Low-field MRI: Clinical promise and challenges.

Modern MRI scanners have trended toward higher field strengths to maximize signal and resolution while minimizing scan time. However, high-field devices remain expensive to install and operate, making them scarce outside of high-income countries and major population centers. Low-field strength scanners have drawn renewed academic, industry, and philanthropic interest due to advantages that could dramatically increase imaging access, including lower cost and portability. Nevertheless, low-field MRI still faces inherent limitations in image quality that come with decreased signal. In this article, we review advantages and disadvantages of low-field MRI scanners, describe hardware and software innovations that accentuate advantages and mitigate disadvantages, and consider clinical applications for a new generation of low-field devices. In our review, we explore how these devices are being or could be used for high acuity brain imaging, outpatient neuroimaging, MRI-guided procedures, pediatric imaging, and musculoskeletal imaging. Challenges for their successful clinical translation include selecting and validating appropriate use cases, integrating with standards of care in high resource settings, expanding options with actionable information in low resource settings, and facilitating health care providers and clinical practice in new ways. By embracing both the promise and challenges of low-field MRI, clinicians and researchers have an opportunity to transform medical care for patients around the world. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 6.

Coronavirus Disease (COVID-19)-Related Disseminated Leukoencephalopathy: A Retrospective Study of Findings on Brain MRI.

Among 2820 inpatients with coronavirus disease (COVID-19), 59 (2.1%) underwent brain MRI. Of them, six (10.2%) had MRI findings suspicious for COVID-19-related disseminated leukoencephalopathy (CRDL), which is characterized by extensive confluent or multifocal white matter lesions (with characteristics and locations atypical for other causes), microhemorrhages, diffusion restriction, and enhancement. CRDL is an uncommon but important differential consideration in patients with neurologic manifestations of COVID-19.

Radiologic-pathologic evidence of brain injury: hypoperfusion in the Papez circuit results in poor neurodevelopmental outcomes in neonatal hypoxic ischemic encephalopathy.

PURPOSE: To provide radiologic-pathologic correlation of brain injury in the Papez circuit in hypoxic-ischemic encephalopathy (HIE) neonates and correlate radiologic findings with long-term neurodevelopmental outcomes. METHODS: Twenty full-term HIE neonates were evaluated. Cerebral blood flow (CBF) values, obtained through pulsed arterial spin labeling (ASL) perfusion-weighted MRI, were compared by permutation test to identify brain regions with statistically significant perfusion changes between 14 HIE neonates without evidence of developmental delay by Bayley-III (mean age 8.2 ± 7.2 days) and 6 HIE neonates with evidence of developmental delay (mean age 13.1 ± 8.0 days). Four histopathologic studies on specimens were taken from post-mortem brains of another group of infants (mean age 10 ± 6.8 days) with HIE. The infants were not the same ones who had MRIs. RESULTS: Significantly decreased perfusion in Papez circuit was found in HIE neonates with developmental delay compared with HIE neonates without delay. Decreased ASL perfusion values were seen in Papez circuit structures of the fornix (p = 0.002), entorhinal cortex (p = 0.048), amygdala (p = 0.036), hippocampus (p = 0.033), and thalamus (p = 0.036). In autopsy specimens of neonates with HIE, anoxic (eosinophilic) neurons, reactive astrocytes, and white matter rarefaction were observed in these regions, providing pathology correlation to the imaging findings of HIE. CONCLUSION: The Papez circuit is susceptible to hypoxic-ischemic injury in neonates as demonstrated by perfusion-weighted imaging and histopathology. This sheds new light onto a possible non-familial mechanism of neuropsychiatric disease evolution initiated in the infant period and raises the potential for early identification of at-risk children.

Unenhanced MRI as an Alternative to 99mTc-Labeled Dimercaptosuccinic Acid Scintigraphy in the Detection of Pediatric Renal Scarring.

