Contrast-enhanced transcranial Doppler ultrasonography in the diagnosis of brain death

[Prospective investigation of extracranial duplex sonography for the detection of cerebral circulatory arrest in patients with irreversible loss of brain function]

BACKGROUND

A broader distribution of bedside color-coded duplex sonography (CCD) for detection of cerebral circulatory arrest (CCA) would be important to improve its use in the diagnosis of irreversible loss of brain function (ILBF-Dx).

QUESTION

Is extracranial compared to the commonly applied transcranial CCD of the brain-supplying vessels (ECCD vs. TCCD) equivalent for the detection of CCA in ILBF-Dx regarding specificity and sensitivity?

MATERIAL AND METHODS

Study period January 2019-June 2022, screening of 136 and inclusion of 114 patients with severe brain lesions > 24 h after onset of fixed and dilated pupils, apnea and completed ILBF-Dx. Exclusion of patients without brainstem areflexia and guideline-conform applicability of CCD. Complementary ECCD (and TCCD, if other method used for irreversibility detection).

RESULTS

Detection of ILBF (ILBF+) in 86.8% (99/114), no ILBF (ILBF-) in 13.2% (15/114). ECCD was fully feasible in all patients; findings matching CCA were found in 94/99 ILBF+ cases (ECCD+) and not in 5 patients (ECCD-). All 15 patients with ILBF- showed ECCD- findings. Thus, the specificity of ECCD was 1.0, and the sensitivity was 0.949. TCCD showed CCA in 56 patients (TCCD+), and ECCD+ was also found in all of them. An inconclusive result of TCCD in ILBF+ was found in 38 cases, with parallel ECCD+ in all of these patients. In 20 cases, TCCD did not show CCA (TCCD-), these also showed ECCD-. Of these patients 15 were ILBF- and 5 were ILBF+.

DISCUSSION

TCCD was not completely feasible or inconclusive in one third of the cases, whereas ECCD was always feasible. ECCD showed high validity with respect to the detection of CCA. Therefore, the possibility of using ECCD alone to detect CCA in ILBF-Dx should be discussed.

The Use of Contrast-Enhanced Ultrasound (CEUS) in the Evaluation of the Neonatal Brain

In recent years, advancements in technology have allowed the use of contrast-enhanced ultrasounds (CEUS) with high-frequency transducers, which in turn, led to new possibilities in diagnosing a variety of diseases and conditions in the field of radiology, including neonatal brain imaging. CEUSs overcome some of the limitations of conventional ultrasounds (US) and Doppler USs. It allows the visualization of dynamic perfusion even in the smallest vessels in the whole brain and allows the quantitative analysis of perfusion parameters. An increasing number of articles are published on the topic of the use of CEUSs on children each year. In the area of brain imaging, the CEUS has already proven to be useful in cases with clinical indications, such as hypoxic-ischemic injuries, stroke, intracranial hemorrhages, vascular anomalies, brain tumors, and infections. We present and discuss the basic principles of the CEUS and its safety considerations, the examination protocol for imaging the neonatal brain, and current and emerging clinical applications.

Contrast-Enhanced Ultrasound (CEUS) as an Ancillary Imaging Test for Confirmation of Brain Death in an Infant: A Case Report

The practices for determining brain death are based on clinical criteria and vary immensely across countries. Cerebral angiography and perfusion scintigraphy are the most commonly used ancillary imaging tests for brain death confirmation in children; however, they both share similar shortcomings. Hence, contrast-enhanced ultrasound (CEUS) as a relatively inexpensive, easily accessible, and easy-to-perform technique has been proposed as an ancillary imaging test for brain death confirmation. CEUS has established itself as a favourable and widely used diagnostic imaging method in many different areas, but its application in delineating brain pathologies still necessities further validation. Herein, we present a case report of a 1-year-old polytraumatised patient in whom CEUS was applied as an ancillary imaging test for confirmation of brain death. As CEUS has not been validated as an ancillary test for brain death confirmation, the diagnosis was additionally confirmed with cerebral perfusion scintigraphy.

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.

Clinical applications of transcranial Doppler in non-trauma critically ill children: a scoping review

BACKGROUND

Many applications of transcranial Doppler (TCD) as a diagnosis or monitoring tool have raised interest in the last decades. It is important that clinicians know when and how to perform TCD in this population, what parameter to assess and monitor and how to interpret it.

OBJECTIVE

This review aims to describe the emerging clinical applications of TCD in critically ill children excluding those suffering from trauma.

METHODS

Databases Web of Science, Cochrane and PubMed were searched in May 2020. We considered all publications since the year 2000 addressing the use of TCD as a prognostic, diagnostic or follow-up tool in children aged 0 to 15 years admitted to intensive care or emergency units, excluding neonatology and traumatic brain injury. Two independent reviewers selected 82 abstracts and full-text articles from the 2011 unique citations identified at the outset.

