Perspectives of B-mode transcranial ultrasound

A systematic review of ultrasound imaging and therapy in mental disorders

BACKGROUND

Increasing evidence suggests that ultrasound (US) imaging may provide biomarkers and therapeutic options in mental disorders. We systematically reviewed the literature to provide a global overview of the possibilities of US for psychiatry.

METHODS

Original English language articles published between January 2000 and September 2019 were identified through databases searching and analyzed to summarize existing evidence according to PRISMA methodology.

RESULTS

A total of 81 articles were included. Various US techniques and markers have been used in mental disorders, including Transcranial Doppler and Intima-Media Thickness. Most of the studies have focused on characterizing the pathophysiology of mental disorders, especially vascular physiology. Studies on therapeutic applications are still scarce.

DISCUSSION

US imaging has proved to be useful in characterizing vascular impairment and structural and functional brain changes in mental disorders. Preliminary findings also suggest potential interests for therapeutic applications. Growing evidence suggests that US imaging could provide a non-invasive, portable and low-cost tool for pathophysiological characterization, prognostic assessment and therapeutic applications in mental disorders.

Transcranial B-Mode Sonography in Movement Disorders

Applying a 2-4MHz probe at the temporal bone window transcranial B-mode sonography (TCS) enables the depiction of the brain parenchyma through the intact skull. Meanwhile it has been applied for the diagnosis and the differential diagnosis of movement disorders for decades. In the first part of this chapter, we summarize the technical requirements and describe the ultrasound method for optimal TCS examination. Imaging planes and the relevant structures are explained in detail. In the second part of the chapter, we focus on the role of substantia nigra hyperechogenicity for the diagnosis of Parkinson's disease (PD) and prodromal PD. In this part, we also mention the role of TCS in atypical and secondary Parkinsonian syndromes and other movement disorders. Summarizing all these information we explain how TCS can be helpful for the differential diagnosis of movement disorders. The current data show that TCS is an easily applicable and economic imaging method which can be used as an additional tool for the diagnosis of PD with a high sensitivity (>85%), specificity (>80%) and inter-rater reliability (>84%) as well as for the differential diagnosis of movement disorders. Lately, TCS has also been utilized in further areas such as the detection of individuals at risk for PD or the determination of electrode localization in patients with deep brain stimulation. An insufficient temporal bone window especially in the elderly and the necessity of an experienced investigator are limitations of this method.

Post-Operative Localization of Deep Brain Stimulation Electrodes in the Subthalamus Using Transcranial Sonography

OBJECTIVES

The correct positioning of deep brain stimulation electrodes determines the success of surgery. In this study, we attempt to validate transcranial sonography (TCS) as a method for early postoperative confirmation of electrode location in the subthalamic nucleus (STN).

MATERIALS AND METHODS

Nineteen patients diagnosed with Parkinson's disease were enrolled in the study. Postoperative TCS was applied to measure the distance between the implanted electrodes and the third ventricle in the axial plane. Whether the electrodes were positioned within or outside the substantia nigra (SN) was evaluated through measurements in the coronal plane. The obtained metrics through TCS were compared with those from postoperative computed tomography (CT) and magnetic resonance imaging (MRI).

RESULTS

A statistically significant correlation between distances from electrode to third ventricle by TCS and CT/MRI (r = 0.75, p < 0.01) was observed. Distances from third ventricle to electrodes tips were different when sonographically they showed to be inside or outside the SN (p < 0.01). A cut-off value of 8.85mm in these distances was the most sensitive (100%) and specific (90.5%) to predict if electrodes were positioned inside the SN (CI 95% 0.81-10.30, p = 0.001).

CONCLUSIONS

Transcranial sonography is a useful technique to reliably identify targeted positioning of deep brain stimulation electrodes in or out of the SN.