OBJECTIVE: The purpose of this study was to determine whether unenhanced MRI without sedation is a feasible substitute for dimercaptosuccinic acid (DMSA) scintigraphy in the detection of renal scars in pediatric patients. SUBJECTS AND METHODS: Patients scheduled for 99mTc-labeled DMSA scintigraphy for assessment of possible renal scars were recruited to undergo unenhanced MRI (free-breathing fat-suppressed T2-weighted single-shot turbo spin-echo and T1-weighted gradient-echo imaging, 13 minutes' total imaging time). Scintigraphic and MRI studies were evaluated by two independent blinded specialty-based radiologists. For each imaging examination, readers identified scars in upper, middle, and lower kidney zones and rated their diagnostic confidence and the quality of each study. The scintigraphic readers' consensus score opinion for the presence of scars was considered the reference standard. RESULTS: DMSA scintigraphy showed scarring in 19 of the 78 (24.4%) evaluated zones and MRI in 18 of the 78 (23.1%). The two MRI readers found mean sensitivities of 94.7% and 89.5%, identical specificities of 100%, and diagnostic accuracies of 98.7% and 97.4%. Interobserver agreement was 98.7% for MRI and 92.3% for DMSA scintigraphy. The MRI readers were significantly more confident in determining the absence rather than the presence of scars (p = 0.02). MRI readers were more likely to rate study quality as excellent (84.6%) than were the scintigraphic readers (57.7%) (p = 0.024). CONCLUSION: Unenhanced MRI has excellent sensitivity, specificity, diagnostic accuracy, and interobserver agreement for detecting renal scars in older children who do not need sedation. It may serve as a substitute modality, especially when DMSA is not available.

Automating Structured Results Communication to Expedite Imaging-Directed Care in Spine Oncology.

Cancers frequently metastasize to the spine, where they can cause severe morbidity, including pain, vertebral collapse, and paralysis. Accurate assessment and timely communication of actionable imaging findings are critical. We developed a scoring mechanism to capture the key imaging features of examinations performed to detect and characterize spinal metastases in patients with cancer. An automated system was developed to relay those findings to the institution's spine oncology team to expedite treatment. This report describes the scoring scheme, the automated results communication platform, and initial clinical experience with the system. The scoring system and communication platform enable prompt, imaging-directed care of patients with spinal metastases.

Striving to be of Value: Building a Virtual Radiology Consult Service for Patients.

PURPOSE: Direct interactions between patients and diagnostic radiologists are uncommon, but recent medicolegal developments in the United States may increase patient interest in communicating directly with radiologists. Patient participation rates in prior attempts at direct radiology consultation vary widely in the literature. Our objective was to design and build a virtual radiology consult service for a subset of patients undergoing lung cancer screening CTs to enable communication between patients and radiologists regarding imaging results and radiology recommendations. METHODS: Patients scheduled for lung cancer screening CTs were identified using a custom scheduling system and offered via text message a free 15-minute consultation with a radiologist to discuss the results. RESULTS: Of 38 patients texted, 10 (26.3%) responded. Nine (90%) scheduled a consultation, but 5 (55.5%) subsequently cancelled. Of the remaining four, 3 (75%) attended their appointments, with an overall 3/38 (7.9%) text-to-consult conversation rate. The 3 consults averaged 18 (±8.2) minutes. CONCLUSION: The recruitment rate for our virtual service was between the low rate of a prior phone consult line study and the high rate in consults integrated into another physician visit. Further research is needed to identify patients most interested in a radiology consultation and optimize consultation modality by patient population.

Evaluation of the Cerebrospinal Fluid Flow Dynamics with Microvascular Imaging Ultrasound in Infants.