RESULTS

TCD provides crucial additional information at bedside about cerebrovascular hemodynamics. Many clinical applications include the diagnosis and management of various medical and surgical neurologic conditions (central nervous system infections, arterial ischemic stroke, subarachnoid hemorrhage and vasospasm, brain death, seizures, metabolic disease, hydrocephalus) as well as monitoring the impact systemic conditions on brain perfusion (hemodynamic instability, circulatory assistance).

CONCLUSION

To conclude, TCD has become an invaluable asset for non-invasive neuromonitoring in critically ill children excluding those suffering from trauma. However, the scope of TCD remains unclearly defined yet and reference values in critically ill children are still lacking.

In vivo Biodistribution of Radiolabeled Acoustic Protein Nanostructures

PURPOSE

Contrast-enhanced ultrasound plays an expanding role in oncology, but its applicability to molecular imaging is hindered by a lack of nanoscale contrast agents that can reach targets outside the vasculature. Gas vesicles (GVs)-a unique class of gas-filled protein nanostructures-have recently been introduced as a promising new class of ultrasound contrast agents that can potentially access the extravascular space and be modified for molecular targeting. The purpose of the present study is to determine the quantitative biodistribution of GVs, which is critical for their development as imaging agents.

PROCEDURES

We use a novel bioorthogonal radiolabeling strategy to prepare technetium-99m-radiolabeled ([^99mTc])GVs in high radiochemical purity. We use single photon emission computed tomography (SPECT) and tissue counting to quantitatively assess GV biodistribution in mice.

RESULTS

Twenty minutes following administration to mice, the SPECT biodistribution shows that 84 % of [^99mTc]GVs are taken up by the reticuloendothelial system (RES) and 13 % are found in the gall bladder and duodenum. Quantitative tissue counting shows that the uptake (mean ± SEM % of injected dose/organ) is 0.6 ± 0.2 for the gall bladder, 46.2 ± 3.1 for the liver, 1.91 ± 0.16 for the lungs, and 1.3 ± 0.3 for the spleen. Fluorescence imaging confirmed the presence of GVs in RES.

CONCLUSIONS

These results provide essential information for the development of GVs as targeted nanoscale imaging agents for ultrasound.

Doppler Ultrasonography of the Central Retinal Vessels in Children With Brain Death

OBJECTIVE

The purpose of this observational study is to explore if bedside Doppler ultrasonography of the central retinal vessels has the potential to become an ancillary study to support the timely diagnosis of brain death in children.

DESIGN

Seventeen-month prospective observational cohort.

SETTING

Forty-four bed pediatric medical and surgical ICU in an academic teaching hospital.

PATIENTS

All children 0-18 years old who were clinically evaluated for brain death at Children's National Health Systems were enrolled and followed until discharge or death.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All patients had at least one ophthalmic ultrasound within 30 minutes of each brain death examination. The central retinal artery peak systolic blood flow velocity, resistive index, pulsatility index, and Doppler waveforms were evaluated in each patient. Thirty-five ophthalmic ultrasounds were obtained on 13 patients, 3 months to 15 years old, who each had two clinical examinations consistent with brain death. The average systolic blood pressure during the ultrasound examinations was 102 mm Hg (± 28), diastolic blood pressure 65 mm Hg (± 24), mean arterial pressure 79 mm Hg (± 23), heart rate 133 beats/min (± 27), temperature 36°C (± 0.96), arterial CO2 35 mm Hg (± 9), and end-tidal CO2 23 mm Hg (± 6). For all examinations, the average peak systolic velocity of the central retinal artery was significantly decreased at 4.66 cm/s (± 3.2). Twelve of 13 patients had both resistive indexes greater than or equal to 1, average pulsatility indexes of 3.6 (± 3.5) with transcranial Doppler waveforms consistent with brain death. Waveform analysis of the 35 ultrasound examinations revealed 11% with tall systolic peaks without diastolic flow, 17% with oscillatory flow, 29% showed short systolic spikes, and 23% had no Doppler movement detected. A rippling "tardus-parvus" waveform was present in 20% of examinations.

CONCLUSION

This study supports that the combination of qualitative waveform analysis and quantitative blood flow variables of the central retinal vessels may have the potential to be developed as an ancillary study for supporting the diagnosis of brain death in children.

Recent advances in molecular, multimodal and theranostic ultrasound imaging

Ultrasound (US) imaging is an exquisite tool for the non-invasive and real-time diagnosis of many different diseases. In this context, US contrast agents can improve lesion delineation, characterization and therapy response evaluation. US contrast agents are usually micrometer-sized gas bubbles, stabilized with soft or hard shells. By conjugating antibodies to the microbubble (MB) surface, and by incorporating diagnostic agents, drugs or nucleic acids into or onto the MB shell, molecular, multimodal and theranostic MBs can be generated. We here summarize recent advances in molecular, multimodal and theranostic US imaging, and introduce concepts how such advanced MB can be generated, applied and imaged. Examples are given for their use to image and treat oncological, cardiovascular and neurological diseases. Furthermore, we discuss for which therapeutic entities incorporation into (or conjugation to) MB is meaningful, and how US-mediated MB destruction can increase their extravasation, penetration, internalization and efficacy.