Developments in the role of transcranial sonography for the differential diagnosis of parkinsonism

In the last two decades transcranial sonography (TCS) has developed as a valuable, supplementary tool in the diagnosis and differential diagnosis of movement disorders. In this review, we highlight recent evidence supporting TCS as a reliable method in the differential diagnosis of parkinsonism, combining substantia nigra (SN), basal ganglia and ventricular system findings. Moreover, several studies support SN hyperechogenicity as one of most important risk factors for Parkinson's disease (PD). The advantages of TCS include short investigation time, low cost and lack of radiation. Principal limitations are still the dependency on the bone window and operator experience. New automated algorithms may reduce the role of investigator skill in the assessment and interpretation, increasing TCS diagnostic reliability. Based on the convincing evidence available, the EFNS accredited the method of TCS a level A recommendation for supporting the diagnosis of PD and its differential diagnosis from secondary and atypical parkinsonism. An increasing number of training programmes is extending the use of this technique in clinical practice.

Transcranial sonography of the substantia nigra and its correlation with DAT-SPECT in the diagnosis of Parkinson's disease

INTRODUCTIONS

Transcranial sonography (TCS) of the substantia nigra is a new and promising method to diagnose Parkinson's disease (PD) but its effectiveness is controversial.

METHODS

All 55 PD patients involved in the study underwent single photon emission computed tomography (SPECT) imaging using the labeled dopamine transporter radiotracer (99m)Tc-TRODAT-1 to assess nigrostriatal dopaminergic function. The echogenicity of the substantia nigra was measured by TCS in all patients who received DAT-SPECT scanning. Finally, statistical analysis was carried out to determine the diagnostic accuracy of TCS as well as its correlation with (99m)Tc-TRODAT-1 SPECT, its positive predictive value (PPV), and negative predictive value (NPV).

RESULTS

Contralateral striatal (99m)Tc-TRODAT-1 uptake was significantly reduced compared to ipsilateral striatal uptake, and had a negative correlation with UPDRS-Ⅲ(r = -0.334, p = 0.013), disease duration (r = -0.393, p = 0.003) and H-Y stage (r = -0.330, p = 0.014). After TCS measurement, the contralateral SN echogenic area was similar to the ipsilateral SN echogenic area (27.77 ± 13.19 vs 25.98 ± 11.94 mm(2), p = 0.402, n = 24). No correlation was identified between TCS and UPDRS-Ⅲ (r = 0.383, p = 0.065), disease duration (r = 0.371, p = 0.075) or H-Y stage (r = 0.259, p = 0.222). The sensitivity and specificity of SN TCS for the diagnosis of PD were calculated as 64.70% and 60% according to DAT-SPECT, respectively, while the positive predictive value and negative predictive value was calculated as 91.67% and 20%, respectively.

CONCLUSIONS

Compared to DAT-SPECT, TCS is a non-radioactive and convenient procedure to perform. In our investigation, TCS had no correlation with DAT-SPECT. However, the high positive predictive value of TCS highlights its possible utility as a routine diagnostic test.

The study of deep brain structures by transcranial duplex sonography and imaging resonance correlation

Transcranial duplex sonography (TCS) currently provides us with images of deep brain structures with sufficient resolution. We chose 2 sonographic quantitative parameters: the diameter of the third ventricle and a measurement not used by TCS to date, the midbrain area. Their reliability and reproducibility were assessed using magnetic resonance imaging (MRI) as the reference. A total of 99 patients free from neurodegenerative disorders were examined using TCS, and both parameters were measured by 2 independent explorers. Measurements of third-ventricle diameter by TCS showed very good correlation (r = 0.80) and agreement (ICC = 0.89) with measurements obtained by MRI. Measurements of the midbrain area by TCS also provided acceptable values with moderate correlation (r = 0.36) and agreement (ICC = 0.53). Interexplorer correlation values were good (ICC = 0.98 and 0.79 for the third ventricle and midbrain areas, respectively). Further studies will be required to determine the potential diagnostic usefulness of these parameters.

Biopsable neural tissues: toward new biomarkers for Parkinson's disease?