PURPOSE: Microvascular imaging ultrasound (MVI) can detect slow blood flow in small-caliber cerebral vessels. This technology may help assess flow in other intracranial structures, such as the ventricular system. In this study, we describe the use of MVI for characterizing intraventricular cerebrospinal fluid (CSF) flow dynamics in infants. MATERIALS AND METHODS: We included infants with brain ultrasound that had MVI B-Flow cine clips in the sagittal plane. Two blinded reviewers examined the images, dictated a diagnostic impression, and identified the third ventricle, cerebral aqueduct, fourth ventricle, and CSF flow direction. A third reviewer evaluated the discrepancies. We evaluated the association of visualization of CSF flow as detectable with MVI, with the diagnostic impressions. We also assessed the inter-rater reliability (IRR) for detecting CSF flow. RESULTS: We evaluated 101 infants, mean age 40 ± 53 days. Based on brain MVI B-Flow, a total of 49 patients had normal brain US scans, 40 had hydrocephalus, 26 had intraventricular hemorrhage (IVH), and 14 had hydrocephalus+IVH. Using spatially moving MVI signal in the third ventricle, cerebral aqueduct, and fourth ventricle as the criteria for CSF flow, CSF flow was identified in 10.9% (n = 11), 15.8% (n = 16), and 16.8% (n = 17) of cases, respectively. Flow direction was detected in 19.8% (n = 20) of cases; 70% (n = 14) was caudocranial, 15% (n = 3) was craniocaudal, and 15% (n = 3) bidirectional, with IRR = 0.662, p < 0.001. Visualization of CSF flow was significantly associated with the presence of IVH alone (OR 9.7 [3.3-29.0], p < 0.001) and IVH+hydrocephalus (OR 12.4 [3.5-440], p < 0.001), but not with hydrocephalus alone (p = 0.116). CONCLUSION: This study demonstrates that MVI can detect CSF flow dynamics in infants with a history of post-hemorrhagic hydrocephalus with a high IRR.

Advanced Ultrasound Techniques for Neuroimaging in Pediatric Critical Care: A Review.

Because of its portability, safety profile, and accessibility, ultrasound has been integral in pediatric neuroimaging. While conventional B-mode and Doppler ultrasound provide anatomic and limited flow information, new and developing advanced ultrasound techniques are facilitating real-time visualization of brain perfusion, microvascular flow, and changes in tissue stiffness in the brain. These techniques, which include contrast-enhanced ultrasound, microvascular imaging, and elastography, are providing new insights into and new methods of evaluating pathologies affecting children requiring critical care, including hypoxic-ischemic encephalopathy, stroke, and hydrocephalus. This review introduces advanced neurosonography techniques and their clinical applications in pediatric neurocritical care.

Contrast-Enhanced Ultrasound of Brain Perfusion in Cardiopulmonary Resuscitation.

ABSTRACT: To evaluate the feasibility and potential utility of contrast-enhanced ultrasound for real-time imaging of whole-brain perfusion during cardiopulmonary resuscitation (CPR), cardiac arrest was induced in 8- to 7-week-old 10-kg piglets ( Sus scrofa domesticus ). Contrast-enhanced ultrasound was performed through a parietal cranial window in the coronal plane visualizing the thalami during hemodynamic-directed CPR. Whole-brain mean and maximum pixel intensities in each slice during resuscitation were calculated. Piglets were monitored for 24 hours postarrest. Seven piglets achieved return of spontaneous circulation and 6 survived to 24 hours. Of the 6 surviving piglets, 2 piglets demonstrated greater intra-CPR brain enhancement at maximum 73.2% and 42.1% and mean 36.7% and 31.9% enhancement above background, respectively, compared with maximum 5.8%, 22.9%, 6.0%, and 26.6% and mean 5.1%, 8.9%, 2.9%, and 6.6% above background, respectively, in the other 4. Intra-CPR average mean arterial pressures were similar between all 6 surviving piglets. One piglet achieved return of spontaneous circulation but expired 10 minutes later with enhancement maximum 45.2% and mean 18.9% enhancement above background. The final piglet did not achieve return of spontaneous circulation and exhibited minimal enhancement at maximum 2.8% and mean 0.9% enhancement above background. Contrast-enhanced ultrasound can detect brain perfusion during CPR, identifying a spectrum of cerebral blood flow responses in the brain despite similar systemic hemodynamics. This novel application can form the basis for future large animal model studies and eventually human clinical studies to further explore the neurologic implications of cerebral blood flow responses during resuscitation and stimulate novel strategies for optimizing brain perfusion restoration.

