT; im-κ, 0.49-0.52). Markers of small airways disease on MRI were 0.15/12 for centrilobular nodules (CT, 0.34/12), 0.94/12 for air trapping (CT, 0.9/12) and 7.6/12 for perfusion deficits (CT, 0.37/12 for mosaic attenuation; im-κ, 0.1-0.41). The mean lung defect score on MRI was 1.3/12 (CT emphysema score, 5.8/24; im-κ, 0.18-0.26). Airway-/emphysema/mixed COPD phenotypes were assigned in 370, 218 and 10 of 583 cases on MRI (347, 218 and 34 of 599 cases on CT; im-κ, 0.63). For all examined features, inter-reader agreement on MRI was lower than on CT.

CONCLUSION

Concordance of MRI and CT for phenotyping of COPD in a multi-centre setting was substantial with variable inter-modality and inter-reader concordance for single diagnostic key features.

CLINICAL RELEVANCE STATEMENT

MRI of lung morphology may well serve as a radiation-free imaging modality for COPD in scientific and clinical settings, given that its potential and limitations as shown here are carefully considered.

KEY POINTS

• In a multi-centre setting, MRI and CT showed substantial concordance for phenotyping of COPD (airway-/emphysema-/mixed-type). • Individual features of COPD demonstrated variable inter-modality concordance with features of pulmonary hypertension showing the highest and bronchiectasis showing the lowest concordance. • For all single features of COPD, inter-reader agreement was lower on MRI than on CT.

Optimizing Image Quality with High-Resolution, Deep-Learning-Based Diffusion-Weighted Imaging in Breast Cancer Patients at 1.5 T

The objective of this study was to evaluate a high-resolution deep-learning (DL)-based diffusion-weighted imaging (DWI) sequence for breast magnetic resonance imaging (MRI) in comparison to a standard DWI sequence (DWIStd) at 1.5 T. It is a prospective study of 38 breast cancer patients, who were scanned with DWIStd and DWIDL. Both DWI sequences were scored for image quality, sharpness, artifacts, contrast, noise, and diagnostic confidence with a Likert-scale from 1 (non-diagnostic) to 5 (excellent). The lesion diameter was evaluated on b 800 DWI, apparent diffusion coefficient (ADC), and the second subtraction (SUB) of the contrast-enhanced T1 VIBE. SNR was also calculated. Statistics included correlation analyses and paired t-tests. High-resolution DWIDL offered significantly superior image quality, sharpness, noise, contrast, and diagnostic confidence (each p < 0.02)). Artifacts were significantly higher in DWIDL by one reader (M = 4.62 vs. 4.36 Likert scale, p < 0.01) without affecting the diagnostic confidence. SNR was higher in DWIDL for b 50 and ADC maps (each p = 0.07). Acquisition time was reduced by 22% in DWIDL. The lesion diameters in DWI b 800DL and Std and ADCDL and Std were respectively 6% lower compared to the 2nd SUB. A DL-based diffusion sequence at 1.5 T in breast MRI offers a higher resolution and a faster acquisition, including only minimally more artefacts without affecting the diagnostic confidence.

Near-cure in patients with Gadolinium deposition disease undergoing intravenous DTPA chelation

Purpose

To demonstrate and evaluate factors contributing to near-cures in patients with Gadolinium Deposition Disease (GDD) undergoing intravenous (IV) DTPA chelation.

Methods

Patients who had undergone or are currently undergoing DTPA chelation for GDD were included in this report based on their medical records that showed their perceived improvement was at least 80% back to normal. A survey was developed that included factors commonly reported by patients treated in one clinic to determine if these 'near-cured' (pre-MRI baseline health) individuals possessed certain factors and lacked others. The anonymized survey was emailed to these individuals by the principal treating physician, the only investigator not blinded to the subjects. This report describes clinical documentation of patient status and their underlying factors in individuals treated by the primary author, and no research was performed. The survey was sent to sixteen individuals; Fourteen patients completed it (10 females; 41.1 ± 11.2 y/o).

Results

The most common factor was the administration of ≤5 lifetime doses of a Gadolinium-Based Contrast Agents (GBCA) (12/14). Unconfounded agents triggering GDD were seen in nine subjects. Most subjects (12/14) initiated chelation in the first year after the causative GBCA, and most (11/14) underwent ≤10 chelations with DTPA. Good healthcare status prior to MRI was observed in 5 subjects. The majority (11/14) described their immune status as strong. Severe physical disability prior to chelation was seen in 1.

Conclusion

Subjects with GDD can experience near-cure with IV DTPA chelation. Factors surveyed that predict near-cure include the start of chelation in the first year, few GBCA administrations, and good health status before MRI with GBCA injection. Nonetheless, a few patients with predictors of less successful outcomes still experienced near-cure.