Biomarkers for Parkinson's disease (PD) are mainly intended for the early diagnosis of the disease and to monitor its progression, two aspects insufficiently covered by clinical evaluation. In the last 20 years, the search for biomarkers has been supported by technological advances in the fields of molecular genetics and neuroimaging. Nevertheless, no fully validated biomarker is yet available, and there is still a need for biomarkers that will complement those already available. Development of biomarkers for PD has been hampered by the fact that the core pathology lies in the brainstem, hidden from direct study in living patients. In this context, the recent observations that clearly demonstrated the presence of PD pathology in peripheral neural tissues provide new opportunities to develop original histopathological markers of the disease. Some of these peripheral tissues, especially the enteric nervous system, by being assessable using routine biopsies, could represent a window to assess in vivo the neuropathological processes occurring in PD.

Diagnosis of Parkinson's disease--transcranial sonography in relation to MRI

Displaying the echo pattern (echogenicity) of brain tissue transcranial sonography (TCS) may provide new and complementary information to other neuroimaging methods. In contrast to conventional magnetic resonance imaging (MRI), TCS is able to detect highly characteristic changes in signal brightness of the substantia nigra (SN) in patients with idiopathic Parkinson's disease. In this review, TCS findings are related to conventional and advanced high-field brain MRI findings. On the basis of the MRI findings, especially with T2-relaxometry, the possible role of trace metals in the genesis of altered echogenicity on TCS of brain parenchyma, especially of the SN, are discussed.

Sonographic substantia nigra hypoechogenicity in polyneuropathy and restless legs syndrome

Substantia nigra (SN) hypoechogenicity assessed by transcranial B-mode sonography (TCS) is typical for idiopathic restless legs syndrome (RLS). Here, we investigated whether SN hypoechogenicity may differentiate between polyneuropathy (PNP) patients with and without RLS. Seventy-five patients with PNP, 65 healthy controls, and 75 patients with idiopathic RLS were investigated. A total of 41.2% patients with PNP additionally suffered from RLS. A total of 44.1% patients with PNP, 10.2% of healthy controls, and 91.2% of patients with idiopathic RLS exhibited SN hypoechogenicity. SN echogenicity did not differ significantly between PNP patients with and without RLS. Thus, TCS seems not suitable for the diagnosis of RLS in patients with PNP.

Suitability of Temporal Bone Acoustic Window: Conventional TCD Versus Transcranial Color-Coded Duplex Sonography

PURPOSE AND BACKGROUND

To determine whether the proportion of patients with suitable temporal bone acoustic windows is different for conventional transcranial Doppler sonography (TCD) and transcranial color-coded duplex sonography (TCCS), based on a head-to-head comparison in the same population of patients.

SUBJECTS AND METHODS

Ninety patients, age 22-88 years (mean 57.1 +/- 11.7 years), 46 women and 44 men, 66 Caucasian, 19 African-American, and five Hispanic, underwent routine conventional TCD and the TCCS examination close in time to each other. Suitability of temporal bone acoustic window was defined by ability to insonate the middle and posterior and/or anterior cerebral arteries, while partial suitability was defined by ability to detect the posterior cerebral artery but not the middle cerebral artery. To compare proportions of suitable temporal bone windows for both sonographic methods, exact sign test by Liddell was used.

RESULTS

Bilateral absence of temporal bone acoustic window was reported in six patients when studied with both conventional TCD and TCCS, whereas at least unilateral absence was reported in 10 patients. Partial, at least unilateral, suitability was reported in 11 patients with conventional TCD, and in 7 with TCCS. All differences in proportions were not significant (two-sided P>0.05).

CONCLUSIONS

This study suggests that success rate of insonating the intracranial vessels through the temporal bone acoustic window is the same for conventional TCD and imaging TCCS.