Neonatal gastrointestinal emergencies: a radiological review.

BACKGROUND: Abdominal emergencies in neonates require surgical management in almost all cases and complications may include bowel perforation, sepsis, shock, and even death. Radiological imaging has become a very important aid in the clinical setting as it shortens time to diagnosis. OBJECTIVE: The objective of this review is to discuss the more prevalent neonatal gastrointestinal emergencies, review appropriate imaging options, and illustrate common radiological presentations of these entities. CONCLUSION: Despite advancements in imaging techniques, it is important to keep in mind that neonates have a higher susceptibility to the adverse effects of ionizing radiation, and therefore radiography and ultrasonography remain the main diagnostic modalities for ruling out the diseases with the worst prognosis. Other modalities (fluoroscopy, computed tomography, and magnetic resonance imaging) may have limited use in very specific conditions. All providers in an emergency department should be familiar with the basic radiological findings that may indicate a gastrointestinal emergency, especially in health institutions that do not have 24-h radiologist coverage.

Evaluating the Impact of a Call Triage Assistant on Resident Efficiency, Errors, and Stress.

OBJECTIVE: The aim of this study was to evaluate whether a call triage assistant, who answered telephone calls to the main reading room during the busiest hours of weekend call, would impact resident workflow efficiency, diagnostic errors, and stress level. METHODS: The call triage assistant answered all telephone calls to the main reading room from 12 pm to 7 pm on 6 weekend days over a 3-month period. We compared report turnaround times and resident discrepancy rates on these days with control days, when the same residents were on call without the assistant. We also surveyed residents to determine whether the assistants relieved anxiety associated with the call shift. RESULTS: We recorded 168 telephone calls over the study period. We found the majority of telephone calls could be handled by the assistant without disturbing the on-call resident, resulting in a 71% reduction in interruptions. The mean turnaround time for studies read on the days the assistant was on duty was 44.3 min, compared with 75.2 min on the control days (P < .01). Resident major discrepancy rates (0.4% on the intervention days compared to 0.2% on the control days) were similar (P = .58), as were minor discrepancy rates (7.5% on the intervention days compared with 6.7% on the control days; P = .61). Residents reported fewer distractions, improved workflow efficiency, and decreased call-related stress when the assistant was on duty. CONCLUSIONS: A call triage assistant effectively improved workflow efficiency and reduced resident stress on call. Resident error rates were unaffected by the presence of the assistant.

Cerebral Pulsed Arterial Spin Labeling Perfusion Weighted Imaging Predicts Language and Motor Outcomes in Neonatal Hypoxic-Ischemic Encephalopathy.

Rationale and Objectives: To compare cerebral pulsed arterial spin labeling (PASL) perfusion among controls, hypoxic ischemic encephalopathy (HIE) neonates with normal conventional MRI(HIE/MRI⊕), and HIE neonates with abnormal conventional MRI(HIE/MRI⊖). To create a predictive machine learning model of neurodevelopmental outcomes using cerebral PASL perfusion. Materials and Methods: A total of 73 full-term neonates were evaluated. The cerebral perfusion values were compared by permutation test to identify brain regions with significant perfusion changes among 18 controls, 40 HIE/MRI⊖ patients, and 15 HIE/MRI⊕ patients. A machine learning model was developed to predict neurodevelopmental outcomes using the averaged perfusion in those identified brain regions. Results: Significantly decreased PASL perfusion in HIE/MRI⊖ group, when compared with controls, were found in the anterior corona radiata, caudate, superior frontal gyrus, precentral gyrus. Both significantly increased and decreased cerebral perfusion changes were detected in HIE/MRI⊕ group, when compared with HIE/MRI⊖ group. There were no significant perfusion differences in the cerebellum, brainstem and deep structures of thalamus, putamen, and globus pallidus among the three groups. The machine learning model demonstrated significant correlation (p < 0.05) in predicting language(r = 0.48) and motor(r = 0.57) outcomes in HIE/MRI⊖ patients, and predicting language(r = 0.76), and motor(r = 0.53) outcomes in an additional group combining HIE/MRI⊖ and HIE/MRI⊕. Conclusion: Perfusion MRI can play an essential role in detecting HIE regardless of findings on conventional MRI and predicting language and motor outcomes in HIE survivors. The perfusion changes may also reveal important insights into the reperfusion response and intrinsic autoregulatory mechanisms. Our results suggest that perfusion imaging may be a useful adjunct to conventional MRI in the evaluation of HIE in clinical practice.

