Dentate nucleus T1 hyperintensity: is it always gadolinium all that glitters?

Synthetic Post-Contrast Imaging through Artificial Intelligence: Clinical Applications of Virtual and Augmented Contrast Media

Contrast media are widely diffused in biomedical imaging, due to their relevance in the diagnosis of numerous disorders. However, the risk of adverse reactions, the concern of potential damage to sensitive organs, and the recently described brain deposition of gadolinium salts, limit the use of contrast media in clinical practice. In recent years, the application of artificial intelligence (AI) techniques to biomedical imaging has led to the development of 'virtual' and 'augmented' contrasts. The idea behind these applications is to generate synthetic post-contrast images through AI computational modeling starting from the information available on other images acquired during the same scan. In these AI models, non-contrast images (virtual contrast) or low-dose post-contrast images (augmented contrast) are used as input data to generate synthetic post-contrast images, which are often undistinguishable from the native ones. In this review, we discuss the most recent advances of AI applications to biomedical imaging relative to synthetic contrast media.

Cerebral Venous Thrombosis: A Challenging Diagnosis; A New Nonenhanced Computed Tomography Standardized Semi-Quantitative Method

Cerebral venous sinus thrombosis (CVST) on non-contrast CT (NCCT) is often challenging to detect. We retrospectively selected 41 children and 36 adults with confirmed CVST and two age-matched control groups with comparable initial symptoms. We evaluated NCCT placing four small circular ROIs in standardized regions of the cerebral dural venous system. The mean and maximum HU values were considered from each ROI, and the relative percentage variations were calculated (mean % variation and maximum % variation). We compared the highest measured value to the remaining three HU values through an ad-hoc formula based on the assumption that the thrombosed sinus has higher attenuation compared with the healthy sinuses. Percentage variations were employed to reflect how the attenuation of the thrombosed sinus deviates from the unaffected counterparts. The attenuation of the affected sinus was increased in patients with CVST, and consequently both the mean % and maximum % variations were increased. A mean % variation value of 12.97 and a maximum % variation value of 10.14 were found to be useful to distinguish patients with CVST from healthy subjects, with high sensitivity and specificity. Increased densitometric values were present in the site of venous thrombosis. A systematic, blind evaluation of the brain venous system can assist radiologists in identifying patients who need or do not need further imaging.

In Vivo Brain GSH: MRS Methods and Clinical Applications

Glutathione (GSH) is an important antioxidant implicated in several physiological functions, including the oxidation−reduction reaction balance and brain antioxidant defense against endogenous and exogenous toxic agents. Altered brain GSH levels may reflect inflammatory processes associated with several neurologic disorders. An accurate and reliable estimation of cerebral GSH concentrations could give a clear and thorough understanding of its metabolism within the brain, thus providing a valuable benchmark for clinical applications. In this context, we aimed to provide an overview of the different magnetic resonance spectroscopy (MRS) technologies introduced for in vivo human brain GSH quantification both in healthy control (HC) volunteers and in subjects affected by different neurological disorders (e.g., brain tumors, and psychiatric and degenerative disorders). Additionally, we aimed to provide an exhaustive list of normal GSH concentrations within different brain areas. The definition of standard reference values for different brain areas could lead to a better interpretation of the altered GSH levels recorded in subjects with neurological disorders, with insights into the possible role of GSH as a biomarker and therapeutic target.

Apparent diffusion coefficient magnetic resonance imaging (ADC-MRI) in the axillary breast cancer lymph node metastasis detection: a narrative review