Cross-sectional study discloses a positive family history for Parkinson’s disease and male gender as epidemiological risk factors for substantia nigra hyperechogenicity

Hyperechogenicity of the substantia nigra (SN) has been proposed to be a typical finding in Parkinson's disease (PD) and a marker of vulnerability to nigrostriatal dysfunction in healthy subjects. This large cross-sectional study including 1120 subjects older than 50 years without any signs of PD was performed to evaluate the association of SN hyperechogenicity and other proposed epidemiological risk factors for PD. Among all variables assessed only family history of PD and male gender proved to be significantly associated with SN hyperechogenicity, indicating a genetic predisposition for the ultrasound marker.

Transcranial sonography in the evaluation of Parkinson disease

OBJECTIVE

With transcranial sonography (TS), it is possible to visualize hyperechoic signals in the sub-stantia nigra (SN) in patients with Parkinson disease (PD). Our objective was to correlate the level of echogenicity in the SN with clinical status in patients with PD.

METHODS

In our pilot study, using TS, we examined 15 patients with the confirmed presence of PD. Staging of the latest clinical status was evaluated according to the Hoehn and Yahr scale. According to TS, the level of echogenicity was graduated as hypoechogenicity, moderate hyperechogenicity, and severe hyperechogenicity.

RESULTS

Of the patients with severe hyperechogenicity (8 patients), 7 had Hoehn and Yahr stage III disease, and 1 had stage II disease. Of the patients with moderate hyperechogenicity (6 patients), 4 had stage II disease; 1 had stage III disease; and 1 had stage I disease. The patient with hypoechogenicity had stage I disease. Statistical analysis showed that there was a significant correlation between the level of echogenicity in the SN and the clinical stage (r = 0.7735; P = .0007).

CONCLUSIONS

In our pilot study, although only a small number of patients were included, we confirmed the usefulness of TS in the evaluation of PD.

Early diagnosis of Parkinson’s disease

The clinical methods of olfactory testing and color discrimination as well as apparative methods such as transcranial ultrasound, dopamine transporter imaging and MIBG scintigraphy reveal a high sensitivity concerning the diagnosis of idiopathic Parkinson's disease (PD). The specificity of the presented methods, in particular of the dopamine transporter imaging--seems to be limited. All these methods and primarily their combination allow the detection of PD in early and--probably--preclinical stages. This requires sufficient therapeutic strategies to prevent and treat preclinical and early PD.

Transcranial sonography and [123I]FP-CIT SPECT disclose complementary aspects of Parkinson's disease

Hyperechogenic signal of substantia nigra (SN) in transcranial sonography (TCS) and reduced striatal uptake in FP-CIT SPECT are common findings in idiopathic Parkinson's disease (PD). But so far it is unknown whether the extent of SN hyperechogenicity represents a correlate for the degeneration of presynaptic dopaminergic neurons in PD. We performed TCS and 123I-labelled N-(3-fluoropropyl)-2ss-carbomethoxy-3ss-(4-iodophenyl)nortropane ([123I]FP-CIT) SPECT in 53 patients with PD. Striatal FP-CIT uptake was quantified by measuring the striatal/posterior lobe binding of [123I]FP-CIT. SN echogenicity was quantified by planimetric measurement of the maximum extension of hyperechogenic signals. We found no correlation between striatal FP-CIT uptake and echogenicity of the SN, neither contralateral to the clinically more affected body side (r = +0.08, P = 0.57; Pearson's correlation) nor ipsilateral (r = +0.01; P = 0.92). Our data show that the extent of SN hyperechogenicity does not correlate with the degeneration of presynaptic dopaminergic nerve terminals. Obviously SN hyperechogenicity and degeneration of presynaptic dopaminergic nerve terminals exist independently from each other and may be based on different pathomechanisms.