Variations of the CNS Venous System Mimicking Pathology: Spectrum of Imaging Findings.

Variations in the venous drainage of the central nervous system can have imaging and clinical findings that mimic pathology, presenting a challenge for neuroimagers and clinicians. Patients with these variants may undergo unnecessary testing, and patients with pathology may receive delayed diagnoses because of overlap with benign findings. Consequently, the accurate identification of venous variations on cross-sectional imaging and angiography and their potential causes are critical for differentiating benign imaging variants from potential pathologic processes requiring further evaluation. For example, in the epidural space, benign dilation of the epidural venous plexus may be mistaken for evidence of a fistula, abscess, or metastasis. Hypoplasia of a dural venous sinus or an arachnoid granulation may mimic venous sinus thrombosis. The superior ophthalmic vein may demonstrate benign dilation in intubated patients, mimicking thrombosis, increased intracranial pressure, orbital varix, inflammatory pseudotumor, or other conditions. Furthermore, certain venous variations, such as the occipital sinus or emissary veins, may complicate surgery or herald pathology and should be reported. In addition, some supposedly benign variations, such as the developmental venous anomaly, can be complicated by pathology. The objective of this review article is to provide a descriptive and pictorial review of common anatomic and physiologic variations in the venous drainage system of the brain, spine, and orbits that can mimic pathology. Neuroimaging findings of related pathologies and differences in clinical presentations will also be discussed to assist in the approach to differential diagnosis.

Clinical impact of strict criteria for selectivity and lateralization in adrenal vein sampling.

INTRODUCTION: Selectivity index (SI) and lateralization index (LI) thresholds determine the adequacy of adrenal vein sampling (AVS) and the degree of lateralization. The purpose of this study was investigate the clinical outcome of patients whose adrenal vein sampling was interpreted using "strict criteria" (SC) (SIpre-stimuli≥3, SIpost-stimuli≥5 and LIpre-stimuli≥4, LIpost-stimuli≥4). MATERIALS AND METHODS: A retrospective review of 73 consecutive AVS procedures was performed and 67 were technically successful. Forty-three patients showed lateralization and underwent surgery, while 24 did not lateralize and were managed conservatively. Systolic blood pressure (SBP), diastolic blood pressure (DBP), kalemia (K(+)), and the change in number of blood pressure (BP) medications were recorded for each patient before and after AVS and potential surgery were performed. RESULTS: In the surgery group, BP and K(+) changed respectively from 160±5.3/100±2.0 mmHg to 127±3.3/80±1.9 (p <0.001) and from 3.00±0.10 to 4.4±0.09 (p <0.001). In the medically managed group, BP and K(+) changed respectively from 148±7.3/93±4.3 to 135±3.3/86±1.9 (p <0.001) and from 2.68±0.10 to 4.3±0.09. After surgery or AVS, the patients who took ≥3 blood pressure medications were six (14.0%) in the lateralized group and 22 (91.7%) in the non-lateralized group (p <0.001). CONCLUSIONS: AVS interpretation with SC leads to significant clinical improvement in both patients who underwent surgery and those managed conservatively.