The presence of axillary lymph nodes metastases in breast cancer is the most significant prognostic factor, with a great impact on morbidity, disease-related survival and management of oncological therapies; for this reason, adequate imaging evaluation is strictly necessary. Physical examination is not enough sensitive to assess breast cancer nodal status; axillary ultrasonography (US) is commonly used to detect suspected or occult nodal metastasis, providing exclusively morphological evaluation, with low sensitivity and positive predictive value. Currently, sentinel lymph node biopsy (SLNB) and/or axillary dissection are the milestone for the diagnostic assessment of axillary lymph node metastases, although its related morbidity. The impact of magnetic resonance imaging (MRI) in the detection of nodal metastases has been widely investigated, as it continues to represent the most promising imaging modality in the breast cancer management. In particular, diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) values represent additional reliable non-contrast sequences, able to improve the diagnostic accuracy of breast cancer MRI evaluation. Several studies largely demonstrated the usefulness of implementing DWI/ADC MRI in the characterization of breast lesions. Herein, in the light of our clinical experience, we perform a review of the literature regarding the diagnostic performance and accuracy of ADC value as potential pre-operative tool to define metastatic involvement of nodal structures in breast cancer patients. For the purpose of this review, PubMed, Web of Science, and SCOPUS electronic databases were searched with different combinations of "axillary lymph node", "breast cancer", "MRI/ADC", "breast MRI" keywords. All original articles, reviews and metanalyses were included.

Assessment of gadolinium deposition in the brain tissue of pediatric and adult congenital heart disease patients after contrast enhanced cardiovascular magnetic resonance

BACKGROUND

Contrast enhanced magnetic resonance imaging (MRI) is an important tool for the assessment of extracardiac vasculature and myocardial viability. Gadolinium (Gd) brain deposition after contrast enhanced MRI has recently been described and resulted in a warning issued by the United States Food and Drug Administration. However, the prevalence of brain deposition in children and adults with congenital heart disease (CHD) undergoing cardiovascular magnetic resonance (CMR) is unclear. We hypothesized that Gd exposure as part of one or more CMRs would lead to a low rate of brain deposition in pediatric and adult CHD patients.

METHODS

We queried our institutional electronic health record for all pediatric and adult CHD patients who underwent contrast enhanced CMR from 2005 to 2018 and had a subsequent brain MRI. Cases were age- and gender-matched to controls who were never exposed to Gd and underwent brain MRIs. The total number of contrast enhanced MRIs, type of Gd, and total Gd dose were determined. Brain MRIs were reviewed by a neuroradiologist for evidence of Gd deposition using qualitative and quantitative assessment. Quantitative assessment was performed using the dentate nucleus to pons signal intensity ratio (dp-SIR) on T1 weighted imaging. Continuous variables were analyzed using Mann-Whitney U and Spearman rank correlation tests. Normal SIR was defined as the 95% CI of the control population dp-SIR.

RESULTS

Sixty-two cases and 62 controls were identified. The most contrast enhanced MRIs in a single patient was five and the largest lifetime dose of Gd that any patient received was 0.75 mmol/kg. There was no significant difference in the mean dp-SIR of cases and controls (p = 0.11). The dp-SIR was not correlated with either the lifetime dose of Gd (rs = 0.21, p = 0.11) or the lifetime number of contrast enhanced studies (rs = 0.21, p = 0.11). Two cases and 2 controls had dp-SIRs above the upper bound of the 95% confidence interval for the control group. One case had qualitative imaging-based evidence of Gd deposition in the brain but had a dp-SIR within the normal range.

CONCLUSION

In our cohort of pediatric and adult CHD patients undergoing contrast enhanced CMR, there was a low incidence of qualitative and no significant quantitative imaging-based evidence of Gd brain deposition.

Narrative review of multiparametric ultrasound in parotid gland evaluation

Disorders affecting parotid gland represent a heterogeneous group comprising congenital, inflammatory and neoplastic diseases which show a focal or diffuse pattern of appearance. The differentiation of neoplastic from non-neoplastic conditions of parotid glands is pivotal for the diagnostic imaging. Frequently there is evidence of overlapping between the clinical and the imaging appearance of the various pathologies. The parotid gland is also often object of study with the combination of different techniques [ultrasound-computed tomography-magnetic resonance imaging (US-CT-MRI), ex.]. Compared to other dominant methods of medical imaging, US has several advantages providing images in real-time at lower cost, and without harmful use of ionizing radiation and of contrast enhancement. B-mode US, and the microvascular pattern color Doppler are usually used as first step evaluation of parotid lesions. Elastography and contrast-enhanced US (CEUS) has opened further possible perspectives to improve the differentiation between benign and malignant parotid lesions. The characterization of the parotid tumors plays a crucial role for their treatment planning and for the prediction of possible surgical complications. We present, here an updated review of the most recurrent pathologies of parotid gland focusing on the diagnostic power of multiparametric US including CEUS and ultrasound elastography (USE); limitations, advantages and the main key-points will be presented.