Disturbance of iron metabolism in Parkinson’s disease — ultrasonography as a biomarker

A central role of iron in the pathogenesis of Parkinson's disease (PD) has been discussed for many years. So far, however, a biomarker indicating increased iron levels in the substantia nigra (SN) in PD patients has been missing. Performing transcranial ultrasound we detected an increased area of SN echogenicity as a typical echofeature in PD, visible already in the early stages of the disease and in subjects with subclinical impairment of the nigrostriatal system. Animal studies and post mortem analyses of human brain tissue revealed that this echofeature is associated with increased iron levels of the substantia nigra as well as a reduced neuromelanin content. The apparently autosomal dominant inheritance of this echofeature in relatives of patients with idiopathic PD indicates a primary role of disturbances of iron metabolism in PD. Consequently performed mutation analyses in genes involved in brain iron metabolism lead to the discovery of specific mutations in the ferritin-H, IRP2 and HFE gene in single PD patients. Moreover, variations in the ceruloplasmin gene were found to be associated with PD or SN hyperechogenicity. Functional relevance of some of these mutations for iron metabolism could be proven. Therefore, SN hyperechogenicity can be regarded as biomarker for both: impairment of the nigrostriatal system and increased iron levels of the SN. Future studies aim at substantiating the hypothesis that healthy subjects with SN hyperechogenicity indeed represent a population at risk for nigrostriatal degeneration, which would have a significant impact on therapeutical options.

Transcranial ultrasonography system for visualizing skull and brain surface aided by fuzzy expert system

A conventional ultrasonography system can noninvasively provide human tissue and blood flow velocity information with real-time processing. In general, since the human skull prevents the disclosure of brain anatomy, we usually placed the sensor at the anterior and superior attachment site of the upper ear (the posterior temporal window) in adults. Due to this limitation, the conventional system cannot obtain transcranial information from arbitrary places in the skull. This paper describes a transcranial sonography system that can visualize the shape of the skull and brain surface from any point to examine skull fracture and brain disease such as cerebral atrophy and epidural or subdural hematoma. In this system, we develop anatomical knowledge of the human head, and we employ fuzzy inference to determine the skull and brain surface. To evaluate our method, three models are applied: the phantom model, the animal model with soft tissue, and the animal model with brain tissue. In all models, the shapes of the skull and the brain tissue surface are successfully determined. Next, the method is applied to two adults. As a result, we have determined the skin surface, skull surface, skull bottom, and brain tissue surface for the subjects' foreheads. Consequently, our system can provide the skull and brain surface information using three-dimensional shapes.

The diagnosis of Parkinson's disease

The correct diagnosis of Parkinson's disease is important for prognostic and therapeutic reasons and is essential for clinical research. Investigations of the diagnostic accuracy for the disease and other forms of parkinsonism in community-based samples of patients taking antiparkinsonian medication confirmed a diagnosis of parkinsonism in only 74% of patients and clinically probable Parkinson's disease in 53% of patients. Clinicopathological studies based on brain bank material from the UK and Canada have shown that clinicians diagnose the disease incorrectly in about 25% of patients. In these studies, the most common reasons for misdiagnosis were presence of essential tremor, vascular parkinsonism, and atypical parkinsonian syndromes. Infrequent diagnostic errors included Alzheimer's disease, dementia with Lewy bodies, and drug-induced parkinsonism. Increasing knowledge of the heterogeneous clinical presentation of the various parkinsonisms has resulted in improved diagnostic accuracy of the various parkinsonian syndromes in specialised movement-disorder units. Also genetic testing and various other ancillary tests, such as olfactory testing, MRI, and dopamine-transporter single-photon-emission computed-tomography imaging, help with clinical diagnostic decisions.

Spectral image reconstruction for transcranial ultrasound measurement

An approach aimed at improved ultrasound resolution and signal strength through highly attenuating media is presented. The method delivers a series of multiple-cycle bursts in order to construct a discrete spectral (frequency domain) response in one dimension. Cross-correlation of this ultrasound A-mode response with its transmitted signal results in time-localized peaks that correspond to scattering locations. The approach is particularly relevant to the problem of transcranial ultrasound imaging, as it combines numerous smaller signals into a single signal whose net power may exceed that which could be achieved using a single burst. Tests are performed with human skull fragments and nylon-wire targets embedded in a tissue phantom. Skulls are oriented to produce both lateral and shear modes of transcranial propagation. A total of nine locations distributed over three ex vivo human skull samples are studied. Compared with pulsed and chirped signals, results indicate more localized peaks when using the multi-cycle approach, with more accurate positioning when combined with the transcranial shear mode.