Intramolecular Hydrogen Bonding Based CEST MRI Contrast Agents As an Emerging Design Strategy: A Mini-Review

Intramolecular hydrogen bonding-based chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) contrast agents represent an innovative design strategy aiming to overcome limitations in diamagnetic CEST (diaCEST) MRI contrast agent specificity and also those associated with traditional metal-based MRI contrast agents. Ward and Balaban's proposal of small diamagnetic compounds marked a paradigm shift in contrast-based radiologic research, inspiring extensive investigations since 2000. These contrast agents leverage labile hydrogen bonds, serving as chemical exchange sites to induce saturation of water. The selective manipulation of radiofrequency (RF) allows for optimized signal contrast in soft tissue, with a significant signal amplification even at low probe concentrations, mitigating concerns about dose-dependent toxicities. This mini-review delves into the evolution of CEST MRI, its classification, and the strategic design principles of synthetic small molecules containing intramolecular hydrogen bonds. With a focus on applications and potential clinical relevance, the authors highlight the promising role of intramolecular hydrogen bonding-based CEST MRI in diverse medical contexts, especially renal imaging and pH mapping, paving the way for enhanced molecular imaging capabilities. Ongoing research endeavors aim to further optimize and expand the utility of these contrast agents, underscoring their transformative potential in clinical diagnostics and imaging.

Manganese-derived biomaterials for tumor diagnosis and therapy

Manganese (Mn) is widely recognized owing to its low cost, non-toxic nature, and versatile oxidation states, leading to the emergence of various Mn-based nanomaterials with applications across diverse fields, particularly in tumor diagnosis and therapy. Systematic reviews specifically addressing the tumor diagnosis and therapy aspects of Mn-derived biomaterials are lacking. This review comprehensively explores the physicochemical characteristics and synthesis methods of Mn-derived biomaterials, emphasizing their role in tumor diagnostics, including magnetic resonance imaging, photoacoustic and photothermal imaging, ultrasound imaging, multimodal imaging, and biodetection. Moreover, the advantages of Mn-based materials in tumor treatment applications are discussed, including drug delivery, tumor microenvironment regulation, synergistic photothermal, photodynamic, and chemodynamic therapies, tumor immunotherapy, and imaging-guided therapy. The review concludes by providing insights into the current landscape and future directions for Mn-driven advancements in the field, serving as a comprehensive resource for researchers and clinicians.

Diffusion probabilistic versus generative adversarial models to reduce contrast agent dose in breast MRI

BACKGROUND

To compare denoising diffusion probabilistic models (DDPM) and generative adversarial networks (GAN) for recovering contrast-enhanced breast magnetic resonance imaging (MRI) subtraction images from virtual low-dose subtraction images.

METHODS

Retrospective, ethically approved study. DDPM- and GAN-reconstructed single-slice subtraction images of 50 breasts with enhancing lesions were compared to original ones at three dose levels (25%, 10%, 5%) using quantitative measures and radiologic evaluations. Two radiologists stated their preference based on the reconstruction quality and scored the lesion conspicuity as compared to the original, blinded to the model. Fifty lesion-free maximum intensity projections were evaluated for the presence of false-positives. Results were compared between models and dose levels, using generalized linear mixed models.

RESULTS

At 5% dose, both radiologists preferred the GAN-generated images, whereas at 25% dose, both radiologists preferred the DDPM-generated images. Median lesion conspicuity scores did not differ between GAN and DDPM at 25% dose (5 versus 5, p = 1.000) and 10% dose (4 versus 4, p = 1.000). At 5% dose, both readers assigned higher conspicuity to the GAN than to the DDPM (3 versus 2, p = 0.007). In the lesion-free examinations, DDPM and GAN showed no differences in the false-positive rate at 5% (15% versus 22%), 10% (10% versus 6%), and 25% (6% versus 4%) (p = 1.000).

CONCLUSIONS

Both GAN and DDPM yielded promising results in low-dose image reconstruction. However, neither of them showed superior results over the other model for all dose levels and evaluation metrics. Further development is needed to counteract false-positives.

RELEVANCE STATEMENT

For MRI-based breast cancer screening, reducing the contrast agent dose is desirable. Diffusion probabilistic models and generative adversarial networks were capable of retrospectively enhancing the signal of low-dose images. Hence, they may supplement imaging with reduced doses in the future.

KEY POINTS

• Deep learning may help recover signal in low-dose contrast-enhanced breast MRI. • Two models (DDPM and GAN) were trained at different dose levels. • Radiologists preferred DDPM at 25%, and GAN images at 5% dose. • Lesion conspicuity between DDPM and GAN was similar, except at 5% dose. • GAN and DDPM yield promising results in low-dose image reconstruction.

Late/delayed gadolinium enhancement in MRI after intravenous administration of extracellular gadolinium-based contrast agents: is it worth waiting?

The acquisition of images minutes or even hours after intravenous extracellular gadolinium-based contrast agents (GBCA) administration ("Late/Delayed Gadolinium Enhancement" imaging; in this review, further termed LGE) has gained significant prominence in recent years in magnetic resonance imaging. The major limitation of LGE is the long examination time; thus, it becomes necessary to understand when it is worth waiting time after the intravenous injection of GBCA and which additional information comes from LGE. LGE can potentially be applied to various anatomical sites, such as heart, arterial vessels, lung, brain, abdomen, breast, and the musculoskeletal system, with different pathophysiological mechanisms. One of the most popular clinical applications of LGE regards the assessment of myocardial tissue thanks to its ability to highlight areas of acute myocardial damage and fibrotic tissues. Other frequently applied clinical contexts involve the study of the urinary tract with magnetic resonance urography and identifying pathological abdominal processes characterized by high fibrous stroma, such as biliary tract tumors, autoimmune pancreatitis, or intestinal fibrosis in Crohn's disease. One of the current areas of heightened research interest revolves around the possibility of non-invasively studying the dynamics of neurofluids in the brain (the glymphatic system), the disruption of which could underlie many neurological disorders.