Pituitary magnetic resonance imaging vs. bilateral inferior petrosal sinus sampling: comparison between non-invasive and invasive diagnostic techniques for Cushing's disease-a narrative review

Cushing's syndrome is a pathological clinical condition caused by an exposure of elevated cortisol levels over a long period of time. It is therefore essential to establish what the cause of hypercortisolism is. In most cases (about 80%) the pathological process is due to adrenocorticotropic hormone (ACTH), while in a minor part of the cases (about 20%) the cause is represented by a pathology of the adrenal glands and therefore not related to ACTH. Most patients with ACTH dependent Cushing's syndrome have a pituitary microadenoma; in the remaining cases (30%), the high level of cortisol is linked to an ectopic secretion of ACTH. Surgical removal of the pituitary adenoma represents the treatment of choice in Cushing's disease (CD) patients; it is therefore necessary to identify and precisely locate the pituitary tumour responsible for the secretion of ACTH. Adequate diagnostic information is very often, even with magnetic resonance imaging (MRI), and in these cases we rely on bilateral inferior petrosal sinuses sampling (BIPSS). This procedure is considered the gold standard method for the diagnosis, but like any other diagnostic method it is not free from erroneous results such as false positives or false negatives.

Visible T1-hyperintensity of the dentate nucleus after multiple administrations of macrocyclic gadolinium-based contrast agents: yes or no?

OBJECTIVES

To investigate the appearance of visible dentate nucleus (DN) T1-hyperintensity and quantify changes in DN/pons (DN/P) signal intensity (SI) ratio in MS patients after the exclusive administration of macrocyclic GBCAs.

MATERIALS AND METHODS

One hundred forty-nine patients with confirmed MS were evaluated. Patients received at least two administrations of gadobutrol (n = 63), gadoterate (n = 57), or both (n = 29). Two experienced neuroradiologists in consensus evaluated unenhanced T1-weighted MR images from all examinations in each patient for evidence of visible DN hyperintensity. Thereafter, SI measurements were made in the left and right DN and pons on unenhanced T1-weighted images from the first and last scans. A two-sample t test compared the DN/P SI ratios for patients with and without visible T1-hyperintensity.

RESULTS

Visible T1-hyperintensity was observed in 42/149 (28.2%) patients (19 after gadobutrol only, 15 after gadoterate only, 8 after both), typically at the 4th or 5th follow-up exam at 3-4 years after the initial examination. Significant increases in DN/P SI ratio from first to last examination were determined for patients with visible T1-hyperintensity (0.998 ± 0.002 to 1.153 ± 0.016, p < 0.0001 for gadobutrol; 1.003 ± 0.004 to 1.110 ± 0.014, p < 0.0001 for gadoterate; 1.004 ± 0.011 to 1.163 ± 0.032, p = 0.0004 for both) but not for patients without visible T1-hyperintensity (p > 0.05; all groups).

CONCLUSION

Multiple injections of gadobutrol and/or gadoterate can lead to visible and quantifiable increases in DN/P SI ratio in some patients with MS.

Gadobutrol enhances T1-weighted MRI of nerve cells

Three-dimensional T₁-weighted MRI of mouse brain in vivo (9.4 T, 80 μm isotropic resolution) identified assemblies of nerve cell bodies in the habenula, hippocampal formation, locus coeruleus, dorsal motor nucleus of vagus, and nucleus ambiguus as high signal intensities, while suppressing the signals of white matter by magnetization transfer and of extracellular water protons by saturation. These observations indicate the presence of intracellular water protons with T₁ values shortened by paramagnetic ions as the source of the bright signal. One day after an intraventricular injection of gadobutrol, a macrocyclic gadolinium-based contrast agent, T₁-weighted MRI signal intensities of the nerve cell assemblies in the habenula, hippocampal formation, and locus coeruleus increased significantly. With simultaneous saturation of long-T₁ protons of extracellular water, this finding indicates a T₁-shortening of the intracellular water protons as a result of their interaction with gadolinium ions.