Feasibility study: real-time 3-D ultrasound imaging of the brain

We tested the feasibility of real-time, 3-D ultrasound (US) imaging in the brain. The 3-D scanner uses a matrix phased-array transducer of 512 transmit channels and 256 receive channels operating at 2.5 MHz with a 15-mm diameter footprint. The real-time system scans a 65 degrees pyramid, producing up to 30 volumetric scans per second, and features up to five image planes as well as 3-D rendering, 3-D pulsed-wave and color Doppler. In a human subject, the real-time 3-D scans produced simultaneous transcranial horizontal (axial), coronal and sagittal image planes and real-time volume-rendered images of the gross anatomy of the brain. In a transcranial sheep model, we obtained real-time 3-D color flow Doppler scans and perfusion images using bolus injection of contrast agents into the internal carotid artery.

Evaluation of the ventricular system in children using transcranial ultrasound: reference values for routine diagnostics

In children, evaluation of the size of the ventricular system is important. Transcranial Doppler sonography (TCD), a broadly available and easily applicable method that is not hampered by side effects, such as radiation, is a valuable tool for routine examinations. However, standard TCD values of the ventricular system are lacking. In this study, we performed TCD through the temporal acoustic bone window in a large cohort of 1693 healthy children. Of these, 157 had to be excluded because of insufficient bone windows. In the remaining children, a mean width of 1.4 +/- 0.8 mm for the third ventricle, 14.4 +/- 0.8 mm for the right and 14.6 +/- 0.7 mm for the left cella media, and 1.6 +/- 0.7 mm for the right and 1.9 +/- 0.8 mm for the left temporal horn were measured. Side differences are indicated and values are given in relation to age and gender. Inter-rater reproducibility obtained in 25 children was adequate, with no significant difference between the two measurements in any of the parts of the ventricular system measured, rendering these values suitable for reference.

Echogenicity of the substantia nigra in relatives of patients with sporadic Parkinson's disease

Increased echogenicity of the substantia nigra (SN) on ultrasound is a typical sonographic finding in Parkinson's disease (PD). Sonographic signal intensity of the SN is related to tissue iron content with higher iron level being associated with increased echogenicity. Recent findings indicate that hyperechogenicity of the SN represents an important susceptibility factor for nigrostriatal degeneration. In this study we determined the prevalence of a characteristic ultrasound sign of Parkinson's disease in first-degree relatives of PD patients. Fourteen patients with sporadic PD and 58 of their relatives underwent neurological, neuropsychological, and ultrasound examination. In addition, four pairs of relatives (one member of each pair exhibiting increased echogenicity of the SN and the other with regular SN echogenicity) underwent (18)F-Dopa PET examination. On transcranial sonography, 26 of the 58 relatives exhibited SN hyperechogenicity. Twenty-four relatives showed minor signs of motor slowing. Relatives with SN hyperechogenicity more often showed signs of hypokinesia (16 v 8 relatives; U test, P = 0.01) and impaired executive functions (Tower of London task, problems solved with the minimum number of moves; U test, P = 0.012) than relatives without this echo pattern. In addition, (18)F-Dopa uptake (influx constants) at the putamen was reduced in subjects with SN hyperechogenicity compared to their relatives without this ultrasound sign (Wilcoxon, P = 0.03). In conclusion, approximately 45% of relatives of PD patients exhibited an increased echogenicity of the SN. This sign is associated with clinical findings and objective measurements, indicating some degree of impaired nigrostriatal function.